Unstable Unsteady Flow analysis

[murphytm]

I am attempting to run an unsteady flow analysis on a Dam break and the simulation goes unstable.

Attached is the error message.

Can any one give me some insight as to how to resolve this.

Thank you.

Tina

[deccantrap]

The attached error message is too small for me to read, but I will just relate some general troubleshooting steps that I would undertake while doing a dambreak analysis:

1. Firstly, run the simulation without breaching the dam, using with a STEADY flow. Just make up a dummy flow that compares to the peak in your unsteady hydrograph and run it. This should take care of any geometrical inconsistencies, if they are the cause of the problem.

2. Secondly, try running an unsteady simulation without breaching the dam. Often, the problem lies with the fact that there are too few cross sections where the geometry changes dramatically along the reach.

3. Play around with the breach formation time and try out lows and highs across a broad range.

4. Play around with the timestep of the simulation, try out a broad range, and make sure you do many cross-combinations between breach-time and timesteps.

Remember that unsteady simulations are highly sensitive to the durations, so more often than not the problem lies with the way you have timed your run.

[murphytm]

Thank you -

I am going to try all your recomendations. I also found in the User's Manual discussion about Pilot Channels and how they can be used to help prevent the model from going unstable.

I will try that as well.