SWAN user's manual
Contents
1. Brings up the Model parameters dialog where the start and end time the timestep the viewer update frequency the initial water level and the physical constants can be edited The majority of model parameters can be changed on the fly while the simulation is running though there are some exceptions Error messages Too many attributes or boundary conditions Their maximum number is 255 Cannot delete attribute or boundary because it is used in the following map lt name of the map gt First all instances of the ID must be removed from the attribute or boundary map Cannot delete attribute or boundary because at least one is needed First define the replacement then delete the old one Invalid name The objects name may contain up to 31 characters Cannot delete grid because it is used in the calculations Activate another grid of the same category before attempting to delete the old one Zero curvature prescribed at open boundary Error cannot extend in the given driection Check Q position in the boundary definition With the ZeroCurvature and ZeroCurvaturelfOut switches the boundary values are extrapolated from the interior The interior is identified as the side opposite to the one where the discharge is prescribed E g if Q is prescribed on the East side the boundary value is extrapolated from the two West neighbours It is therefore necessary to give the position of the boundary when it is the water level which is pre2. Contents I Table of Contents Part Part Il 1 The program SWAN eee nneen nnn nnne nnn 2 Governing equations nnrrnnnnnnnnnnnnnnnnnennnnnnnnnnnnnnnnnnennnnennnne 3 Host system requirements Part lll CON Oo IRA N Part IV 1 Prescribe boundary conditions 4 Typical river boundary conditions 5 Part V Part VI Part VII af AJ N SWAN Help Overview Model structure BIE o EE NU Data fle Nc Simulation type 1 esee seen ee eene nnn nnn nn Initial conditions ee sees eere eee MESEN c M Modelled period eese Bedre Wetting and drying eese Boundary conditions Bourdary YPES ciadna lvo Leva kw eran eapve e ava aaa Closed DOURGANES uconissneoc ridge emcee Water level DOUNGANY 2 nnietine aor tains Eod utua ERR E ca Ex MEE OUR EEG uuEE Discharg DOUNGALY uarias diras Raus Kx Dux Vies pecu a BED KRE MR ER EA Weir type internal boundary essere Topography based flooding eeeeeeee es Boundary value t Typical flooding boundary conditions Controlling th
3. hydrodynamics o Prescribe discharge or water level e Particle tracking o Analytical advective trajectory calculation within a cell o User defines seeding points by a pattern or by an explicitly given set of points e Flood maps o Largest extent of the flood o Flood arrival time flood residence time o Peak flood level and its time 2005 Tamas Kramer www vit bme hu SWAN user s manual 2 2 e Input and output of simulation results o To from disk with specified interval o Replay a completed simulation o Hotstart continue a completed simulation e Standard Windows interface e Edit solve and visualise in a single program o All parameters are accessible through dialogs o Edit grid data in top view and axonometry o Velocity field visualisation using arrow field streamlines frontlines and particles e Manual control of the simulation start step halt o Simulation results can be viewed and copied on the fly during the calculation e Data exchange with other applications o Input from text and Surfer GRD formats Output to text Surfer GRD Surfer BLN and Tecplot formats Clipboard I O fully supported allowing e g exchange of tabular Excel data Hotstart from RMA2 finite element simulation files Export model to SMS Surface Water Modeling System Import picture in WMF format save graphical window contents to WMF and BMP format to file or clipboard O O O OO Limitations SWAN assumes hydrostatic pressure d
4. Boundary Zout Water level Prescribe given by time series and the previously created 50 48 5 timse series is selected in the list box Discharge S side outflow is positive prescribe value by auxiliary data NoCrossVel ZeroCurvature e Boundary Groin Water level Nothing is prescribed Discharge Prescribe value by auxiliary data Weir Typical flooding boundary conditions The example shown here refers to the modelling of an initially dry floodplain that is flooded following a levee breach The extent of the flooded area changes during the unsteady simulation No specific boundary condition must be specified for the wave front the model handles it automatically like closed boundaries The lake situated on the floodplain is filled initially using a water level boundary We define a condition with topography based flooding FloodFill so that its is sufficient to assign the boundary condition to one single cell on the boundary map The remaining floodplain is initially dry therefore the initial water level is in the model parameters set to a value lower than any terrain elevation The discharge enters the floodplain through the breach boundary Q that is determined by a one dimensional river model or a time series As the boundary is closer to the horizontal gridlines the discharge is positioned on the S cell sides regardless of the stepped representation of the boundary The total discharge is distributed by keeping g
5. content changes which is useful for tracking the evolution of the simulation Four main graphical elements can be laid on top of each other Gridlines that connect cell centres which are not equivalent to cell boundaries A fill shades cells according to the variable value Contours are drawn independently of the pattern with the specified interval and colour coding Vector fields are visualised by an arrow field of arbitrary magnification and distribution uod m Contours 2005 Tamas Kramer www vit bme hu 20 SWAN user s manual The axonometric view offers only a subset of the plan view It does not draw vectors traced particles and background map To configure the grid view window right click or select View Grid view properties from the menu You can also access five zoom factors from the View menu but the zoom magnification factor can be set numerically in the Grid view properties dialog at Magnify Overall In axonometric view Graph type 3D 1 100th of the vertical exaggeration can be given Magnify Vertical The axis scales are plotted with the Scale box When visualising model output grids dry cells can be coloured differently It may be useful in an axonometric view to hide cells located on the land water boundary by checking Invisible shoreline The colour scale the accompanying legend and the field variable on which it is based can be set in each tab The next screenshot explains th
6. domain with the appropriate density and extrapolation is best avoided For a smooth surface and uniformly distributed elevation points the kriging interpolation generally yields good results otherwise linear interpolation with triangulation is recommended The elevation of cells inaccessible to water i e exterior cells plays no role in the calculations it influences only the graphical appearance in the grid viewer SWAN accepts the DEM as an ASCII table with the elevation values listed from the top left to the bottom right corner separated with tab or space and rows ending with a carriage return Decimal points must be used not decimal points Surfer GRD files are also accepted in any flavour ASCII binary or Surfer 7 Attribute map The spatial distribution of the hydraulic resistance and the extent of the flow domain is defined by the attribute map It is generally produced from topographic maps land use maps or aerial photographs The terrain is classified from the perpective of the hydraulic properties Surface characteristics vegetation type and the attributes are defined for these classes Create a vector drawing of the boundaries and rasterise this vector drawing in the resolution of the DEM Like the DEM the attribute map is imported as an ASCII table or a Surfer GRD file The attributes are referred to by their ID in the range 0 255 Time series Unsteady boundary conditions are specified using time series imported into
7. files manually choose Model IO Export flow grids and Model IO Export flood grids which save the above grids in the same folder as the SWN file Warning Keep in mind the following to avoid losing simulation data e To preserve the previously computed GTS files disable flow field writing before resetting or initialising a simulation or enter a new simulation name in the Write to box e Save the SWN project file before closing so that the reference to the GTS files is remembered next time the project is reopened Input By reading the solution of a previous simulation we can use SWAN to visualise flow fields convert the results to a different format or use it as the initial condition for another simulation called hotstarting Hotstart To hot start with a previous solution choose Calculate Hotstart from the menu select the Simulation in the list box from the grid time series available in the project file the Simulation name was given to the stored flow fields in the Write to box Set the timestep to impose as initial condition in the End field The default timestep is the last one in the grid time series It is also possible to overwrite model results with the content of GRD files using Model IO Import flow grids GRD These solution grid files were previously written either by automatic backup or explicitly using Model IO Export flow grids The same function is available for flood grids Use Model IO Update all fields afte
