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Definitions of variables

In SWASH a number of variables are used in input and output. The definitions of these variables are mostly conventional.

Hs Significant wave height, in meters, defined as  
     
  Hs = 4$ \sqrt{{\int E(f) df}}$  
     
  where E(f ) is the variance density spectrum and f is the frequency.  
     
  With respect to output, this quantity is computed as four times the  
  standard deviation of the surface elevation over the duration [dur]  
  (see command QUANTITY) in the final stage of the simulation, which  
  should be long enough to provide statistically reliable wave height.  
  The simulation period should therefore be long enough to establish  
  steady-state conditions.  
     
Hrms RMS wave height, in meters, defined as  
     
  Hrms = $ {\frac{{1}}{{2}}}$$ \sqrt{{2}}$Hs  
     
Tp Peak period, in seconds, defined as inverse of the frequency at which  
  the variance density spectrum is a maximum.  
Tm01 Mean wave period, in seconds, defined as  
     
  Tm01 = $ {\frac{{\int E(f) df}}{{\int f E(f) df}}}$  
     
Directional spread The directional distribution of incident wave energy is given by  
  D($ \theta$) = A cosm($ \theta$) for all frequencies. The power m is related to  
  the one-sided directional spread as given in Table A.1.  
     
Cr Courant number defined as follows:  
     
  Cr = $ \Delta$t $ \left(\vphantom{ \sqrt{g d} + \sqrt{u^2 + v^2} }\right.$$ \sqrt{{gd}}$ + $ \sqrt{{u^2 + v^2}}$$ \left.\vphantom{ \sqrt{g d} + \sqrt{u^2 + v^2} }\right)$ $ \sqrt{{\frac{1}{\Delta x^2} + \frac{1}{\Delta y^2}}}$  
     
  with $ \Delta$t the time step, $ \Delta$x and $ \Delta$y the grid sizes in x - and y -direction,  
  respectively, and u and v the velocity components in x - and y -direction.  
     
VEL Current velocity components in x - and y -direction of the problem  
  coordinate system, except in the case of output with BLOCK command in
  combination with command FRAME, where x and y relate to the x -axis  
  and y -axis of the output frame.  
     
MVEL Mean or time-averaged velocity components in x - and y -direction of  
  the problem coordinate system, except in the case of output with BLOCK  
  command in combination with command FRAME, where x and y relate  
  to the x -axis and y -axis of the output frame. Time-averaging is carried  
  out over the duration [dur] (see command QUANTITY) in the final stage  
  of the simulation.  
     
WIND Wind velocity components in x - and y -direction of the problem  
  coordinate sytem, except in the case of output with BLOCK command in  
  combination with command FRAME, where x and y relate to the x -axis  
  and y -axis of the output frame.  
     
TIME Full date-time string.  
     
TSEC Time in seconds with respect to a reference time (see command QUANTITY).  
     
Cartesian convention The direction is the angle between the vector and the positive x -axis,  
  measured counterclockwise. In other words: the direction where the  
  waves are going to or where the wind is blowing to.  
     
Nautical convention The direction of the vector from geographic North measured  
  clockwise. In other words: the direction where the waves are coming  
  from or where the wind is blowing from.  
     


Table A.1: Directional distribution.
m directional spread (in o)
1. 37.5
2. 31.5
3. 27.6
4. 24.9
5. 22.9
6. 21.2
7. 19.9
8. 18.8
9. 17.9
10. 17.1
15. 14.2
20. 12.4
30. 10.2
40. 8.9
50. 8.0
60. 7.3
70. 6.8
80. 6.4
90. 6.0
100. 5.7
200. 4.0
400. 2.9
800. 2.0


next up previous index
Next: Command syntax Up: swashuse Previous: The importance of parallel   Index
The SWASH team 2017-04-06