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USER MANUAL

1. ccccscssessessceseesececesceeseeeseecesecsecseeseeeeseseeseesaeeseeseenees 5 54 TERRE CRIN RAD TEXT seg teste cant oes chev asec hoped eas colada EREN 5 55 DEFINE HYDRODYNAMIC PROPERTY sanirana E AEE EE E 5 56 DEFINE HYDRODYNAMIC PROPERTY CONNECT ssssessessessssssssssssesssessersseessesseesseessessees 5 57 DEFINE HYDRODYNAMIC PROPERTY SECTION sssssessessesssssssssssssssesssesserssersseeseessessses 5 58 DEFINE HYDRODYNAMIC PROPERTY SECTION ref 2D MORISON ELEMENT 5 59 DEFINE HYDRODYNAMIC PROPERTY SECTION ref 3D MORISON ELEMENT 5 60 DEFINE HYDRODYNAMIC PROPERTY SECTION ref ANCHOR ELEMENT 06 5 61 DEFINE HYDRODYNAMIC PROPERTY SECTION ref DRY ELEMENT cccceeseees 5 62 DEFINE HYDRODYNAMIC PROPERTY SECTION ref POINT MASS 1 0 eccceccesteeeeeteeeees 5 63 DEFINE HYDRODYNAMIC PROPERTY SECTION ref PRESSURE AREA ELEMENT 5 64 DEFINE HYDRODYNAMIC PROPERTY SECTION ref TLP MOORING ELEMENT 5 65 MEE TUE sh sccsns valence soto piaeatas eps ale shea tae E Rv dela ae saa es ac E ava deeds pve a 5 66 EDEL U EEEE EE stamens res Leste A ETA EAE EE 5 67 HELP aerae eto E as eg A A A E E E ah A ede 5 68 PRIN Drinu tee cept A EE A EEEE EN EEEE 5 69 PRINT CORRESPONDANCE venniri ee E e a a a a tests 5 70 PRINT ELEMENT mitona a a a T O decid ise E A ie 5 71 PRINT ENVIRONMENT z ecrini E EE EEE EA EA EEE 5 72 PRINT GENERAD oreco aen aaa a A a Ea E RSE R EaR a ety 5 73 PRINT HY
2. Eg wadamrunt ee s Wizards 14 Analysis Panel DAR 9 gt 5 fi View Listing Fiels 9 WWadamRun1 H Start Output Directory End Output Directory removeAllRunsForAnalysis executeWadam removeAllRunsForAnalysis addRunForAnalysis WadamRun1 executeWadam gt lt Ono Messages A Command Line A Visual Clipbosrd ja v Figure 4 2 The HydroD GUI and the command for executing Wadam SESAM Wadam Program version 8 1 22 JAN 2010 4 3 4 1 1 Star
3. T T BOUNDARY SUPER SUPER SUPER SUPER SUPER SUPER GLOBAL ALL PROPERTY MATERIAL 1 SPRING TO GROUND STIFFNESS 1 H06 0 0 0 0 1 H06 0 0 0 E0 G 0 0 Elk an ae oO FI jo GI D D ole 7 4 zJ ENT SPRING TO GROUND GSPR GLOBAL 1 GLOBAL 1 GLOBAL 1 GLOBAL 1 N N Hes Oye w PFPWNE w A2 2 Input for the Structural Model EXAMPLE 3 1 2 A FLOATING BOX 90M X 90M AT DRAFT OF 40M BOX TETHERED TO SEA BED AT 4 CORNERS OF BOX MOTIONS RESPONSE ANALYSIS AND TRANSFER OF LOADS TO SHELL STRUCTURAL MODEL OF COMPLETE BOX AP AP AP AP oP Wadam SESAM A 4 22 JAN 2010 Program version 8 1 STRUCTURAL MODEL FOR 1 4 OF BOX WITH TOP SUPERELEMENT NO 3 GENERATE SURFACES TO FORM A QUARTER OF THE BOX 45 X 45 X 60 METRES GENERATE SURFACE A 12151215121 6 CARTESIAN 000 45 0 0 END O 45 0 END O 0 60 END REMOVE UNWANTED SIDES OF BOX ON X Z AND Y Z PLANES DELETE GEOMETRY AS111 AT111 END SET THE ELEMENT TYPE TO BE 4 NODE SHELL TO REPRESENT EACH PANEL OF THE HYDRODYNAMIC MODEL SET ELEMENT TYPE SURFACE ALL
4. 22 JAN 2010 Program version 8 1 Node number at the other end of the element windlass of moor ing elements Not to be specified for 3D Morison Point mass TLP mooring and Pressure area elements A group of elements First element number in the group Last element number in the group Step in the element numbering Node number at one end of the first element in the group Node number at the other end of the first element in the group Incremental step for node selection The next element elnol elinc will have its nodes defined by nlell noinc and n2el1 noinc SESAM Wadam Program version 8 1 22 JAN 2010 5 7 DEFINE ENVIRONMENT X AXIS refno locz vel dir CURRENT ENVIRONMENT PURPOSE WAVE DIRECTION END FREQUENCY HEADING PAIRS LINEARISING WAVE HEIGHT SURFACE MODEL WATER DEPTH depth amp WAVE AMPLITUDE END dir WAVE DIRECTION END WAVE FREQUENCY WAVE LENGTH WAVE PERIOD FINITE length INFINITE WAVE LENGTH DEPENDENT END WAVE SPECTRUM WAVE SPREADING FUNC USER DEFINED weights END The command defines environmental data PARAMETERS CURRENT X AXIS WAVE DIRECTION refno locz A current profile used in Morison s equation is specified The current velocities used are calculated by linear interpolation in the table given by this command The current direction will be given
5. PURPOSE The command defines additional global matrices to be used in Wadam The matrices will be added to matri ces calculated by Wadam with a possible exception for the damping matrix where the user specifies whether it is to be added to or replace the matrix computed by Wadam If for instance mooring forces are given through anchor elements and the user specifies a restoring matrix both will contribute to the total restoring forces The matrix is by default a zero matrix The user must only specify those matrix elements which are different from zero There is no assumption of symmetry so all non zero elements must be speci fied on both side of the diagonal The global matrices will not contribute to distributed loads and sectional loads Additional or alternative global damping matrix based on the critical damping of the system in question may be generated or the user may alternatively specify it directly User specified damping matrices will be added to the critical damping matrix Note that the specification of global mass matrices is available for a multiple body system If a single sys tem shall be analysed this command may still be used However giving body identification number equal to 1 Only the body mass matrices are available in a multi body system Hence no mechanical coupling matri ces between the bodies can be specified For body 2 3 aso in a multi body system the MASS MATRIX command is the only available way to spec ify
6. ky o29 heyy XqZ9 k43X3V2 hy3X9 Tz 2 ki 1Y222 ka1X223 ky 3X2V_ ka3X3 Ty 2 2 kiya Zka X2 Ky xq Tyy Tx SESAM Program version 8 1 SESAM Wadam Program version 8 1 22 JAN 2010 B 7 is elastic stiffness force per length T is the constant pre tension L is the specified tether length at a given offset position T is the x component of the pre tension T is the y component of the pre tension T is the z component of the pre tension The matrix is symmetric k k except for the terms ks4 ke4 and kes The direction cosines cosa cos and cosy are defined as follows L L L The separate K matrices for each TLP node are described with respect to the x1 yj z1 and x2 yo Z2 coordinates at the TLP node and the sea bed see Figure B 2 x2 y2 z2 l yl zl Seabed hae Figure B 2 TLP element coordinates Having solved the equation of motion x represents the global motion of the rigid body system The force vector f for each TLP node described in the result reference coordinate system is then computed as f K Xg B 2 Wadam SESAM B 8 22 JAN 2010 Program version 8 1 B3 Calculation Methods B 3 1 Linearisation of Roll Restoring The linear roll restoring moment is based on the initial metacentric height GM calculated from the model geometry and specified mass properties and is only valid at small heeling angles From hydrostatics calcula tio
7. DEFINE HYDRODYNAMIC PROPERTY SECTION ref 2D MORISON ELEMENT dia dm 2D MORISON ELEMENT stot oe cksi czeta aksi azeta RETAINED RETAINED PURPOSE The command defines hydrodynamic properties for 2D Morison elements Two node beam elements on the Input Interface File with cross section reference number equal to the hydrodynamic property section refer ence number ref are defined as 2D Morison elements All other 2 node beam elements are defined as Dry Morison elements with RETAINED mass pr unit length All the sub elements of a 2D Morison element will initially receive the same hydro properties To define a section containing sub elements of varying length and or properties the user must enter the CHANGE command after specifying the hydrodynamic properties PARAMETERS stot Total number of sub elements RETAINED The equivalent diameter or the distributed mass defined on the Input Interface File will be used Retained equivalent diameter may only be used for section type PIPE dia Equivalent diameter dm Distributed mass of element Give mass per unit length cksi Drag coefficient along the axis czeta Drag coefficient along the C axis aksi Added mass coefficient along the axis azeta Added mass coefficient along the C axis NOTES The CHANGE command corresponding to this DEFINE command deviates in that there are two additional parameters selno and sl CHANGE HYDRODYNAMI
8. DNY SESAM USER MANUAL Wadam Wave Analysis by Diffraction and Morison Theory DET NORSKE VERITAS SESAM USER MANUAL DET NORSKE VERITAS SESAM User Manual Wadam Wave Analysis by Diffraction and Morison Theory January 2 2010 Valid from program version 8 1 Developed and Marketed by DET NORSKE VERITAS DNV Software Report No 94 7100 Revision8 January 22 2010 Copyright 2010 Det Norske Veritas All rights reserved No part of this book may be reproduced in any form or by any means without permission in writing from the publisher Published by Det Norske Veritas Veritasveien N 1322 H vik Norway Telephone 47 67 57 99 00 Facsimile 47 67 57 72 72 E mail sales software sesam dnv com E mail support software support dnv com Website www dnv com If any person suffers loss or damage which is proved to have been caused by any negligent act or omission of Det Norske Veritas then Det Norske Veritas shall pay compensation to such person for his proved direct loss or damage However the compensation shall not exceed an amount equal to ten times the fee charged for the service in question provided that the maximum compensation shall never exceed USD 2 millions In this provision Det Norske Veritas shall mean the Foundation Det Norske Veritas as well as all its subsidiaries directors officers employees agents and any other acting on behalf of Det Norske Veritas
9. MAXIMUM DIAGONAL The maximum diagonal of the panels are used NOTES The direct solver is switched to a block iterative solver if the number of panels is larger than the maximum allowed in core matrix size This parameter is found as the fourth number on the WWAMOPT card in the Wadam FEM file last card on the file before IEND The default value is 2000 If you have more than 2000 panels and a computer with sufficient memory consider increasing this number to some number larger than the number of panels The direct solver is quite competitive even for much more than 2000 panels The block iterative solver is always slower than the fully iterative solver but it is more robust The option IRREGULAR FREQUENCY REMOVE will increase the number of panels since additional panels on the interior free surface is automatically added The AREA MAXIMUM DIAGONAL options are only relevant in combination with the ANALYTICAL option If the panels are very elongated we recommend to use ANALYTICAL MAXIMUM DAIGONAL This is always a more robust option but gives a moderate increase in CPU time Wadam 5 30 SESAM 22 JAN 2010 Program version 8 1 DEFINE GENERAL EXECUTION DIRECTIVES PRINT SWITCH DUMP OF LOAD DISTRIBUTION DUMP OF LOAD TRANSFER DUMP OF MODEL DATA PRINT SWITCH MAXIMUM PRINT NO EXTRA PRINT NORMAL PRINT PURPOSE The command sets Wadam print switches Note that a print switch other than NO EX
10. PARAMETERS len Length of the tethers pre Pre tension in the tethers unit force stiff Elastic stiffness of the tethers per length of the tether unit force per length xoff Offset of the platform in x direction in the input coordinate system yoff Offset of the platform in y direction in the input coordinate system Wadam SESAM 5 66 22 JAN 2010 Program version 8 1 DELETE CORRESPONDANCE ELEMENT ENVIRONMENT GENERAL HYDRODYNAMIC PROPERTY END DELETE PURPOSE The command deletes previously given input For explanation of the parameters of this command see the corresponding alternatives in the DEFINE com mand SESAM Program version 8 1 22 JAN 2010 EXIT EXIT PURPOSE The command causes exit from Prewad Wadam 5 67 Wadam SESAM 5 68 22 JAN 2010 Program version 8 1 HELP SUPPORT GENERAL SYNTAX SPECIAL KEYS STATUS LIST HELP PURPOSE The command provides information on subjects PARAMETERS SUPPORT The telephone and telefax numbers and the Internet address for requesting support is printed together with detailed information on the program version used This in formation is of interest in connection with support requests The information is printed in the print window line mode window on Unix GENERAL SYNTAX Information on how to enter commands and text is provided The information is printed in the print window
11. Patran Pre general structures Prefem general structures Submod sub modelling Proban probabilistic risk and sensitivity INTEGRATED PROGRAM PACKAGES Wadam wave loads on general structures Wajac wave loads on frame structures Wasim 3D wave loads on vessels Waveship wave loads on ships Installjac launching of jackets ENVIRONMENTAL ANALYSIS SESAM INTERFACE FILE Sestra Splice linear structure statics and pile soil dynamics interaction Usfos progressive collapse 2 N Pa lt Z lt z Q x gt N GeniE DeepC conceptual modeller deep water mooring including analysis including Wajac Sestra Simo Splice Framework Riflex Figure 1 1 SESAM overview POSTPROCESSING HydroD environmental modeller including Wadam Postresp Postresp presentation of statistical response Xtract presentation amp animation of results Framework frame design Stofat shell plate fatigue Profast probabilistic fatigue and inspection Platework plate design Concode concrete design Wadam SESAM 1 4 22 JAN 2010 Program version 8 1 1 3 How to read this Manual Chapter 2 FEATURES OF WADAM describes the problems Wadam can solve Descriptions of models environment and results produced by Wadam are included Chapter 3 USER S GUIDE TO WADAM presents tutorial examples Each example includes a discussion of the modellin
12. amplitude This amplitude is typically an extreme level of the waves eg a 20 year level For an amplitude A the pressure load on a panel with centroid at level z above the still water level z are then PR wPo 2 22 54 2 35 where Py is the pressure at the panel centroid nearest to still water level approximately vertically below the panel with centroid at z and w is the linear attenuation factor defined by _ A 2 Z y 2 36 eed The reduction is continued down below the still water level but is then applied to the pressure at the panel centroid Pr wP ze AS zZ Z lt 9 2 37 where P z is the pressure at the panel centroid at ze P z and Pg are the standard pressure calculations from the boundary value problem bounded by the still water level Wadam SESAM 2 52 22 JAN 2010 Program version 8 1 2 7 The Save Restart System The save restart option in Wadam provides a mechanism to store potentials from the solution of the radia tion and diffraction problem from one Wadam run to the next Hence for a given model the radiation and diffraction potentials for combinations of incident wave frequencies and heading angles need only be calcu lated once The save restart file may be viewed as a database for the calculated potentials That is potentials for differ ent combinations of frequencies and heading angles may be appended to the save restart file from a sequence of runs Furthermore Wadam may extract potential
13. Japan Soc of Naval Arch Vol 109 1960 7 H Kato Effect of Bilge Keels on the Rolling of Ships Memories of the defence Academy Japan Vol IV No 3 pp 369 384 1966 8 Sarpkaya T and Isaacson M Mechanics of Wave Forces on Offshore Structures Van Nostrand Reinhold Company New York 1981 9 Finne S Grue j and Nestegard A Prediction of the complete second order Wave Drift Damping force for offshore structures Proceedings ISOPE 2000 Seattle Wadam SESAM REFERENCES 2 22 JAN 2010 Program version 8 1 SESAM Program version 8 1 22 JAN 2010 APPENDIX B THEORY B1 Hydrostatic Forces B1 1 Hydrostatic Coefficients Wadam calculates the non zero coefficients Cj in the hydrostatic restoring matrix as follows Here Xp Vp Zp XG YG ZG P pgs Pgs C34 pgS C35 pg Sy V Z_ mgzg pgSi C45 PEV Xg t MEX G pe Si VZ MN amp ZG pgV yet MEVG is the centre of buoyancy is the centre of gravity is the density of the fluid Wadam B 1 Wadam SESAM B 2 22 JAN 2010 Program version 8 1 g is the acceleration of gravity Vy is the volume of the wetted part of the body S is the water plane area S S TEL Oe So Sij Jars ij 1 2 S refers to the body in a static condition B2 Morison Element Formulations B2 1 The Anchor Element Formulation The mooring stiffness matrices K for each anchor element in a Morison model are described below The K ma
14. The Morison model corresponds to a superelement in the structural model such that the tether reaction forces are transferred to the structural model This load transfer is defined by the following commands DEFINE GENERAL EXECUTION DIRECTIVES stalo STRUCTURAL LOADS COMPOSITE STR MODEL NO END END END o DEFINE GENERAL ANALYSIS MODELS ORISON MODEL 100 STRUCTURAL MODEL 301 END END END The structural model contains several static load cases to be used in the dimensioning of the TLP These load cases are numbered in increasing order starting at one in the different first level superelements included in the structural model Subsequently the wave load numbers start at the first idle load case number for each first level superelement Unformatted Loads Interface Files are used in the load transfer to the structural analysis This is specified in Prewad as follows DEFINE GENERAL EXECUTION DIRECTIVES RESULT FILES LOAD TRANSFER OPTION OFFSET IN LOAD CASE NUMBER AUTOMATIC FILE FORMAT UNFORMATTED END END END END END Local load cases for all first level superelements are created There are 40 global load cases in the analysis 8 wave headings and 5 wave periods but the number of local load cases is larger for superelements that are repeated For superelement 111 the total number of local load cases i
15. e Hydrodynamic load definition on outside surfaces PROPERTY LOAD 1 HYDRO PRESSURE wet surfaces OUTSIDE OUTSIDE SURFACE END END The mesh density of the structure is important for the hydrodynamic loads It is of importance that the mesh density reflects the hydrodynamic pressure variation around the structure In areas where the pressure varia tion is large element sizes should be small The following items should be remembered when modelling a panel model The pressure variation as a function of draught is at a maximum close to the surface i e small element heights should be used close to the surface e The pressure variation is large close to the edges in the structure i e element sizes normal to the edge length should be small e The elements should be modelled as planar as possible Elements which are too twisted should be divided into smaller elements e Large changes in element size for neighbouring elements should be avoided The largest element diagonal should be smaller than one quarter of the wave length for all wave periods contributing significantly to the wave pressure at given locations It is also noted that the mesh refinement of a hydro model normally needs to be high if the mean drift forces by pressure integration shall be obtained This compared to the calculation of rigid body responses where reliable results may be obtained with a considerably coarser mesh Morison Model The
16. 1 1 1 2 1 3 1 4 1 5 1 6 2 1 2 2 2 3 2 4 2 5 INTRODUCTION icssssacucccsosussegssdesductoousssabatssesdbescca ccvedsstqadesbesductoanegenbeteschddeauseccenadeceanssdss 1 1 Wadam Wave Analysis by Diffraction and Morison Theory ccsccesseeseceteceeeeeeeeneeeseeseeees 1 1 Wadam in the SESAM System cccccccscsscsescesseessecseeeeceseeeseeesecaaecseseeeeeeeesaecsaeceseeeceseecseeeeenseeags 1 2 How to read this Mamtaal ccccccccccssecsecsseceseesseeesceeseceseceseceseessecsaecaeseeeseeeeseecauececeeeeeneeeeeensenaeeaas 1 4 Terminology and Notations s iscessichecssnehoes the odasedhecuuetcodadesEesavelbeleidegeusdecladavacdscteaedastedecastinedeues ecaetedt 1 4 Stat E E Te xt E ca chiea tes cate eaceeehebs a Lobb Sev Fl T E A AR 1 5 Wadan Extensions eenia a e a E e a a Cab evideads coded nt e e ede e estes 1 5 FEATURES OF WADAM ssseessssesssoscssccocsessecsessooccssosocssoososcsosseccsoosessoecssossosssssseesssseessso 2 1 Definition of Model Types in Wadam c ceccccsccsseeseceseceseeeseecsecaeceseeeeceeeeeseecaaeceseneeseeeeseeeseneenes 2 1 2 1 1 The Co rdinate Systems ceiien e a e a a 2 3 2122 I E e OT E EE A E E dur de leas hag ood theds ta otans 2 5 21 3 The Morison Model ormer nei eoi ee iE nee E A EEE OER is 2 7 24 The Dial Modeleren e AR A A A a a iaat 2 16 2 1 5 The Composite Model 00 0 ccccecccesceescesseessecsecsecseeeseeeeseecseeeseceseceseceseeesecaaeceseseeeeeeeeeeesaees 2 18 2 1 6 Si
17. CONT VARIOUS PRINT ALT ERNATIVES PING sie sats Gases ens She We eee OS ae SE IF BATCH CARD INPUT ROL DATA INCLUDING XE CUT LON DTRECTTME S 2 siete ite AEE EAE A E n I Sire ena b be dene E MOD TOL DATA DUMP INPUT DUMP CHECK OF SUMMARY ENVIRON RISON SPECIFYING THE INPUT INTERFACE P OF OF INTERFACE OF INTERFACE FILE DATA SPECIFYING THE INPUT INTERFACE P OF INTERFACE FILE P OF MASS DATA DATA SPECIFYING THE RESTORING DATA FOR WAVE OF ANALYSIS INTERFACE FILES ELE PANEI 1 MODI CONTROL DATA ORISON M PILES pe paneis ENT TRANSFORMATION MATRICI SPECIFYING THE xj ua H m aj w DATA ON SAVE ETS ENE ORMAITON 332d os so cette EE gS ace a a ene EEE Se Ste J1ERANCES AND CRITICAL CONSISTENCY PANELS AND DEFINITI DATACHEC Sk EXECUTION a2 23 4 COMMENTS RAG VISCO ORISON ON OF n GENERATION OF D FORCE K SUMMARY MESSAGES SAVE RI ESTORING INPUT INFORMATION INCLUDING EACH INDIVIDUAL INPUT MODEL FILI OF MODEL PROPERTIE ENTA Iie DATA carii pa e E a a E ore wee Oa a E EES O ELEMEN L DATA ymn a ist er E ve E A a e ari ele E ey en s
18. Calculation of hydrodynamic exciting forces added mass damping and global motion response for the TLP e Eigenvalue calculations for rigid body motions One set of eigenvalues is calculated for each wave period e Detailed load calculations and load transfer to structural model This includes Nodal accelerations for all nodes in the structure Line loads on the beams corresponding to Morison elements The loads are obtained from integration of panel pressures in a dual model see Section 2 1 4 Tether reaction forces caused by rigid body motions of the TLP Preparations for this analysis in Wadam consist of the following steps e Creation of the panel model in Patran Pre or Prefem Symmetry of the structure is used and only one quarter of the TLP is modelled e Creation of beam elements in Genie or Patran Pre for the Morison and structural models e Creation of the remaining part of the structural model in Genie and or Patran Pre and Presel Transfer of Input Interface Files to the directory where the Wadam analysis is performed Definition of execution directives additional elements environmental properties etc in HydroD or Pre wad e Definition of correspondence between panels in the panel model and elements in the Morison model for transfer of integrated pressure loads Potential wave theory is used for all wave periods and the panel model is thus used for calculation of all wave loads The mass from the structural m
19. E SG Q aa aC oe qo oO Q m X S oe Gen dp oe oe S moO G J x oe o CO aed aO oe Q Oo 0 4 a Fy oe 4 o ie aO aO OHO oe Fx ol G aod r eal ole ole p Gow ag oe M oe 2 oe oe H O H op oe AY O AE O Sa n oe a N wH Ea oe ae oO ad O O ag ao Fy oe U d bo Wo Ay ole ole o A O G l X O H L HH pP O ol oe UY 4 aA oe oe N 3 fH 0 3 H A ae Q oO n Z nn O pi ae ale U H oO T oe Z oe oO oO of O oe a H ue A TAO ad Ae Fx oe 4 H GH o kA oe aO 5 n x on w Q al ae ae n e L IBK H my fy ole ole H 2 5 Om ole ole ea Con Hp oe oe qo oO Q cp ale ae G FH v vo ao I a aO H P 99 Ga GO AH oe oe G i Z od pP pP aa oe oe N p H Ww pD H H ae ae oO T oO oo Q A Ww oe oe QA WH H HAAR AHE CHAA amp Z ea kl A A DA A ol ol fx Yn ca Ea ao amp oe oe ae AP Al ae oO oP AP AP AP AP AP AP oP Ae SESAM Wadam Program version 8 1 22 JAN 2010 A 3 A2 Motion Response of a Floating box Tethered to the Sea Bottom This section presents the following e Preframe input for creating a Morison model also represented in the structural model consisting of four nodes only input for creating a quarter of the structural model e Presel input for assembling the structural model The Prewad input is given in Section 3 1 2 The Prefem input for creating the panel model is presented in Appendix A 1 299999909 29999909 SUPERELEMENT No 2 O O O O O G
20. File data types The naming convention for Loads Interface Files is simi lar to that of the Input Interface Files except that the identifying letter T is replaced by an L That is Ln FEM The Loads Interface Files are by default unformatted They may optionally be specified as formatted In addition the utility program Waloco may convert between formatted and unformatted Loads Interface Files If the Loads Interface Files contain dynamic load cases in the frequency domain format an additional analy sis control data file for the subsequent Sestra analysis is created This is the S file containing standard anal ysis control data for the Sestra analysis The naming convention for the S file is Sn FEM where n is the superelement number of the top level superelement in the structural model Hydrodynamic Results Interface File The Hydrodynamic Results Interface File is created if a global response analysis is performed in Wadam It contains transfer functions for rigid body responses together with transfer functions for off body kinematics and the rigid body matrices The naming convention for the Hydrodynamic Results Interface File is G1 SIF for formatted sequential file G1 SIU for unformatted sequential file G1 SIN for Norsam direct access format Print File The print file contains major results information from a Wadam analysis The full description of the result types in the print file is included in Section 2 5 in this manual 4 1 5 The S
21. Ln FEM Hydrodynamic Results Interface File G1 SI S File Sn FEM Figure 4 1 HydroD or Prewad Wadam communication Wadam SESAM 4 2 22 JAN 2010 Program version 8 1 As depicted in Figure 4 1 the entire set of permanent files associated with a Wadam run is Analysis control data mandatory input Input Interface File mandatory input Print file mandatory output Loads Interface File optional output Hydrodynamic Results Interface File optional output Additional analysis control data for Sestra S file optional output Save restart file for velocity and source potentials optional input output In addition to the permanent files Wadam will generate a set of temporary files during the execution These files will be opened on the directory where the process is located unless specific assignments are provided in the command procedures HydroD is normally started directly from a shortcut on the desktop HydroD can also read Prewad jnl files G wadam course course hyd HydroD l File Edit View Insert Tools Help SE course Le mar 2004 11 04 4 Environment E a HydroModels FL HydroModel1 B HydroProperties 5 _HydroStructure ef LoadCrossSections lt BBP PanelModel1 wh StripModel1 A BilgeKeel1 lt M StructureModel1 LoadingConditions LoadingCondition1 Y Addtionalmatrices MassModel1 amp lt gt FAL HydroModel2 Utilities ViewSettings WadamAnalysis
22. Local load cases for all first level superelements are created starting on load case 1 since no static load cases are included There are 160 global load cases in the analysis 8 wave headings and 20 wave periods The loading on the elements and nodes in the structural model is written to Loads Interface Files used in the structural analysis One file containing all local load cases is written for each superelement In addition the S file S302 FEM is created containing input to Sestra about wave periods headings and load cases This file must be located in the same physical directory as the Input Interface Files when the structural analysis is performed If this file is not included in the structural analysis fatigue postprocessing cannot be performed e L100 FEM Tether reaction loads due to rigid body motions line loads from hydro pressure and nodal accelerations for superelement 100 Morison model e L101 FEM Nodal accelerations for superelement 101 Connection superelement e L12 FEM Nodal accelerations for all other first level superelements e 302 FEM Input file for subsequent Sestra analysis 3 2 4 Global Response of a Semi Submersible using Dual Model This example shows the use of Wadam in a typical global response calculation of a semi submersible The analysis is mainly used for selection of wave periods and headings to be used in analyses similar to the one described in Section 3 2 2 The Morison model
23. Morison model is a beam element model see Figure 3 9 The model consists of 2 node beam elements and spring elements representing the tethers These spring elements are neglected by Wadam and may actu ally be omitted in the Morison model for this analysis Node masses are used to include the mass above the still water level Except for the mass distribution the same Morison model is used for all the analyses for the TLP This shows the similarity of the analyses The same input coordinate system as for the panel model is used This is required by Wadam The Morison model is used to connect the tether elements specified in HydroD or Prewad All additional elements specified in Prewad must be connected to existing elements or nodes in the Morison model The tether elements are consequently connected to appropriate nodes in the Morison model The mass distribution used in the sectional force calculations is taken from the Morison model It is there fore important that the distribution is correct SESAM Wadam Program version 8 1 22 JAN 2010 3 15 Figure 3 9 Morison model Additional Elements For this analysis the following additional elements are defined in Prewad TLP mooring elements The TLP mooring elements are specified for inclusion of tether stiffness One element is specified for each tether The inclusion of stiffness for one tether in Prewad is defined as follows g EFINE ELEMENT TLP MOORING ELEMENT lno nodel 11 131 E
24. SURFACES INCLUDED SHELL 4NODES END END MESH ALL SUFACES MESH ALL SET THE INSIDE SURFACE OF THE PANEL ELEMENTS TO BE INSIDE THE BOX USING A POINT A AT CENTRE OF BOX EFINE POINT A 0 0 30 END END END D SET INSIDE A POINT A END J EFINE YOUNGS MODULUS POISSONS RATIO DENSITY OF STE EI a AP AP AP WP o PROPERTY MATERIAL ELAST THICKNESS OF ALL T D 2 1 X 10 11 N M 2 0 3 7850 KG M 3 SURFACES AS 0 1M LASTIC 21E 12 3 7850 0 0 0 RFACES INCLUDED 1 NO 1 TO TELL WADAM THAT ALL SURFACES YDRODYNAMIC PRESSURE WHERE RELEVANT END THICKNESS ALL SU END END CONNECT MATERIAL ELAST ALL SURFACES INCLUDED END DEFINE DUMMY LOADCASE ARE TO BE LOADED WITH H I E BELOW STILL WATER LINE PROPERTY LOAD 1 HYDRO PRE ti zZ l SSURE ALL SURFACES INCLUDED OUTSID Gl OUTSIDE SURFACE SESAM Wadam Program version 8 1 22 JAN 2010 A 5 DEFINE SUPERNODES ON PLANES OF SYMMETRY AND AT CORNER WHERE ER IS TO BE CONNECTED AP iP AP oP E a r PROPERTY BOUNDARY CONDITION ATI11 amp AJ11 amp AK121 AK211 PERNODE SUPERNODE SUPERNODE SUPERNODE SUPERNODE SUPERNOD eal eal eal T Me
25. Sestra In the hydrostatic restoring contribution from the Morison elements the local waterplane moment for each Morison member is not included This can cause errors if some of the beams have a large diameter The fix to this problem is to include this restoring contribution as an additional restoring matrix Global Mass Matrix A 6 by 6 mass inertia coefficient matrix is reported for each body It is generated according to the input def inition and hence may be calculated from either e The hydro model e The structural model e A specific mass model e The input definition of an inertia mass matrix based on Specifying the centre of gravity and the radii of gyration together with the total mass Specifying the 6 by 6 global mass matrix Wadam SESAM 2 38 22 JAN 2010 Program version 8 1 2 5 7 Added Mass Matrix The 6 by 6 added mass matrix is reported for each separate body The added mass interaction matrices between any two bodies in a multi body system are also reported The added mass matrix is calculated according to the type of the hydro model as follows e Frequency dependent added mass from potential theory e Frequency independent added mass from Morison s equation For the composite hydro model the added mass at a given frequency is reported with both frequency dependent and independent contributions 2 5 8 Damping Matrix The 6 by 6 damping matrix is reported for each separate body The potential dampin
26. Ship This example illustrates how Wadam may be used in a typical global response analysis for a ship with no forward speed This calculation is in principle equal to global response analysis for other types of structures SESAM Wadam Program version 8 1 22 JAN 2010 3 29 The two significant differences are the non linear viscous roll damping and the corrections in restoring forces due to the non linear GZ curve Both effects are introduced in a linearised form The following calculations are performed in Wadam for this analysis The first two tasks are automatically calculated while the others are specified for this analysis e Hydrostatic calculation in which both the hydrostatic and inertial properties for the structure are calcu lated e Calculation of hydrodynamic exciting forces added mass damping and global motion response for the ship Eigenvalue calculations for rigid body motions Added mass for the first wave period is used in the cal culations e Calculation of sectional forces in specified sections e Calculation of linearised viscous roll damping and restoring terms Preparations for the analysis in Wadam consist of the following steps e Creation of the panel model in Patran Pre Prefem and Presel Symmetry of the structure is exploited and only one half of the ship is modelled e Creation of beam elements for the mass model in Genie or Patran Pre Transfer of Input Interface Files to the directory where the Wadam
27. Wadam from Manager as illustrated in Figure 3 4 The HydroD wizard for this example is shown in Figure 3 6 Since we now have a Morison model included we Select Composite model and we tick off for inclusion of TLP elements SESAM Program version 8 1 AP oP ol AP AP AP AP AP AP AP AP AP AP AP P AP AP AP CP ol ol j Y Y W W i Y e Wadam 22 JAN 2010 3 7 i i N E i T Figure 3 5 Structural model assembly of simple box model tethered to the sea bed Define general information about the model DEFINE GENERAL Specify the analysis mass model panel model Morison model structural model models to be used for Global mass matrix generated from structural model Superelement No 1 1 4 Box Superelement No 2 Tethers Superelement No 21 Box 3 Tethers 2 The Structural model comprises T21 T21 created by Presel T3 models 1 4 of Box T2 models the 4 Tethers T3 T3 T3 T3 T2 Note Structural model is also used as mass model No mass is generated for the Tethers ANALYSIS END MODELS MASS MODEL GLOBAL MASS MATRIX GENERATE 21 STRUCTURAL MODEL 21 MORISON MODEL 2 SINK SOURCE 1 Wadam Specify JP AP AP AP AP AP oP AP AP AP AP AP AP AP AP OP AP AP AP AP AP OP AP CP AP AP SESAM 22 JAN 2010 Program version 8 1 the constants cha
28. also be used with a time domain output option to calculate drag forces due to time independent current The same analysis model may be applied to both the calculation of global responses in Wadam and the sub sequent structural analysis For shell and solid element models Wadam also provides automatic mapping of pressure loads from a panel model to a differently meshed structural finite element model The 3D potential theory in Wadam is based directly on the Wamit program developed by Massachusetts Institute of Technology Ref 1 and Ref 2 1 2 Wadam in the SESAM System Wadam is an integrated part of the SESAM suite of programs It is tailored to calculate wave loads on mod els created by the SESAM preprocessors Patran Pre Prefem Genie and Presel The models are read by Wadam from the Input Interface File T file The Wadam analysis control data is generated by the Hydrody namic design tool HydroD or by the Wadam preprocessor Prewad The results from the Wadam global response analysis may be stored on a Hydrodynamic Results Interface File G file for statistical postprocessing in Postresp The loads mapped to structural finite elements may be stored on the Loads Interface File L file for a subsequent structural analysis in Sestra Figure 1 1 shows Wadam in the SESAM system A detailed description of the input and output files is given in Chapter 4 SESAM Program version 8 1 22 JAN 2010 Wadam PREPROCESSING ASSOCIATED
