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AQWA-DRIFT Manual

1. 3 1 2 where the various terms in the stiffness matrix are Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 14 of 119 AQWA DRIFT User Manual Theoretical Formulation K33 A K34 K43 ydA A K35 K53 xdA A K44 y dA zop vol A K45 K54 xydA A K46 X gp vol K55 x dA Zgb vol A K56 Ygp vol The integrals are with respect to the body s cut water plane and the total area of the cut water plane is A The displaced volume of the fluid is given by vol The following coordinates are also used x y z are the coordinates defined in the body fixed axes see Figure 3 1 in the AQWA LINE user manual x y and z give the centre of buoyancy w r t the centre of gravity Note If the body is in a free floating equilibrium state with no external forces acting on it then the terms K46 and K56 will be equal to zero and the stiffness matrix will be symmetric 3 2 MORISON FORCES Morison forces which are applicable to small tubular structures or parts of structures can be included in an AQWA DRIFT AQWA NAUT or AQWA LIBRIUM analysis by the use of TUBE elements The forces are calculated at each timestep AQWA DRIFT and AQWA NAUT or at each iteration AQWA LIBRIUM The force normal to the tube axis on a TUBE element is given by a taD uf U up Us PAC git p PA Cm Ditts 2 3 2 1 Drag Force Wave fo
2. Figure 7 6 Wave Parameters 7 3 DESCRIPTION OF FLUID LOADING This information is only output when starting at Stage 1 or 2 or when the PRDL option is used to echo the information from backing file from AQWA LINE The output detailing the various types of fluid loadings will now be described and this is done by way of the different categories of loading 7 3 1 Hydrostatic Stiffness The hydrostatic stiffness matrix output by AQWA DRIFT when printing from backing file is in the analysis position used in AQWA LINE for the diffraction radiation analysis An example output is shown in Figure 7 7 If used independently the stiffness matrix output is the sum of the hydrostatic stiffness and the additional stiffness input by the user Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 65 of 119 AQWA DRIFT User Manual Description of Output Pie Oe BOY DRO Di NVA MTC PARAMETERS BUOYANCY FORCE oc ay a a Go ay amp a amp a amp 4 3 2566E 09 Z POSITION OF THE CENTRE OF GRAVITY 1 0620E 01 STIFFNESS MATRIX Figure 7 7 Hydrostatic Stiffness Matrix Output 7 3 2 Added Mass and Wave Damping The added mass and wave damping are functions of wave frequency and are therefore output for all specified values of frequency or period The added mass and wave damping are expressed in matrix form and Figure 7 8 shows a typical added mass matrix for
3. 13 Perform a DATA run i e with the DATA option switched on which will provide preliminary checks on the card image data file 14 After a successful DATA run select mode of analysis on the first card of the card image input data drift motion or drift plus wave frequency and re run with the restart option The usual analysis procedure is to first look at the drift motions of a structure in a drift simulation The relative importance of wave frequency effects can then be determined by performing a drift plus wave frequency motion simulation It is usual to perform this wave frequency simulation starting at some point just before the maximum drift response to see how the peak response is aggravated or reduced by the wave frequency effects From the output listing of the drift run it is possible to pick off the structure s position and velocity at some time just before the peak drift motion and use these as the initial conditions for the wave frequency simulation Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 50 of 119 AQWA DRIFT User Manual Description of Output CHAPTER 6 DATA REQUIREMENT AND PREPARATION This chapter describes the form in which data is expected by the program and it is not intended as a detailed list of the data requirements and general format for each type of analysis that may be performed when running AQWA DRIFT The detailed format may be found in the A
4. 39E 05 8 33E 04 38E 05 8 29E 04 5 99E 02 8 11E 02 Figure 7 10 Mean Wave Drift Forces Moment 7 4 FREE FLOATING NATURAL FREQUENCIES AND RESPONSE AMPLITUDE OPERATORS 7 4 1 Natural Frequencies Periods AQWA DRIFT calculates the uncoupled natural frequency period for each structure at each user specified wave frequency added mass being a function of wave frequency The damping values of the body motions are compared with and expressed as a percentage of critical damping values see Figure 7 11 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 69 of 119 AQWA DRIFT User Manual Description of Output NATURAL FREQUENCIES PERIODS FOR STRUCTURE N B THESE NATURAL FREQUENCIES DO NOT INCLUDE STIFFNESS DUE TO MOORING LINES FREQUENCY FREQUENCY UNDAMPED NATURAL FREQUENCIES RADIANS SECOND NUMBER PERIOD PERIOD UNDAMPED NATURAL PERIOD SECONDS NUMBER SECONDS PITCH RY FREQUENCY FREQUENCY APPROXIMATE PERCENTAGE CRITICAL DAMPING NUMBER ROLL RX PITCH RY Figure 7 11 Natural Frequencies Periods 7 4 2 Response Amplitude Operators The Response Amplitude Operators which are not required to calculate the wave drift frequency motion will be output as zero if the user has not specified them in Deck 7 unless the user has used the CRNM option Calculate RAOs with No Moorings If they are printed from an AQWA LINE backing file the
5. 4 7 1 Hydrostatic Stiffness The hydrostatic stiffness matrix is calculated in AQWA LINE and then transferred automatically via backing file to the other programs in the suite when they are used as post processors to AQWA LINE More details may therefore be found in the AQWA LINE manual in Section 4 7 1 When AQWA DRIFT is used independently the linear hydrostatic stiffness matrix is required as input data Note that although this matrix is termed linear hydrostatic a matrix may be input which includes other linear stiffness terms However the user is advised to consider other linear stiffness terms as ADDITIONAL stiffness to be modelled separately as described in the following section 4 7 2 Additional Linear Stiffness The additional linear stiffness is so called to distinguish between the linear hydrostatic stiffness calculated by AQWA LINE or from any other source and linear stiffness terms from any other mechanism or for parametric studies As this stiffness matrix is transferred automatically from backing file when AQWA DRIFT is used as a post processor the following notes refer to AQWA DRIFT when used as an independent program Although all terms in the additional linear stiffness can be included in the hydrostatic stiffness matrix the user is advised to model the two separately The most common reasons for an additional stiffness model are modelling facilities for a particular mechanism are not available in the AQWA suite
6. Page 91 of 119 AQWA DRIFT User Manual xe WIND CU FORCES FREQUENCY DUE TO RADIANS SEC SURGE X 32E 03 SWAY Y 00E 00 HEAVE Z 00E 00 ROLL RX 00E 00 PITCH RY 00E 00 YAW RZ 00E 00 CURRENT 95E 06 00E 00 OOE 00 ROLL RX 00E 00 PITCH RY 00E 00 YAW RZ 00E 00 40 00 00 00 00 07E 03 07E 03 00E 00 00E 00 00E 00 00E 00 40E 06 E 06 E 00 E 00 E 00 E 00 Figure 8 6 Wind Current Loads and Thruster Forces THRUS TER FOR CES NO THRUSTER FORCES 00OE 00 32E 03 OOE 00 00E 00 00E 00 00E 00 00E 00 95E 06 OOE 00 00E 00 00E 00 00E 00 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Example of Program Use Page 92 of 119 AQWA DRIFT User Manual Example of Program Use ER CON STR A EN Teg oe ee STRUCTURE ACTIVE FREEDOMS TABLE NUMBER Figure 8 7 Constraints Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 93 of 119 AQWA DRIFT User Manual CABLE MOORING LINE CONFIGURATION CABLE ATTACHMENTS STRUCTURE 0 IS GROUND fe STRUCT ELEM NO STRUCTURE NO LASTIC LASTIC LASTIC ATTACHED TO NODE LINKED TO NODE UNSTRETCHED LENGTH STIFFNESS FORCE OR TENSION 472E 06 472E 06 472E 06 472E 06 Figure 8 8
7. the hydrostatic stiffness matrix is incomplete the user wishes to investigate the sensitivity of the analysis to changes in the linear stiffness matrix In practice only in unusual applications will the user find it necessary to consider the modelling of additional linear stiffness 4 8 WAVE FREQUENCIES AND DIRECTIONS The wave frequencies and directions are those at which the wave loading current and wind coefficients Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 38 of 119 AQWA DRIFT User Manual Modelling Techniques are defined and as they are transferred automatically from backing file when AQWA DRIFT is used as a post processor the following notes refer to AQWA DRIFT when used as an independent program These coefficients which are required as input data further details may be found in the following sections are dependent on frequency and or direction A range of frequencies and directions is therefore required as input data which are those at which the coefficients are defined There are only two criteria for the choice of values of the frequency and direction which may be summarised as follows 1 The extreme values must be chosen to adequately define the coefficients at those frequencies where wave energy in the spectrum chosen see Section 4 14 is significant and at ALL possible directions of the subsequent response analysis If geometric symmetry has been
8. Time seconds Position of cog in x direction Timet seconds Wave Freg position in x direction Time seconds Slow position in x direction Figure 8 22 Time Histories of Total Surge Motion and Fast and Slow Components Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 109 of 119 AQWA DRIFT User Manual Example of Program Use Time seconds Mooring Force Line 1 tension 3225 0 Ti me seconds Mooring Force Line 3 tension 1 520 ZPE 1 510E 4 a ee yb HE 2 es Poe eee a a eee 1490 IES AES As Eee ees aS Ne Pa eae ial 1 470 3200 0 3225 0 3250 0 yeigtt Time seconds Mooring Force Line tension Figure 8 23 Time History of Tension in Hawsers 1 3 and 4 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 110 of 119 AQWA DRIFT User Manual Running the Program CHAPTER 9 RUNNING THE PROGRAM 9 1 File Naming Convention for AQWA Files The user is recommended to adopt the following convention of naming the files to be used by the AQWA programs Every file name consists of three parts the file prefix the run identifer the file extension Example a two character string used to identify a particular AQWA program The file prefixes are as follows Program Prefix AQWA LINE al AQWA LIBRIUM ab AQWA FER af AQWA DRIFT ad AQWA NAUT an AQWA WAVE aw
9. 00 eee ceseceecseeceeceeeeeeeeeeeeeeesecsecsaecsaecnaecaaecaaecaeseseeeeeeeeesseeeeeeaeenaes 26 3 14 4 Slow Drift and Wave Frequency Positions einser ienen EE ESEE EENE EEE iS 27 3 14 5 Response Amplitude Operator Based Position eee eeeeeeeeeeeeeceeecesecesecaeceaecsaecseecaeseseeeeeeeseseeeseeeaeenaes 27 3 14 6 Filtering of Slow Position from Total Position 00 00 eee ceeeeeceeeeeeceeecesecesecaecsaeceaecseecaeseseseeeeeeeseeeenaeenas 28 3 14 7 Initial Position and Transients serci iinei ces oee schon Eee eE rE EEE EE ERES vanepcabvecusovants EE EEE NE EEES dncoupbvasevees 28 3 15 TIME HISTORY SOLUTION IN REGULAR WAVES 0000 eccesccssecssecseecseecaeeeeecaeecaeseneseaeeeseeeeenaeenseeaeenaes 29 3 16 LIMITATIONS OF THEORETICAL APPLICATIONS 00 eceeceescesecesecesecesecaecaeecseecaeseaeseaeeeeeeeeeeeenseenseenaes 29 3 17 THE USE OF CONVOLUTION FOR THE EVALUATION OF THE RADIATION FORCES IN THE TIME DOMAIN eiic 3 cates nad seescaeescaseh hod ET EE 30 CHAPTER 4 MODELLING TECHNIQUES iic s sssisessctescesbtetssesceesspenthoesbetsathastslavesopessseosgetbpesbebesebssdetosasdeesseessspesesdescee 32 4 1 INTRODUCTION rren a steaseeayty Ship abvegnebineius iaietaneevoen A N E A E 33 4 2 MODELLING REQUIREMENTS FOR AQWA DRIFT ooo eecesecssecssecseecseeeseseeeeeeeeeeeeseeaecaecsaecsaecseeeaeeeneeeas 33 4 2 1 When Used as an Independent Program isien ea n e aE a E AR e E S E SSRS ER 33 4 2 2 Following an AQW A LINE RUD s sse lt c s ceissesces as
10. Cable Mooring Line Configurations Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates WINCH FRICTION WIND IN PAY OUT Example of Program Use Page 94 of 119 AQWA DRIFT User Manual Example of Program Use RR RR TN De TAGs POSITION STRUCTURE PARAMETER DIRECTION COSINES NUMBER POSITION 10 611 1 0000 0 0000 0 0006 0 0000 1 0000 0 0000 0 0006 0 0000 1 0000 VELOCITY Figure 8 9 Initial Position of the Centre of Gravity Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 95 of 119 AQWA DRIFT User Manual Example of Program Use wrew E EME INTEGRATION PA RAMETERS tok STARTING RECORD NUMBER NUMBER OF TIME STEPS PRESENT TIME STEP PRESENT TIME EXPECTED ERRORS FOR INTEGRATION OF SINUSOIDAL MOTION FOR TIME STEP OF 5 0000 FREQUENCY PERIOD AMPLITUDE ERROR PHASE ERROR RAD SEC SECONDS PER CENT DEGREES 0 0 0 0 0 0 0 Q Q 0 1 Is 2 5 Figure 8 10 Time Integration Parameters Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 96 of 119 AQWA DRIFT User Manual Example of Program Use STRUCTURE NODE WITH RESPECT TO THE FIXED REFERENCE AXES RELATIVE TO THE CENTRE OF GRAVITY NUMBER NUMBER Figure 8 11 Position of User Requested Nodes Contains proprietary and confidential informat
11. drift frequency velocity wave frequency velocity which is the default since version 5 0C Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 117 of 119 AQWA DRIFT User Manual Appendix A TRAN TRANSIENT ANALYSIS This option switches off the slow axis system and stops printout of harmonic analysis at the end of a simulation run This option should not in general be used It is only provided as a workaround for DRIFT analysis for both drift and wave frequency motions if it diverges in the time integration TRAO TRANSIENT RAO MOTION When this option is used AQWA DRIFT will recalculate the forces based on the RAOs which can be input by the user in Deck 7 This allows RAOs obtained from e g Tank tests to be used with the CONV option in transient analyses If the RAOs are not modified this option has little effect PBIS PRINT FORCE COMPONENTS AT EACH ITERATION STEP Prints out positions and forces on each structure at each timestep The scope of the printout can be controlled by selections in Deck 18 PPEL PRINT PROPERTIES OF EACH ELEMENT This option allows the user to output complete details of each element used in the body modelling All important details of the body elements are output together with the resultant properties of the bodies It is only applicable when running Stage 1 of the analysis PRCE PRINT CARD ECHO FOR DECKS 1 to 5 This option informs the program
12. see the AQWA LINE and AQWA LIBRIUM manuals when this is not the case Note that a hydrostatic or hydrodynamic model as such is not required see Section 4 2 1 only the hydrostatic stiffness matrix see Section 3 1 3 and hydrodynamic loading coefficients see Section 3 3 4 4 1 Coordinates Any point on the structure in the modelling process is achieved by referring to the X Y and Z coordinate of a point in the FRA which is termed a NODE The model of structure geometry and mass distribution consists of a specification of one or more elements see also Sections 4 1 4 4 2 whose position is that of a node Each node has a NODE NUMBER which is chosen by the user to be associated with each coordinate point Nodes do not contribute themselves to the model but may be thought of as a table of numbers and associated coordinate points which other parts of the model refer to Although several coordinates must be defined if several elements are used to define the geometry mass distribution normally a single point mass is used which means that only a single node is defined at the centre of gravity of the structure Note that nodes are also used to define the positions of other points not necessarily on the structure e g the attachment points at each end of a mooring line 4 4 2 Elements and Element Properties As stated in the previous section the structural geometry and mass distribution of the model for AQWA DRIFT used independently of A
13. 0 0000E 00 0 0000E 00 MOORING 2 7515E 06 0000E 00 1336E 02 0000E 00 2 9111E 07 0 0000E 00 THRUSTER 0 0000E 00 0000E 00 0000E 00 0000E 00 0000E 00 0000E 00 TOTAL REACTION FORCE 0000E 00 0000E 00 0000E 00 0000E 00 0000E 00 0000E 00 TOTAL FORCE 7677E 06 5894E 01 2747E 05 6387E 02 3813E 07 0156E 04 ERROR PER TIMESTEP 5447E 03 0078E 09 3408E 03 1949E 09 2074E 05 5691E 15 POSITION NODE 501 45 9257 0 0000 POSITION NODE 502 0 9257 45 0000 POSITION NODE 503 44 0743 0 0000 POSITION NODE 504 0 9257 45 0000 Figure 8 13 Output Listing Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 99 of 119 AQWA DRIFT User Manual Example of Program Use JOB TITLE NATURAL FREQUENCY DATA RUN TIME SECS STRUCTURE POSITION FORCES NUMBER AND MOMENTS AT RECORD NO CENTRE OF GRAVITY POSITION 0 7558 0 0000 10 6105 0 0000 0 0365 0 0000 VELOCITY 0 0344 0 0000 0 0000 0 0000 0 0000 0 0000 ACCELERATION 0 0042 0 0000 0 0011 0 0000 0 0057 0 0000 GRAVITY 0000E 00 0000E 00 3 2566E 09 0000E 00 0000E 00 0 0000E 00 HYDROSTATIC 0000E 00 0000E 00 3 2558E 09 4208E 02 5549E 07 0 0000E 00 CURRENT DRAG 4962E 03 6962E 06 0 0000E 00 0000E 00 0000E 00 0 0000E 00 YAW DRAG 0000E 00 0000E 00 0 0000E 00 0000E 00 0000E 00 0 0000E 00 WIND 5644E 00 2064E 09 0 0000E 00 0000E 00 0000E 00 0 0000E 00 LINEAR DAMPING 0000E 00 0000E 00 0 0000E 00 0000E 00 00
14. 000E 00 0 000E 00 LOSYMY 000E 00 0 000E 00 0 000E 00 0 000E 00 0 000E 00 0 000E 00 1ODIRN 000E 00 4 500E 01 9 000E 01 0 000E 00 0 000E 00 0 000E 00 LOCUFX 950E 06 2 400E 06 0 000E 00 0 000E 00 0 000E 00 0 000E 00 LOCUFY 000E 00 2 400E 06 2 950E 06 0 000E 00 0 000E 00 0 000E 00 LOWIFX 320E 03 1 070E 03 0 000E 00 0 000E 00 0 000E 00 0 000E 00 ENDLOWIFY 000E 00 1 070E 03 1 320E 03 0 000E 00 0 000E 00 0 000E 00 DECK 11 12DACF 12DACF END12DACF DECK 13 14LINE 472E 06 1 000E 02 0 000E 00 0 000E 00 0 000E 00 14LINE 472E 06 1 000E 02 0 000E 00 0 000E 00 0 000E 00 14LINE 472E 06 1 000E 02 0 000E 00 0 000E 00 0 000E 00 END14LINE 472E 06 1 000E 02 0 000E 00 0 000E 00 0 000E 00 END1I5POS1 DECK 16 END16TIME DECK 17 18PREV 18NODE 18NODE 18NODE END18NODE Figure 8 4 Card Echo for Decks 9 to 18 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 90 of 119 AQWA DRIFT User Manual ROR ORR COR YD ROOD XN ALM Te PARAMETERS 0000 2132 0000 0000 0000 DAMPING AT DRIFT Figure 8 5 Drift Frequency Added Mass and Damping E 00 E 08 E 00 E 00 E 00 0734E OOO00E 5538E OOO0E OOO00E 00 10 00 00 FREQUENCY Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Example of Program Use
15. 4199E11 kgm 2 I 3 5991E11 kgm ZZ The centre of gravity position vector is 0 0 0 0 10 62 measured with respect to the FRA The environmental parameters are defined as Water depth 250 0 metres Water density 1025 0 kg metre Wave periods 12 to 18 seconds Wave directions 0 0 45 0 and 90 0 degrees Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 79 of 119 AQWA DRIFT User Manual Example of Program Use The box structure is moored by horizontal soft moorings attached to the mid sides of the box at the water line as shown in Figure 8 1 Unstretched length of each mooring line E 100 0 metres Stretched length of each mooring line 101 0 metres Extension of each mooring line 1 0 metres Stiffness of each mooring line 1 4715E6 N m Pre tension in each mooring line 1 4715E6 newtons It is required to obtain the response of the box in irregular waves for a given sea state with particular attention being paid to the hawser tensions In the first instance only the drift oscillations of the structure will be investigated After this has been completed the effect of the wave frequency forces will be investigated Note that the analysis is performed using SI units Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 80 of 119 AQWA DRIFT User Manual Example of Program Use my ATIGIN Figure 8 1 Mooring Lin
16. Parameters sssi esien tives sirsenis Ee eree E Epe Eko sobasusdevesves oo SESE EES Toe S ESERSE e 37 AT LINEAR STIFFNESS aa Aeethied spaniel acting E r E EE E E EEE TET EE E S EE aoe ee 38 4 7 1 Hydrostatic StIffNeSS sieren asses srao bhgesdehaseis tana sbbesscessdetbeescenoceh abt desasdees sees so REES E o rta dtsseedeoesveassetaestencds 38 41 2 Additional Linear Stiffness esre reker ro eaa a EEEE EEE EE TESTE E E SEER SE EET E Eiris 38 4 8 WAVE FREQUENCIES AND DIRECTIONS 5 isc sscvsscesscascssescesscetssnscetsscvasescsnscosbesoecssobsonsousosvnsb sesiuasvctestensgesseesceoees 38 4 9 WAVE LOADING COEFFICIENTS sx ceira esras eer eere ero E t rE eeso rE Teer EEr E rE EEE SEESE ETES 39 4 10 WIND AND CURRENT LOADING COEFFICIENTS s sseeeeereessesetseeseenersretissererererescenerorerereesstsrerosrererererecesrere 40 4 11 THRUSTER FORCES ereere E EE EAEE E EEE E E A E EEEa 40 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 5 of 119 AQWA DRIFT User Manual Contents 4 12 STRUCTURAL ARTICULATIONS eeii ois bet b a e A Ea a E eens ke ae SE Aes 40 AAD VATECULAIONS e oireann bes Sy a e EAE E duke E RO e Oa EE EEES OEE EE sete 40 412 2 Constraints in i ona e aaeoa e a o A E HAL AT EL e RAD AAG OE N OE OE EE OEE 41 4 13 WAVE SPECTRA WIND AND CURRENT SPECIFICATION sesessssessseeessereeresesrssrrrrsrerrenresrenresrerreresreeresrent 41 4 14 MOORING LINES rs a E A E E E E R 41 4 14 1 Linear
17. SIMULATION RUN OPTIONS CONV FOQTF PBIS PRDL REST END RESTART 4 5 ALBOX22 09 DRM1 ENDO 9FIDD 3 4758E7 4758E7 9253E7 3 0156E9 3 0156E9 3 0002E9 0 HLD1 OSYMX OSYMY ODIRN OCUFX OCUFY OCURX OCURY OWIFX OWLFY OWIRX OWIRY 1 NONE 2 NONE 3 SPEC 3CURR 3WIND 3SPDN 3PSMZ 4 4L 4715E6 100 4L 4715E6 100 4L 4715E6 100 4L 4715E6 100 5 0 0 45 0 90 0 9500E6 4000E6 0000E0 0000E0 4000E6 9500E6 0000E0 2500E7 7700E7 7700E7 2500E7 0000E0 3200E3 0700E3 0000E0 0000E0 0700E3 3200E3 0000E0 9400E4 2 3900E4 3900E4 9400E4 0000E0 as S ae a S W U U UUUUUUW N ae E a gt E E a 0 0000 10 6878 0 0000 0 1493 0 0000 0 0000 0 0168 0 0000 0 0259 0 0000 6 6TIME S 3200 0 NONE 8 PROP 8 PREV 20 8PTEN 1 Figure 8 21 Data File for Drift Wave Frequency Simulation Run Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 108 of 119 AQWA DRIFT User Manual Example of Program Use 8 1 18 Output from Drift Wave Frequency Simulation Run Figure 8 22 shows the resulting time history of surge motion The slow and fast components of this total motion are shown also From these plots it is clear that the wave frequency motion is of comparable magnitude to the drift motion in this case The increase in line tensions due to the addition of wave frequency forces on the line tensions is shown in Figure 8 23 1 0 3200 0 3225 0 3250 0
