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Initial and boundary conditions


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          | -> CONstant [wlev] [vx] [vy] [tke] [epsilon]
          |
INITial  <   ZERO
          |
          |  STEAdy

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This command can be used to specify the initial values for flow variables.

CONSTANT the initial flow and turbulence quantities are set to a constant.  
[wlev] the water level.  
[vx] the u -component of velocity.  
[vy] the v -component of velocity.  
[tke] the turbulent kinetic energy.  
[epsilon] the dissipation rate of turbulent kinetic energy.  
ZERO Both the initial water level and velocity components are set to zero.  
STEADY If this option is specified, the initial velocities will be derived from  
  the water levels using the Chezy formula for steady flow. This can  
  shorten the spin-up time of the SWASH run and can be meaningful  
  in the case of quasi-steady flow condition (e.g. flow in a river).  


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                   |    PM                |
                   |                      |    | -> SIG |    | -> PEAK  |
BOUnd SHAPespec   <  -> JONswap  [gamma]   >  <          >  <            >   &
                   |                      |    |    RMS |    |    MEAN  |
                   |    TMA               |

                        | -> POWer      |
                DSPR   <                 >
                        |    DEGRees    |

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This command BOUND SHAPESPEC defines the shape of the spectra (both in frequency and direction) at the boundary of the computational grid in case of parametric spectral input (see command BOUNDCOND).


PM Pierson-Moskowitz spectrum will be used.  
JONSWAP JONSWAP spectrum will be used. This is default.  
[gamma] peak enhancement parameter of the JONSWAP spectrum.  
  Default: [gamma]=3.3  
TMA A modified JONSWAP spectrum for finite depth will be used.  
SIG The significant wave height (for definition, see Appendix A) is used as  
  the characteristic wave height.  
  This is default.  
RMS The RMS wave height (for definition, see Appendix A) is used as  
  the characteristic wave height.  
PEAK The peak period is used as the characteristic wave period.  
  This is default.  
MEAN Tm01 (for definition, see Appendix A) is used as the characteristic wave period.  
DSPR option for expressing the width of the directional distribution; the distribution  
  function itself is cosm($ \theta$).  
POWER the directional width is expressed with the power m itself.  
  This option is default.  
DEGREES the directional width is expressed in terms of the directional standard deviation  
  of the cosm($ \theta$) distribution (for definition, see Appendix A).  

If this command is not used, the JONSWAP option will be used by SWASH with [gamma]=3.3 and POWER for the directional width.



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                       | North |
                       | NW    |
                       | West  |
                       | SW    |   | -> CCW     |
           | -> SIDE  <  South  > <              >          |
           |           | SE    |   | CLOCKWise  |           |
           |           | East  |                            |
           |           | NE    |                            |
           |                                                |
BOUndcond <                                                  >                    &
           |                                                |
           |                                                |
           |              | -> XY  <  [x]  [y]  >  |        |
           |    SEGMent  <                          >
                          |    IJ  <  [i]  [j]  >  |


              BTYPe WLEV|VEL|DISCH|RIEMann|LRIEmann|WEAKrefl|SOMMerfeld|OUTFlow   &

              LAYer [k] | HYPerbolic | LOGarithmic                                &

              SMOOthing [period] SEC|MIN|HR|DAY                                   &

              ADDBoundwave                                                        &

                       | FOURier  [azero] < [ampl] [omega] [phase] >
                       | REGular  [h] [per] [dir]
           | CONstant <  SPECTrum [h] [per] [dir] [dd] [cycle] SEC|MIN|HR|DAY
           |           | SERIes   'fname' [itmopt]
           |           | SPECFile 'fname' [cycle] SEC|MIN|HR|DAY
          <                                                                       &
           |           | FOURier  < [len] [azero] < [ampl] [omega] [phase] > >
           |           | REGular  < [len] [h] [per] [dir] >
           |           | SPECTrum < [len] [h] [per] [dir] [dd] [cycle] S|MI|HR|DA >
           | VARiable <  SERIes   < [len] 'fname' [itmopt] >
                       | SPECFile < [len] 'fname' [cycle] SEC|MIN|HR|DAY >
                       | SPECSwan 'fname' [cycle] SEC|MIN|HR|DAY

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This command BOUNDCOND defines a boundary condition at the boundary. It consists of two parts, the first part defines the boundary side or segment where the boundary condition will be given, the second part defines the parameters.


