Menu

Discussion Forum

New Discussion
Filtern

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 The information provided may be out of date.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.

matlab/comsol unit problem

Posted 09.04.2010, 06:07 GMT-4 Fluid & Heat, Interfacing, Heat Transfer & Phase Change, Parameters, Variables, & Functions Version 4.4 4 Replies

Priya Pathak
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

My problem is

Diffusion eq + Navier–Stokes eq
I am solving diffusion equation which has unit (mm) in Matlab and Navier–Stokes eq in Comsol (SI unit).

I could not decide how to get out of unit problem.

what unit I should take in Comsol?

If I have structure of 35 mm length 5 mm width geometry.

4 Replies Last Post 17.12.2014, 06:27 GMT-5
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 09.04.2010, 11:00 GMT-4
Hi

I always use SI units, its easier to handle, othervise you must always check that you have the right scaling factors everywhere, and you almost always miss a couple ;)

Ivar
Hi I always use SI units, its easier to handle, othervise you must always check that you have the right scaling factors everywhere, and you almost always miss a couple ;) Ivar
Guo Shusen
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 04.08.2014, 05:53 GMT-4
thanks Ivar！
I have a question in transport of the diluted species，when I set the diffusion of the species to 1.77e-9[m^2/s], it is very slow to convergence,and there is a error says"the following feature has encounted a problem:
undefined value found
-Detail:NaN or Inf found when solving linear system using SOR
-Feature:stationary solver1(sol1/s1)"
I think it is because i set the diffusion coefficient to small， so i change the unit of my pde，I change all coefficients' unit to 1（you can see it in picture），but in comsol the geometry and physics still have the unit such as [m] and so on, my question is whether it will influence the solution of the pde，will i get the solution i want by inverse transformation.
thanks a lot!
thanks Ivar！ I have a question in transport of the diluted species，when I set the diffusion of the species to 1.77e-9[m^2/s], it is very slow to convergence,and there is a error says"the following feature has encounted a problem: undefined value found -Detail:NaN or Inf found when solving linear system using SOR -Feature:stationary solver1(sol1/s1)" I think it is because i set the diffusion coefficient to small， so i change the unit of my pde，I change all coefficients' unit to 1（you can see it in picture），but in comsol the geometry and physics still have the unit such as [m] and so on, my question is whether it will influence the solution of the pde，will i get the solution i want by inverse transformation. thanks a lot!
Aaron Ayal
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 10 years ago 17.12.2014, 05:00 GMT-5
I have a similar problem.

I am trying to implement a MATLAB script to explore a set parameter space in a fluid problem.
The issue is that I am working with dimensionless equations and numbers.
I know how to implement this with the COMSOL desktop, but I've no idea how to set the unit system to dimensionless in the model created with MATLAB. I also seem to be unable to find it in the manuals provided for Livelink implementation.

EDIT.
The problem has been resolved.
I have a similar problem. I am trying to implement a MATLAB script to explore a set parameter space in a fluid problem. The issue is that I am working with dimensionless equations and numbers. I know how to implement this with the COMSOL desktop, but I've no idea how to set the unit system to dimensionless in the model created with MATLAB. I also seem to be unable to find it in the manuals provided for Livelink implementation. EDIT. The problem has been resolved.
Lasse Murtomäki
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 10 years ago 17.12.2014, 06:27 GMT-5
In the uppermost level, in the end of the screen, select Unit System to None.
In the uppermost level, in the end of the screen, select Unit System to None.

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