

November 4, 2022 at 7:58 pmxiaoSubscriber
Hi Community,
I have a question about the node ID (after meshing) and its associated DOF.
I use the following command to get the Dense Mass and Stiffness Matrix:
In the output, the matrix is of dimension 6936x6936. I want to condense the stiffness matrix according to the nodes I'm interested in.
The question is how to find the DOF related to the node ID. For example, if the node ID is 76, which DOFs are related to it? I use a beam element; each node should have 6 DOFs.
Thanks,
Xiao

November 5, 2022 at 1:20 amMike RifeAnsys Employee
Hi Xiao
Instead of creating a dense matrix, create sparse matrices with the *smat. There is an option to also create the DOF to node mapping vector.
Mike

November 7, 2022 at 4:31 pmxiaoSubscriber
Hi Mike,
@ Mike Rife
Thanks for your kind response. I have tried using *SMAT to export the sparsed mass and stiffness matrix using the following command line:
From the command line, I also tried to use NOD2BCS to infer the nodal DOF. I tried to link the nodal DOF from the output files as follows:
In the figure above, I tried to get the DOFs associated with node 289. My initial understanding is that the left column in the bracket is the DOF with the boundary nodes (For example, each node has 6 DOFs. Hence for node 289, the DOFs should be 1728:1733. The column after the semicolon is the DOF for node 289 in the stiffness & mass matrices.
After this, I applied a 1N force at node 289 in the X direction and applied 1N force in the force_vector (same size as the stiffness matrix) at DOF 1705. But the results differ from ANSYS and the calculated displacement from the extracted stiffness matrix.
Can you tell me which is the correct understanding of the exported file? Or the command I used is wrong.
Thanks,
Xiao

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