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Volume Expansion

Posted Jan 28, 2011, 8:02 a.m. EST Version 4.0a 4 Replies

Rose
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Hi

I'm modeling Volume expansion of a disk shaped material.

I have used a ODE with this Expression :

v-vt=0
v=Vol1 , initial


But I got some errors

Failed to evaluate variable Jacobian.
- Variable: vt
- Global scope
4 Replies Last Post Feb 8, 2011, 10:25 a.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 28, 2011, 8:22 a.m. EST
Hi

Could itbe that you are in structural and that v and vt are already used by COMSOL ?

Always use "private names, most 1-2 letter names are already used by COMSOL, sometimes you want to redefine them, but often it gives errors, as you need to know exactly what you are doing

--
Good luck
Ivar
Hi Could itbe that you are in structural and that v and vt are already used by COMSOL ? Always use "private names, most 1-2 letter names are already used by COMSOL, sometimes you want to redefine them, but often it gives errors, as you need to know exactly what you are doing -- Good luck Ivar
Rose
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Posted: 1 decade ago Jan 28, 2011, 8:26 a.m. EST
Thanks a lot for you reply.

I'm not using Structural. I have chosen ODEs and DAEs.

I have attached the Model.

I'd appreciate it if you could take a look.
Thanks a lot for you reply. I'm not using Structural. I have chosen ODEs and DAEs. I have attached the Model. I'd appreciate it if you could take a look.

Attachments:

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 29, 2011, 1:04 p.m. EST
Hi

you cannot try to solve for an ODE alone as you have not defined any dependent variables What is v ?, and vol1 ?

You need to define some physics via an PDE and possibly add an ODE if required

--
Good luck
Ivar
Hi you cannot try to solve for an ODE alone as you have not defined any dependent variables What is v ?, and vol1 ? You need to define some physics via an PDE and possibly add an ODE if required -- Good luck Ivar
Certified Consultant
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Posted: 1 decade ago Feb 8, 2011, 10:25 a.m. EST

Ivar is right (of course!).
But you can in fact solve an ODE, as a global space independent problem. You to define the dependent variable, as Ivar points out, and you can do this by setting Name to v in the Global Equations settings, also, change vol1 to 0 or something else that is defined.

If you want to solve a distributed ODE on a 2D domain (where sources may change with position, but you have no gradient driven transport), use rather a General form PDE and only use the f and da terms.

--
Niklas
Ivar is right (of course!). But you can in fact solve an ODE, as a global space independent problem. You to define the dependent variable, as Ivar points out, and you can do this by setting Name to v in the Global Equations settings, also, change vol1 to 0 or something else that is defined. If you want to solve a distributed ODE on a 2D domain (where sources may change with position, but you have no gradient driven transport), use rather a General form PDE and only use the f and da terms. -- Niklas

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