18. Structure 1 at a single frequency Wave damping is output in a similar fashion Summary tables of variation of added mass and wave damping with wave frequency period are also output Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 66 of 119 AQWA DRIFT User Manual Description of Output RO KORO YS DOR Ou D AGN ACM LS PARAMETERS WAVE PERIOD 62 832 WAVE FREQUENCY 0 1000 ADDED MASS Figure 7 8 Added Mass Matrix Output 7 3 3 Wave Excitation Forces The wave loading output from AQWA LINE is presented in tabular form for all the directions and frequencies specified by the user The output gives the variation of wave force moment with frequency for each direction see Figure 7 9 Output is also given with the wave force moment varying with direction for each frequency The wave forces moments are output in terms of amplitude and phase The phase is related to the incident wave form see Appendix C of the AQWA Reference Manual The wave forces moments are divided into their various components and output in terms of the following Froude Krylov forces moments Diffraction forces moments Total wave forces moments Figure 7 9 shows only the Froude Krylov component but the other forces are output in a similar format Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 67 of 119 AQWA DRIFT User
19. about all axes and not free to rotate at all 4 12 2 Constraints A constraint can be applied to any degree of freedom This has the effect of stopping the calculation of forces or moments and stopping motion in the specified constrained degrees of freedom The facility of de activating degrees of freedom is most often used in the simulation of the drift motion of a structure Here only the surge sway and yaw degrees of freedom are of interest and it is therefore not required that the roll pitch and heave degrees of freedom be integrated The position of these non active freedoms will stay constant and equal to the initial defined value throughout the simulation It is therefore important to specify these correctly Great care must be exercised if degrees of freedom are de activated in a structure which is articulated either to another structure or to a fixed point It is recommended that this should not be done 4 13 WAVE SPECTRA WIND AND CURRENT SPECIFICATION The user may specify only one spectrum wind and current speed and their associated directions For the majority of applications specification is quite straightforward and no knowledge of the way in which the spectra are used in any program is required The two rules for specification of the spectrum are as follows 1 The value of the spectral ordinate at the beginning and end of the frequency range should be small If the values are not small only part of the spectrum has effecti
20. al ues 3 14 5 j l 3 14 6 Filtering of Slow Position from Total Position In the case where both drift motion and wave frequency motions exist the current drag force when using SDRG card and wave drift forces are applied to the structure in an axis system which follows the SLOW position But the wind forces are applied using an axis system which follows the total position The slow position is obtained from the total position by filtering the position through a low pass band filter which separates out the slow and fast oscillations This is achieved by integrating the following equation at each time step X t 20 ex t 07 x x 0 3 14 6 where Ky koX the filtered slow acceleration velocity and position x the total position Ww the filtering frequency c the filter damping The filtering frequency is chosen by the program to eliminate the wave frequency effects The damping is set to 20 of critical damping The SLOW position is filtered out of the TOTAL position leaving the WAVE FREQUENCY position It is clear that for simple cases the RAO BASED POSITION will be very similar to the WAVE FREQUENCY position This can often prove a useful check on the wave frequency position in runs where wave frequency forces are added 3 14 7 Initial Position and Transients AQWA DRIFT solves the second order differential equations of motion for each structure integrating them to form a time history For this the program require
21. and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 78 of 119 AQWA DRIFT User Manual Example of Program Use 8 1 BOX STRUCTURE 8 1 1 General Discussion Although in general concept the response of a structure in irregular waves is quite straightforward errors are often encountered due to the failure to perform simple preliminary calculations to estimate the order of magnitude of the expected results It is clearly not desirable or necessary to repeat the complicated calculations performed by AQWA DRIFT However certain preliminary calculations which are shown in this example are ESSENTIAL in order to Minimise input data errors Minimise misinterpretation of the input data requirements Enable the user to predict and isolate areas of interest in the analysis Enable intelligent interpretation of the results of the analysis 8 1 2 Problem Definition The first example is a rectangular box structure for which the analysis has been run using AQWA LINE for Stages 1 to 3 This is the simplest and most common form of analysis AQWA LINE run of Stages 1 to 3 followed by an AQWA DRIFT run It is assumed that the user is familiar with the box structure example in AQWA LINE The characteristics of the body are as follows Length 90 0 metres Breadth 90 0 metres Depth E 55 0 metres Draught 40 0 metres Mass of the body 3 321E8 kg 3 321E5 tonnes 2 Mass inertial 3 6253E11 kgm 2 ae F 3
22. are required to model the forces and moments on the structure due to wind and current These forces are proportional to the square of the relative velocity For a simple box shape or similar bluff bodies these coefficient may be reasonably well approximated by consideration of projected frontal areas and a suitable drag coefficient For hydrodynamic geometries e g a tanker net lift forces may also be important O C I M F has published results of model tests on various tankers OCIMF 1994 4 11 THRUSTER FORCES Thruster forces can be applied on any point of the structure in any direction Two thrusters can produce a moment by acting in parallel directions but not through the same point 4 12 STRUCTURAL ARTICULATIONS AND CONSTRAINTS 4 12 1 Articulations Structures in an AQWA DRIFT analysis can be freely floating moored or connected to other structures by points of articulation There are four different types of articulation available These are as follows 0 Ball and Socket Free to rotate about all axes 1 Universal Free to rotate about two axes transmitting a moment about the third axis at right angles to the first two 2 Hinged Transmitting a moment about two axes and free to rotate Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 40 of 119 AQWA DRIFT User Manual Modelling Techniques about the third axis at right angles the first two 3 Locked Transmitting a moment
23. at the following time step and so the time history of the structure motion is constructed The program can be used to calculate the response of structures to drift forces only but wave forces can also be added with the restriction that the length of time between calculation of the forces and integration of the structure motions must be decreased to accommodate the more rapid variation in wave force Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 10 of 119 AQWA DRIFT User Manual Theoretical Formulation 2 2 THE COMPUTER PROGRAM The program AQWA DRIFT may be used on its own or as an integral part of the AQWA Suite of rigid body response programs using the data base from AQWA LINE When AQWA LINE has been run a backing file called the HYDRODYNAMIC DATABASE File is automatically created which contains full details of the fluid loading acting on the body Another backing file called the RESTART FILE is also created and this contains all modelling information relating to the body or bodies being analysed These two files may be used with subsequent AQWA LINE runs or with other AQWA programs The use of backing files for storage of information has two great advantages which are e Ease of communication between AQWA programs so that different types of analyses can be done with the same model of the body or bodies e g AQWA LINE regular wave hydrodynamic coefficients and drift forces being
24. coefficients for the superstructure Current loading coefficients for the hull Thruster force magnitude and direction Wind and current speed and direction Profiled current data Degrees of freedom of structures which are to be deactivated Constraints between structures Wind speed and direction for each spectrum Current speed and direction for each spectrum Description of the wave spectra and or wind spectra Description of each mooring line property Description of layout for each mooring configuration Initial position for each structure Number of time steps time step length and start time Morison element parameters Additional printing options Note If the start stage is less than 5 and finish stage equals 6 Deck 19 to Deck 21 are required Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 58 of 119 AQWA DRIFT User Manual Description of Output Usually not all the above data items are required for any particular analysis In this case the user simply omits the items which are not applicable Note also that other data items may not be required as a consequence of omissions 6 5 STAGE 5 NO INPUT Motion Analysis Stage 5 is the motion analysis stage only and therefore requires no input 6 6 STAGE 6 LOADS ON MORISON ELEMENTS Stage 6 is used to calculate the loads on Morison elements for use in a structural analysis At present this is only available
25. correct then the program would be restarted at next stage of the analysis by using the RESTART option END This is used to indicate the end of the option list Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 115 of 119 AQWA DRIFT User Manual Appendix A FQTF USE FULL QTF MATRIX This option specifies that the full matrix of difference frequency QTFs is to be used when calculating slowly varying drift forces LAAR LOCAL ARTICULATION AXIS SYSTEM FOR ARTICULATION REACTION FORCE OUTPUT LAA This option is used to output articulation reaction force in the local articulation axis system This means that the moments in unconstrained freedoms e g the hinge axis will always be zero within roundoff LSAR LOCAL STRUCTURAL AXIS SYSTEM LSA FOR ARTICULATION REACTION FORCE OUTPUT This option is used to output articulation reaction force in the local structural axis system This means that the direction of the output reaction force will follow the structure MCNV CALCULATE C LF USING ADDED MASS AND DAMPING From version 5 3K onward the default method for calculation of the Convolution Integral Function uses the radiation damping only This option forces the program to use the previous method based on both added mass AND damping MRAO CALCULATE MOTIONS USING RAO s ONLY This option instructs AQWA DRIFT to calculate motions using RAOs only These may be defined by the user
26. define a set of force RAOs The radiation force time history can then be derived from the force RAOs and the wave energy packet This assumption is only valid if the response of the structure at wave frequency is essentially linear i e the structure s motion matches the RAOs in frequency amplitude and phase Since RAOs are calculated for steady state oscillation under linear forces the actual structure response especially when non linear mooring force is involved or when the motion has not reached a steady state i e transient motion may differ from what is predicted by the RAOs Consequently the RAO based radiation force calculation may no longer be accurate In order to address the above problem users of AQWA have the option of using the convolution method CONV in the time domain programs AQWA DRIFT and AQWANAUT The convolution of the added mass and damping from the frequency domain to the time domain is a rigorous treatment of the radiation force which uses the actual structure motion instead of RAOs With this method the radiation force is evaluated separately from the other forces and uses the actual velocity acceleration of the structure rather than the velocity acceleration based on the RAOs The convolution as a method of evaluating the radiation forces can be summarized as follows is more general is more accurate for any non linear response simplifies the concept of radiation forces automatically takes account o
27. frequency motions and low period oscillatory drift motions may be considered Wind and current loading may also be applied to the body If more than one body is being studied coupling effects between bodies may be considered Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 11 of 119 AQWA DRIFT User Manual Theoretical Formulation AQWA WAVE Used to transfer wave loads on fixed or floating structure calculated by AQWA LINE to a finite element structure analysis package Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 12 of 119 AQWA DRIFT User Manual Theoretical Formulation CHAPTER 3 THEORETICAL FORMULATION The topic headings in this chapter indicate the main analysis procedures used by the AQWA suite of programs However detailed theory is given here only for those procedures used within AQWA DRIFT The theory of procedures used by other programs within the AQWA suite is described in detail in the appropriate program user manual References to these user manuals are given in those sections of this chapter where no detailed theory is presented Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 13 of 119 AQWA DRIFT User Manual Theoretical Formulation 3 1 HYDROSTATIC LOADING 3 1 1 Hydrostatic Forces and Moments The hydrostatic forces in common with all for
28. guide to the expected errors in statistical properties derived from a finite length simulation The variance of the mean square value can be calculated from the following 4o T t 9 EZ Mee t dt 4 16 1 where C the true mean squared value p y the auto correlation function of the process T the length of the simulation or process Assuming light damping and linearity in the restoring stiffness and damping the auto correlation function is 2 p t e cos t 4 16 2 where W natural frequency of oscillation c surge damping as a fraction of critical damping Equation 4 16 1 can thus be evaluated Since the statistical variation about the mean square value will be approximately Gaussian the 98 per cent and 68 per cent confidence limits in simulated motion can be deduced and are plotted as Figure 4 2 The graph shows that for a system with 10 percent damping the length of simulation must be at least 40 times the structure s natural period to achieve an estimate of the significant motion correct to 20 per cent Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 45 of 119 AQWA DRIFT User Manual Modelling Techniques eo Sas sc ST wE t Sozatlontengih where Ca funge damoing coeMicte Matin Suse Panni Figure 4 2 Confidence Limits on Computation of Significant Motion 4 16 3 Initial Conditions and Start Time It is important that the sim
29. in Deck 7 Note that this option suppresses all motion except that defined by the RAOs In particular current wind drift forces moorings etc have no effect on the motions of the structure NOBL NO BLURB DO NOT PRINT LIS BANNER PAGE This option switches off printing of the banner page in the LIS file NOCP NO CURRENT PHASE SHIFT This option switches off the wave phase shift due to a current speed This is only applicable to versions 5 0C and onwards NODL NO DATA LIST This option switches off all extended data output in the LIS file NOST NO STATISTICS Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 116 of 119 AQWA DRIFT User Manual Appendix A This option stops the automatic calculation of statistics at the end of each simulation run Statistical processing can be lengthy for long simulations This option can be used to reduce processing time if statistics are not required NOWD NO AUTOMATIC WAVE DRIFT DAMPING CALCULATION This option stops the automatic calculation of wave drift damping for a floating structure in AQWA DRIFT When this option is used the wave drift damping should be defined in deck 9 Otherwise the program will do the calculation Please note that the wave drift damping calculated by the program is only for the floating structure defined in AQWA LINE damping from risers etc is not included The NYWD option stops calculation of wave drift
30. is a registered trademark of Mathsoft Engineering amp Education Inc Microsoft Windows Windows 2000 Windows XP and Excel are registered trademarks of Microsoft Corporation NASTRAN is a registered trademark of the National Aeronautics and Space Administration PATRAN is a registered trademark of MSC Software Corporation SentinelSuperPro is a trademark of Rainbow Technologies Inc SESAM is a registered trademark of DNV Software Softlok is a trademark of Softlok International Ltd All other trademarks or registered trademarks are the property of their respective owners Disclaimer Notice THIS ANSYS SOFTWARE PRODUCT AND PROGRAM DOCUMENTATION INCLUDE TRADE SECRETS AND ARE CONFIDENTIAL AND PROPRIETARY PRODUCTS OF ANSYS INC ITS SUBSIDIARIES OR LICENSORS The software products and documentation are furnished by ANSYS Inc its subsidiaries or affiliates under a software license agreement that contains provisions concerning non disclosure copying length and nature of use compliance with exporting laws warranties disclaimers limitations of liability and remedies and other provisions The software products and documentation may be used disclosed transferred or copied only in accordance with the terms and conditions of that software license agreement ANSYS Inc and ANSYS Europe Ltd are UL registered ISO 9001 2000 Companies Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 2 o
31. on the ANSYS web page If you are unable to access the third party legal notices please contact ANSYS Inc Published in the United Kingdom Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 3 of 119 AQWA DRIFT User Manual Contents CONTENTS CHAPTER T INTRODUCTION ws said eat avai atiis Hg ais GEE Ry Sa AROS A es 9 Tl PROGRAM neea a a aes nes a E E hasan EE i the aves eA a eee eh ake ee Reese he ees 9 Ts MANU AI oasis toe Bet OU hs ee i Oh a ed A e 8 ba et ee Ben Soe 9 CHAPTER 2 PROGRAM DESCRIPTION oo ececeeccesscesecssecssecssessecsaecsaecaaecaeseseseaeseeeseeeseeesesesecsaecaecsaecsaecaaecseseneeegs 10 2 1 PROGRAM CAPABILITY oz is cssccsscesces preet cadecestessschsedstanectesdspueedeansesbes ssvhasdsdasasous dacessceupsesdenegebasdpapsasveedsgessepeestevess 10 2 2 THE COMPUTER PROGRAM jas sevissepcas shecbestat en saeassevebeageeg Ees E Ee o rE EErEE EEEE EEE SEESE ESTE T EEEE ESES 11 CHAPTER 3 THEORETICAL FORMULATION asaina n A E aA A a 13 3 LAY DROSTATIC LOA NO ui beaver oc eee a E A E E R E R E S tess 14 3 1 1 Hydrostatic Forces and Moments sic 3 35ssssccseecdsctesazssiehsstess sobssesees dashes sods vacostevsess Godscascensctesd co dhsasceessoessebesestevess 14 31D Hydrostatic Equi lt Druin 52 83 sesssenscbscv5s teesveenesion R aides eveeeenion Sedge Ai heoe E Soe nee unteeseene a 14 31 3 Brydrostatic Stutiness MatriX ssa coders pesoto Sise apera E ne E Hesa RE ae
32. to output the input received by the program in reading Decks to 5 This is the body modelling Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 118 of 119 AQWA LINE User Manual Appendix B APPENDIX B REFERENCES 1 Newman J N 1974 Second Order Slowly Varying Forces on Vessels in Irregular Waves Int Symp on the Dynamics of Marine Vehicles and Structures in Waves University College London 2 Berteaux H O 1976 Buoy Engineering J Wiley amp Sons New York 3 Barltrop N D P 1998 Floating Structures a guide for design and analysis Oilfield Publications Limited and CMPT 4 Bailey P A Hudson D A Price W G and Temarel P 1998 A Validation of Speed and Frequency Dependence in Seakeeping Proc Intl Shipbuilding Conf St Petersburg 5 Bishop RED Burcher R K and Price W G 1973 The Fifth Annual Fairey Lecture on the Linear Representation of Fluid Forces and Movements in Unsteady Flow Journal of Sound and Vibration 29 1 113 128 6 Oil Companies International Marine Forum 1994 Prediction of Wind and Current Loads on VLCCs 2 Edition Witherby amp Co Ltd London 7 Rainey R C T Cash D G F and Withee S G 1982 Experience in Analysis of SPM Systems OTC 4346 8 Molin B and Bureau G 1980 A Simulation Model For the Dynamic Behaviour of Tankers Moored to Single Point Moorings Int Symposium of Ocean Enginee
33. 00E 00 0 0000E 00 L WAVE DRIFT DAMPING 0000E 00 0000E 00 0000E 00 0000E 00 0000E 00 0 0000E 00 DRIFT 0000E 00 0000E 00 0000E 00 0000E 00 0000E 00 0 0000E 00 MOORING 2665E 06 2500E 01 1834E 03 0000E 00 4202E 07 3 1562E 00 THRUSTER 0000E 00 0000E 00 0 0000E 00 0000E 00 0000E 00 0 0000E 00 TOTAL REACTION FORCE 0000E 00 0 0000E 00 0 0000E 00 0000E 00 0000E 00 0 0000E 00 TOTAL FORCE 4114E 06 8 4387E 01 3 6967E 05 6286E 02 4176E 07 2 3482E 00 ERROR PER TIMESTEP 9396E 04 2 7735E 10 2 0894E 07 3461E 13 0334E 05 1 5468E 12 POSITION NODE 0 0000 POSITION NODE 45 0000 POSITION NODE 0 0000 POSITION NODE 45 0000 Figure 8 13 Output Listing continued Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 100 of 119 AQWA DRIFT User Manual Example of Program Use 80 0 120 0 320 0 360 0 Ti me seconds Position oF cog in x direction 160 0 200 0 240 0 280 0 320 0 360 0 400 0 Timet seconds Position oF cog about z axis Figure 8 14 Transient Surge Yaw Oscillation 8 1 14 Input Preparation for Drift Motion Data Run For the full drift motion simulation in an irregular sea several additions to the data file for the preliminary run are required These are as follows Deck 9 The drift damping which was not required for the natural frequency run is input optionally for each active degree of freedom Deck 13 The requir
34. 88 of 119 AQWA DRIFT User Manual Example of Program Use DATE 12 01 09 TIME 10 03 46 JOB BOX1 DRIF DRET TITLE NATURAL FREQUENCY DATA RUN OPTIONS REST END RESTART 4 4 ALBOX22 x x INFORMATION ADBOX21 RES copied from ALBOX22 RES AQWA DRIFT VERSION 12 0 01 1 AAAAAA Q00000 WW DDDDDDD RRRRRR PFFFFFEF TTTTITTTT AAAAAAAA QQQ00000 WW WW DDDDDDDD RRRRRRRR PEEFFER CPETACELEET QQ QQ WW WW DD DD RR RR F TT QQ QQ WW WW DD DD RR RR p TT QQ QQ WW WW DD DD RRRRRRRR TI QQ QQ WW WW WW DD DD RRRRRRRR TT QQ QQ WW WW WW DD DD RRRRR TT QQ QQ QQ WW WW WW DD DD RR RRR TT QQQQQQQQ WWWWWWWWWW DDDDDDDD RR RRR Q00000 WWWWWWWW DDDDDDD RR RRR QQ TKK KKK KK KK KK KK KK KK KKK KK KK KK RK KK KK KK KK KK KKK KK AQWA 12 0 LEGAL NOTICES tee A eee ee ee ee eee eee ee ee ee eee ee eee ee ee ee eee eee k k COPYRIGHT AND TRADEMARK INFORMATION Copyright 2008 Ansys Inc All rights reserved Unauthorized use distribution or duplication is prohibited See the AQWA manuals for the complete Legal Notice g TKK OK KK OK RK RK RK RK KK KK KK KK KK KK KK KK KK KK KK KK KK KKK KK KK KK KK KK JOB TITLE NATURAL FREQUENCY DATA RUN Figure 8 3 AQWA DRIFT Header Page used for identification Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 89 of 119 AQWA DRIFT User Manual Example of Program Use LOSYMX 000E 00 0 000E 00 0 000E 00 0 000E 00 0