29. are calculated for the beam elements and nodes corresponding to the Morison elements The method of load calculation depends on the connection between the hydro model and the structural model If the hydro model is a Morison model then the hydrodynamic pressure loads obtained by Morison s equation are represented directly as line loads and nodal loads on the beam element model If the hydro model is a panel model then the hydrodynamic loads are first calculated as panel pres sures and then transferred to a Morison model according to a panel to Morison element correspond ence The Morison element loads are subsequently represented as line loads and nodal loads on the beam element model 2 44 Environmental Description 2 4 1 Surface Waves The models in Wadam may when first order potential theory and Morison s equation are applied be exposed to planar and linear harmonic waves i e waves described by the Airy wave theory For the second order option for the potential theory see Ref 3 for a detailed description of the theoretical background The incident waves may be specified by either wave lengths wave angular frequencies or wave periods The direction of the incident waves are specified by the angle B between the positive x axis and the propagating direction as shown in Figure 2 25 a The incident wave used in Wadam is defined as n Re Ae t E cosp ysinp 2 2 which alternatively may be written as SESAM Wadam Pr
30. by 6 linearised viscous damping matrix C represents the 6 by 6 hydrostatic restoring matrix Co represents the 6 by 6 external restoring matrix F is the 6 by 1 complex exciting force vector for frequency and incident wave heading angle The eigenvalues and eigenvectors of the rigid body system is obtained for a given incident wave fre quency by solving the eigenvalue problem A M A C 0 2 31 The natural periods of the rigid body system at a given incident wave frequency is expressed as 2T Pa As T 2 32 Wadam SESAM 2 50 22 JAN 2010 Program version 8 1 2 6 6 Calculation of Tank Pressures Wadam calculates by an approximate algorithm the harmonic pressure load on the wet finite element sides in internal tanks The loads are calculated by applying a hydrostatic pressure distribution in the accelerated reference frame fixed with respect to the tank The pressure load is divided in a constant and an oscillating part and repre sented by separate load cases The pressure gradient is given by Vp p g a 2 33 where g is the acceleration due to gravity a is the complex acceleration of the mid point of the tank and p is the mass density of water The gravity vector described in a coordinate system oscillating with the body has a constant and an oscillating part Accordingly the pressure gradient described in the body fixed coordinate system has a constant part pg and an oscillating dynamic or fluctuating pa
31. element a b Figure B 6 The DISTOL and ANGTOL functionality Wadam reports information from the actual mapping on the form NDIST NANG NOPP where NDIST shows the number of the closest panels which has been checked against Equation B 3 and NANG corre spondingly shows the number of panels which has been checked against Equation B 4 NOPP shows the number of panels which has been checked against Equation B 4 with the modification that is replaced by o 180 NOPP is indicating that normal vectors of the panel and finite element are pointing in the opposite direction The number of finite elements in the structural model with no matching panel is reported by Wadam B3 4 Calculation of Tank Pressures The loads are calculated by applying a hydrostatic pressure distribution in the accelerated reference frame fixed with respect to the tank The pressure load is divided in a constant and an oscillating part and repre sented by separate load cases The pressure gradient is given by Vp p g a B 5 where g is the acceleration due to gravity a is the complex acceleration of the mid point of the tank and p is the mass density of water The gravity vector described in a coordinate system oscillating with the body has a constant and an oscillating part Accordingly the pressure gradient described in the body fixed coordinate system has a constant part pg and an oscillating or fluctuating part Vp P 8 a B 6 where gris the fl
32. for infinite and finite water depths and both single bodies and multiple interacting bodies can be analysed The flow is assumed to be ideal and time harmonic The free surface condition is linearised for the first order potential theory while the non linear free surface condition is imposed for the second order potential theory computation The radiation and diffraction velocity potentials on the wet part of the body surface are determined from the solution of an integral equation obtained by using Green s theorem with the free surface source potentials as the Green s functions The source strengths are evaluated based on the source distribution method using the same source potentials The integral equation is discretisised into a set of algebraic equations by approximating the body surface with a number of plane quadrilateral panels The source strengths are assumed to be constant over each panel Two one or no planes of symmetry of the body geometry may be present The solution of the alge braic equation system provides the strength of the sources on the panels The equation system which is complex and indefinite may be solved by a direct LU factorisation method or by an iterative method Boundary Value Problem Formulation The assumption of potential flow allows defining the velocity flow as the gradient of the velocity potential that satisfies the Laplace equation yaa 2 18 in the fluid domain The harmonic time dependence allows def
33. given in the body coor dinate system Y coordinate of the origin of the input coordinate system given in the body coordi nate system SESAM Program version 8 1 zm delta XZ PLANE YZ PLANE YZ XZ PLANE NONE Wadam 22 JAN 2010 5 45 Z coordinate of the origin of the input coordinate system given in the body coordi nate system Angle between the input x axis and the body x axis in degrees The angle is given from the input x axis to the body x axis Positive direction is counter clockwise The panel model has the xz plane as its symmetry plane The panel model has the yz plane as its symmetry plane The panel model has both the yz plane and xz plane as symmetry planes The panel model has no planes of symmetry Wadam 5 46 SESAM 22 JAN 2010 Program version 8 1 DEFINE GENERAL MULTI BODY STRUCTURE IDENTIFICATION STRUCTURE IDENTIFICATION body cleng xb yb zb delta ORIGIN OF BODY END PURPOSE The command defines the structure dependent data for each body These data are common for all different models representing the structure PARAMETERS body cleng xb yb zb delta ORIGIN OF BODY Body identification number Note that the body numbers must be consecutively or dered Characteristic length of the body Usually the largest horizontal distance between 2 points on the average immersed surface X coordinate of the origin
34. is read from the file or the specified number of commands have been read Exit from this command is carried out by typing either or PARAMETERS ncomnd Number of commands to be read from command input file When the same command is re peated in the command input file the command lines will count as one command only ALL Prewad will read and execute all commands available on the command input file Wadam SESAM 5 82 22 JAN 2010 Program version 8 1 SESAM Wadam Program version 8 1 22 JAN 2010 A 1 APPENDIX A TUTORIAL EXAMPLES This appendix includes the preprocessor input for the simple examples described in Section 3 1 Also the table of contents common for all Wadam print files is given for reference purposes A1 Motion Response of a Floating Box This section presents the Prefem input for creating a quarter of the double symmetric box model of Section 3 1 1 ole o o ole ole ole oP oP ole ole o o ole ole oP o ole ole o o ole ole o o ole ole o o ole ole oP oP ole ole oO o ole oe oP o ole ole o o ole ole o o o ole ole foe oP ole ole o oP ole ole oP o oe ole oP oP ole oP oe o ole ole oP o ole ole o Example 3 1 1 z A Floating Box 90m x 90m at draft of 40m Motions response analysis only Output from as the panel H H 1 FEM will be used in Wadam n model T T n O B Q o o o oe oe oe o o o o o
35. is represented as a sequence of constant line load segments Each segment will automatically correspond to a sub element of a 2D Morison element The load evaluated at the centre of gravity of each Morison sub element is represented as constant load intensities with x y and z force components acting over the line segments This is so both for hydrostatic and hydrodynamic loads The line loads produced by Wadam do not include any eccentricities which may exist in the actual load Figure B 4 shows the line load representation on a beam element with four line seg ments subelement centre of gravity gt Figure B 4 Line loads in Wadam B 3 3 The Mapping of Loads from Panel Models to Finite Element Models The hydrodynamic pressure distribution on a panel model is described as a piece wise constant pressure var iation Each panel is represented with a constant pressure value which is calculated at its centroid The map ping of loads from panels to finite elements is based on a minimal distance criteria between the centroids of panels and structural finite elements That is each wetted side of a finite element will receive the constant pressure of the closest panel while satisfying user specified distance and out of plane criteria Wadam SESAM B 10 22 JAN 2010 Program version 8 1 The mapping algorithm may be described as For each element assign normal pressure from the closest panel centroid to centroid provided that Equation B 3 an
36. moments at specified phases of the incident waves with given wave amplitudes For fixed structures the deterministic Morison option may be used to include the following non linear effects in Morison s equation SESAM Wadam Program version 8 1 22 JAN 2010 2 39 e Non linear viscous drag formulation e Time invariant current may be superimposed on the fluid velocities e Forces and moments may be calculated up to the free surface by constant extrapolation of the linear wave profile 2 5 10 Rigid Body Motion The transfer functions for rigid body motion due to the incident waves are reported for each body for all the combinations of wave frequencies and heading angles The roll pitch and yaw motions are reported in radi ans The equation of motion is assembled from the calculated global matrices and transfer functions as described in the previous sections The HydroD or Prewad specified damping and stiffness matrices will be added to the otherwise calculated matrices By specifying the time domain output format the motions will be reported as deterministic motions at speci fied phases of the incident waves with given wave amplitudes 2 5 11 Second Order Mean Drift Forces The second order mean drift forces due to the linear incident waves are reported both on the print file and in the Hydrodynamic Results Interface File They are calculated by one of the following methods e Momentum conservation in the three horizontal degrees of f
37. one superelement is modelled the superelements must be assembled in Presel The ele ments accepted in the panel model are defined in Table 2 1 Note that panels are constructed by drawing straight line segments between the corner nodes of the finite element sides Therefore twisted panels are forced to be planar by projecting element corner nodes onto panel vertices in the plane defined by the line segment midpoints The wet surface of a panel model is identified by defining a dummy load on the panel model in Patran Pre or Prefem In Prefem this is achieved by applying a so called HYDRO PRESSURE load with load case number one to all wet surfaces of the model Panels will be generated for all element sides below the still water level and above the sea bed where HYDRO PRESSURE load is defined The model may be verified in Prefem by displaying the mesh on the wet surface and adding the HY DRO PRESSURE load The load is illustrated by arrows pointing from the fluid onto the wet element sides In Patran Pre the corresponding option is the Hydro Element Uniform load Wadam will automatically adjust the wet element sides extending above the still water level into panels with its uppermost edge and vertices in the still water level Depending on the shape and orientation of the wet element sides this may actually lead to either an adjustment or a division of a wet element side into new pan els as shown by examples in Figure 2 6 This automatic algorithm is al
38. platform with transfer of loads to a 3D beam model of the pontoons columns braces and deck e Motion response analysis of a ship hull Wadam SESAM 3 2 22 JAN 2010 Program version 8 1 3 1 Simple Examples 3 1 1 Motion Response of Floating Box The panel model representing the box is shown in Figure 3 1 see the input in Appendix A 1 The box dimensions are 90 by 90 metres with a draft of 40 metres The box is freely floating Since the box is dou ble symmetric the panel model need only represent the part of the box in the first quadrant The arrows in the figure pointing from the fluid onto the panel model defines the wet surface of the model See also the definition of wet surfaces in Section 2 1 2 Figure 3 1 Prefem plot of the panel model representing a quarter of the box Notice the arrows show ing the direction of the HYDRO PRESSURE load This example is a plain global analysis for a panel model The Wizard for setting up the input for such an analysis in HydroD is shown in Figure 3 2 Figure 3 3 shows the box model as it may be viewed in HydroD with the HYDRO PRESSURE load displayed This picture shows a finer discretisation than the Prefem model The Prewad input for motion response analysis of the freely floating box is presented below Bold font high lights the commands as opposed to comments If this input is found in a file with name Prewad_in jnl then start Prewad and Wadam from Manager as illustra
39. relative to the x axis The current direction will be given relative to the wave direc tion Reference number of the vertical position in the current profile Up to 30 values may be specified Vertical position in the input coordinate system Wadam 5 8 vel dir FREQUENCY HEADING PAIRS LINEARISING WAVE HEIGHT SURFACE MODEL WATER DEPTH depth WAVE AMPLITUDE amp WAVE DIRECTION dir WAVE LENGTH WAVE FREQUENCY WAVE PERIOD length FINITE INFINITE WAVE LENGTH DEPENDENT SESAM 22 JAN 2010 Program version 8 1 Absolute value of current velocity at given vertical position Direction of current at given vertical position given in degrees Frequency heading pairs used in the computation of sum and difference forces will be defined Specification of wave linearisation curves Surface model will be defined Specification of water depth Water depth Specification of wave amplitude used in the time domain out put format Wave amplitude value Specification of wave heading Wave heading in degrees The angle between the positive x axis of the global coordinate system and the direction of wave propagation Specification of wave lengths Specification of wave frequencies Specification of wave periods Wave length period or frequency Finite water depth is used for calculation of Green s functions This option is recommended Note FINITE INFINITE must be given for all wave lengths frequencies pe
40. the Morison model 5000 Maximum number of sub elements in the Morison model when diffracted wave 2000 kinematics is used in Morison s equation Maximum number of sub elements in one Morison element 5 Maximum number of superelements in the Morison model 1 Maximum number of panels corresponding to one Morison sub element 99 Maximum number of sections for sectional loads 25 Maximum number of bodies 15 Analysis limitations Maximum number of wave frequencies 60 Maximum number of wave headings 36 Maximum number of wave headings using Haskin s relation 36 Maximum number of phase angles with the time output format 14 Maximum number of current profiles l Maximum number of levels in one current profile 30 4 4 Warnings and Error Messages Warning and error messages may occur in the print file or on the job log file Error messages will halt the execution Warnings are less serious and the execution will continue However the warnings may be a SESAM Wadam Program version 8 1 22 JAN 2010 4 7 symptom of a more serious problem Henceforth the program may abort with an error message at a later stage in the program execution In any case warning messages should be carefully interpreted Warnings and Error Messages in the Print File Problems and errors discovered during the check of analysis control data and the input models are reported on the print file The input data check includes e Check of analysis control data e Check of input model
41. the Wadam analysis control data file Wadam SESAM 5 78 22 JAN 2010 Program version 8 1 SET COMMAND INPUT FILE com name DATASET number NEW MODEL FILE prefix mod name OLD FILE DESTINATION SCREEN LINEPRINTER FILE SET NAME print name E PRINT FORMAT F G FILE PAGESIZE lines SCREEN END END PURPOSE The command sets different parameters for print batch execution and changing of command file database or dataset PARAMETERS COMMAND INPUT FILE com name DATASET number MODEL FILE Open a command input file containing Prewad commands The command is used to read a specified number of commands Name on the command input file It must be different from the command log and database files of Prewad Switch to another dataset The dataset number forms a part of the analysis control data file name New dataset number Close the current Prewad database model file and open anoth er without exiting and re entering the program Identify the al ternative database file by giving prefix and file name without extension mod name Use NEW for a currently non existing file a new one will be opened and OLD for a currently exist ing file SESAM Program version 8 1 DESTINATION FILE FORMAT PAGESIZE Wadam 22 JAN 2010 5 79 The destination of the print may either be the SCREEN or a FILE Use SET PRINT FILE NAME to give the name of
42. the input data controlling the analysis to be performed by Wadam The file is generated by HydroD or Prewad The input data are established based on the Prewad commands in Chapter 5 of this manual or by HydroD Input Interface Files The Input Interface Files contain the model to analyse The files are established by the preprocessors A detailed description of the Input Interface File format may be found in the Input Interface File Description The Input Interface Files are formatted files There is one Input Interface File for each separate superelement Wadam imposes the naming convention that the Input Interface Files must exist in the default directory for the analysis and that there must be no prefix for the Input Interface Files That is the Input Interface File names must be of the form Tn FEM where the T identifies the file as an Input Interface File and n is the superelement number With the multi body option there is no restriction on the file prefix Hence with the multi body option the Input Interface Files may be of the form prefixTn FEM where the prefix is specified in Prewad SESAM Wadam Program version 8 1 22 JAN 2010 4 5 4 1 4 Output Files Loads Interface File The detailed finite element loads from Wadam will be stored in Loads Interface Files see Section 2 1 9 The Loads Interface Files are generated for the first level superelements only The Loads Interface Files consti tute a subset of the Input Interface
43. the structure are calcu lated e Calculation of hydrodynamic exciting forces added mass damping and global motion response for the TLP e Eigenvalue calculations for rigid body motions One set of eigenvalues is calculated for each wave period e Sectional forces in specified sections These are used for selection of waves to be used in a structural analysis e Calculation of constant drift forces and moments including the effect of motion These are used in a suc ceeding analysis where the maximum offsets for the TLP are calculated e Calculation of fluid kinematics in specified points used for air gap and wave up welling analyses The fluid kinematics include the effect of radiation and reflection of waves from the TLP Preparation for this analysis in Wadam consists of the following steps e Creation of the panel model in Patran Pre or Prefem Symmetry of the structure is used and only one quarter of the TLP is modelled e Creation of beam elements for the Morison model in Patran Pre or Genie Transfer of Input Interface Files to the directory where the Wadam analysis is performed Definition of execution directives additional elements environmental properties etc in Prewad A Morison model is used for inclusion of mass The tether stiffness is as required by Wadam connected to elements in the Morison model The TLP considered is a typical double symmetric structure with rectangular pontoons and circular col umns All t
44. units used in Wadam is controlled by the acceleration of gravity L T and the fluid density M L All other input data must be expressed in terms of these units For example Fluid kinematic viscosity L7 T e Fluid velocity L T Wadam SESAM 2 34 22 JAN 2010 Program version 8 1 2 5 2 Result Reference Point For single body structures the results from Wadam are reported with respect to a result reference point which is coinciding with the origin of the global coordinate system see Section 2 1 1 For multi body struc tures there is one result reference point for each body coinciding with the body coordinate systems see Sec tion 2 1 7 2 5 3 Dimensioning of Results Wadam reports results on dimensionalised and non dimensionalised form as follows e The Hydrodynamic Results Interface File contains dimensionalised results e The Loads Interface Files contain dimensionalised results e The Wadam print file contains both forms as follows Chapters 2 and 5 contain dimensionalised results Chapter 4 contains non dimensionalised results The non dimensionalising factor D specified in Table 2 4 and Table 2 5 may be used to obtain dimensional ised results Fy from the formula F D F 2 12 where F is a non dimensionalised result reported in chapter 4 in the Wadam print file The factors used in the tables are p Density of the fluid g Acceleration of gravity L Characteristic length V Displaced volume of t
45. where N4 is the first node defining the 2D Morison element as shown in Figure 2 12 a e The C axis is the third axis in the right handed cartesian coordinate system defined by amp and n e The axis is parallel with the x axis if the y axis is parallel with the Zinp axis see Figure 2 12 b In addition to the 2D Morison elements connected to 2 node beam elements defined by preprocessors 2D Morison elements may also be defined directly by HydroD or Prewad Such additional Morison elements must however be related to existing nodes in the Morison model defined in a preprocessor Additional Mori son elements may be used to include specific load contributions in a global response analysis Note The loads from additional 2D Morison elements will however not be transferred to loads in a subsequent structural analysis thus resulting in load imbalances in the structural analysis Wadam SESAM 2 12 22 JAN 2010 Program version 8 1 Yinp Xinp b Figure 2 12 Local coordinate system of 2D and 3D Morison elements 3D Morison Elements A 3D Morison element is defined in HydroD or Prewad and can only be connected to nodes in the Morison model A 3D Morison element may be used to include loads which cannot be represented with a 2D Morison ele ment in a hydro model Drag forces and added mass forces in the longitudinal direction of a 2D Morison ele ment are examples of forces that can be included with a 3D Morison element A 3
46. 135 VEDI Kne mati CS asn anre a a a aad a a S e a a e a 2 39 2 544 Waye Drift Dampingi poeira eiaa E aE AR eE a ea RESE 2 40 2 5 15 Distributed Hydrostatic Loads cecccccceccessesseesceeseceseceseeeeeeesecaaecsesneeeseecseecseceeeeseeenes 2 40 2 5 16 Distributed Hydrodynamic Loads 0 cccccesesscesseesceeeceeceseeeseeesecaeseeeseeeeseecsaeeeeeseeeaes 2 41 ZS 07 gt Load SunisReports iis s05 E EE EEE dodaons casaeastdente laigoied seeg de aousdncaabevens 2 42 Dd 1Bo Sectional Loads xc h seve ees shk ye eahees ole bes a e e r Ae 2 43 2 5 19 R lt Damping Coefficients saia E ane EAEEREN s 2 44 2 5 20 Global drag coefficient for roll damping ccceeccesceeeeeseeeseceteceseeeeeeeeeesseceeeseeseeenaes 2 45 Calculation M th ds ae a a a a a a a a a a aea e aS 2 46 2 6 1 Calculation of Wave Loads from Potential Theory ccccceesccsseceteeeeeeeeeenseeseceteeeseeenes 2 46 2 6 2 Calculation of Wave Loads from Second Order Potential Theory ccsccsesseeseeeees 2 47 2 6 3 Removal of Irregular Frequencies cccccecscecseesseceneceeceeeeescecsaececeeceseeeseecseeeeeseeeseeenes 2 47 2 614 Morison SEUI ON entenien ne e e E E teduiada Woes EEE EER 2 47 2 6 5 The Equation of Motion c cccccsccsssecssceseceseeeseeeseesseceseceeeeesecesecaaecsaeseeeseeeessecsaeceeeeenaes 2 49 2 6 6 Calculation of Tank Pressures 0 cceceseesceeseescesecaecseeaeeeeceecaecaceaeeeeeeseeaecaecaeeaeeaeeeeenaes 2 50 2 6 7 Pressure Loa
47. 2 212 repeated for all angles on the curve END END END END The non linear contributions above are linearised according to the maximum expected roll angle for each wave heading in the sea state considered These roll angles are found from a sequence of analyses per formed until convergence between input roll angles and computed extreme roll angles is achieved Satisfac tory convergence is analysis dependent but should at least be achieved when the error in the angle is less than 0 1 degrees Check of Results In addition to the checkpoints mentioned in Section 3 2 1 the following should be checked in a global response analysis of a ship e Roll angles The computed roll angles should be transferred to Postresp for statistical postprocessing For the given sea state considered the maximum roll angles should be equal to the roll angles given in the Prewad input Wadam SESAM 3 32 22 JAN 2010 Program version 8 1 SESAM Wadam Program version 8 1 22 JAN 2010 4 1 4 EXECUTION OF WADAM 4 1 Program Environment Wadam is a batch program It may be started from Manager from a command window or from HydroD The input to Wadam is prepared by the Prewad or HydroD Both these programs creates the Wadam analysis control data file WADAMn FEM as shown in Figure 4 1 ENVIRONMENTAL ANALYSIS Wadam wave loads on general structures ea 5 ie v Q amp Q es Loads Interface File
48. 2 JAN 2010 5 27 DEFINE GENERAL EXECUTION DIRECTIVES OUTPUT FORMAT FREQUENCY DOMAIN OUTPUT FORMAT phase TIME DOMAIN GROUP phf phl inc PURPOSE The command defines the domain in which the results from Wadam shall be given This concerns both results on the print file and loads on the Loads Interface File PARAMETERS FREQUENCY DOMAIN TIME DOMAIN phase GROUP phf phl inc All results will be presented as complex values All results will be presented as real values for a set of phase an gles When the TIME DOMAIN format is specified wave am plitudes must be specified by the DEFINE ENVIRONMENT WAVE AMPLITUDE command Phase angle s for which the results are given Up to 8 phase an gles may be specified The specified phase angles will be used for all wave directions Phase angles given as a group Using this option Wadam may handle up to 14 phase angles in the same run First phase angle in the group Last phase angle in the group Increment between the phase angles Wadam 5 28 22 JAN 2010 SESAM Program version 8 1 DEFINE GENERAL EXECUTION DIRECTIVES POTENTIAL THEORY POTENTIAL THEORY DIRECT EQUATION SOLUTION ITERATION NO REMOVAL IRREGULAR FREQUENCY REMOVE alpha NUMERICAL LOGARITHM SINGULARITY ANALYTICAL NUMERICAL INTEG TYPE ONE NODE GAUSSIAN FOUR NODE GAUSSIAN PANEL DIMENSION AREA MAXIMUM DIAG
49. 2010 2 27 In this very simple example there is a one to one correspondence between occurrence numbers and Presel index numbers This one to one correspondence is not required However when the occurrence numbers and the Presel indices do not match the load combination in Presel should be carefully performed to ensure that the indices correspond to the correct occurrence numbers The one to one correspondence may be violated for particular choices of using the same first level superele ment in several sub hierarchies of a multi level superelement model 2 2 Global Response Analysis 2 2 1 General The global response feature in Wadam computes the response of fixed and floating structures due to wave loads Results computed are forces and response transfer functions assuming rigid bodies Also global matrix results data sectional loads and off body kinematics results may be produced The results can be transferred to the statistical postprocessor Postresp for graphics presentation and further results processing through a Results Interface File The statistical postprocessing in Postresp consists of statistical analysis of transfer functions including cal culation of response spectra and short and long term statistics Postresp also includes the option to calculate the equation of motion from the global matrices and exciting forces transferred from Wadam The global response analysis is performed for a system consisting of a hydro model and a mas
50. 5 2 GENERATION OF GLOBAL RESPONSE INTERFACE FILE 5 3 GENERATION OF GLOBAL RESPONSE FILE NV1473 SUMMARY OF TIMING INFORMATION 2 cc ce ewww ee eee eee eee SUMMARY OF SBE LE USAGE 8 6 a a a ar terete eile che Spe aye ee enr aE aided x mK PS OS x x x xX x xX DM OX x xX OX x x Wadam A 7 x OX x XM MM KK KM KM xO x mM KM MM XK x x x lt x KM XM KM KX x MM KM KK XM KM OX lt x MM MM KM XK x x lt KOK MM KM K KO KOKK MM KM KM XM lt x MM MM KM XM x x K MM KM KM KM OX x MM KM KM KM KM KM MK XM K MM KM KM KM KM OX x Wadam SESAM A 8 22 JAN 2010 Program version 8 1 SESAM Wadam Program version 8 1 22 JAN 2010 REFERENCES 1 REFERENCES 1 Newman J N Marine Hydrodynamics The MIT Press 1977 2 WAMIT Users Manual Version 5 3S Department of Ocean Engineering Massachusetts Institute of Technology 3 C H Lee J N Newman M H Kim amp D K P Yue The computation of second order wave loads Published in the OMAE 91 conference proceedings Stavanger Norway 1991 4 The Implementation of Second order Force Computation in Wadam DNV Sesam Report No 93 7081 Rev 0 Oct 1993 5 M H Patel and E J Lynch Coupled dynamics of tension buoyant platforms and mooring tethers Eng Struct Vol 5 October 1983 6 N Tanaka A Study on the Bilge Keel Part 4 On the Eddy Making Resistance to the Rolling of a Ship Hull
51. AL THEORY ccceeeseceeees 5 28 DEFINE GENERAL EXECUTION DIRECTIVES PRINT SWITCH ccccscccssssseeesseseeeees 5 30 DEFINE GENERAL EXECUTION DIRECTIVES RESULT FILES 00 cccecsceceeseceeeenees 5 31 DEFINE GENERAL EXECUTION DIRECTIVES SAVE RESTART ccccceeccecceesseseeetteeeeeees 5 35 DEFINE GENERAL EXECUTION DIRECTIVES SECOND ORDER RESULTS 4 5 36 DEFINE GENERAL EXECUTION DIRECTIVES TOLERANCES eccccceesssceeesteeeeenteeeneaes 5 38 DEFINE GENERAL EXECUTION DIRECTIVES WAVE DRIFT DAMPING 0000 5 39 DEFINE GENERAL GLOBAL MATRICES 1 00 ccccccccessscessesseeceesceceeeaseecsesseseeesaececesaeeeeneaeeeeneaes 5 40 DEFINE GENERAL MULTI BODY 0 ccccccccccccsssscceessneceensneceessseceessnecessssaecensneceesseaeeessaaecensaes 5 43 DEFINE GENERAL MULTI BODY MODELS cccccccccccccccesseceeeesecesesceeeeneseeecessaeeeeesseeenaes 5 44 DEFINE GENERAL MULTI BODY STRUCTURE IDENTIFICATION ceccceceesseeeeeees 5 46 DEFINE GENERAL OFFBODY POINTS cccccscccssssssesecececescesesesaececesaeeecseseseeseaaeeeseaseseeaes 5 47 DEFINE GENERAL PANEL PRESSURE cccccsessesssesececceeseeseeeeceseeseesecseseeeeecesscsaesaeeseeeeaees 5 48 DEFINE GENERAL ROLL DAMPING MODE LL ccccccccccssccessecesesceeecessesesessececesaeeeeneaeeeeeeaes 5 49 DEFINE GENERAL SECTIONAL LOADS 0 eccececcessessseseesecseeseeseeeeecsecseeseeeeseecsaeesaeeseeseenees 5 53 DEFINE GENERAL TANK PRESSURE
52. AN 2010 5 37 Restriction The program will currently compute all MODES irrespective of the specifications in this command Wadam 5 38 SESAM 22 JAN 2010 Program version 8 1 DEFINE GENERAL EXECUTION DIRECTIVES TOLERANCES COMPUTED TOLERANCES _ tolwl toleg distol angtol TOLERANCES CRITICAL WAVE LENGTH wave END PURPOSE The command sets user defined tolerances for the analysis distol and angtol are tolerances on geometrical matching between elements of the shell solid structural model and panels of the panel model If exceeded by the 25 closest panels no pressure load is transferred to the structural element in question PARAMETERS COMPUTED TOLERANCES tolwl tolcg distol angtol CRITICAL WAVE LENGTH wave Computed tolerances is used by Wadam in different internal checks to verify the consistency of the input model and various parameters Tolerance on the computed z coordinate of the water line as a percentage of the characteristic length If this tolerance is ex ceeded the program stops Tolerance on the horizontal distances between the centre of gravity and the centre of buoyancy measured along the coordi nate axes x and y as a percentage of the characteristic length If this tolerance is exceeded the program stops Marginal difference between the area of the panel and the area of the triangles defined by the vertices of the panel model and the geometri
53. ATIONS All the combinations of frequencies and headings specified with the ENVIRONMENT WAVE DIRECTION and WAVE LENGTH commands will be used to define pairs of frequencies and headings for sum and difference frequency forces SELECTED COMBINATIONS This option does not work NOTES If statistical postprocessing by Postresp is to be performed then both SUM FREQUENCIES and DIFFER ENCE FREQUENCIES must be specified Furthermore the wave components specified at least two in DEFINE ENVIRONMENT must be equally spaced with respect to frequencies SESAM Program version 8 1 Wadam 22 JAN 2010 5 11 DEFINE ENVIRONMENT LINEARISING WAVE HEIGHT LINEARISING WAVE HEIGHT niin For each wave direction give tlin 1 hlin 1 tlin 2 hlin 2 tlin nlin hlin nlin PURPOSE This command must be used if the regular wave linearisation method is to be used The linearising wave periods and heights describe the curve in the T H space to be used for the drag force linearisation The peri ods used in the motion analysis will be used to interpolate on this curve The curves are given individually for the wave directions For computing maximum motion response hlin will correspond to the maximum wave height according to maximum steepness or Hmax Tmax contour curves tlin and hlin must be given in pairs For the next wave direction enter a new sequence of tlin and hlin data The same number of pai
54. All beam elements in the Morison model that receive hydrodynamic loads are identified in Prewad The reference number 11 below is the same as a section number specified in the Morison model All the loads are automatically transferred to the correct elements Retained mass termed dm below means that the mass defined on the Input Interface File will be used DEFINE HYDRODYNAMIC PROPERTY SECTION ref stot dia dm cksi czeta aksi azeta 11 2D MORISON ELEMENT 1 7 4035 RETAINED 0 7 0 7 1 0 10 END END END Retained mass means that the distributed mass on the Input Interface File will be used The 3D Morison element One 3D Morison element is defined at all ends of the pontoons In this way the effect of added mass in the longitudinal direction of the pontoons is included The commands for inclusion of one 3D Morison ele ment are shown below DEFINE ELEMENT 3D MORISON ELEMENT elno nodel DEFINE HYDRODYNAMIC PROPERTY SECTION ref dia dm drag addmass X2 y2 22 201 3D MORISON ELEMENT HYDRODYNAMIC 12 3608 0 0 000 0 700 0 0 0 END END END Wadam SESAM Program version 8 1 3 28 22 JAN 2010 DEFINE HYDRODYNAMIC PROPERTY CONNECT ref elno 201 201 END END END The pressure area element A total of 72 pressure area elements are included to account for free ends diameter changes and junct
