Learning Forum

[J_S]

Hi members, 

I am working in the field of vibro-acoustics. I export the coupled vibro-acoustic matrices with *EXPORT and a matrix marked format. However, later on I want to do some MOR and these schemes require the exported matrices to be in a special format with respect to the DOF order. The matrices must have such a format: M = [M_uu , 0; C, M_pp], where M_uu is the mass matrix of the pure structural part and M_pp is the mass matrix of the acoustic enclosure, while C is a coupling matrix. What I am getting so far is a matrix that is not so cleanly separated into a structural and an acoustic part. Is there any way to achieve this before exporting the matrices? 

Best

[Sheldon Imaoka]

Hi J_S Unfortunately, there isn't a straightforward way to accomplish this, as the assembled matrix can't be subdivided directly by the user.
If you use shared nodes, then the nodes at the interface could be identified, and if you go from solver ordering -> internal ordering -> user ordering (user ordering = node ID # you see in mesh), you could isolate the terms associated with coupling. Otherwise, the nodes with 3 DOF could be identified as structural, 4 DOF are the coupling vibroacoustic nodes, and 1 DOF are acoustic nodes.
Sorry that I can't think of a direct way to separate the matrix for export in the manner you are seeking.
Regards Sheldon

[J_S]

Hi Sheldonl,
thanks for the answer. The identification of structural and acoustic elements in the subsequent proceeding of the matrix works. However, reordering elements does not necessarily preserves the eigenvalues of the K, M combination of the coupled system. I was hoping to create the matrices already with this ordering. However now I'm searching if the solution you offered can still help or if there is some method to reorder the elements in the Mass and stiffness matrix according to the demands while preserving the dynamics.

Best
Julian