SWMM-USERS Digest - 26 Nov 2009 to 27 Nov 2009 (#2009-125)

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There is one message totalling 416 lines in this issue.

Topics of the day:

1. orifice in SWMM5

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Date: Fri, 27 Nov 2009 02:04:27 -0700
From: Robert Dickinson <Robert.E....@US.MWHGLOBAL.COM>
Subject: Re: orifice in SWMM5

Hi Maurizio,

The behavoir of the side outlet orifice in your model does seem problematical but I just noticed that if you switch to a bottom orifice type that:

1. The oriice flow will stable,
2. The orifice flow will match the weir flow, and
3. There will be a small continuity error.

There are important computational differences between the flow in a side outlet and bottom orifice. The bottom orifice computes head across the orifice according to the equaton head = h1 - h2 where h1 and h2 are head at upstream node and downstream node of the orifice respectively, the side orifice uses a more complicated head difference equation. Please try the bottom orifice type in this model and we will further investigate the behavoir of the side outlet orifice in your particular model.

Best and Kind Regards,
Robert Edgar Dickinson | Technical Engineering Specialist
MWH Soft Inc.
Robert.E.Dickinson@�mwhglobal.com | www.mwhsoft.com
P. 813-712-0664
Burlington | Chicago | Cincinnati | Denver | Harrisburg | Kansas City | Logan | Pasadena | Olympia | Tampa | Sacramento | Waterbury
________________________________________
From: SWMM-USERS [SWMM-...@listserv.uoguelph.ca] On Behalf Of Maurizio Cingi [mrz...@GMAIL.COM]
Sent: Thursday, November 26, 2009 11:48 AM
To: SWMM-...@listserv.uoguelph.ca
Subject: Re: [SWMM-USERS] orifice in SWMM5

Hi Robert,
thank you for your kind reply.

Just a few comments:

about 2nd - the continuity error decrease with a longer run (as %) but it is
only an "error dilution". Observing data you can see that the error (during
first ten minutes) is the same, then, when storage is full, it stops but the
total volume increases (due to overflow) so error % is less.....
attacched file -> graphic with Storage O2 volume and volume calculated as
integration of Q*dt

5th flow throught orefice is near correct (average value on more than few
time steps) but awfully unstable. I know that it can be viewed as a mere
aestethic problem but it is a strange behavior compared to the weir
stability in the same condition.
attacched file -> graphic with flow throught orifice (from swmm at time step
and average on 20 seconds

7th I recognize my example is an atipical model: at the beginning it was a
tipical model, then I purged it to eliminate every unnecessary
device/detail.

