I am trying to solve a basic problem. First of all, I created line body (BEAM188) which is 2 beam element 2 fixed support and the middle node have 6DOF. Afterward I got the results in ANSYS workbench.
However, I exported stiffness and mass matrix from ANSYS and import these matrices into MATLAB to calculate iegenfrequencies and I had different results than ANSYS Workbench. Moreover, the stiffness and mass matrices have totally different structure than the theoretical stiffness and mass matrices. I have zeros matrices, where they shouldn't be, accordingly to theoretical global stiffness and mass matrices.
Also, ANSYS Workbench add midside nodes automatically to use quadratic shape function which leads to more nodes at the structure (18x18 matrices instead of 6x6 matrices)
Please explain that:
**Why I have different results than ANSYS WB when I calculate the eigenfreqeuncies with ANSYS stiffness and mass matrices?
**How does ANSYS setup these matrices with midside nodes mathematically?