8. is generally adequate to judge the level of convergence by following the evolution of a representative nodal water surface or velocity value in a grid viewer window or by recording the time series Unsteady simulations By default SWAN yields an unsteady solution In contrast to steady state simulations the inaccuracy of initial conditions affects the first stage of the simulation 2005 Tamas Kramer www vit bme hu Model structure 7 3 4 Initial conditions We must prescribe the initial water level and volume flux at each grid node Cold start With a cold start the simulation starts with water at rest all wettable cells are filled up to the user defined initial water level and velocities are set to nil To set the initial water surface choose Definitions Model parameters from the menu and edit the corresponding field in the dialog box Cells in which the bottom elevation is above the initial water level will become dry We can set a variety of initial conditions using boundary conditions supplemented with the nitOnly switch To fill ponds individually by controling water level or volume use the topography based flooding facility Hot start Hot starting means that initial conditions are supplied by the final result of a previous simulation This is especially convenient if the siimulation is to be repeated with a slight change in the parameters In SWAN hot starting is accomplished by reading stored simu
9. of the grid are in fact equivalent to the cell centres HM ode Cell The digital elevation model and the attribute map are in the same resolution as the computation The grid nodes are indexed so that the row index runs faster than the column index Indexes range from 0 to n 1 where n 7 n n is the number of cells in the given direction 0 0 Hr l 0 Data file Except optional hotstart and replay files all input data of a simulation is contained in a single project file with extension SWN The file is binary and can only be edited within SWAN Besides that the software also provides text based export import for grids and data series The simulation results are not stored in the SWN file Those results are lost unless we make sure from the beginning that they are written to output files see Result output Simulation type The model solves the unsteady governing equations and in addition allows steady state simulations Steady state simulations We let the unsteady solution converge to the steady state solution by holding all boundary conditions constant Theoretically convergence takes extremely many iteration steps to reach machine accuracy Practical accuracy requirements are generally more relaxed and permit shorter simulations Since SWAN does not provide an automatic convergence stopping criterion the user must monitor the simulation and stop it either manually or by pre programming the end time of the simulation It
10. of using actual dates and times is that modelled flow parameters can be compared directly with measurements Of course the absolute times have no significance with steady state simulations Dates are given according to the Regional settings of Windows also shown in the dialog box for example m d y means month day year i e Dec 24 2005 is entered as 12 24 05 3 7 Bed resistance Bed resistance is calculated by the Manning formula Es Lam PP 2005 Tamas Kramer www vit bme hu SWAN user s manual 3 8 where k m s is the Strickler smoothness coefficient the inverse of the Manning roughness coefficient k 1 n SWAN takes into account the distribution of k according to the land use vegetation type and bed characteristics The Manning formula is used to describe resistance due to both surface roughness and vegetation with the assumption that k is independent of the local water depth Attributes The Strickler smoothness coefficient is not directly specified on the grid Instead the coverage is classified into a limited number of coverage types and an attribute definition is created for each type These attributes describe the value of k and whether the cell is accessible to water A new project defines by default two types of attributes Land and Water and assigns the ID 0 and 1 to them respectively We can add further attribute types which are automatically numbered with a unique ID some software re
11. the active velocity field then display streamlines in a grid viewer window Define seeding points Seeding points are defined through a list of points with their I J grid indexes The list of points is either a generated by SWAN or b imported into the project a Seeding points generated by SWAN cover the whole flow field uniformly in a random fashion or in a regular array Once the model has been initialised in order to delimit wet cells select Define Seed locations from the menu The mean horizontal and vertical spacing as well as the maximum number of points must be defined The generated list of points will be added to the project under the category Vector time series in the project window and can also be used as the pattern of vector field arrows JE b o5 ho h bod h h b o Regular Random b To explicitly define seeding points import their list as Vector time series Cartesian with the time information disregarded This list can be created in Notepad or Excel by entering the fractional and J index of each seeding point one point on a line Use the following formulae to convert physical coordinates x y to grid indexes J for grid alilgned physical coordinate systems X Xien dx J Ytop Y dy where Xje and Yio are the left and bottom coordinates specified in the Grid properties Compute flow lines The flow lines are computed according to the actual velocity field therefore the simu
12. the auxiliary data the whole pit is filled up to this level however the right pit is flooded only after the separating ridge is exceeded Furthermore the subsequent lowering of the water level leaves the right pit flooded to the level of the ridge In all cases the velocity components are set to zero 2005 Tamas Kramer www vit bme hu Boundary conditions 13 4 3 Specifying ByVolume instead of ByWLevel in the auxiliary data changes the water level until the prescribed water volume has been spread around the boundary We obtain a piecewise discontinuous water surface in general When a ridge is exceeded the model follows the steepest descent from the lowest point of the ridge to find the next recipient water body behind the ridge where the distribution can continue Even though the FloodFill ByVolume boundary is of water level type the boundary value is exceptionally interpreted as the water volume to be distributed in m This can be a negative number to specify extraction A variant of topography based flooding by volume is topography based flooding by discharge This is specified with the follwing line in the auxiliary data field FloodFill ByDischarge With that line the procedure is the same as with the ByVolume parameter but the volume increment or decrement will be timestep dependent The boundary value is the discharge in that case in m s though this is not reflected in the dialog window It is emphasise
13. the simulation with the command Calculate Initialise the simulation window is opened on the right The top panel in the window informs about the progress of the simulation The model output grids and the recorded time series appear below the top panel The category Model input grids lists the active grids from the project window the Model result grids category lists the fields of the model output If the menu item View Show internal grids is checked the internal grids are displayed beneath the output These contain the grids of internal variables useful for debugging or to inspect intermediate results such as staggered discharge components or the indicator grid The category model time series is present only if time series are being recorded An entry is added for each recorded variable and each recording point Opening the simulation window simultaneously resets the simulation to the initial conditions and enables relevant commands under the Calculate e Initialise Opens the project window and initialises the simulation 2005 Tamas Kramer www vit obme hu User interface 29 e Start Launches the simulation or the replay e Increment Performs one timestep then stops e Stop Pauses the simulation e Reset Resets the simulation to the beginning or rewinds the replay All results are overwritten according to the initial conditions e Record time series Inserts a new time series that tracks the flow variab
14. time when the peak occurred flood residence time Before starting the simulation switch on the calculation of Flood maps in the dialog box brought up by the menu command Define Flow The flood maps are available for visualisation or copying in the simulation window To track flood variables record time series on the flood maps at any number of nodes 8 Export results 8 1 Export graphics Contents of a grid viewer window can be exported to file or copied to the clipboard in raster BMP and vector WMF formats using Edit Copy or Edit Export respectively Both file formats are native to Windows and supported by all major office and illustration software To copy graphics to the clipboard you can use the keyboard shortcut Ctrl Ins Data appears on the clipboard in four flavours Picture and Picture Enhanced metafile are the vector formats Bitmap and Device independent bitmap are the raster formats SWAN does not provide any printing function To print graphics copy the data to a printing enabled application such as Word When pasting the graphics to an office application choose the vector formats for unlimited printing resolution and the raster formats for quick robust display at screen resolution 8 2 Record and export time series Record time series to track the evolution of field variables at discrete nodes Recording points A list of named Recording points must first be entered in the dialog Define Recording points