MC



2009/11/26 Robert Dickinson <Robert.E....@us.mwhglobal.com>

> Hi Maurizio,
>
>
>
> 1st Thank you for a very interesting example file,
>
> 2nd You can eliminate the continuity error at the downstream node of your
> oriice if you run the model for 1 hour instead of 10 minutes,
>
> 3rd The equations for orifice flow and weir flow are different and the weir
> switches to an orifice flow equation when the depth is above the crown of
> the weir or the weir is surcharged. In effect in your model you are
> comparing a larger orifice for the surcharged weir and a smaller orifice for
> the surcharged orifice.
>
> 4th If you plot the weir and orifice flow together on a one run you can see
> the effect of the smaller orifice - the flow is delayed by 15 minutes.
>
> 5th If you use the SWMM 5 Statistics Tool on the Weir and Orifice for any
> length run you will see that the total flow through the Weir and Orifice
> have the same volume.
>
> 6th We should still investigate however, why a shorter model run shows an
> apparent continuity error at the downstream storage node, and finally
>
> 7th You model is atypical because it does not have any active outfalls but
> only ending storage nodes.
>
>
>
> I hope this helps.
>
>
>
> Robert E Dickinson
>
> SW/WW Technical Engineering Specialist
>
> MWH Soft, Inc
>
> 9340 Pontiac Drive Tel: 813-712-0664
>
> Tampa, Florida, 33626 Alt: 813-494-2919
>
> USA
>
> robert.d...@mwhsoft.com
>
> www.mwhsoft.com
>
>
>
> -----Original Message-----
> From: SWMM-USERS [mailto:SWMM-...@listserv.uoguelph.ca] On Behalf Of
> Maurizio Cingi
> Sent: Thursday, November 26, 2009 5:49 AM
> To: SWMM-...@listserv.uoguelph.ca
> Subject: [SWMM-USERS] orifice in SWMM5
>
>
>
> I've found a problem using orifices in SWMM5 (5.0.018) .
>
> In the attacched model you can see that the orice flow becomes unstable
> when
>
> water height on both sides is between top and bottom of the orifice.
>
> Then, when the orifice is completely submerged, the flow is stable at 0.5
>
> cms (the correct value).
>
> With a weir instead of orefice there isn't any problem.
>
> Another problem: the volume in storage 02 increases less than the
>
> OrificeFlow*timestep ( Q* dt ) and generates a big (huge) continuity
> error.
>
>
>
> Best regards
>
> M.Cingi
>
>
> ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
>
>
> orifice_BUG.inp
>
> [TITLE]
>
>
>
> [OPTIONS]
>
> FLOW_UNITS CMS
>
> INFILTRATION HORTON
>
> FLOW_ROUTING DYNWAVE
>
> START_DATE 11/25/2009
>
> START_TIME 00:00:00
>
> REPORT_START_DATE 11/25/2009
>
> REPORT_START_TIME 00:00:00
>
> END_DATE 11/25/2009
>
> END_TIME 00:10:00
>
> SWEEP_START 01/01
>
> SWEEP_END 12/31
>
> DRY_DAYS 0
>
> REPORT_STEP 00:00:01
>
> WET_STEP 00:05:00
>
> DRY_STEP 01:00:00
>
> ROUTING_STEP 0:00:01
>
> ALLOW_PONDING NO
>
> INERTIAL_DAMPING PARTIAL
>
> VARIABLE_STEP 0.75
>
> LENGTHENING_STEP 0
>
> MIN_SURFAREA 0
>
> NORMAL_FLOW_LIMITED BOTH
>
> SKIP_STEADY_STATE NO
>
> FORCE_MAIN_EQUATION H-W
>
> LINK_OFFSETS DEPTH
>
> MIN_SLOPE 0
>
>
>
> [EVAPORATION]
>
> ;;Type Parameters
>
> ;;---------- ----------
>
> CONSTANT 0.0
>
>
>
> [OUTFALLS]
>
> ;; Invert Outfall Stage/Table Tide
>
> ;;Name Elev. Type Time Series Gate
>
> ;;-------------- ---------- ---------- ---------------- ----
>
> 0 0 FREE NO
>
>
>
> [STORAGE]
>
> ;; Invert Max. Init. Storage
>
> Curve Ponded Evap.
>
> ;;Name Elev. Depth Depth Curve
>
> Params Area Frac. Infiltration Parameters
>
> ;;-------------- -------- -------- -------- ---------- -------- --------
>
> -------- -------- -------- -----------------------
>
> O1 0 5 0 FUNCTIONAL 50 0
>
> 0 0 0
>
> O2 0 5 0 FUNCTIONAL 50 0
>
> 0 0 0
>
> W1 0 5 0 FUNCTIONAL 50 0
>
> 0 0 0
>
> W2 0 5 0 FUNCTIONAL 50 0
>
> 0 0 0
>
>
>
> [ORIFICES]
>
> ;; Inlet Outlet Orifice Crest
>
> Disch. Flap Open/Close
>
> ;;Name Node Node Type Height
>
> Coeff. Gate Time
>
> ;;-------------- ---------------- ---------------- ------------ ----------
>
> ---------- ---- ----------
>
> ORIFICE O1 O2 SIDE .5
>
> 0.65 NO 0
>
>
>
> [WEIRS]
>
> ;; Inlet Outlet Weir Crest
>
> Disch. Flap End End
>
> ;;Name Node Node Type Height
>
> Coeff. Gate Con. Coeff.
>
> ;;-------------- ---------------- ---------------- ------------ ----------
>
> ---------- ---- -------- ----------
>
> WEIR W1 W2 TRANSVERSE 0.5
>
> 1.84 NO 0 0
>
>
>
> [XSECTIONS]
>
> ;;Link Shape Geom1 Geom2 Geom3
>
> Geom4 Barrels
>
> ;;-------------- ------------ ---------------- ---------- ----------
>
> ---------- ----------
>
> ORIFICE RECT_CLOSED 1 1 0 0
>
> WEIR RECT_OPEN 1 1 0
>
> 0
>
>
>
> [DWF]
>
> ;; Average Time
>
> ;;Node Parameter Value Patterns
>
> ;;-------------- ---------------- ---------- ----------
>
> O1 FLOW 1.0 "" ""
>
> W1 FLOW 1.0 "" ""
>
>
>
> [REPORT]
>
> INPUT NO
>
> CONTROLS NO
>
> SUBCATCHMENTS ALL
>
> NODES ALL
>
> LINKS ALL
>
>
>
> [TAGS]
>
>
>
> [MAP]
>
> DIMENSIONS 0.000 0.000 10000.000 10000.000
>
> Units None
>
>
>
> [COORDINATES]
>
> ;;Node X-Coord Y-Coord
>
> ;;-------------- ------------------ ------------------
>
> 0 5810.185 5586.420
>
> O1 964.506 5000.000
>
> O2 3973.765 4984.568
>
> W1 1010.802 5987.654
>
> W2 4050.926 6003.086
>
>
>
> [VERTICES]
>
> ;;Link X-Coord Y-Coord
>
> ;;-------------- ------------------ ------------------
>
>
>
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End of SWMM-USERS Digest - 26 Nov 2009 to 27 Nov 2009 (#2009-125)
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