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Mechanical vibrations, force applied to the armature

  1. Mar 20, 2012 #1
    1. The problem statement, all variables and given/known data

    FYI - I don't have any knowledge on the mechanical aspects of electric motors.

    you're given a 400 hp electric motor that needs to run at varying rpms. The armature is 1200 lbs and is 800mm long with a diameter of 500 mm. the air gap that exists is 2.5 mm. At 800 rpm the air gap was reduced to 1.75 mm (the armature displaced 0.75 mm from its equilibrium position).

    I need to find the stiffness of the armature and the rotor unbalance.

    - how exactly do I find the force applied to the armature ?

    2. Relevant equations

    I don't know any

    3. The attempt at a solution

    finding the force applied to the armature is something I can't figure out. I want to think that using the centripetal force = mv^2/r. However, since the armature is a mass rotating around its central axis, and not a point mass rotating around a point, Im sure my guess is wrong.

    finding the force on the armature as a function of speed will let me find the stiffness of the shaft supporting the armature. with the stiffness and the damping ratio I can find the resulting equation of motion (describing the displacement of the armature from the center) using a response to harmonic excitation
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
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