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Reference Manual
180 MIKE 21 BW - © DHI
Please see Setup of internal generation lines (p.128) and Examples of
wave fields (p.131).
7. Finally, you should evaluate the CPU, RAM and hard disk requirements.
Evaluation
If you have experienced that your first model set-up takes far to long time to
run and requires much more internal memory than available, then you have
to reconsider your model set-up. Most often you have to increase the mini-
mum wave period and/or reduce the maximum water depth, reduce the size
of the computational domain, etc. In other words, you have to prepare the
next iteration starting from point 1 in this recipe.
5.5.9 Hardware requirements
CPU requirements
You can evaluate the required computational time if you know the computa-
tional speed (CPS) of your PC running MIKE 21 BW. An estimate is given in
the pop-up dialog when you start executing the program. For a 4-500 MHz
Pentium II processor the CPS is in order of 100000 points/second for 2D
applications and about 15000 points/second for 1D applications (including
surf zone dynamics).
When you know the number of grid points in both x- and y-directions (N
x
and
N
y
), the ratio between number of water points and total number of points (

),
and the number of time steps N
t
, you can evaluate the required CPU time
using the formula
(5.18)
where the unit of CPU is seconds. The CPU can be calculated in the MIKE 21
BW Model Setup Planner (Java script) included in the Online Help.
Hard disk requirements.
To keep storage requirements within reasonable bounds, the following sug-
gestions are made:

for plotting purposes you should not store results from the whole model
area too frequently (store e.g. every 10th, 50th or 100th time step, and
most often only the levels/surface elevation).

for time series analysis (including spectral analysis, etc.) you should
store results at every time step (e.g. at every 5th or 10th grid point and
most often only the levels/surface elevation).
CPU

N
x
N
y
N
t
CPS
----------------------- =