Restricting Axial Shaft Movement in Modal Analysis of Vertical Pumps

- April 29, 2025 at 11:05 am
  
  Zeeshan.Ali
  Subscriber
  
  Dear Ansys Community,
  I’m working on modal analysis for vertical-type pumps, and we often notice that in the first mode, the shaft moves freely in the longitudinal (axial) direction without any restriction.
  I’m wondering if there is a contact type or restraint used to limit this motion. I’ve attached a representative image to illustrate the issue.
  Would appreciate your thoughts on this.
  Best regards
- April 29, 2025 at 3:43 pm
  
  peteroznewman
  Subscriber
  
  Modal is a linear analysis, so nonlinear contacts that work in one direction and not the other such as frictional don't work that way in a Modal analysis. All contacts in a Modal analysis are converted to linear contacts such as Bonded or No Separation. I suggest you add a No Separation contact with a Hub to either the top of the shaft or the bottom of the shaft or both. Maybe you can run three copies of the Modal analysis to study each case. No Separation will allow the shaft the freedom to spin on its axis, but be axially connected to one or both hubs.