55. C LOAD len INERTIA LOAD NO ACCELERATIONS ON INERTIA RELIEF LOAD TRANSFER OPT OFF NO SYMMETRY XZ PLANE ANTI LOAD SYMMERY ONE PLANE SYM YZ PLANE BOTH TWO PLANE SYM SYMM OFFSET IN LOAD CASE N len AUTOMATIC ON TANK PRESSURE OFF ON WAVE STRETCHING OFF END STRUCTURAL LOADS BEAM STRUCTURAL MOD anc add stalo COMPOSITE STRUCTURAL stalo SHELL STRUCTURAL MOD stalo END Wadam 5 32 PURPOSE SESAM 22 JAN 2010 Program version 8 1 The command specifies which analysis results files to generate and their contents PARAMETERS GLOBAL RESPONSE NONE SIF FORMATTED SIN NORSAM SIU UNFORMATTED LOAD TRANSFER OPTION FILE FORMAT FORMATTED UNFORMATTED GRAVITY LOAD lcn NO GRAVITY LOAD HYDRO DYNAMIC LOAD NO DYNAMIC LOAD HYDRO STATIC LOAD NO STATIC LOAD INERTIA LOAD Generation of a Hydrodynamic Results Interface File No Hydrodynamic Results Interface File will be generated The global responses will be written to a sequential formatted Hydrodynamic Results Interface File named Gn SIF The global responses will be written to a direct access Hydro dynamic Results Interface File named Gn SIN The global responses will be written to a sequential unformat ted Hydrodynamic Results Interface File named Gn SIU To specify load cases load case options and format of the Loads Interface Files Except for FILE
56. C PROPERTY SECTION ref 2D MORISON ELEMENT stot selno sl selno and sl are the sub element number and sub element length correspondingly Wadam SESAM 5 60 22 JAN 2010 Program version 8 1 DEFINE HYDRODYNAMIC PROPERTY SECTION ref 3D MORISON ELEMENT BOTH 3D MORISON ELEMENT HYDRODYNAMIC HYDROSTATIC dia dm cksi czeta ceta aksi azeta aeta x2 y2 z2 PURPOSE The command defines hydrodynamic properties for 3D Morison elements PARAMETERS HYDROSTATIC Only buoyancy force will be calculated HYDRODYNAMIC Only wave exciting forces inertia and drag will be calculated BOTH Both wave exciting forces and buoyancy force will be calculated dia Equivalent diameter dm Mass of element cksi Drag coefficient along the axis czeta Drag coefficient along the C axis ceta Drag coefficient along the y axis aksi Added mass coefficient along the axis azeta Added mass coefficient along the C axis aeta Added mass coefficient along the n axis x2 The x coordinate of a guiding point for the local coordinate system Give zero if the element coordinate system is parallel with the global coordinate system See Figure 2 12 y2 The y coordinate of the guiding point z2 The z coordinate of the guiding pint SESAM Wadam Program version 8 1 22 JAN 2010 5 61 DEFINE HYDRODYNAMIC PROPERTY SECTION ref ANCHOR ELEMENT ANCHOR ELEMENT ang
57. D Morison element may be viewed as a submerged sphere which can receive both hydrostatic and hydrodynamic loads It will not contribute to the restoring matrix The hydro property description for a 3D Morison element includes added mass and viscous drag coefficients in three directions together with a diameter of the submerged sphere The local coordinate system for a 3D Morison element n 6 will by default coincide with the coordinate system of the Morison model Xinp Yinp gt Zinp If the local coordinate system shall be different from that of the Morison model a guiding point defining the local n axis must be specified Figure 2 12 shows this with node N being the 3D Morison element and node N gt being the guiding point The and C axes are defined as described above for 2D Morison elements The forces on a 3D Morison element is acting at the node to which the 3D Morison element is connected Pressure Area Elements A pressure area element is defined in HydroD or Prewad and connected to a node in the Morison model The node represents the centre of the circular pressure area element The direction of the element is defined by a guiding point and the area with diameter d as shown in Figure 2 13 SESAM Wadam Program version 8 1 22 JAN 2010 2 13 guiding point Figure 2 13 The pressure area element definition The pressure area element includes the hydrostatic and Froude Krylov pressure force The Froude Krylov force is the f
58. DRODYNAMIC PROPERTY 0 e cc ceecccescesseceeseecesaecnsneeceneeceaeecaeeeeaaeeeaaeceaeecneeeesseeees 5 75 JEA SVAN DEN Retin er rer Ot eter cP nce eRe tee ptt tithe OPS Set Crary PEC OE feo ee Per CTE TN MEE Te 5 77 SI A E ENEA E ing vs Se utadv sea hehb gud ea neds gdh aces Heb ccsoddanaek AT 5 78 WRIT Epesoes sia enaena a E EEE R a Seoteest a a a a 5 80 i E E A AE E EE O 5 81 APPENDIX A TUTORIAL EXAMPLES eesseeesooessoesssesssesssocssoossoessseessoossoossosssssssssesssosee A 1 A1 Motion Response of a Floating BOX c cccccccsssesscesscesseeseeeseceseeeeeeeseeseecaseseeeseeeeseecseceseeeeenseeeaeens A 1 A2 Motion Response of a Floating box Tethered to the Sea Bottom sssesssesesserssssssessrsrsersssrseesrses A 3 A2 1 Preframe Input for the Morison Model Tethers sssesseeseesesssesssssesessssesssseseesssessesesee A 3 A2 2 Inputfor the Structural Modelis issen eensinr eiseres sdeiis ienei pi in ei nrt A 3 A2 3 Presel Input for Assembling the Structural Model essseeeeeseseesssesessesessessersessssesesseses A 5 A3 The Wadam Print File List of Contents 00 0 0 eceeesccsceeseeseeseceecaeeaeeaeeecaceaecaecaeeeeeeeeeaecaaeaeeaeeeees A 6 REFERENCES wy ccssaccssassccnsisesessesctceccsscsssuneaeseatcsbunsecassasseudsnashtavaesausenenasnescescers REFERENCES 1 APPENDIX B THEORY osscissscsssecatvotasssadeshossasnssussssavessdunssvevaSeeiedsvencnseavesnstessensabodsiunchavevessee B 1 BI Hydrostatic POOE S a A R T AR B 1 BAA
59. Distributed Hydrostatic Loads The hydrostatic loads on a structural model is calculated directly on the individual finite elements of the model It is represented on the Loads Interface Files as a real load case Structural Beam Models For wet beam structural superelements the hydrostatic load case is represented as line loads on the beam finite elements and as nodal loads on nodes receiving loads from 3D Morison elements and pressure area elements In addition the pre tension from Morison anchor and TLP elements are included as nodal loads in the hydrostatic load case The gravity component of the static load is only included as direct loads if the mass model is specified as a distributed mass model When using other types of mass models the gravity acceleration only will be written to the Loads Interface File SESAM Wadam Program version 8 1 22 JAN 2010 2 41 A general description of line loads on beam finite elements is included in Appendix B 3 2 Note Pressure Area Elements should always be defined at the end of vertical members such as the legs on a semi submersible Structural Shell or Solid Models For wet surfaces of shell and solid elements in a structural model the hydrostatic loads are represented as normal pressures Because the hydrostatic pressure intensities are evaluated individually at the z coordinate of each node the normal pressure on wet element sides will have a variation in the z direction as opposed to the hydrod
60. ECTIVES DETERMINISTIC MORISON DETERMINISTIC MORISON DIFFRACTED WAVE STILL WATER LEVEL NONLINEAR DRAG FINITE WAVE ELEVATION INCIDENT WAVE LINEAR DRAG PURPOSE The command defines parameters for use in deterministic Morison calculation This option is available with the time domain output format PARAMETERS DIFFRACTED WAVE Velocity and acceleration due to the diffracted wave are used in Morison s equation Radiation diffraction theory must be used for parts of the structure INCIDENT WAVE Velocity and acceleration due to the incident wave are used in Morison s equation LINEAR DRAG Linearised drag formulation is used in Morison s equation with the linearised velocity given and amp defined by the DEFINE GENERAL CONSTANTS command NONLINEAR DRAG Non linear drag formulation is used in Morison s equation STILL WATER LEVEL Loads will be calculated up to still water level FINITE WAVE ELEVATION Loads will be calculated up to finite wave elevation Wadam SESAM 5 22 22 JAN 2010 Program version 8 1 DEFINE GENERAL EXECUTION DIRECTIVES DRAG LINEARISATION DRAG LINEARISATION durhr trac rotc maxit PURPOSE This command is used for two different purposes Case 1 Drag linearisation This can be stochastic linearisation if combined with the commands DEFINE ENVIRONMENT WAVE SPECTRUM and DEFINE ENVIRONMENT WAVE SPREADING FUNCTION or regular wave linea
61. FORMAT this option can only be used for shell models Specify format of the Loads Interface File The generated Loads Interface Files will be formatted The generated Loads Interface Files will be unformatted Set load case number for the gravity load It is not recommend ed to use this option Global load case number to start off each load type If zero Wadam will set load cases numbers according to the type of analysis which have been specified The static load written to the Loads Interface File will not in clude gravity Set start load case number for the hydrodynamic loads It is not recommended to use this option No hydrodynamic loads will be written to the Loads Interface File Set load case number for the hydrostatic load It is not recom mended to use this option No hydrostatic load will be written to the Loads Interface File Set start load case number for the inertia loads It is not recom mended to use this option SESAM Program version 8 1 NO ACCELERATIONS INERTIA RELIEF LOAD SYMMETRY NO SYMMETRY ONE PLANE SYM XZ PLANE YZ PLANE ANTI BOTH SYMM TWO PLANE SYM OFFSET IN LOAD CASE NUMBERS AUTOMATIC TANK PRESSURE WAVE STRETCHING STRUCTURAL LOAD BEAM STRUCTURAL MODEL anc add Wadam 22 JAN 2010 5 33 No inertia loads will be written to the Loads Interface File Switch inertia relief ON or OFF Specify type of symmetry No symmetric or antisymmetric loads will be calcu
62. Hydrostatic Coefficients rierien teen eis ei ea eea Haken EEP EE EEE EE B 1 B2 Morison Element Formulations 0 0 0 0 cceccescceeesseeseeseesececesceeseeseseeceeceaecaeeaeeeceaeaecaeeeeeereesecaecaaeaaeees B 2 B2 1 The Anchor Element Formulation cccccceccecssseeseceececeeseeseeseceaeeaecaecaeeeeeeeeeaecaeaeeneeaees B 2 B2 2 The TLP Mooring Element Formulation eccceecceceseecseeeeeceseesecaeeeeseneeseeseceaeneeeeeeeees B 4 B37 Calculation Methods sei scctissieyceatiusasteiatig vekasiscpiacay a sees pod E a EA E A vate easter uaenee aaa B 8 B3 1 Linearisation of Roll Restoring cccccceccccsceseeseeseeeeceseeeseeesecesecsseseceeeseensecnsecneeenseenaes B 8 W w w w W W WW UPLULRN Calculation of ime Eoadsrar neinei e E E E E feb B 9 The Mapping of Loads from Panel Models to Finite Element Models cesses B 9 Calculation of Tank Pressures ccccccscessecsseesecesceesceeseceseceseeeseeesecesesecseeeeseecsaeseeeeeeaes B 11 Global drag coefficient for roll cececccecccesceesecseceeeceeeeeseecseensecsseceseeeseeeseceseceeeeneeeaes B 12 SESAM Wadam Program version 8 1 22 JAN 2010 1 1 1 INTRODUCTION 1 1 Wadam Wave Analysis by Diffraction and Morison Theory Wadam is a general analysis program for calculation of wave structure interaction for fixed and floating structures of arbitrary shape e g semi submersible platforms tension leg platforms gravity base structures and ship hulls The analysi
63. M Wadam Program version 8 1 22 JAN 2010 5 23 DEFINE GENERAL EXECUTION DIRECTIVES DRIFT FORCES YES NO DRIFT FORCES PURPOSE The command defines whether second order mean drift forces in six degrees of freedom shall be calculated or not These forces are computed by pressure integration hence this method may be used to compute the drift forces on each body in a multi body analysis PARAMETERS YES Second order mean drift forces will be calculated NO Second order mean drift forces will not be calculated NOTE Computation of drift forces by pressure integration requires a much finer discretisation to converge than the computation of drift forces by far field integration HORISONTAL DRIFT Also the CPU cost for a given discretisation increases by a factor of 2 when this option is included Wadam SESAM 5 24 22 JAN 2010 Program version 8 1 DEFINE GENERAL EXECUTION DIRECTIVES FIXED FLOATING XZ PLANE YZ PLANE YZ XZ PLANE NONE XZ PLANE YZ PLANE YZ XZ PLANE NONE FIXED FIXED FLOATING YES FLOATING NO PURPOSE The command specifies the structure to be fixed or floating as well as symmetry plane s PARAMETERS FIXED Fixed structure only exciting and drift forces may be calculated FLOATING Floating structure added mass and damping is calculated and the equation of mo tion is solved Answer YES or NO to whether natural periods eigenval
64. ND END END EFINE HYDRODYNAMIC PROPERTY SECTION ef len pre stiff xoff yoff P MOORING ELEMENT 965 0 5 0E7 9 59E7 35 0 35 0 END END END RODYNAMIC PROPERTY CONNECT o oO o l l l J o J N K J fg oO 1 l l oO zj trj H z al Ham K oO ref elno 21 it END END END Check of Results Several checks should be performed during a Wadam analysis The following checks should as a minimum be made after a global response analysis Wadam SESAM 3 16 22 JAN 2010 Program version 8 1 Error and warning messages Wadam will give error or warning messages if the Prewad input data and the input models contain incon sistencies Hydrostatic properties calculated on the model All hydrostatic data are printed in the Wadam listing These properties are more closely explained in Sec tion 2 5 5 e Mass properties A summary of the mass calculations is given in the Wadam listing e Rigid body eigenperiods for the structure The eigenperiods show whether Wadam has interpreted the stiffness and mass properties as expected and is an extra check of these values Transfer functions for exciting forces added mass damping and rigid body motions The transfer func tions should generally not be too irregular Large jumps in the transfer functions especially for added mass and potential damping m
65. ONAL PURPOSE END The command defines execution directives for solving the radiation diffraction problem in Wadam PARAMETERS EQUATION SOLUTION DIRECT ITERATION IRREGULAR FREQUENCY NO REMOVAL REMOVE alpha LOGARITHM SINGULARITY NUMERICAL ANALYTICAL NUMERICAL INTEG TYPE Specify in which way the equation system shall be solved Equation system solved by direct method This is the recom mended option when number of panels is less than 2000 Equation system solved by iteration default Specify whether irregular frequencies shall be removed or not Do not remove irregular frequencies default Remove irregular frequencies Not used A dummy value must be given Specify numerical or analytical integration of the logarithmic singularities of the Green s function Gauss quadrature is used numerical integration default The logarithmic singularities are integrated analytically Specify type of numerical integration of Green s function and its derivatives SESAM Wadam Program version 8 1 22 JAN 2010 5 29 ONE NODE GAUSSIAN Single node Gauss quadrature is used default FOUR NODE GAUSSIAN Four node Gauss quadrature is used PANEL DIMENSION Specify the panel dimension to which the distance between the panel centroids are compared in determining those pairs of pan els where the above analytical integration is required AREA Square root of the panel areas are used default
66. ORISON NODE PANEL DATA FOR BASIC EMENTS CORR ECTIONS FOR SECTIONAL LOADS ON THE CALCULATI SAVE FILE ON PE RFORMANC E SPONDANCE LINEARISATION BY ITERATION US ROLL DAMPING MODE ESTART VISCOUS FORCES KOO O MK OX x lt x lt x X KOX K xx MM XM XM x x x mM MK KOS OX x x xX x eM x XM OX x lt x lt x lt KOO OK KM KK S x XM KX x x MM KX x x xX x xX xxx x MM KK KM KM x x XM OX x x MM XM XM x lt x x Xx x xX x KM KM KM KK KO OS OK OO x x KX MMMM KM KM KM KM KM KM MM MM MM KM MM MM KM KK XX x x x xX SESAM Program version 8 1 5 4 4 2 STATIC R 4 4 4 4 Be BBO eL lt 3 4 mo 6 wl 8 ES 22 JAN 2010 PRESENTATION OF RESULTS EXPLANATION OF THE RESULT Sissi eised oc tse we Sia eee a ee ere ies FSU LTS J remteeitesca GLOBAL HYDRODYNAMIC RESULTS INCLUDING s FREQUENCY INDEPENDENT MATRICES gee saad ea e e en E e ee eee e PENDENT MATRITER S oaa aa na a e Ge algae A EE A AE ee FREQUENCY DE RESULTS FRO EIGEN SOLUTIONS See EES ore INDIVIDUAD THEORIES ie eena k n ieiel 6 arti b eie eisi O PARSER XACT TING FORCE S eua a E SS D hyo A A E RS MOTIONS DRIFT FORCES SUM OF DISTRIBUTED LOADS orra ie ie gn ee ene ete ig lee eid e
67. OTES The density is the same in all tanks The density of the fluid in all the tanks Tank number This is the same number as the load case number used in the defini tion of the Hydro Element uniform HYDRO PRESSURE load cases The density of the fluid in tank number tank_i To perform the actual load transfer of pressure in tanks the command RESULT FILE LOAD TRANSFER TANK PRESSURE ON must be given SESAM Wadam Program version 8 1 22 JAN 2010 5 55 DEFINE GENERAL TEXT text END TEXT PURPOSE The command defines identification text strings for the analysis PARAMETERS text Text given by the user to describe the analysis Maximum 3 lines can be given Enclose each text line in apostrophes when spaces are used Wadam SESAM 5 56 22 JAN 2010 Program version 8 1 DEFINE HYDRODYNAMIC PROPERTY CONNECT HYDRODYNAMIC PROPERTY SECTION END PURPOSE The command defines sectional dependent hydrodynamic data of the Morison model and connects specified section numbers to Morison elements defined in Prewad The definition of the hydrodynamic properties will also select 2 node beam elements given on the Input Interface File containing the Morison model as 2D Morison elements All other 2 node beam elements will become Dry Morison elements SESAM Wadam Program version 8 1 22 JAN 2010 5 57 DEFINE HYDRODYNAMIC PROPERTY CONNECT el
68. PLANE body PANEL MODEL direc topsel xm ym zm delta MODELS YZ XZ PLANE NONE END PURPOSE The command is used for two purposes e Definition of the analysis model for each body by their prefix and superelement number Presently only the panel models may have multiple body specification The other analysis models shall be specified using the DEFINE GENERAL ANALYSIS MODELS command and the DEFINE GENERAL GLOBAL MATRICES MASS MATRIX command e Reading of panel model from Wamit gdf files Multi body panel models cannot presently be interpreted from the gdf format Note that the definition of symmetry plane and zm will override equivalent information specified with other Prewad commands Furthermore the WADAMn FEM file created by Prewad must be manually ed ited by altering the third parameter the fourth field counting the record name field of the HY DMODID record from 1 to 11 PARAMETERS body PANEL MODEL direc topsel xm ym Body identification number Note that the body numbers must be consecutively or dered In case of reading gdf files this parameter must be 1 Panel model used in the hydrodynamic analysis File prefix or directory where the file s are stored In case of reading gdf file this is the file name of the Wamit gdf file without the gdf extension Top superelement number In case of reading gdf file this parameter is not used X coordinate of the origin of the input coordinate system
69. RY 1 1 VERY 2 1 VERY 3 1 VERY 4 1 VERX 1 NPF VERX 2 NPF VERX 3 NPF VERX 4 NPF VERY 1 NPF VERY 2 NPF VERY 3 NPF VERY 4 NPF PARTR is the dimensional radius R of the partition circle measured in the same units as the characteristic length The partition circle must enclose the body It should be determined according to the decaying rate of local waves An appropriate approximation is R O h h is water depth for shallow water and R O A A longest wavelength involved for deep water h gt gt A The actual constants of proportionality R A may have to be substantially larger than one to achieve accuracy in deep water e NPF is the total number of panels on the free surface SESAM Wadam Program version 8 1 22 JAN 2010 5 13 e NTCL is the total number of segments panels on the partition circle e NAL is the number of annuli in intermediate region may be 0 e DELR is the radial increment for each annulus e NCIRE is the number of nodes in the azimuthal integration in each annulus is INCRE e NGSP is the number of nodes in radial integration on each annulus e VERX K I K 1 4 is the dimensional x coordinate of the K th vertex of the I th panel e VERY K D K 1 4 is the dimensional y coordinate of the K th vertex of the I th panel SESAM 22 JAN 2010 Program version 8 1 DEFINE ENVIRONMENT WAVE SPECTRUM WAVE SPECTRUM JONSWAP hs tz or tp gam siga sigb PIERSON MOSKOWIT
70. TRA PRINT and NORMAL PRINT may result in large output print files Note The print switches are referred to as print level numbers in the table of contents of the Wadam print file Wadam LIS PARAMETERS DUMP OF LOAD DISTRIBUTION DUMP OF LOAD TRANSFER DUMP OF MODEL DATA MAXIMUM PRINT NO EXTRA PRINT NORMAL PRINT Detailed load distribution in addition to dump of model data level 3 In addition more load sums and details of the mass distribution is printed Detailed loading on all elements in the Morison model in addi tion to the dump of load transfer level 4 Detailed model data in addition to normal print level 2 Maximum print value level 5 This gives an extensive amount of maintenance print relevant only for debugging purposes Minimum amount of print level 0 This is the default Almost only results from the data check are printed Normal amount of print level 1 This is the most commonly used level This option includes print of hydrodynamic coeffi cients rigid body motion and sectional loads SESAM Wadam Program version 8 1 22 JAN 2010 5 31 DEFINE GENERAL EXECUTION DIRECTIVES RESULT FILES RESULT FILES NONE SIF FORMATTED GLOBAL RESPONSE SIN NORSAM SIU UNFORMATTED FORMATTED FILE FORMAT UNFORMATTED len GRAVITY LOAD NO GRAVITY LOAD len HYDRO DYNAMIC LOAD NO DYNAMIC LOAD len HYDRO STATIC LOAD NO STATI
71. TUDE WATER DEPTH WAVE DIRECTION WAVE LENGTH All specified environmental data will be printed The current profile will be printed Frequency heading pairs used in the computation of sum and difference forces will be printed A summary of the environmental data will be printed Surface model defined will be printed All specified wave amplitudes will be printed Specified water depth will be printed All specified wave headings will be printed All specified wave lengths will be printed If wave period or wave frequency is used as input this option will be WAVE PE RIOD or WAVE FREQUENCY respectively SESAM Program version 8 1 PRINT GENERAL Wadam 22 JAN 2010 5 73 ALL ANALYSIS MODELS CONSTANTS EXECUTION DIRECTIVES GLOBAL MATRICES CRITICAL DAMPING DAMPING MATRIX MASS MATRIX RESTORING MATRIX END ibody PANEL MODEL MODELS GENERAL END MULTI BODY ibody STRUCTURE IDENTIFICATION END END OFFBODY POINTS OVERVIEW ROLL DAMPING MODEL SECTIONAL LOADS TANK PRESSURE TEXT END PURPOSE The command prints user specified general parameters or matrices PARAMETERS ALL ANALYSIS MODELS CONSTANTS EXECUTION DIRECTIVES All specified general parameters will be printed All analysis models specified will be printed All constants specified will be printed All execution directives specified will be pri
72. URFACE MODEL option must be used for animation of free surface elevation in Xtract The SUR FACE MODEL option must not be used for Postresp The CHANGE command corresponding to this DEFINE command deviates in that there is an additional parameter refno CHANGE GENERAL OFFBODY POINTS refno xcoor ycoor zcoor refno is the reference number of the offbody point to change 1 2 3 Wadam SESAM 5 48 22 JAN 2010 Program version 8 1 DEFINE GENERAL PANEL PRESSURE ALL ELEMENTS INTERVAL iel first iel last step PANEL PRESSURE selno index iel ELEMENT NUMBER END END PURPOSE The command transfers computed pressures to the Hydrodynamic Results Interface File G file These pressures can then be read as transfer functions and presented by Postresp In Postresp the panel pressures are identified by the Wadam internal panel index and a reflection index The correspondence between the element data and the panel indices is printed on the Wadam print file if the print switch is set to DOUMP OF MODEL DATA or higher PARAMETERS selno Superelement number within the sink source model index Superelement index of the given superelement ALL ELEMENTS Pressures for all elements of the superelement will be written to the Hydrodynamic Results Interface File G file INTERVAL Pressures for all elements in a specified interval will be written to the Hydrodynam ic Results Interface File G fil
73. Z hs tz TORSETHAUGEN hs tp PURPOSE The command specifies the wave spectra to be used for the wave directions The wave directions must already have been defined DEFINE ENVIRONMENT WAVE DIRECTION The spectra are given for the directions one by one PARAMETERS JONSWAP PIERSON MOSKOWITZ TORSETHAUGEN hs tz or tp gam siga sigb tp NOTES Use wave spectrum of type JONSWAP Use wave spectrum of type Pierson Moskowitz Use wave spectrum of type Torsethaugen Significant wave height Relevant for JONSWAP spectrum only tz or tp gt 0 Zero up crossing wave period tz tz or tp tz or tp lt 0 Peak spectral wave period tp tz or tp Peak enhancement factor for JONSWAP Left width parameter for JONSWAP Right width parameter for JONSWAP Peak spectral period for Torsethaugen Either long or short crested waves may be used for roll motion When short crested wave are used only one main wave direction can be run In a subsequent Postresp run the same wave spectra and spreadings must be used to obtain consistent results SESAM Program version 8 1 22 JAN 2010 DEFINE GENERAL GENERAL ANALYSIS MODELS CONSTANTS EXECUTION DIRECTIVES GLOBAL MATRICES MULTI BODY OFFBODY POINTS PANEL PRESSURE ROLL DAMPING MODEL SECTIONAL LOADS TANK PRESSURE TEXT END PURPOSE The command defines general parameters such as execu
74. a or connection between section numbers and Morison elements PARAMETERS ALL CONNECT 2D MORISON ELEMENT 3D MORISON ELEMENT ANCHOR ELEMENT DRY ELEMENT POINT MASS PRESSURE AREA ELEMENT TLP MOORING ELEMENT OVERVIEW All specified sectional hydrodynamic properties will be print ed Connection between section reference numbers and elements will be printed Print all connected 2D Morison elements Print all connected 3D Morison elements Print all connected anchor elements Print all connected dry Morison elements Print all connected point mass elements Print all connected pressure area elements Print all connected TLP mooring elements A summary of the sectional hydrodynamic properties will be printed Wadam SESAM 5 76 22 JAN 2010 Program version 8 1 SECTION Section properties will be printed ref Reference number of section SESAM Wadam Program version 8 1 22 JAN 2010 5 77 READ READ prefix number PURPOSE The command reads an old Wadam analysis control data file and sets the specified dataset number as cur rent The file name must be prefixWADAMdataset number FEM where dataset number is an integer If the dataset number already exists in the Prewad database then the Wadam analysis control data file must be renamed use another dataset number Alternatively exit Prewad and re enter creating a new database PARAMETERS prefix File name prefix number Dataset number of
75. ad transfer from a panel model to a shell solid model each of the four load types above may optionally be either suppressed or divided into separate load cases This is controlled from HydroD or Pre wad For structural models consisting of one superelement only Wadam will by default generate a hydrostatic load case for the still water condition and a sequence of hydrodynamic load cases one for each specified combination of wave frequency and wave direction If deterministic load calculation is specified separate SESAM Wadam Program version 8 1 22 JAN 2010 2 25 load cases are also created for each specified phase angle The load cases generated by Wadam will be the global load cases for single superelement structural models For structural models defined from a hierarchy of superelements the hydrostatic and hydrodynamic load cases for each superelement will include the load cases for all the occurrences of each particular superele ment Equation 2 1 is used to assign the unique load case numbers for all occurrences of superelements Furthermore for structural models defined from a hierarchy of superelements the load cases created by Wadam for first level superelements are combined into new higher level load cases in Presel The load case combination is performed recursively i e repeated for each new higher level superelement created in Presel At the structure level the load case combinations coincides with the global load cases See also th
76. am 5 36 22 JAN 2010 SESAM Program version 8 1 DEFINE GENERAL EXECUTION DIRECTIVES SECOND ORDER RESULTS EXECUTION DIRECTIVES SECOND ORDER RESULTS MODES dof1 dof2 dof3 dof4 dof5 dof6 QUADRATIC SECOND ORDER FORCES FORCE BY INDIRECT METHOD FORCE BY DIRECT METHOD PRESSURE ON BODY PRESSURE IN FLUID WAVE ELEVATION ON OFF NO COMPUTATION END PURPOSE The command defines the second order calculation types for the sum and or difference frequencies defined on the DEFINE ENVIRONMENT FREQUENCY HEADING PAIRS command PARAMETERS MODES dofl dof2 dof3 dof4 dof5 dof6 QUADRATIC SECOND ORDER FORCES FORCE B Y DIRECT METHOD FORCE BY INDIRECT METHOD PRESSURE ON BODY PRESSURE IN FLUID WAVE ELEVATION Specify which degrees of freedom shall be com puted ON OFF for each of the six degrees of freedom Compute ON the quadratic second order forces Compute ON second order forces by direct method Compute ON second order forces by indirect method Note Always use FORCE BY INDIRECT METHOD ON when second order re sults are wanted Compute ON second order pressure on the body Compute ON second order pressure in the fluid domain output only in Wamit format Compute ON second order wave elevation out put only in Wamit format SESAM Program version 8 1 NO COMPUTATION Wadam 22 J
77. analysis is performed Definition of execution directives damping models environmental properties etc in HydroD or Prewad The ship used in this example is a typical Aframax tanker with a 62 4 metre long bilge keel on each side Panel Model The total panel model of the ship is shown in Figure 3 17 The basic part of the panel model consists of one half only The total model is generated in Wadam through reflection mirroring of the basic part Figure 3 17 Total panel model of the ship including reflected part The basic part of the panel model is modelled as one first level superelement in Prefem The coordinate sys tem for the model is located at the water level above the centre of gravity of the ship Modelling advice for the panel model is given in Section 2 1 2 Wadam SESAM 3 30 22 JAN 2010 Program version 8 1 Mass Model The mass model for the ship is shown in Figure 3 18 This is a global response calculation where the local mass distribution is modelled in a manner adequate for the sectional force calculations The mass is simply modelled as transverse beams representing the mass of each section thereby ensuring that the roll radius of gyration and metacentric heights are correct Large additional masses are modelled with point masses Vit ag KK COT dys Ly Ml Figure 3 18 Mass model for the ship Roll Damping Model For a ship or barge the roll motions will generally be much larger than for floating offshore str
78. and beam elements see Section 2 1 4 The Morison model is put together from a set of Morison elements The Morison elements are based on 2 node beam elements and single nodes in a first level superelement generated by Patran Pre Prefem or Genie The Morison elements are actually defined by assigning hydrodynamic properties to nodes and beam elements in HydroD or Prewad The different types of Morison elements available for calculation of hydrostatic and hydrodynamic effects are 2D Morison elements for calculation of hydrostatic and hydrodynamic loads on wet 2 node beam ele ments e 3D Morison elements for calculation of hydrostatic and hydrodynamic loads in three directions in spe cific nodes e Pressure area elements for calculation of hydrostatic and hydrodynamic loads at the ends of 2D Morison elements e Dry Morison elements for transfer of hydrostatic and hydrodynamic loads from potential theory to 2 node beam elements e Point mass elements for modelling of additional nodal mass in specific nodes Wadam SESAM 2 8 22 JAN 2010 Program version 8 1 e Mooring and tether elements for calculation of additional restoring contributions in specific nodes The inertia loads due to the mass of Morison elements may also be calculated This option is available for all elements except the mooring and tether elements Note The Morison model must be modelled as one single first level superelement No symmetry plane options are available f
79. are automatically calculated while the others are specified for this analysis e Hydrostatic calculation in which both the hydrostatic and inertial properties for the structure are calcu lated e Calculation of hydrodynamic exciting forces added mass damping and global motion responses for the TLP e Eigenvalue calculations for rigid body motions One set of eigenvalues is calculated for each wave period 3 17 Wadam ET TAR W ER DE R gt RISSE ANN SESAM 22 JAN 2010 Program version 8 1 Detailed load calculations and load transfer to a structural model This includes Rigid body accelerations and fluctuating gravity Pressure loads caused by waves damping and added mass Tether reaction forces caused by rigid body motions of the TLP Preparations for this analysis in Wadam consist of the following steps Creation of the panel model with Patran Pre or Prefem Symmetry of the structure is used and only one quarter of the TLP is modelled Creation of beam elements for the Morison model with Patran Pre or Genie Pre and Presel Patran Creation of the structural model with Genie Transfer of Input Interface Files to the directory where the Wadam analysis is performed environmental properties etc in HydroD or Pre Definition of execution directives additional elements wad Potential wave theory is used for all the wave periods and the panel model is thus used for calc
80. ase angle between the incident wave and the time varying response is defined from Wadam SESAM 2 36 22 JAN 2010 Program version 8 1 R o B A Re H B e t 7 2 14 where H is the amplitude of the transfer function The transfer function and the phase angle may be expressed as H H Hp iH and atan 2 15 Re The time varying response can alternatively be expressed as R o 8 t ALA cos t Aj sinat 2 16 The phase lead of the response relative to an incident wave with the wave crest at the origin of the global coordinate system is shown in Figure 2 27 response response j A H coslwt p surface elevation o gt 0 in the figure at origin Figure 2 27 Definition of phase between the response and the incident wave 2 5 5 Hydrostatic Restoring Results Wadam calculates the hydrostatic restoring results from the hydro model It is given with dimensions and include The sum of displaced volume of the panel and Morison part of the model The total displaced volume is reported together with the separate contributions from the panel and Mori son parts For the panel model the volume is reported from three different calculations i e from summing up of con trol volumes in the three different directions The reported total volume is taken as the median of the three volumes not mean but middle value of three values Note If the separate control volumes are differing by a significant numb
