Hi everyone,

In the framework of my Masters Thesis at TU Munich, my goal is to extract a physical mass matrix,stiffness matrix and mode shapes of my model (made up of beam188 elements) from Ansys Mechanical APDL. I am new to Ansys workbench as well as APDL and therefore want to be sure not to make any rough mistakes.

I built the model (geometry and mesh) in ANSYS workbench, then exported the input file and extracted the lumped mass and stiffness matrices using the following commands in Mechanical APDL:

/solu

antype,substr

seopt,file,2,1

lumping,yes

m,all,all

/output,StiffnessFile

solve

/output

I do get an output for both, however I am not sure how to interpret the resulting mass matrix. What I want is a physical mass matrix for the whole model which has on its diagonal the individual mass matrices of each node, with the latter each being made up of a unit matrix multiplied by the respective lumped mass, the inertia tensor and mixed terms, as can be seen in the attached file.

The mass matrix which I get with the lumped output option is however not of the desired form when I assemble the rows in the output file, and I am not quite sure how to interpret the terms off the diagonal.

As far as the mode shape calculation is concerned, I was wondering what the option to normalize the mode shapes to the mass matrix means. Am I right to assume that if I want extract the mode shapes in order to formulate the** absolute** displacements of all nodes as a superposition of the mode shapes, it would be wrong to choose this option?

Thanks a lot in advance!