15. with the syntax name I Jd e g dam 12 7 A 58 23 B 152 20 The indices I J refer to grid nodes and can be read on top of the floating Value box in a grid viewer window If the Value box is not visible double click on any node to display it Record time series To record the history of a field variable right click the respective grid in the simulation window and select Record time series at any stage of the simulation This brings up a dialog with the recording parameters The time nterval is set independently of the simulation timestep Recording is done in an integral fashion the element in the time series represents the nodal time average of that field variable during the interval To record at a single node enter its J indices in the Position fields and press OK To record at all predefined recording points close the dialog box by clicking All points Recorded time series are listed on the bottom of the simulation window Repeat the procedure above for other field variables to record simultaneously any number of time series The time series will be truncated if the simulation is reset which causes the previously recorded data to be discarded Similarly to simulation field variables the time series are not saved in the swn file and are lost with the closing of the simulation window Export time series Export time series to the clipboard or to an ASCII file with the menu command Edit Copy and Edit 200
16. with the method of Jobard amp Lefer 1997 The average spacing s of the pathlines is controled by the user With evenly spaced streamlines the seed 2005 Tamas Kramer www vit bme hu 24 SWAN user s manual 7 6 locations are not given explicitly they are instead determined automatically with respect to the desired spacing To bring flowlines closer where the velocity is high specify a factor for the smallest spacing called f The spacing of the pathlines will vary gradually with the local velocity between s to f s The evenly spaced streamlines are calculated once the dialog box is closed with the Add button It may take several minutes especially with high number of grid nodes and small spacings therefore these pathlines are not updated if the velocity field changes they must be instead recalculated manually Streamlines can be Added Replaced Deleted or Copied to the clipboard at any time during the simulation Visualise flow lines Once calculated flow lines can be displayed in grid viewer windows of model output by pressing the Flow lines button in the Grid view properties dialog The button is grayed if this is an input grid viewer or if no flow lines have been calculated Pathlines Time lines and Particles may switched on and edited individually The value in the Skip field controls the interval for drawing path lines or time levels Setting Skip 1 will draw all traces and flow lines To have
17. 5 Tamas Kramer www vit bme hu 26 SWAN user s manual 8 3 8 4 Export respectively after having selected the time series in the list box The time series will be copied without any header consisting of the average values recorded at the given time interval To export all recorded time series simultaneously preceded by a date time column choose Model I O Copy all time series Export grid data To export the numerical contents of a grid to the clipboard or to a file right click the grid in the simulation window or the project window and choose Copy or Export from the context menu You can also use find these commands in the Edit menu When exporting to a file several file formats are available By saving in text format a table of values delimited by tabs is written The three Surfer GRD formats save it for reading into the Surfer program For attribute maps and indicator maps the Surfer BLN format will replace Surfer GRD and will export the boundary of the wet cells for blanking in Surfer More precisely the following boundary is generated depending on the grid Field variable Boundary in BLN file for Attribute map Cells with wettable attribute Indicator Currently wet cells Indicator flow Cells with wettable attribute Flood indicator Cells flooded at some point during the simulation The Tecplot PLT format binds all variables in a single Tecplot data file Tecplot and Surfer
18. Q is the total discharge L is the boundary length If the depth or the smoothness has a varied distribution along the open boundary option d may give the most realistic steady state approximation It is expected that the error made by an inaccurate distribution of Q is reduced with distance from the boundary because the governing equations rearrange the discharge according to the actual hydraulic situation It is therefore advised to set up the open boundaries at locations with predictable close to uniform flow distribution extending by some distance the limits of the studied domain The internal layout of the computational grid is such that the components of the specific discharge lie at the midpoint of the perpendicular cell side not at the cell center this is the so called staggered layout As the boundary conditions are assigned to cells through the boundary map the open side of the boundary cells must be specified explicitly in the definition of the boundary condition The open side is adjacent to an external and an internal cell we must assign the BC to the internal cell Finally we must specify whether positive discharges mean outflow or inflow Two exampes are shown for discharge boundaries and their definition Cout F C Side W Side H Positive for inflow Positive for outflow Weir type internal boundary Flow over weirs and levees undergoes large acceleration so the assumption of hydrostatic pressure conditions introduces e
19. colour scale concurrently To set the colour scale for a grid go to the Grid properties dialog box of the respective grid either a in the grid list of the project simulation window or b in the display properties by right clicking in the grid viewer window or by selecting View View properties when that window is active then pressing the Grid button When visualising simulation grids dry cells can be distinguished from wetted or wettable cells by selecting a different colour Three land detection methods are available Wet vs dry cells according to the current water surface Water accessible vs land type cells according to the attribute definition Flooded vs never flooded cells meaningful when wetting and drying is enabled All grid cells may be treated without distinction 2005 Tamas Kramer www vit bme hu 22 SWAN user s manual Input grids visualised from the project window do not see any wet dry information even when a simulation is running therefore no land detection is available in those windows Legend axis scale Check the Legend box in the tab of the graphical element to show the legend key to the colour scale The legend relates the colours to the field variable values if they are gradient coloured otherwise no legend is displayed Arrow fields express the magnitude also with their size therefore they may have a legend even if they are uniformly coloured Set the p
20. const Any other choice would cause an error because the depth is initially zero along the boundary The area is crossed by a road whose embankment is modelled as a weir Not only the road is inclined relative to the gridlines but it also has variable elevation consequently the weir crest elevation must be specified through the topography grid 2005 Tamas Kramer www vit obme hu Boundary conditions 17 Model grid e Boundary Q Water level Nothing is prescribed Discharge S side distribution g const inflow is positive prescribe given by time series e Boundary Zjake Water level Prescribe constant value 57 4 m runup 0 auxiliary data nitOnly FloodFill ByWLevel Discharge Nothing is prescribed e Boundary Road Water level Nothing is prescribed Discharge Prescribe position and distribution is indifferent given by auxiliary data Weir 5 Controlling the simulation Before starting the simulation set all model parameters select the active topography attribute map and boundary map To begin the simulation open the simulation window which initialises internal variables and sets the model to the initial state Once the simulation window is open the simulation can be started paused stepped manually or reset to the initial state using the toolbar buttons or the menu The project window may be closed at the end of the simulation Initialise With the initialisation Calcu
21. d in the grid viewer is accomplished by clicking the Base map button in the Grid view properties and selecting one of the Pictures already imported to the project The base map is by default drawn on top of the fill but a different position can be selected from the Drawing order listbox Portions of the base map that extend beyond the grid rectangle can be cropped by checking Crop to grid Some pictures such as those exported from Autocad have a non transparent background that would obstruct all of the graphics below To avoid this check the No fill box so that filled entities in the picture will be drawn with their hollow contour 2005 Tamas Kramer www vit bme hu Visualise simulation results 23 7 5 Flow lines Flow lines facilitate the visualisation of velocity fields These lines are locally tangent to the velocity and are computed by the piecewise analytical particle tracking method of Pollock 1988 e The pathline shows the path followed by a particle released from the seeding point e The streakline connects the particles released continuously from a seeding point and advected by the flow equivalent to a plume e The time line connects particles released simultaneously along a curve and advected by the flow equivalent to a smoke ring In stationary flow fields the stream line and the streak line are equivalent To visualise streamlines in SWAN you need to define seeding points compute streamlines using
