Learning Forum

[Gabriel Oliveira]

I am conducting a modal analysis of a clamped-clamped beam using Ansys APDL. The beam mesh contains 200 elements and 201 nodes, and I am using BEAM188, which has 6 degrees of freedom at each node.

I expected that the extracted mass and stiffness matrices would have dimensions of 1206x1206, since each node has 6 DOF, thus 201*6 = 1206.

The extracted matrices have dimensions of 1194x1194, apparently, the DOF from the fixed ends (12 DOF) are removed. I would like to know if it is possible to extract the mass and stiffness matrices including the fixed ends, that is, to extract the matrices with dimensions of 1206x1206.

To extract the matrices, I use the following commands:

 

! Stiffness

*DMAT,MatKD,D,IMPORT,FULL,beam_apdl.full,STIFF 
*PRINT,MatKD,Kdense.matrix

! Mass

*DMAT,MatMD,D,IMPORT,FULL,beam_apdl.full,MASS
*PRINT,MatMD,Mdense.matrix

! below the commands create sperse matrix

*SMAT,MatKS,D,IMPORT,FULL,beam_apdl.full,STIFF 
*PRINT,MatKS,Ksparse.matrix

*SMAT,MatMS,D,IMPORT,FULL,beam_apdl.full,MASS
*PRINT,MatMS,Msparse.matrix

 

I thank you in advance for your attention!

[dlooman]

Perhaps you could remove the constraints before writing the matrices?  In a modal analysis it's common for the model to be unconstrained, so that shouldn't be an issue.

[Gabriel Oliveira]

Thank you very much, this has solved my problem!