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 The information provided may be out of date.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.

Nearly incompressible material

Posted Jun 6, 2012, 9:55 a.m. EDT Structural Mechanics Version 3.5a 2 Replies

Giacomo Cerretti
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hi,

I have a question about the nearly incompressible materials: in the hyperelastic materials model there is an option for nearly incompressible material. If it is active I have to insert the value of the bulk modulus, so the question is: activating this option the material is considered as incompressible or not? If the material is incompressible I do not understand why it asks me to enter a value of the bulk modulus.

Thanks so much,

Giacomo Cerretti
2 Replies Last Post Jun 13, 2012, 9:01 a.m. EDT
Jean-Christophe Lavocat
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Jun 13, 2012, 6:27 a.m. EDT
Indeed, I had exactly the same question. If you find out, I would be very interested in knowing the answer!
Indeed, I had exactly the same question. If you find out, I would be very interested in knowing the answer!
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 Jun 13, 2012, 9:01 a.m. EDT
Interesting question. When you select nearly incompressible COMSOL applies a mixed formulation meaning that it adds pressure as an independent degree of freedom. This mixed formulation is good because it does not “lock” for high values of bulk modulus. It also works in theory for the case of perfectly incompressible materials (infinite bulk modulus). However, the infinite bulk modulus is more demanding when it comes to solvers since it results in zeros on the diagonal terms of the pressure equations. A very high value of bulk modulus (using the mixed formulation) would be equally accurate and easier to solve. This is my reasoning based on FE theory and I guess it applies to COMSOL as well.

Nagi Elabbasi
Veryst Engineering
Interesting question. When you select nearly incompressible COMSOL applies a mixed formulation meaning that it adds pressure as an independent degree of freedom. This mixed formulation is good because it does not “lock” for high values of bulk modulus. It also works in theory for the case of perfectly incompressible materials (infinite bulk modulus). However, the infinite bulk modulus is more demanding when it comes to solvers since it results in zeros on the diagonal terms of the pressure equations. A very high value of bulk modulus (using the mixed formulation) would be equally accurate and easier to solve. This is my reasoning based on FE theory and I guess it applies to COMSOL as well. 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