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Shaft - find natural frequency of horizontal shaft with bearings

  1. May 2, 2014 #1
    shaft -- find natural frequency of horizontal shaft with bearings

    how to find natural frequency of horizontal shaft with bearings at either sides, using (Ansys-classic).
    Please reply, Thank you.
  2. jcsd
  3. May 4, 2014 #2
    I'm sorry you are not generating any responses at the moment. Is there any additional information you can share with us? Any new findings?
  4. May 7, 2014 #3
    Is the shaft rotating fast enough that the rotation might alter the frequency?

    If not, then just put appropriate restraints where the bearings are and solve it. You'll need to decide if the bearings give it freedom to rotate like simple supports or only allow axial rotation like a sleeve bearing.
  5. May 7, 2014 #4


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    It is not clear if you want the critical angular frequency for whirl, or the torsional or lateral vibration frequency.

    Simulators are often too perfect to self destruct. You may need to add an imbalance or some white noise while sweeping over an RPM range.
  6. May 7, 2014 #5


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    I agree the question doesn't specify what the OP really wants to calculate.

    And if you do want to include the effect of whirling, without a drawing of the rotor it's not obvious whether a simple "rigid disks on a flexible shaft" model is appropriate, or whether you need to include the flexibility of all parts of the system.

    The lateral vibration frequencies ARE whirl frequencies, but not synchronous ones. In some situations non-synchronous whirl is just as much a problem as synchronous. Even if it doesn't cause the device to fail catastrophically, it can eat up the structure's fatigue life like there was no tomorrow!
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