### Defining Ansys Superelement SUB File Manually

Photo by  James Owen  on  Unsplash A surprisingly popular blog-post written here is Exporting Stiffness Matrix from Ansys . A sensible follow up question is what can one do with the exported stiffness matrix? In a recent Xansys Forum post, a question was raised on how we can edit the stiffness matrix of a superelement and use it for our model.  An approach presented below is to first create a superelement that has the same number of DOF and nodal location that will serve as a template. An APDL script can then be written to edit the stiffness matrix entries as desired before exporting to a new superelement *.SUB file for use in future models. The self-contained script below demonstrates this.  /prep7 et ,1, 185 mp , ex, 1, 200e3 mp , prxy, 1, 0.33 w = 0.1 ! single element (note nodal locations) n , 1, w, -w, -w n , 2, w, w, -w n , 3, -w, w, -w n , 4, -w, -w, -w n , 5, w, -w, w n , 6, w, w, w n , 7, -w, w, w n , 8, -w, -w, w e , 1, 2, 3, 4, 5, 6, 7, 8 /solu antype , substr     ! analy

### Precise Mass Summary

Precise Mass Summary Output

One of the many checks one can do in FEA is to compute the mass, inertia and center of gravity. Besides doing this for the normal models, it can quickly extract out the mass and inertia of the superelement (SE) to verify the MATRIX50 that you're bringing in  has the same mass and inertia as the genuine article.

If the mass comes in too low, try specifying more modes in CMSOPT to see if it fixes it. My previous co-worker also came across intermittent issues with using constraints equation (CE) inside a superelement. He replaced it with really stiff beams instead before generating the superelement.

Personally, I would take a bit of time to select master nodes (M) not just at the connections but at various points on the model to properly capture the modal mass. This would be similar to identifying accelerometer locations on your part to properly identify modes of interest for a modal test.

Here's the command to calculate it all :
ALLS $/SOLU$ IRLF,-1 $PSOLVE,ELFORM$ PSOLVE,ELPREP \$ IRLIST