Learning Forum

[xan2]

We have been trying to determine how to create a cylindrical support in Workbench for LS-DYNA. This forum post suggests that you need to open the mesh in LS PrePost and create the boundary condition there.

 

The suggested solution creates a tangential coordinate system at every node and sets dofx & dofy to unconstrained using BOUNDARY_SPC_NODE.

 

We thought that we may be able to create a similar effect by creating a coordinate system at the center of rotation and using a BOUNDARY_SPC_SET card with the translational DOFs constrained and the rotational DOFs unconstrained but this doesn't seem to work. For example, in the example here I have created a cylinder with its center on the y-axis, a BOUNDARY_SPC_SET card using the global coordinate system that constrains the nodes on the cylinder to only have rotational DOFs, and an applied angular velocity about the y-axis. Despite having free rotational DOFs the cylinder does not rotate. If the translational constraints are removed from the card then the cylinder will rotate.

• What is the actual behavior and intended use of the rotational DOFs in BOUNDARY_SPC_SET?
• Is there a way to do this with cards that doesn't require opening in LS PrePost? I think I've read that there may be a way to do it using BOUNDARY_PRESCRIBED_MOTION but I'm not entirely sure.

[Jim Day]

I assume the cylinder is deformable.   You're confusing motion of the body (the cylinder) with motion of individual shell nodes.   A shell node has 6 dof, 3 of which are translational.   The BOUNDARY_SPC_SET command is constraining dof of individual nodes.   For the cylinder to spin, the the nodes must translate and so translations of the individual nodes must not be fixed.