SWMM-USERS Digest - 7 Jun 2008 to 8 Jun 2008 (#2008-103)

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Jun 9, 2008, 12:00:19 AM6/9/08

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Topics of the day:

1. Preissman slot -- NOT IN SWMM 5! (2)

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Date: Sun, 8 Jun 2008 08:30:11 -0400
From: Trent Schade <trent....@DELTAQPARTNERS.COM>
Subject: Re: Preissman slot -- NOT IN SWMM 5!

Can we please confirm that SWMM 5 does NOT use a Preissman Slot?

Previous versions of SWMM may have had the Preissman Slot as an option,
but SWMM 5 does not use it, and there is no option for it.

Please see the wonderful write up of the surcharge algorithm available
from EPA's website in the QA document:

http://www.epa.gov/ednnrmrl/models/swmm/epaswmm5_qa.zip

My understanding is that the surcharge algorithm used in SWMM 5 is
primarily based on an idea of Larry Roesner's. Many others have added
tweeks over the years, but it is primarily the same idea Dr. Roesner had
many years ago.

The idea behind the Preissman Slot is that you can approximate a
pressurized closed conduit geometry with an open channel model.
Preissman Slot makes sense (and are probably necessary) for models like
those derived from FLOWSED (HEC-RAS, FLDWAV, MOUSE?, InfoWorks?, etc.)
where the computational elements are between geometric definitions. You
basically have a cross-section on either end of the computational
element, so how do you deal with a closed-cross section on one end and
an open one on the other? Preissman Slot is a necessary kludge here.

Because SWMM is a link-node model the transition from open-to-closed
occurs at the junction point. SWMM surcharge algorithm solves the same
system by assuming flow in = flow out for surcharged nodes--akin to
water distribution models.Simple, clean -- none of the silly volume
errors you get with Preissman Slot.

Trent
Delta Q Partners, LLC

Gabriele Freni wrote:
> Dear SWMMers,
> I'm playing a little with SWMM5 and some experimental data we have
> collected in laboratory studies about pipe pressurization.
> Is there any simple way to change Preissman slot properties in SWMM5
> (i.e. dimensions)?
> I suppose that the answer should be "No, unless you modify the source
> code and recompile the executable" so here is my second question:
> Where exactly I have to look at for modifying such properties?
> The idea is to evaluate "how bad/good is Preissman approximation in
> case of rapid pipe surcharge".
> Thank you for your always valuable help.
> Regards,
> Gabriele
> ________________________________
> Gabriele Freni
> Ph.D. in Hydraulic Engineering
> Dipartimento di Ingegneria Idraulica ed Applicazioni Ambientali
> Università di Palermo
> Viale delle Scienze
> 90128 Palermo
> tel: +39 0916657730
> fax: +39 0916657749
> E-mail: fr...@idra.unipa.it
> Alt E-mail: gabrie...@gmail.com
>
> **********************************************************
> * To sign off, email to: list...@listserv.uoguelph.ca *
> * In the body of the message type: signoff swmm-users *
> **********************************************************
>
>

*Trent **Schade**, P.E.*

*Principal*

*Delta **Q** Partners*

_Trent...@deltaqpartners.com_ | _www.deltaqpartners.com_

3162 Bellewood Ave.

Cincinnati, Ohio 45213

P. 513.351.4188

/This e-mail and any attachments are confidential and intended only for
the named recipient. If you are not the named addressee you should not
disseminate, distribute or copy this e-mail. Please notify the sender
immediately by e-mail if you have received this message by mistake and
delete this e-mail from your system./

------------------------------

Date: Sun, 8 Jun 2008 09:11:01 -0400
From: Robert E Dickinson <robert.d...@GMAIL.COM>
Subject: Re: Preissman slot -- NOT IN SWMM 5!

Hi Trent,

The surcharge algorithm was developed by John Aldrich and Larry Roesner fo=
r
SWMM 3 and it is essentially the same in SWMM 5 with some modifications.
SWMM really has a conical hat at the nodes to handle the transition between
open-to-closed flow. The hat area decreases from the full nodal area at th=
e
node crown elevation to nothing at 1.25 * the crown elevation (a lot of the
details in the code are for computing the nodal crown elevations). The
differences in the SWMM 4 and SWMM 5 codes for the conical hat are in the
transition computations but essentially you are correct in your statement
that SWMM 5 uses a point iteration process based on the concept that inflow
should equal outflow at the surcharged node.

