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Weak Form of a transient heat problem in solid
Posted 6 giu 2018, 11:49 GMT-4 Computational Fluid Dynamics (CFD), Heat Transfer, Modeling Tools & Definitions 2 Replies
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Hi to everyone. I am writing here because I have created two files, one is built using heat transfer module and the second is built using the weak form module.
I do not understand why the results are so different.
these are the caractheristics:
Module: heat transfer in solids Geometry: 0.5m x 0.5m Mesh normal Initial temperature 293.15 left edge=293.15 Right edge=303.15 transient: time step size 0.001; from 0 to 0.1 k=cp=rho=1
weak file: dependent variabile: T Dirichlet boundary conditions: left 293.15; right 293.15 initial value:293.15 the other characteristics are the same. weak formula: -rhocp(Tttest(T)-(kTxx)test(T)-(kTyy)test(T))
Can someone help me with this issue?
I am struggling.
Best Regards
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Hello,
I have two suggestions for you :
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Hello,
It probally comes from your Weak Form. Firstly, you have a parenthesis problem. You souldn't multiply rho x Cp with k.
Secondly, in ordre to calculate the weak form, you should :
1) Multiplie your PDE by the test function
2) Intergrate the expression on the volume
3) Use the Integration By Parts and the Green Theorem to reduce the derivation degree (avoid the Txx and transform them into Tx) on the dependent variable. For the state-stady part of the heat equation, the method is given step by step in this COMSOL article. You will notice that an intergral on the boundaries appears. Do not enter it in the Weak Form PDE node, it is taken care of by the Zero Flux node.
In tested this equation and it worked :
Hope it helps !