81. at the damping starts to increase when the width of the bilge keel decrease The exact limit is case dependent but as an indication the width of the bilge keel should not be smaller than 10cm 2 5 20 Global drag coefficient for roll damping A global coefficient for quadratic damping of the roll motion can be given as user specified input This makes it possible to use results from model tests directly The quadratic damping is linearized by stochastic linearization This way model tests performed independent of sea states can be used in connection with any given sea state valid for the actual location of the structure The formulation of the method of stochastic lin earization is explained in Appendix B 3 5 Note This kind of damping should not be combined with any other types of damping effects except the potential dampimg In other words the old roll damping model the Morison model or user specified linear damping are not to be combined with the global tortional drag Wadam SESAM 2 46 22 JAN 2010 Program version 8 1 2 6 Calculation Methods 2 6 1 Calculation of Wave Loads from Potential Theory The potential theory as described in Newman Ref 1 is applied in Wadam to calculate first order radiation and diffraction effects on large volume structures The actual implementation is based on Wamit Ref 2 which uses a 3D panel method to evaluate velocity potentials and hydrodynamic coefficients This implementation can be used
82. ave Restart File The save restart file contains the velocity and source potentials obtained from solving the radiation and dif fraction problems The save restart file also contains hydro model data used in consistency checking when the potentials are used in a restart run The naming convention for the save restart file is Wadam RSQ The file is formatted Wadam SESAM 4 6 22 JAN 2010 Program version 8 1 4 2 Program Requirements The disk space requirements in Wadam depend on the type of analysis and of the input models The execu tion time is dominated by the solution of the radiation and diffraction problems that is performed for each incident wave frequency 4 3 Program Limitations Wadam imposes restrictions on the size of the hydro model analysis The size of the structural model used in the detailed load calculation is virtually unlimited The size dependent limitations are listed below Note however that the limits may vary between different installations The actual list of limitations is printed in the status list and in section 1 2 in the Wadam print file The limit values specified in the list below applies to the standard installation Geometry limitations Maximum number of panels for the basic part of the model 15000 Maximum number of free surface panels for the basic part of the model 3000 Maximum number of off body points 2000 Maximum number of nodes in the Morison model 5000 Maximum number of elements in
83. ay be caused by too large wave period steps the presence of irregular fre quencies or numerical problems in Wadam The irregular frequencies may usually be removed by the removal of irregular frequency option This option is specified in Prewad by the following command DEFINE GENERAL EXECUTION DIRECTIVES POTENTIAL THEORY IRREGULAR FREQUENCY REMOVE alpha END END END This feature should however be used with care as there is no alpha value that will remove the irregular frequencies for all geometries The selection of alpha must be based on trial and error A key point is to observe that the responses are not disturbed in a large frequency range for some ALPHA values For most geometries 0 2 has shown to be a good starting value See Section 2 6 3 for further description 3 2 2 TLP Load Transfer to a Shell Structural Model Load transfer to a structural shell model for the TLP shown in Figure 3 7 is performed The transferred loads are used in a subsequent structural analysis and are together with other load cases used to check the capacity of the hull The panel and Morison models used in this analysis are the same as those in Section 3 2 1 except that the Morison model is without mass Reference is therefore made to Section 3 2 1 for model descriptions and a description of the additional elements The following calculations are performed in Wadam for this analysis The first two tasks
84. c centre of the structural element surface in per cent of the panel area Maximum angle between the normal vectors of the panel model and the structural element surface given in degrees This option does not function as initially planned and as indi cated by the option name The given wave length must be larg er than all given wave lengths Wave length larger than all given wave lengths SESAM Wadam Program version 8 1 22 JAN 2010 5 39 DEFINE GENERAL EXECUTION DIRECTIVES WAVE DRIFT DAMPING YES NO WAVE DRIFT DAMPING PURPOSE The command defines whether the 3x3 Wave Drift damping matrix for the modes surge sway and yaw shall be calculated or not PARAMETERS YES Wave Drift damping matrix will be calculated NO Wave Drift damping matrix will not be calculated Default NOTES Wave Drift damping like Drift forces require a finer mesh for convergence than other global results Computation of Wave Drift damping requires a free surface model Wadam SESAM 5 40 22 JAN 2010 Program version 8 1 DEFINE GENERAL GLOBAL MATRICES delem frac CRITICAL DAMPING MATRIX END elem damp wavlen END DAMPING MATRIX elem damp INDEPENDENT END elem mass ibody _ jbody GLOBAL MATRICES MASS MATRIX END END elem rest RESTORING MATRIX END ADD DAMPING MATRIX USE OF INPUT MAT OVERWRITE END END
85. chical coordinate system definition 2 1 8 Mass Modelling Global mass information is required in Wadam for analysis of floating structures The mass is used both in the hydrostatic calculations to report imbalances between weight and buoyancy of the structure and in the equation of motion Wadam provides two methods to establish global mass matrices Direct input specification of a global mass matrix e Assembling ofa global mass matrix from a mass model no utilisation of symmetry planes Wadam transfers accelerations to Loads Interface Files for subsequent structural analysis A consistent cal culation of inertia loads from these accelerations is ensured in Wadam and Sestra by access to the same module for finite element mass generation For beam element models there is the alternative option to calculating inertia loads in Wadam and transfer ring the loads to the Loads Interface Files SESAM Wadam Program version 8 1 22 JAN 2010 2 21 The remaining part of this section describes the two methods for establishing global mass information Direct Input Specification of Global Mass Matrix The direct input specification of a global mass matrix comprises giving the total mass of the structure together with the centre of gravity the gyration radii and the products of inertia The centre of gravity is specified with respect to the input coordinate system The gyration radii and the products of inertia are spec ified with respect to the
86. cident wave potential On the undisturbed position of the body boundary the radiation and diffraction potentials are subject to the conditions 2 25 where n1 n2 n3 n and n4 ns ng r x n r x y z The unit vector n is normal to the body boundary and points out of the fluid domain The boundary value problem must be supplemented by a condition of outgoing waves applied to the velocity potentials j 1 7 2 6 2 Calculation of Wave Loads from Second Order Potential Theory The second order theory applied in Wadam is described in Ref 3 and Ref 4 Wadam calculates sum and difference frequency components of the second order forces moments and rigid body motions Quadratic Transfer Functions in the presence of bi chromatic and bi directional waves 2 6 3 Removal of Irregular Frequencies Wadam provides an option to remove the irregular frequencies from the radiation diffraction solution This method is based on a modified integral equation obtained by including a panel model of the internal water plane The panel model of the water plane is automatically created by Wadam 2 6 4 Morison s Equation Morison s equation is used in Wadam to calculate contributions to the equation of motion Equation 2 30 and to calculate the detailed forces F acting on 2D Morison elements and 3D Morison elements The form of Morison s equation used in this calculation is given in Equation 2 26 with the effect of relative motion in
87. cluded F M pVyC amp 0 pV C Dx i B x f f f 2 26 Where Wadam SESAM 248 AJANDA Programmversion 8 1 O Incident wave frequency M 3 by 3 diagonal mass inertia matrix C 3 by 3 diagonal added mass coefficient matrix I 3 by 3 identity matrix p Density of water Vu Displaced volume of the Morison element B Linearised viscous damping matrix expressed as B sp0Cp Vi as Cp 3 by 3 diagonal drag coefficient matrix o Projected area of the Morison element x Complex amplitude of the incident wave field E Complex amplitude of the motion f Fluctuating hydrostatic restoring force representing the first order restoring contributions in tegrated in the equation of motion f Fluctuating gravity force representing the acceleration of gravity calculated in a coordinate system fixed with the Morison model f Fluctuating buoyancy force calculated in a coordinate system fixed with the Morison model The linearised viscous damping matrix B in Morison s equation Equation 2 26 is obtained from lineari sation of the general viscous drag force Fp expressed as Fp spoC pv x lv x POC DV pan X B v x 2 27 The term 8 2 28 Im Ak 2 28 is a standard result obtained by assuming equal work done at resonance by the non linearised and the equiv alent linear damping term Vmax is a linearising velocity amplitude specified as input to Wadam The one and same Vmax is applied in the li
88. d Equation B 3 are satisfied Figure B 5 visualises the mapping in a situation where the finite elements are smaller than the panels The points Cp and Cg represent the panel and finite element centroids respectively The shaded rectangular ele ments represent finite elements receiving pressure loads Figure B 5 The mapping of loads from panels to finite elements The functionality of the user specified tolerance parameters DISTOL and ANGTOL which controls the mapping between panels and finite elements may be described as follows The panel with its centroid closest to the finite element centroid is a candidate as the source for pressure transfer to a finite element if the formula Az _ lt DISTOL A 100 panel B 3 is satisfied Here Ay is the sum of the four shaded triangles S i 1 2 3 4 shown in Figure B 6 a and Apanel is the area of a candidate panel If the nearest panel is not accepted by Equation B 3 then the program will check in increasing order of centroid distance all the 25 closest panels for a panel satisfying Equation B 3 No pressure load is transferred to the finite element for which Equation B 3 is not satisfied Panels which satisfies Equation B 3 will be accepted as a source for pressure transfer if the ANGTOL cri teria lt ANGTOL B 4 is accepted is defined by Figure B 6 b Both and ANGTOL are given in degrees SESAM Wadam Program version 8 1 22 JAN 2010 B 11 finite
89. dimensions and shapes as well as to minimise the number of panels in the panel model Structural mass is distributed with a high degree of accuracy in the model This is necessary in order to include the inertia forces transferred as nodal accelerations in a proper way in the structural analysis Load Transfer The following loads are transferred to the structural model e Hydrodynamic wave pressures Pressure distribution from exciting forces added mass and potential damping are transferred to each wet element in the structural model e Inertia loads Rigid body accelerations are transferred to all nodes in the structural model SESAM Wadam Program version 8 1 22 JAN 2010 3 19 e Tether reaction forces The rigid body tether reaction forces are transferred to the nodes in the Morison model where the tether elements are connected Loads are automatically transferred to the structural model in Wadam Tether loads may however only be transferred to nodes in a beam structural model corresponding to a Morison model Such loads are conse quently written to a composite structural model Wave exciting forces added mass and damping are transferred to the structural model as pressure loads on the elements with specified hydro pressure Inertia forces due to rigid body motions are transferred as nodal accelerations to all the nodes in the structural model Tether reaction forces are transferred to the appropriate nodes in the Morison model
90. ds up to Free Surface ecann ona EE TE EAER E 2 50 2 6 8 Reduced pressure up to the free surface oo eee eccesceecesececeeeecnseeeeceseeeseecseenseceteseneeenes 2 51 The Save R estart Systemen reer 3 ceced da decal Sede esdaceewnda ved ca heed bon de eesa cle i gested eects vs E E A Ei EES 2 52 USER S GUIDE TO WADAM sssssssssrssesressrssesocorsssrscsstsssesovsssosssostssosorsssoccssse stoso sss tsss 3 1 Spl Prale S i a a a a a e a tes 3 2 3 1 1 Motion Response of Floating BoX ccccccccscssesssceeseeceeseceseceseeeeeeeseesaecaecnsceeeeeseecseeneenes 3 2 3 1 2 Motion Response of Floating Box Tethered to the Sea Bed seesesesesessssssersssrssrssrseses 3 6 Engineering Application Examples cccccccessesssesseceseceseeeeeeeeeeseecsecnsecseeeseecssenseceaeseseesaeeaeensenaes 3 10 3 2 1 TLP Global Response Analysis cccecccscccssesseessecseceseeeseesseceseceseseeeeeeeeseeesaeceeeeeeaeensees 3 12 3 2 2 TLP Load Transfer to a Shell Structural Model ccccccccccsseeseceseeeeesteceseeneeeeeeeeseenaes 3 16 3 2 3 TLP Load Transfer to Beam Element Model ccecccecsecsseesseeseceeeceseesseenseeneesneeenseenaes 3 20 3 2 4 Global Response of a Semi Submersible using Dual Model cccesscssceteeeteeeeeeees 3 24 3 2 5 Global Response for a SHIP ccccecceescesseesseecenseceseceseeeeecsaecsseeeeseeeeseecseecsecnaeeeeeseeeesaees 3 28 EXECUTION OF WADAM ii sssssssssssssensssdensesseedsoviidsocesestunctesvosebueucsedacssdtacdecnta
91. dynamics on the Loads Interface Files Answer NO involves that added mass is only included in added mass force Wadam SESAM 5 34 22 JAN 2010 Program version 8 1 stalo Answer YES or NO to writing both static and dynamic loads on the Loads Interface Files Answer NO involves that only dy namic loads are written COMPOSITE STRUCTURAL MODEL Loads Interface Files Ln FEM will be generated with loads on a combined beam and shell solid structural model In this case the shell solid model is specified as the structural model The beam model is assumed identical to the Morison model SHELL STRUCTURAL MODEL Loads Interface Files Ln FEM will be generated with loads on a shell solid structural model SESAM Program version 8 1 Wadam 22 JAN 2010 5 35 DEFINE GENERAL EXECUTION DIRECTIVES SAVE RESTART AUTO SAVE RESTART SAVE RESTART NO SAVE RESTART RESTORE POTENTIAL SOLUTION SAVE POTENTIAL SOLUTION PURPOSE The command specifies use of save and restart facilities in Wadam PARAMETERS AUTO SAVE RESTART NO SAVE RESTART RESTORE POTENTIAL SOLUTION SAVE POTENTIAL SOLUTION Wadam will automatically restart and append new calculated data to an existing save file otherwise Wadam will create a new save file No saving no restart this is the default option Restore the radiation diffraction solution for the panel model Save the radiation diffraction solution for the panel model Wad
92. e iel first First element in interval iel last Last element in interval step Increment in element number ELEMENT NUMBER Pressures for a listed sequence of elements will be written to the Hydrodynamic Results Interface File G file iel List of element numbers closed by END SESAM Wadam Program version 8 1 22 JAN 2010 5 49 DEFINE GENERAL ROLL DAMPING MODEL ROLL DAMPING MODEL xfr bilgl bilgb Z hi BILGE KEEL 3 Z K NONE han Z GZ CURVE z END thmd MAXIMUM ROLL ANGLE END FP TO AP l STRIP MODEL nos xoff xbow bst bilgr sect AP TO FP LAMINAR WATER PARAMETERS visc TURBULENT END PURPOSE The command defines a roll damping model based on ordinary strip theory Note The roll damping model can only be applied when xz symmetry is used Note The y z and phi parameters are repeated for each strip that is fully or partly intersected by the bilge keel PARAMETERS BILGE KEEL Defining parameters for a bilge keel The strip model must be defined first See note above on repetition of the y z and phi pa rameters NONE No bilge keel model specified xfr X coordinate of the front part of the bilge keel bilgl Length of bilge keel along the ship bilgb Beam width of bilge keel Note Be careful with very small bilge keels cf Section 2 5 19 y Distance from centre line to bilge keel hull intersection point GZ CURVE han
93. e SESAM System Manual for a description of the assembling of superelement hierarchies and load combinations The term superelement occurrence number defines the actual location of a superelement in a superelement hierarchy The number is found by counting the occurrences of a superelement from left to right in a superelement hierarchy or from top and down in hierarchy as printed by Presel Two simple examples are included to describe the relation between global load case numbers and the load case numbers generated by Wadam In both examples the set of global loads include one static load case and 6 dynamic load cases defined as the combinations of three incident wave frequencies and two heading angles Example 2 1 Load case numbering for a single superelement model This example consists of a structural model built from one single superelement Here the load case numbers generated by Wadam directly coincides with the global load case numbers Table 2 2 shows the correspond ence between the global load case numbers and the wave frequency and heading combinations Table 2 2 Load case numbering for a single superelement structural models Load case number global Wadam Load case description 1 Hydrostatic B 0 a 0 0 B 0 a 0 1 B 0 0 2 B 90 0 0 B 90 0 1 B 90 0 2 IAJ AJ N Wadam SESAM 2 26 22 JAN 2010 Program version 8 1 Example 2 2 Load case numbe
94. e hydro model when this includes a Morison model These local coordinate systems are discussed in the sections where they are referred to 2 1 2 The Panel Model The panel model is used to calculate the hydrodynamic loads and responses from potential theory The panel model may be a single superelement or a hierarchy of superelements It may describe either the entire wet surface or it may take advantage of either one or two planes of symmetry of the wet surface With symmetry planes employed the computational effort to solve the potential problem is reduced both with respect to CPU and disk space resources When the panel model includes more than one body see Section 2 1 7 there is the restriction that no planes of symmetry can be exploited The symmetry plane option requires that the basic part i e the actually modelled part is modelled on the positive side of the symmetry planes as shown in Figure 2 5 Figure 2 7 also shows the basic part of a Ten sion Leg Platform TLP panel model Note No panels are allowed in the symmetry plane s x z plane of symmetry y z plane of symmetry x z and y z plane of symmetry Figure 2 5 Symmetry plane definitions Wadam SESAM 2 6 22 JAN 2010 Program version 8 1 The basic part of a panel model consists of quadrilateral or triangular panels representing the wet surfaces of a body The panel model is modelled in the Patran Pre or Prefem preprocessor using standard finite ele ments If more than
95. e number IPHA 1 if complex loads are generated I is zero for static load cases and one for dynamic load cases NSEL is the number of occurrences of the first level superelement in question ISEL is the actual occurrence number of the first level superelement in question For a given first level superelement with complex loads Equation 2 1 will generate load case numbers 1 through NSEL as static load cases and load cases number NSEL 1 through NOK NOH NSEL 1 as dynamic load cases Table 2 2 illustrates the correspondence between superelement occurrence and wave frequency and heading angle The relation between superelement occurrence numbers in Wadam and the superelement index numbers in Presel is important when performing load case combinations in Presel This is discussed in Example 2 2 For loads transferred to a structure modelled with shell or solid elements Wadam includes some options to manipulate the generation of loads on the Loads Interface Files and the numbering of load cases More spe cifically for floating structures Wadam by default generates four different types of loads represented as static and dynamic loads respectively These are e Hydrostatic pressure and gravity summed together in the first global load case e Hydrodynamic pressure loads and nodal accelerations summed together for each combination of incident wave frequency and heading angle into global load cases starting with load case number two For the case of lo
96. e represented with a hydro model and optionally a structural model and a mass model The bodies may be either fixed or floating A hierarchical set of coordinate systems is introduced in which the individual structures and their input models are specified The coordinate systems applied in a multi body analysis are therefore different from those of a single body analysis see Figure 2 21 The coordinate systems are defined as follows The global coordinate system Xgjo Y gio glo 18 a right handed cartesian coordinate system with its ori gin at the still water level and with the z axis normal to the still water level and the positive z axis point ing upwards e The individual body coordinate systems Xp Yg Zp Of each structure are specified relative to the global coordinate system Wadam SESAM 2 20 22 JAN 2010 Program version 8 1 e The input coordinate system Xinp Yinp Zinp Of each input model included in a body is specified relative to the body coordinate system of that body The body independent coordinates are described in the global coordinate system e g the fluid kinematics evaluation points The coordinates related to a particular body are described in the corresponding body coordinate systems e g the result reference coordinate system The coordinates related to the individual input models are described in the input coordinate systems e g nodal coordinates of the input models Figure 2 21 The hierar
97. e will be no roll damping from this section NOT SPECIFIED The program will determine the section type for this strip If the section is in the forward 1 4 of the ship and BOG BS gt 1 2 the section is set as a BOW SECTION If the section is in the back 1 4 of the ship and BS BOG gt 1 0 the section is set as a STERN SECTION If the section is in the middle half of the length and the sectional area coefficient is larger than 0 95 the section is set as a MID SECTION In other cases no roll damping will be computed for the section Note It may well be relevant to use the MID SECTION model for sections in the first and last quarter of the length In such cases the sections must be explicitly defined as MID SECTIONs For barge type vessels this type should be used for all sections Note BOG is the distance from the bottom of the strip to a line through the centre of gravity of the ship and parallel with the x axis Note BS is the beam of the strip at the water plane Water dependent parameters like viscosity and flow informa tion Laminar flow around the hull used when comparing calcula tion results and model tests performed with laminar flow around the ship hull Turbulent flow around the hull recommended Wadam SESAM 5 52 22 JAN 2010 Program version 8 1 visc Kinematic viscosity of water NOTES The warning Panels are not connected in the Wadam print file means that the strips will not contribute to the ro
98. ea elements must always be used to include end effects of Morison elements which are not part of a dual model The panel model included in a dual model may utilise the standard symmetry plane options for panel mod els In this case Wadam will map the panel pressures to the symmetric parts of the Morison model although a correspondence is only specified for the basic part of the panel model Figure 2 19 indicates the modelling of a dual model which includes a two plane symmetric panel model and a Morison model Note Itis not possible to have a correspondence from a panel to a beam which lies in a plane of sym metry Figure 2 19 Dual model with a two plane symmetric panel model 2 1 5 The Composite Model The composite model is a hydro model suitable for structures consisting of both slender and large volume parts The slender parts are represented with a Morison model and the large volume parts with a panel model The hydrodynamic forces on a composite model are computed from potential theory for the panel model and from Morison s equation for the Morison model The hydrodynamic exciting forces and matrices from both theories are accumulated in the system of equation of motions for the composite model The wave kinematics applied in Morison s equation may either be taken from the incident wave field or it may be specified to depend on the diffracted wave field generated from solving the diffraction problem for the panel part of the composi
99. eas where the pressure variation is high element size should be small Reference is also made to Section 2 1 2 for modelling princi ples of panel models Morison Model The Morison model is a beam element model created in Preframe see Figure 3 16 today Genie or Patran Pre would have been used The model consists of 2 node beam elements and point masses Additional ele ments are defined in Prewad in order to include correct hydrostatic and hydrodynamic behaviour The inclu sion of these elements is described in Section 2 1 3 The input coordinate system used is the same as for the panel model as required by Wadam Dry Morison elements are included to model the structural properties and weight of parts of the structure above the still water level as well as other internal parts of the structure e g the inside of the junction between the columns and pontoons No hydro properties will be defined for these elements This means that the section numbers used for dry and 2D Morison elements modelled in Genie or Patran Pre both repre sented by beam elements must be different This is the case even if the beam elements have identical struc tural properties SESAM Wadam Program version 8 1 22 JAN 2010 3 27 Figure 3 16 Beam elements of the Morison model Additional Elements Hydrodynamic properties for 2D Morison elements are together with the consecutive additional elements defined in Prewad The 2D Morison element
100. ectional forces combination is performed in the statistical postprocessor Postresp Based on the global responses acceleration components and combined accelerations in specified points may be calculated in Postresp This is of less importance for the tanker used in this example but may be important for other types of ships or barges transporting heavy equipment For both alternatives the roll response is of major importance Non linear roll damping and restoring are therefore included according to a linearising procedure Potential theory is used for all wave periods For ward speed is not allowed in Wadam and is consequently not included Wadam SESAM 3 12 22 JAN 2010 Program version 8 1 The different steps in the analyses are described in the following sections A short description of each anal ysis including examples of some analysis steps is presented An extensive set of examples is enclosed in Appendix A 3 2 1 TLP Global Response Analysis This example shows the use of Wadam in a typical global response analysis of a TLP The analysis is mainly used for selection of wave periods and headings to be used in the analysis described in Section 3 2 Potential theory is used for all wave periods The following calculations are performed in Wadam for this analysis The first two points are automatically calculated while the rest is chosen for this analysis e Hydrostatic calculation in which both the hydrostatic and inertial properties for
101. ed with the same input coordinate system The coordinates of the off body points are given in the global coordinate system The relation between the global coordinate system and the input coordinate system is defined as follows e The origin of the input coordinate system must lie along the positive or negative Z axis of the global coordinate system It may also coincide with the origin of the global coordinate system e A parameter is used to define the position of the origin of the input coordinate system relative to the ori gin of the global coordinate system If the origin of the input coordinate system is below the still water level then this parameter called ZLOC shall have a negative value e The x and y axes of the input coordinate system must be parallel with the x and y axes of the global coordinate system and point in the same direction If the Hydrodynamic preprocessor HydroD is used there are no constraints on the position or orientation of the input coordinate system The input coordinate system is then specified in relation to the global coordi nate system by 3 translations and 3 Euler angles swl Figure 2 3 2D representation of a TLP hull with input coordinate system below the swl ZLOC h SESAM Wadam Program version 8 1 22 JAN 2010 2 5 swl Figure 2 4 2D representation of a semi submersible with centre of gravity along the global z axis ZLOC h Local finite element coordinate systems are also used in th
102. el pressures are transferred specifically to each sub element as shown in Figure 2 18 The loads on Morison elements are transferred to a beam model as line loads for 2D Morison elements and dry Morison elements For the 3D Morison element and the pressure area element the loads are transferred as nodal loads The hydrostatic load transferred to the structural model is computed from the Morison model including the pressure area elements Panel 2D Morison Column pressure area element always included Panels with correspondence to subelement 1 Panels with correspondence to subelement 2 Panels with correspondence to subelement 3 Area of panels with correspondence to a pressure area element Note that wave length dependency should be specified to avoid pressure area elements to be included for the short waves subelement 1 subelement 2 subelement 3 Figure 2 18 The correspondence between panels and a 2D Morison element In a dual model all the panels must be connected to Morison elements There may however be Morison ele ments in a dual model without connections to panels as shown in Figure 2 2 Wadam SESAM 2 18 22 JAN 2010 Program version 8 1 Note that no moment loads will be transferred to a Morison element from integration of panel pressures That is the transfer of panel pressures will only be correct if the pressures integrated gives no resulting moment with respect to the Morison element Pressure ar
103. elds dynamic restoring forces SESAM Wadam Program version 8 1 22 JAN 2010 2 15 acting in the mooring element nodes They are mapped onto the structural model as nodal loads No nodal moment loads are transferred to the structural model Note Spring elements on the Input Interface File are neglected ssc lt co mooring line side view top view Q 150 a 30 Fairlead swl o One oe 3 One 30 fe y inp Xinp a b Figure 2 15 Mooring element definitions TLP Mooring Elements A TLP mooring element is defined in HydroD or Prewad and connected to nodes in the Morison model It is based on the formulation given in Ref 5 In addition Appendix B 2 2 summarises the description of the TLP mooring element formulation A TLP mooring element may be used to include external restoring forces from a weightless tether with lin ear tether characteristics The hydro properties of a TLP mooring element include the length L of the tether the pre tension and the elastic stiffness parameter A A horizontal offset position Xo fet Yoffset May also be specified as shown in Figure 2 16 Note that the tether length shall be the actual length at the offset position Wadam SESAM 2 16 22 JAN 2010 Program version 8 1 inp co X inp offset y offset Seabed Figure 2 16 The TLP mooring element The restoring contributions from the TLP mooring elements are assembled into the body restori
104. ence coordinate system is then computed as i ae B 1 mooring line side view chal Windlass _ I I Fairlead I I swl o a Onc 305 3 T Sine one e y z al y x is b Figure B 1 Anchor element definitions B2 2 The TLP Mooring Element Formulation The mooring stiffness matrices K for each TLP element in a Morison model are accumulated into the glo bal restoring matrix for the rigid body equation of motion The K matrices are established directly in the SESAM Wadam Program version 8 1 22 JAN 2010 B 5 motion reference coordinate system and hence no transformations are needed in the accumulation process The non zero terms in the matrix K are defined as follows k hoos a sin a ky 2 2 cosacosp Kis kn Acos B sin kx 2 F cosacosy kis kz 2 2 cosBcosy ky ky Acos y sin y ky k32 kzz2 ki4 ksi kzz k31x2 kis Wadam B 6 where kyyxX kyyy kaya kaz ky Z kyyXq kax kay k33V kyZ kz 1Z k33x kis Koa kos ky k34 ks KyXo k31V gt kz 2 2 k33V9 2k33V223 k9Z9 22 JAN 2010 2 kzi Y2Z2 k2123 k33Y2X2 k33X223 Ty 2 k31V222 k2122 k33 2X2 k32X227 Tx 2 kyyXoVq k32 ka2X323 kz1Y3Z3 T Z 2 KxyX V9 k3 1Y3 ka2X223 kz Y2Z22 TX 2 2 Ki 1Z5 2k31X2Z3 hx T x Tz 2
105. ence point which is located at the intersection between the still water level and a vertical line through the common origin of the models used in the analysis The coordinate systems in Wadam are described in Section 2 1 1 The results available from a global response analysis of a hydro model include transfer functions for e Wave exciting forces and moments e Motion responses e Sectional loads e Rigid body matrices Off body kinematics e Surface elevations Section 2 5 describes all these results types in more detail 2 3 The Calculation of Detailed Loads on a Structural Model 2 3 1 General The detailed load calculation feature provides a tool for automatically transferring wave loads from a hydro dynamic analysis into finite element loads for a structural analysis SESAM Wadam Program version 8 1 22 JAN 2010 2 29 Both hydrostatic and hydrodynamic loads on a structural model may be calculated The results which may be both FE pressure loads and nodal loads will be transferred to Loads Interface Files for subsequent linear static or dynamic analysis in Sestra Wadam also transfers environmental information and load case num bering information to Sestra on a separate file the S file The latter is specifically required for a subsequent stochastic fatigue analysis using Framework 2 3 2 The Structural Load Types Three different load types may be generated by Wadam and transferred to a structural model These are e Hyd
106. er this normally indicates that the wet surface of the model is not properly defined SESAM Wadam Program version 8 1 22 JAN 2010 2 37 The centre of buoyancy e The water plane area e The metacentric height The global hydrostatic restoring matrix assembled from both hull restoring and additional stiffness terms The additional hydrostatic stiffness terms included in the hydro model may include contributions from e Risers mooring lines or tethers represented with Morison mooring or tether elements Stiffness matrices specified directly on the analysis control data For multi body models the hydrostatic restoring matrix for each body is reported Note Note Note 2 5 6 By definition the global hydrostatic restoring matrix from the dual part of a hydro model is calculated from the panel model The hydrostatic restoring from the Morison elements with no panels connected are also assembled to the global hydrostatic restoring data The global hydrostatic restoring calculation differs from the calculation of the hydrostatic load case in a subsequent detailed load calculation As described in Section 2 5 15 the hydro static loads on a structural beam model is calculated directly from the beam elements irrespec tive of any dual model This definition requires a high degree of hydrostatic similarity between a panel model and its dual beam model if consistency shall be preserved between Wadam and a structural analysis in
