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Unstable Weirs- Please Help!

4 REPLIES 4
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Message 1 of 5
kdave
262 Views, 4 Replies

Unstable Weirs- Please Help!

I have developed a model for a project that I am working on. It is a small but complicated model. I have 3 structures with 2 chambers and have weirs and orifices between the chambers. when I ran the model for 100 year storm and look at the animation, weirs go crazy  with zillion peaks. I am not sure why weirs are so unstable. Can anyone please suggest any solution? I have attached the model here.

 

Thanks,

KD

4 REPLIES 4
Message 2 of 5
ccoles
in reply to: kdave

You could try to increase your time step. Just don't go crazy with it or you could miss your true peak if the time step is too large.

Windows 7 64-bit
Dell Precision T5610, Dual-Xeon 2.6Ghz, 16 Gig RAM
Civil 3D 2013
Message 3 of 5
Matt.Anderson
in reply to: kdave

The best advice is to reduce your time step. When you use a large time step, the volume into the pond pushes the pond highwater level up, which corresponds to a discharge that allows more water to leave than the prior time step. Be sure your pond has sufficient stage information as it increments near the weir level.
Matthew Anderson, PE CFM
Product Manager
Autodesk (Innovyze)
Message 4 of 5
kdave
in reply to: Matt.Anderson

Matt, Do you mean reducing the routing time under "Analysis Options"? Currently I have it set at 30 sec (default value).

Message 5 of 5
Matt.Anderson
in reply to: kdave

Yes, reduce the hydraulic routing time step in Analysis options.

Matthew Anderson, PE CFM
Product Manager
Autodesk (Innovyze)

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