22. d that the two latter applications ByVolume and ByDischarge also require a boundary condition of water level type like ByWLevel Boundary value The water level or discharge imposed at the boundary may be constant or unsteady Unsteady boundary values denoted in the following by X t are either periodic or specified by time series When stepping from time level t to t t the model actually uses the average value of X t during the interval t t A Constant boundary value For constant X t the steady value X onst and an optional runup ramping of duration t nu is given ATE fn Periodic boundary value The periodic value is generated by the harmonic function X d ante ws ducis Phe ER cce e T ahol t time since model start s substituted by the solver when evaluating the function Xmin Xmax minimum and maximum value toy phase offset s T period s The last four parameters are supplied by the user ATA Value given with time series Any variation of the boundary value can be prescribed using time series with uniform time resolution The time series must be first imported into the project window with Scalar type The absolute model time must be in accordance with the interval of the time series e g a time series for the period March 1 10 2000 will provide boundary values for a 5 day simulation starting with a model time of March 5 2005 Tamas Kramer www vit bme hu 14 SWAN u
23. e Boundaries to access the dialog where boundary conditions BC can be defined The following typical situations arise e River sections the inflow and the outflow BC must be supplied e Flooded terrain a BC is supplied for each levee breach e Bays a BC is supplied for the open boundary at the entrance of the bay e Lakes reservoirs closed boundaries are automatically handled by the model Boundary conditions added to the list are assigned an ID which is used to mark cells where that BC is active Boundary map To relate boundary conditions to the computational grid we use the boundary map The boundary map is a grid that contains the IDs integer numbers between 0 255 identifying the boundary condition No more than one BC can be prescribed in a cell and the value 0 is reserved for cells where no boundary condition is prescribed typically the boundary map is 0 in most of the domain To edit the boundary map open a grid editing window in SWAN or use another application to edit the tabular map and paste it into SWAN through the clipboard It is important that BCs must be defined prior to entering their IDs in the boundary map A SWAN file may contain several such boundary maps in which case the one to be used in the simulations must be activated The simulation must be restarted if the boundary map is altered Boundary types Closed boundaries At closed boundaries i e levees shoreline the velocity components perpendicular to the b
24. e downstream side of the weir cells disregarding the the boundary side specified in the definition of the boundary condition This procedure ensures that the weir functions as a closed wall while the surface elevation in adjacent cells is below the crest elevation As the following figure shows it the impervious effect is already created by diagonally connected weir cells The curve designates the approximated weir centerline cells shaded with gray are those marked as boundary cells in the boundary map 2005 Tamas Kramer www vit bme hu 12 SWAN user s manual Grid aligned weirs with horizontal crest are more conveniently specified using the auxiliary data We must include the line WeirLevel 146 12 where the value stands for the absolute elevation of the weir crest in m Unlike in the previous method the active topography grid must initially contain the surrounding average terrain elevation in the weir cell not the crest elevation With this method the weir formula is applied only to the cell side defined in the boundary definition the same side for all weir cells of that boundary ID That is why it is advisable to employ the WeirLevel line for grid aligned weirs only The crest elevation or the weir width may change in time To prescribe time dependent b or z specify the name of an existing time series added to the project window as scalar time series which contains the time variation of b t or z t Unlike other bo
25. e function four controls Grid view properties i Magnify Overall 9 ox Vertical 1 5 x100 Gridlines Arrcws v visible Gradient colour G How lines Legend Auto Colour DE Rainbow h 1 Grid Bottom topography M Edit pa 200 opography 25x25 Set scale Edit grid Select field Edit calaur to value range properties variable from list gradient The graphical elements that are independent from the field variables Flow lines the Caption and the Base map can be set using the three buttons on the right The Base map button is enabled only if the project already contains an imported picture The available settings depend on whether the view was initiated from the project or the simulation window according to the following table 2005 Tamas Kramer www vit bme hu Visualise simulation results 21 View was open from the View was open from the project window simulation window Arrows Not available N A Based on grids of the velocity and specific discharge Gridlines Based on topography grids Based on any model output grid except indicator grids Flow lines N A Available if flow lines have already been calculated Land detect N A Wet and dry cells can be coloured differently but only wet cells can have a gradient colour Edit grid Select the edited grid in the Edit listN A box 1 2 Colour scale The four graphical elements gridlines pattern contours arrows ca
26. e simulation Data requirements Visualise simulation results Grid VEN Luren Colour scale Ludde bnsedmaddddaee GN aa EE ENERE BaSe Map vedde HOW UNOS Lee 2005 Tam s Kr mer www vit bme hu SWAN user s manual MA Flood AS RTT CE 24 Part VIII Export results 25 1 EXPOr tile RR 25 2 Record and export time series r arrrnnrnnnennnennnennnnnnnennnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnunnnunnnne 25 3 Export grid II 26 A SONE c KKKNS S 26 Part IX User interface 27 1 FO ilte on MERE UU TT e 27 2 Simulation WU OW ETE Tm 28 3 Grid view edit iom nnne 29 4 Model parameters dialog rnnnrnnnnnnnnnnnnnernnnnnnnnnnnnnnnnnennnnernnnnnnnnnnnnennnnernnnernnnnnnnnnnnnennnnennnnnnnnunnnnuee 29 Part X Error messages 30 Part XI More information 30 Part XII References 31 Index 0 2005 Tamas Kramer www vit bme hu SWAN Help 3 1 SWAN Help SWAN User s manual Budapest 1 24 2006 This manual describes the use of the two dimensional flow model SWAN It is expected that the reader knows the basics of typical Windows software 2 Overview 2 1 The program SWAN SWAN is a graphical Windows software that allows the user to set up run and post process the built in depth averaged shallow flow model It describes free surface subcritical flow fields by calc
27. ector time series Grid time series Pictures The titles of empty categories do not appear in the project window The Edit menu and the context menu contains the commands available for the selected item e Edit Opens a grid viewer window for the selected grid which allows the editing e Resolution Reinterpolates the grid to a different cell resolution This method may produce crude results therefore it is recommended that the grids are recreated from the original data e Activate selects the grid for use in the simulation Active grids ara marked with the text active e Cut Moves the selected item to the clipboard then removes it from the project e Copy Copies the item to the clipboard e Paste Insert the clipboard contents to the project Specify in the dialog boxes the type of item whether to overwrite the selected item The pasted item will be placed to the last position in its category e Delete Removes the item from the project Active grids cannot be deleted When deleting grid time series the corresponding GTS files are deleted only with the user s confirmation e Export Copies the item to a file e Import Pastes an item from a file The procedure is the same as with Paste e Properties Edit the object s name and other properties Closing the project window is equivalent to closing the file A confirmation is asked if the project has been changed since the last save Simulation window By initialising
28. entarily from the calculation and by gradually switching of terms in the momentum equation vanishing with depth 2 3 Host system requirements Hardware requirements The program runs on all tested PC s equipped with 32 bit processors Simulations on large grids gt 40 000 nodes may be so demanding that concurrent applications slow down considerably All data including inactive grids in the file must simultaneously fit in the memory but the explicit nature of the solver means that no coefficient matrix must be built therefore the RAM in today s 2005 desktop computers is never a limiting factor If the simulation is written to disk incrementally the written files typically use several hundred megabytes The application consists of one executable of less than 1 megabyte Software environment SWAN requires any Microsoft Windows operating system newer than Windows 95 Due to the limitation of the compiler the code is 16 bit so it works only with old DOS style folder and file names How to install and uninstall Copy files SWAN EXE and CTL3D DLL to the desired destination folder The software is removed by simply deleting these files 2005 Tamas Kramer www vit bme hu SWAN user s manual 3 1 3 2 3 3 Model structure Discretisation For the numerical solution the flow domain is split to identical rectangular cells We use the regular grid defined by the cell centres to discretise the domain The nodes