107. erred as nodal accelerations in a proper way in the structural analysis In this analysis the same superelement represents the Morison model in the Wadam analysis and is a part of the structural model The structural spring stiffness defined in the tether attachment points are used as sup port conditions in the structural analysis Such spring stiffness is disregarded by Wadam Tether elements are defined in Prewad to include the tether stiffness in the Wadam analysis SESAM Wadam Program version 8 1 22 JAN 2010 3 23 Morison Model The Morison model is equal to the one used in Section 3 2 1 except that the point masses used to include mass above the still water level is removed This mass is now included in the structural model Unlike the global response calculations performed in Section 3 2 1 the structural stiffness of the Morison model is now very important This stiffness is modelled with 2 node beam and bar elements for columns and pontoons respectively The stiffness is calibrated against the shell element model in Section 3 2 2 to ensure correct stiffness Load Transfer The following loads are transferred to the structural model e Hydrodynamic wave pressures Pressure forces are summed up from exciting forces added mass and potential damping It is transferred as line load to each element specified in the correspondence command in Prewad e Inertia loads Accelerations from rigid body motions are calculated for all nodes in the
108. erties hydrodynamic elements hydrodynamic properties connection between Morison elements defined by Prewad and hydrody namic properties and correspondence between Morison and panel models Wadam SESAM 5 4 22 JAN 2010 Program version 8 1 DEFINE CORRESPONDANCE ssno elno selno seltyp index GROUP ssnol ssno2 ssno3 ssinc END CORRESPONDANCE END PURPOSE The command defines correspondence between elements in the Morison model and panels in the basic panel model correspondence for mirror images of panel model is handled automatically This correspondence will define a dual part of the Morison model used when Morison and radiation diffraction theory is com bined and or when radiation diffraction pressures are to be transferred to a structural beam model Correspondence must be given for all basic panels PARAMETERS elno External element number of 2D Morison 3D Morison or pressure area element in the Mori son model to which panels are linked selno Sub element number of present element in the Morison model The sub element selno may be 0 when the element elno is a 2D Morison beam generated by a preprocessor or when the element is a 3D Morison or pressure area element seltyp Superelement number of the superelement in the panel model to which the current panels ssnol ssno2 belong index Superelement occurrence of seltyp ssno External element numbe
109. eseeeseeceeseeeeeaes 5 10 DEFINE ENVIRONMENT LINEARISING WAVE HEIGHT cccccccessscceesteceeesesenesseeeeesaes 5 11 DEFINE ENVIRONMENT SURFACE MODEL 2 0 cccccccccessscesesseseseeseeeceesseeceeseeeesesseeenesseseneaas 5 12 DEFINE ENVIRONMENT WAVE SPECTRUM ou ccccccccecscceeessececeseeecseseeeesesseeenessesenssaeeeensaes 5 14 DEFINE GENERAL iele e a a n e eenaa aa aa T aE aE Eae E ted eack AN t 5 15 DEFINE GENERAL ANALYSIS MODELS cccccccccssessesscssesseeseeeeeecesecseeseeeeeeecssecaeessesseeseenees 5 16 DEFINE GENERAL CONSTANTS ecccceesescesesseeseeeseeeeeseeseceaeeaeeaeseeceeceaecaeeaeeeeeeeeaecaecaeeneenees 5 18 DEFINE GENERAL EXECUTION DIRECTIVES 20 0 ccc ccccccccessececeesececeseeeeseseeeesesseeeneseeeenaes 5 19 DEFINE GENERAL EXECUTION DIRECTIVES ANALYSIS TYPE ccccccccsssceesseeeeeenees 5 20 DEFINE GENERAL EXECUTION DIRECTIVES DETERMINISTIC MORISON 5 21 DEFINE GENERAL EXECUTION DIRECTIVES DRAG LINEARISATION ccccccceeees 5 22 DEFINE GENERAL EXECUTION DIRECTIVES DRIFT FORCES ccecccccceesceeeeseeeeeenaes 5 23 DEFINE GENERAL EXECUTION DIRECTIVES FIXED FLOATING ce ceecceceesseeeeeees 5 24 DEFINE GENERAL EXECUTION DIRECTIVES HORISONTAL DRIFT ccceeeeeceees 5 25 DEFINE GENERAL EXECUTION DIRECTIVES MORISON EQUATION ccc ccceessseeeees 5 26 DEFINE GENERAL EXECUTION DIRECTIVES OUTPUT FORMAT ee ceecccceeseeeeeees 5 27 DEFINE GENERAL EXECUTION DIRECTIVES POTENTI
110. et it be 1 Check the box Run wave load analysis after Prewad if you want to automatically start Wadam once Pre wad has finished and written the Wadam analysis control data file If you are uncertain as to whether your Prewad input is correct you may leave this box unchecked If you thereafter decide to run Wadam then give Load Wave Loading Wadam select the proper Dataset and start the execution Note If your Command input file constitutes the complete input then make sure the Database status is set to New You need to change Old to New if you previously have run Prewad in which case there will exist a Prewad database causing the Database status to come up as Old Note You may also read a Command input file from inside Prewad by using the SET COMMAND INPUT FILE command followed by the command see these Wadam SESAM 4 4 22 JAN 2010 Program version 8 1 7 F SESAM MANAGER 5 2 01 Project Floating box Superelement 1 Iof x Result 2 ei belele e ala Opened new project Floating box Hydro Modelling xi Program used PREWAD Database status New Input mode Graphics z Conmendieaiie Feraro z I Run interactively after command input file processing Dataset E M Write dataset on exit IV Run Wave load analysis after PREWAD Loc cma Figure 4 3 Manager and the Hydro Modelling window with Command input file specification 4 1 3 The Input Files Analysis Control Data The file WADAMn FEM contains all
111. ethers three in each column are connected to the TLP in the column bottom Tether pre tension is equal for all tethers A sketch of the TLP is shown in Figure 3 7 SESAM Wadam Program version 8 1 22 JAN 2010 3 13 Figure 3 7 TLP geometry Panel Model The basic part of the panel model for the TLP is shown in Figure 3 8 Since the TLP is double symmetric only one quarter of the panel model is modelled The remaining parts of the model are generated in Wadam by the yz xz symmetry option BAAN IIU RANTA WC Do LY uN ea sey ga N LA A TAN LIAI a Lo Figure 3 8 Basic part of the TLP panel model from two view points The basic part of the panel model is modelled as one first level superelement in Patran Pre or Prefem It is required that it is modelled in quadrant one that is with x y gt 0 The input coordinate system is located at the water level in the centre of the TLP The wet sides of the panel model are identified in Prefem by Wadam SESAM 3 14 22 JAN 2010 Program version 8 1 e An inside outside definition That is Wadam must know which side to calculate pressures on DEFINE POINT INS1 x val y val z val END END SET INSIDE wet surfaces POINT INS1 END END
112. for line loads on beam elements These loads originate from forces at the centre of gravity of 2D Morison sub elements and dry Morison elements The calculation of line loads on 2 node beam elements is described in Appendix B 3 2 Transfer functions for loads at nodes which are connected to Morison elements An acceleration field acting on all the nodes in the structural model The inertia components are only included as loads if the mass model is specified as a distributed mass model Wadam and the structural analysis program Sestra both employ the standard SESAM finite element library to generate a mass representation This implies that the connection between accelerations and inertia loads is consistently handled in the two programs 2 5 17 Load Sum Reports Load sums are important tools to verify both the correctness of input models to Wadam and of the consist ency between Wadam and subsequent structural analyses Wadam reports load sums on both the structural model and the hydro model in chapter 5 1 in the print file Note that these load sums are reported with dimensions Load sums for the loads transferred to the structural beam model The sum of hydrostatic loads transferred to a beam model is reported in the print file as static loads It includes the hydrostatic forces from each Morison type of element as follows The buoyancy and pre tension components from mooring and TLP elements are always included e The gravity comp
113. from the preprocessor generated beam model or specified by HydroD or Prewad The section numbers play an important role in the analysis of a Morison model The use of section numbers to include different hydrodynamic effects in the Morison model should therefore be carefully planned before section numbers are assigned to 2D beam elements in the preprocessor E g if different drag and inertia coefficients shall be used in different locations this should be reflected by the section definitions The hydrodynamic coefficients specified for a 2D Morison element apply to circular cross sections For ele ments with non circular cross sections the hydrodynamic coefficients in the and directions are directly related to an equivalent cross sectional diameter Wadam calculates this equivalent diameter as the circum scribing diameter shown for the examples in Figure 2 10 Wadam SESAM 2 10 22 JAN 2010 Program version 8 1 Equivalent diameter Figure 2 10 Equivalent diameters for non circular cross sections The 2D Morison elements may be divided into sub elements each of which may be assigned different hydro property sections The sub elements may have equal or varying lengths Figure 2 11 shows three different locations of a Morison element with respect to the still water level The figure illustrates how Wadam automatically performs the subdivision of elements depending on whether they intersect the still water level or not Fig
114. g gz MAXIMUM ROLL ANGLE thmd STRIP MODEL nos xoff xbow FP TO AP AP TO FP bst SESAM 22 JAN 2010 Program version 8 1 Distance from mean water line to bilge keel hull intersection point Bilge keel angle in degrees I e angle between the line from the origin to the bilge keel hull intersection point and a line through the web of the bilge keel the sign is of no consequence as only the cosine of the angle is used GZ curve data as input Heel angle in degrees Restoring moment arm in roll GZ Note Maximum number of points on GZ curve is 50 Estimated maximum roll angle for each wave direction The number of angles and their sequence correspond to the wave di rections previously defined This option is mandatory for the roll damping model Estimated maximum roll angle in degrees It will be used to cal culate a linearised viscous and eddy making damping and will therefore significantly affect the transfer functions at wave lengths close to resonance The angle cannot be set to zero but it may be set to a very low value 0 001 in which case all vis cous effects are neglected The chosen value of the angle may strongly affect the calculation results if roll resonance occurs at wavelengths at which appreciable wave energy is present Defining parameters for the strip model Note that this must be specified before defining a bilge keel model The strips should always be given from bow to stern meani
115. g execution and results interpretation phases Both simple examples and engineering applica tions are included Chapter 4 EXECUTION OF WADAM describes the input and output files of Wadam The memory and disk storage requirements are discussed together with some rules of thumb on execution time for different types of analysis Finally the chapter lists the problem size limitations in Wadam Chapter 5 PREWAD COMMAND DESCRIPTION contains a detailed description of the input commands available in Prewad for establishing the Wadam analysis control data Appendix A contains input and output for tutorial examples of Chapter 3 Appendix B includes additional theory description for Wadam 1 4 Terminology and Notation Composite model A hydro model consisting of a panel model and Morison model representing separate parts of the structure See Section 2 1 5 Dual model A hydro model consisting of a panel model and Morison model representing the same part of the structure See Section 2 1 4 FE Abbreviation for finite element like in FE model HydroD The hydrodynamic design tool This is a modern graphical tool for modelling the input data to Wadam Wadam is started di rectly from within this application Hydrodynamic Results Interface File A file containing results from a global response analysis This file is termed G file for short The postprocessor Postresp per forms statistical postprocessing of these results See Section 2 2 and Sec
116. g interaction matrices between any two bodies in a multi body system are also reported The damping matrix is calculated accord ing to the type of the hydro model as follows e Frequency dependent damping from potential theory e Frequency independent linearised viscous damping from Morison s equation e HydroD or Prewad specified frequency dependent or frequency independent 6 by 6 damping matrices For the composite hydro model type the damping for a given frequency is reported as both frequency dependent and independent contributions 2 5 9 Exciting Forces and Moments The transfer functions for exciting forces and moments due to the incident waves are reported for each body at all the combinations of frequencies and wave headings The transfer functions for rigid body forces and moments are calculated as follows e By integration of exciting forces from all types of Morison elements obtained from the linearised Mori son s equation e By integration of pressures on all the panels obtained by solving the diffraction problem e By applying the Haskind relation on the radiation potentials if no detailed panel pressures shall be calcu lated For the dual and composite model types the exciting forces from the panel and Morison parts are reported both separately and as the combination used in the subsequent analysis e g in the equation of motion By selecting time domain output the above results will be reported as deterministic forces and
117. global coordinate system The direct input specification of a global mass matrix cannot be used together with the option to integrate forces on sectional planes in the hydro model This is because the global mass matrix does not include any information of the mass distribution on the particular elements and hence the inertia force contributions from these elements cannot be computed As described below the option to generate the mass from a mass model must be used to obtain these sectional forces Assembling of Global Mass Matrix from Mass Model The mass model used in the assembling of a global mass matrix may be defined using one of two options It may be defined using the global generate option which interprets a finite element model built from an arbitrary superelement hierarchy With this option mass contributions are assembled from the element types defined in Table 2 1 It may be generated with the distributed mass option which only works with the Morison model This implies that the entire mass description must be represented in the Morison model With the distributed mass options contributions are assembled from the following types of Morison elements 2D Morison elements 3D Morison elements Dry Morison elements Point mass elements The assembling of a global mass matrix from a mass model must be used together with the option to inte grate forces on sectional planes in the hydro model The mass model must be defi
118. h incident wave frequency and heading It includes the pressures acting at the centroid of each panel in the hydro model Note that this load sum does not include inertia loads 2 5 18 Sectional Loads Wadam calculates sectional loads by integration of distributed forces on specified sides of given planes intersecting a hydro model The frequency dependent exciting and inertia forces are included in the integra tion The sectional planes are specified in the input coordinate system and must be normal to one of the main axes of the global coordinate system A moment reference point is specified for each plane Figure 2 28 dis plays a simple submerged beam model with a sectional plane x 0 The moment reference point is inp defined in the input coordinate system Xinps Yinp Zinp Centre of gravity of subelement Figure 2 28 Sectional loads at a plane through x 0 The sectional loads are reported in the Wadam print file and on the Hydrodynamic Results Interface File as complex transfer functions Still water sectional loads are reported on the Wadam print file The sectional loads are integrated with respect to a body fixed coordinate system The sectional load on a cut comes from the integration of F ma over that part of the structure which is on the positive or negative side of the cut The components of the load are in the global system This means that for the dynamic loads the load computed by integration over the positive side and
119. he body A Amplitude of the incoming wave equal to one for harmonic results Table 2 4 Dimensionalising factors for matrices Dy entry 2 E i 1 3 j 4 6 EA Result type PERES i 4 6 j 1 3 mi ae Inertia matrix pV pVL pVL Added mass matrix pV pVL p VL SESAM Wadam Program version 8 1 22 JAN 2010 2 35 Table 2 4 Dimensionalising factors for matrices Dy entry j Result type E as a ee BE Ja Damping matrix pVsqrt g L pVsqrt gL pVLsqrt gLl Restoring matrix pVg L pVg pVeL Table 2 5 Dimensionalising factors for results D mode Result type i 1 3 J 4 6 Exciting forces pVgA L pVgA Motion A AIL Drift forces pgLA pgL A Sectional loads pVgA L pVgA Fluid pressures pgA Fluid velocities Asqrt g L Fluid accelerations Ag L 2nd order forces pgL A peL A 2nd order motions AIL AIL 2nd order pressures pgA7 L 2 5 4 Transfer Functions and Phase Definitions The transfer functions in Wadam describe responses for bodies in harmonic waves The reported responses are normalised with respect to the incident wave amplitudes With a transfer function H B the corre sponding time dependent response variable R w f f can be expressed as R B t A Re H o B e 2 13 where A is the amplitude of the incoming wave is the frequency of the incoming wave B describes the direction of the incoming wave and denotes time The ph
120. i Z Z O oO 7j SUPI CJ RNODE SUP 7 RNODE SUPERNODE CJ aJ ep UPERNODE SUPERNODI zZ S HAaAnNnP AN ORI N AN ran A2 3 Presel Input for Assembling the Structural Model ASSEMBLY OF MODEL OF TETHERED BOX Superelement NO 21 JP oP Al READ 2 3 END ASSEMBLY NEW 2 INCLUDE 3 NOPRINT CHECK INCLUDE PERFORM INCLUDE 3 ROTATE GLOBAL AXIS Z AXIS 90 0 NOPRINT CHECK INCLUDE PERFORM INCLUDE 3 ROTATE GLOBAL AXIS Z AXIS 180 0 NOPRINT CHECK INCLUDE PERFORM INCLUDE 3 ROTATE GLOBAL AXIS Z AXIS 90 0 NOPRINT CHECK INCLUDE PERFORM INCLUDE 2 NOPRINT CHECK INCLUDE PERFORM INCLUDE Wadam A3 22 JAN 2010 The Wadam Print File List of Contents SESAM Program version 8 1 The Wadam print file begins with a list of contents This list of contents shows which data will be printed depending on the chosen print switch see DEFINE GENERAL EXECUTION DIRECTIVES PRINT SWITCH The list of contents which is common for all analyses is presented below for reference purposes CONTENT S OF THE WADAM LISTING PRINTED RESULTS 1 CO 1 1 Ped 2s DATA Ziad NNMNMNNNNDN NH Oo OONA BwWNMOFH CO FOR THE T NTENTS AND LIMITATIONS CONTENTS LIMITATI OF THE WADAM LIS ONS IN THIS VERSION OF WADAM AND MODEL GENERATION INPUT CARD DECK ANALYSIS
121. in angx force skh skv PURPOSE The command defines hydrodynamic properties for mooring anchor elements See Figure 2 15 PARAMETERS angin Angle in degrees between the mooring line and the water surface at fairlead angx Angle in degrees between projection of mooring line onto the horizontal plane and the global X axis force Static mooring line force pre tension unit force skh Spring constant for horizontal displacement of the structure unit force per length skv Spring constant for vertical displacement of the structure unit force per length Wadam SESAM 5 62 22 JAN 2010 Program version 8 1 DEFINE HYDRODYNAMIC PROPERTY SECTION ref DRY ELEMENT DRY ELEMENT stot dm PURPOSE The command defines hydrodynamic properties for additional dry Morison elements Each section is given a reference number Properties assigned to a given section may contain several sub elements of equal length To define a section containing sub elements of different lengths the user must enter the CHANGE command after specifying the hydrodynamic properties PARAMETERS stot Total number of sub elements dm Distributed mass of element specified in mass per unit length NOTES The CHANGE command corresponding to this DEFINE command deviates in that there are two additional parameters selno and sl CHANGE HYDRODYNAMIC PROPERTY SECTION ref DRY ELEMENT stot selno sl dm selno and sl a
122. indicate that the command sequence is to be continued by another command sequence B JC A ID JE END The characters A B C and D in the examples above represent parameters being COMMANDS written in upper case and numbers written in lower case All numbers may be entered as real or integer values Note The command END is generally used to end repetitive entering of data Using double dot rather than END to terminate a command will depending on at which level in the command it is given save or discard the data entered Generally if the data entered up to the double dot is complete and self contained the double dot will save the data If in doubt it is always safest to leave a command by entering the required number of END commands Note Command alternatives in Prewad not documented here are obsolete Wadam SESAM 5 2 22 JAN 2010 Program version 8 1 CHANGE CORRESPONDANCE ELEMENT ENVIRONMENT GENERAL HYDRODYNAMIC PROPERTY END CHANGE PURPOSE The command changes previously given input For explanation of the parameters of this command see the corresponding alternatives in the DEFINE com mand SESAM Wadam Program version 8 1 22 JAN 2010 5 3 DEFINE CORRESPONDANCE ELEMENT ENVIRONMENT DEFINE GENERAL HYDRODYNAMIC PROPERTY END PURPOSE The command specifies all Wadam analysis control data such as environmental prop
123. ining a complex velocity potential related to by D Re de 2 19 where is the frequency of the incident wave and f is time The associated boundary value problem will be expressed in terms of the complex velocity potential with the understanding that the product of all com plex quantities with the factor e applies The linearised form of the free surface condition is o Ko 0 z 0 2 20 where K o g and g is the acceleration of gravity The velocity potential of the incident wave is defined by igA cosh kz H gK cosp ysinB 2 21 bo coshkH ey where the wave number is the real root of the dispersion relation and f is the angle between the direction of propagation of the incident wave and the positive x axis 1 Wamit is a computer program developed by Massachusetts Institute of Technology SESAM Wadam Program version 8 1 22 JAN 2010 2 47 Linearisation of the problem permits decomposition of the velocity potential o into the radiation and diffrac tion components gt det Op 2 22 ey 2 23 j 1 6 Oe dot 0 2 24 The constants denote the complex amplitudes of the body oscillatory motion in its six rigid body degrees of freedom and 9 the corresponding unit amplitude radiation potentials The velocity potential 7 represents the disturbance of the incident wave by the body fixed at its undisturbed position The total diffraction potential p denotes the sum of p and the in
124. ion forces due to the rigid body motions Hydrostatic loads are not transferred Potential theory is used for all wave periods e Global response calculations for a dual model of a semi submersible see Section 3 2 4 This analysis is basically equal to the analysis described in Section 3 2 1 except that it is only used for selection of wave periods and headings These are used in a subsequent structural analysis Four similar sections are used for sectional load calculation One vertical section in the centre of the platform and one close to the columns One horizontal section is just above the pontoons and the other below the topsides Potential theory is used for low wave periods while Morison s equation is used for higher wave periods wavelengths longer than 600 m Morison s equation is used in order to include viscous damping for the heave eigenperiod of 21 5 seconds e Global response calculations for a ship see Section 3 2 5 This analysis is used for two different purposes Sectional forces are calculated for several sections along the ship As the ship in principle is equal to a beam with loads sectional forces may be used directly for dimensioning purposes within certain limits Combinations of the sectional force components are used to calculate stresses in various posi tions of the ship It should however be remembered that this is a simplification Structural analysis should be used for more detailed stress calculations The s
125. ion 8 1 Non coupled Morison and panel models This type of hydro model is termed a composite model and is described in Section 2 1 5 With the com posite model the wave kinematics applied in Morison s equation may optionally be modified to take into account the diffracted wave field due to the presence of a panel part in the hydro model A Morison model partly or completely coupled to a panel model This type of hydro model is termed a dual model and is described in Section 2 1 4 The dual model serves two purposes It provides a mechanism to add viscous drag forces from Morison s equation to the damping terms calculated from potential theory It also provides a mechanism to calculate hydro dynamic pressure loads on a panel model and to subsequently represent these loads as line loads on beam elements in a structural model The motion responses for a hydro model is obtained by solving the equations of motion for a set of wave frequencies and heading angles The rigid body added mass damping and restoring matrices used in the equations of motion may be calculated by applying Morison s equation the potential theory or the compos ite method as described above Except for frequency dependent added mass matrices these matrices may alternatively be specified directly by the user 2 2 3 The Global Response Results The wave induced forces and moments and the motion responses calculated by Wadam are reported with respect to a motion refer
126. ions between beam elements Since each pressure area element must have a unique point specifying the direc tion of the force there must be a separate set of hydro properties for each element The Prewad definition for one element is shown below DEFINE ELEMENT PRESSURE AREA ELEMENT elno nodel node2 601 1 1 END END END a Ea r aa Se Ses Se ee SS SSS a SS DEFINE HYDRODYNAMIC PROPERTY SECTION 6 xref dia x2 y2 Z2 601 PRESSURE AREA ELEMENT WAVE LENGTH DEPENDENT 9 885 27 36 27 36 0 0 END END END a n Aei al imi E O E E E S DETARE RR EO E E S OEE EEA E EEE E AO E DEFINE HYDRODYNAMIC PROPERTY CONNECT ref elno 601 601 END END END Anchor element The mooring system consists of four anchor elements one for each column The fairlead is defined at the bottom of the columns and windlass at the third node from the top of the column The Prewad definition for the element in the first quadrant is shown below z2 skv 0 0 DEFINE ELEMENT ANCHOR ELEMENT elno nodel node2 101 2 5 END END END DEFINE HYDRODYNAMIC PROPERTY SECTION ref angin angx force skh 101 ANCHOR ELEMENT 30 0 45 0 0 0 265 END END END DEFINE HYDRODYNAMIC PROPERTY CONNECT ref elno 101 101 END END END 3 2 5 Global Response for a
127. is applied to a floating structure By specifying the time domain output format the fluid kinematics will be reported as deterministic pressure and velocities at specified phases of the incident waves with given wave amplitudes The surface elevation n in a radiated and diffracted wave field is obtained from potential theory as n E 2 17 where p is the non dimensionalised pressure at the still water level 2 5 14 Wave Drift Damping The Wave Drift Damping describes the rate of change of the Mean Drift force with forward speed computed at zero speed The sign of this rate of change is in most cases negative meaning that this will represent a damping mechanism for the slow drift motion excited by the second order difference frequency forces or due to the interaction of the waves with a current The 3x3 Wave Drift Damping matrix surge sway yaw is reported in the Hydrodynamic Results Interface File This matrix is computed according to the methods described in Ref 9 The computation of the wave drift damping requires a free surface mesh which is defined as input exactly like the free surface mesh for second order analysis The mesh used in the Wave Drift Damping computa tions does however not need to have a circular outer boundary A Morison model can not be used if Wave Drift Damping is to be computed The iterative equation solver for the potential solution can not be applied if Wave Drift Damping is com puted 2 5 15
128. is used to include viscous damping for the heave eigenperiod of 21 5 seconds The following calculations are performed in Wadam for this analysis The first two tasks are automatically calculated while the others are specified for this analysis e Hydrostatic calculation in which both the hydrostatic and inertial properties for the structure are calcu lated e Calculation of hydrodynamic exciting forces added mass damping and global motion response for the semi submersible e Eigenvalue calculations for rigid body motions One set of eigenvalues is calculated for each wave period e Sectional forces and moments in specified sections Preparations for the analysis in Wadam include the following steps e Creation of a panel model in Patran Pre Prefem and Presel Symmetry of the structure is used and only one quarter of the semi submersible is modelled e Creation of beam elements for the Morison model in Genie or Patran Pre Transfer of Input Interface Files to the directory where the Wadam analysis is performed e Definition of execution directives additional elements environmental properties etc in Prewad e Definition of correspondence between panels and Morison elements SESAM Wadam Program version 8 1 22 JAN 2010 3 25 The mass is included as distributed mass on the Morison model The semi submersible considered in this example is a typical double symmetric twin pontoon structure with the connection between the pontoons and
129. ison s equation e A combination of a panel and a Morison model called a composite model The composite model is used when potential theory and Morison s equation are applied to different parts of the hydro model e A combination of a panel and a Morison model called a dual model The dual model is used when both potential theory and Morison s equation shall be applied to the same part of the hydro model The dual model must be used when pressure distribution from potential theory shall be transferred to a beam structural model The legal combinations of panel and Morison models are shown in Figure 2 2 L G Morison model Composite model Dual model Panel model Dual model Figure 2 2 Hydro model combinations The element types interpreted by Wadam are listed in Table 2 1 Other element types present in the various Wadam models will be neglected Table 2 1 Overview of SESAM element types interpreted in the various Wadam models Type of element Number Panel Morison Mass Structural of nodes model model model model Beam elements Beam 2 Ni NI J Curved beam 3 N Shell elements SESAM Wadam Program version 8 1 22 JAN 2010 2 3 Table 2 1 Overview of SESAM element types interpreted in the various Wadam models Tye of element eae des Triangular flat thin shell 3 Ni NI Quadrilateral flat thin shell 4 Ni Ni N Subparametric curved tria
130. ison 3D Morison or pressure area element in the Mori son model to which panels are linked ALL All specified correspondence will be printed OVERVIEW A summary of the specified correspondence will be printed SESAM Program version 8 1 22 JAN 2010 PRINT ELEMENT 2D MORISON ELEMENT 3D MORISON ELEMENT ALL ANCHOR ELEMENT ELEMENT DRY ELEMENT OVERVIEW POINT MASS PRESSURE AREA ELEMENT TLP MOORING ELEMENT Wadam 5 71 END PURPOSE The command prints additional Morison elements PARAMETERS 2D MORISON ELEMENT 3D MORISON ELEMENT ALL ANCHOR ELEMENT DRY ELEMENT OVERVIEW POINT MASS PRESSURE AREA ELEMENT TLP MOORING ELEMENT Print 2D Morison elements Print 3D Morison elements All additional defined elements will be printed Print mooring elements Print dry Morison elements A summary of the additional defined elements will be printed Print point mass elements Print pressure area elements Print TLP mooring elements Wadam 5 72 PRINT ENVIRONMENT SESAM 22 JAN 2010 Program version 8 1 ALL CURRENT FREQUENCY HEADING PAIRS OVERVIEW ENVIRONMENT SURFACE MODEL WAVE AMPLITUDE WATER DEPTH WAVE DIRECTION WAVE LENGTH END PURPOSE The command prints environmental data PARAMETERS ALL CURRENT FREQUENCY HEADING PAIRS OVERVIEW SURFACE MODEL WAVE AMPLI
131. lated Symmetric and or antisymmetric loads about the XZ or YZ PLANE XZ plane symmetry will be generated YZ plane symmetry will be generated Antisymmetric loads will be generated Both symmetric and antisymmetric loads will be generated Symmetric loads will be generated Symmetric and or antisymmetric load about both the XZ and the YZ plane will be generated Lowest load case number used by Wadam when generating loads for the Loads Interface Files The load case numbers used by Wadam will start with the high est load case number found on each Input Interface File for each superelement type of the structural model plus one This option cannot be used in connection with fatigue calculations the S file will then not be created Switch ON or OFF calculation of tank pressure when transfer ring pressures to the Loads Interface Files Switch ON or OFF calculation of wave pressures to finite water surface by stretching when transferring pressures to the Loads Interface Files This option is valid only for time domain To specify generation of Loads Interface Files Loads Interface Files Ln FEM will be generated with loads on a beam structural model Answer YES or NO to whether the static and dynamic mooring forces shall be included in the loads written to the Loads Inter face File default Answer YES or NO to writing added mass from wet beams and 3D Morison elements only as separate inertia forces for structural
132. line mode window on Unix SPECIAL KEYS Information on some special keys is provided The information is printed in the print window line mode window on Unix STATUS LIST If the program is used in line mode Unix only the Status List is printed on the screen If the program is used in graphic input mode the Status program is started SESAM Wadam Program version 8 1 22 JAN 2010 5 69 PRINT ALL CORRESPONDANCE DATASET ELEMENT PRINT ENVIRONMENT GENERAL HYDRODYNAMIC PROPERTY OVERVIEW END PURPOSE The command prints selected information on the screen or to a file The options are the same as for the DEFINE command except for the three additional options ALL DATASET and OVERVIEW that give sta tus of the interactive run PARAMETERS ALL This gives a print of all the data existing on the Prewad data base DATASET This gives a list of available datasets on the Prewad data base and which one of these that is current OVERVIEW This gives a table containing a global overview of the different data available in the Prewad data base and a summary of the data defined Wadam SESAM 5 70 22 JAN 2010 Program version 8 1 PRINT CORRESPONDANCE elno ALL CORRESPONDANCE OVERVIEW END PURPOSE The command prints specified correspondence between elements in the Morison model and panels in the panel model PARAMETERS elno External element number of 2D Mor
133. ll damping SESAM Program version 8 1 Wadam 22 JAN 2010 5 53 DEFINE GENERAL SECTIONAL LOADS XY PLANE POSITIVE SIDE secno YZ PLANE ax ay az SECTIONAL LOADS NEGATIVE SIDE XZ PLANE END PURPOSE The command defines sectional planes where sectional loads will be calculated PARAMETERS secno XY PLANE YZ PLANE XZ PLANE POSITIVE SIDE NEGATIVE SIDE ax ay az Section identification number The section is parallel with the xy plane of the input coordinate system The section is parallel with the yz plane of the input coordinate system The section is parallel with the xz plane of the input coordinate system Sectional loads are calculated on the positive side of the sectional plane Sectional loads are calculated on the negative side of the sectional plane The x coordinate with respect to the input coordinate system of a point in the sec tional plane This point defines the position of the sectional plane and of the axis used for the calculation of the sectional moments The moment axis are parallel with the input axis The y coordinate of the point The z coordinate of the point SESAM 22 JAN 2010 Program version 8 1 DEFINE GENERAL TANK PRESSURE TANK PRESSURE ALL tho_all tank_i rho_i END PURPOSE The command defines density of the fluid in the tanks PARAMETERS ALL rho_all tank i rho i N
