Menu

Discussion Forum

New Discussion
查找

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.

How to Export Stiffness and Mass Matrices in COMSOL Eigenfrequency Study

Posted 2025年4月22日 GMT+8 09:52 General, Studies & Solvers, User Interface Version 6.2 2 Replies

Nelson Leon
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hello,

I'm using COMSOL Multiphysics to perform an eigenfrequency analysis of a cryogenic suspension beam for a gravitational-wave detector project. I want to export the stiffness matrix (K) and mass matrix (M) for each mode, so I can compute the energy using the quadratic form:

externally.

Issue: I followed these steps:

  • Created an Eigenfrequency study (with or without prestress).

  • Added a Matrix Export node under "Derived Values."

  • Selected “Stiffness Matrix” and “Mass Matrix” with options "Global" and "Sparse."

However, when I try to export, COMSOL gives the error:

"K is not stored."

I’ve also tried switching to frequency-domain or stationary studies and adding Input Matrix nodes under the solver configuration, but nothing has worked so far.

My Questions:

  1. Is there a correct way to configure the eigenfrequency study so that the stiffness and mass matrices are stored and exportable?

  2. Does this feature require enabling something before solving?

  3. Is there any workaround if I don’t have LiveLink for MATLAB or Java API access?

Any guidance would be very appreciated

2 Replies Last Post 2025年4月22日 GMT+8 19:05
Sebastian Müller
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 6 months ago 2025年4月22日 GMT+8 18:32
Updated: 6 months ago 2025年4月22日 GMT+8 18:37

Is there a correct way to configure the eigenfrequency study so that the stiffness and mass matrices are stored and exportable?

In study right-click on solution(sol 1) and use Other->Assemble and choose the data you want to store. After solving: in Results right-click' Derived Values' and use System Matrix.

https://www.comsol.com/blogs/implementing-the-weak-form-with-a-comsol-app#equation1

Nice Greetings

> Is there a correct way to configure the eigenfrequency study so that the stiffness and mass matrices are stored and exportable? In study right-click on solution(sol 1) and use Other->Assemble and choose the data you want to store. After solving: in Results right-click' Derived Values' and use System Matrix. [https://www.comsol.com/blogs/implementing-the-weak-form-with-a-comsol-app#equation1](https://www.comsol.com/blogs/implementing-the-weak-form-with-a-comsol-app#equation1) Nice Greetings
Henrik Sönnerlind COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 6 months ago 2025年4月22日 GMT+8 19:05

However, for this purpose there is no need to do this operation at all, since the energy is available as a built-in variable.

-------------------
Henrik Sönnerlind
COMSOL
However, for this purpose there is no need to do this operation at all, since the energy is available as a built-in variable.

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