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How can I solve a PDE with variable coefficients?

Posted Feb 26, 2018, 4:59 a.m. EST General, Computational Fluid Dynamics (CFD), Materials, Modeling Tools & Definitions 5 Replies

Julio Gonzalez
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Hello everyone, this post will be so brief. I would like to know if the module "Coefficient form of PDE can be applied for variable coefficient case. I mean , coefficients which depend on the field variable. For instance:

The coefficients Xc and and Dc depend on the field variable .

Thanks

5 Replies Last Post Mar 2, 2018, 1:52 a.m. EST
Jeff Hiller COMSOL Employee

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Posted: 7 years ago Feb 26, 2018, 8:15 a.m. EST

Yes. Jeff

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Jeff Hiller
Yes. Jeff
Julio Gonzalez
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Posted: 7 years ago Feb 27, 2018, 10:26 p.m. EST
Updated: 7 years ago Feb 27, 2018, 10:36 p.m. EST

Yes. Jeff

Hello Jef, thanks for your reply. I am having problems with this module. My problem consist of two domains, where the aforementioned equation is applied. Such that, we are going to have D_{c}1X_{c}1 and D_{c}2X_{c}2 respectively. Consequently, in the Coefficient Form PDE1 module, i set this a=f====0, d_{a}=X_{c}1 y c=Dc1*Xc1 .

Unfortunately, I am getting the following error message

  • Feature: Time-Dependent Solver 1 (sol1/t1) Undefined variable.

    • Variable: Dc2
    • Geometry: geom1
    • Domain: 2 Failed to evaluate Jacobian of expression.
    • Expression: dvol_spatial(Xc2(-(Dc2*comp1.ux))) Failed to evaluate Jacobian of expression.
    • Expression: (Xc2(-comp1.uttest(comp1.u)-Dc2comp1.uxtest(comp1.ux)))*(dvol_spatial)

    where Dc1 has been defined as Analytic function module. Any suggestion? Thanks

>Yes. >Jeff Hello Jef, thanks for your reply. I am having problems with this module. My problem consist of two domains, where the aforementioned equation is applied. Such that, we are going to have D_{c}1X_{c}1 and D_{c}2X_{c}2 respectively. Consequently, in the Coefficient Form PDE1 module, i set this a=f=\alpha=\beta=\gamma=0, d_{a}=X_{c}1 y c=Dc1*Xc1 . Unfortunately, I am getting the following error message - Feature: Time-Dependent Solver 1 (sol1/t1) Undefined variable. - Variable: Dc2 - Geometry: geom1 - Domain: 2 Failed to evaluate Jacobian of expression. - Expression: dvol_spatial*(Xc2*(-(Dc2*comp1.ux))) Failed to evaluate Jacobian of expression. - Expression: (Xc2*(-comp1.ut*test(comp1.u)-Dc2*comp1.ux*test(comp1.ux)))*(dvol_spatial) where Dc1 has been defined as Analytic function module. Any suggestion? Thanks
Jeff Hiller COMSOL Employee

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Posted: 7 years ago Feb 28, 2018, 8:33 a.m. EST

Hello Julio, Please contact Technical Support at support@comsol.com. We'll need to look at your file. Best, Jeff

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Jeff Hiller
Hello Julio, Please contact Technical Support at support@comsol.com. We'll need to look at your file. Best, Jeff
Julio Gonzalez
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Posted: 7 years ago Mar 1, 2018, 2:56 a.m. EST

I have already sent an email to the support staff, I look forward to hearing from a sooner reply. Thanks

I have already sent an email to the support staff, I look forward to hearing from a sooner reply. Thanks
Julio Gonzalez
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Posted: 7 years ago Mar 2, 2018, 1:52 a.m. EST

Hi I think that comsol is not updating the values of the coefficients of my PDE because the profile are almost the same at different moments. Any suggestions??

Hi I think that comsol is not updating the values of the coefficients of my PDE because the profile are almost the same at different moments. Any suggestions??

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