Posted Thu, 11 Sep 2014 00:28:44 GMT by Aileen G

I got blow-up message which stopped my simulation.

---------- B L O W  -  U P  detected ---
  ** Very high water level ,near:  158  669 of area no.    1 **
Error number:  -24
Job terminates.

When I got to the actual cell (158,669) the water level is only about 50mm so I don't understand why it stopped. Other cells in this area are not really flooded either, all with relatively low water level. Other cells in the model are flooded much more (up to 12m) and are running fine.

Can you please help me to fix this?

Posted Thu, 11 Sep 2014 08:40:12 GMT by Mathieu Hellegouarch
Hi Aileen,

The reason why you don't see this blow-up in the results is probably because you don't save the results for each simulated time step: the last saved time step in the result file may therefore be far earlier than the blow-up.

A blow-up is related to an instability, and instabilities often occur at places where high velocities occur: so it is often due to velocities more than water depths, and it's hence not surprising that yours is detected at a location with low water depth.

The first thing to check is that you use an appropriate simulation time step. This time step usually needs to be such that the Courant number remains lower than 1. If you're working on flood applications, this results in a time step which is usually lower or equal to the cell size divided by a factor 5. I suggest that you check if this is a case in your model, and reduce the time step if necessary.

If the instability occurs close to a boundary, the problem may also be fixed by smoothing the bathymetry along the boundaries.

I hope these tips can help. Your issue may however be due to something different but it's difficult to give more advices without additional description of the model. So don't hesitate to give more details if that doesn't help.

Best regards,

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