134. m It may optionally also be interpreted directly from the Wamit version 5 3S free surface format Ref 2 The part of the free surface actually modelled by surface panels is defined by the radius of a circle as shown in Figure 2 23 This so called partitioning radius R must enclose the hydro model It should be determined according to the decaying rate of local waves An appropriate approximation is R O h for shallow water and R O A for deep water Here h is the water depth and A gt gt hA is the longest wave length involved The ratio h may have to be substantially larger than 1 to achieve accuracy in deep water Ref 3 Figure 2 23 Free surface mesh The free surface must be meshed with 4 node shell elements no 3 node elements The HY DRO PRES SURE load case must point in the negative z direction The free surface model shall have the same symmetry properties as the panel model Wadam SESAM 2 24 22 JAN 2010 Program version 8 1 2 1 11 Load Case Numbering and Load Case Combinations The default load case numbers LC generated by Wadam on the Loads Interface Files are given from the fol lowing equation LC MM 1 NOK LL 1 NPHA IPHA I NSEL ISEL 2 1 where MM is the actual heading number NOK is the total number of frequencies LL is the actual frequency number NPHA is the number of phase angles if the time output option is specified NPHA 1 if complex loads are generated IPHA is the actual phase angl
135. n of hydrodynamic loads is per formed on a dry Morison element A dry Morison element includes only the mass per unit length and the diameter of the element A dry Mori son element may alternatively be defined directly in HydroD or Prewad The end nodes of the dry Morison element must in this case be connected to nodes existing in the Morison model A dry Morison element specified directly in HydroD or Prewad is not part of a structural model Therefore when the loads on a structural model are calculated panel pressures connected to dry Morison elements defined directly in HydroD or Prewad will not be mapped onto the structural model and load imbalance will occur Point Mass Elements A point mass element is defined in HydroD or Prewad and can only be connected to existing nodes in the Morison model A point mass element may be used to include nodal masses in a Morison model whereby point masses defined by the preprocessors are created as point mass elements in Wadam The point mass element num bers are generated automatically starting at element number 400 000 The point mass section numbers are generated in the range 1001 to 1999 Note that no other element or section numbers may coincide with those automatically generated for the point mass elements The property description for a point mass element includes the mass of the node The point mass elements may alternatively be defined directly in HydroD or Prewad Note Contrary to some
136. nearised drag force calculation for all the motion modes and for all the incident wave frequencies SESAM Wadam Program version 8 1 22 JAN 2010 2 49 For deterministic analysis of fixed structures Morison s equation is expressed on the form F pV 1 C v spoCpvlv 2 29 where time independent current may be included in v The contributions from Morison elements are calculated in the particular element local coordinate systems The contributions are transformed into the body coordinate system prior to the assembling of rigid body quantities The wave kinematics in Equation 2 26 and Equation 2 29 may be taken from the incident wave field as described in Section 2 4 1 Optionally the wave kinematics may also be taken from the diffracted wave field calculated from potential theory 2 6 5 The Equation of Motion The equation of motion in Wadam is established for harmonic motion of rigid body systems expressed in the global coordinate system By applying Newtons law and including the added mass damping and exciting force contributions acting on the panel and Morison parts of a hydro model the complex 6 by 1 motion vector X f can be found from the equation of motion 0 M A 1a B B C C X B F B 2 30 where M represents the 6 by 6 body inertia matrix A represents the 6 by 6 frequency dependent added mass matrix B o represents the 6 by 6 frequency dependent potential damping matrix B represents the 6
137. ned in the same coordinate system as used for the other input models This is described in more detail in Section 2 1 1 The mass model may be identical to the structural model or it may be a completely different superelement hierarchy 2 1 9 Structural Modelling Wadam may be used to calculate hydrostatic and hydrodynamic loads on a structural model see also Sec tion 2 3 The structural model may be built from an arbitrary large superelement hierarchy It may include any of the finite element types defined in SESAM However only the finite element types listed in Table 2 1 will receive hydrostatic and hydrodynamic loads Wadam SESAM 2 22 22 JAN 2010 Program version 8 1 The finite elements which shall receive hydrostatic and hydrodynamic loads must be identified in the mod elling phase The technique to identify elements differs between beam elements and element types with sur faces shells and volumes as described in the two subsections below Nodal accelerations from rigid body motion will be calculated for all the nodes in a structural model If the structural model consists of more than one superelement a combination of loads from different superelements is required in the superelement assembling performed in Presel The combination of loads is described in Section 2 1 11 Loads on Superelements with Beams The beam elements and nodes which shall receive hydrostatic and hydrodynamic loads from Wadam must be included in a Mori
138. ng matrix and hence contribute to the rigid body motion The rigid body motion computed yields dynamic restoring forces acting in the mooring element nodes They are mapped onto the structural model as nodal loads Note No nodal moment loads are transferred to the structural model 2 1 4 The Dual Model The dual model is a hydro model where a panel model and a Morison model represents the same part of a structure see Figure 2 17 The basic idea with the dual model is that panel model with potential theory is used to include the forces related to added mass and potential damping whereas the Morison model is used to include the viscous drag forces Figure 2 17 A dual model with both a panel model and a Morison model representing a structure SESAM Wadam Program version 8 1 22 JAN 2010 2 17 The dual model is mandatory when hydrodynamic loads from potential theory shall be used in the structural analysis of a beam model In a dual model the hydrodynamic loads are always transferred from a panel model to a Morison model The viscous drag forces are calculated from Morison s equation on the Morison model while the contributions from potential theory are represented as loads on Morison sub elements according to a panel to Morison element correspondence defined by the user Panel pressures may be transferred to loads on 2D Morison ele ments 3D Morison elements pressure area elements and dry Morison elements For 2D Morison elements the pan
139. ng that for the FP TO AP option the strips are given in the order of increasing x value while they are given in the order of decreasing x value for AP TO FP option Number of strips used in the roll damping calculations Maxi mum is 25 X coordinate of fore perpendicular FP in global coordinate system dummy X coordinate of the midpoint of the first strip X axis positive from fore perpendicular FP to aft perpendicu lar AP default X axis positive from aft perpendicular AP to fore perpendic ular FP Length of each strip This is repeated nos times SESAM Program version 8 1 bilgr sect WATER PARAMETERS LAMINAR FLOW TURBULENT FLOW Wadam 22 JAN 2010 5 51 Radius of a bilge at strip This is repeated nos times Parameter for eddy making roll damping calculations It is de termined by the sectional area coefficient BOG BS where BOG is the distance from the bottom of the strip to a line through cen tre of gravity of the ship and parallel with the x axis in the glo bal coordinate system and BS is the beam of the strip at the water plane This is repeated nos times sect can take the following BOW SECTION Apply the roll damping model for bow sec tions MID SECTION Apply the roll damping model for mid sec tions STERN SECTION Apply the roll damping model for stern sections OTHER TYPE To be used for all section types not defined by the parameters for bow midship and stern ther
140. ngle Super element Composite model cccecceeccesseesseesseeseceseceseeseecsaeenscseeeeeeeeeeesaes 2 19 ZET Multi Body Modelling iss 5 s sccccscocesse a a aaa a aa ien tates aoa 2 19 DAB Mass Modelling sare sarerari nati eiea ia E R A a E AR ATERAT 2 20 2 1 9 Structural Modelling ccc ccceccccescceseeeseeeeesecesecneeeeeeeeeecsaecaeneeeseeeeseeeseecseceaeeeeeeeesenees 2 21 2 1310 Free Surface Modelling nerro eerie eee T E A aati GE E dvuteous eueetivees 2 23 2 1 11 Load Case Numbering and Load Case Combinations cccccccccsseeseeeteceeeeseeeeseeteeennees 2 24 Gl bal Response A Maly sisives siacisds cactedececaecankcatlessvbvd eceaconagets a a a a a a n E a 2 27 221 Gepef l eenst oiala e a a a a e eT aaa a E 2 27 2 2 2 Computation of Wave Loads cecccccecssesseceteceseseeeeeeecseecssesseceeceseeeseecsecesecneeeeeseaeeaaees 2 27 2 2 3 The Global Response Results ccccccecssesssesseceseceeceeeeeesecseeceeseeceseeeseecseceseeeeeeeeseneeaees 2 28 The Calculation of Detailed Loads on a Structural Model cceccccccesccessceseeeneeesecnscseeeeeeeeeeenaes 2 28 DBed GEM Al se cvseds E EEA E E TE cen Boies Seagate deen wea ebacees 2 28 2 3 2 The Structural Load Types isiin roisean arei iasi iino Eae aE E na aR i 2 29 2 3 3 Deterministic Loads sdin miria n a en en ia aeia beria d erana 2 29 2 3 4 Detailed Loads Transfer to a Model with Shell or Solid Elements 0cccsseseeetees 2 29 2 3 5 Detailed Loads T
141. ngular thick shell 6 y y y Subparametric curved quadrilateral thick shell 8 y y y Multilayered curved triangular shell 6 y y y Multilayered curved quadrilateral shell 8 y y y Solid elements Triangular prism 6 Ni Ni NI Linear hexahedron 8 y Ni NI Tetrahedron 4 Ni NI Isoparametric triangular prism 15 y y y Isoparametric hexahedron 20 y NI Isoparametric tetrahedron 10 y y Mass elements One node mass element 1 Ni NI 2 1 1 The Coordinate Systems Wadam uses three different coordinate systems for single body hydro models e A global coordinate system e An input coordinate system Local finite element coordinate systems For multi body hydro models a more general definition applies to the coordinate systems see Section 2 1 7 The global coordinate system denoted Xgjo Y gio Zglo iS right handed with the origin in the still water level The Z axis is normal to the still water level and the positive Z axis is pointing upwards as shown in the Figure 2 3 and Figure 2 4 Note The results refer to the global coordinate system The origin is termed the result reference point or the motion reference point Wadam SESAM 2 4 22 JAN 2010 Program version 8 1 The input coordinate system denoted Xinp Yinp Zinp is the coordinate system in which the hydro model and the structural model are defined Wadam imposes the restriction that all input models i e the panel Morison mass and FE models must be modell
142. no ref GROUP el e2 einc CONNECT END GROUP refl ref2 rinc er einc END PURPOSE The command connects additional Morison elements defined in Prewad with hydrodynamic properties PARAMETERS ref Reference number of section to be connected elno Element number of a single element GROUP A group of elements and sections to be connected el First element number in the group e2 Last element number in the group einc Step in the Element numbering ref First reference number in the group ref2 Last reference number in the group rinc Step in the reference numbering er First element in a group of elements to be coupled to a group of sections SESAM 22 JAN 2010 Program version 8 1 DEFINE HYDRODYNAMIC PROPERTY SECTION ref SECTION 2D MORISON ELEMENT 3D MORISON ELEMENT ANCHOR ELEMENT DRY ELEMENT POINT MASS PRESSURE AREA ELEMENT TLP MOORING ELEMENT END PURPOSE The command defines hydrodynamic properties for different element types Hydrodynamic properties are connected to sections Each section is given a reference number PARAMETERS ref Reference number of section The reference number of sections to be connected to additional elements defined in Prewad must be different from any cross section reference numbers de fined on the Input Interface File containing the Morison model SESAM Wadam Program version 8 1 22 JAN 2010 5 59
143. ns the GZ curve is normally known also for large heeling angles This information may be utilised in Wadam by specifying the appropriate GZ curve as input to Prewad The restoring roll moment at an angle n4 gt may be written as Mo pgVGZ o where V is the submerged volume of the hull and GZ is the righting arm The work performed by rotat ing the ship through an angle n4 from 0 to may be written as o gt W f M v dv pgV GZ v dv pgVA o 0 0 where A is the area under the righting arm curve as shown in Figure B 3 Rightin gh i arm A GZ Result of first 74 estimate Compare with from equation of motion solution Linear YY Yj Figure B 3 Linearised Roll Restoring Moment from the GZ curve User defined GZ curve Yi of Wp gt 14 Angle of heel At small angles the restoring work may be expanded in a Taylor series giving 1 oes Wi 5PEVGZ pgVA SESAM Wadam Program version 8 1 22 JAN 2010 B 9 where GZ the initial moment arm is related to GM the initial transverse metacentric height as follows a GZ GMr ny At large angles the linearised roll restoring coefficient is defined as C44 f GMr where the factor fis defined as the ratio between the area 4 under the GZ curve from 0 to and the area 4 below a straight line from 0 to with slope equal to GZ Na GM B3 2 Calculation of Line Loads The line load on a beam finite element
144. nted Wadam 5 74 GLOBAL MATRICES CRITICAL DAMPING DAMPING MATRIX MASS MATRIX RESTORING MATRIX MULTI BODY MODELS ibody PANEL MODEL STRUCTURE IDENTIFICATION OFFBODY POINTS OVERVIEW ROLL DAMPING MODEL SECTIONAL LOADS TANK PRESSURE TEXT SESAM 22 JAN 2010 Program version 8 1 Specified global matrices will be printed The critical damping matrices will be printed All specified damping matrices will be printed All specified mass matrices will be printed The restoring matrix will be printed Data connected to multiple bodies will be printed Print specific analysis model connected to body Body identification of body number i Analysis model is a panel model Print structure dependent data for given body All off body points will be printed A summary of the general parameters will be printed All data connected to a roll damping model based on strip the ory will be printed All specified sections will be printed All specified tanks with given fluid density will be printed All text strings specified will be printed SESAM Program version 8 1 Wadam 22 JAN 2010 5 75 PRINT HYDRODYNAMIC PROPERTY 2D MORISON ELEMENT 3D MORISON ELEMENT ANCHOR ELEMENT DRY ELEMENT POINT MASS PRESSURE AREA ELEMENT TLP MOORING ELEMENT ref ALL CONNECT HYDRODYNAMIC OVERVIEW SECTION END PURPOSE The command prints sectional dependent hydrodynamic dat
145. ntegrating the hydrostatic pressure loads on the panel model are also reported in the print file LIS file For dual models the forces represented at the centre of gravity of the Morison sub elements are included This implies that the potential pressures transferred to the Morison sub elements according to a corre spondence list are included together with the viscous forces calculated directly on the Morison element Note Sectional loads calculation should be used with care when global matrices are specified directly as input to Wadam This is because the global matrices do not provide the detailed information required to integrate distributed force contributions In addition to the total sectional loads it is also possible to compute and write to the Global Results Interface File G file differnt parts of the sectional load This includes sectional added mass matrix sectional damp ing matrix sectional body mass matrix and sectional excitation force These quantities cannot be handled by Postresp but they may be read into DeepC To compute these sectional load details a modification of the Wadam FEM file must be done manually Open this file in an editor an find the card WADAMAI This is one of the first cards on the file Change the 19th number on this card from 0 to 1 2 5 19 Roll Damping Coefficients Wadam calculates the roll damping coefficient B44 by including contributions from the following hydrody namic effects e Pote
146. ntial damping from surface wave radiation e Linearised viscous damping from eddy making of the bilge keel e Linearised viscous damping from skin friction of the hull e Linearised viscous damping from bilge keel The potential damping effect is included in the radiation potentials and is defined within the regular linear theory The linearised viscous roll damping effects from eddy making due to the naked hull is computed based on empirical data given by Tanaka Ref 6 while the damping coefficient from skin friction and eddy making from bilge keels are computed according to Kato Ref 7 These originally non linear viscous damping contributions are linearised in order to be included in the harmonic equations of motion The potential damping and the skin friction contributions are calculated from a strip model which is auto matically generated from a panel model The other two effects are calculated from information about the bilge keel SESAM Wadam Program version 8 1 22 JAN 2010 2 45 The viscous damping coefficient is generally defined as Bag Kn 4 max In Wadam the coefficient K is calculated approximately as a function of the wave frequency the hull form and the bilge keel dimensions The variable n4 is the maximum expected roll angle When viscous roll damping is included in the equation of motion the roll angle amplitude is not known in advance rather it is a part of the solution Therefore the user has to estimate the maxim
147. o o ole foe o o o o o oe oe foe o oe o o oO o ole foe foe o o o o oe ole o o o o o o o ole o oO o o o oO o oe oe o o o o oO o o oe foe oP o o oO o oe oe foe o o o o Generate surfaces to form a box 45 x 45 x 40 m i e 1 4 of structure AP oO AP AP AO AP AP O OP AP OP Q ENERATE SURFACE A 121512151214 CARTESIAN 000 45 0 0 END 0 45 0 END O O 40 END 7 Remove unwanted sides of box on x z and y z planes and the top AP iP oP DELETE GEOMETRY AS111 AT111 AU112 END Set the element type to be 4 node shell to represent each panel of the hydrodynamic model SET ELEMENT TYPE SURFACE ALL SURFACES INCLUDED SHELL 4NODES END SESAM Program version 8 1 22 JAN 2010 Wadam ae ae ae ole ae ae ale ale ae ae ae ale ale ae ae ale ole ole ole ole ae ae x ale ae O oe oe Q aO aO ae ae oO ale ae Ee oO oO p ae ae Ea oO oO oO Q ae ae I ae ae srd Yn ae ae nN oO HH ale ae H oe oe H O oe a Q ae oe oO Q oe ae Q oO ea ale aie Oo Q ae ae O OG D oe oe pP 9 p H oe BH ry oO ae ae n n zZ oe D oe P n Oo H oe oe G oO oe AY H A w oe oe E Q x ae Z oe x oe vo ae ae qo on x ne de H oe odo bb Oo fy ol ol
148. oP AP iP oP o oO END TEXT WADAM USER MANUAL EXAMPLE 3 1B Tethered Floating Box 90 x 90 metres and Draft 40 metres Global motions response analysis with transfer of loads END Define the environmental data to be used for the motions response water depth metres wave directions degrees wave periods finite or infinite water depth ENVIRONMENT WATER DEPTH 100 WAVE DIRECTION 0 45 END WAVE PERIOD 8 FINITE 10 FINITE 12 FINITE END END Define the input data for the 4 tethers element no s and nodes no s to which they attach el no 1 to node no 1 el no 2 to node no 2 etc ELEMENT TLP MOORING ELEMENT 1 1 2 2 3 3 4 4 END END Define section types one type for each different set of properties in this case all tethers have the same properties length metres pre tension N elastic stiffness N metre platform offset in x direction metres platform offset in y direction metres HYDRODYNAMIC PROPERTY SECTION 101 TLP MOORING ELEMENT 965 9 59E7 2 0E7 20 20 END Connect section type no 101 to each of the four tethers CONNECT 101 1 2 3 4 END END END END This file contains input data for Wadam Wadam SESAM 3 10 22 JAN 2010 Program version 8 1 4 Wadam Wizard Settings 4 Wadam Wizard Settings Wizard Wadamwizard2 Wizard Wadamwizardd Panel Model Morison Model Composite Model Panel Model Morison Model Composite Model C Dual M
149. odel C Dual Model Information Settings Information Settings Time domain Frequency domain 92 Time domain Frequency domain 92 I Stochastic drag 92 I Stochastic drag 92 I Drag by waveheights 9 I Drag by waveheights 92 I Load crossections 92 I Load crossections 9 I Load transfer 92 I Load transfer 9 I Tank pressure 9 I Tank pressure 9 J Pressure panels 92 J Pressure panels 9 I Anchor elements 9 I Anchor elements 9 D 3D Morison elements 92 T 3D Morison elements M ee M TLP elements 92 9 IV Offbody points 92 I Second order results 92 I Second order results 92 I Damping matrix 92 J Damping matrix 9 I Critical damping matris 92 I Critical damping matris 92 J Restoring matrix 92 I Restoring matrix ee Figure 3 6 HydroD wizard for the tethered box example left and the TLP example in Section 3 2 right 3 2 Engineering Application Examples This section describes how Wadam may be applied for typical engineering problems The examples have been selected to demonstrate the main features of Wadam They do not cover all options in the program The text for each example explains the options used in that specific example only The panel models shown in this section may be used as guidance during the modelling phase It is however important to create a panel model suitable for the type of analysis to be performed A panel model that is suitable for global response analysis is not necessarily acceptable f
150. odel is used in the calculation of motions in Wadam Structural Model The structural model is equal to the one used for load transfer to the shell element model see Section 3 2 2 except that the sub sea part of the structure is substituted by the Morison model One extra superelement is also used to connect the Morison model to the rest of the structural model This extra superelement is shown in Figure 3 12 Figure 3 13 shows the geometry assembly for the structural model Wadam SESAM 3 22 22 JAN 2010 Program version 8 1 beam model eee eee ee _ _ supernode coupling a b Figure 3 12 a Extra superelement for connection of Morison model to the rest of the structural model and b Example of use of the extra superelement Deck area and hull above water level Ww Q N 101 Connection element 100 Morison model Figure 3 13 Geometry assembly for the TLP structural model The model is built up from first level superelements created in Patran Pre and Genie and then built together in the hierarchy shown in Figure 3 13 Both the geometry assembly and the description of load case num bers is built up using Presel As this is a fatigue analysis only wave loads from Wadam are included in the load combinations See Section 2 1 11 for further description Structural mass is distributed with a high degree of accuracy in the model This is necessary in order to include the inertia forces transf
151. ody no i and body no j for given element The use of input global matrices will be specified By default the input matrices including any generated critical damping matrices will be added to the corresponding matrices calculated by Wadam The input matrices in question will be added to the correspond ing matrices calculated by Wadam The input matrices in question will overwrite the corresponding matrices calculated by Wadam Wadam SESAM 5 42 22 JAN 2010 Program version 8 1 NOTES This command may create imbalance in the loads for a load transfer analysis This may also lead to inaccu rate or erroneous sectional loads due to lack of detailed information SESAM Wadam Program version 8 1 22 JAN 2010 5 43 DEFINE GENERAL MULTI BODY MODELS MULTI BODY STRUCTURE IDENTIFICATION END PURPOSE The command defines multiple body parameters If any of this data is specified some of the single body related data specified elsewhere will be neglected by Wadam These are e Sink source or panel model specified using DEFINE GENERAL ANALYSIS MODELS e Symmetry plan definition using DEFINE GENERAL EXECUTION DIRECTIVES e Characteristic length using DEFINE GENERAL CONSTANT e Calculation of sectional loads by using DEFINE GENERAL SECTIONAL LOADS Wadam 5 44 SESAM 22 JAN 2010 Program version 8 1 DEFINE GENERAL MULTI BODY MODELS XZ PLANE YZ
152. of finite element type of loads to a structural model The environmental definition including both surface waves and current profiles is introduced in Section 2 4 The description of the results produced by Wadam is included in Section 2 5 Basic calculation methods are described in Section 2 6 Additional information on calculation methods is included in Appendix B 2 1 Definition of Model Types in Wadam The definition of models in Wadam includes three main model types 1 the hydro model which is used to calculate hydrodynamic forces 2 the structural model where hydrodynamic and hydrostatic loads are rep resented as finite element loads and 3 the mass model The mass model is relevant for floating structures only and may be defined either as finite elements with mass properties or as a global mass matrix The dif ferent model types see Figure 2 1 are described in this section Wadam reads the various models from Input Interface Files generated by e g the SESAM preprocessors Patran Pre Prefem Genie and Presel Structural model FE model Mass model Dual model Composite FE model Global ee model matrix Figure 2 1 Overview of model types in Wadam Panel model Monson model Wadam SESAM 2 2 22 JAN 2010 Program version 8 1 The hydro model may see Figure 2 1 consist of either A panel model for calculation of hydrodynamic results from potential theory e A Morison model for calculation of hydrodynamic loads from Mor
153. of the body coordinate system given in the global coor dinate system Y coordinate of the origin of the body coordinate system given in the global coor dinate system Z coordinate of the origin of the body coordinate system given in the global coor dinate system Angle between the body x axis and the global x axis in degrees The angle is given from the body x axis to the global x axis Positive direction is counter clockwise The origin of the body coordinate system will be used as the results reference point SESAM Wadam Program version 8 1 22 JAN 2010 5 47 DEFINE GENERAL OFFBODY POINTS xcoor ycoor zcoor OFFBODY POINTS END SURFACE MODEL prefix topsel PURPOSE The command defines points in the fluid where wave kinematics shall be calculated All points must be given because no symmetry is taken into account PARAMETERS xcoor The x coordinate with respect to the global coordinate system of the point in the fluid ycoor The y coordinate with respect to the global coordinate system of the point in the fluid Zcoor The z coordinate with respect to the global coordinate system of the point in the fluid SURFACE MODEL The off body points are given as nodes as part of a 4 node shell element model on an Input Interface File prefix File prefix or directory where the file is stored topsel The superelement number which must be a single first level superelement NOTES The S
154. of the other element types specified directly in HydroD or Prewad the nodal loads from point mass elements will be mapped onto the structural model Mooring Elements A mooring element is defined in HydroD or Prewad and can only be connected to nodes in the Morison model Appendix B 2 1 includes a detailed description of the mooring element formulation The mooring element is also termed anchor element A mooring element may be used to include external restoring forces from weightless mooring lines with lin ear stiffness characteristics The mooring elements are connected to nodes in the Morison model The first connection node for the mooring element is the guiding point also termed the fairlead The second connection point may be at a windlass as shown in Figure 2 15 a The two mooring element connections may optionally be the same node The hydro properties of a mooring element include the element orientation the pre tension and the restoring characteristics The element orientation includes two different angles The angle a between the still water level and the mooring line and the angle a between the positive x axis and the mooring line as shown in Figure 2 15 b Note that the angle dinc lt 7 2 with respect to the negative x axis for nodes with x lt 0 The restoring contributions from the mooring elements are assembled into the body restoring matrix and hence contribute to the rigid body motion The rigid body motion computed yi
155. ogram version 8 1 22 JAN 2010 2 31 n Acos t k xcosB ysinB 2 3 This represents a wave with its crest at the origin for t 0 as shown in Figure 2 25 b X ee a wave propagation direction b wave phase at t O Figure 2 25 Surface wave definitions The fluid velocity v v i v j vk and acceleration a a i a j a k for the incident waves are v nity j loa cos t k x 2 4 v A sin t k x _ait tai A 2k cosh kz kd ator ka an ay K Oa aao i 2 5 a A cos t k x where d Depth k Absolute value of wave number 0 Wave angular frequency A Wave amplitude x xi yj location in the x y plane k k i cos j sinB two dimensional wave number Z Vertical coordinate with z axis upward z 0 0 at still water level B Direction of wave propagation Wadam SESAM 2 32 22 JAN 2010 The finite depth dispersion relation used in the above expressions is gktanh kd The wave period is given by at 0 T and the wave length is 20 oam For a more detailed description of linear wave theory see Ref 8 Program version 8 1 2 6 2 7 2 8 The fluid kinematics above the still water level is obtained by constant extrapolation in Wadam 2 4 2 Current Profiles Wadam provides the option to specify time invariant current profiles for the calculation of deterministic Morison element forces Note The current can only be used for fixed structures The cur
156. on s equation See Section 2 4 2 for the description of current profiles in Wadam Note Deterministic loads cannot be computed for a dual model 2 3 4 Detailed Loads Transfer to a Model with Shell or Solid Elements The transfer of detailed loads to a large volume structure modelled with shell or solid elements is performed as follows Wadam SESAM 2 30 22 JAN 2010 Program version 8 1 The hydrostatic load at still water condition is calculated as normal pressures directly on the shell and solid element surfaces defined as wet sides The hydrodynamic pressure loads on shell or solid elements can only be obtained from a potential theory calculation based on a panel model The actual mapping of panel pressures into normal pressure loads in a structural model is automatically performed by the algorithm described in Appendix B 3 3 e Independent nodal loads require a Morison model to be used together with the panel model More specif ically if loads from mooring lines and tethers shall be included in a structural system a Morison model consisting of the connection nodes must be created 2 3 5 Detailed Loads Transfer to a Model with Beam Elements The transfer of loads to a slender structure for example a jacket or a jackup modelled with beam elements is performed as follows The hydrostatic load at the still water condition is represented as loads on beam elements and nodes in the structural model The hydrodynamic loads
157. onents are only included if the mass model is specified as a distributed mass model The sum of hydrodynamic loads acting on the beam model is reported in the print file for each inci dent wave frequency and wave heading It includes the hydrodynamic forces from each Morison type of element as follows The hydrodynamic pressure components acting on beams and nodes e The inertia components are only included if the mass model is specified as a distributed mass model Load sums for the loads transferred to the structural shell solid model The sum of hydrostatic loads transferred to a shell solid model is reported in the print file as static loads It includes the buoyancy of the structure The sum of hydrodynamic pressure loads transferred to the shell and solid structural model is reported in the print file for each incident wave frequency and wave heading It includes the part of the hydrodynamic loads actually transferred to normal pressure loads on shell and solid elements Note that this load sum does not include inertia loads The sum of pressures and inertia loads acting on the structural model may be calculated from the Ses tra data check where the accelerations transferred from Wadam are converted into inertia loads see Section 2 5 16 Load sums for the hydro model SESAM Wadam Program version 8 1 22 JAN 2010 2 43 The sum of hydrodynamic forces acting on a panel model is reported in the print file for eac
158. or Vp this gives F m g a B 9 mpis the mass of the fluid in the tank Similarly the total moment M on the tank can be seen to be given by M xx F B 10 where xy 1s the position of the centroid of the tank This shows that the force and moment from the fluid is balanced by the gravity force on the fluid and the inertia force and moments of the fluid This is independent of the reference level of the pressure Provided an exact load integration and an exact centroid calculation the load balance will then be exact if the mass of the fluid is placed in the centroid of the tank in the mass model B3 5 Global drag coefficient for roll The quadratic roll damping coefficient may be found in model tests for given ship hull types independent of sea state For the actual sea state in which the ship is to be analysed stochastic linearization of the quad ratic damping may be performed The quadratic drag in the roll motion gives a contribution to the moment about the x axis on the form Zo ONE It Fy B14 Malna B 11 2 where Bay is the quadratic drag coefficient and n4 is the velocity in roll Substituting BI Inal with a linearized damping coefficient B Y the error random process due to linearization is 2 1 e t BH nan Bua na B 12 The requirement that the expectation value of the squared error has a minimum is SESAM Wadam Program version 8 1 22 JAN 2010 B 13 a BY Edd BG a where E is the ex
159. or other types of analyses This remark is equally important for the structural model Section 3 2 1 through Section 3 2 3 show typical steps in the wave analysis of a tension leg platform TLP type of structure and covers in principle all necessary analyses for calculation of first order wave loads on the TLP Section 3 2 4 and Section 3 2 5 cover typical wave load analysis for semi submersible platforms and ships An overview of the various analysis types discussed in this chapter is included below e Global response calculations for a TLP see Section 3 2 1 This analysis covers several aspects that are important for a TLP Rigid body motions are calculated for all six degrees of freedom These motions may be used to cal culate displacements velocities and accelerations for specified points in the structure Such calcula tions are performed with the statistical postprocessor Postresp Constant drift forces are calculated They may be used to find the maximum offset positions by exter nal programs SESAM Wadam Program version 8 1 22 JAN 2010 3 11 Sectional forces are calculated for four sections There is one vertical section in the centre of the plat form and one close to the columns The other horizontal sections are just above the pontoons and below the topsides The wave periods and headings that give maximum response in the structure are selected on basis of these forces It may however be difficult to select the w