Regards,
Robert Dickinson

On Sun, Jun 8, 2008 at 8:30 AM, Trent Schade <
trent....@deltaqpartners.com> wrote:

> Can we please confirm that SWMM 5 does NOT use a Preissman Slot?
>
> Previous versions of SWMM may have had the Preissman Slot as an option,
> but SWMM 5 does not use it, and there is no option for it.
>
> Please see the wonderful write up of the surcharge algorithm available
> from EPA's website in the QA document:
>
> http://www.epa.gov/ednnrmrl/models/swmm/epaswmm5_qa.zip
>
> My understanding is that the surcharge algorithm used in SWMM 5 is
> primarily based on an idea of Larry Roener's. Many others have added
> tweeks over the years, but it is primarily the same idea Dr. Roesner had
> many years ago.
>
> The idea behind the Preissman Slot is that you can approximate a
> pressurized closed conduit geometry with an open channel model.
> Preissman Slot makes sense (and are probably necessary) for models like
> those derived from FLOWSED (HEC-RAS, FLDWAV, MOUSE?, InfoWorks?, etc.)
> where the computational elements are between geometric definitions. You
> basically have a cross-section on either end of the computational
> element, so how do you deal with a closed-cross section on one end and
> an open one on the other? Preissman Slot is a necessary kludge here.
>
> Because SWMM is a link-node model the transition from open-to-closed
> occurs at the junction point. SWMM surcharge algorithm solves the same
> system by assuming flow in =3D flow out for surcharged nodes--akin to
> water distribution models.Simple, clean -- none of the silly volume
> errors you get with Preissman Slot.
>
> Trent
> Delta Q Partners, LLC
>
>
> Gabriele Freni wrote:
>
>> Dear SWMMers,
>> I'm playing a little with SWMM5 and some experimental data we have
>> collected in laboratory studies about pipe pressurization.
>> Is there any simple way to change Preissman slot properties in SWMM5
>> (i.e. dimensions)?
>> I suppose that the answer should be "No, unless you modify the source
>> code and recompile the executable" so here is my second question:
>> Where exactly I have to look at for modifying such properties?
>> The idea is to evaluate "how bad/good is Preissman approximation in
>> case of rapid pipe surcharge".
>> Thank you for your always valuable help.
>> Regards,
>> Gabriele
>> ________________________________
>> Gabriele Freni
>> Ph.D. in Hydraulic Engineering
>> Dipartimento di Ingegneria Idraulica ed Applicazioni Ambientali
>> Universit=E0 di Palermo
>> Viale delle Scienze
>> 90128 Palermo
>> tel: +39 0916657730
>> fax: +39 0916657749
>> E-mail: fr...@idra.unipa.it
>> Alt E-mail: gabrie...@gmail.com
>>
>> **********************************************************
>> * To sign off, email to: list...@listserv.uoguelph.ca *
>> * In the body of the message type: signoff swmm-users *
>> **********************************************************
>>
>>
>>
> --
>
> *Trent **Schade**, P.E.*
>
> *Principal*
>
> *Delta **Q** Partners*
>
> _Trent...@deltaqpartners.com_ | _www.deltaqpartners.com_
>
> 3162 Bellewood Ave.
>
> Cincinnati, Ohio 45213
>
> P. 513.351.4188
>
> /This e-mail and any attachments are confidential and intended only for
> the named recipient. If you are not the named addressee you should not
> disseminate, distribute or copy this e-mail. Please notify the sender
> immediately by e-mail if you have received this message by mistake and
> delete this e-mail from your system./
>
> **********************************************************
> * To sign off, email to: list...@listserv.uoguelph.ca *
> * In the body of the message type: signoff swmm-users *
> **********************************************************
>

--=20
Best and Kind Regards,
Robert Edgar Dickinson
MWH Soft Inc.

------------------------------

End of SWMM-USERS Digest - 7 Jun 2008 to 8 Jun 2008 (#2008-103)
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