Ansys Learning Forum Forums Discuss Simulation General Mechanical How to Create a Stiffness Matrix in APDL Reply To: How to Create a Stiffness Matrix in APDL

Awlad
Subscriber
Dear Mr. Erik:
Many, many thanks. Yes, I made some progress. If any Support Engineer could answer my questions or clarify my understanding that will be highly appreciated. These are my understanding:
The stiffness matrix, provided by the *dmat command, is associated with the DOFs which are NOT constrained. For example, I made my FE model using Truss Element (Link180). I used only two nodes, Node # 1 and Node # 2. So, I have only one element, which is aligned along the global x-direction. I applied force also along x-direction. If I consider only 1 DOF (Ux) per node, then the size of global stiffness (K) matrix will be a (2x2) matrix. However, Node # 1 is fixed. Hence, the stiffness matrix, provided by the *dmat command, is NOT including the components under the "Row # 1 and Column # 1". It is providing the stiffness components ONLY under the "Row # 2 and Column # 2". So, it becomes a (1 x 1) matrix.
Then, I repeated the same simulation using 4 nodes. So, I have 3 elements. Each element is aligned along global x-direction. If I consider only 1 DOF (Ux) per node, then the size of global stiffness (K) matrix will be a (4 x 4) matrix. However, Node # 1 is fixed. Hence, the stiffness matrix, provided by the *dmat command, is NOT including the components under the "Row # 1 and Column # 1". It is providing the stiffness components under the "Row # 2 to 4 and Column # 2 to 4". So, it becomes a (3 x 3) matrix. And, those components are matching with the stiffness matrix provided by MATLAB. Here is the image of stiffness matrix provided by *dmat command.
If any Support Engineer could clarify my understanding that will be highly appreciated. Thanks Awlad.