29. every 10th pathline or streakline set Skip 10 under Pathlines streaklines To display every 10th time line or particle trace set Skip 10 under Time lines Additionally pathlines streaklines can be dashed by checking Draw with alternating colour Length 1 is length 2 are the number of traces to show with Co our and Colour 2 respectively The segment length between two consecutive traces is the distance the trace travelled during the time interval of the flow line the dashes are therefore proportional to the velocity The following examples show how to use flow lines to visualise the east directed flow around a spur dike The seed points were distributed along the inflow section for the first three cases and near the square corners in the last figure eee s s a ll ee ee ee e Uc lt uh i ar a ee Oee nm Pathlines Time lines Flood maps By post processing the flow solution of flood problems flood dynamics and floodplain vulnerability can be expressed with flood maps The flood maps offered by SWAN show the distribution of the following field variables e flood arrival time since the start of the simulation 2005 Tamas Kramer www vit ome hu Visualise simulation results 25 flood retreat time peak flood level and peak flood depth
30. fer to attribute as material type Attribute map In the end the attribute ID is assigned to each grid cell through the attribute map This map is in fact a grid of the same size as the elevation grid but contains IDs that refer to the corresponding attribute The attribute map can be edited graphically within SWAN or exchanged with other software such as Excel as an ASCII table A SWAN project file may contain more than one attribute maps in which case we must activate the one that is used in the simulation In a typical river model the main riverbed and the floodplain are distinguished by their own attribute For further differentiation the cleared cultivated and forested floodplain can all have their own attribute Seasonal variability of the hydraulic resistance is then implemented by changing k in the attribute definitions To exclude cells from the flow domain their attribute ID is set to 0 on the attribute map Or if all cells with a given attribute are to be excluded the definition of that attribute is modified to inaccessible to water Wetting and drying Following general practice cells are considered dry if the depth is less than a truncation depth i e h lt hunc Otherwise they are wet Dry cells are excluded from the flow computation in that timestep To increase robustness of the solution two intermediate depths are introduced Amin Pori by which the terms of the momentum equations sensitive to shallowness are gradua
31. ffective turbulent stress tensor are obtained using au Ou gv ov EE SV x My M P A SV ay The symbols used in the above equations are the following X V horizontal Cartesian coordinates m f time 5 B g x and y components of the unit discharge q m s h water depth m U Y x and v components of the depth averaged velocity v m s Zh terrain elevation m n water surface elevation m 4 2 Z j g acceleration due to gravity m s Vet effective horizontal eddy viscosity coefficient m s Tes Tey x and v components of the bottom shear stress Pal Te Tay X andy components of the surface shear stress due to wind Pa p water density kgim Fer Strickler terrain smoothness m c The governing equations in SWAN are in the so called nonconservative form which assumes that the solution is continuous therefore it is only applicable to subcritical flow More about the model can be found in the paper by J zsa et al 1999 The shallow water equations are described in detail in the book by Kozak 1977 Numerical solution The solution is obtained numerically in finite timesteps on an equidistant Cartesian grid using the finite difference method Spatial derivates are approximated by second order central differences Time marching is accomplished with an explicit first order Euler or second order Runge Kutta scheme Wetting and drying is handled by excluding very shallow cells mom
32. files are written in terms of physical coordinates respecting the Left and Bottom coordinates specified in the grid properties Store flow fields Store intermediate flow fields for replaying the simulation or for resuming the calculations later Output The parameters controlling the output of flow fields are accessible by selecting Define Flow from the menu that brings up the Flow computation dialog then by pressing the Settings button under the Time stepping category Check Write to enter a name for the simulation in the box below and the Time interval between two outputs The simulation must be reset if these output settings are changed On reset SWAN will create two entries under Grid time series in the project window one for the depth and one for the specific discharge vector These entries are links to external GTS files in the same folder as the SWN project file To see the details of the external files look at the properties of the grid time series right click then Properties The reference contains a relative path therefore these GTS files must be moved together with the SWN project file The depth and the specific discharge fields are sufficient to reconstruct the flow field at the time resolution given in Time interval A trade off is often necessary between time resolution and the file sizes In fact GTS files can grow quite large several hundred megabytes is not uncommon for long unsteady simulations Nevertheless the
33. ift Insert which copies the clipboard contents to the Edit field The new value can be accepted by e pressing Enter or e selecting another node with the mouse or e moving the cursor with the arrow keys which at the same time moves the cursor to the next node Pressing the Esc key in the edit box returns to the original value Once a value is accepted it is directly written to the grid contents so there is no need to save the editing to the original grid There is no undo facility in SWAN The grid view is redrawn with the changed value in all windows where it is displayed 9 4 Model parameters dialog Model parameters are set by choosing the commands in the Definitions menu e Attributes dialog to edit the list of attributes e Boundaries dialog to edit the list of boundary conditions 2005 Tamas Kramer www vit bme hu 30 SWAN user s manual 10 11 Recording points Enter the name and coordinates of points used to record time series Seed locations Generate a series of points that cover the flow domain uniformly in a random or regular pattern used for arrow placement in grid viewers and for seeding flow lines The generated points are inserted as Vector time series in the project window Available only after model initialisation Flow Set the solved form of the governing equations reading and writing of simulation grids wall slip and calculation of flood grids Model parameters
34. istribution and subcritical flow regime Its use is not recommended for problems where the horizontal 2D description is inaccurate processes with scale of the depth or less in stratified conditions due to density differences and generally in cases where the vertical acceleration significantly affects the Reynolds averaged flow The model s capacity is in general constrained by the available RAM and CPU The following limits are imposed on the modeller Number of attributes lt 255 Number of boundary conditions lt 255 Number of grid nodes lt 10 000 in any direction Number of tracked particles lt 10 000 Governing equations The motion of free surface waters is described by the Reynolds averaged and depth integrated form of the Navier Stokes equations the so called shallow water equations This set of PDEs describes the evolution of the flow state variables namely the water depth h and the two Cartesian components of the horizontal volume flux aka specific discharge The governing equations take the following form eae ree e d dx dy 2 op 9 PC 2 24 2 Er 2 Of dxl Ay A dx oO aye ala M PIRE Tay 2 ax pe 2 A ETE go 2 E 28 a Of Ox ay Oxigc aye ala Ty TE n 4 E D 2 Oy where the bottom shear stress is calculated by the Manning formula 2005 Tamas Kramer www vit bme hu Overview 5 _ FE 3 3 i 7 Yay P ta p Tay cO Jp tgg the elements of the depth averaged e
35. late Initialise the model allocates internal structures in memory and fills them according to the initial conditions This step opens the simulation window appear on the right which lists the input and output grids and time series The active input grids should not be resized while the simulation window is open Start The command Calculate Start launches the simulation If it is grayed then the model must be first initialised Step The command Calculate Step advances the simulation with a single timestep then stops Stop The simulation can be stopped paused by the command Calculate Stop or the F8 key After the completion of each timestep the execution is returned to Windows If we open a dialog window while the simulation is running in the background the simulation is automatically suspended till the dialog is closed SWAN will propose to finish the simulation when the End time given with the model parameters has been reached If that field is left blank the simulation can be stopped only manually Closing the model window stops the simulation closes output grid viewers and frees memory allocated to internal structures To put away the simulation window without terminating the simulation minimise 2005 Tamas Kramer www vit bme hu 18 SWAN user s manual the window instead of closing it Reset The command Calculate Reset rewinds the simulation to the initial state The latest results will be lost but
