Accession Number:

ADA045587

Title:

NATFREQ. A Computer Program for Calculating the Natural Frequency of Rotating Cantilevered Beams,

Descriptive Note:

Corporate Author:

DAVID W TAYLOR NAVAL SHIP RESEARCH AND DEVELOPMENT CENTER BETHESDA MD AVIATION AND SURFACE EFFECTS DEPT

Personal Author(s):

Report Date:

1977-01-01

Pagination or Media Count:

49.0

Abstract:

A computer program was developed to evaluate the natural frequencies of model helicopter rotor blades for use in wind tunnel evaluations. This program, NATFREQ, calculates the uncoupled natural frequency and corresponding mode shape of the first, second, and third natural bending modes for a nonuniform cantilever beam rotating in a vacuum. The program includes centrifugal stiffening effects and allows for arbitrary radial distributions of blade mass and stiffness properties. The fundamental uncoupled torsional natural frequency may also be calculated for a nonrotating cantilevered nonuniform beam. The blade is represented by a series of concentrated masses connected by massless flexures. The method of calculation for both bending and torsion is by the use of influence coefficients and martix algebra. Comparison of calculated results for a uniform beam with the exact solution shows that good results are obtained in the fundamental mode for as few as five mass elements. However, calculated frequencies for the second and third modes of vibration show progressive error. This suggests that up to 20 elements should be used for satisfactory results in the higher modes for nonuniform properties. Author

Subject Categories:

  • Helicopters
  • Computer Programming and Software
  • Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE