VM48

VM48
Natural Frequency of a Motor-Generator

Overview

Reference: W. T. Thomson, Vibration Theory and Applications, 2nd Printing, Prentice-Hall, Inc., Englewood Cliffs, NJ, 1965, pg. 10, ex. 1.3-3
Analysis Type(s): Mode-frequency Analysis (ANTYPE = 2)
Element Type(s):
3D 2 Node Beam Element (BEAM188)
Structural Mass Elements (MASS21)
Input Listing: vm48.dat

Test Case

A small generator of mass m is driven off 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 65: Motor-Generator Problem Sketch

Motor-Generator Problem Sketch

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

Analysis Assumptions and Modeling Notes

The motor is modeled as a circular solid using SECTYPE and SECDATA commands. All degrees of freedom are constrained, except for the rotational degree of freedom along the x direction at mode 2.

Results Comparison

TargetMechanical APDLRatio
f, Hz48.78148.7791.00