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Electrostatic vs. Electric current module

The below post is related to an archived discussion Hello, I am getting different simulation results when I am using Electrostatic vs. when I use Electric current module and consider conductivity to be zero. My model includes a two-phase fluid flow and a capacitor with one side applying a step voltage and one side being ground. My question is that why should I get different results while the conductivity is zero? Could that be because of the transient response, where the voltage is stepped high? Thanks,

If I recall correctly, it's considered a bad idea, due to the numerical operations that are involved in finding solutions (when using the electric current module), to set the conductivity to zero. -------------------
Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara

If I recall correctly, it's considered a bad idea, due to the numerical operations that are involved in finding solutions (when using the electric current module), to set the conductivity to zero.

Indeed in most cases even the solver would not converge with zero conductivity in EC physics. Cheers Edgar -------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com

Indeed in most cases even the solver would not converge with zero conductivity in EC physics. Cheers Edgar

The electric current equation is div(-sigma gradV)=0, so when sigma=0 it reduces to 0=0 and gives no way to solve for V. In more sophisticated terms, the Jacobian ("stiffness matrix" in mechanical terminology) is singular and cannot be inverted. Jeff -------------------
Jeff Hiller

The electric current equation is div(-sigma gradV)=0, so when sigma=0 it reduces to 0=0 and gives no way to solve for V. In more sophisticated terms, the Jacobian ("stiffness matrix" in mechanical terminology) is singular and cannot be inverted. Jeff

Thanks for the help. I am actually having the same issue when I put a very low number for the conductivity (For both conductivity being zero and a very small number, the solution converged) but I am getting different values in my electric force when using Electrostac vs EC. In fact the material I am using is an insulator with a relative permittivity of 40. I guess I am trying to understand what is the physics that results in such a difference in the electric force results. Could that be because the Electrostatic equations are solved in steady state and do not consider the transient at the moment when the step voltage is applied, while EC does? Thanks

Thanks for the help. I am actually having the same issue when I put a very low number for the conductivity (For both conductivity being zero and a very small number, the solution converged) but I am getting different values in my electric force when using Electrostac vs EC. In fact the material I am using is an insulator with a relative permittivity of 40. I guess I am trying to understand what is the physics that results in such a difference in the electric force results. Could that be because the Electrostatic equations are solved in steady state and do not consider the transient at the moment when the step voltage is applied, while EC does? Thanks

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