Learning Forum

[Shangru Liu]

Hello,

 

I have a simple model with a long pipe and a ring on it in the middle, which is just slightly bigger than the pipe. To make convergence easier, I made the inner side of the ring touches with the upper side of the pipe at the beginning.

 

Both objects were meshed with pipe elements. The pipe was fixed on one end, Fy and Fz were applied on the other end. It was applied in two steps, first Fz and then Fy. I supposed the ring should deform with the pipe, but it only deforms in the Z direction but not the Y direction. The behavior is shown in the pictures below.

Figure 1. Mesh

Figure 2. Initial configuration

Figure 3. Fz applied, behaves normal

Figure 4. Fy applied, the ring doesn't move in Y direction

I tried playing around with all different settings of the contact pair but none of them helps. Please offer me some hints on how to proceed, thank you!

[Erik Kostson]

 

Hi

See if this helps (you need internal pipe contact):

https://forum.ansys.com/forums/topic/how-to-define-no-separation-contact-between-beams/

51.2. Problem Description (ansys.com)

If you are not able to open the links, refer to this forum discussion: How to access the ANSYS Online Help

Guidelines for Posting on Ansys Learning Forum

Hope that helps

Erik

 

[Shangru Liu]

Hi Erik,

Thanks for your reply!

I have activated internal pipe contact, but that was not the issue. I found out just now that the 'Time Step Controls' helps. It shouldn't be 'None'. I think this helps to increase the number of substeps and prevents the model from missing the contact when it deforms.

This feels similar to what we do in APDL, we can increase the number of substeps to help identify the contact and ease the convergence. Therefore, I have a further question regarding this. How can I adjust the number of substeps manually in Mechanical? Is there something similar to the 'nsubst' in APDL?

Besides, I found the Time Step Controls option doesn't always help. There are two situations:

1. If I don't activate Fz, but only Fy, the ring will still fall off.
2. If I turn off Small Sliding, the ring will also fall off when Fy applied. However, I do need large sliding in X-direction. If I don't turn off Small Sliding, the ring will have unrealistic deformation when Fx or Ux is applied at the end of the pipe.

Best Regards,

Shangru

[Erik Kostson]

 

Hi

Yes the steps is similar and exact to apdl since in the end of the day Workbench generates a ds.dat apdl input file to be solved by the apdl solver.

See here more about steps (also the help manual has some good info.)

https://www.padtinc.com/2011/11/08/you-dont-wanna-step-to-this-breaking-down-loadsteps-and-substeps-in-ansys-mechanical/

 

All the best

Erik