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Rotating Shaft FEA Study

Question asked by Baktash Bariz on Aug 3, 2011
Latest reply on Aug 4, 2011 by Baktash Bariz

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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

Baktash Bariz Aug 4, 2011 9:23 AM

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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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Michael Feeney Aug 3, 2011 1:10 PM
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Are those supports only suppressing the vertical degrees of freedom?
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- Baktash Bariz @ Michael Feeney on Aug 3, 2011 1:29 PM
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  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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  - Michael Feeney @ Baktash Bariz on Aug 3, 2011 1:38 PM
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    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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    - Baktash Bariz @ Michael Feeney on Aug 3, 2011 2:06 PM
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      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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  - Tim Goddard @ Baktash Bariz on Aug 3, 2011 2:06 PM
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    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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    - Baktash Bariz @ Tim Goddard on Aug 3, 2011 2:12 PM
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      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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      - Michael Feeney @ Baktash Bariz on Aug 3, 2011 2:27 PM
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        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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        Baktash Bariz @ Michael Feeney on Aug 3, 2011 2:35 PM
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        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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        Tim Goddard @ Baktash Bariz on Aug 3, 2011 3:11 PM
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        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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        Deepak Gupta @ Baktash Bariz on Aug 3, 2011 5:04 PM
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        Did you tried using motion studies.
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        Baktash Bariz @ Deepak Gupta on Aug 3, 2011 5:21 PM
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        No but I think I got it.
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Baktash Bariz Aug 4, 2011 9:23 AM
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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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Rotating Shaft FEA Study

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