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 The information provided may be out of date.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.

Deravites in 2D-axisymmetric models

Please login with a confirmed email address before reporting spam

Hi guys,
I was wondering if we should add any extra parts for calculating the derivative of a variable in 2D-axisymmetric models? Under Definition ----Variables--If the goal is to define a new variable based on the derivative of the default variable like electric field (E), does this work or not?

new = d(es.Er , r )

Is this correct in axi-symmetric models ? our new variable is now the derivative of the E with respect to r?

1 Reply Last Post 2013年4月1日 GMT-4 16:17
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 2013年4月1日 GMT-4 16:17
Hi

it is possible to do it that way, if COMSOL has not already defined a Err) but you might get only "0" out as if you derive many times, you need to ensure that our dependent variables are resolved with higher order discretization (at least one more than the number of sucessive derivatives used)

Sometimes its better to define new global PDEs and define new variables for the elements higher than 2nd derivatives, and not the way to derive continuosly the exsiting ones

--
Good luck
Ivar
Hi it is possible to do it that way, if COMSOL has not already defined a Err) but you might get only "0" out as if you derive many times, you need to ensure that our dependent variables are resolved with higher order discretization (at least one more than the number of sucessive derivatives used) Sometimes its better to define new global PDEs and define new variables for the elements higher than 2nd derivatives, and not the way to derive continuosly the exsiting ones -- Good luck Ivar

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.