36. lation must be initialised beforehand In addition stationary pathlines require that the simulation has already converged to steady state To initiate the calculation of flowlines choose Calculate flow lines from the menu The Line type defines whether only the last trace or vertex of the flowlines is advected pathline or all the vertices of the flowlines streakline during a timestep The third line type evenly spaced streamlines works somewhat differently and is discussed in the next paragraph Time resolution sets the time interval between the traces of the flow lines a smaller value gives smoother flow lines at the expense of more computation However the accuracy of the individual trace positions is not influenced by the time resolution just the number of traces Control the maximum length of the flowlines by specifying the upper limit for the number of traces up to 10 000 If the flowlines grow past this length the oldest traces will be deleted to keep the length at the specified maximum The seeding points the initial trace positions are selected from the list It is also possible to generate uniform seed locations within the Flow lines dialog box To delete unnecessary seed locations close the dialog box go to the project window and delete them from the Vector time series If you select evenly spaced streamlines the whole field is filled at once by pathlines with a uniform distribution by freezing the current velocity field
37. lations from disk 3 5 Timestep The timestep is selected not only according to the desired time resolution but also considering stability and accuracy constraints Variations of the flow or boundary conditions that are faster than the timestep are described only in an average sense The so called CFL Courant Friedrich Lewy stability crierion imposes an upper limit to the timestep of the explicit time marching scheme Ar man iv a uM A48 thay Ay where the minimum is taken over all cells AVE instability manifests itself in excessively oscillating solution negative depths and unrealistically high velocities The stability of the solution may require that the timestep dictated by the CFL criterion is reduced by a factor amp czz 0 5 0 95 If we enter a value for crz then SWAN estimates t with the above formula in each timestep If only At is specified and the field amp czz is left blank then the timestep is kept constant and the model does not check whether it fulfils the CFL criterion dba In a flood application the minimal value of At was found near the inflow boundary with 100 m g 9 81 m s h 3 m u 1 5 m s the allowed timestep is approximately 100 Af 5 11 4 881 315 3 6 Modelled period The start time of the simulation is given with an actual date and time If the end time is entered the simulation is paused automatically after reaching it otherwise it must be stopped manually The advantage
38. le selected in the simulation window e Flow lines Controls the calculation of flow lines e Replay Activates the replay mode where the evolution of the flow variables is read from grid time series stored on disk Closing the simulation window is equivalent to terminating the simulation Therefore if the simulation window unnecessarily obstructs the screen minimise it instead of closing 9 3 Grid view edit window Selecting Edit Edit from the project window or Edit View from the simulation window or double clicking while a grid is selected opens a grid viewer window to graphically edit or view the contents of the field variable Model grids can only be viewed not edited Edit grids In editing mode the active node is highlighted with a round cursor The variable value at the highlighted node is displayed in the Edit field of the floating Value window If that window is not visible double click on the node or select View Show values from the menu To move the cursor click a node with the mose to make it the active node or use the arrows keys on the keyboard Holding down the Shift key jumps by 10 nodes at once holding down the Ctrl key jumps to the respective end of the row or column To change the grid value enter the new value in the Edit field of the floating window This is done like in Excel pressing F2 left clicking in the text box of the Edit field or entering the first digit of the new value or pressing Sh
39. lly switched off with a factor a Burchard 1998 h hun Cas Pan if S Peri The value of Amin and h is problem specific generally in the order of 0 01 to 0 1 m To set their value select Definitions Flow model in the menu choose Method Burchard and click on Wetting and drying Setup The meaning of the fields e Minimal depth Value of Amin e Critical depth Value of hori e Truncate depth Value of Nino A cell is considered dry if its depth is smaller than that To have at least this deep water in all cells swith on the Truncate very small depth values flag e Additional viscosity Experimental Should be set to 0 The following relationship must be respected 0 lt Aine lt Amin lt hos 2005 Tamas Kramer www vit bme hu Boundary conditions 9 4 1 4 2 4 2 1 Boundary conditions Prescribe boundary conditions Along open boundaries of the flow domain the solution of the governing equations must be extended by boundary conditions that prescribe water level or discharge The shoreline constitutes a closed boundary where normal flow is not permitted The flow state h p q set at open boundaries may given as a constant an analytically function or a time series To prescribe boundary conditions BC in SWAN we must first define the list of boundary conditions then assign those conditions to cells that make up the open boundary List of boundary conditions Select Defin
40. n be individually switched on to show the variation of a flow variable across the field with gradually changing colours The colour scale is either a gradual transition between two selected basic colours C Cmax or it is one of the predefined colour scales Rainbow LR linear rainbow BTC blue to cyan Kelvin LOCS linearized optimal color scale and Topography The advantage of using the LR BTC Kelvin and LOCS scales is that they reduce to linear grayscale when printed in black and white The scale consists of 16 grades for the gridlines contours and arrows 2 4 8 16 32 64 or 128 grades for the pattern The colour scale limits S Smax are set independenly of the value range Xmin Xmaxl so that a smaller subrange can be visualised with high contrast for example Go to the grid properties and switch on Automatically update scale to stretch the colour scale limits dynamically to the varying value range while the simulation is running For vector field variables e g velocty specific discharge wind the colour scale reflects the magnitude of the vector wm ET wax D qo uda a s C uis Jw The pattern of attribute and boundary maps is coloured according to the colour set in the attribute and boundary definition respectively and the gradient colour settings are ignored The scale limits are set for the grid not for the grid viewer window so that two windows displaying the same grid cannot use a different
41. n both sides the weir will inhibit any flow like an impervious wall Weirs are implemented in SWAN as internal boundary conditions of discharge type defined by weir specific auxiliary data No boundary value is directly given The row Weir must be included in the auxiliary data which tells the model that the discharge is instead calculated by the weir formula according to the previously detailed procedure The optional line WeirCoeff 1 7 overrides the default weir coefficient C 1 6 m 7s If the weir width is not equal to the cell size the actual width 150 m in this example is specified with the line WeirWidth 150 When no width is given SWAN takes b equal to the cell size The crest level may be specified in two ways through the topography grid or using the auxiliary data The more common use is that the model takes z from the topography grid so that levees with variable elevation can be described In the shallow water solution qsye the model calculates with the average terrain elevation of the adjacent cells instead of the weir elevation as z is generally representative only to a small portion of the cell We note that the topography grid listed in the model window is already the modified version of the input topography grid where the elevation in weir cells were overridden by the average elevation of adjacent non weir cells When crest elevation is given through the topography grid SWAN applies the weir formula on th
