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Info of Eliminated stiffness matrix

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Hi,

The reply from Remi Magnard perfectly answered how to extract the imformation of the assembled matrice, such as stiffness matrix "K" or mass matrix "E".

But now my question is how to extract the imformation of the eliminated matrice, such as "Kc" and "Ec". Are those informations also in the "mphxmeshinfo"? For reference, we are using those matrics to calculate the natural frequency and eigen values.

Thank you very much,

Yan


2 Replies Last Post 2021年9月6日 GMT-4 21:36
Remi Magnard COMSOL Employee

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Posted: 3 years ago 2021年8月31日 GMT-4 08:07

The xmesh info is always on the full assembled system. The relation between the full and the eliminated system can be retrieved using the constraint null-space basis matrix and the constraint force null-space matrix . These are used for the constraint elimination as:

With LiveLink for MATLAB you can extract these matrices using the command below:

str = mphmatrix(model, <soltag>, 'out', {'Null','Nullf'});

where <soltag> is the tag of the solution node.

The xmesh info is always on the full assembled system. The relation between the full and the eliminated system can be retrieved using the constraint null-space basis matrix Null and the constraint force null-space matrix Nullf. These are used for the constraint elimination as: K_c = Nullf^{T} K Null With LiveLink for MATLAB you can extract these matrices using the command below: str = mphmatrix(model, , 'out', {'Null','Nullf'}); where ** is the tag of the solution node.

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Posted: 3 years ago 2021年9月6日 GMT-4 21:36

Thank you very much, Remi Magnard!

Very helpful!

Yan

Thank you very much, Remi Magnard! Very helpful! Yan

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