Modeling swelling using Eqauation based Weak Formulation

Dear all,

Hello. I am new in Comsol for my thesis I was working on a model of swelling and frictional phenomenon. I stuck in Comsol. Following are my equations in weak form:

-S*(test(ux)+test(uy)+test(uz))
(Jac-(1/J0)-ohm*c)*test(p)
cdot*(test(C))-hf*(test(Cx)+test(Cy)+test(Cz))-q*(test(C))
(mu-muext)*test(cb)

I got following error.

Test function column Jacobian cannot be evaluated. weak function must be linear in the test functions

Kindly suggest.

Regards,

Mujtaba