There are two ways to define the part of the boundary at which the boundary condition is imposed. The first (SIDE) is easiest if the boundary is one full side of the computational grid, although it should not be used for curvilinear grids. The second (SEGMENT) can be used if the boundary segment goes around the corner of the grid, or if the segment is only part of one side of the grid.


This BOUNDCOND command can be given a number of times, i.e. to define boundary conditions on various sides or segments of the boundary. One BOUNDCOND command can be used for only one side or one contiguous segment.

SIDE the boundary is one full side of the computational grid (in 1D cases either  
  of the two ends of the 1D grid).  
  SHOULD NOT BE USED IN CASE OF CURVILINEAR GRIDS!  
NORTH, ... indicates on which side the boundary condition is applied. N means the  
  boundary is the north edge (if present) of the computational area, likewise  
  for W is west, S is south, E is east, NW is northwest, NE is northeast,  
  SW is southwest and SE is southeast. The side does not have to face exactly  
  the given direction (the nearest direction of the normal to the side is taken;  
  this direction is determined as the normal to the sum of the vectors joining  
  the grid points on the boundary; there is an interruption in the boundary  
  (due to the occurrence of exception values) then this interruption is ignored  
  in the summation).  
  Note: in case of Cartesian coordinates, the direction of the problem coordinate  
  system must be defined by the user (see the SET ...[north] command), by  
  default the positive x -axis points East.  
CCW, see description of [len] below; these option are only effective if the  
CLOCKWISE option VARIABLE is used (see below).  
SEGMENT is used if SIDE is not used, i.e. either the boundary segment goes  
  around a corner of the grid, or the segment is only part of one side of the  
  grid. The distance along the segment (see [len] below) is measured  
  from the first point of the segment (see XY or IJ).  
XY the segment is defined by means of a series of points in terms of problem  
  coordinates; these points do not have to coincide with grid points. The  
  (straight) line connecting two points must be close to grid lines of the  
  computational grid (the maximum distance is one hundredth of the length of  
  the straight line).  
  This option is default.  
[x], [y] problem coordinates of a point of the boundary segment (see command COORD).  
IJ the segment is defined by means of a series of computational grid points  
  given in terms of grid indices; not all grid points on the segment have to be  
  mentioned. If two points are on the same grid line, intermediate points are  
  assumed to be on the segment as well.  
[i], [j] grid indices of a point of the segment. Values of [i] range from 1 to [mxc]+1  
  and values of [j] from 1 and [myc]+1 ([mxc] and [myc] as defined in the  
  command CGRID).  
BTYPE with this option the type of boundary condition is given.  
WLEV water level is imposed.  
  Required further specification by means of Fourier series or time series.  
VEL velocity normal to the boundary is imposed.  
  Required further specification by means of Fourier series or time series.  
DISCH discharge per unit width normal to the boundary is imposed.  
  Required further specification by means of Fourier series or time series.  
RIEMANN Riemann invariant is imposed. It is defined as u$ \pm$2$ \sqrt{{gh}}$ with  
  u the velocity normal to the boundary and h the water depth.  
  The sign depends on the location of the boundary. The plus sign refers  
  to an inflow velocity at the western/left and southern/lower boundaries,  
  and the minus sign refers to inflow velocity at the eastern/right and  
  northern/upper boundary. This boundary condition is particularly meant  
  for a supercritical flow or hydraulic jump in e.g. rivers or open channels.  
  Required further specification by means of Fourier series or time series.  
LRIEMANN linearized Riemann invariant is imposed. It is defined as u$ \pm$$ \zeta$$ \sqrt{{g/d}}$  
  with u the velocity normal to the boundary, $ \zeta$ the water level and d the  
  bottom level. The sign depends on the location of the boundary. The plus  
  sign refers to an inflow velocity at the western/left and southern/lower  
  boundaries, and the minus sign refers to inflow velocity at the eastern/right  