35. AL ARTICULATIONS AND CONSTRAINTS 3 7 1 Articulations Articulations are modelled in AQWA DRIFT by specifying a point on a structure about which 0 1 2 or 3 rotational freedoms are constrained see Section 4 13 Mathematically this corresponds to additional constraint equations in the formulation of the equations of Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 18 of 119 AQWA DRIFT User Manual Theoretical Formulation motion At each articulation between two structures or a structure and ground the constraint equation relates the acceleration of the articulation point on one structure to the acceleration of the articulation point on the other structure These accelerations must be identical for compatibility i e Gi p Gg O x O x x74 Ging gy By xP Oy X X F2 3 7 1 where a pi the translational acceleration of a point on structure i da gi the translational acceleration of the centre of gravity of structure i 0 the angular acceleration of structure i i the vector from the centre of gravity to the articulation on structure i for each constrained freedom in the constraint equations 3 7 2 Constraints Constraints are modelled in AQWA DRIFT by modifying the equations of motion so that the accelerations in the constrained degrees of freedom are forced to be zero 3 8 WIND AND CURRENT LOADING 3 8 1 Wind and Current The wind and current
36. AQWA DRIFT MANUAL Release 12 0 April 2009 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 1 of 119 Revision Information The information in this guide applies to all ANSYS Inc products released on or after this date until superseded by a newer version of this guide This guide replaces individual product installation guides from previous releases Copyright and Trademark Information 2009 Ansys Inc All rights reserved Unauthorized use distribution or duplication is prohibited ANSYS ANSYS Workbench CFX AUTODYN ASAS AQWA and any and all ANSYS Inc product and service names are registered trademarks or trademarks of ANSYS Inc or its subsidiaries located in the United States or other countries ICEM CFD is a trademark licensed by ANSYS Inc ABAQUS is a registered trademark of ABAQUS Inc Adobe and Acrobat are registered trademarks of Adobe Systems Incorporated Compaq is a registered trademark of Compaq Computer Corporation Delphi is a registered trademark of Borland Software Corporation DXF is a trademark of Autodesk Inc FEMGV FEMGEN and FEMVIEW are trademarks of Femsys Limited FLEXIm and FLEXnet are registered trademarks of Macrovision Corporation Formula One is a trademark of Visual Components Inc GINO is a registered trademark of Bradly Associates Ltd IGES is a trademark of IGES Data Analysis Inc Intel is a registered trademark of Intel Corporation Mathcad
37. BOX22 09 DRM1 ENDO 9FIDD 3 4758E7 4758E7 9253E7 3 0156E9 3 0156E9 3 0002E9 0 HLD1 OSYMX OSYMY ODIRN OCUFX OCUFY OCURX OCURY OWIFX OWIFY OWIRX OWI WWWWWW WW Ww 4715E6 4715E6 4715E6 4715E6 0 0000 0 0000 0 0365 0 0000 8PREV 8PTEN Figure 8 16 Data File For Drift Motion Simulation Run Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 103 of 119 AQWA DRIFT User Manual Example of Program Use 8 1 16 Output from Drift Motion Simulation Run The results once again consist of an output listing file which contains a description of positions and all forces at every eightieth time step as requested in Deck 18 of the data file with statistics calculated at the end of the simulation for all printed parameters The plotting file is also created from which all time histories can be plotted In this example we are interested in the surge motions of the structure and the resulting tensions in the hawsers Figure 8 17 shows the time history of surge motion and Figure 8 18 is an extract from the output listing which describes the statistics of the structure s position Figure 8 19 shows the time histories of tension in hawsers 1 3 and 4 Figure 8 17 shows that the structure is oscillating about a surge displacement of about 1 0 metres but there is a high degree of asymmetry in the surge motions Figure 8 19 shows that for long periods of ti
38. E 4 TIMES SQUARE ROOT OF RASTER AREA S W H NUMBER WAVE NUMBER FREQUENCY 7478E 03 0088E 02 0872E 02 1508E 02 2068E 02 2584E 02 3071E 02 3539E 02 3994E 02 4441E 02 1 2 3 4 5 6 7 8 9 0 O OOO O O OO 0O 0 Ui GO a MRR I A 7591E 02 4414E 02 4194E 02 0043E 02 Figure 7 13 Wave Spectral Lines 7 6 TIME HISTORY AND FORCE PRINTOUT At each requested time step the full description of the position of the structure and the magnitude of all relevant forces is printed on the output listing Figure 7 14 shows a typical example The example printout is record number 21 of a simulation i e it is a description of the state of affairs at the twenty first time step of the run and occurs at a time of 3210 seconds Starting time 3200 seconds The printout refers to Structure 1 which has three degrees of freedom active i e surge heave and pitch Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 72 of 119 AQWA DRIFT User Manual Description of Output When degrees of freedom are deactivated there is no printout for that freedom unless there are user requested nodes or tensions being printed in which case the X Y Z and any other active freedoms are printed The value of each variable is stated in the chosen set of consistent units and are with respect to the Fixed Reference Axis System JOB TITLE DRIFT WAVE FREQUENCY SIMULAT
39. Froude Krylov forces Deck 8 Second order drift forces 6 2 6 Input for AQWA DRIFT with Results from a Previous AQWA LINE Run and a Source other than AQWA LINE The new user is advised to ignore this facility If the user wishes to APPEND to or CHANGE the parameters calculated by a previous AQWA LINE run for the current analysis this can be achieved by using the card image input as described in the previous section in addition to reading the results from a previous AQWA LINE run As the program does not expect a database HYD file from AQWA LINE to exist at Stage 2 of the analysis the ALDB option must be used in the options list see Section 6 0 to indicate that it exists and must be read Using this option means that the Stage 2 data is input twice once from the backing file and once from the card image deck Alternatively use FILE CSTR CPDB cards in deck 6 to copy the hydrodynamic data from a backing Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 56 of 119 AQWA DRIFT User Manual Description of Output file HYD from a previous run in order to DUPLICATE the data base for the structure indicated by the deck header see AQWA Reference 4 6 7 To APPEND to the parameters calculated in a previous run additional frequencies which differ from those existing may be input in Deck 6 together with values of the appropriate frequency dependent parameters in Decks 7 and 8 at thes
40. ION RUN TIME SECS STRUCTURE POSITION FORCES NUMBER AND MOMENTS AT RECORD NO CENTRE OF GRAVITY POSITION VELOCITY ACCELERATION RAO BASED POSITION RAO BASED VELOCITY WAVE FREQ POSITION WAVE FREQ VELOCITY WAVE FREQ ACCEL 5 O SLOW POSITION S s ca SLOW VELOCITY 0 A 0 SLOW ACCEL 0 0 GRAVITY 0 0000E 00 0000E 00 2566E 09 0000E 00 0 0000E 00 0000E 00 HYDROSTATIC 0 0000E 00 0000E 00 2152E 09 6267E 02 6 4483E 07 0000E 00 CURRENT DRAG 1 0136E 06 6010E 02 0000E 00 2831E 01 5175E 06 0000E 00 YAW DRAG 0 0000E 00 0000E 00 0000E 00 0000E 00 0 0000E 00 0000E 00 WIND 2 8859E 05 2841E 02 0000E 00 3426E 01 2253E 06 0000E 00 DIFFRACTION 5 7944E 07 1934E 00 7798E 07 9661E 01 9000E 07 4530E 00 LINEAR DAMPING 7 4324E 06 1 5797E 01 3237E 07 6263E 01 4798E 06 3228E 01 L WAVE DRIFT DAMPING 3220E 03 5 2329E 05 0000E 00 0000E 00 0000E 00 8110E 02 DRIFT 2039E 05 1 1600E 01 2979E 04 3133E 00 3571E 07 5399E 01 MOORING 1421E 06 2 5000E 01 7117E 04 4000E 01 2719E 07 9531E 01 THRUSTER 0 0000E 00 0 0000E 00 0000E 00 0000E 00 0 0000E 00 0000E 00 RADIATION FORCE 3339E 07 1 8927E 00 5764E 06 4425E 02 6 2582E 07 0646E 01 TOTAL REACTION FORCE 0 0000E 00 0 0000E 00 0000E 00 0000E 00 0 0000E 00 0000E 00 TOTAL FORCE 2 6217E 07 5 1515E 00 1171E 07 8185E 02 4 2145E 07 0194E 01 ERROR PER TIMESTEP 9 3614E 05 1 2896E 10 5325E 06 1573E 13 4 6043E 08 2283E 13 TENSION
41. LINE 1321E 05 3 4520E 02 5818E 03 TENSION 4 1322E 05 TENSION LINE 0549E 04 1 4771E 06 4246E 03 TENSION 1 4772E 06 TENSION LINE 5342E 06 4326E 01 6859E 03 TENSION 2 5342E 06 TENSION LINE 0549E 04 4771E 06 4247E 03 TENSION 1 4772E 06 Figure 7 14 Timestep Printout The following describes each of the variables the sequence numbers of the variables are listed in the AQWA Reference Manual 4 18 6 1 POSITION Total position of structure centre of gravity in the Fixed Reference Axis 2 VELOCITY Total velocity of structure centre of gravity in the Fixed Reference Axis 3 ACCELERATION Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 73 of 119 AQWA DRIFT User Manual Description of Output 10 11 12 14 17 19 Total acceleration of structure centre of gravity in the Fixed Reference Axis RAO BASED POSITION FAST position of structure centre of gravity calculated by summing the real part of the product of complex response amplitude operator and the wave spectrum for each frequency forming the wave spectrum RAO BASED VELOCITY FAST velocity of structure centre of gravity calculated by summing the real part of the product of complex response amplitude operator of velocity and the wave spectrum for each frequency which forms the wave spectrum WAVE FREQ POSITION Rapidly varying part of total position filtered from POSITION WAVE FREQ VELOCITY Rapidl
42. Manual Description of Output x HYDRODYNAMIC PARAMETERS FOR STRUCTURE PERIOD FREQ DIRECTION 73E 06 90 50E 00 E 83E 07 52E 06 90 09E 01 65E 07 89E 07 90 76E 01 39 42E 07 70E 07 90 91E 01 18 L6E 07 22E 06 90 S7TE 06 90 83E 07 87E 06 90 260E 06 90 65E 07 64E 07 90 00 54E 07 44E 07 48E 07 90 00 47E 07 18E 07 output line continued below 60E 01 21E 07 O1E 01 60E 01 24E 07 s 41E 01 5 10E 00 p 29E 08 3 43E 01 82 80E 00 25E 08 g 09E 01 10 1 61E 07 89E 07 1 57E 03 0 2 00E 07 84E 07 4 40E 03 0 62E 07 09E 08 3 97E 07 18E 07 03E 08 44E 07 Figure 7 9 Froude Krylov Forces Moments 7 3 4 Mean Wave Drift Forces The mean wave drift forces and moments as a function of wave period and direction are output as shown in Figure 7 10 They are given for each body and for the range of user specified frequencies Note that the mean wave drift forces are proportional to wave amplitude squared and are given for Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 68 of 119 AQWA DRIFT User Manual unit wave amplitude x WAVE DRIFT LOADS FOR UNIT WAVE FORCES FREQUENCY DIRECTION DEGREES DUE TO RADIANS SEC Description of Output AMPLITUDE 2 21E 03 2 03E 03 2 29E 03 23E 02 7 43E 03 1 95E 04 03E 05 18E 05 94E 05 01E 05
43. ND STATIC ENVIRONMENT Input for Stage 1 of the analysis is only necessary if the restart stage at which the analysis begins is 1 see Chapter 5 If the restart stage is greater than 1 there is NO INPUT for Stage 1 of the analysis 6 1 1 Description Summary of Physical Parameters Input The data input in these decks relates to the description of each structure and the environment which normally remains unchanged throughout the analysis This includes any point referenced on or surrounding the structure the mass inertia hydrostatic and hydrodynamic model and the constant water depth i e the coordinates of any point on the structure or its surroundings referenced by any other deck element description of the structure mass and geometry using plate point mass point buoyancy and tube elements see Appendix H of the AQWA Reference Manual a table of material values associated with each element a table of geometric values associated with each element the depth and density of the water and acceleration due to gravity The data requirement for each program in the AQWA suite is not the same and also depends on the type of analysis to be performed These requirements are listed in detail in the later sections of this chapter 6 1 2 Description of General Format The input format of these decks is designed to provide checking on the data for the average user and outputs a suitable message to inform the user if the instructions for da
44. Non Linear Elastic Hawsers ec eceescescesscesecssecsseceecseecseeeseeeseseseseceseceseceaecsaecsaecsaecsaseaeseaeeeneeeens 41 4 14 2 Constant Tension Winch Lame ys cc cococecces cs eicdsh sence eck she cocasneeus ce ete cocbathevecb inte se cioensses cebu eS E EEE Oae ches 42 4 14 3 Constant Force Lines erore eo er EEE EE E EEE abst E data awed bins E cele itetoad ates 42 4 14 4 Composite Catenary LINE isi sc sss sce iesse e ae suas eeinetan rieh eE R EEEE EE ENEE E rov Ee E S E E EEES 43 4 14 35 Steel Wire Cables e sc erraien eaa REO EE o E E a e ESEE N E EE E ESAEREN ES e 43 4 14 6 Intermediate Buoys and Clump Weights cece cesecssecssecseeeeeeeeeeeeeeseeecesecaecsaecsaecsaecaeecaeseaeseneseeeeereeeeens 43 414 7 Pulley PULY veaa oe a ines vec aaie ienee pra e oeae Sa e ae SKI E ae EE Ee sadeshestestaa as veestheey 43 474 8 Drum Winch A NDW rrin a a a a E E E E NSN 43 4 149 Benders PEND e r a E A r p A e a a aE RAE a a E e ERSEK 43 4 15 ITERATION PARAMETERS FOR SOLUTION OF EQUILIBRIUM AQWA LIBRIUM ONLY 44 4 16 TIME HISTORY INTEGRATION IN IRREGULAR WAVES 000 ccceceeeeeeceseceeeeeeeeseeesecaecnaecsaecaaesaeeeaeeees 44 41 6 1 Time step for Simulations icenian r aeee pes ao a E rE ar EEE sash bees ea re Eor TT REE aE 44 4 16 2 Simulation Length and Accuracy Limits eseseessseeeseeesseesesrreresreerssrsrtststentesrentssrerinertentestentsseeersserrrsesent 44 4 16 3 Initial Conditions and Start Times ccssce
45. OSITION 0 9248 0 0000 10 6878 0 0000 0 1493 VELOCITY 0 0031 0 0000 0 0168 0 0000 0 0259 Figure 8 20 Slow motion position and velocity at 3200 seconds Figure 8 21 shows the data file for the drift wave frequency simulation Several changes to the data deck used for the drift analysis need to be made for the wave frequency simulation These are as follows JOB CARD The analysis type for a run in which wave frequency forces is added must be indicated by WFRQ Deck 9 Since the simulation will have all six degrees of freedom active the diagonal damping coefficients are input Deck 12 Since the simulation will have all six degrees of freedom active no freedoms are de activated Deck 15 The slow position and velocity obtained from the drift run are input Deck 16 The timestep is set to 0 5 second typical for wave frequency response The total number of time steps is 200 as explained above The simulation starts at time 3200 seconds this is when the slow position and velocity in Deck 15 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 107 of 119 AQWA DRIFT User Manual Example of Program Use occurred and ensures that the structure is subjected to the same force time history as before Deck 18 Hawser tensions are the only additional information required information is printed every twentieth time step JOB BOX1 DRIF WFRQ TITLE DRIFT WAVE FREQUENCY
46. QWA LINE is achieved by specifying one or more elements which in total describe the whole structure The only elements required are POINT MASS elements A point mass has a position a value of mass e g 12 tonnes and a mass inertia These in turn are defined by the specification of a node number a material number a geometric group number The node number described in the previous section and the material and geometric group number are numbers which refer to a table of values of coordinates masses and structural inertias respectively Once defined in the table the numbers may be referred to by any number of elements Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 35 of 119 AQWA DRIFT User Manual Modelling Techniques 4 5 MORISON ELEMENTS There are three Morison elements available within AQWA DRIFT and AQWA NAUT namely Tube element TUBE Slender Tube element STUB Disc element DISC Tube elements are defined by specifying end nodes diameter wall thickness and end cut lengths over which the forces are ignored Each tube element may have a different drag and added mass coefficient associated with it Drag coefficients can be defined as functions of Reynolds Number Full consideration is given to the variation of local fluid motion over the tube length and to partial submersion of members Morison drag and added mass are evaluated on all submer
47. QWA Reference Manual The data file is constructed by a series of data decks A summary of all possible data that may be input is listed together with a summary for various forms of analysis In this latter case a TYPICAL input data summary is used where the more unusual facilities have been omitted Most data requirements listed are optional unless specified otherwise and if not input the program defaults are used These defaults may be found together with the detailed format description in the AQWA Reference Manual Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 51 of 119 AQWA DRIFT User Manual Description of Output 6 0 ADMINISTRATION CONTROL DECK 0 PRELIMINARY DECK This deck is always required when performing AQWA program analysis runs The information input relates directly to the administration of the job being done and the control of the AQWA program being used Program control has the following functions identification of the program to be used within the AQWA suite the type of program analysis to be performed i e if choice exists the analysis stage to be performed i e restart stages Administration of the analysis being performed is as follows user title identification given to the analysis choice of output required from program run i e program options The above information is input to the program through the following cards containe
48. RIFT User Manual Theoretical Formulation from the damping by a Fourier transform and inverse non symmetric transform and vice versa In other words a frequency dependent damping implies the existence of a frequency dependent added mass and vice versa If user input of frequency dependent added mass and damping is accepted in the future for convolution then it will be required to obey this criterion By using the convolution method the motion responses are determined by t MM M o fi t Ka t h t r 7 de F t 3 17 1 0 where M the structural mass matrix M the added mass at infinite frequency K the hydrostatic stiffness X t the acceleration response vector F t total external forces including wave exciting forces mooring forces drift forces drag forces constraint forces etc h t the acceleration convolution integral function matrix CIP The convolution method as implemented in AQWA DRIFT and NAUT has 4 distinct stages 1 Extrapolation of added mass damping from zero to infinite frequency 2 The calculation of the time history convolution integral function CIF 3 Interpolation of the CIF at an integral number of time steps 4 Calculation of the radiation force at any time by integrating the CIF Steps to 3 are performed for each analysis before starting the time history simulation The convolution method as a method of evaluating the radiation as well as the diffraction forces appea
49. T is not symmetric In general only a structure in static equilibrium will have a t symmetric stiffness matrix where T is the transpose matrix of T However this also means that if the mooring forces are in equilibrium with all other conservative forces then the total stiffness matrix will be symmetric The force at the centre of gravity Fg in terms of the forces at the attachment point F4 is given by Fel y Fl 3 10 4 3 10 6 Stiffness Matrix for a Mooring Line Joining Two Structures When two structures are attached by a mooring line this results in a fully coupled stiffness matrix where the displacement of one structure results in a force on the other This stiffness matrix may be obtained Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 23 of 119 AQWA DRIFT User Manual Theoretical Formulation simply by considering that the displacement of the attachment point on one structure is equivalent to a negative displacement of the attachment point on the other structure Using the definitions in the previous section the 12x12 stiffness matrix K is given by I 0 0 0 0 t Ta 0 PT 0 0 K _ K T 1 T a vate wee ah 3 10 5 t t T 0 0 0 P T where 0 Z Sy 0 Pe Py T z 0 x P P 0 Py y x Py i 0 X Y Z Coordinates of the attachment point on the second structure relative to its centre of gravity Px Py Pz X Y and Z components of the tens
50. UN eee ese ereeeeeeeeeeeeeeeees CHAPTER 9 RUNNING THE PROGRAM 00 cieceeceecceseceecesecseeaecaeceaecaaecaeecaeseaeseeeeeeeeeenes 9 1 File Naming Convention for AQWA Files cece ee ceecesecssecseecseeeeeeeeeeeseeeenseeeseeaeenaessaeeaes 9 2 AQWA Pile Organisation veseo epeei epee eea i e e dopder thd dvedesbeestesteav eee 9 3 Program Size REQUIFEMENIS sene R A E S R E E E 9 4 R n COMMMANGS 5 the esn ienei E ESR S e E Ea a SE HS IAS RES SEs e ETENE APPENDIX A AQWA DRIFT PROGRAM OPTIONS 1 00 eeeceeecseeseeeeeeeeeeeseeseenseeesecaeesaeeaee APPENDIX B REFERENCES wees odes eee hain ae Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Contents Page 8 of 119 AQWA DRIFT User Manual Introduction CHAPTER 1 INTRODUCTION 1 1 PROGRAM AQWA DRIFT is a computer program which simulates the motion of floating structures arbitrarily connected by articulations or mooring lines under the action of wind wave and current forces The program has the following two modes of operation 1 Slow drift mode in which the structure is subjected to only the second order wave forces steady wind and current 2 Wave frequency mode in which both slow drift and wave frequency forces are included along with wind and current The program requires a full hydrostatic and hydrodynamic description of each structure This can either be input as data or transferred directly from the output re
51. User Manual Theoretical Formulation vector 3 10 MOORING LINES The types of mooring lines available include both linear and non linear cables These can be summarized as follows A Linear Cables Linear elastic cables LINE Winch cables WINCH Constant force cables FORC Pulleys PULY Drum winch cable LNDW B Non Linear Cables Steel wire cables SWIR Non linear cables described by a POLYNOMINAL of up to fifth order POLY Composite catenary cables COMP Intermediate buoys and clump weights BUOY Finally fixed and floating fenders FEND can be defined These are classified as a type of mooring line and have non linear properties 3 10 1 Force of Constant Magnitude and Direction The constant FORCE line acts at the centre of gravity of the body in question The force magnitude and direction are assumed fixed and DO NOT CHANGE with movement of the body Thruster forces which do change direction with the body are described in Section 3 9 3 10 2 Constant Tension Winch Line The WINCH line maintains a constant tension provided the distance between the ends of the line is greater than a user specified unstretched length The direction of the tension depends on the movement of the end points 3 10 3 Weightless Elastic Hawsers The elastic hawser tensions are simply given by the extension over the unstretched length and their load extension characteristics The load extension characterist
