General Mechanical

General Mechanical

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ANSYS Substructuring and extract Stiffness Matrix

    • Jonas.F.Berger
      Subscriber

      Hello, 

      my problem is a bit complicated to explain. I try to sketch my workflow below:

      1. I model a shaft in ANSYS Workbench/Mechanical and mesh it.
      2. Boundary conditions are defined with the ANSYS option cylindrical bearings. The shaft is free in circumferential direction. Other BC are used to get a fully constrained model. The picture below shows them left and right of the gearing:
      3. After meshing, I create a substructuring model and define some points at the gearing as masterpoints. 
      4. Forces are defined at a tooth
      5. The substructured stiffness matrix and the Load vector are extracted via the HB-Format (command HBMAT in an APDL script).
      6. Stiffness Matrix and Load vector are imported in Matlab and the System K*u=f is solved. 

      To test my workflow, I did the calculation in Matlab and ANSYS directly. Results for u should be the same in both cases. 

      Now to my problem:

      • For the configuration with the cylindrical bearing boundary condition, the deformation u from Matlab (derived with the load vector and stiffness matrix from Ansys) differs from the deformation calculated with ANSYS directly .
      • Changing the cylindrical bearing boundary condition to fully constrained boundary condition (u = 0 at the cylindrical surfaces in the picture above), the solution from ANSYS directly and Matlab are the same.

      So it can be assumend, that in my model with the cylindrical bearing boundary conditions, something is wrong with the exported stiffness matrix. Maybe I have some commands missing?

      It would be nice if someone has done something like this before or has an idea of what to look out for to solve the problem.

      Best,

      Jonas

    • dlooman
      Ansys Employee

      Could you be more specific about what you mean by "cylindrical bearing."  There is a cylindrical support boundary condition, a bushing element and a bearing element to name a few of the possibilities.

    • Jonas.F.Berger
      Subscriber

      I am using the cylindrical support bearing. In the meantime I found the solution. Before exporting the HB-Stiffmat, the nodes at the cylindrical support bearing surface have to be rotated in a polar coordinate system with its center in the cylindrical support bearing center.

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