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Dependant variable

Posted Mar 10, 2011, 3:37 a.m. EST Version 3.5a, Version 4.1 4 Replies

M R
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Hello ,

How could I define a dependant variable in comsol a specific quantity like Displacment or displacment e.g suppose we have dependent variable u(x,y,t) and I want this dependant variable to be displacment.

Thank you
4 Replies Last Post Mar 10, 2011, 5:41 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 Mar 10, 2011, 4:08 a.m. EST
Hi

your question is not easy to understand, the displacement are defined as _u_ =(u,v,w) in most physics (in fact where relevant).

if you are in PDE mode you can rename the dependent variables in the main node, or better during definition

--
Good luck
Ivar
Hi your question is not easy to understand, the displacement are defined as _u_ =(u,v,w) in most physics (in fact where relevant). if you are in PDE mode you can rename the dependent variables in the main node, or better during definition -- Good luck Ivar
M R
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Posted: 1 decade ago Mar 10, 2011, 4:15 a.m. EST
Hi Ivar,

I am in PDE's- wave equation(waeq)-2D and I have u as the dependent variable. I want u(x,y,t) and then I want to consider a pulse at one boundary. But I want the dependent variable be dispalcment in x or y direction.

How could I do that?

thank you
Hi Ivar, I am in PDE's- wave equation(waeq)-2D and I have u as the dependent variable. I want u(x,y,t) and then I want to consider a pulse at one boundary. But I want the dependent variable be dispalcment in x or y direction. How could I do that? thank you
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Mar 10, 2011, 5:20 a.m. EST
Hi

make a "new model: 2D structural physics" and check the dependent variables there you have (u,v) for the displacements. This is called _u_ in bold as vector field in x,y.
When you select a time dependent /transient solver COMSOL adds the time derivatives such as ut, vt wich is to be read as d(u)/dt and d(v)/dt

Read the doc and try out a simple model to understand the default conventions of COMSOL

--
Good luck
Ivar
Hi make a "new model: 2D structural physics" and check the dependent variables there you have (u,v) for the displacements. This is called _u_ in bold as vector field in x,y. When you select a time dependent /transient solver COMSOL adds the time derivatives such as ut, vt wich is to be read as d(u)/dt and d(v)/dt Read the doc and try out a simple model to understand the default conventions of COMSOL -- Good luck Ivar
M R
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Posted: 1 decade ago Mar 10, 2011, 5:41 a.m. EST
Ivar,

for structural mechnaic I did it easily but for PDE's it is a bit confusing. The problem I have is that I can not assign the dependent varaible u to be considered displacment in x or y in PDE. In structuaral physics easyly I can define pressure, displacment and its deriviative because dependent variable is displacment but in PDE dependent variable is u that could be everthing like pressure displacmnet ,... how to make comsol to get dependent variable (u) in comsol displacment or something else I am confused.

however thank you very much Ivar.
Ivar, for structural mechnaic I did it easily but for PDE's it is a bit confusing. The problem I have is that I can not assign the dependent varaible u to be considered displacment in x or y in PDE. In structuaral physics easyly I can define pressure, displacment and its deriviative because dependent variable is displacment but in PDE dependent variable is u that could be everthing like pressure displacmnet ,... how to make comsol to get dependent variable (u) in comsol displacment or something else I am confused. however thank you very much Ivar.

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