AutoCAD Civil 3D - Stormwater

AutoCAD Civil 3D - Stormwater

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Registered: ‎12-23-2009
Post 1 of 4

Orifice Rating Curve Calculated Incorrectly in SSA

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09-14-2012 08:40 AM

I noticed today that the orifice rating curve for orifices is being calculated incorrectly in SSA.  The head is being calculated to the orifice invert instead of to the orifice centerline.  This probably has a minor (or no) effect if tailwater conditions are present, but it is still annoying.

 

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Post 2 of 4

Re: Orifice Rating Curve Calculated Incorrectly in SSA

11-28-2012 02:26 PM in reply to: kahligsm

 

Is it doing it beyond the unsubmerged orifice calculation that uses weir flow until orifice submergence? Let me know.  See below:

Capture.JPG

Fred Ernst, PE
C3D 2015 SP2
Ernst Engineering
www.ernstengineering.com
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Post 3 of 4

Re: Orifice Rating Curve Calculated Incorrectly in SSA

12-06-2012 04:45 PM in reply to: kahligsm

I didn't find this to be the case running a quick test on a headwater submerged 1' diameter circular side orifice with g=32.2 ft/s^2 and PI out to 15 digits.

 

Their diagram in the Help is incorrect (see second image below). H for a headwater submerged orifice should be measured to the centroid of the orifice.

 

I hope they are using EPA SWMM engine release 5.0.019 or higher, where the Villemonte correction for downstream submergence in partially full orifices was added.

 

jjCapture.JPG

 

 

 

jjCapture2.JPG

 

 

Fred Ernst, PE
C3D 2015 SP2
Ernst Engineering
www.ernstengineering.com
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Post 4 of 4

Re: Orifice Rating Curve Calculated Incorrectly in SSA

12-07-2012 12:25 PM in reply to: kahligsm

The dialog box rating curve incorrectly calculates orifice flow's H.  This rating curve is not used in the hydraulic routing calculations performed by the analysis engine.  I have notified the development team of the issue in the dialog box and in the help file.

 

The Villemonte correction changes from the EPA SWMM 5.0.19 engine are included in SSA 2012 and 2013.

Matthew Anderson, PE
Product Manager
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