52. When only drift wave forces are present the structure will execute drift oscillations This motion is termed the slow motion and its position the SLOW POSITION When both drift and wave frequency forces are present the structure will still perform drift oscillations but these will be accompanied by wave frequency oscillations about the slow position The oscillation about the SLOW position is called the WAVE FREQUENCY POSITION The sum of the slow position and the wave frequency position is called the TOTAL position referred to as simply the POSITION 3 14 5 Response Amplitude Operator Based Position The wave frequency response of the structure is determined by AQWA LINE and is stored in the form of response amplitude operators at a series of frequencies A time history of the wave frequency response can be fabricated by combining the response amplitude operators with the wave spectrum This is done for each degree of freedom as follows Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 27 of 119 AQWA DRIFT User Manual Theoretical Formulation NSPL latik F wr Re Dy aga ol E a 3 14 4 j l This is called the response amplitude operator based position RAO BASED POSITION and is used to calculate the initial FAST position to minimise transients see Section 3 14 7 A similar expression is used to calculate the RAO BASED VELOCITY using the fact that NSPL EE w Re iaja x
53. a short name up to 26 characters to identify a particular run It is suggested that lower case names be used All the filenames associated with the run will contain the same run identifier in their names a three character string to identify the type of the AQWA file restart file hydrodynamics file etc The file extension is separated from the rest of the filename by a character The filename alvicc dat consists of the prefix al short for AQWA LINE the run identifier vlcc e g name of vessel the extension dat input data file Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 111 of 119 AQWA DRIFT User Manual Running the Program 9 2 AQWA File Organisation Every run of an AQWA program involves the use of a number of specially named input output and backing files The following files are used by AQWA DRIFT res file restart file backing file The restart file is used to store all information relating to the structures being analysed This information can easily be retrieved on the next run of the analysis sequence so the input data for the next run can be considerably simplified This file is an unformatted binary file hyd file hydrodynamics database file backing file This file is read by AQWA DRIFT and contains a subset of the restart file It is read only if the ALDB option is used or restart from stages to 5 pos file
54. ad pI AAE W A Le UU I LO 1000 0 Mooring Force Line tension See 2S ES SSS SS SUL Ve Lh ee Ae V 0 0 1000 0 Mooring Force Line 3 tension 0 0 1000 0 Mooring Force Line tension 2000 0 Tinel seconds A WY wy eye 2000 0 i i Timed seconds Sar ae ie nen al Male eas Seah see eee a niet a d 2000 0 Timed seconds Figure 8 19 Time History of Tension in Hawsers 1 3 And 4 8 1 17 Input for Drift Wave Frequency Simulation Run Now that the user has an indication of the drift motions of the structure the effect of adding in wave frequency forces can be investigated Since this requires a much shorter time step it is usual to perform a simulation which includes wave frequency forces only over a short segment of the drift time history In this example the wave frequency simulation will start at 3200 secs and end at 3300 seconds a range which spans the instant of maximum surge displacement in the drift time history Inspection of the output listing from the drift run yields the slow position and velocity at time 3200 seconds as shown in Figure 8 20 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 106 of 119 AQWA DRIFT User Manual Example of Program Use JOB TITLE DRIFT MOTION RUN FREEDOM TIME SECS STRUCTURE POSITION FORCES NUMBER AND MOMENTS AT RECORD NO CENTRE OF GRAVITY SURGE SWAY HEAVE ROLL PITCH P
55. ader page used for identification Card echo mandatory for Decks 9 to 18 This is used to check data input Yaw rate drag and Drift Frequency Added mass and Damping An echo of the data input in Deck 9 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 87 of 119 AQWA DRIFT User Manual Example of Program Use Figure 8 6 Figure 8 7 Figure 8 8 Figure 8 9 Figure 8 10 Figure 8 11 Wind Current Loads and Thruster Forces A tabulation of the data input in Deck 10 The omission of thruster forces is also brought to the user s attention Constraints The table shows X Y RZ freedoms active Cable Mooring Line Configurations Tabulation of the mooring lines input in Deck 14 Note that the cable group number is only applicable to non linear mooring lines Initial Conditions of the Centre of Gravity Tabulation of the initial position and velocity input in Deck 15 Time Integration Parameters Details of the simulation length and timestep The expected errors for the specified timestep are indicated Note that the error for the expected response period of 92 seconds is about 0 3 per cent Position of User Requested Nodes Tabulation of the nodes and their positions input in Deck 18 Note that the positions shown are those in the last analysis position input in Deck 15 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page
56. aj the amplitude of the regular wave component Xp the distance from the origin of the wave system perpendicular to the wave Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 26 of 119 AQWA DRIFT User Manual Theoretical Formulation direction Ej random phase at frequency Oj the j th frequency kj the wave number at frequency j gt fi the complex total wave force at frequency j gt xy the complex position at frequency i e the complex response amplitude operator ij Equation 3 14 2 shows how a mass difference correction and a damping difference correction are applied to the total wave force to correct for the variation of added mass and damping with frequency This correction involves a best estimate of the wave frequency response at each frequency calculated from the linear equation of motion at that frequency The modified total wave force is calculated and added to the sum of all other forces to form the equation of motion for drift and wave frequency motions M My i t Fy t Fe t Fyy t F t Fy t Fa t Fyp t 8 14 3 where all terms are as previously defined 3 14 4 Slow Drift and Wave Frequency Positions The total motion of the structure can be thought of as comprising a slow drift motion and a fast wave frequency position These slow and wave frequency positions added together give the total position
57. ange of variation For example in Figure 7 15 the X or surge position is greater than 1 76 and less or equal to 2 0 for 3 5 of the time Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 76 of 119 AQWA DRIFT User Manual Description of Output A FEE Re So AE LETER Rebs SUV AE ee oe STRUCTURE 1 POSITION OF COG MEAN VALUE 2 x RMS MEAN HIGHEST 1 3 PEAKS MAXIMUM PEAKS MINIMUM PEAKS PROBABILITY PER CENT RANGE RANGE PER CENT RANGE PER CENT RANGE PER CENT RANGE DISTRIBUTION LIMITS OCCUR LIMITS LIMITS OCCUR LIMITS OCCUR LIMITS OCCUR LIMITS Figure 7 19 Statistics Summary Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 77 of 119 AQWA DRIFT User Manual Example of Program Use CHAPTER 8 EXAMPLE OF PROGRAM USE In this chapter an example problem using AQWA DRIFT is illustrated The problem is one in which AQWA LINE has been used to perform the analysis Stages 1 to 3 All steps in the subsequent analysis procedure are clearly shown from the problem definition through the data preparation to the final analysis run itself The method used in this chapter can be easily followed by the user and if so desired the user can repeat the whole procedure using the same data as used here to obtain the same results In this manner the new user can quickly gain confidence in using the program Contains proprietary
58. ant Tension Winch Line The winch line is characterised by its constant tension attachment points and unstretched length The attachment points are specified as nodes and determine the direction of the constant tension The unstretched length allows the line to go slack when the distance between the end points is less than it If the user requires constant tension at all times a zero unstretched length may be input 4 14 3 Constant Force Line The program allows the user to input a force of constant magnitude and direction The force is always assumed to act at the centre of gravity of the body The direction of the force is specified using a node on the body and a second node chosen such that the force vector is directed from node 1 to node 2 Once the Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 42 of 119 AQWA DRIFT User Manual Modelling Techniques direction is defined the program maintains the magnitude and direction despite movement of the body This facility can be used to input environmental forces where details of the forces e g wind coefficients are not available 4 14 4 Composite Catenary Line The composite catenary model admits elastic catenary lines Current drag on the line itself is ignored if without cable dynamics option The line is specified by the end nodes length weight in air per unit length and equivalent cross sectional area The equ
59. ave system perpendicular to the wave direction aj the amplitude of the regular wave component Ej a random phase angle A t the instantaneous wave elevation at time t and the sum is over the number of regular wave components in the wave spectrum NSPL Similarly the total wave force at each time step is given by the following expression NSPL i oj tk xp Fy t Ref gt ajfje E R es a 3 3 2 j l where a the complex total wave force per unit wave amplitude at frequency and again the summation is over all the frequencies forming the spectrum Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 16 of 119 AQWA DRIFT User Manual Theoretical Formulation 3 4 MEAN WAVE DRIFT FORCES AQWA DRIFT does not explicitly calculate the mean wave drift force on each structure in a spectrum The mean drift force is the average effect of the slowly varying wave drift force which is calculated as described in Section 3 5 The program requires the regular mean wave drift force coefficients over a range of frequencies These are calculated by AQWA LINE or an equivalent program The theory of regular wave drift forces is contained in Section 3 4 of the AQWA LINE manual 3 5 SLOWLY VARYING WAVE DRIFT FORCES When a body is positioned in a regular wave train it will experience a mean wave drift force which is time invariant If the wave environment is composed of more than one wave
60. bove 8 1 4 Low Frequency Added Mass and Damping It may be assumed that at low frequency the added mass and damping remain constant as values of drift added mass for the horizontal freedoms tend towards finite values at low frequency The values often used are those of the lowest wave frequency input in AQWA LINE This is normally a good approximation However for damping empirical values may be input based on either the experience of the user or experimental results For this example values of added mass at the lowest frequency defined in the AQWA LINE run will be used Note that for the evaluation of undamped natural periods no drift damping is used This applies to the initial AQWA DRIFT run 8 1 5 Hull and Superstructure Loading Coefficients Data for the force coefficients for wind and current in this example are based on the projected area through the centroid in the three directions specified in Deck 10 as well as the drag coefficients at each heading Wind and Current forces per unit velocity acting on the body are given by Force 0 5 Density Area Drag coefficient cos relative heading In this example the drag coefficient at heading 0 or 90 degree is 1 6 whilst at 45 degree it is 1 3 Thus the forces in the X and Y directions due to currents at 0 45 and 90 degree headings are Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 82 of 119 AQWA DRIFT User Man
61. ces are recalculated at each time step in the displaced position The forces are determined from the linear stiffness matrix the defined vertical position of the centre of gravity and the buoyancy force acting on the structure at equilibrium This is given by F t B K X 0 3 1 1 where B the buoyancy force on the structure at equilibrium K the six degree of freedom stiffness matrix at the equilibrium position i the position and orientation of the centre of gravity w r t the FRA x t the position and orientation of the structure at time t w r t the FRA F hys t the hydrostatic force and moment at time t 3 1 2 Hydrostatic Equilibrium The description of all wave forces and the added mass damping and stiffness matrices of a particular structure must be calculated and input at a position of hydrostatic equilibrium i e the net hydrostatic and gravitational forces and moments must be zero It is the motions about this position that AQWA DRIFT calculates For more details of rules governing hydrostatic equilibrium see AQWA LINE manual 3 1 3 Hydrostatic Stiffness Matrix For rigid body motion analysis about a mean equilibrium position AQWA DRIFT requires a hydrostatic stiffness matrix for each body If the matrix is expressed in terms of motions about the centre of gravity it will take the following form 00 0 0 0 0 00 0 0 0 0 err 0 K33 K34 K35 0 0 0 K43 K44 K45 K46 0 0 K53 K54 K55 K56 10 0 0 0 0 0
62. d in Deck 0 JOB Card This contains information stating the program to be used the type of program analysis to be undertaken and the user identifier for the run in question TITLE Card This lets the user prescribe a title for the run OPTIONS Card Various program options are available within the AQWA suite which are common to all programs while others are for use with specific programs The options within AQWA DRIFT control the type of output required from the program and the restart stages of analysis to be performed see Appendix A RESTART Card If the restart option is used then the start and finish stages of the analysis must be prescribed via the restart card For complete details of the above card formats see the AQWA Reference Manual For a list of options for use within AQWA DRIFT see Appendix A One option commonly used is the DATA option and it is worth noting its purpose The DATA option performs Stages 1 to 4 of an AQWA DRIFT analysis This means that all information relating to the analysis is read in allowing all data checking to be performed After the user is satisfied with the acceptance of data then the analysis can be undertaken by restarting the program at Stage 5 to perform the analysis itself Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 52 of 119 AQWA DRIFT User Manual Description of Output 6 1 STAGE 1 DECKS 1 TO 5 GEOMETRIC DEFINITION A
63. d wave frequency motions A suitable time step in this case will be much shorter since the response to wave frequency forces is being investigated A time step of 0 5 seconds is typical Once a time step has been selected the program outputs an indication of the expected errors using the chosen time step This is explained in Section 7 6 in the description of the output The program also outputs the error at each time step in each degree of freedom which is related to the chosen time step These errors can always be reduced by shortening the time step 4 16 2 Simulation Length and Accuracy Limits For the time history of motion in an irregular sea to be representative of the structure s motion characteristics in that sea the time history has to be of sufficient length to allow averaging of maximum and minimum response Motions simulated over a finite length of time contain some statistical error because the sample may by chance contain an unrepresentative number of large or small oscillations Rainey et al 1982 explained that the variance of the mean square value of the slow drift position can be Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 44 of 119 AQWA DRIFT User Manual Modelling Techniques Reference 5 explains that the variance of the mean square value of the slow drift position can be calculated assuming linear mooring stiffness and linear damping This can provide a useful
64. damping for yaw motion only NYWD NO YAW WAVE DRIFT DAMPING This option suppresses the calculation of wave drift for yaw motion To prevent the calculation of ALL wave drift damping use the NOWD option RDDB READ DATABASE Read the hydrodynamics database from the restart RES file created by a previous AQWALINE run This option is used if the user wishes to modify the hydrodynamic data calculated in a previous AQWA LINE run without having to re run the AQWA LINE radiation diffraction analysis Note Normally this would be done using the option ALDB see above The RDDB option is only needed if the hydrodynamics file from the previous AQWA LINE run has been accidentally deleted Note that as the model definition has to be read from the restart file before the hydrodynamics can be read there is no possibility to change the model definition when using this option use ALDB instead REST RESTART This option is used when the program is being restarted at any stage greater than the first see Section 5 2 of the AQWA program manual A restart card must follow the options list when the restart option is used This card indicates the stage at which the program is to continue and the stage at which the program is to stop see Chapter 2 SDRG USE SLOW VELOCITY FOR HULL DRAG CALCULATION This option is used if users wish to use the slow velocity drift frequency velocity for the hull drag calculation instead of the total velocity
65. drag are both calculated in a similar manner from a set of user derived environmental load coefficients covering a range of heading angles The input coefficients are defined as ee 3 8 1 drag force or moment wind or current velocity The force is calculated at each time step by Fj C u u u u 3 8 2 where F the force vector for degree of freedom j C 0 the value of the wind or current coefficient for wind relative angle of incidence 0 uU Us the velocity relative to the slow position of the structure for the current or the velocity relative to the total position of the structure for the apparent wind Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 19 of 119 AQWA DRIFT User Manual Theoretical Formulation The wind or current velocity in the above expression u u is calculated to be the relative velocity between the absolute wind or current velocity and the velocity of the structure If the time scale of the wind and current flow is much longer than the typical wave periods so the wind and current flows do not have time to develop in response to the wave frequency variations of position an optional card SDRG in DECK 0 can be used to use the SLOW velocity drift frequency velocity for the hull drag calculation instead of the total velocity which is drift frequency velocity plus wave frequency velocity According to the above definition the coe
66. dy Material properties of the various elements Geometry group properties of the elements The information received by AQWA DRIFT to define the mass distribution body characteristics is output for checking and the body s resultant centre of mass and inertia matrix are also output The nodal coordinates are output in the Fixed Reference Axes and the format is shown in Figure 7 1 x COORDINATE DATA INPUT NODE SEQUENCE NO Figure 7 1 Nodal Coordinate Output Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 61 of 119 AQWA DRIFT User Manual Description of Output Following the nodal coordinates each element s topology is output as shown in Figure 7 2 Each structure element is numbered 1 2 3 etc in the order which it appears in the intput It is also worth noting that this element topology output may be enhanced by more detailed information This is obtained by using the PPEL program option i e Print Properties of ELements ee Re OE E Mi Ey NE T O B0 Ta OG y ELEMENT NODE NODE NODE NODE MATERIAL GEOMETRY NUMBER TYPE NUMBER NUMBER NUMBER NUMBER NUMBER NUMBER AANA OF WN EF PRrPRPRPER BwWNE OW a ol HGO GG ee I EPS E a OO aTr a HOGG T O AD A Ds a a O a ja Ov Figure 7 2 Element Topology Output The body topology output references the material group number which has a mass value associated with it The material group nu
67. e The result of this excitation at periods close to resonance is large amplification factors in the motions of the structure These motions are the drift frequency motions The equation of motion for the drift frequency motions is M My x t Fy t F t Fy t F t Fy t Fy t 3 14 1 where xX the acceleration vector M the structural mass and inertia M the added mass and inertia at drift frequency Fs the slowly varying drift force F the current drag force Fy the wind drag force F the mooring force F the hydrostatic force Fq the damping force It is assumed that the values of drift added mass inertia and damping are constant 3 14 3 Motions at Drift and Wave Frequency As well as being excited by drift forces the structure will also be subjected to the first order wave frequency forces These forces are added to the list of forces in the drift equation of motion in Section 3 14 2 Since the added mass inertia and damping are not constant over the wave frequency range these forces are modified to allow for this variation The total wave frequency force i e diffraction plus Froude Krylov in each degree of freedom is calculated by NSPL A theo jttk jxpt e Fal Re gt E T E J JP j 3 14 2 j 1 where CS eS xjj OFX x j 10 jx j the imaginary quantity y 1 M the drift added mass M _ the added mass at frequency j c the drift damping cj the damping at frequency
