Menu

Discussion Forum

New Discussion
Filter

Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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.

temperature control in heat transfer

Posted Nov 12, 2012, 1:50 p.m. EST RF & Microwave Engineering, Heat Transfer & Phase Change Version 4.3 2 Replies

Cong Liu
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hello, I am modelling a heat transfer problem, and the details are: when the temperature increases to 315K, heating is stopped; however, when temperature drops belows 310K, heating restarted. If the upper and lower bound temperatures are the same, it can be easily solved by step function. i want to ask how to describe temperature increase phase in Comsol. I tried to define a step function of Tt, and with this function to differentiate the heating up and cooling down processes. however, an error message poped out: Failed to evaluate variable Jacobian. Can anyone suggest some ways to solve this? Thanks a lot.
Cong
2 Replies Last Post Nov 12, 2012, 10:55 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Nov 12, 2012, 2:32 p.m. EST
Hi

when you use bolean or Dirac type fnctions, you have no derivatives at the transition points, this makes life complicated for the solver tht relies on the continuity of your BCs. try using a "rect" function with smoothed transition, or perhaps even a sinus function.

--
Good luck
Ivar
Hi when you use bolean or Dirac type fnctions, you have no derivatives at the transition points, this makes life complicated for the solver tht relies on the continuity of your BCs. try using a "rect" function with smoothed transition, or perhaps even a sinus function. -- Good luck Ivar
Nagi Elabbasi Facebook Reality Labs
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Nov 12, 2012, 10:55 p.m. EST
You can also use the nojac() operator to inform COMSOL to not evaluate the Jacobian of an expression. Use it carefully however.

Nagi Elabbasi
Veryst Engineering
You can also use the nojac() operator to inform COMSOL to not evaluate the Jacobian of an expression. Use it carefully however. Nagi Elabbasi Veryst Engineering

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