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From: Ross Singleton
To: “Hydrojock [via HEC-RAS Bloggery Forum]”

Date: Wed, 30 Oct 2013 08:58:29 +0200
Subject: RE: Instability in unsteady lateral culvert model
Thread-Topic: Instability in unsteady lateral culvert model
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Hi James,

Thanks for your reply,

The problem was actually lying in the storage connection. I had mis-typed t=
he mannings by a factor of 10. Once I corrected it the instabilities were g=
one and I was able to bring my inertial terms back in up to 10. (and get a =
better culvert size for that connection)

Cheers,

Ross

From: Hydrojock [via HEC-RAS Bloggery Forum] [mailto:ml-node+s1091112n434h3=
[email protected]]
Sent: 29 October 2013 19:39
To: Ross Singleton
Subject: Re: Instability in unsteady lateral culvert model

Ross,

A couple of quick thoughts:
1) do you have an initial water surface elevation defined in the storage a=
reas?
2) the profile plot you provided shows the culverts are quite submerged. =
at the start of the simulation, is the water surface below the invert of th=
e culverts? if it is already above the invert of the culverts for the firs=
t time step, the model might be having difficulty coming up with a valid st=
arting solution. best to start below the culvert invert and gradually brin=
g it up.
3) presumably you’ve checked the obvious things like the Cd for the culver=
ts, geometry integrity (elevations for all connections make sense), etc…
Regards,
James

Every 15 seconds a child dies of a
disease caused by unsafe water.

Find out what you can do about it
http://www.Lifewater.org<http://www.Lifewater.org>

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Hi James,=

 <= /p>

Thanks for your reply,

=

 

The problem was actually lying in the storage connection. I had mi=
s-typed the mannings by a factor of 10. Once I corrected it the instabiliti=
es were gone and I was able to bring my inertial terms back in up to 10. (a=
nd get a better culvert size for that connection)

 

Cheers,

 

Ross

 

<= span lang=3DEN-US style=3D'font-size:10.0pt;font-family:"Tahoma","sans-seri= f"'>From: Hydrojock [via HEC-RAS Bloggery Forum] [mailto:ml=
[email protected]]
Sent: 29 October 2013 19:39=

To: Ross Singleton
Subject: Re: Instability in unstead=
y lateral culvert model

&nbs=
p;

Ross,

A couple of quick thoughts: =

1)  do you have an initial water surface elevation defined in the =
storage areas?
2)  the profile plot you provided shows the culvert=
s are quite submerged.  at the start of the simulation, is the water s=
urface below the invert of the culverts?  if it is already above the i=
nvert of the culverts for the first time step, the model might be having di=
fficulty coming up with a valid starting solution.  best to start belo=
w the culvert invert and gradually bring it up.
3)  presumably you=
‘ve checked the obvious things like the Cd for the culverts, geometry integ=
rity (elevations for all connections make sense), etc…

Regards,
James
Every 15 seconds a child dies of a
disease caused by unsafe water.=

Find out what you can do about it
http://www.Lifewater.org

 

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