2D solution went unstable

[Simon Roberts]

Hi everyone,

I’m new to HEC RAS so sorry if a silly question!

I’m trying to build a 1D-2D model of a river with a bridge on it. I’ve managed to import the cross sections from a survey and I’ve imported a 2D area and Lateral Weir into my model.

Everything looks OK but when I try and run the model I keep getting the 2D solution went unstable error even with really small timesteps, and there’s not a lot of information I can see that tells me where the problem is. My 2D area is a 5×5 grid.

When I imported my Lateral Weir the levels seem to have been picked up from the terrain I’m using, and I had to modify a few of the levels so they were above the terrain. I was trying to set them as the bank levels but I’ve not been able to as of yet.

Any help would be really appreciated as this is stopping me in my tracks!

Thanks,
Simon

[Chris Goodell]

Impossible to know for sure what is causing your model to crash without seeing it. I suggest try deconstructing your model, one element at a time, running between each one so that you can isolate the element that is causing the crash. That may help inform you how to fix it.

[Simon Roberts]

Hi Chris,

Thank you so much for your reply.

I’ve spent today re-building my model from scratch and taking extra care, thankfully this time it is running OK. But still not sure what happened in the previous runs that made it unstable!

Thanks again,
Simon

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