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 The information provided may be out of date.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.

Inconstant result between 3D and 2D axial symmetry PDE model.

Please login with a confirmed email address before reporting spam

Hi, anybody.
I met a problem. It is related with the inconstant result
between 3D PDE mode and 2D axial symmetry model.
Maybe I set some error parameters in PDE.

-------------------------------------------------------------------
My model is very simple half sphere with a hole in center.
Inter radius is 1.3mm, and outer radius is 40mm. The model is
heated with Joule heat and the heat power density is in inverse proportion
to the 4th power of position's distance to center -- r.
In the position r=1.3mm, the heat power density is 100000000 [W/m3]
I want to get the temperature distribution plot after 60 seconds.
Initial temperature is 293.15K

Please check attached sketch map
-------------------------------------------------------------

I build 2 models, one is 3D model and the other one is 2D axial symmetry
model. For each model, two methods is applied: one is standard comsol
heat transfer equation, and the other one is PDE equation.
In PDE equation, both 2D and 3D, parameter is same.
"c" item is set to thermal conductivity (k)
"Da" item is set to density*specified heat (rho*c)
"f" item :
in 3D model, f= 100000000*(0.0013^2/(x^2+y^2+z^2))^2
in 2d model, f= 100000000*(0.0013^2/(r^2+z^2))^2
For detail information, please check attached mph file.

The following is result,
*******************************************************************

3D Standard 3D PDE 2D Standard 2D PDE

386K 386K 386K 435K

*******************************************************************

Obviously, the 2D PDE case result is inconstant with the other 3 cases.
It has no relationship with model mesh size.

if I set the heat source power density to a constant value, the 4 results
are same.

So I suspect there are some problem for "f" item in 2D PDE mode.

Anyone can help me?

======================================================================


0 Replies Last Post 17 nov 2011, 23:20 GMT-5
COMSOL Moderator

Hello Hsiang-An Chan

Your Discussion has gone 30 days without a reply. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help.

If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base.

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.