68. e 21 3 10 2 Constant Tension Winch Line sissioni seseo seisne a erten eare ao EE iE EE eSEE r k ere pIi Ea ooie 21 3 10 3 Weightless Elastic Hawsers seir tee ese een enro ta aerer N Eee e ee e Ea SN e ret EiS IE En e EE Vek 21 3 10 4 Composite Elastic Catenary Chains sessseeessseessseeessseserestsresesteereserrsertesterteetesrertnsertrssestentesrertnseereneesreneset 22 3 10 5 Translation of the Mooring Line Force and Stiffness Matrix esessesseseesssreesesreeresesresesreeresrenresrerensesrenesre 23 3 10 6 Stiffness Matrix for a Mooring Line Joining Two Structures 00 cee eeceeeeceeseesecesecesecssecaecsuecseecseseneeeas 23 3 I WAVE SPECTR Acts foci food ition ata Mob ee ha AU aes a eA ie eG ee et a reani 24 3 12 STABILITY ANAL YSIS ennes se ieee te n E A A A A A chen eee eg 25 3 13 FREQUENCY DOMAIN SOLUTION jcciie acne cei hn DR Me RA hs ae Ree ht ae 25 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 4 of 119 AQWA DRIFT User Manual Contents 3 14 TIME HISTORY SOLUTION IN IRREGULAR WAVES 000 icececcesecsecsseceecaeeeaecaeecaeeeneseaeeeeeeeeeeenseeseenaes 25 3 14 1 Time Integration of Equation of Motion cece cece cece cseeeeeeeeeeeecesecesecaecsaecsaecaaecaeecseseaeseeeeeseseeeseenaeenaes 25 3 14 2 Motions at Drift Frequency cinas ceneni einne atetecucbeceble SubccecnpUuseosh Vek oOo deantebechsdhevacbunelocsinersbebses 25 3 14 3 Motions at Drift and Wave Frequency
69. e additional frequencies Note that as all parameters are defined for a unique range of directions these directions must not be redefined To change the parameters calculated in a previous run these parameters are simply input in Decks 7 and 8 and depending on the type of input see individual deck sections in the AQWA Reference Manual the parameters will be either overwritten with the input values or become the sum of input values and original values 6 3 STAGE 3 NO CARD IMAGE INPUT DIFFRACTION RADIATION ANALYSIS There is no input data for Stage 3 as this is purely a calculation stage namely the calculation of the hydrodynamic properties by AQWA LINE Note that if AQWA DRIFT is being run independently then the data which would have been calculated by AQWA LINE must be input by the user from some other source in Stage 2 6 4 Stage 4 DECKS 9 to 18 INPUT OF THE ANALYSIS ENVIRONMENT Input to Stage 4 of the analysis is only necessary if the restart stage at which the analysis begins is less than or equal to 4 see Chapter 5 If the restart stage is greater than 4 there is NO INPUT for Stage 4 of the analysis 6 4 1 Description Summary of Parameters Input The data input in these decks relates to the description of the analysis environment and the structure coefficients associated with the environment Low frequency added mass and damping It is optional to input the added mass and damping associated with the low frequency mot
70. e backing file and this stage is completely omitted i e these decks are not required at all and must be removed from the card image data deck as the analysis is restarted at the beginning of Stage 4 6 2 5 Input for AQWA DRIFT with Results from a Source other than AQWA LINE Although the parameters calculated by AQWA LINE can be transferred automatically to other programs in the AQWA suite this is NOT mandatory This means that if the backing file produced by an AQWA Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 55 of 119 AQWA DRIFT User Manual Description of Output LINE run is NOT available e g AQWA LINE has not been run previously or the user wishes to input values from a source other than AQWA LINE then data may be input in these decks All data appropriate to the analysis summarised in Section 6 2 3 may then be input in card image format The exact input will depend on the type of analysis and the particular structure analysed Typically input data required is as follows a For a run analysing the drift motions only Deck 6 A range of frequencies A range of directions Deck 7 Linear stiffness matrix Deck 8 Second order drift forces b For a run analysing both the wave frequency and drift motions Deck 6 A range of frequencies A range of directions Deck 7 Linear stiffness matrix Added mass matrix Radiation damping matrix Diffraction forces
71. e commands available in the command file are listed below They are very similar to standard DOS commands comment line REM ECHO END RUNDIR RUN COPY RENAME MOVE DELETE Below is an example of running AQWA using a command file The run command could be C Program Files ANSYS Inc v120 aqwa bin win32 aqwa exe STD test com The file test com could be REM Example of a command file for multiple AQWA analyses RUN alt0001 echo TO001L AQWA LINE test complete copy alt0001 res abt0001 res RUN abt0001 RUN adt0001 RUNDIR C AQWA Projects Tests MODEL2 echo Change directory to path C AQWA Projects Tests MODEL RUN alt0002 END ALL RUNS COMPLETE Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 114 of 119 AQWA DRIFT User Manual Appendix A APPENDIX A AQWA DRIFT PROGRAM OPTIONS The options listed below may be used when running the program AQWA DRIFT They should appear on the options card which follows the job identification card in Administration Deck 0 see Section 6 0 ALDB READ AQWA LINE DATABASE Read the hydrodynamics database from the hydrodynamics HYD file created by a previous AQWA LINE run This option is used I If the user wishes to modify the hydrodynamic data calculated in a previous AQWALINE run or add modify nodes and non diffracting elements without having to re run the AQWA LINE radiation diffraction analysi
72. e to body motions and may be calculated by investigating the radiated wave field arising from body motions The active or wave excitation loading which induces motion is composed of diffraction forces due to the scattering of the incident wave field and the Froude Krylov forces due to the pressure field in the undisturbed incident wave The incident wave acting on the body is assumed to be harmonic and of small amplitude compared to its length The fluid is also assumed to be ideal imcompressible and irrotational hence potential flow theory is used Effects which are attributable to the viscosity of the fluid are taken into account in the calculation of the current loads and other hull forces The hydrostatic fluid forces may also be calculated using AQWA LINE and these when combined with the hydrodynamic forces and body mass characteristics may be used to calculate the small amplitude rigid body response about a mean position The mean second order wave drift forces may be calculated by AQWA LINE after the first order fluid flow problem has been solved These are used by AQWA DRIFT to calculate the slowly varying drift force on each structure The drift force is calculated at each time step in the simulation together with the instantaneous value of all other forces These are applied to the structure and the resulting acceleration calculated From this the position and velocity are determined at the subsequent time step The process is then repeated
73. ea Sa E pE AR S Eh OE i esas 14 3 2 MORISON FORCES sicesscisses cssceesites ekessanbestobin caesseahebeessegcheesseghbeksoes EEE EEE TEE EO EE T SEER E EEEE EE EErEE cts 15 3 3 DIFFRACTION RADIATION WAVE FORCES vietor cecccseeeceeecesscesecesecesecsecsaecsaecsaecaaecseseseseaeseeeeseeerenseenaeenaes 16 3 4MEAN WAVE DRIFT FORCES enera reker esre re Eer rE E TEOT S ey SEEE EE EEO ee DEEE rE asis 17 3 5 SLOWLY VARYING WAVE DRIFT FORCES i o 0 c ccsscccsscsscesssshsvessetessbastedssesoeeescensqebsbescebesehsetebssesdeossensssadesstevess 17 3 6 INTERACTIVE FLUID LOADING BETWEEN BODIES 1 0 ccc ecescceseceseceseceseceeecaeecaeeeaeeeaeeseeeseeeeeseenseenaes 18 3 7 STRUCTURAL ARTICULATIONS AND CONSTRAINTS ooo ceecssecneecaeeeaecaeecaeseeeesaeeeeeeeeneeseenseenaes 18 B71 Articulations srein a bees e estates E E EEE E SEE E E E EEEE ESEE E Sr r EEEE Eees 18 oE ORIEN E EE A EEE A E ET 19 3 8 WIND AND CURRENT LOADING i200 isc sscescissis cesssteebenssegcbenssaghbeksnes ches EE ENEE ESTE rE E E SEEE EE EEE EET E EErEE 19 3 821 Wand anid Et in nai a Ae EE E EEEE EE EEEN 19 3 8 2 Yaw Rate Drag Force sss scessehicisie sapessaebstines tecbeetee iin EE EEr E E eaten EEO rE E E deere 20 3 9 THRUSTER PORGES E E E T E se eaasteeess 20 3 10 MOORING LINES vpete rer aaeeea aeara rE ET E E EEEE EEE AEE TETEE E EEE E EE EE TEETE i 21 3 10 1 Force of Constant Magnitude and Direction e sessesseseesesrssresssteerssterrsrtstesresrestesretsertensrsrentsseeresseerreresreeesr
74. ed by program options 5 2 RESTART STAGES All programs in the AQWA suite have the facility of running one or more stages of the analysis separately These stages are referred to in the documentation as RESTART STAGES see Chapter 2 of the AQWA Reference Manual Use of the restart process thus implies that information is available on a backing file from a previous program run and not via the normal card image file This process is also used to transfer information from one program to another program in the AQWA suite These stages are as follows Stage 1 Geometric Definition and Static Environment Stage 2 Input of the Diffraction Radiation Analysis Parameters Stage 3 The Diffraction Radiation Analysis Stage 4 Input of the Analysis Environment Stage 5 Motion Analysis Note that the graphics will allow visualisation of the geometric model and parameters at any point in the analysis e g Stages 2 to 5 are not required to visualise the data input in Stage 1 This only applies to the graphics as all other programs must progress from one stage to another with NO stages omitted As Stage 3 has no direct calculations in programs other than AQWA LINE the programs will correct a request to finish at Stage 2 to one to finish at Stage 3 This remains transparent and requires no action by the user 5 3 STAGES OF ANALYSIS An analysis using AQWA DRIFT independently uses the items to 7 of the following If the program is Contains
75. ed spectrum and its direction are input here as well as definitions of current and wind Deck 15 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 101 of 119 AQWA DRIFT User Manual Example of Program Use The expected mean position from AQWA LIBRIUM Deck 16 The simulation length is 4000 seconds 800 steps of 5 seconds Deck 18 Output details at every eightieth time step are requested to avoid excessive printout The hawser tensions are requested as additional output JOB BOX1 DRIF DRFT TITLE DRIFT MOTION RUN OPTIONS CONV PBIS FOTF REST END RESTART 4 4 ALBOX22 09 DRM1 ENDO9FIDD 3 4758E7 3 4758E7 9253E7 3 0156E9 3 0156E9 3 0002E9 0 HLD1 OSYMX OSYMY ODIRN OCUFX OCUFY OCURX OCURY OWIFX OWLFY OWIRX OWIRY WWWWWWWwW WwW Ww 4715E6 4715E6 4715E6 4715E6 0 0000 0 0000 0 0365 0 0000 8PREV 8PTEN Figure 8 15 Data File For Drift Motion Data Run Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 102 of 119 AQWA DRIFT User Manual Example of Program Use 8 1 15 Drift Motion Simulation Run When the data run has been completed successfully without error the full drift motion simulation analysis can be performed The data file required to run the simulation is as follows JOB BOX1 DRIF DRFT TITLE DRIFT MOTION RUN OPTIONS CONV PBIS FOTF REST END RESTART 4 5 AL
76. efficients can be increased significantly in shallow water In AQWA there is the option of including the second order incident and diffracted potential and performing difference frequency calculations using the full QTF matrix as opposed to Newman approximation If the full difference frequency calculation is performed then the in phase component Pi in equation 3 5 2 consists of 5 components including waterline integral Bernoulli acceleration momentum and 2 order potential terms See AQWA LINE Manual 3 4 3 for detail The evaluation of the out of phase components Qj is similar to that followed for the in phase components Pj In AQWA LINE all the out of phase and in phase components can be evaluated 3 6 INTERACTIVE FLUID LOADING BETWEEN BODIES The importance of fluid interaction between structures will depend on both body separation distances and the relative sizes of the bodies All the programs in AQWA can now handle full hydrodynamic interaction including radiation coupling for up to 20 structures This is essential for accurate modelling of vessels which are in close proximity The hydrodynamic interaction is applicable to all AQWA programs and includes not only the Radiation coupling but the Shielding Effects as well There are some restrictions the main ones being that shear force bending moment and splitting force cannot be calculated in the AGS if two or more hydrodynamically interacting structures are modelled 3 7 STRUCTUR
77. erererersererererserersrerereersrerersreereererereseesersrerersererererereerere 59 6 6 1 Ruin Stage G AlOME si scx dieses eeraa e eeaeee a Nae eean ee e aa Eo sev Mb ceageneed ied ncbleleecsde nl eei 59 6 6 2 Run Stage 6 with starting stage less than 5 s sesseeessersesssesreeseseeereseerrsstrrrssestentssrerssrerstestesresreeresrerrsserrrnresreet 59 CHAPTER 7 DESCRIPTION OF OUTPUT rtre sarrere rosero aaao eoe EE EEEE ra TESSE E Eeee SEa EKSE a Poa EEES Esri 60 7 1 STRUCTURAL DESCRIPTION OF BODY CHARACTERISTICS 000 eee ceeecseecsecseecseeeeeeeaeeeeeeeeenseenseesseenaes 61 7 1 1 Coordinates and Mass Distribution Element 00 0 0 ccc eecesecesecesecnseceeecseeeeeeeeeeeeceeeesecsecaecsaecsaecaaeeseeeneeeas 61 7 2 DESERIPTION OF ENVIRONMEND s csitsveek iitintiaid a Athi aaron oi E E T devi R E oy 64 7 3 DESCRIPTION OF FLUID LOADING gj visesscescestecastcsssessiescspecssetssesvet datas sssnuesostssseoscedscesoesssepstcpansasesossoessesbeosscsvede 65 73 AA ydrostatic Strittiess 5205 seessetes chop chpessauebeeenes capeteesbsbes sheebsterkebsaes onpageenesysece cdpcbscusbethouseapesssteanbuensheessernetsoea ees 65 7 3 2 Added Mass and Wave Damping iss cs2csensscecseesoseveepsupsvecn cite ssae su pevseubessceabsopveyeh os SENK ENEKEN ENPE Sy Eaa De SE EAEE EES Hee 66 7 3 3 Oscillatory Wave Excitation POrces siscsissc cosisseesssasoes skeedbeesstsaey ipis ir EE EEEE rE erT io EE E EEEE ETa 67 7 34 Mean Wave Drit FOLCeS asiera isre seese e e
78. es Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 81 of 119 AQWA DRIFT User Manual Example of Program Use 8 1 3 Natural Frequencies It is good practice when using AQWA DRIFT to perform some short and simple preliminary runs to ensure that the model has been formed correctly before embarking on long simulation runs where errors in modelling may be more difficult to identify The first check is to ensure that the model has the correct natural periods This is achieved by performing a short run with the structure initially displaced from its still water equilibrium position and allowing it to oscillate at its natural frequency about the equilibrium position The observed natural periods of the motion can be checked against simple calculations Since we are restricting the investigation to the structure s drift motion response in this example only the natural frequencies in the horizontal degrees of freedom surge pitch yaw need be investigated In the horizontal freedoms AQWA LINE gives no natural frequencies as the hydrostatic stiffness in these freedoms is zero With the addition of the four mooring lines in this AQWA DRIFT analysis all these freedoms will have stiffness and corresponding natural frequencies The added mass at low or drift frequency will not generally be the same as that at the lowest wave frequency but is sufficiently close for the purpose of the calculations a
79. es and affiliates Page 24 of 119 AQWA DRIFT User Manual Theoretical Formulation 3 12 STABILITY ANALYSIS AQWA DRIFT performs no formal stability analysis Some physical systems which can be modelled by AQWA DRIFT may be inherently statically or dynamically unstable This may be detected by careful inspection of the resulting time histories Note that dynamic instability is dependent on the initial conditions of the simulation AQWA LIBRIUM is designed to investigate the stability of systems and details are in the AQWA LIBRIUM manual 3 13 FREQUENCY DOMAIN SOLUTION AQWA DRIFT is a time domain program for analysis of non linear systems in irregular waves Linear systems or linearised systems in irregular waves can be analysed in the frequency domain by AQWA FER 3 14 TIME HISTORY SOLUTION IN IRREGULAR WAVES 3 14 1 Time Integration of Equation of Motion At each time step in the simulation the position and velocity are known since they are predicted in the previous time step From these all the position and velocity dependent forces i e damping mooring force total wave force drift force etc are calculated These are then summed to find the six total forces and moments for each structure one for each degree of freedom The total force is then equated to the product of the total mass structural and added and the rigid body accelerations The acceleration at the next time step can thus be determined It has been found necessary to
80. f 119 U S Government Rights For U S Government users except as specifically granted by the ANSYS Inc software license agreement the use duplication or disclosure by the United States Government is subject to restrictions stated in the ANSYS Inc software license agreement and FAR 12 212 for non DOD licenses Third Party Software The products described in this document contain the following licensed software that requires reproduction of the following notices Copyright 1984 1989 1994 Adobe Systems Incorporated Copyright 1988 1994 Digital Equipment Corporation Permission to use copy modify distribute and sell this software and its documentation for any purpose and without fee is hereby granted provided that the above copyright notices appear in all copies and that both those copyright notices and this permission notice appear in supporting documentation and that the names of Adobe Systems and Digital Equipment Corporation not be used in advertising or publicity pertaining to distribution of the software without specific written prior permission Adobe Systems amp Digital Equipment Corporation make no representations about the suitability of this software for any purpose It is provided as is without express or implied warranty Microsoft Windows Windows 2000 and Windows XP are registered trademarks of Microsoft Corporation The ANSYS third party software information is also available via download from the Customer Portal
81. f non linear transient response does not require de coupling of low wave frequency motions automatically calculates interaction between low wave frequency effects With the convolution method the radiation force is now treated as a totally separate force Remember that the added mass and damping calculated by AQWA LINE is only a mechanism for the calculation of the forces created on a structure by moving that structure in still water in simple harmonic motion at a specific frequency Strictly speaking the radiation force in the time domain can only be calculated if the response of the structure is infinitely small and at freqencies calculated by AQWA LINE In general the response of a structure will be made up of all frequencies which implies that the added mass and damping coefficients must be known at all frequencies For the convolution method to be viable the maximum frequency range practicable must be calculated by AQWA LINE For a tanker this should be from about 0 1 to 1 25 radians sec or 5 60 second periods This also implies that a minimum of about 800 1000 elements total all quadrants is required It is also fundamental to understand that the frequency dependent added mass and damping coefficients of linear systems are not independent The added mass from zero to infinity can be calculated totally Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 30 of 119 AQWA D
82. fficients are dimensional and the user must conform to a consistent set of units For details see Appendix A of the Reference Manual 3 8 2 Yaw Rate Drag Force It is clear that the wind and current loads when calculated as described in Section 3 8 1 have no dependence on yaw rotational velocity This contribution is calculated separately and the yaw rate drag moment F is given as follows xX max 2 gt 9 Fs Cyaw Nera c u Us oF x fe cy x0 xdx 3 8 3 where C yaw the yaw rate drag coefficient which is moment per unit length per unit velocity Cy u u cos0 Cy u u sin0 0 the relative angle of incidence the integration is along the length of the structure between xmin and xmax If the centre of gravity is not at the geometric centre of the structure s projection on the water surface the yaw rate drag will have a lateral component given by a very similar expression i e To Cyaw ae cy u us e x6 fe cy x dx 3 8 4 3 9 THRUSTER FORCES Up to ten thruster forces may be applied to each body The magnitude of the thrust vector is constant and the direction of the vector is fixed to and moves with the body The program calculates the thruster moments from the cross product of the latest position vector of the point of application and the thrust Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 20 of 119 AQWA DRIFT
83. for TUBE elements in AQWA DRIFT and NAUT 6 6 1 Run Stage 6 Alone Deck 21 Request for output of loads on Morison elements 6 6 2 Run Stage 6 with starting stage less than 5 Deck 19 None Deck 20 None Deck 21 Request for output of loads on Morison elements Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 59 of 119 AQWA DRIFT User Manual Description of Output CHAPTER 7 DESCRIPTION OF OUTPUT This chapter describes the comprehensive program output provided by AQWA DRIFT The various program stages perform different types of analysis and the output for each stage of analysis is described in detail in the following sections Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 60 of 119 AQWA DRIFT User Manual Description of Output 7 1 STRUCTURAL DESCRIPTION OF BODY CHARACTERISTICS This information is only output when starting at Stage 1 or when the PRDL option is used to echo the information from backing file 7 1 1 Coordinates and Mass Distribution Elements Note that the body s surface geometry is not used in AQWA DRIFT Only the mass characteristics are input These together with coordinates referenced by later decks are input in Decks 1 to 4 see Section 6 1 These data decks define the following parameters see AQWA Reference Manual Node numbers and positions Elements used to model the bo
