12 Replies Latest reply on Aug 4, 2011 9:23 AM by Baktash Bariz

Rotating Shaft FEA Study

Baktash Bariz Aug 3, 2011 10:36 AM

Hello all,

I seem to have run into an issue with a FEA study and can't seem to get the correct setup for fixture and load application. I am hoping someone will provide the much needed feedback!!!

PROBLEM:

1. Horizontally rotating shaft with both ends supported vertically (not fixed).

2. Vertically downward force acting at the middle of shaft.

ISSUE: Study fails because of fixture/constraint issues.

I have tried numerous fixture/load combinations but still get a study failure!!! Should I be performing a static study first and then modify to a frequency study? Or is there a another approach?

Thank you and hope to hear back!

Baktash

Re: Rotating Shaft FEA Study

Michael Feeney Aug 3, 2011 1:10 PM (in response to Baktash Bariz)

Are those supports only suppressing the vertical degrees of freedom?
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- Re: Rotating Shaft FEA Study
  
  Baktash Bariz Aug 3, 2011 1:29 PM (in response to Michael Feeney)
  
  Michael,
  
  The goal is to fix all degrees of freedom except one rotaional at those supports. I require the shaft to rotate along its axis only. The picture does not show all DOFs.
  
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  - Re: Rotating Shaft FEA Study
    
    Michael Feeney Aug 3, 2011 1:38 PM (in response to Baktash Bariz)
    
    I don't fully understand what you're trying to do. Determine when the shaft will fail due to a static load with a non-rotating shaft? Natural frequency analysis? What exactly is it?
    
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    - Re: Rotating Shaft FEA Study
      
      Baktash Bariz Aug 3, 2011 2:06 PM (in response to Michael Feeney)
      
      I have already determined the stresses due to static loading as shown on the picture. Now I am trying to study what happens to the stresses when the shafts starts to rotate at a constant rpm with the same load pointing vertically down. I can predict that the load will reverse every 180 degrees. Does that help Michael?
      
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  - Re: Rotating Shaft FEA Study
    
    Tim Goddard Aug 3, 2011 2:06 PM (in response to Baktash Bariz)
    
    Maybe my SW simulation is license limited or it's my knowledge of the product, but how exactly are you rotating the shaft? (i.e. loads etc). Is this paired with a motion study?
    
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    - Re: Rotating Shaft FEA Study
      
      Baktash Bariz Aug 3, 2011 2:12 PM (in response to Tim Goddard)
      
      The shaft doesn't have to rotate. It could be simulated using cyclic loading. My problem arises when I get fixture errors which means my part isn't fully fix or support properly.
      
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      - Re: Rotating Shaft FEA Study
        
        Michael Feeney Aug 3, 2011 2:27 PM (in response to Baktash Bariz)
        
        So you want to follow a single element or point on the shaft and determine the stress fluctuation at that point as the shaft rotates? I wonder why this is important to know from a failure standpoint seeing as the maximum stress will be clear with a static analysis. Tim is right about the being a motion study. You have your model set up there, correct?
        
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        Re: Rotating Shaft FEA Study
        
        Baktash Bariz Aug 3, 2011 2:35 PM (in response to Michael Feeney)
        
        Correct, that would be another way of saying it. You can think of it as bearing problem where we need to find out the fatigue stress.
        
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        Re: Rotating Shaft FEA Study
        
        Tim Goddard Aug 3, 2011 3:11 PM (in response to Baktash Bariz)
        
        I'm interested in how SW handles this. I'm limited to the standard Simulation with SW Premium so nothing but static-linear for me.
        
        From a fatigue-solution point of view, the static solution is all you need. The cyclic stress is represented by the stress around the circumference. From a stationary point of view, the stress on a rotating shaft with stationary load will never change position (max tensile is opposite load application, compression on load side). Only from the viewpoint of a point on the shaft will it appear cyclical.
        
        If this problem isn't academic then you should consider the dynamic stability of a rotating shaft and see whether you are operating near any critical speed.
        
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        Re: Rotating Shaft FEA Study
        
        Deepak Gupta Aug 3, 2011 5:04 PM (in response to Baktash Bariz)
        
        Did you tried using motion studies.
        
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        Re: Rotating Shaft FEA Study
        
        Baktash Bariz Aug 3, 2011 5:21 PM (in response to Deepak Gupta)
        
        No but I think I got it.
        
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Re: Rotating Shaft FEA Study

Baktash Bariz Aug 4, 2011 9:23 AM (in response to Baktash Bariz)

I figured it out on my own. The trick was to fix the ends of the shaft and apply a reversing cyclic load (max to max) on one plane. This would simulate the load applied every 180 degrees. Thank you all for your feedback. Very helpful.

Baktash
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