  and northern/upper boundary. Note that linearized Riemann invariants can  
  only be applied if the water level ($ \zeta$) is small compared to the local bottom  
  level (d). This is mainly applicable for a subcritical flow in relative deep  
  waters. Examples are tidal flows in a continental shelf or in a harbour.  
  Required further specification by means of Fourier series or time series.  
WEAKREFL the boundary condition is weakly reflective.  
  Required further specification by means of Fourier series or time series  
  of water level, or regular or irregular waves by means of a spectrum.  
SOMMERFELD Sommerfeld radiation condition is imposed.  
  No further specification is needed.  
OUTFLOW water depth is aligned to bottom level (for supercritical flow only).  
  No further specification is needed.  
LAYER indicates a layer where the boundary condition is given.  
[k] layer index (1 $ \leq$ [k] $ \leq$ [kmax]).  
HYPERBOLIC the vertical hyperbolic cosine profile for velocity at the boundary is assumed.  
LOGARITHMIC the vertical logarithmic profile for velocity at the boundary is assumed.  
SMOOTHING with this option a ramp function is applied to start up the simulation smoothly.  
[period] the smoothing period of which the unit is indicated in the next option:  
  SEC unit seconds  
  MIN unit minutes  
  HR unit hours  
  DAY unit days  
ADDBOUNDWAV with this option second order bound long wave is added to the first order,  
  irregular waves.  
CONSTANT with this option the boundary condition is constant along the side or segment.  
FOURIER the Fourier series is defined by means of the following parameters:  
[azero] the amplitude for zero frequency is given (in m).  
[ampl] the amplitudes for a number of components are given (in m).  
[omega] the angular frequencies for a number of components are given (in rad s-1).  
[phase] the phase for a number of components are given (in degrees).  
REGULAR monochromatic, long-crested wave is defined with the following parameters:  
[h] the wave height (in m).  
[per] the wave period (in s).  
[dir] the wave direction (in degrees; Cartesian or Nautical convention, see  
  command SET).  
  Default: no specification of [dir] means incident direction is perpendicular  
  to the boundary (only in case of rectilinear grid).  
SPECTRUM the wave spectrum is defined by means of the following spectral parameters  
  (see command BOUND SHAPE for spectral shape):  
[h] the characteristic wave height (in m).  
  [h] is the value of the significant wave height, if option SIG was chosen  
  in command BOUND SHAPE or  
  [h] is the value of the RMS wave height, if option RMS was chosen  
  in command BOUND SHAPE.  
[per] the characteristic wave period (in s).  
  [per] is the value of the peak period, if option PEAK was chosen  
  in command BOUND SHAPE or  
  [per] is the value of the mean period Tm01, if option MEAN was chosen  
  in command BOUND SHAPE.  
[dir] the peak wave direction (in degrees; Cartesian or Nautical convention, see  
  command SET).  
  Default: no specification of [dir] means incident direction is perpendicular  
  to the boundary (only in case of rectilinear grid).  
[dd] coefficient of directional spreading; a cosm($ \theta$) distribution is assumed.  
  [dd] is interpreted as the directional standard deviation in degrees,  
  if the option DEGREES is chosen in the command BOUND SHAPE.  
  [dd] is interpreted as the power m, if the option POWER is chosen  
  in the command BOUND SHAPE.  
  Default: [dd] = 0., i.e. no directional spreading.  
[cycle] the cyclic period of the time series of surface elevation to be synthesized.  
  This may correspond to the time period over which surface elevation is  
  outputted after steady-state condition has been established. The  
  corresponding unit is indicated in the next option:  
  SEC unit seconds  
  MIN unit minutes  
  HR unit hours  
  DAY unit days  
SERIES the time series is given in a file.  
  This file is for only one location; it has a number of lines which each contain  
  2 numbers, i.e.: time, quantity. The notation of time is indicated by [itmopt]  
  (see below). However, if time is represented as a real number in seconds, then  
  do not specify [itmopt]. The quantity depends on the type of boundary  
  condition (see command BTYPE).  
  Example of such a file containing surface elevation in meters ([itmopt] = 7):  
     
