testing orifice

Dear swmmers,

I'm testing the orifice function. There is a short pipe 50 m long, connected to a storage node, I wish to fix the discarge from the pond with an orifice. If you run extran (ver. 44h) it will show you two 'Warnings'. Does them affect the results of simulation, here or in a larger model?

Thank You in advance.
Best regards
Giovanni Di Conza
giovanni_diconza@LIBERO.IT

Giovanni - I got three warnings as shown below. All are harmless - your model works fine. You can eliminate the first warning by changing the SW line from

SW 1 9 10 to SW 1 9 0

WARNING : JOUT WAS SET TO NONZERO BUT FILE NAME WAS NOT SPECIFIED THROUGH @ LINES JOUT WAS SET TO ZERO TO AVOID WRITING DATA TO UNSAVED SCRATCH FILE

===> Warning all conduits connecting to Junction 1 lie above
the Junction invert.
===> WARNING !!! THE INVERT OF CONDUIT 0 LIES ABOVE THE CROWN
OF ALL CONDUITS AT JUNCTION 1

Both the junction and conduit warnings are artifacts of older versions of SWMM, although they can still help point out input problems in some cases. It's still good practice not to have a junction invert below all the conduit inverts, but that doesn't apply in the case of a pump or orifice connection.

Good luck with your model.
Regards,
Mitch Heineman
HeinemanM@CDM.COM

Mitch,

Can you also tell me why into SWMM44h report the equivalent conduit, in witch the orifice is transformed, has the length 200 (metrics units!!??).

According to the SWMM4 manual (the blue book!) it say: 'the length of the equivalent pipe is computed as the maximum of 200 feet (61 m) or L=2*DELTA time*SQRT(gD), to ensure that the celerity (stability) criterion for pipe is not violated...'

I've set up the SI units and using a DELTA time of 1 second for a diameter of 0.3 m, the length should be about 3.4 m, thus The length used by the program should be 61 m (SI units), so why 200??

Furthermore, which discharge coefficients are typical for orifice?
Thanks!
Giovanni Di Conza

Giovanni,

You have identified a metric bug in SWMM 4.4. The minimum orifice length was hard wired to a value of 200. You were getting a length of 200 meters and a roughness of 0.003454. If SWMM internally was using a length of 60.96 meters than the roughness will be 0.00641 as you can see
below:

PIPE LENGTH.......................... 200.00
MANNINGS ROUGHNESS................... 0.00354

PIPE LENGTH.......................... 60.96
MANNINGS ROUGHNESS................... 0.00641

While SWMM should have been using 60.96 meters for the orifice length the effect of the extra length was to decrease the roughness so that at least you should have the same flow and the same velocity in the shorter and longer equivalent pipe - even though the program was contradicting the blue book.

Regards,
Bob Dickinson

[rajesh4918]

hello Giovanni
The typical values used for an orifice will depend on its type but a generalized value that can be used is 0.6 for a smoothly cut orifice and 0.4 for a orifice with corrugated edges.

hope this helps you
Regards
Rajesh

[GiovanniDiConza]

Thank you Rajesh.

[sara sangiorgi]

ciao...finalmente ho trovato un italiano!!!
non è che per caso sai usare EPANET2.0

ne ho bisogno per fare la tesi e non capisco alcune parti del manuale!!

ti lascio la mia mail, non si sa mai... saraesse@libero.it

spero di sentirti

ciao

Sara