Problems in Variable Coupled Material

[Yingjie Wu]

Hi~

Recently, I set some physical parameters in Materials(eg. friction coefficient) which vary according to some variables(eg. pressure, temperature).

I choosed  the type ParsedMaterial and used some variables in it. However I really don't know the method the code works.

Is it same to use variable coupling kernel? Or the value of the variables which ParsedMaterial used is the last step result?

Maybe I didn't explain it very clearly. I just want to find out the difference between Variable Coupled Material and Variable Coupled Kernel.

I would be really appreciated if you can reply~

Thank you

[Cody Permann]

- Materials compute point-wise values. 

- Kernels compute residuals (e.g. contribute to a numeric vector for solving your linear system). 

They are very different objects in terms of their purpose. The fact that they can both couple to other variables is a strength of MOOSE. It means you can perform complex nonlinear coupling without doing a bunch of extra work. Which object you use is determined by what you are using it for. Are you implementing a term from your PDE? (Use a Kernel), Are you producing a value (i.e. a material property) that feeds into a term in your PDE (Use a Material).

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[Anil Kunwar]

Dear Wu,

Can you try defining friction coefficient as a material of type DerivativeParsedMaterial, with f_name = friction_coefficient, args = variables (e.g. p, T) and define the relation with variables under function = expression(f(variables))? If you are just using the function in the the residual, then you can put derivative_order = 0.

Yours Sincerely, 

Anil Kunwar