42. osition of the legends to the left or bottom of the window or to an automatic placement Te 222 The physical size of the flow domain is shown by the axis scale Grid view properties window scale check box Coordinates are relative to the origin in the bottom left corner of the grid Absolute coordinates cannot be displayed 7 3 Caption A multiline caption may be inserted into grid views to add text to the graphics such as the title of the simulation The caption may contain static or dynamic fields that are substituted with the respective value and are updated in the course of the simulation The recognized codes are the following MT Model time date and time ET Elapsed time date and time MTT MTD Model time time only date only Elapsed time ETT ETD ETH time only date only decimal hours only SC Simulation step count incremented by one at each timestep N Filename FN Full filename with folder Z 1 Water surface elevation at boundary 1 m Q 3 Discharge at boundary 3 m s WB 1 Weir width at boundary 1 m WZ 1 Weir crest elevation at boundary 1 m The caption can be aligned horizontally and vertically to the window frame or to the bounding rectangle of the grid To turn on caption in grid views bring up the Grid view properties dialog and press Caption 7 4 Base map A base map laid on the grid facilitates the interpretation of the flow fields Laying a base map onto the gri
43. oundary will automatically be set to 0 so that the user does not have to define any boundary condition here The discharge component parallel to the closed boundary pw is also determined by the model pw A p where p is the closest specific discharge inside the domain see figure below and A is a wall slip coefficient The value of A is any number between 0 1 A 0 lateral flow is reduced to 0 A 1 lateral flow is unaffected by the wall ST Fi P The value of A is given universally for all closed boundaries by choosing the command Define Flow from the menu and filling the wall slip coeff field 2005 Tam s Kr mer www vit bme hu 10 SWAN user s manual 4 2 2 4 2 3 4 2 4 Water level boundary The absolute water level and not the water depth is prescribed in the center of the cells Discharge boundary At these open boundaries the total discharge Q is prescribed The model then distributes the discharge among the boundary cells by keeping vh vj v h or Sy uniform where v the velocity component normal to the boundary h local water depth Sm the energy slope computed using the Manning formula Sy v I K h distribution of Q weight of g weight of v a vh const 1 h b v const 1 h 1 c v h const 1Ih 1 h d S const 1 kh 1 kh Option a is equivalent to setting the specific discharge q Q L where
44. r any modification of the solution grids Replay A previous solution can be replayed for the purpose of animation or time series recording Choose Calculate Replay mode from the menu select the Simulation from the available grid time series in the file the Start date and End date and the timestep Initialise the model if not yet done open any grid viewers and use start step pause and reset buttons to navigate in the stored results with the specified timestep No backward stepping is currently possible only full rewind 7 reset While in replay mode all steps can be written to a single Tecplot file the steps being represented by zones with Model IO Export replay To exit from replay mode choose Calculate Replay mode and remove the check from Enable replay mode 9 User interface 9 1 Project window The software has a familiar so called Multiple Document Interface that is client windows can be opened and rearranged in the main window and provides standard functionality Familiar menus Right clicking brings up the context menu Toolbar Data exchange through the Windows clipboard The project window is the main window that opens when a file is opened or created It lists the items added to the project and allows their editing 2005 Tamas Kramer www vit bme hu 28 SWAN user s manual 9 2 The items are listed arranged by type Topography grids Attribute maps Boundary maps Scalar time series V
45. reamlines of arbitrary density Proc Visualization in Scientific Computing 97 pp 45 55 Boulogne sur Mer France 1997 Kozak M A szabadfelszinu nem permanens raml sok sz m t sa Akad miai Kiad Budapest 1977 Pollock D W Semianalytical computation of path lines for finite difference models Ground Water 1988 26 743 750 2005 Tamas Kramer www vit bme hu
46. rror in the solution At these places the stage discharge relationship used for weirs is more accurate than the shallow water momentum equations The weir formula yields the specific discharge in function of the upstream water level weir crest elevation and downstream water level g 80 red szig where 2005 Tamas Kramer www vit bme hu Boundary conditions 11 B submergence factor see below b weir crest width across flow An grid interval across flow V R upstream water surface elevation Zi weir crest elevation Cw weir flow coefficient C 1 6 1 7 C may be expressed by the discharge coefficient used in some weir formulations as 4 w 6 gt Pg The effect of submergence caused by tailwater above the crest elevation is accounted for by the following correction factor proposed for broad crestesd weirs 1 0 y 20671 e 3 1 0 27 8ly 0 67 y gt 0 67 in which Zsu Zw Zsa Zw and zs a is the downstream surface elevation When submergence occurs the model takes the linear combination of the flow determined by the weir formula q and the solution of the shallow water equations Qswg a Agy til Og seg Consequently free overflow Zsa lt Zw is calculated purely by the weir fomula whereas above submergence corresponding to F 0 67 the shallow water solution dominates more and more If the surface is lower than the weir crest o
47. ry value X t with the ZeroCurv zero curvature extrapolation if the flow points out of the flow domain Like ZeroCurv this keyword is valid only for cells adjacent to the outer boundary For water level boundaries e FloodFill Achieves the desired water level or volume change by filling or draining the surrounding cells with piecewise horizontal water surface The value ByWLevel ByVolume or ByDischarge is required e AreaSource A global source or sink evaporation infiltration negative value or rainfall positive value The rate of evaporation infiltration rainfall is given by the boundary value the unit being not m but mm d in this special case If this boundary condition is defined and enabled it is applied over the whole domain without the need for representation on the boundary map For discharge boundaries e NoCrossVel The velocity component perpendicular to the prescribed q is set to O E g if the position of the boundary is the eastern side the vertical velocity components on the N and S sides are set to O e NoCrossVellfOut Similar to the NoCrossVel switch except that the transverse velocity components are set to 0 only if the actual flow is outward which happens with positive outflow or negative inflow e Weir This signals an internal boundary condition where the specific discharge is determined with a weir formula It is specified only with auxiliary data 2005 Tamas Kramer www vit bme hu Bo
48. scribed with the ZeroCurvature Grid time series data file is missing The data of grid time series is stored in external GIS files These must be moved with the SWN project file A boundary condition prescribes time series instead of a value in the Auxiliary data e g WeirLevel WeirWidth but the time series is not found or of the wrong type SWAN has found that a weir type discharge boundary is specified with unsteady width or crest elevation because the name of a time series was assigned to WeirLevel or WeirWidth Make sure that the time series really exists in the project window or if the value was meant to be a numeric value but mistyped More information Inquire here for more information about the SWAN program Tamas Kramer Budapest University of Technology and Economics Department of Hydraulic and Water Resources Engineering H 1111 Budapest Muegyetem rkp 3 K mf 4 Tel 36 1463 1495 email kramer Qvit bme hu Web www vit bme hu 2005 Tamas Kramer www vit bme hu References 31 12 References Burchard H Presentation of a new numerical model for turbulent flow in estuaries and wadden seas Proc Hydroinformatics 98 Copenhagen A A Balkema Rotterdam 1998 J zsa J Kramer T Bakonyi P rt ri bl zetek t lt sszakad st k vet el nt si folyamatainak modellez se II Az rt ri modell Hidrologiai K zl ny 1999 4 234 240 Jobard B Lefer W Creating evenly spaced st
49. se GTS files can later be compressed efficiently for archiving Similarly to recorded time series the GTS files are rewound and truncated when the simulation is reset SWAN will give a warning in such a case and offer to switch off writing to avoid overwriting the old results that may be the result of a long simulation To back up the latest result of the simulation at regular intervals without keeping the previous results check the appropriate box under Automatically export at each interval This is especially useful for steady state simulations to mitigate the effect of a crashing computer or sudden numerical instability Saving the Flow field saves the fields h and g to grids which are sufficient to resume the simulation 2005 Tamas Kramer www vit obme hu Export results 27 from that stage Saving the Flood maps saves the flood field variables the peak flood level the flood arrival time etc The Tecplot format saves to a flow plt or flood plt file in the same folder as the SWN file The Surfer GRD format saves e Flow fields to h grd depth vx grd vy grd velocity components gx grd gy grd discharge components and qsx grd gsy grd half staggered discharge components grid files e Flood maps to t_arriv grd arrival time t_resid grd residence time t_retr grd retreat time t zmax grd peak time zmax grd peak level hmax grd peak depth grid files To write the actual solution to GRD and Tecplot
