Menu

Discussion Forum

New Discussion
Filter

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Electrostatic vs. Electric current module

Posted Mar 4, 2021, 7:23 p.m. EST Low-Frequency Electromagnetics 4 Replies

Nazanin Farjam
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

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,

4 Replies Last Post Mar 5, 2021, 11:20 a.m. EST
Robert Koslover Certified Consultant
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 4 years ago Mar 4, 2021, 7:45 p.m. EST

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.
Edgar J. Kaiser Certified Consultant
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 4 years ago Mar 5, 2021, 3:15 a.m. EST

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
Jeff Hiller COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 4 years ago Mar 5, 2021, 10:18 a.m. EST
Updated: 4 years ago Mar 5, 2021, 10:19 a.m. EST

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
Nazanin Farjam
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 4 years ago Mar 5, 2021, 11:20 a.m. EST
Updated: 4 years ago Mar 23, 2021, 1:04 p.m. EDT

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

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content