Degree of Freedom Ordering of [M] and [K]

[r.brown]

I am able to extract the mass and stiffness matrices using the following codes in APDL:
*SMAT, MatK, D, import, full, file.full, stiff
*SMAT, MatM, D, import, full, 2d_beam.full, mass
*export, MatK, mmf, matkMMF.txt
*export, MatM, mmf, matMMMF.txt

I then read them in MATLAB as two full matrices.

The modal analysis results in MATLAB are consistent with those from ANSYS. This proved the correctness of the two matrices.
However, I am wondering how the degrees of freedom are indexed in these two matrices by ANSYS.

From this webpage

https://www.sharcnet.ca/Software/Ansys/17.0/en-us/help/ans_apdl/apdldofordering.html,

I tried to read the Nod2Bcs vector and map with the node numbering in APDL. They don't match.
I also tried this one:

http://www.ansystips.com/2017/10/export-stiffness-matrix-from-ansys.html.

The DOF's do not match as well.

Does anyone have experience in the DOF ordering of these matrices?

 

[scheah]

Does anyone have experience in the DOF ordering of these matrices?

I've played with it a little...

How did you determine the DOFs does not match?
Did you use both MapForward & Nod2Bcs?


Kind regards,
Jason

 

[r.brown]

Hi Jason,

I've figured out the DOF ordering of [M] and [K] using MapForward and Nod2Bcs. Thanks for your tips.
I'm looking for a method to transform them back to the user ordering in MATLAB for other analyses. Do you have any thought on it?

Raymond

 

[scheah]

Hi Raymond,

Matrix from the .FULL file is in BCS ordering. The index array from MapForward and Nod2Bcs maps in both directions of User Ordering & BCS Ordering.

Perhaps look into SPMWRITE to see if it fit your needs better in Matlab. The matrix is in state-space and allows for simpler DOF identification. From the help:

If Inputs is an array parameter, the first column is the node number and the second column is the structural degree of freedom (1=UX, 2=UY, 3=UZ, 4=ROTX, 5=ROTY, 6=ROTZ) indicating input points.

Kind regards,
Jason