160. or the Morison model Figure 2 8 shows a beam model and Figure 2 9 the corresponding Morison model representation with 2D Morison elements and pressure area elements The modelling principles for establishing different types of Morison elements are discussed in the following subsections Figure 2 8 2 node beam element model of a semi submersible platform SESAM Wadam Program version 8 1 22 JAN 2010 2 9 4 Pressure area element ML Morison element partitioned into 3 sub elements Figure 2 9 Morison model representation of a semi submersible platform with 2D Morison elements and pressure area elements 2D Morison Elements A 2D Morison element is most conveniently defined as a 2 node beam element in a preprocessor and assigned a section number to be matched by a hydro property section specified in HydroD or Prewad A 2D Morison element is used to include added mass and drag forces according to Morison s equation see Section 2 6 4 It is also used to include hydrostatic restoring contributions The hydro property description for a 2D Morison element include added mass and viscous drag coefficients in the two directions perpendicular to the longitudinal element axis The hydrodynamic coefficients are specified in a coordinate system local to each 2D Morison element see Figure 2 12 In addition the mass per unit length and the diameter of the element is specified The length and diameter may either be taken
161. orce due to the undisturbed incoming wave The force is applied in node N1 in the direction of the element normal i e from N1 to the guiding point The Froude Krylov pressure force represents a sim plified approximation to the correct pressure Therefore 3D Morison elements must be used to include the end effects of added mass and viscous damping The pressure area element has three main application areas These are e Include normal pressure at submerged ends of a cylinder see Figure 2 14 a e Adjust subtract the pressure at intersection between cylinders see Figure 2 14 b e Include longitudinal forces due to varying cylinder diameters see Figure 2 14 c l a b c Figure 2 14 Application areas for the pressure area element The use of pressure area elements in the dual and composite hydro model types requires some special atten tion This is described in more detail in Section 2 1 4 and Section 2 1 5 Dry Morison Elements A dry Morison element is defined as a 2 node beam element with no assigned hydro properties This is most conveniently achieved by defining a beam element in the preprocessor with a section number not matching any hydro property section number specified in HydroD or Prewad Wadam SESAM 2 14 22 JAN 2010 Program version 8 1 A dry Morison element may be used to transfer panel pressures directly to 2 node beam elements in a struc tural model by means of the dual model see Section 2 1 4 No calculatio
162. orst waves only on the basis of sectional forces The use of simplified structural analysis may also be a valuable help for selection of waves for a more detailed global analysis Wave kinematics is calculated for points around the columns These are used for calculation of the wave up welling around the columns and subsequent air gap calculations Potential theory is used for all the wave periods e Load transfer to a TLP shell structural model see Section 3 2 2 This analysis shows how the loads calculated in Wadam are transferred to a structural shell model The ultimate limit state ULS capacity of the hull is checked in a subsequent structural analysis All wave pe riods and headings selected in the global response calculation in Section 3 2 1 are combined with static load cases in the capacity check The transferred loads include hydrodynamic pressure loads inertia loads and tether reaction forces due to the rigid body motions Hydrostatic loads are not transferred e Load transfer to a TLP beam element model see Section 3 2 3 This is a typical fatigue analysis of the topsides where Wadam is used to calculate wave loads for many wave periods and headings Due to the large number of load cases from waves a simplified model of the hull is used for the structural analysis This model is calibrated against the shell structural model above The transferred loads include line loads from hydrodynamic pressures inertia loads and tether react
163. pectation operator Obviously EMA o B 14 Assuming n4 is normally distributed the half normal distribution for Inal gives B B 15 E nal E oe We where OF is the standard deviation of 4 Substituting the two expectation values above in the for 4 mula for Bo gives the well known relation for stochastic linearization of a quadratic drag term 2 8 B 16 44 o m m N8 pO pO an 2 826 B 44 is 44 N4 The equation of motion 1 Ne with the stochastically linearized roll drag included may be written 1 M my bim Bag dn cim X B 17 1 Here M is the sum of the body mass matrix and added mass matrix b is the potential damping and cj is the restoring X is the excitation force An initial estimate of n for all wave frequancies is made giving a corresponding estimate of the standard deviation and thereby B re Then an iteration proc ess is runon N until a reasonable agreement between the estimate of G from the previous and next 4 calculation of motion is obtained The motion will then be correct in the least square sense
164. r of a panel to be linked to the present element and sub element in the Morison model GROUP A group of panels to be linked to the present element and sub element in the Morison model ssnol First panel number in the group ssno2 Last panel number in the group ssinc Panel numbering step Note Only elements that are below the mean free surface can be included in the panel number list SESAM Program version 8 1 Wadam 22 JAN 2010 5 5 DEFINE ELEMENT 2D MORISON ELEMENT 3D MORISON ELEMENT ANCHOR ELEMENT DRY ELEMENT ELEMENT POINT MASS PRESSURE AREA ELEMENT TLP MOORING ELEMENT END elno nodel node2 GROUP elnol elno2 elinc nlell n2ell noinc END PURPOSE The command defines additional Morison elements Note Additional 2D Morison elements and dry elements should not be used when load transfer is specified PARAMETERS 2D MORISON ELEMENT 3D MORISON ELEMENT ANCHOR ELEMENT DRY ELEMENT POINT MASS PRESSURE AREA ELEMENT TLP MOORING ELEMENT elno nodel Define 2D Morison elements Define 3D Morison elements Define anchor elements Define dry Morison elements Define point masses Define pressure area elements Define TLP mooring elements for a tether system Element number of a single element Node number at one end of the element fairlead of anchor elements Wadam 5 6 node2 GROUP elnol elno2 elinc nlell n2ell noinc SESAM
165. racteristic length metres mass density of water kg m 3 accn due to gravity m sec 2 linearising velocity not relevant here z location of input coord system metres 3 dummy values 0 or gt 0 CONSTANTS 90 1025 9 81 0 40 0 O 0 Specify the execution directives computed tolerances analysis type global motion response calculation of drift forces model is a floating structure with 2 planes of symmetry YZ XZ and YES calculate eigenvalues for rigid body degrees of freedom for potential solution panel model use an iterative solution do not remove irregular frequencies from solution normal amount of output in print file store motions results on file and generate Loads interface file wher structural model is composite i e shell beam in Morison superelement and YES store hydrostatic loadcase as lst loadcase EXECUTION DIRECTIVES TOLERANCES COMPUTED TOLERANCES 1 0 1 0 0 1 0 1 END ANALYSIS TYPE STRUCTURAL LOADS HORISONTAL DRIFT YES FIXED FLOATING FLOATING YZ XZ PLANE YES POTENTIAL THEORY EQUATION SOLUTION ITERATION IRREGULAR FREQUENCY NO REMOVAL END PRINT SWITCH NORMAL RESULT FILES GLOBAL RESPONSE SIF STRUCTURAL LOADS COMPOSITE STR MODEL YES LOAD TRANSFER OPTION FILE FORMAT FORMATTED OFFSET IN LOAD CASE NUMBERS AUTO END END SESAM Wadam Program version 8 1 22 JAN 2010 3 9 oe HP AP AP AP AP AP AP AP AP JP AP AP AP AO AP AP AP
166. rad xzrad yzrad tmass NOTES Radius of gyration square root of the moment of inertia divid ed by total mass about an axis parallel with the input x axis and through the motion reference point Radius of gyration about an axis parallel with the input y axis and through the motion reference point Radius of gyration about an axis parallel with the input z axis and through the motion reference point The negative of the specific product of inertia The negative of the product of inertia divided by total mass about axis parallel with the input x and y axis and through the motion reference point Negative specific product of inertia about axis parallel with the input x and z axis and through the motion reference point Negative specific product of inertia about axis parallel with the input y and z axis and through the motion reference point Total mass of the body See also DEFINE GENERAL GLOBAL MATRIX for definition of user specified global mass matrices Wadam SESAM 5 18 22 JAN 2010 Program version 8 1 DEFINE GENERAL CONSTANTS CONSTANTS cleng rho grav amp zloc voll jarl vcb1 PURPOSE The command defines general constants used in the analysis PARAMETERS cleng Characteristic length for the hydrodynamic model rho Density of sea water in SI units 1025 kg m3 grav Constant of gravity in SJ units 9 81 m s2 amp Linearising velocity for the viscou
167. ransfer to a Model with Beam Elements cccccccscceseeeteeeteeeteeteees 2 30 Enviromental Descripti ns sisseoste irn ee e a a a a a a aeie 2 30 ZAA Surface Waves vstist shin one ane a E ET ARE aT E AE n a TE 2 30 242 7 Current Profle Senn a a a A EEEE Ea E 2 32 PA Ee TET E a De o1 EEA E E R E T 2 33 Results Types Reported from Wadam ccccccccesscessesssecseceeceeeeeecsaecaeeeecseeeeseeeseeeaeceaeeneseneesaees 2 33 AP AEE i St A A AAE T A ab uh ot A E EA AE 2 33 2 5 27 Result Reference Pointisnoninaon ei iae inane a a aE A O RAET 2 34 2 5 3 Dimensioning of Results cceccccccescessecseceeceeeceeeeeseeeseeeseceseceseeeseesaecseseeeseeeeeeeneesseees 2 34 2 5 4 Transfer Functions and Phase Definitions 0 cccccccccccesssssccsccesesssssceseesecssaeseecessessnaees 2 35 2 6 2 7 3 1 3 2 4 1 2 5 5 Hydrostatic Restoring Results ccccccccssccsseessceeeceeecseececeseeeseeeseceaeceeseeeeeseeaecnseeneeeaes 2 36 2 5 6 Global Mass MatriX scenerna ian A E A E E 2 37 23d Added Mass Matrix eieiei i e i E E E E E 2 38 25 8 Dapa M A a A a ls MEM a e an eis 2 38 2 5 9 Exciting Forces and Moments peresen esia en E E a AE EE E 2 38 25 10 Rigid Body Motions a eae aiadis es 2 39 2 5 11 Second Order Mean Drift Forces s eseseeessssesssssesesssstsessesessssesersstsrseseerestssesessesesesseses 2 39 2 5 12 Second Order Sum and Difference Frequency Results 00 0 cccecceseeceeeeeseeseeseeeseeeees 2 39 225
168. re the sub element number and sub element length correspondingly SESAM Wadam Program version 8 1 22 JAN 2010 5 63 DEFINE HYDRODYNAMIC PROPERTY SECTION ref POINT MASS POINT MASS dm PURPOSE The command defines hydrodynamic properties for point mass elements This will be additional to nodal masses on the Input Interface File PARAMETERS dm Mass of element Wadam SESAM 5 64 22 JAN 2010 Program version 8 1 DEFINE HYDRODYNAMIC PROPERTY SECTION ref PRESSURE AREA ELEMENT ALWAYS PRESSURE AREA ELEMENT dia x2 y2 z2 WAVE LENGTH DEPENDENT PURPOSE The command defines hydrodynamic properties for pressure area elements PARAMETERS ALWAYS Pressure area element always used WAVE LENGTH DEPENDENT Pressure area element is not used for dynamic loading when the wave length is less than or equal to the critical wave length dia Equivalent diameter x2 The x coordinate of the guiding point for the direction of the pressure force on the pressure area element in the input coordi nate system y2 The y coordinate of the guiding point Z2 The z coordinate of the guiding point SESAM Wadam Program version 8 1 22 JAN 2010 5 65 DEFINE HYDRODYNAMIC PROPERTY SECTION ref TLP MOORING ELEMENT TLP MOORING ELEMENT len pre stiff xoff yoff PURPOSE The command defines hydrodynamic properties for TLP mooring elements See Figure 2 16
169. reedom e Pressure integration in all six degrees of freedom This method will also give the mean drift forces on each individual body in a multi body analysis 2 5 12 Second Order Sum and Difference Frequency Results The transfer functions for sum and difference frequencies are reported in the print file and on the Hydrody namic Results Interface File The following second order results are available The quadratic second order force The second order forces on the body by an indirect calculation method The second order forces on the body by a direct calculation method The second order pressure distribution on the body only available in the print file e The second order wave elevation at specified points only available in the Wamit output file format 2 5 13 Fluid Kinematics The transfer functions for pressure and particle velocity in specified points in the fluid is reported both on the print file and in the Hydrodynamic Results Interface File The fluid kinematics points are specified in the fluid domain outside the hydro model The fluid kinematics depends on the type of hydro model Wadam SESAM 2 40 22 JAN 2010 Program version 8 1 e Itis obtained from the incident undisturbed wave field if only Morison s equation is applied Itis obtained from the diffracted wave field if the potential theory is applied to a fixed structure e It is obtained from the radiated and diffracted wave field if the potential theory
170. rees wave periods 8 10 12 secs with finite water depth Wadam SESAM 3 6 22 JAN 2010 Program version 8 1 ENVIRONMENT WATER DEPTH 100 WAVE DIRECTION 0 45 END WAVE PERIOD 8 FINITE 10 FINITE 12 FINITE END END END ole This file contains input data for Wadam 3 1 2 Motion Response of Floating Box Tethered to the Sea Bed This section describe the motion response analysis of a tethered box with transfer of loads to a shell finite element model of the same box The hydro model used in this example includes the panel model shown in Figure 3 1 and a Morison model consisting of the tether nodes only The Preframe input defining this Morison model is given in Appendix A 2 1 Today this would be done in Patran pre or Genie The structural model receiving pressure loads is assembled in Presel The structure is shown in Figure 3 5 The springs correspond to the tethers included in the hydro model The Prefem and Presel inputs for creating the structural model are given in Appendix A 2 2 and Appendix A 2 3 respectively The Prewad input for this analysis is presented below Note that compared with the commands for the freely floating box this Prewad input includes a structural model definition and transfer of loads to a composite model see Section 2 1 5 Tether element characteristics are also specified and connected to nodes in the Morison model If this input is found in a file with name Prewad_in jnl then start Prewad and
171. rent profile may be specified at a set of positions along the z axis of the global coordinate system Current values at intermediate z positions are obtained by linear interpolation The direction of the current in the horizontal plane is specified at each positions Figure 2 26 Current profile definition SESAM Wadam Program version 8 1 22 JAN 2010 2 33 2 4 3 Water Depth Wadam provides the option to specify a water depth The water depth is used in two different calculation phases in the program e Itis used in the processing of the panel model to remove all panels below the sea bed e Itis used in the calculation of Green s functions for finite water depth 2 5 Results Types Reported from Wadam 2 5 1 Units When performing an analysis with SESAM the user must apply a set of consistent units The same units must be used in all programs throughout the analysis from modelling to results presentation The basis for determining a set of consistent units is the fundamental equation f ma 2 9 In terms of the fundamental units of mass M length L and time T this equation may be written ML A 2 10 Force stress density etc are not fundamental units and must be derived in terms of the units of mass length and time Whenever possible it is simplest to use S I units L Length in meters m M Mass in kilograms kg T Time in seconds s Force will then be in Newton N kg m IN a 2 11 The
172. ring for a model assembled in a superelement hierarchy This example is a model consisting of a first level superelement superelement number 10 used in two dif ferent positions in a two level superelement hierarchy The top level superelement number is 100 Adopting the terms used above there are two occurrences of the same first level superelement in this hierarchy Figure 2 24 shows the superelement hierarchy 100 1 10 1 10 2 Figure 2 24 Two level superelement hierarchy with occurrence 1 and 2 of superelement 10 included in superelement 100 Table 2 3 shows the correspondence between the global and Wadam generated load case numbers The table also includes the superelement occurrence numbers a description of the separate load cases and the Presel generated superelement index numbers Table 2 3 Load case numbering for a model assembled in a superelement hierarchy Globalload Wadam load MEE Occurrence of Presel case number case number PRE SARS TRAC ODED superelement 10 index 1 l static l 1 l 2 static 2 2 2 3 B 0 0 0 1 1 2 4 B 0 0 0 2 2 3 5 6B 0 0 1 1 1 3 6 B 0 0 1 2 2 4 7 B 0 0 2 1 1 4 8 B 0 0 2 2 2 5 9 B 90 0 0 1 1 5 10 B 90 0 0 2 2 6 11 B 90 0 1 1 1 6 12 B 90 0 1 2 2 7 13 B 90 0 2 1 1 7 14 B 90 0 2 2 2 SESAM Wadam Program version 8 1 22 JAN
173. riods but the option specified for the first one will be used for all Infinite water depth approximation used for calculation of Green s functions Note If INFINITE is specified a large value at least larger than the longest wave length must be given for the WATER DEPTH This option is no longer supported and will be substituted by FINITE if used SESAM Wadam Program version 8 1 22 JAN 2010 5 9 WAVE SPECTRUM Specification of wave spectrum for each heading wave direc tion WAVE SPREA DING Specification of wave spreading USER DEFINED User definition is currently the only option for specifying wave spreading weights Weights given one by one for all wave directions The weights must add up to 1 If at least one value is 1 0 then long crested sea is assumed for all wave directions Note Roll damping iteration requires long crested sea so in this case at least on weight must be given as 1 0 Wadam SESAM 5 10 22 JAN 2010 Program version 8 1 DEFINE ENVIRONMENT FREQUENCY HEADING PAIRS FREQUENCY HEADING PAIRS SUM FREQUENCIES ALL COMBINATIONS DIFFERENCE FREQUENCIES SELECTED COMBINATIONS END PURPOSE The command defines pairs of frequencies and headings for the computation of second order sum and dif ference frequency forces PARAMETERS SUM FREQUENCIES Defining sum frequency combinations DIFFERENCE FREQUENCIES Defining difference frequency combinations ALL COMBIN
174. risa tion if combined with the command DEFINE ENVIRONMENT LINEARISING WAVE HEIGHT Case 2 Roll damping When used together with the command DEFINE GENERAL ROLL DAMPING MODEL the command is used to specify that the roll angle iteration is to be performed The maximum roll angle estimates thmd val ues on DEFINE GENERAL ROLL DAMPING MODEL MAXIMUM ROLL ANGLE are then used as start values in the iteration process If this command is not specified it is assumed that the input thmd values are used as estimates according to the traditional method hence no iteration will be performed PARAMETERS durhr trac When drag linearisation is applied to the roll damping model this parameter is the duration of the sea state in hours typically 3 It used to calculate the maximum roll angle from the standard deviation as the most probable largest value assuming a Rayleigh distribution When drag linearisation is applied to the Morison model this parameter is the convergence criterion for the translational modes rotc Convergence criterion for the roll mode in case of roll damping model and for all angular modes in case of Morison model It is given in percentage of the consecutive error Default 0 1 maxit Maximum number of iterations in the drag linearisation Default 10 maximum allowed 19 NOTES Since there is only room for one command of this type iterative drag linearisation and roll damping cannot be used in the same Wadam run SESA
175. rostatic loads with contributions from forces in the still water condition and pre tension from moor ing and tether systems e Gravity load representing the weight of the structure e Hydrodynamic loads with contributions from exciting forces from incident waves forces from wave induced motion and rigid body accelerations Detailed descriptions of distributed loads are included in Section 2 5 15 and Section 2 5 16 Wadam generates separate load case numbers for the hydrostatic load and for each of the hydrodynamic loads 1 e for each wave frequency and heading These loads may be combined into new load cases with Presel The new combined load cases will be used during subsequent structural analysis and postprocessing Section 2 1 11 contains a more detailed description of load case numbering and load case combinations in SESAM 2 3 3 Deterministic Loads Wadam also provides the option to report transfer functions for FE loads as deterministic loads time domain That is loads represented for specified phase angles of incident waves with given wave ampli tudes The deterministic results presentation may also be used together with the option to calculate the following types of loads e Non linear viscous drag forces from Morison s equation for fixed structures e Pressure loads up to the instantaneous free surface see Section 2 6 7 Time invariant current profiles added to the incident wave field in the calculation of forces by Moris
176. rs nlin are used for all wave directions PARAMETERS nlin tlin 1 tlin 2 tlin nlin hlin 1 hlin 2 hlin nlin Number of points on the T H curves for all wave directions Maximum 20 tlin is the linearising wave period hlin is the linearising wave height Wadam SESAM 5 12 22 JAN 2010 Program version 8 1 DEFINE ENVIRONMENT SURFACE MODEL SIF prefix topsel radius ntcl WAMIT filename SURFACE MODEL PURPOSE The command defines the surface model for the second order sum and difference frequency computation The free surface model shall have the same symmetry properties as the panel model PARAMETERS SIF The surface model is found on an Input Interface File prefix File prefix or directory where the file s are stored topsel Top superelement number of the surface model radius Dimensional radius of the partition circle given in the same units as the model length unit ntcl The total number of segments panels on the partition circle Note The radius and ntcl parameters are dummy in the case of Wave Drift Damping WAMIT The surface model is represented on the WAMIT free surface format described below filename The name of the WAMIT free surface file without the mandatory extension FDF NOTES The WAMIT free surface format is defined as follows header PARTR NPF NTCL NAL DELR NCIRE NGSP VERX 1 1 VERX 2 1 VERX 3 1 VERX 4 1 VE
177. rt Vp P S a 2 34 where gyis the fluctuating part of gravity A detailed outlining of the tank pressure calculation is included in Appendix B 3 4 The tanks are modelled by assigning the HY DRO PRESSURE load to those surfaces which are the walls of the tanks The number of the HYDRO PRESSURE load will be the number of the tank This numbering must start at 2 since the HY DRO PRESSURE with load case 1 is the external pressure All surfaces with the same HYDRO PRESSURE number will be assumed by Wadam to be the same tank The filling of the tanks is controlled by assigning the hydro pressure load only to the wet part of the tank walls No sloshing effects are included 1 e the fluid is assumed to move like a rigid body Note The mass of the tank fluid must be included in the mass model for Wadam In the structural FE model the inertia forces from the tank fluid are represented as pressure loads and should therefore not be included in the structural mass 2 6 7 Pressure Loads up to Free Surface Wadam may be used to extrapolate to the free surface the panel pressures calculated by first order potential theory up to the still water level Note that this implies that the dry finite elements below the still water level will receive no loads when the free surface is below the still water level as shown in Figure 2 29 A constant extrapolation also called stretching of pressures above the still water level is applied This pres sure ex
178. s 320 8 occurrences each with 40 load cases The loading on the elements and nodes in the structural model is written to Loads Interface Files used in the structural analysis One file containing all local wave load cases is written for each first level superelement In addition an S file is created containing input to Sestra about wave periods headings and load cases This file S301 FEM must be located in the same physical directory as the Input Interface Files when the struc tural analysis is performed The S file is mandatory for the structural analysis only if information about wave periods and headings is used in the postprocessing and could be omitted for this analysis e L100 FEM Tether reaction forces due to rigid body motions for superelement 100 Morison model e L111 FEM Pressure loads and nodal accelerations for superelement 111 Pontoon Wadam SESAM 3 20 22 JAN 2010 Program version 8 1 e L112 FEM Pressure loads and nodal accelerations for superelement 112 Intersection area e L113 FEM Pressure loads and nodal accelerations for superelement 113 Lower part of the column e L114 FEM Pressure loads and nodal accelerations for superelement 114 Middle part of the column e L12 FEM Nodal accelerations for all other first level superelements e 301 FEM Input file for subsequent Sestra analysis Check of Results In addition to the checkpoints mentioned in Section 3 2 1 the following points sho
179. s capabilities in Wadam comprise Calculation of hydrostatic data and inertia properties Calculation of global responses including First and second order wave exciting forces and moments Hydrodynamic added mass and damping First and second order rigid body motions Sectional forces and moments Steady drift forces and moments Wave drift damping coefficients Internal tank pressures Calculation of selected global responses of a multi body system Automatic load transfer to a finite element model for subsequent structural analysis including Inertia loads Line loads for structural beam element analysis Pressure loads for structural shell solid element analysis Pressure loads up to the free surface Wadam calculates loads using Wadam SESAM 1 2 22 JAN 2010 Program version 8 1 e Morison s equation for slender structures e First and second order 3D potential theory for large volume structures e Morison s equation and potential theory when the structure comprises of both slender and large volume parts The forces at the slender part may optionally be calculated using the diffracted wave kinematics calculated from the presence of the large volume part of the structure The Wadam results may be presented directly as complex transfer functions or converted to time domain results for a specified sequence of phase angles of the incident wave For fixed structures Morison s equa tion may
180. s drag This should be a representative relative velocity be tween the structure and the fluid zloc The z coordinate of the origin of the input coordinate system zloc is negative if the origin of the input coordinate system is below still water level voll Not used A dummy value must be given arl Not used A dummy value must be given vcb1 Not used A dummy value must be given SESAM Wadam Program version 8 1 22 JAN 2010 5 19 DEFINE GENERAL EXECUTION DIRECTIVES ANALYSIS TYPE DETERMINISTIC MORISON DRAG LINEARISATION DRIFT FORCES FIXED FLOATING HORISONTAL DRIFT MORISON EQUATION OUTPUT FORMAT POTENTIAL THEORY PRINT SWITCH RESULI FILES SAVE RESTART SECOND ORDER RESULTS TOLERANCES WAVE DRIFT DAMPING END EXECUTION DIRECTIVES PURPOSE The command defines control parameters for execution of Wadam Wadam SESAM 5 20 22 JAN 2010 Program version 8 1 DEFINE GENERAL EXECUTION DIRECTIVES ANALYSIS TYPE DATACHECK ANALYSIS TYPE GLOBAL RESPONSE STRUCTURAL LOADS PURPOSE The command defines the calculation type PARAMETERS DATACHECK Only data check and hydrostatic calculation will be performed GLOBAL RESPONSE Global response calculation will be performed STRUCTURAL LOADS Global response and detailed load calculation will be per formed SESAM Wadam Program version 8 1 22 JAN 2010 5 21 DEFINE GENERAL EXECUTION DIR
181. s for a subset of the frequencies and heading angles stored on the file If the model is changed the save restart database Wadam RSQ must be deleted Otherwise Wadam will not run Notice however that when Wadam is executed from HydroD this application allows for management of multiple restart databases SESAM Wadam Program version 8 1 22 JAN 2010 3 1 3 USER S GUIDE TO WADAM This chapter describes how to use Wadam to analyse typical hydrodynamic problems involving fixed float ing and tethered structures Simple tutorial examples as well as more real life engineering problems are pre sented Some practical modelling guidance is also provided The examples cover the most common Wadam applications They do not cover all program features or all ways in which the program may be used Section 3 1 describes the following two simple examples e Motion response analysis of a floating box e Motion response analysis of a tethered floating box with transfer of loads to a shell finite element model of the box For the simple examples of Section 3 1 descriptions are given together with the appropriate input commands for Prewad The preprocessor inputs required for establishing the models are included in Appendix A Section 3 2 describes three engineering application examples e Motion response analysis of a TLP with transfer of loads to a shell finite element model of the TLP hull and deck e Motion response analysis of a semi submersible
182. s including the balance between buoyancy and weight of the hydro model Execution errors due to malfunctioning of a program procedure will result in a short message and a trace back of all the calling procedures Wadam SESAM 4 8 22 JAN 2010 Program version 8 1 SESAM Wadam Program version 8 1 22 JAN 2010 5 1 5 PREWAD COMMAND DESCRIPTION The Wadam analysis is controlled by the analysis control data file WADAMn FEM see Section 4 1 This fixed format file is created by the interactive program Prewad or by HydroD This chapter describes the Pre wad commands The hierarchical structure of the commands and numerical data is documented by use of tables How to interpret these tables is explained below Examples are used to illustrate how the command structure may diverge into multiple choices and converge to a single choice In the example below command A is followed by either of the commands B and C Thereafter command D is given Legal alternatives are therefore A B D and A C D B A D C In the example below the three dots in the left most column indicate that the command sequence is a contin uation of a preceding command sequence A block with any number of rows in this case two concluded by the command END signifies that the rows may be repeated any number of times The sequence is concluded by END Legal alternatives are for example A B C D E END and A D E B C B C END The three dots in the right most column
183. s model The latter is only required if the system is specified to be floating Additional mooring and tether stiffness char acteristics may also be provided for floating systems The hydro model may consist of either a panel model a Morison model built from beam elements or a com bination of these two model types The hydro model represents different types of hydrostatic and hydrody namic loads The hydro model concept is described in detail in Section 2 1 A mass model is required when the global response analysis includes calculation of motions A mass model may either be defined as a FE model where the mass of each finite element contributes to a 6 by 6 body mass matrix also termed the global mass matrix Alternatively the mass model may be specified directly as an input global mass matrix The mass model is described in more detail in Section 2 1 8 2 2 2 Computation of Wave Loads Wadam calculates wave induced forces for a specified set of wave frequencies and heading angles by one of the following three calculation methods e Morison s equation applied to a Morison model e The MacCamy Fuchs formula applied to a Morison model e The potential theory applied to a panel model e A method in which Morison s equation and the potential theory both are applied to compute hydrody namic loads on the same hydro model This calculation method restricts the hydro model to be built from either Wadam SESAM 2 28 22 JAN 2010 Program vers
184. se ee ge LOAD DISTRIBUTION ON THE MORISON MODEL 2222 PRESSURE DISTRIBUTION ON THE PANEL MODEL OFFBODY CALCULATIONS INCLUDING FLUID PRESSU RE AT SPE CLET ED POT NES esses evan d a E Pee oceuie te FLUID VELOCI TLES AT SPECT ELED POINTS ane ace ca Stereos 9 sip ete SECTIONAL LOADS ON TH SECTIONAL LOADS ON TH 8b SECTIONAL LOADS ON TH kaj PANE EMODE Trinen nei 1d ahane aa E e EE EEUE aE ORISON MODE Dis scsi ote EAE E oe E E EA E E A COMPOSITE MODE Dana eana a EAEn E EEAS ti m GLOBAT SECOND ORDER FORCES 66 moea e me e e eie ticle EE a ae E ee ES 10 SECOND ORDER PANEL PRESSURE DISTRIBUTION sssesesoses T TRANSFER OF RESULTS FOR FURTHER ANALYSIS AND PRESENTATION 5 1 GENERATION OF LOADS INTERFACE FILES INCLUDING INPUT ITNTETEREACE EILE Soo gine E R E EAE le velo ladles E E E eee SUBELEMENT LOADS TRANSFERRED TO LOADS INTERFACE FILES LOADGASE OVERVIEW ee neede i ao lace Sire Oh he eei e GG ale BS lee oe E elev 3 le MATCHING INFORMATION FOR LOADS TO A SHELL SOLID MODEL SUM OF LOADS WRITTEN TO THE LOADS INTERFACE FILE SUM OF CALCULATED LOADS ON THE PANEL MODEL
185. seonessaidecees 4 1 Programe EnVviTOMMe nt 53 ys schse cove tescevzsh vas tsoe sede cdeks beatae cased be athens Ma Gade A hoes aaaE As 4 4 1 1 Starting Prewad from Manager ccccsscsssessceescesceeseecseceseceseeeeeeeseesaecaecesesereeeseeaeessees 4 3 4 1 2 Reading a Command Input File into Prewad and Running Wadam eceeceeeeseeeeees 4 3 AMS lt The dinputsEilesie css dteseceese take dees suetece reaver tedcdettsdcectaca ccsessadiecal ae ERr 4 4 4 2 4 3 4 4 ANA Output Filesi n e r a ec Make nee ee a a RAO a ia a ree eben oats 4 5 AAS The Save Restat File secs cose tisde chess nia E E alee T AE E 4 5 Program Requirements ccccccscccssessecsecssceeeceeeeeseeesseeseceseseneeesecaaeceaeseeeeeeeesaecsaeceseeeseaeeeseeneeseeags 4 6 Program Limitations ie raene eeri neea oaee a e ai Eei EEr a ia dates EE eee 4 6 Warnings and Error Messages ccccssesssesseceseceseeeseeeseesaecseceeeseeeeseecssenseceseeeseesaecsaecneeseeesesectenseenes 4 6 PREWAD COMMAND DESCRIPTION cssssscsssssccssssscccsssssccscsssescscssssscesesseees 5 1 CHANGE nirestart 5 2 DEINE EEEE ER EE ade EEA EA Sedat E TES 5 3 DEFINE CORRESPONDANCE ccceceesceseesessseseeeseesesececeeseeseeseceeceaecaeeaceeeeaecaecaaeeaeeaeeaeeeeenaeeaeeas 5 4 DEFINE ELEMEN Tren n esa a a a a E e a E E 5 5 DEFINE ENVIRONMENT o n an a a a a a a e e ee E re 5 7 DEFINE ENVIRONMENT FREQUENCY HEADING PAIRS ceeccccceesseeeees