84. ged or partially submerged tubes but if the user wishes to suppress these calculations the drag and added mass coefficients on any or all tubes of a given structure may be set to a very small number but greater than 1 0e 6 Slender tube STUB elements differ from TUBE elements in the following respects 1 STUB elements permit tubes of non circular cross section to be modelled by allowing the tube properties diameter drag coefficient added mass coefficient to be specified in two directions at right angles 2 Longer lengths of tube can be input as the program automatically subdivides STUB elements into sections of shorter length for integration purposes 3 An improved second order version of Morison s equation is used to calculate the drag and inertia forces on STUB elements This is particularly useful in the study of dropped objects 4 STUB elements should only be employed if the mean diameter is small compared with the length A DISC element DISC has no thickness and no mass users can define a PMAS and attach it to a disc if necessary but has drag coefficient and added mass coefficient in its normal direction Therefore a DISC does not have Froude Krylov or hydrostatic forces A DISC element has only a drag force and an added mass force 4 5 1 Reynolds Number Dependent Drag Coefficients Reynolds number effects on drag can be important at model scale Drag coefficients are normally considered constant as is often the ca
85. gt gy AQWAWAVE A ansys A ANSYS Product Launcher AX ANSYS Workbench Se AQWAWE Clicking on AQW AGS starts the AGS directly Clicking on AQWA brings up a dialog box that allows you to browse to an input file OPEN DAT FILE Look in E Desktop amp Fe My Documents 4 My Computer My Recent My Network Places Documents Desktop lt r My Documents r BL My Computer im a ETM File name F DAT v Places Files of type E DAT 7 If a desktop icon is created for AQWA analyses can be run by dropping a DAT file from Windows Explorer onto the icon Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 113 of 119 AQWA DRIFT User Manual Running the Program Running from a Command Prompt It is also possible to run AQWA by issuing a command at a command prompt If the file is installed in the default location the command will be C Program Files ANSYS Inc v120 aqwa bin win32 aqwa exe option FileName where option is an optional command line option and FileName is the name of the dat file Possible command line options are STD tells AQWA to accept commands from an AQWA command file In this case FileName will be the name of the command file NOWIND will automatically close all progress and message windows allowing AQWA to be run from a conventional DOS batch file without user intervention The AQWA command file Th
86. gular wave frequencies This information corresponds to categories 1 and 2 of Section 4 2 1 which if requested is automatically transferred to the AQWA DRIFT run the remaining information being provided by a user prepared data file Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 33 of 119 AQWA DRIFT User Manual Modelling Techniques 4 3 DEFINITION OF STRUCTURE AND POSITION Full details may be found in the AQWA Reference Manual 4 3 1 Axis Systems AQWA DRIFT uses several axis systems for different purposes 1 Fixed Reference Axes FRA The OXY plane of the FRA lies on the free surface and OZ points vertically upwards 2 Local System Axes LSA The LSA axis are fixed to the vessel with their origin at the centre of gravity 3 Slow Axis System SLA The slow axis system is similar to the LSA in that its origin is located at the centre of gravity but differs in that it follows only the slow drift motion of the structure 4 3 2 Conventions The AQWA suite employs a common sign convention with the axes defined in the previous section Translations of a body in the X Y and Z direction are termed SURGE SWAY and HEAVE and are positive in the positive direction of their respective axes Rotations about the X Y and Z axes of the FRA are termed ROLL PITCH and YAW The positive sense of these is determined by the right hand screw rule 4 3 3 The Structural Definition and Anal
87. ics can either be linear like a spring or Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 21 of 119 AQWA DRIFT User Manual Theoretical Formulation take the following polynomial form P e aje aze aze age ase 3 10 1 where P line tension extension o I 3 10 4 Composite Elastic Catenary Chains Catenaries in AQWA are considered to be uniform As the solution of the catenary equations is well documented e g Berteaux 1976 Bartrop 1998 the summary of the solution used in AQWA is presented The equations can be expressed in an axis system whose local X axis is the projection of the vector joining the attachment points on the sea bed and whose Z axis is vertical For catenaries which have zero slope at the contact attachment point on the sea bed these equations can be written as T 2wZ H AB 1 AE AE AE va a C w H AE V wL D 2 T vH V 3 10 2 where L unstretched suspended length w submerged weight per unit length AE stiffness per length X horizontal distance between fairlead point on the structure and contact point on seabed Z vertical distance between fairlead point on the structure and contact point on seabed H horizontal tension V vertical tension force at the fairlead point T total tension force at the fairlead point A non linear composite mooring line in terms of one or more elastic cate
88. input to AQWA DRIFT for irregular wave simulation Efficiency when using any of the AQWA programs The restart facility allows the user to progress gradually through the solution of the problem and an error made at one stage of the analysis does not necessarily mean that all the previous work has been wasted The programs within the AQWA SUITE are as follows AQWA LIBRIUM AQWA LINE AQWA FER AQWA NAUT AQWA DRIFT Used to find the equilibrium characteristics of a moored or freely floating body or bodies Steady state environmental loads may also be considered to act on the body e g wind wave drift and current Used to calculate the wave loading and response of bodies when exposed to a regular harmonic wave environment The first order wave forces and second order wave drift forces are calculated in the frequency domain Used to analyse the coupled or uncoupled responses of floating bodies operating in irregular waves The analysis is performed in the frequency domain Used to simulate the real time motion of a floating body or bodies while operating in regular or irregular waves Non linear Froude Krylov and hydrostatic forces are estimated under instantaneous incident wave surface Wind and current loads may also be considered If more than one body is being studied coupling effects between bodies may be considered Used to simulate the real time motion of a floating body or bodies while operating in irregular waves Wave
89. interpreted In any event the interpretation of the data input in these decks is output automatically in order that the user may check the results before proceeding to the next stage of the analysis For AQWA DRIFT parameters are read from a backing file automatically or may be input manually In the latter case the ranges of frequencies and directions specified in Deck 6 are those at which the parameters are to be input within these decks 6 2 3 Total Data Input Summary for Decks 6 to 8 Deck 6 a range of frequencies a range of directions details relating to alterations of the results of a previous run Deck 7 linear hydrostatic stiffness matrix additional stiffness matrix usually not required the buoyancy force at equilibrium added mass matrix additional mass matrix usually not required radiation damping matrix additional linear damping matrix usually not required diffraction forces Froude Krylov forces response motions or RAOs For checking only Deck 8 Second Order Drift Forces It is unusual for all the data above to be required for any particular analysis in which case the user simply omits the data which is not applicable The following sections show the required data input for the available modes of analysis 6 2 4 Input for AQWA DRIFT using the Results of a Previous AQWA LINE Run If there are no changes to the results from a previous AQWA LINE run all the data is read automatically from th
90. ion These are assumed constant Wind and current loading coefficients These coefficients which are defined at directions specified in Deck 10 or in Deck 6 if DIRN card is not presented in Deck 10 are associated with the hull forces which are proportional to the square of the relative wind current velocity Wave spectrum wind and current The sea state is defined by a wave spectrum together Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 57 of 119 AQWA DRIFT User Manual Mooring lines Starting position Description of Output with wind and current speed and direction see Section 4 14 The physical characteristics and attachment points of mooring lines hawsers and tethers may be input if required see Section 4 15 The initial position of each structure should be specified Time integration parameters The time step to be used throughout the simulation and the number of time steps required is specified The user also specifies the start time of the simulation Morison element parameter This may be either the Local Reynolds Number or a drag scale factor applied to the drag coefficients of Morison elements already specified in Deck 4 6 4 2 AQWA DRIFT Data Input Summary for Decks 9 to 18 Deck 9 Deck 10 Deck 11 Deck 12 Deck 13 Deck 14 Deck 15 Deck 16 Deck 17 Deck 18 Low frequency added mass Low frequency damping Wind loading
91. ion from backing file The global environmental parameters in AQWA DRIFT are the fluid depth and density The static environment is output as shown in Figure 7 5 and is seen to contain the water depth and density Note that the gravitational acceleration is also output ROR KER TO BA L PARAMETERS Oe X A WATER DEPTH 250 000 DENSITY OF WATER 1025 000 ACCELERATION DUE TO GRAVITY 9 806 Figure 7 5 Static Environment The wave environment is now output AQWA LINE may have up to 50 wave frequencies periods and 41 associated wave directions for each body in the analysis The output summary of wave frequencies and directions is shown for Structure 1 in Figure 7 6 The output also shows details of other wave related parameters Wave number i e 2 0 2 wavelength Maximum element size applicable to AQWA LINE NAUT Depth ratio The final piece of information given in Figure 7 6 relates to the frequency dependent parameters i e added mass etc If these parameters have not already been input for certain frequencies then these frequencies are listed as having undefined parameters Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 64 of 119 AQWA DRIFT User Manual Description of Output He RW BONE FREQUENCIES PERIODS STRUCTURE FREQUENCY FREQUENCY PERIOD WAVE WAVE MAX ELEM DEPTH RATIO PARAMETERS RAD SEC HERTZ SECONDS NUMBER LENGTH SIZE 45 00 67 50
92. ion in the mooring line at the attachment point on the second structure 3 11 WAVE SPECTRA The method of wave forecasting for irregular seas is achieved within the AQWA suite by the specification of wave spectra For further details of spectral forms the reader is referred to Appendix E of the AQWA Reference Manual Because of the manner in which the drift force is calculated it is required that the spectrum be defined such that the spectral area between adjacent spectral lines is equal Thus spectral lines will be close together when the spectral density is large around the spectral peak and spaced further apart when spectral density is low at either end of the spectrum The program does this by calculating the spectral density at a very large number of raster points on the frequency scale which are equally spaced between the defined spectrum end frequencies The program uses a default of 5000 raster lines The raster is then divided into the required number of spectral packets such that the spectral area of each packet is equal Linear interpolation is used between the raster points to help define the limits of the packets A spectral line is then placed at the frequency such that the first moment of area of the spectral energy in the packet is zero This is equivalent to defining the spectral line which represents the packet at the centre of area of the packet Contains proprietary and confidential information of ANSYS Inc and its subsidiari
93. ion of ANSYS Inc and its subsidiaries and affiliates Page 97 of 119 AQWA DRIFT User Manual Example of Program Use 8 1 12 Natural Frequency Simulation Run Once the user is satisfied that the data input in Decks 9 to 18 are correct the full natural frequency simulation can be performed As a program restart is being performed the user must copy over the RESTART file created by the previous program DATA run The RESTART file is used to supply the program with the information contained within Decks 1 to 18 previously input The only data required to be input is in the Preliminary Deck This contains merely the information to indicate that a Stage 5 analysis is required as shown below in Figure 8 12 JOB BOX1 DRIF DRFT TITLE NATURAL FREQUENCY DATA RUN OPTIONS CONV REST END RESTART D aS ADBOX21 Figure 8 12 Data File for Natural Frequency Simulation Run Alternatively it is possible to modify the data file used for the DATA run by making the two changes of removing the DATA option and changing the RESTART card to run from Stage 4 to Stage 5 8 1 13 Output from Natural Frequency Run The program outputs results to two different sources the listing file and the graphics file The listing file contains a full description of the structure at every tenth time step as requested The position velocity and acceleration plus all the relevant forces for a drift motion analysis are printed for each of the active degrees of freedom Fig
94. ivalent cross sectional area is numerically equal to the volume of water displaced by a unit length of the chain The user may specify maximum tension in the line and possible highest and lowest vertical relative positions between two attachment points The program evaluates the line tension and stiffness The program allows the line to lift off the sea bed i e the tangent to the line at the anchor has non zero slope up to the point where the line tension exceeds a user specified default maximum AQWA admits catenary mooring lines between a body and the sloped sea bed for cable dynamic mooring line the seabed is assumed to be horizontal and a catenary mooring line joining two bodies 4 14 5 Steel Wire Cables The Steel Wire SWIR facility allows modelling of the non linear properties of a new steel wire rope Although the SWIR cable is classified as a non linear cable it is possible to model steel wire using linear LINE or non linear NLIN lines 4 14 6 Intermediate Buoys and Clump Weights The buoy card BUOY defines the properties of intermediate buoys and clump weights Intermediate buoys cannot be used between structures but only between a structure and the sea bed 4 14 7 Pulley PULY The PULY facility allows the use of a pulley positioned on a line A maximum of 2 pulleys is allowed for each pulley set A PULY card must be proceeded by a LINE card 4 14 8 Drum Winch LNDW The LNDW card is used to model a winch or dru
95. jor limitations due to assumptions inherent in AQWA DRIFT are listed below AQWA LINE assumptions 1 The theory at present relates to a body or bodies which have zero or small forward speed 2 The fluid domain is assumed ideal and irrotational in the calculations of the added mass damping and wave forces 3 The second order mean wave drift force is calculated using near field or far field solution methods For more information consult the AQWA LINE manual AQWA DRIFT assumptions 4 The calculation of the slowly varying drift force is accurate only for low frequencies if the Newman s approximation is used 5 The drift force coefficients are calculated in the free floating position of the structure and include components due to the first order wave frequency response of the structure Should the wave frequency response be appreciably altered by the addition of mooring lines not previously considered or any other external influence then the drift forces will clearly be in error Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 29 of 119 AQWA DRIFT User Manual Theoretical Formulation 3 17 THE USE OF CONVOLUTION FOR THE EVALUATION OF THE RADIATION FORCES IN THE TIME DOMAIN By default the AQWA time domain programs NAUT and DRIFT assume that the radiation forces can be calculated by using the velocity acceleration RAOs and added mass damping coefficients at all frequencies to
96. m winch which winds in or pays out a linear elastic line starting at a user specified time 4 14 9 Fenders FEND Fixed and floating fenders are available in AQWA A fixed fender is graphically shown as a sphere in the AGS or if the axis is defined a cone whose axis is normal to the structure plane to which it is fixed A Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 43 of 119 AQWA DRIFT User Manual Modelling Techniques floating fender will be shown as a short cylinder Emphasis has been put on the realistic graphical representation of the fender distortion Fixed and floating fenders in AQWA can be modelled together with conventional mooring lines 4 15 ITERATION PARAMETERS FOR SOLUTION OF EQUILIBRIUM AQWA LIBRIUM ONLY Not applicable to AQWA DRIFT see AQWA LIBRIUM manual 4 16 TIME HISTORY INTEGRATION IN IRREGULAR WAVES 4 16 1 Time step for Simulation The time step for a simulation should be chosen to be a small fraction of the period of variation of the most rapidly varying force or response A different time step is applicable if investigating only drift motions as opposed to drift and wave frequency motions Drift motions In this case only drift motions are being integrated and the time step should be about one twentieth of the smallest natural period of drift oscillation A 5 to 10 second time step is usual for a typical offshore structure Drift an
97. mbers are output as shown in Figure 7 3 RR OR XXMA TE RL AG PROPERTIE MATERIAL GROUP NUMBER DENSITY PARAM 1 3 3210E 08 0 0000E 00 0 0000E 00 Figure 7 3 Material Property Output Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 62 of 119 AQWA DRIFT User Manual Description of Output The topology output also references the geometry group numbers used by the user Each geometry group has an inertia tensor associated with it The geometry group numbers and the inertias specified for each group are output as shown in Figure 7 4 Here the point mass element has a full six geometric parameters which are the prescribed inertia values It is also seen that the localised element drag and added mass coefficients are also printed which are zero for a point mass element ROPE PG EO Mun ER DG PR O BYE R DP BABS Pe ee GEOMETRY INPUT GROUP ELEMENT GEOMETRIC PARAMETER SEQUENCE 3 6253E 11 0 0000E 00 0 0000E 00 3 4199E 11 output line continued below ADDED MASS COEFFICIENT COEFFICIENT 0 0000E 00 3 5991E 11 Figure 7 4 Geometric Property Output Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 63 of 119 AQWA DRIFT User Manual Description of Output 7 2 DESCRIPTION OF GLOBAL ENVIRONMENT This information is only output when starting at Stage 1 or when the PRDL option is used to echo the informat
98. me hawser 1 has no tension i e it is slack It is this slackening of the hawser that produces the asymmetry in the surge motions Inspection of Figure 8 18 which describes the statistics of the surge motion shows this asymmetry clearly The peak surge displacement of 2 987 metres occurs at about 3525 seconds and the maximum hawser tension in hawsers 3 and 4 occur at the same time Abs 3986 877 Ord 1 414165 Min 0 490845 Max 2 986505 Mean 1 045223 2 RMS 0 69449 Area 4159 170 WD ie Eaa 77 0 1000 0 2000 0 3000 0 Time seconds Position of cog in x direction Figure 8 17 Time History of Surge Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 104 of 119 AQWA DRIFT User Manual Example of Program Use OPE OE ST Ae I Se Ss REG UT T w ee STRUCTURE 1 POSITION OF COG MEAN VALUE 2 x R M S MEAN HIGHEST 1 3 PEAKS MAXIMUM PEAKS MINIMUM PEAKS PROBABILITY DISTRIBUTION RANGE PER CENT RANGE PER CENT RANGE PER CENT RANGE PER CENT RANGE PER CENT RANGE PER CENT LIMITS OCCUR LIMITS OCCUR LIMITS OCCUR LIMITS OCCUR LIMITS OCCUR LIMITS OCCUR Figure 8 18 Statistics of Structure Position Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 105 of 119 AQWA DRIFT User Manual ia dal a not wM 6 0 5 0 Ti Al Li veg 1 sal 1 525 1 500 1 ATS Aa veg Example of Program Use To
99. naries can be defined in AQWA with intermediate buoys or clump weights between catenaries Numerical approach is used to calculate the stiffness matrix of composite mooring line Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 22 of 119 AQWA DRIFT User Manual Theoretical Formulation 3 10 5 Translation of the Mooring Line Force and Stiffness Matrix The formulation of a vector translation may be applied directly to a force and displacement in order to translate the stiffness matrix K from the point of definition to the centre of gravity It should be noted however that if the stiffness matrix is defined in a fixed axis system which does not rotate with the structure an additional stiffness term is required This relates the change of moment created by a constant force applied at a point when the structure is rotated The full 6x6 stiffness matrix K for each mooring line relating displacements of the centre of gravity to the change in forces and moments acting on that structure at the centre of gravity is therefore given by K i T I 3 10 3 t a t gt LU ane 0 P T where 0 z y 0 Poa Py Ta z 0 x Ey See 0 Py y x P Py 0 X Y Z Coordinates of the attachment point on the structure relative to the centre of gravity Px Py Pz The x y and z components of the tension in the mooring line at the attachment point on the structure t Note The term P
100. nd Wind The following spectrum and its associated directions will be used in the drift and wave frequency analyses Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 83 of 119 AQWA DRIFT User Manual Example of Program Use Spectrum Type Frequency Range Significant Wave Zero Crossing Period radians sec Height 0 2 1 0 The wind and current speeds and directions used were as follows Wind speed 15 0 m s Wind direction 0 0 degrees Current speed 0 8 m s Current direction 0 0 degrees 8 1 7 Specification of the Mooring Lines The mooring lines are simple linear elastic hawsers and therefore require one line of input data for each mooring line Each line contains stiffness unstretched length and the structure numbers and node numbers of the two attachments points For a line joining a structure to a fixed point the structure number corresponding to the fixed point should be set to zero The node numbers and their positions to which the mooring lines are attached must be input in the coordinate Deck 1 Each mooring line of unstretched length 100 metres has a stiffness of 1 47E6 newtons per metre Each mooring line is pre tensioned to 1 47E6 newtons i e extended by metre to give the structure a significant yaw stiffness 8 1 8 Start Position for Analysis If the starting position is offset from the equilibrium position of the structure there will be a transient
101. oprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 47 of 119 AQWA DRIFT User Manual Analysis Procedure CHAPTER 5 ANALYSIS PROCEDURE This chapter assumes that the user is familiar with the theory of the analysis and how to model the structure in its environment It deals with the method of analysis associated with running the program and links the modelling information in the previous chapter with the stages of analysis necessary to solve a given type of problem This involves classification of the types of problem and details of the program runs and stages within each program run together with their associated options Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 48 of 119 AQWA DRIFT User Manual Analysis Procedure 5 1 TYPES OF ANALYSIS There are several different common types of analysis that the program has been designed to perform These are the same whether used independently or as a post processor to AQWA LINE and are as follows 1 Investigation of transient response of coupled moored structures 2 Simulation of drift motions of coupled moored structures 3 Simulation of drift and wave frequency motions of coupled moored structures In each of these analyses any chosen variables can be analysed statistically and plotted if required The different types of analyses and the results that are produced are mainly controll
102. ough the inertia forces do not usually alter the motions of the main vessel the drag forces may be significant in contributing to a lightly damped vessel e g in surge The user should therefore estimate the additional overall drag type loading for input into Deck 10 as Hull Drag or estimate the equivalent linear damping for input into Deck 7 for the wave spectrum used using the R M S wave velocity and Morison equations for all the Morison elements If the user is in doubt as to the accuracy of the results he should run first with no additional damping and then with the drag damping described above to ascertain the sensitivity of the overall motion of the vessel to the forces on the Morison elements 4 6 STATIC ENVIRONMENT 4 6 1 Global Environmental Parameters The global or static environmental parameters are those which remain constant or static throughout an analysis and comprise the following Acceleration due to Gravity Used to calculate all forces and various dimensionless variables throughout the program suite Density of Water Used to calculate fluid forces and various dimensionless variables throughout the program suite Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 37 of 119 AQWA DRIFT User Manual Modelling Techniques Water Depth Used in AQWA DRIFT through the wave number to calculate phase relationships for various parameters 4 7 LINEAR STIFFNESS
103. positions file backing file This file is created and contains the structure positions for each time step It is used by AGS to plot trajectories plt file graphics file backing file This file is created and contains positions velocities accelerations and all forces acting on the structure at every timestep of the simulation It is used by AGS to produce time history plots dat file input data file The input data file contains all the AQWA format data decks needed for the current stage of analysis Information from previous stages of analysis may be supplied from the restart file It is a normal ASCII text file lis file output data file listing file The output data file receives the main results from a program run It is a normal ASCII text file 9 3 Program Size Requirements Not applicable for the PC 9 4 Run Commands Running from the Windows Start Menu Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 112 of 119 AQWA DRIFT User Manual Running the Program After installation the AQWA programs appear on the Start Menu under ANSYS 12 0 AQWA runs the batch programs and AQWAGS starts the AQWA Graphical Supervisor AGS They can be run from here or the user can create icons on the desktop 2 ANSYS 11 0 gt f ANSYS 12 0 2 ANSYS FLEXIm License Manager Asas gt Be AQWA E RM gt Se AQWAGS ANSYS Client Licensing
104. proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 49 of 119 AQWA DRIFT User Manual Analysis Procedure being used as a post processor to AQWA LINE then this information is automatically transferred from AQWA LINE to AQWA DRIFT 1 Select a consistent set of units 2 Assemble geometric and material data for all the structures 3 Specify one or more point masses to represent the mass and mass inertia of each of the structures In the case of tubes structural mass may be input through the geometric properties 4 Calculate the coordinates of the node points for each of the mooring attachments and the elements used in the modelling of the body 5 Specify the water depth and the density of the water 6 Specify the wave diffraction radiation coefficients and the frequencies and directions at which they are defined for each structure 7 Specify the wave drift coefficients if drift motions are significant for each structure The following items 8 to 14 are required for AQWA DRIFT used independently or as a post processor to AQWA LINE 8 Determine mooring line properties 9 Prepare coefficients for wind and current drag for each structure 10 Specify the wave damping and added mass applicable to low frequency motion for each structure 11 Specify initial positions for each spectrum and details of the simulation length and time step length 12 Create a data file as described in Chapter 6
105. rce Inertia Force where Cy drag coefficient D characteristic drag diameter u fluid velocity in the transverse direction of tube u structure velocity in the transverse direction of tube Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 15 of 119 AQWA DRIFT User Manual Theoretical Formulation C inertia coefficient area of cross section fluid density D gt I ll 3 3 DIFFRACTION RADIATION WAVE FORCES The total wave frequency force acting on a structure is the sum of the diffraction forces due to the disturbance of the incident waves by the structure and the Froude Krylov force due to the dynamic pressure inside the waves For large floating structures these two components are of comparable magnitude and are calculated for regular waves by AQWA LINE or similar programs Details of the calculation can be found in the AQWA LINE manual In AQWA DRIFT the diffraction force and Froude Krylov force are added together to form the TOTAL WAVE FORCE which is calculated at each time step This section describes how the wave spectrum is discretised such that the wave at any time instant is given by NSPL i j tt k xpt e 3 J J P J A t Ref aje 3 3 1 j 1 where Re denotes the real part of the complex expression Oj the frequency of each regular wave component in the spectrum k j the wave number of frequency Oj p the distance from the origin of the w
106. response which will decay to the steady state under the action of the specified damping Such an offset is necessary to investigate the natural period of the structure However it is best to keep this offset small in order to minimise the influence of the initial transient on the statistics of the complete run The equilibrium position given by AQWA LIBRIUM for the specified spectrum is Surge X Sway Y Heave Z Roll RX Pitch RY Yaw RZ 0 9325 0 0000 10 6105 0 0000 0 0365 0 0000 8 1 9 Time Integration Parameters The structure s natural periods of oscillation in surge and yaw have been calculated to be 85 and 207 seconds A suitable time step therefore is 5 seconds minimum period 20 To determine the natural period of oscillation a simulation of about 4 cycles is sufficient So for surge oscillations 80 time steps are used For the complete simulation 800 time steps are used Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 84 of 119 AQWA DRIFT User Manual Example of Program Use 8 1 10 Input Preparation For Natural Frequency Data Run The AQWA LINE run see AQWA LINE example has been performed and the following information is contained on the RESTART backing file produced by AQWA LINE input of the node coordinate data input of the model s element topology with associated material and geometry properties input of the static environment the detailed p
107. ring Ship Handling SSPA 9 Loken A E and Olsen O A 1979 The Influence of Slowly Varying Wave Forces on Mooring Systems OTC 3626 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 119 of 119
108. ripi aeea eepe re eSa SpE eNe EE PEE E NESSES HSS 68 7 4 FREE FLOATING NATURAL FREQUENCIES AND RESPONSE AMPLITUDE OPERATORS saene 69 JAA Natural Freg encies PeriodS sihen eessen pr teie Eee OTE sa ESKE r e EErEE seb code casneu eesupvasdgndeguredrebdh SEIA E SSRS 69 7 4 2 Response Amplitude Operators cs ssccsssessescocesseessvasbesskeesseevsebsaes Eri EEr EEEE ETET SEE E EEr Er EES EErEE Torit 70 7 39 SPECTRAL LINE PRINTOUT aa rere rerep rea ran r o e se tssnsostsavhessssavasostessnsscedsensceeegenst co IPERS EUP ERRES PESER EE OSS 72 7 6 TIME HISTORY AND FORCE PRINTOUT on s ccccsscees csc csciecsscncnebiees coeegsecesvbsuvpshoessctivaessey coeuseddebegiecn ri EEEE Eres t 72 TT STATISTICS PRINT OUT E oo sbtesheastess staat tots dactescssees E ET 75 CHAPTER 8 EXAMPLE OF PROGRAM USE cniris rsrs reiser sece ees rensek reer rk e EE es E EESO rE E EESE EAE TE PEP EE ENS eSEE 78 8 L BOX STRUCTURE patre ereere secven evsessavaesdncegeesdhdese caenauseesupvevagadeaspeesebdusesouvsugevoeearaedenigadech Merdtense EES 79 SAA General Discussi a a i este he A E T A E eee eure EE 79 8 1 2 Problem DENION vsere reure eie eeoa e esa raare enh a Ea sev Seear ees meae Sps r ear 79 8 1 3 Natural Frequentie Simars a get A E E R E E S 82 8 1 4 Low Frequency Added Mass and Damping ou ee ee ceeceseceseceseceecseeeseeeneeeeeeseeeseensecaecsaecsaecnaecsaecaaesaaeeneeegs 82 8 1 5 Hull and Superstructure Loading Coefficient eee ee eecesecsecseecneee
109. roperties of elements used in each body the final mass and inertia properties of each body the preliminary diffraction modelling checks the wave periods and directions the analysis position of each body the secondary diffraction modelling checks hydrostatic calculations for each body diffraction radiation analysis giving wave loading coefficients The input decks for the AQWA DRIFT DATA run are shown in Figure 8 2 and are described below Note that the DATA option is equivalent to a program RESTART which starts at the beginning of Stage 4 and finishes at the end of Stage 4 JOB card provides identifier program and type of analysis to be used TITLE card prescribes a title header for the run OPTIONS card containing the selected options REST indicates that a restart run is required DATA selects performance of up to Stage 4 only END indicates the end of the options list RESTART card specifies start and finish stages Deck 9 This deck has no input and so has a NONE deck header Deck 10 Wind and current loading coefficients Deck 11 This deck has no input and so has a NONE deck header Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 85 of 119 AQWA DRIFT User Manual Example of Program Use Deck 12 Since only the horizontal degrees of freedom are being used the heave roll and pitch freedoms are de activated Deck 13 This deck ha
110. rs extensively in the literature Users wishing to study the convolution method in more detail may refer to the reference papers Bailey et al 1998 Bishop et al 1973 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 31 of 119 AQWA DRIFT User Manual Modelling Techniques CHAPTER 4 MODELLING TECHNIQUES This chapter relates the theory in the previous section to the general form of the input data required for the AQWA suite The sections are closely associated with the sections in the program input format All modelling techniques related to the calculations within AQWA DRIFT are presented This may produce duplication in the user manuals where the calculations are performed by other programs in the suite Other modelling techniques which are indirectly related are included to preserve subject integrity these are indicated accordingly Where modelling techniques are only associated with other programs in the AQWA suite the information may be found in the appropriate sections of the respective manuals the section numbers below correspond to those in the other manuals as a convenient cross reference Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 32 of 119 AQWA DRIFT User Manual Modelling Techniques 4 1 INTRODUCTION When using AQWA DRIFT we do not require a description of the full structure surface Instead the proper
111. rssesrenresreee 54 6 2 2 Description f General FOrmat shosse a a eea aoo ctesbicesavbenessteguneescgbdesupddecpdbeecsepsegevaenets 55 6 2 3 Total Data Input Summary for Decks 6 t0 8 oo eee ec eeceeecesecesecsecsaecaeecseeeaeseaeeseeseeeseesecsaecnaecsaecaaecaaeeaeeegs 55 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 6 of 119 AQWA DRIFT User Manual Contents 6 2 4 Input for AQWA DRIFT using the Results of a Previous AQWA LINE Run eee cee cesecesecneeeeeeeeeeneeene 55 6 2 5 Input for AQWA DRIFT with Results from a Source other than AQWA LINE cceecceceseceeeeeeeeeceeeeeenaeeeeee 55 6 2 6 Input for AQWA DRIFT with Results from a Previous AQWA LINE Run and a Source other than AQWA E E sesso concen 3 A Gidewstcuoanwstnt E A E E E tederee secu tersteunen ess 56 6 3 STAGE 3 NO CARD IMAGE INPUT DIFFRACTION RADIATION ANALYSIS 0 0 cece cseereeeeeees 57 6 4 Stage 4 DECKS 9 to 18 INPUT OF THE ANALYSIS ENVIRONMENT 1 ceecseeeeeeeeeeeeeeeeeneenseenaes 57 6 4 1 Description Summary of Parameters Input 0 eee ee eecceeecesecesecaecsaecsaecaeecseseaeeeeeeeseeesesecaecsaecsaeesaecneeeas 37 6 4 2 AQWA DRIFT Data Input Summary for Decks 9 to 18 eee cee ceee cee cree cseeeeeeeeeeseeeseenseeesecsecsaecsaessaesneeeas 58 6 5 STAGE 5 NO INPUT Motion Analysis eee reeeo aeae See hesa aren Eene SE SEE PESES EES hee SEEE 59 6 6 STAGE 6 LOCADS ON MORISON ELEMENTS seeser
112. ructure 1 TOTAL FORCE The sum total of all forces applied to structure 1 7 7 STATISTICS PRINTOUT At the end of the simulation time step printout those parameters which have been printed at each time step are then analysed statistically over the whole length of the simulation The results are tabulated in the form shown in Figure 7 15 This example shows the statistics for the position of Structure 1 For each of the active degrees of Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 75 of 119 AQWA DRIFT User Manual Description of Output freedom the following are calculated MEAN VALUE the sum of all the values divided by the number of time steps 2 x R M S two times the root mean squared value This is often termed the significant value MEAN HIGHEST 1 3 the mean value of the highest third positive and negative peaks For PEAKS simulation of a linear system this should be equal to twice the root mean square A large difference between this value and the significant value is an indication that the variation of the parameter is not following a normal distribution A large difference between the values for positive and negative peaks is an indication of skewness or asymmetry of variation MAXIMUM PEAKS the three maximum peak values MINIMUM PEAKS the three minimum peak values The values of each parameter are then sorted into small ranges or bins covering the total r
113. s Il If the user is setting up an analysis with several structures and wishes to pick up the hydrodynamic data for one or more structures calculated in a previous AQWA LINE run Note Very often there is data for only one structure in the hydrodynamics file in which case the data is associated with Structure in the new run The RDDB option may also be used if the hydrodynamics file contains more than one structure provided that all the structures appear in the same order in the new run CONV CONVOLUTION Instructs AQWA DRIFT or NAUT to use convolution method in radiation force calculation This is a more rigorous approach to the radiation force calculation in time domain and will enhance the capability of handling non linear response of structures CRNM CALCULATE RAOs WITH NO MOORINGS This option may be used with AQWA LINE but is more useful with the program AQWAFER This option investigates the calculation of RAOs using the values of added mass wave damping stiffness and wave forcing specified by the user The RAOs are then written into the database DATA DATA CHECK ONLY This option is used to check the data input to the program and provides a means by which the user may check all input data whilst incurring minimum cost of the program run This option is equivalent to performing the analysis up to the end of the second stage in AQWA LINE and up to the end of Stage 4 in AQWA DRIFT FER LIBRIUM NAUT If the data proved to be
114. s are required for the range of frequencies AND for the range of directions AQWA DRIFT combines the diffraction and Froude Krylov forces from AQWA LINE into a resultant total wave force If the forces are being input manually the user can input Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 39 of 119 AQWA DRIFT User Manual Modelling Techniques wave forces as either Froude Krylov or diffraction since the program does not differentiate between the two For drift frequency motion a single added mass and damping matrix are required These approximate the values of added mass and damping for low frequency motions which normally include those at drift frequency The drift forces are calculated by AQWA DRIFT from the regular wave drift force coefficients which are defined for the range of frequencies and directions Physically the added mass varies with frequency of oscillation However as the frequency of oscillation tends to zero the added mass tends to an asymptotic value This asymptotic value is a good approximation to the drift added mass In practice the added mass of a typically large floating structure e g a 100 000 tonne DWT tanker is close to its asymptotic value at periods of 25 sec The longest period wave frequency run should be chosen to provide a suitable value of drift added mass 4 10 WIND AND CURRENT LOADING COEFFICIENTS The wind and current loading coefficients
115. s no input and so has a NONE deck header Deck 14 Description of each mooring line property and combination Deck 15 The structure is given a surge displacement of 0 9325 metre from the origin of the FRA the equilibrium position for this run Deck 16 The time integration parameters Deck 17 This deck has no input and so has a NONE deck header Deck 18 Additional output requests information at every tenth time step is required positions of nodes 501 to 504 the hawser attachment points are required Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 86 of 119 AQWA DRIFT User Manual JOB BOX1 TITLE OPTIONS RE RESTART 09 0 OSYMX OSYMY ODIRN OCUFX OCUFY OWIFX OWILFY sa ia Ea fies P O n pany 1 2 2 2 2 3 4 4 4 4 4 5 5 6 DRIF DRFT NATURAL FREQUENCY DATA RUN ST END 4 4 ALBOX22 NONE HLD1 0 0 9500E6 0000E0 3200E3 0000E0 NONE CONS 45 0 4000E6 4000E6 0700E3 0700E3 4715E6 4715E6 4715E6 4715E6 0 0000 90 0 0000E0 9500E6 0000E0 3200E3 100 100 100 100 10 6105 0 0000 0 0365 Example of Program Use 0 0000 Figure 8 2 Data File for Natural Frequency Data Run 8 1 11 Output from Natural Frequency Data Run The DATA run produces the output shown in Figures 8 3 to 8 12 described below Figure 8 3 Figure 8 4 Figure 8 5 AQWA DRIFT he
116. s only necessary if the restart stage at which the analysis begins is Stage 1 or 2 see Chapter 5 If the restart stage is greater than Stage 2 there is NO INPUT for Stage 2 of the analysis 6 2 1 Description Summary of Physical Parameters Input The data input in these decks relates to the equation of motion of a diffracting structure or structures in regular waves for a range of frequencies and directions Note that the structural mass is input in Deck 3 For each specified frequency and direction the equation of motion is written as M s X M a X CX KX F d F f F 2 6 2 1 where the parameters in the equation of motion are M s Structure Mass Matrix K Linear Hydrostatic Stiffness Matrix and for each frequency M a Added Mass Matrix C Radiation Damping Matrix and for each frequency and each direction X Response Motion F d Diffraction Force Ff Froude Krylov Force F 2 Second Order Drift Force Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 54 of 119 AQWA DRIFT User Manual Description of Output 6 2 2 Description of General Format The input format and restrictions in these decks are designed to provide maximum cross checking on the data input when the more advanced facilities are used This ensures that the program is able to output a suitable message to inform the user that the instructions for data preparation have been mis
117. s the initial conditions in order to begin the integration Initial conditions are required for the SLOW position and the TOTAL position Details of how this is done can be found in Section 4 15D of the AQWA Reference Manual As explained there for simulations including wave frequency forces it is usual for the user to allow the program to calculate the Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 28 of 119 AQWA DRIFT User Manual Theoretical Formulation initial FAST position which is added to a defined SLOW position to form the TOTAL POSITION The FAST or RAO based position is calculated as described in Section 3 14 5 This ensures that the TOTAL initial condition contains a FAST component equal to the steady state solution in response to the wave frequency forces at that instant By giving the structure an initial SLOW position close to its equilibrium position transients can be minimised 3 15 TIME HISTORY SOLUTION IN REGULAR WAVES Only available within AQWA NAUT see AQWA NAUT manual 3 16 LIMITATIONS OF THEORETICAL APPLICATIONS The main theoretical limitations of AQWA DRIFT should be clearly understood by the user Since the program uses data calculated by AQWA LINE the limitations of the input data must also be understood Refer to AQWA LINE manual Section 3 15 for details of the assumptions made The AQWA LINE assumptions which affect the analysis together with the ma