  000000.000 0.0000000E+00  
  000001.000 4.2307975E-08  
  000002.000 1.6923190E-07  
  000003.000 3.8077177E-07  
  000004.000 6.7692758E-07  
  000005.000 1.0576993E-06  
  000006.000 1.5230870E-06  
  000007.000 2.0730906E-06  
     
'fname' name of the file containing the time series.  
[itmopt] time coding option. The following format can be employed:  
  1 : ISO-notation 19870530.153000  
  2 : (as in HP compiler) '30-May-87 15:30:00'  
  3 : (as in Lahey compiler) 05/30/87.15:30:00  
  4 : 15:30:00  
  5 : 87/05/30 15:30:00'  
  6 : as in WAM 8705301530  
  7 : 153000.000  
  Default: no specification of [itmopt] means time is represented as  
  a real number in seconds.  
SPECFILE the wave spectrum is given in a file. There are two types of files:  
  $ \bullet$ files containing 1D or non-directional wave spectrum  
  (usually from measurements), and  
  $ \bullet$ files containing 2D or directional wave spectrum  
  (possibly from a SWAN run).  
  A file containing the 1D wave spectrum is for only one location; it has  
  the string SPEC1D on the first line of the file and a number of lines which  
  each contain 2 numbers, i.e.: frequency in Hz, variance density in m2/Hz.  
  Example of such a file:  
     
  SPEC1D  
  3.8602E-03 5.2168E-01  
  5.7903E-03 1.0230E+00  
  7.7204E-03 1.4567E+00  
  9.6505E-03 1.7232E+00  
  1.1581E-02 1.8832E+00  
  1.3511E-02 1.7570E+00  
  1.5441E-02 1.3429E+00  
  1.7371E-02 9.8666E-01  
     
  The structure of the files containing directional spectrum is described in  
  Appendix D of the SWAN User Manual. These files may only contain  
  stationary wave spectra, and can be used for one location only.  
'fname' name of the file containing the wave spectrum.  
[cycle] the cyclic period of the time series of surface elevation to be synthesized.  
  This may correspond to the time period over which surface elevation is  
  outputted after steady-state condition has been established. The  
  corresponding unit is indicated in the next option:  
  SEC unit seconds  
  MIN unit minutes  
  HR unit hours  
  DAY unit days  
VARIABLE with this option the boundary condition can vary along the side or segment.  
  The boundary condition is prescribed at a number of points of the side or  
  segment, these points are characterized by their distance from the begin  
  point of the side or segment.  
[len] is the distance from the first point of the side or segment to the point along  
  the side or segment for which the incident wave spectrum is prescribed.  
  Note: these points do no have to coincide with grid points of the computational  
  grid. [len] is the distance in m or degrees in the case of spherical  
  coordinates, not in grid steps. The values of [len] should be given  
  in ascending order. The length along a SIDE is measured in clockwise or  
  counterclockwise direction, depending on the options CCW or CLOCKWISE (see  
  above). The option CCW is default. In case of a SEGMENT the length is  
  measured from the indicated begin point of the segment.  
SPECSWAN the wave spectra are given in a file and are obtained from a SWAN run. The  
  structure of this file is described in Appendix D of the SWAN User Manual.  
  This file must contain more than 1 stationary wave spectrum, either 1D or 2D.  
  The coordinates of the locations will be taken into account and SWASH will  
  interpolate the spectra to the given boundary side or segment. The coordinate  
  system of the SWAN run must be the same as the one used by the current  
  SWASH run. See also Section 2.6.  
  CANNOT BE USED IN 1D-MODE.  
'fname' name of the file containing the wave spectra.  
[cycle] the cyclic period of the time series of surface elevation to be synthesized.  
  This may correspond to the time period over which surface elevation is  
  outputted after steady-state condition has been established. The  
  corresponding unit is indicated in the next option:  
  SEC unit seconds  
  MIN unit minutes  
  HR unit hours  
  DAY unit days  

Note that by specifying regular or irregular waves at the boundary, the vertical hyperbolic cosine velocity profile is assumed. Hence, no type of boundary condition should be specified, except BTYPE WEAKREFL if a weakly reflective boundary is assumed.



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             | North  |
             |        |
             | West   |
SPONgelayer <          >  [width]
             | South  |
             |        |
             | East   |

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This command can be used to specify the sponge layers around the computational domain.


Sponge layers are very effective in absorbing wave energy at open boundaries where waves are supposed to leave the computational domain freely. So, they prevent reflections at open boundaries. A sponge layer may have a width of 3 to 5 typical wave lengths.


Note that by including a sponge layer of [width] meters, the computational domain needs to be extended with [width] meters as well (see command CGRID).

NORTH sponge layer is placed at the north edge of the domain.  
WEST sponge layer is placed at the west edge of the domain.  
SOUTH sponge layer is placed at the south edge of the domain.  
EAST sponge layer is placed at the east edge of the domain.  
[width] the width of sponge layer in meters.  


next up previous index
Next: Physics Up: Model description Previous: Input grids and data   Index
The SWASH team 2017-04-06