186. so used to adjust panels extending below the sea bed Panel vertex a Original panel 175 Adjusted and 7 divided panel a b c Figure 2 6 Panel adjustments at the still water level The Wadam data check reports all the panels extracted from the input panel model noting specifically those panels which have been adjusted or divided into two separate panels The modelling of a panel model with thick shell elements which often is the case when the panel model is defined as the wet surface of a structural model may introduce significant deviations in the representation of volume and area exposed to wave forces It may be required to establish a separate panel model with nodes on the outer surface of the thick shell structural model SESAM Wadam Program version 8 1 22 JAN 2010 2 7 TE VAAL Figure 2 7 The basic part of a TLP panel model 2 1 3 The Morison Model The Morison model is used to calculate hydrodynamic loads based on Morison s equation In addition to representing the complete or parts of the structure the Morison model is used to include external forces from mooring lines and tethers in a hydro model Furthermore if hydrodynamic loads from potential theory i e pressure loads calculated on panels shall be transferred to a beam structural model then the Morison model is used as an intermediate step to define correspondence between panels
187. son model The loads are transferred to the beam elements and nodes which are con nected to Morison elements in HydroD or Prewad see Section 2 3 5 Note that both hydrostatic and hydrodynamic load contributions on free ends of beam elements require the element ends to be closed with Morison pressure area elements as described in Section 2 1 3 Note also that additional 2D Morison elements defined in HydroD or Prewad do not correspond to beam elements in the structural model and hence cannot contribute to the structural loads The additional Morison elements should be used with care They are a source to imbalances between the loads calculated in a global response analysis and the element and nodal forces transferred to a structural model Loads on Superelements with Shell and Solid Elements For shell and solid elements loads are transferred to the finite element sides which are identified as wet The so called HYDRO PRESSURE load option in Prefem or Hydro Element uniform load in Patran Pre is used to identify the wet element sides The definition of wet sides of the structural model is equivalent to the definition of panels in the panel model see Section 2 1 2 Wet element sides may be included in several superelements of a structural model Wadam transfers pressure loads to both the external wet surface of a structural model and to the wet surfaces of internal tanks The dummy load case number of the HY DRO PRESSURE load must be used to identif
188. structural model e Tether reaction loads The rigid body tether reaction forces are calculated on the Morison model This means that the reactions forces are written to the nodes specified in Prewad All wave induced loads are written to the structural model The line loads are written to the Morison model The Morison model is now a part of the structural model defined in Presel and the load transfer is defined through the following commands in Prewad DEFINE GENERAL EXECUTION DIRECTIVES mass stalo STRUCTURAL LOADS BEAM STR MODEL YES NO NO END END END oP w Ho Q w Q Q DEFINE GENERAL ANALYSIS MODELS STRUCTURAL MODEL 302 END END END The transfer of pressure loads from the panel model to the Morison model is not automatic Correspondence between panel model and Morison model must be defined through the following command in Prewad DEFINE CORRESPOND lno selno seltyp index ssnol ssno2 ssinc 114 1 99 1 GROUP 713 897 8 END 115 1 99 1 GROUP 714 898 8 END END END Pressure loads on the panel model are summed up and applied as line loads on the corresponding elements in the Morison model i e no moments are transferred It is thus important to specify load transfer to the cor rect elements in the Morison model Inertia loads are included as rigid body accelerations Wadam SESAM 3 24 22 JAN 2010 Program version 8 1
189. sums for the wave loads in the structural analysis The sum of loads printed in the Wadam listing contains pressure loads on wet elements only Inertia forces are not included and thus the total load sums cannot be checked The total load sums must therefore be checked in the structural analysis Since all loads are transferred from Wadam including the tether re storing loads the load sums for wave load cases should be close to zero in the structural analysis Large forces in the load sums indicate errors either in the load transfer or in the load combinations in Presel 3 2 3 TLP Load Transfer to Beam Element Model Load transfer to a structural beam model for the TLP shown in Figure 3 7 is performed The transferred loads are used in a subsequent structural analysis where fatigue damage is calculated for parts of the topside structure The beam element model is used to reduce CPU consumption and disk requirements The panel model is the same as in the previous examples Reference is made to Section 2 1 2 for description of the panel model and to Section 2 1 3 for a description of the additional elements The following calculations are performed in Wadam for this analysis The first two tasks are automatically calculated while the others are specified for this analysis SESAM Wadam Program version 8 1 22 JAN 2010 3 21 e Hydrostatic calculation in which both the hydrostatic and inertial properties for the structure are calcu lated e
190. tained from Software Support Software Support dnv com Alternatively you may use the program Status for looking up information in the Status List In Manager click E Then give File Read Status List and select Wadam In the Status List Browser window narrow the number of entries listed e Entries relevant to a specific version only e Entries of a specific type e g Reasons for Update e Entries containing a given text string Click the appropriate entry and read the information in a Print window 1 6 Wadam Extensions Wadam has the following extensions which require separate passwords 2ORD Calculation of second order sum and difference frequency transfer functions for bodies in monochromatic and bi chromatic incident waves NBOD Calculation of first order hydrodynamic analysis of multiple bodies Wadam SESAM 1 6 22 JAN 2010 Program version 8 1 STRU Transfer of hydrodynamic loads to structural finite element models with beam shell and sol id elements WDD Computation of Wave Drift damping coefficients SESAM Wadam Program version 8 1 22 JAN 2010 2 1 2 FEATURES OF WADAM This chapter describes the features of the Wadam program The chapter is organised with Section 2 1 describing the modelling concepts adopted in Wadam Thereafter Section 2 2 and Section 2 2 describe the two main analysis capabilities e Global response analysis for calculating rigid body type of results e Detailed load calculation for transfers
191. te model Figure 2 20 shows a composite model where the risers modelled with 2D Morison elements may optionally be exposed to loads from a diffracted wave field caused by the shaft of the large volume structure With a composite model the pressure area element shall normally be included in the Morison model for all wave lengths SESAM Wadam Program version 8 1 22 JAN 2010 2 19 Panel model Figure 2 20 Example of a composite model with a panel model and a non overlapping Morison model 2 1 6 Single Super element Composite model From version 8 1 09 of Wadam the beams receiving loads from the Morison model and the shells or solids receiving loads from the panel model may be modelled in the same 1 level super element The panel model may then be defined separately whereas the Morison model is the same super element as the structural model It is also possible to have the panel model the Morison model and the structural model all in the same super element 2 1 7 Multi Body Modelling The hydrodynamic and mechanical interaction between a number of structures can be analysed with the multi body option The hydrodynamic interaction is computed from the potential theory as applied for a sin gle structure with the principal extension that the number of degrees of freedom is increased from 6 to 6N where N is the number of structures A stiffness coupling between structures cannot be described directly in Wadam Each of the bodies may b
192. ted in Figure 3 4 SESAM Program version 8 1 22 JAN 2010 Wadam 3 3 4 Wadam Wizard Settings wizard Wadamwizardt Information Settings Time domain Frequency domain 92 T Roll damping 92 I Stochastic roll damping 92 J Load crossections T Load transfer I Tank pressure I Pressure panels J Offbody points J Second order results T Damping matrix JT Critical damping matrix 9 Ge 92 Re 92 92 Ge ee ee 3 Mar 2004 09 08 loating box KON ANAL AL ge ea a AEN LT T VIE TN PERRI re ALAR AR AR ARATAT Y x Figure 3 3 Display of HYDRO PRESSURE load in HydroD Wadam SESAM 3 4 22 JAN 2010 Program version 8 1 Model Check here to create Wadam analysis control data Figure 3 4 Starting Prewad and Wadam from SESAM Manager ae ol Define general information about the model ole DEFINE GENERAL ol ole Specify the analysis models to be used for mass model Global Mass Matrix panel model Superelement 1 Morison model Not needed in this example ae ol For the user specified global mass matrix give coordinates of c g in input coord syst radii of gyration about global x y z axes products of inertia about global x y z axes total mass of box ANALYSIS MODELS MASS MODEL GLOBAL MASS MATRIX USER SPECIFIED 0 0 29 38 33 04 32 09 32 92 0 0 0 332 1E06 AP oP oe SINK SOURCE 1 END ole SESAM Wadam Program
193. the print file Set the NAME of the print file print name Do not include the extension The full name of the print file will be print name LIS Alternatively direct the print to an on line printer LINE PRINTER Set the format of numbers in the print The letter refer to FOR TRAN E F and G formats F is the default format Set the page size of the print to FILE or SCREEN in terms of number of lines Wadam SESAM 5 80 22 JAN 2010 Program version 8 1 WRITE WRITE prefix number PURPOSE The command writes a new Wadam analysis control data file with a user defined dataset number This inte ger number need not be the same as the current dataset number The file will be named prefixWADAMdata set number FEM where dataset number is the dataset number an integer Note Subject to proper setting when starting Prewad from Manager the Wadam analysis control data is automatically written PARAMETERS prefix File name prefix number Dataset number of the Wadam analysis control data file SESAM Wadam Program version 8 1 22 JAN 2010 5 81 ncomnd ALL PURPOSE The command reads commands from the command input file The command input file is opened by the command SET COMMAND INPUT FILE The command input file can either be a log file from a previous run or a file prepared by a text editor The program will execute commands until either an end of file is detected a Z
194. the deck consisting of four columns two transverse braces and four diagonal braces The upper part of the structure consists of an upper and a lower deck and a derrick in the middle of the upper deck The geometry of the semi submersible is shown in Figure 3 14 A symmetrical mooring system is used with mooring lines connected at the fairlead and windlass of the platform Figure 3 14 Geometry of the semi submersible Panel Model The basic part of the panel model for the semi submersible is modelled as two first level superelements in Prefem and combined into a second level assembly in Presel The superelements and the assembly are shown in Figure 3 15 Since the semi submersible is double symmetric only one quarter of the panel model is modelled The remaining parts of the model are generated in Wadam by reflection mirroring of the basic part Wadam SESAM 3 26 22 JAN 2010 Program version 8 1 Figure 3 15 Quarter of a double symmetric panel model for the semi submersible The element sizes for this model may seem very large at first glance However no waves with periods below six seconds are assumed to give dimensioning stresses Hence only higher periods are included in the analysis Thus the element size is acceptable for this analysis The mesh density of the structure is of major importance for the hydrodynamic loads It is important that the mesh density reflects the hydrodynamic pressure variation around the structure In ar
195. the load computed by integration over the nega tive side will be equal in magnitude but have a phase difference of 180 degrees As an example we consider a ship cut at x 0 normal to the x axis If integration over the positive side is specified the sectional load will be the force acting on the part of the hull with x lt 0 from the part with x gt 0 This means that the static bouyancy force will give a positive vertical shear force and a negative vertical bending moment We will also find that the phase angle of the vertical bending moment in a hogging situation is close to zero for long waves If integration over the negative side is specified the static bouyance force will give a positive vertical shear force and a positive vertical bending moment The phase angle for the vertical bending moment in a long wave will be close to 180 degrees The contributions to the sectional loads from different hydro models are computed as follows Wadam SESAM 2 44 22 JAN 2010 Program version 8 1 e For Morison models the exciting and inertia forces obtained at the centre of gravity of each Morison sub element on the specified side of the sectional plane are included e For panel models the exciting forces at the centroid of each panel are included The inertia forces are included with respect to a centre of gravity calculated for the part of the model that is on the specified side of the sectional plane For panel models the sectional loads from i
196. the mass data SESAM Program version 8 1 Wadam 22 JAN 2010 5 41 All matrices are to be given in the Body Coordinate system see Section 2 1 7 For single body computa tions the Body Coordinate system is identical to the Global system PARAMETERS CRITICAL DAMPING MATRIX delem frac DAMPING MATRIX MASS MATRIX RESTORING MATRIX INDEPENDENT wavlen elem damp rest ibody jbody mass USE OF INPUT MAT ADD OVERWRITE Information related to generation of damping matrices based on critical damping will be given Diagonal element for which the fraction of critical damping will be specified 11 66 only the diagonal entries may be given Fraction of critical damping of the degree of freedom in ques tion Default values are zero A damping matrix frequency wave length dependent or not will be given One mass matrix for each body may be specified A restoring matrix will be given A frequency independent matrix is specified Wave length period frequency for which a frequency depend ent matrix will be specified The wave length period frequency must be specified by the DEFINE ENVIRONMENT command beforehand Selected element in the 6x6 matrix This element number must be given as 11 12 13 16 21 66 Actual damping value for given element Actual restoring value for given element Body identification of body number i Body identification of body number j Actual mass for b
197. ting Prewad from Manager Prewad is started from Manager by Model Hydro Modelling Prewad The Prewad window opens up in which the interactive commands may be clicked in the column at the right or typed in the area at the bottom Commands may be abbreviated as long as they are unique The most practical way of using Prewad is often to edit a previously created Prewad input file and use this as a command input file This is described in Section 4 1 2 4 1 2 Reading a Command Input File into Prewad and Running Wadam In the Hydro Modelling window opening up when giving Model Hydro Modelling Prewad in Manager there is a box for specifying a Command input file see Figure 4 3 By default this is set to None Changing this to File name a new box appears in which you may specify a Command input file that will be automati cally read into Prewad once the program is started by clicking OK If the box Run interactively after command input file processing is checked Prewad will after processing the input await interactive user input You may then add more Prewad commands Use the EXIT command to leave Prewad If your Command input file contains all input required there is no need to check this box Check the box Write dataset on exit if you want Prewad to create the Wadam analysis control data file This is normally what you want to do The Dataset number may be used to distinguish separate Wadam runs If you only intend to perform a single Wadam analysis l
198. tion 4 1 4 Hydro model Hydrodynamic model A model used for calculating hydrody namic loads from potential theory and Morison s equation See Section 2 1 Hydro property Hydrodynamic properties including added mass drag coeffi cients element diameters and anchor characteristics required for calculating hydrodynamic loads Input Interface File A file containing geometrical information of the structure FE model plus hydro model This file is termed T file for short See Section 4 1 3 SESAM Wadam Program version 8 1 22 JAN 2010 1 5 Loads Interface File A file containing loads for a subsequent structural analysis This file is termed L file for short See Section 4 1 4 Prewad Wadam s interactive preprocessor RSQ File Wadam s save restart file named WADAM RSQ see Section 2 7 and Section 4 1 5 S file A file containing information on the relation between load cas es and wave frequencies See Section 2 3 swl Abbreviation for still water level 1 5 Status List There exists for Wadam as for all other SESAM programs a Status List providing additional information This may be e Reasons for update new version e New features e Errors found and corrected Etc The most recently updated status lists can be accessed over the internet Go to www dnv com software and select the Support tab Then click on the SESAM Status lists entry A user name and password is required to access this site These can be ob
199. tion directives for Wadam Wadam 5 15 SESAM 22 JAN 2010 Program version 8 1 DEFINE GENERAL ANALYSIS MODELS MASS MODEL DISTRIBUTED MASS GENERATE topsel GLOBAL MASS MATRIX USER SPECIFIED ANALYSIS MODELS MORISON MODEL topsel SINK SOURCE MODEL topsel STRUCTURAL MODEL topsel END xg yg zg xrad yrad zrad xyrad xzrad yzrad tmass PURPOSE The command defines the various analysis models PARAMETERS MASS MODEL MORISON MODEL SINK SOURCE MODEL STRUCTURAL MODEL topsel DISTRIBUTED MASS GLOBAL MASS MATRIX GENERATE USER SPECIFIED xg yg zg To specify the mass input information To specify the Morison model to be used To specify the panel model to be used To specify the structural model to be used Top superelement number A distributed mass formulation will be used The mass distribu tion is defined by the Morison model A global mass formulation will be used The global mass matrix will be generated by Wadam from the mass model The global mass matrix will be specified directly by the user The x coordinate of the centre of gravity in the input coordinate system The y coordinate of the centre of gravity in the input coordinate system The z coordinate of the centre of gravity in the input coordinate system SESAM Wadam 22 JAN 2010 5 17 Program version 8 1 xrad yrad zrad xy
200. trapolation option depends on the amplitudes of the waves and hence this option is only available when results in the time output format is specified Note that the pressures only will be received by the finite elements above the still water level defined as wet in the structural model For a panel model this option is available for both fixed and floating structures but the intersection of the structure and the free surface must be vertical If a Morison model is included the option is only available for fixed structures SESAM Wadam Program version 8 1 22 JAN 2010 2 51 elements with extrapolated swl pressure instantaneous dry elements Figure 2 29 Constant extrapolation of panel pressures to the free surface 2 6 8 Reduced pressure up to the free surface One of the stretching methods is the approach referred to as reduced loads This is a kind of mean stretching applied in frequency domain In this procedure the loads are multiplied with a linearly attenuated reduction factor in a zone between some given distance below and above the still water level Below the still water level the reduction factor is applied directly Above the still water level the reduction factor is applied to the loads extrapolated from just below ideally at the still water level The loads are attenuated linearly down to zero as the level increases from still water level and up to a given
201. trices are accumulated into the global restoring matrix for the rigid body equation of motion Since the K matrices are established directly in the motion reference coordinate system no transformations are needed in the accumulation process SESAM Wadam Program version 8 1 22 JAN 2010 B 3 The non zero terms in the matrix K are defined as follows 2 S cos a ka S cosa sina z2 ky S sin a k33 S Kay kz kzz Ks k z kz x Key kax kyy Kay kY kz Ksy ky 12 k33X Key kax kay k43 k3yy kz k3 kZ k33x ke3 k3ax kay ky kyy kyz Pz P y ks4 kiaz kax P y gt kas kiz kax Pyz ke4 kax kay Pyz gt k4s kx kyy Px kss ks z ksx Px Pz Kos ksx kay Pyz gt kse ksx kyy Py kes kex key Pyy Pix where Wadam SESAM B 4 22 JAN 2010 Program version 8 1 Sh is the horizontal spring constant Sy is the vertical spring constant ay is defined in Figure B 1 x y Z are the coordinates of the fairlead relative to the motion reference point Py is the x component of the pre tension Py is the y component of the pre tension P is the z component of the pre tension The matrix is symmetric k k except for the terms ksq ke4 and kgs Having solved the equation of motion x represents the global motion of the rigid body system The force vector f for each fairlead node described in the result refer
202. uctuating part of gravity The mid point is taken as the centroid of the extreme coordinates of the tank For a cubic tank the extreme coordinates are the comers of the tank If the tank is spherical the extreme coordinates will be the corners in a cube circumscribing the sphere In both these cases the centroid of the corner points will coincide with the centroid of the tank but generally for arbitrary geometrical shapes it is an approximation The oscillating contribution to the total pressure is represented as a complex load case The zero level for the pressure is the extreme point of the tank where the real part of the total pressure has its minimum value This is actually approximately correct only for the phase equal to zero and can be a quite crude approxima Wadam SESAM B 12 22 JAN 2010 Program version 8 1 tion for other phases If the pressure loads are applied for other phases the user should therefore find the minimum pressure value and subtract this from all the pressure loads on the tank for the given phase That way a correct reference level zero level for the pressure will be obtained The pressure loads should preserve load balance The total force from the fluid on the tank is given by F J pads B 7 where n is the unit normal vector pointing out of the tank and S is the surface inside the tank By Gauss the orem we then have F Vpdv i B8 where V is the space inside the tank filled with fluid Substituting f
203. uctures These large roll motions increase the viscous damping significantly The non linear damping contributions are therefore included in a linearised manner in Wadam see Section 2 5 19 The non linear behaviour of the roll restoring is also linearised and included in the model Reference is made to Appendix B 3 1 for further description The following non linear contributions are included in the model e Viscous damping from skin friction and eddy making for the naked hull This part of the viscous damping is included for all sections of the ship model as follows DEFINE GENERAL ROLL DAMPING MODEL nos xoff xbow STRIP MODEL 25 113 412 112 112 FP TO AP bst bilgr sect 2 6 0 0 BOW SECTION 12 0 1 8 MID SECTION repeated for all 25 sections 526 02 0 STERN SECTION END END END e Viscous damping and eddy making from the bilge keel The effect of the bilge keel is included in the following way DEFINE GENERAL ROLL DAMPING MODEL xfr bilgl bilgb BILGE KEEL 29 862 62 4 0 38 y Z phi 19 85 13 67 0 0 SESAM Wadam Program version 8 1 22 JAN 2010 3 31 repeated for all sections with bilge keel END END END e Roll restoring from the GZ curve The roll restoring coefficient is modified on basis of the given GZ curve as shown below DEFINE GENERAL ROLL DAMPING MODEL o 5 GZ CURVE 5 hang gz 0 0 0 0 SO 0
204. ues for rig id body degrees of freedom shall be computed or not XZ PLANE The panel model has the xz plane as its symmetry plane YZ PLANE The panel model has the yz plane as its symmetry plane YZ XZ PLANE The panel model has both the yz plane and xz plane as symmetry planes NONE The panel model has no planes of symmetry NOTE No panel may have more than two nodes in the free surface or at the sea bed In addition no panel must have more than one node in a plane of symmetry SESAM Wadam Program version 8 1 22 JAN 2010 5 25 DEFINE GENERAL EXECUTION DIRECTIVES HORISONTAL DRIFT YES NO HORISONTAL DRIFT PURPOSE The command defines whether second order mean horizontal drift forces shall be calculated or not This computation give the surge and sway force and yaw moment The forces are computed by far field integra tion hence in a multi body case this will only give the total drift force on all bodies If drift forces on indi vidual bodies in a multi body problem is wanted the similar command DRIFT FORCES must be given PARAMETERS YES Second order mean horizontal drift forces will be calculated NO Second order mean horizontal drift forces will not be calculated Wadam SESAM 5 26 22 JAN 2010 Program version 8 1 DEFINE GENERAL EXECUTION DIRECTIVES MORISON EQUATION MORISON EQUATION PURPOSE This command is currently not in use SESAM Program version 8 1 Wadam 2
205. ulation of all wave loads A Morison model is used to include the tether reaction loads transferred to the structural model Structural Model The underwater part of the structural model is shown in Figure 3 10 The geometry assembly for the entire structural model is shown in Figure 3 11 ST A At LLA A L I a ea SS PT ZZ IIE Figure 3 10 The sub sea part of the structural shell model Wadam SESAM 3 18 22 JAN 2010 Program version 8 1 Pontoon Pontoon Column Pontoon intersection area Column Pontoon intersection area Lower part of column Column up to still water level Deck area and hull above water level Morison model Figure 3 11 The geometry assembly for the structural shell model The model is built from first level superelements created in e g Patran Pre and Genie and then built together in the hierarchy shown in Figure 3 11 Both the geometry assembly and the description of load case numbers is built using Presel The load case number description includes wave loads from Wadam and loads defined in the preprocessors See Section 2 1 11 for further description Wet surfaces on the structural model are identified in Patran Pre or Prefem by use of the same modelling steps as for the panel model See Section 2 1 9 for further description The structural model could also have been used as the hydro model for calculation of hydrodynamic loads Separate models are normally used to optimise panel
206. uld be checked in the analysis to make sure that the results are reliable e Information about matching between elements in the panel model and the structural model All wet elements in the structural model should receive wave pressure loads from the analysis If the dis tance from one element in the structural model to the nearest element in the panel model or the difference in orientation of the element normals is too large then Wadam will not transfer any loads to the element A warning will be given in the print file see Appendix B 3 3 In such cases the tolerances specified in Prewad i e distol and angtol should be increased It is however important to be aware of the possible problems when the tolerances are increased The transferred pressures may not be correct for these ele ments and the load sums for the structural model and the panel model may not be satisfactory e Difference between calculated loads on the panel model and loads transferred to the structural model The total pressure loads transferred from the panel model to the structural model are printed in the Wadam listing These load sums should be checked against the sum of calculated pressures on the panel model A large difference indicates that a new analysis should be performed changing either the tolerance the panel model or the structural model The transfer of pressure loads from the panel model to the structural model is described in detail in Appendix B 3 3 e Load
207. um expected roll angle for each wave heading The calculated transfer function for roll motion is compared with the maxi mum value specified for that heading If the computed roll motion is close to the specified angle then the roll transfer function for that value is assumed to be correct If the difference is not acceptable then another n estimate must be made and the roll motion re computed Note however that the potential solution is inde pendent of n Hence the potential should be saved during the first computation and the program should be submitted with a restart option during this iteration process If the maximum roll angle is taken from short term statistics only one sea state then Wadam can perform the iteration process automatically If the maxi mum roll angle is taken from long term statistics then the iteration must be carried out manually It should be kept in mind that these coefficients are only valid within the range of tests and models used in the experiments Extrapolation outside this range should be performed with care The roll damping option in Wadam also includes a linearised roll restoring coefficient in the equation of motion The calculation of this coefficient is described in Appendix B 3 1 Note The Roll damping model can only be used for ship like structures with symmetry about the XZ plane Note The computation of the bilge keel damping breaks down when the bilge keel is very small The symptom is th
208. ure 2 11 a shows an element with five sub elements as specified in HydroD or Prewad It has one node on each side of the still water level This element is first divided into five sub elements The sub element intersecting the still water level is further divided into two new sub elements such that a sub element border lies in the still water level The result is actually six sub elements of which the first five receives hydro loads and optionally inertia forces The last sub element will only receive inertia forces Figure 2 11 b shows elements with one node below and one in the still water level Note that the sub ele ment numbering starts at the deepest node irrespective of which is the first and which is the second node when defining the Morison element This forced ordering of sub element numbers is performed for all ele ments with one node below and the other either at or above the still water level For completely submerged or dry elements the sub element division is straight forward i e increasing sub element numbers from the first to the second node see Figure 2 11 c SESAM Wadam Program version 8 1 22 JAN 2010 2 11 Figure 2 11 The sub element division of 2D Morison elements The local coordinate system for a 2D Morison element n 6 is defined as follows e The axis is normal to the element and parallel with the xy plane of the input coordinate system e The 1 axis points along the element from node N to node N
209. version 8 1 22 JAN 2010 3 5 AP AO AP AP AP oP AP AP AO AP AP AP AP AP AP AP AP CP OP AP iP oP JP AP AP AP AP Specify the constants characteristic length 90 metres mass density of water 1025 Kg m 3 accn due to gravity 9 81 m sec 2 linearising velocity not relevant here z location of input coord system 40 metres 3 dummy values 0 or gt 0 CONSTANTS 90 1025 9 81 0 40 0 O 0 Specify the execution directives analysis type is global motion response calculation of horizontal drift forces the model is a floating structure with 2 planes of symmetry YZ XZ yes calculate eigenvalues for motions for potential solution panel model use an iterative equation solution and do not remove the irregular frequencies store motions results on file for further postprocessing in e g Postresp EXECUTION DIRECTIVES ANALYSIS TYPE GLOBAL RESPONSE HORISONTAL DRIFT YES FIXED FLOATING FLOATING YZ XZ PLANE YES POTENTIAL THEORY EQUATION SOLUTION ITERATION IRREGULAR FREQUENCY NO REMOVAL END RESULT FILES GLOBAL RESPONSE SIF END END Give 3 lines of text to appear in output listing from Wadam TEXT WADAM USER MANUAL EXAMPLE 3 1A Floating Box 90 x 90 metres and Draft 40 metres Global motions response analysis END Define the environmental data to be used for the motions response water depth 100 metres wave directions 0 and 45 deg
210. y which of the wet elements shall receive external and which shall receive internal HY DRO PRESSURE loads The rules for this dummy load case numbering is the following External wet surface The HYDRO PRESSURE load case number must be equal to one Internal wet surface The HYDRO PRESSURE load case for the first internal wet surface tank must be equal to two Additional internal tanks are numbered consecutively with load case number three assigned to tank number two and so on It is important in the definition of wet element sides that the direction of the pressure load is pointing from the fluid towards the element side For this purpose both Patran Pre and Prefem provides an option to visu alise the direction of the pressures defined on the finite element mesh Figure 2 22 shows an idealised view of the normal vectors pointing towards wet element sides This load can also be visualized and verified in HydroD SESAM Wadam Program version 8 1 22 JAN 2010 2 23 swl lt lt lt lt H Figure 2 22 Idealised view of hydro pressures on structural element sides The dummy HYDRO PRESSURE load cases used to identify wet structural elements will not be in conflict with load cases generated by Wadam or other load cases defined by the preprocessors 2 1 10 Free Surface Modelling The free surface model used in the second order sum and difference frequency force calculation in Wadam may be generated by Patran Pre or Prefe
211. ynamic loads which are constant over each element The gravity component of the static load is included by writing the acceleration of gravity to the Loads Interface File 2 5 16 Distributed Hydrodynamic Loads The distributed hydrodynamic loads are calculated in a body fixed coordinate system and include the fol lowing contributions e Exciting forces from incident waves e Forces from wave induced motion e Fluctuating hydrostatic pressure forces due to the body motion The distributed forces presented in the Wadam print file are Transfer functions for pressures on the panels in the hydro model l Transfer functions for forces acting at the centre of gravity for 2D Morison and dry Morison elements Transfer functions for nodal forces acting on nodes in the hydro model which are connected to the fol lowing Morison element types 3D Morison elements Pressure area elements Mooring and TLP elements Point mass elements The distributed loads transferred to the Loads Interface Files are Transfer functions for normal pressures on the wet sides of shell and solid elements The pressures are constant over the elements These loads originate from pressures at the centroid of panels according to the mapping algorithm described in Appendix B 3 3 They include fluctuating hydrostatic pressure 1 Not including fluctuating hydrostatic pressure Wadam SESAM 2 42 22 JAN 2010 Program version 8 1 Transfer functions

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