118. scescsesssssasspeseesscosetsocecbsuscdessonsnenstsessdvssonsecssseucoussennsoepeosessdenantsb ends 46 4 17 TIME HISTORY INTEGRATION IN REGULAR WAVES AQWA NAUT ONLY 47 4 18 SPECIFICATION OF OUTPUT REQUIREMENTS 000 ceseceecseeceeceeeeeeseeeeeceaeeeeeeseenseenseceseesaecsaeseaesnaeeas 47 CHAPTER 5 ANALYSIS PROCEDURE E a E aE rar r EEn dutectenes Megpeusag PIE o Res ea SEEE 48 XI TYPESOFANALEYSIS Kenn R A E R E E E E E S 49 52 RES TART STAGES a e aar aaa E E oT OR E RSSa 49 313 STAGES OFSANAL YSIS r e a E N S E A A E EEI EG 49 CHAPTER 6 DATA REQUIREMENT AND PREPARATION 00 ececeeceescesecesecesecaecaaecaeecsessneeseeeeeeseeeseenseenaes 51 6 0 ADMINISTRATION CONTROL DECK 0 PRELIMINARY DECK ssesesesesssseesesreeesrrressrrreeresrerreserrreserreeresre 52 6 1 STAGE 1 DECKS 1 TO 5 GEOMETRIC DEFINITION AND STATIC ENVIRONMENT 00 eee ee eects 53 6 1 1 Description Summary of Physical Parameters Input ee ee cee cesecese cee caeeeseseeeeeeeeseeesecesecesecaecsaecaeeneeees 53 6 1 2 Description of General Format eee erreren ese sorak e En ee eE a eE Ken oE E ERESSE E Eet 53 6 1 3 Data Input Summary for Decks 1 to 5 essssessesesssseesssresrssesreerertesresterrsstetensestentssternsertrerertentesrentesrerrsserrenresrent 53 6 2 STAGE 2 DECKS 6 TO 8 THE DIFFRACTION RADIATION ANALYSIS PARAMETERS oseese 54 6 2 1 Description Summary of Physical Parameters Input sssseseseeeseseeesesteeresrstterssrerrrsrrrrnresrensesrenresrer
119. se at full scale i e large Reynolds numbers However experimental evidence shows that the Reynolds number is not just a simple function of the velocity and diameter for cylinders with arbitrary orientation to the direction of the fluid flow Considerable improvement in agreement with model tests can be obtained by using a scale factor to obtain a local Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 36 of 119 AQWA DRIFT User Manual Modelling Techniques Reynolds Number and interpolating from classical experimental results UD 1 v Scale factor 4 5 1 Local Reynolds Number where U Local velocity transverse to the axis of the tube D Tube diameter v Kinematic viscosity of water from which drag coefficients can be interpolated from the Wieselberg graph of drag coefficient versus Reynolds number for a smooth cylinder see AQWA Reference Appendix G Alternatively a general multiplying factor for drag can be used 4 5 2 Morison Forces For AQWA DRIFT with no Wave Frequency Motions When the wave frequency motions are omitted in an AQWA DRIFT analysis i e when it has been specified that only drift motions are required the user has effectively requested that the wave frequency forces on the Morison elements should be omitted i e the forces are to be calculated using only the low frequency motions of structures including riser and space frame structures Alth
120. seseseceeeeseeecensecaecsecsaecnaecsaecaeeeaeeeaeeeas 82 8 1 6 Seas pectra Current and WIN eepe ear eeo aeeoea nnper S e pitch dosdes RES pesene SE oaee CeeS ERIRE NES ESES SE Ear 83 8 1 7 Specification of the Mooring Lines ssiri risie esteen setr a eoi E i rrei eston ir k rer PEE ere eSEE 84 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 7 of 119 AQWA DRIFT User Manual 8 1 8 Start Position for Analysis ee eeceecesecesecssceecesecsecseecseseseseaeeseeseessecnseeseesaecsaeeaes 8 1 9 Time Integration Parameters 00 0 0 eee eecceesceseeeeceesceecesecsecaecsaecseecaaecaeeeneeeaeeneeeaeenes 8 1 10 Input Preparation For Natural Frequency Data RUD eee ceeeceeeceecnseeeeenee 8 1 11 Output from Natural Frequency Data Run ee eee cee cnse cee caeesaeeeeeeeeeeeeeeeeees 8 1 12 Natural Frequency Simulation RUM ee eeceeceeeceeecesecesecaecsaecaeecseseaeeeeeeeeeeeenes 8 1 13 Output from Natural Frequency RUD eee cee cee ceeecneeeeeeeeeeeeeeseeesecseesecaessaeeaes 8 1 14 Input Preparation for Drift Motion Data RUD ee eeeeeeeeeeeeseeeeceseensecaeenaeeaes 8 1 15 Drift Motion Simulation Run eee ceseesecesecneecseecaeeeaeseaeeseeeeensecseeaeeaessaeaes 8 1 16 Output from Drift Motion Simulation Run oe eee ceeeeeeeeeeeeeeeecesecesecaeesaeeaes 8 1 17 Input for Drift Wave Frequency Simulation RUM eee ee eee ceecseeereeeeeeeeeeeeeeereees 8 1 18 Output from Drift Wave Frequency Simulation R
121. sis ssvasestessesscebssesseesssnsscoansssssdesensscodasuseesesensb ESEESE PEO PERE RSET eror 33 4 3 DEFINITION OF STRUCTURE AND POSITION 00 ee eceeceecesecesecesecsecseecaeeeaeseaeeeaeeseesseesessecsaessaesnaesnaeees 34 A TAXIS SYSE MS sevice Bescsisoetpeence techs e a TRE Ee REE su A E NE Sea eaa NKE E EE EE e EENE a EE pA SIERE e 34 43 2 COMVENHONS iese eoe Eaa E a E E E E E E E EN stead E E EE E EEE EErEE 34 4 3 3 The Structural Definition and Analysis Position 00 0 0 cece eee cseeseeeeeeeeceeseeeeeesecseceaecsaecsaecaeecseseaeseeeseeeerenseens 34 4 4 STRUCTURE GEOMETRY AND MASS DISTRIBUTION cece cee eseeeeeeeeeeeeeeeceseensecaecnaecsaecsaeeaeeeneeeas 35 FAM COOLKIMALES annA eei perane ennen snes dec gusteevtgadesupevsenesbevsce E ENE aE Sea ee RIESE EEE a EA bests aude dened 35 4 4 2 Elements and Element Properties csssctssescseessesesvass epcveesseeeantscey cheasstessoasnep skpeastensetso ESEE SEE EEEE ESEE EErEE aso 35 45 MORISON ELEMENTS rererere raea irera eea qa Era E eao REPERA A AREAS S E EEE Es aea O SEERE EErEE S E EER EEO ERE OERE sie 36 4 5 1 Reynolds Number Dependent Drag Coefficients sessesessssieseseeessseerssstsrteresteetssreresenrestesrenteseerrnsesresersrenens 36 4 5 2 Morison Forces For AQWA DRIFT with no Wave Frequency Motions esseesseeeesesrsereresreeresreersserreseesreeess 37 4 6 STATIC ENVIRONMENT a irern oreore e E EErEE VK EEEE S E Ter EEE TE E SEE EER EErEE oest 37 4 6 1 Global Environmental
122. specified only those directions for the defined quadrants are required 2 Sufficient values are required to adequately describe the variation of these coefficients defined Clearly if either of these criteria is violated approximate results will be obtained Where possible the program will indicate this accordingly However this should not be relied on as anticipation of the intentions of the user is not usually possible 4 9 WAVE LOADING COEFFICIENTS The wave loading coefficients are calculated by AQWA LINE and then transferred automatically from backing file when AQWA DRIFT is used as a post processor Thus the following notes refer to AQWA DRIFT when used as an independent program This information falls into five categories These are 1 Frequencies and directions at which the regular wave loading has been calculated 2 Added mass and inertia matrices at each frequency 3 Damping coefficient matrices at each frequency 4 Diffraction and Froude Krylov wave forces at each frequency and direction 5 Mean drift forces at each frequency and direction or full QTF matrix It is important that the wave frequency parameters are defined over the range of expected wave excitation frequencies and that the direction dependent parameters are defined over the expected RELATIVE angle of incidence For wave frequency motion the added mass and damping matrices are required for the range of frequencies The diffraction and Froude Krylov force
123. sults of an AQWA LINE analysis 1 2 MANUAL The AQWA DRIFT Program Manual describes the various uses of the program together with the method of operation The theory and bounds of application are outlined for the analytical procedures employed within the various parts of AQWA DRIFT The method of data preparation and modelling is fully described and reference is made to the AQWA Reference Manual The Reference Manual contains information common to one or more programs and a complete guide to the format used for input of data into the AQWA Suite It is desirable that the AQWA DRIFT Program Manual and AQWA Reference Manual be available when using the program AQWA DRIFT Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 9 of 119 AQWA DRIFT User Manual Theoretical Formulation CHAPTER 2 PROGRAM DESCRIPTION AQWA DRIFT is a time domain program which uses linear hydrodynamic coefficients and second order hydrodynamic forces supplied by AQWA LINE or an equivalent source of linear hydrodynamic data plus other hydrodynamic and hydrostatic information to simulate the motions of large floating structures 2 1 PROGRAM CAPABILITY AQWA LINE computes the linearised hydrodynamic fluid wave loading on a floating or fixed rigid body using 3 dimensional radiation diffraction theory The hydrodynamic forces are composed of radiation forces and wave excitation forces The radiation fluid loading is du
124. ta preparation have been misinterpreted or are unusual When running with a DATA option for the first time it is recommended that the PRCE PRint Card Echo option is used see Appendix A as the data input in these decks 1 5 is not echoed automatically The user may then check the results before proceeding to Stage 2 of the analysis 6 1 3 Data Input Summary for Decks 1 to 5 Deck 1 The coordinates of points describing the elements The coordinates of the mooring line attachment points The coordinates of any points whose position or motions are requested by the user specified options Deck 2 Element description of the mass properties Element description of the hydrostatic model Element description of the hydrodynamic model Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 53 of 119 AQWA DRIFT User Manual Description of Output Deck 3 A table of material values associated with each element Deck 4 A table of geometric values associated with each element Deck 5 Static environmental parameters i e the depth and density of the water and the acceleration due to gravity The above information is required before an AQWA DRIFT simulation can be performed The format of the information contained within Decks to 5 may be found in the AQWA Reference Manual 6 2 STAGE 2 DECKS 6 TO 8 THE DIFFRACTION RADIATION ANALYSIS PARAMETERS Input to Stage 2 of the analysis i
125. ties of the structure are described numerically The hydrostatic properties are defined by a stiffness matrix and the hydrodynamic properties are defined by hydrodynamic loading coefficients and wave forces which are the RESULTS of calculations by programs like AQWA LINE which use models involving geometric surface definitions When AQWA LINE is run all these parameters are transferred automatically to backing files for future use with other AQWA programs 4 2 MODELLING REQUIREMENTS FOR AQWA DRIFT 4 2 1 When Used as an Independent Program AQWA DRIFT requires the following categories of modelling information 1 Body mass and inertia characteristics 2 Wave hydrodynamic and hydrostatic description 3 Wind and current force coefficient description 4 Description of mooring configuration 5 Analysis environment description 6 Time integration parameters These categories will be described in the following sections 4 2 2 Following an AQWA LINE Run After an AQWA LINE run or a series of runs has been completed then it may be required to utilise the results in an AQWA DRIFT analysis AQWA LINE automatically produces a HYDRODYNAMICS DATABASE file and a RESTART file These contain all the information required by AQWA DRIFT concerning the structure s mass and inertia properties the hydrostatic properties and the wave hydrodynamic properties in the form of a description of the added mass damping and wave forces at a series of re
126. train i e a spectrum then the total wave drift force acting on the body is characterised by a mean component and a slowly varying wave drift force The second order wave exciting force can be written as 2 NSPL NSPL _ 3 F t D j cos 1 O t J Pi cost a 0 t 6 e MI i l j l NSPL NSPL lo sin O QO t Ej I Qi sin O t j 3 i l j l 3 5 1 where P ijj and Qij are the in phase and out of phase components of the time independent transfer function i jare the frequencies of each pair of wave components fi F jare the random phase angles If we neglect the sum frequency components equation 3 5 1 can be written as NSPL NSPL Fy t 2i gt IP cost 0 t 6 e I i l j l NSPL NSPL gt by al tie ay il i l j l 3 5 2 Newman s approximation Newman 1974 implies the following Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 17 of 119 AQWA DRIFT User Manual Theoretical Formulation E 3 5 3 0 Based on the above approximations equation 3 5 2 can be written as NSPL NSPL Fy tj X Wy cosl t e 3 5 4 i l j l The assumption by Newman is valid for regular wave components closely separated in frequency in deep water Newman s approximation becomes increasingly inaccurate in shallow water It has been found that the QTF s drift force co
127. ual Example of Program Use respectively 2 2 F 0 F 90 0 5 1025 0 40 0 90 0 1 6 cos 0 2 95E6Ns m 2 ia F 0 F 0 0 5 1025 0 40 0 90 0 1 6 sin 0 0 00EO Ns m 2 2 F 45 F 45 0 5 1025 0 40 0 127 0 1 3 cos 45 2 40E6Ns m The moments at the centre of gravity 10 62 metres below the waterline centre of area at Z 20 0 are At a heading of 0 M 0 0 00E0 M 0 F 0 10 62 20 0 2 77E7 At a heading of 45 M 45 Fy 45 10 62 20 0 2 25E7 M 45 F 45 10 62 20 0 2 25E7 At a heading of 90 M 00 F 90 10 62 20 0 2 77E7 M 90 0 00E0 2 The units for the moment coefficients are Ns m Similarly the forces on the superstructure due to the wind at 0 45 and 90 degree headings in the X and Y directions respectively for unit velocity are 2 2 1 32E3 Ns m ae 0 00EO Ns m 2 2 1 07E3 Ns m F 0 F 90 F 0 F 90 F 45 F 45 0 5 1 22 15 0 90 0 1 6 cos 0 0 5 1 22 15 0 90 0 1 6 sin 0 0 5 1 22 15 0 127 0 1 3 cos 45 The moments at the centre of gravity 10 62 metres below the waterline and centre of area at Z 7 5 are At a heading of 0 M 0 0 00E0 M 0 2 39E4 At a heading of 45 M 45 1 94E4 M 45 1 94E4 At a heading of 90 M 90 2 39E4 M 90 0 00E0 The units for the moment coefficients are Ns m 8 1 6 Sea Spectra Current a
128. ulation should have as small an initial transient at the start as possible especially if the user requires accurate statistics of the responses transients at the start will invalidate the statistics of the run It is usual when performing a drift motion simulation to position the structure close to the equilibrium position of the structure under the influence of steady forces The user may then wish to add in the wave forces over a short segment of the drift run starting just before a peak drift response This would for example indicate how much the wave frequency effects will modify the peak motions and tensions in mooring lines To do this the user must pick off the slow position and velocity at some appropriate time in the drift run and then perform another simulation with these slow positions and velocities as the starting conditions It is very important for the user to remember to give this second simulation a starting time equal to that at which the slow position and velocity occurred so that the second simulation has exactly the same wave force time history as the first Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 46 of 119 AQWA DRIFT User Manual Modelling Techniques 4 17 TIME HISTORY INTEGRATION IN REGULAR WAVES AQWA NAUT ONLY Not applicable to AQWA DRIFT see AQWA NAUT manual 4 18 SPECIFICATION OF OUTPUT REQUIREMENTS See options list in Appendix A Contains pr
129. ure 8 13 shows the output for the first two time steps only It is very difficult to see what the structure is doing by inspection of the listing file Plotting the results however shows very clearly how the structure is behaving Figure 8 14 shows the plot of the surge oscillations From this it is easily recognised that the structure is responding in surge and yaw at the predicted periods of 85 and 207 secs respectively Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 98 of 119 AQWA DRIFT User Manual Example of Program Use JOB TITLE NATURAL FREQUENCY DATA RUN TIME SECS STRUCTURE POSITION FORCES NUMBER AND MOMENTS AT RECORD NO CENTRE OF GRAVITY POSITION 0 9325 0 0000 10 6105 0 0000 0 0365 0 0000 VELOCITY 0 0000 0 0000 0 0000 0 0000 0 0000 0 0000 ACCELERATION 0 0053 0 0000 0 0013 0 0000 0 0023 0 0000 GRAVITY 0000E 00 0000E 00 3 2566E 09 0 0000E 00 0 0000E 00 0000E 00 HYDROSTATIC 0000E 00 0000E 00 3 2558E 09 9 4210E 02 5550E 07 0000E 00 CURRENT DRAG 0000E 00 0000E 00 0 0000E 00 0 0000E 00 0000E 00 0000E 00 YAW DRAG 0000E 00 0000E 00 0 0000E 00 0000E 00 0000E 00 0000E 00 WIND 0 0000E 00 0000E 00 0 0000E 00 0000E 00 0000E 00 0000E 00 LINEAR DAMPING 0 0000E 00 0000E 00 0 0000E 00 0000E 00 0 0000E 00 0 0000E 00 L WAVE DRIFT DAMPING 0 0000E 00 0 0000E 00 0 0000E 00 0 0000E 00 0 0000E 00 0 0000E 00 DRIFT 0 0000E 00 0000E 00 0 0000E 00 0000E 00
130. use an extremely reliable two stage predictor corrector integration scheme to predict the position and velocity of the structures at the following time increment The forces are then recomputed with the new position and velocity and the process is repeated to create step by step the time history of motion 3 14 2 Motions at Drift Frequency Large floating structures which are moored at sea because of their large mass and flexible or soft moorings tend to have natural periods of oscillation in the horizontal degrees of freedom which are of the order of minutes At these periods there is no first order spectral energy so they are not appreciably excited by first order forces in these degrees of freedom The structures may of course have heave roll or pitch resonances within the range of wave excitation but for the moment we shall consider only the motions in the horizontal freedoms i e surge sway and yaw Section 3 5 explains that in irregular waves there also exist what are termed second order wave forces which oscillate at frequencies which are the difference between pairs of first order wave frequencies These difference frequencies can be very small Small frequencies imply large periods which may Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 25 of 119 AQWA DRIFT User Manual Theoretical Formulation coincide with the natural period of oscillation of a large floating structur
131. vely been specified 2 The frequency defining the lower range of the spectrum must be higher than the lowest frequency specified in Deck 6 as the frequency at the lower end of the range is used as both an upper limit to the drift frequencies and a lower limit to the wave frequencies 4 14 MOORING LINES 4 14 1 Linear Non Linear Elastic Hawsers Hawsers are defined by their unstretched lengths end nodes on respective bodies and their load extension characteristics For linear hawsers the line stiffness load per unit extension is required For non linear hawsers the program permits up to a fifth order polynomial approximation of the elastic property of the following form Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 41 of 119 AQWA DRIFT User Manual Modelling Techniques P e qe Fie aze Fage ase gt 4 14 1 where line tension extension iss I The use of a higher order polynomial than necessary could lead to erroneous negative stiffness while a lower order polynomial could be a perfectly adequate fit to the load extension curve A typical load extension curve is shown in Figure 4 1 It is always useful to check the polynomial fit prior to its use as input data Note that the term a is usually a good approximation to the linear stiffness for small extensions Tension p Extension e Figure 4 1 Load Extension Characteristics 4 14 2 Const
132. y varying part of total velocity filtered from VELOCITY WAVE FREQ ACCEL Rapidly varying part of total acceleration filtered from ACCELERATION SLOW POSITION Slowly varying part of total position filtered from POSITION SLOW VELOCITY Slowly varying part of total velocity filtered from VELOCITY SLOW ACCEL Slowly varying part of total acceleration filtered from ACCELERATION MOORING The total force and moments on structure 1 due to all the mooring lines catenaries and hawsers LINEAR DAMPING The total linear damping force on structure 1 DRIFT The total second order drift force on structure 1 Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 74 of 119 AQWA DRIFT User Manual Description of Output 21 22 24 25 2T 28 29 30 31 50 GRAVITY The total gravity force on structure 1 CURRENT DRAG The total drag force on structure 1 due to relative current HYDROSTATIC The total hydrostatic force on structure 1 WIND The total drag force on structure 1 due to relative wind THRUSTER The total force on structure 1 due to all applied thruster forces YAW DRAG The drag on structure 1 due to its yaw velocity WAVE FREQ FORCE The total diffraction and Froude Krylov force on structure 1 ERROR PER TIMESTEP The maximun error in the position for the present time step TOTAL REACTION FORCE The total reaction force due to articulations on st
133. y will be those calculated by AQWA LINE The output gives the variation of RAOs with frequency for each direction see Figure 7 12 Output is also given with the RAOs varying with direction for each frequency Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 70 of 119 AQWA DRIFT User Manual Description of Output The RAOs are output in terms of amplitude and phase the phase being related to the incident wave form see Appendix C of the AQWA Reference Manual x x HYDRODYNAMIC PARAMETERS FOR STRUCTURE Lp oA RY E PERIOD FREQ DIRECTION 0 575 0 2583 69 0 600 0 2266 64 output line continued below 0 07 3 12 0090 131 Figure 7 12 Response Amplitude Operators Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 71 of 119 AQWA DRIFT User Manual Description of Output 7 5 SPECTRAL LINE PRINTOUT The program outputs the frequency and the spectral density of each of the discrete spectral lines that form the wave spectrum in the form shown in Figure 7 13 The printout shows the wave number frequency random phase number and spectral density for each spectral line By taking four times the square root of the sum of the contributions from each of the raster lines the program provides an exact indication of the significant wave height S W H of the defined spectrum KE RE a ea a E SPECTRAL Bs NAE AG
134. ysis Position In the description of the body geometry and mass distribution the user may define the structure in any position There are however important considerations when choosing the position in which to define the structure If the structure is a ship or barge conventional terminology for motion along and rotation about the longitudinal axis is SURGE and ROLL However if the longitudinal axis is defined parallel to the FRA Y axis then rotational motion about this axis will be termed PITCH and translational motion along this axis SWAY Thus conventional body surge and roll will be termed sway and pitch by the program For other structures e g semi submersibles this may not be so relevant The user must take due note of the terms associated with the motions about the axes and is recommended to define all ship barge shaped structures with the longitudinal axis parallel to the FRA X axis Contains proprietary and confidential information of ANSYS Inc and its subsidiaries and affiliates Page 34 of 119 AQWA DRIFT User Manual Modelling Techniques 4 4 STRUCTURE GEOMETRY AND MASS DISTRIBUTION When AQWA DRIFT is used following an AQWA LINE run the normal mode of analysis procedure the structure geometry and mass distribution are transferred automatically from the backing files produced by AQWA LINE This section therefore describes the modelling of the structure geometry and mass distribution when AQWA DRIFT is used independently

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