AutoCAD Civil 3D - Stormwater

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Contributor
kdave
Posts: 19
Registered: ‎09-13-2011
Message 1 of 5 (174 Views)

Unstable Weirs- Please Help!

174 Views, 4 Replies
01-05-2012 06:30 AM

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

Valued Mentor
ccoles
Posts: 312
Registered: ‎06-26-2007
Message 2 of 5 (156 Views)

Re: Unstable Weirs- Please Help!

01-10-2012 12:25 PM 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.

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Matt.Anderson
Posts: 2,909
Registered: ‎05-13-2005
Message 3 of 5 (102 Views)

Re: Unstable Weirs- Please Help!

01-29-2012 08:13 AM 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
Product Manager
Contributor
kdave
Posts: 19
Registered: ‎09-13-2011
Message 4 of 5 (94 Views)

Re: Unstable Weirs- Please Help!

01-30-2012 05:38 AM 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).

Employee
Matt.Anderson
Posts: 2,909
Registered: ‎05-13-2005
Message 5 of 5 (91 Views)

Re: Unstable Weirs- Please Help!

01-30-2012 06:47 AM in reply to: kdave

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

Matthew Anderson, PE
Product Manager

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