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SSA - Weir Modeling

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Message 1 of 3
jmiller0621
821 Views, 2 Replies

SSA - Weir Modeling

I have an outflow from a existing detention basin that I am not sure how to correctly model in SSA.  The outlet from the basin is a 36" pipe, however, blocking the entrance to this pipe is a weir 12" high with a 12" wide notch cut out (see image below.)

 

My first thought was to have 36" outlet culvert with junctions at ends.  Then connect detention basin to upstream junction with a weir... but in creating the weir in the dialogue box it is effectively a 12"x12" space and I don't think SSA would account for the water height above 12" spilling into the remaining open section of the 36" pipe.  Please let me know if I am wrong.

 

My thought now is to use a short (1') length of user defined pipe in the opening shape between the detention basin and upstream junction.

 

Does anyone have a different idea?  Thanks for your input!  Jesse 

 

 00000001.JPG

 

 

 

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Message 2 of 3
Matt.Anderson
in reply to: jmiller0621

If you define the 12" wide weir, you would cap it when it reached the 36".  SSA would assume weir flow for 12" wide until the top of the pipe when that would effectively become orifice flow.

 

 The remainder of the stepup weir would need to be modeled as a 2nd different weir, but since its a circle - the top would get trickey. You would need to calculated an average "top" for the rest of the weir.

 

I think your plan for a custom shaped is also appropriate.

Matthew Anderson, PE CFM
Product Manager
Autodesk (Innovyze)
Message 3 of 3
jmiller0621
in reply to: Matt.Anderson

Hi Matt

I created my custom pipe using the geometry editor, but have the issue that I need to ascending values on the X-axis.  This obviously doesn't work with a pipe where my values increase, then decrease to close the cirlcle.  Have I missed something?

 

This is what I input into the editor:

Pipe.jpg

But when running the analysis I get errors 119 & 171.

Allowing SSA to sort the data in ascending order results in the following shape:

Pipe2.jpg

Any solutions?  Thanks Jesse

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