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How to make equations nonlinear in PZD interface?

Konstantin Barzilovich

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I have made a model of piezo resonator on base of piezoelectric interface. Now I try to take into account the nonlinearity.
So Comsol use formula1(attach) to calculate stress tensor from stain tensor. I want to use formula2 or formula3 to get nonlinearity and temperature dependence of model.
I cant find the way to change piezoelectric interface equations because there is no place to add new material properties as third order elastic constants (Cijklmn).
I tried to use physics builder to make my own piezoelectric interface, but the problem is I cant multiply elasticity matrix (6x6 matrix) by strain matrix (3x3 matrix). I know, that elasticity matrix is tensor 4th order (3x3x3x3) but Comsol use 6x6 matrix.

Thanks in advance
Konstantin


1 Reply Last Post Aug 9, 2012, 6:38 a.m. EDT
Konstantin Barzilovich

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Posted: 1 decade ago Aug 9, 2012, 6:38 a.m. EDT
I ran into one more problem.

I try to declare new variable "strain" in physics builder. It should be symmetric matrix 3x3.
When I make definition of this variable

0.5*(gradient(u)+transpose(gradient(u)))

I get error "Variable definition is non-symmetric for a symmetric variable", although i believe this definition is symmetric.
How can I correct this definition?
I ran into one more problem. I try to declare new variable "strain" in physics builder. It should be symmetric matrix 3x3. When I make definition of this variable 0.5*(gradient(u)+transpose(gradient(u))) I get error "Variable definition is non-symmetric for a symmetric variable", although i believe this definition is symmetric. How can I correct this definition?

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