Learning Forum

[skpb]

The image shown below is My model with Displacement Boundary conditions.

I tried to impose the Pin-Pin simply supported Boundary conditions for this model by restricting the x and y displacements and making z displacement free on Both the ends.

But I'm getting the following errors in ANSYS Workbench.

• Not enough constraints appear to be applied to prevent rigid body motion.  This may lead to solution warnings or errors.  Check the results carefully.

Am I making mistakes in simulating the Pin-Pin Boundary Conditions on the Model could someone please guide on this.

[peteroznewman]

That is probably a warning and not an error.  Did you get results?

To get a true pinned constraint, replace each Displacement with a Remote Displacement on the same face. Then a single point will control the face. The Remote Displacement can fix X,Y,Z,Rx,Ry leaving Rz free and do the same on the other Remote Displacement. Don't pick two faces and try to use a single Remote Displacement, that would be wrong.

If you leave Y free on the one end, that will be like a pinned-roller constraint, but you can't leave Y free on both ends as that would allow rigid body motion along Y.

It looks like the geometry and load are symmetric. You can save time solving the model if you slice the geometry in half (or quarter). Apply a Symmetry Region at the center cut face, make sure the Normal is pointing in the right direction).

Another kind of Support constraint for cylindrical faces is Bearing, where the load is only on the compression face. That should be used with Quarter Symmetry so that the shaft is adequately supported.

[skpb]

Sir, Thanks but I have applied your idea for the simpler model, but I encountered a warning says " One or more Remote Boundary Conditions have been scoped to a solid vertex.  Stiff beams have been employed to connect the remote point to the vertex.  Check the results carefully. You may visualize the created beams on the Solution Information Folder.

So, when I went with the solution information I could see the beams from the remote displacement points, and I have attached the image. It could be really helpful if gets what does scoped to a solid vertex means. And whether this solution is correct though the warning is given or it should be corrected.

[peteroznewman]

I would use two Remote Displacements, one for each end, and select each end face to be the scoped entity. A pinned constraint means all DOF is set to 0 except for one, such as Rotation Z, which is left Free.  Some people might want to leave Rotation X free also and call that pinned. This kind of pinned has no preferred axis of rotation.

[skpb]

Thanks, Peter!  It helped. When I scoped the end faces and used remote displacements, I was getting no warnings in the solution.

Could you share some knowledge why does scoping the end face removed the rigid beams?

And I have attached the behavior of the beam in SSB ( simply supported beam ) conditions for both the cases vertex scoped and end face scoped. 

I could see the nuance between the displacement results of both the scoping methods. So which one is correct