Dam break analysis – too much slow time computation

[igorce]

Hello all
On the picture below i’m trying to show you couple of my steps where i made a dam break model.
Here i want to tell, that the calculation start and working cca 40 hours!!
I think this is long long time for any softwere analysis!!
Maybe i make some mistake before a start with computation, i’m not sure.

Any coments!?

[cameron]

Cannot read anything as it is blurry. 2D models can take a lot longer than 1D models. It all depends on time step, cell size, and number of elements.

Dam breaches have highly dynamic fast moving flow so in general you will need a smaller time step than other applications.

[igorce]

I hope is more clear now. Exactly like you say, if i need more stabiliti results i must use smaller time step.
This is big area who is modeled with DX=5, DY=5 computation mesh (2.033.000 cells) , Computation interval is 2 second, mapping output interval is 6 second, hydrograph output interval is 1 minute.

Here i will repet my dilemma: Till now my computer work (you can see, from 06jul2018 10:03:48AM) cca 75 hours.
Did someone have experience with this?
Did you make analyse with this software more than 5 days?

[Scott Miller]

1. Use Alt+PrtScn, if they’re on your keyboard, to capture screenshots of individual dialog boxes.
2. Make sure your computer is up to par. This may help: http://hecrasmodel.blogspot.com/2016/08/optimizing-your-computer-for-fast-hec.html
3. Take a look at the maximum velocities and the average cell size to calculate a Courant number. Is it reasonable for the equation set you’re using (dynamic wave vs. full momentum)?

Use the full momentum equation set for dam breaks.

Consider using refinement regions to tailor the mesh. It is probably reasonable to have larger cell sizes farther away from the break. It’s probably reasonable also to have longer time steps as the flood wave attenuates. Control the time step with the Courant condition (version 5.0.5).

Try writing output much less frequently and see if that speeds the model up. An I/O bottleneck will slow things down, especially with 2 million mesh cells.

[Anonymous]

HEC-RAS version 5.0.5 has a variable time step ability. You may be able to take advantage of that in order to get it to run faster.

[cameron]

with 2 million elements at 5 meters (hope it is meters) the model will take a very long time to run.

Did you check to see how long you actually need to run it? For instance, check when the peak occurs at the downstream end and maybe you can trim the model run time. The other comments provided should help as well. Another thing to think about is how deep the water is. If the max depth is really deep, you can probably get away with larger cells and get the same answer.

It is common for very large models with small grid cells to take a long time to run.

[Author]

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