50. ser s manual 2000 As the next figure illustrates if the time series is queried for a time beyond its time interval the first or last value is returned ALT Time senes pu f Auxiliary data We can provide auxiliary data to extend the functionality of basic water level and discharge boundary conditions The auxiliary data field contains keywords and their values separated by an equal sign and any number of spaces Keyword Value The keyword can be a switch in which case the value is 1 or O in order to switch it on and off respectively If only the keyword is specified it is switched on In some cases the auxiliary data fully define the boundary condition and no boundary value needs to be explicitly defined with the constant periodic or time series fields The list table gives the complete list of keywords by category available in the auxiliary data field For any boundary types e InitOnly The boundary condition is in fact an initial condition applied only when initialising the model e ZeroCurv The boundary is obtained by extrapolation from the interior so that the second derivative is 0 For a boundary on e g the east side this gives X t 2X t 1 X t 2 This method is valid only for cells adjacent to the outer boundary of the domain otherwise an error message is shown The boundary value is therefore given purely by the auxiliary data e ZeroCurvlfOut Overrides any explicitly given bounda
51. the project file These time series consist of scalar values water level discharge evaporation weir width etc sampled at constant interval Time series are imported as ASCII files organised in a column The timestep and the start time is set in a dialog box 2005 Tamas Kramer www vit bme hu Data requirements 19 Base map The flow solver does not need it but it can be used to enhance the grid viewer with a background map SWAN accepts Windows metafiles WMF A WMF file is given in drawing coordinates therefore the geographic coordinates of the bounding rectangle must be specified graphically in the Picture properties dialog box T Visualise simulation results 7 1 Grid viewer Fields represented on grids are visualised in plan or axonometric view in the grid viewer window SWAN offers numerous graphical elements to present the two dimensional information with eye catching graphics nevertheless suitable for technical analysis These elements include color scales contours vector fields and particle traces Any number of grid viewer windows may be open simulaneously each of them configured individually Many software such as Excel Matlab etc are available to visualise time series therefore no such possibility is offered in this version of SWAN Instead time series data are quickly exported to other applications through text files or the clipboard The grid viewer is updated automatically if the grid
52. the settings of open grid viewers and recorded time series are preserved Most model parameters may be changed on the fly some changes however require an immediate Reset Editing the active topography attribute map and boundary map Switching the Accessible to water property of an active attribute Changing the type of an active boundary condition water level to discharge or the other way Switching the Read write simulation results Requesting flooding statistics Simulation stops with an error The simulation can also stop due to numerical overflow caused for example by division with a very small number To have the model stop with an error message instead of program termination in such cases switch on the checking of water depth and discharge with the command Define Model parameters then the button Overflow handling Data requirements Digital elevation model A digital elevation model DEM based on a regular grid is necessary to represent the topography The values it contains are the average elevation of the cell above a given datum in metres The resolution of the DEM defines at the same time the resolution of the simulation The grid must not necessarily be oriented north but the cells sides are named according to the default orientation when defining the discharge boundary position An interpolation technique is generally necessary to create the DEM One must generally try to ensure that the elevation points cover the whole
53. ulating the evolution of the water surface and horizontal depth integrated velocities The equations governing the model are the unsteady shallow water equations in Cartesian coordinates derived by integrating the Reynolds averaged Navier Stokes equations in the vertical direction Losses are calculated by the Manning formula turbulence and momentum dispersion are estimated using a constant eddy viscosity coefficient Development of SWAN SWAN is developed by Tamas Kramer and Janos Jozsa at the Budapest University of Technology and Economics Department of Hydraulic and Water Resources Engineering The original purpose of the model was the simulation of wind induced flow and sediment dynamics in shallow waters Later improvements allowed the simulation of river flow and flooding Capabilities of the model Two dimensional unsteady description on a uniform possibly stretched Cartesian grid Coverage maps allowa distributed assignment of the Manning Strickler coefficient Constant and isotropic eddy viscosity Boundary conditions o Prescribe water level and discharge o Distribute discharge along the boundary using four different methods o Boundary value in simple analytical for or with time series o Slip or non slip closed boundaries e One dimensional weirs e Robust handling of wetting and drying e Topography based flooding o Fast solution no stability constraint o Distributes water volume with horizontal free surface without accounting for
54. undary conditions 15 e WeirLevel Weir crest elevation m Optional Used only when the Weir switch is also defined e WeirCoeff Weir coefficient m s Optional Used only when the Weir switch is also defined e WeirWidth Weir width m Optional Used only when the Weir switch is also defined The details of each auxiliary data keyword is summarised in the following table Keyword z bnd Q bnd Value Default X t value AreaSource yes switch 0 S t mm d FloodFill yes ByWLevel ByWLevel z t m ByVolume V t m ByDischarge Q t m s InitOnly yes yes switch 0 anything NoCrossVel yes switch 0 anything NoCrossVellfOut yes switch 0 anything Weir yes switch 0 WeirCoeff z yes Cy 1 6 m s WeirLevel yes Zw zp i j WeirWidth yes b AX Ay ZeroCurv yes yes switch 0 ZeroCurvlfOut yes yes switch 0 4 4 Typical river boundary conditions To simulate steady state flow on river sections a discharge boundary Qp is set up at the inflow boundary and a water level boundary Z is set up at the outflow boundary The initial water surface elevation is set high enough to submerge both the inflow and outflow boundaries The study area is extended by a distance of several river widths both in the upstream and downstream direction so as to reduce boundary effects The boundaries should possibly lie in well defined sections
55. undary types this is not selected from the list of time series in the boundary definition window which would define Q t directly Example the lines WeirLevel Z w t WeirWidth B w t take the crest level and width from the time series named Z w t and B w t respectively A restriction is that the name of the time series must letters other than digits otherwise the time series named 12 3 wil be recognised as the constant value 12 3 for example 4 2 5 Topography based flooding Any water level boundary can be extended to cells surrounding the boundary by including the line FloodFill in the auxiliary data with one of ByWLevel ByVolume ByDischarge as parameter With the line FloodFill ByWLevel all cells connected to the boundary will be flooded to the given water level if their elevation is lower Cells separated from the boundary by a ridge higher than the prescribed water level are not affected Flooding to a certain water level has two primary uses e combined with the nitOnly switch it sets the initial water level in topographic depressions independently from the global initial water level e if the prescribed water level is time dependent it becomes the instrument of topography based flooding The next series of figures illustrates the working of the flood algorithm The boundary condition imposes a time dependent water level in the cell under the arrow located at the bottom of a left pit Thanks to the FloodFill switch in
56. with more or less uniform velocity distribution The boundary values are constant for the steady state simulation To minimise the generation of artificial waves due to the imperfect initial conditions the discharge increases gradually by specifying a runup of at least one hour As an example the discharge starts at 0 and reaches its final value of 1000 m s in 1 h Meanwhile the outflow water level decreases from 50 0 m to 48 5 in 1 h SInce the built in analytical functions do not provide such a variation the time series 50 48 5 is imported with one hour interval and set as boundary value for the water level To improve stability at the outflow boundary we enter NoCrossVel in the discharge auxiliary data of the outflow boundary condition Any groins are modelled as weirs Since they are inclined relative to the gridlines they must be represented with stepped cells The cell side cannot be prescribed uniformly therefore the weir crest elevation must be given through the topography The river banks constitute a closed boundary that is handled automatically by the model without any explicit boundary condition 2005 Tamas Kramer www vit bme hu 16 SWAN user s manual 4 5 Nu Flow direction Feach to be investigated e Boundary Q Water level Nothing is prescribed Discharge W side distribute by keeping Sy const inflow is positive prescribe value is constant Q 1000 m s runup 3600 s e
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