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Can I use COMSOL to solve this?

Posted Feb 16, 2012, 2:03 p.m. EST 4 Replies

Mads Sondergard
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I got a set of coupled PDEs where one of them reads:

dv/dt + v*dv/dx +dp/dx = 0

It is hard to see how the "Coefficient Form PDE" can inplement the "v*dv/dx +dp/dx" part. Any suggestions?
4 Replies Last Post Feb 17, 2012, 9:23 a.m. EST
Murali Venkatraman
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Posted: 1 decade ago Feb 17, 2012, 1:43 a.m. EST
Why don't you use the general form ?
Why don't you use the general form ?
Francois Gregoire
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Posted: 1 decade ago Feb 17, 2012, 8:26 a.m. EST
have you tried to put dp/dx as the source term 'f' in the coefficient form? Correct me if I'm wrong: source term can be anything, the Comsol solver will deal with it.
have you tried to put dp/dx as the source term 'f' in the coefficient form? Correct me if I'm wrong: source term can be anything, the Comsol solver will deal with it.
Mads Sondergard
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Posted: 1 decade ago Feb 17, 2012, 9:18 a.m. EST
Hi Murali, I can't see how that would change things... the general form should just be the compact version of the Coefficient Form PDE.
Hi Murali, I can't see how that would change things... the general form should just be the compact version of the Coefficient Form PDE.
Mads Sondergard
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Posted: 1 decade ago Feb 17, 2012, 9:23 a.m. EST
Ah, I think I get what you are saying is that I should rewrite things like:

dv/dt + v*dv/dx +dp/dx = 0 ==>

1/v * dv/dt + dv/dx = -1/v * dp/dx ==>

1/v * dv/dt + dv/dx = -K/v , where: dp/dx = K

So I just add another equation! Well I think this trick should work.
Thanks Francois.
Ah, I think I get what you are saying is that I should rewrite things like: dv/dt + v*dv/dx +dp/dx = 0 ==> 1/v * dv/dt + dv/dx = -1/v * dp/dx ==> 1/v * dv/dt + dv/dx = -K/v , where: dp/dx = K So I just add another equation! Well I think this trick should work. Thanks Francois.

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