VM-WB-MECH-079

VM-WB-MECH-079
Natural Frequency of a Motor-Generator

Overview

Reference:

Thomson, W. T. (1965). Vibration Theory and Applications (2nd Printing) (pp. 10, ex. 1.3-3). Englewood Cliffs, NJ: Prentice-Hall, Inc.

Solver(s):

Ansys Mechanical

Analysis Type(s): Mode-Frequency Analysis
Element Type(s): Pipe Element

Test Case

A small generator of mass m is driven by a main engine through a solid steel shaft of diameter d. If the polar moment of inertia of the generator rotor is J, determine the natural frequency f in torsion. Assume that the engine is large compared to the rotor so that the engine end of the shaft may be assumed to be fixed. Neglect the mass of the shaft also.

Figure 104: Schematic

Schematic

Material PropertiesGeometric PropertiesLoading
E = 31.2 x 106 psi
m = 1 lb-sec2/in
d = .375 in
= 8.00 in
J = .031 lb-in-sec2

Results Comparison

ResultsTargetMechanicalError (%)

Lower Order F, Hz

 48.781 48.781 0

Higher Order F, Hz

 48.781 48.781 0