Reference Manual
174 MIKE 21 BW - © DHI
4. That the water depth is sufficient at all active grid points to ensure that
they do not dry out (if moving shoreline is not included)
5. That the correct still water level (SWL) has been specified, and that the
boundary conditions and initial surface elevation have been specified rel-
ative to the still water level
6. That the boundary/internal generation data are physically realistic
7. That the coefficients used for sponge layers and porosity layers are con-
stant and realistic
If all your efforts fail, you can contact your local DHI Software Support Centre.
Blow-up after some time steps
General description
You have started the execution of a simulation and it stops after a number of
time steps (e.g. 100, or 3892).
Near the end of the .log file you get the message:
“-----BLOW-UP detected-----”
In other words, you have encountered a numerical instability.
Instabilities which develop some time into a model simulation may also be the
result of inconsistencies in your input specifications. This is because the
Boussinesq wave model is relatively robust, and it can take some time before
the effects of inconsistencies in your input lead, ultimately, to instability. Other
possible causes of late instabilities are an accumulation of reflected wave
energy within the model area, and wave breaking.
What to do?
To determine the cause of instability you should make a plot of levels/surface
elevation of the last time step stored in the output file. If you have also stored
fluxes, you can also make a vector plot. If these plots are too messy, you
should plot the results from the previous time step, and so on, until you get a
plot which clearly shows where the instability starts (e.g. where unrealistic
surface elevations begin to appear). Note, that you may first need to re-run
the simulation storing the results at every time step and in every grid point.
The plots not only show you where the instability starts, they may also be
used as a guide to determine the cause. What action needs to be taken will
depend on the main cause of the instability.
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