Accession Number:

ADA456991

Title:

Natural Frequencies and Mode Shapes of a Nonlinear, Uniform Cantilevered Beam

Descriptive Note:

Master's thesis

Corporate Author:

AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH DEPT OF AERONAUTICS AND ASTRONAUTICS

Personal Author(s):

Report Date:

2006-09-01

Pagination or Media Count:

207.0

Abstract:

A series of experiments in 1975, referred to as the Princeton Beam Experiments, were performed to measure natural frequencies and create a nonlinear elastic deformation model to improve helicopter main beam designs. These experiments used a homogeneous 7075 aluminum beam and have been referenced as a baseline for the past thirty years to validate computer models and theories in an effort to build beams capable of withstanding aero-elastic, static, and dynamic loading. The purpose of this study is to measure the dynamic nonlinear bending and torsion response of a cantilever beam. The natural frequencies are measured in the flatwise and edgewise directions at different static root pitch angles with varying levels of tip weights. The measured natural frequencies were compared to linear equations of motion, a nonlinear computer model and previous experiments to verify the nonlinear effects of root pitch angle and tip weights. The experiment produced promising results in that the first mode in the edgewise and flatwise directions were within the error bands of the Princeton Beam Experiment and that the linear model matched the experimental case with no tip weights. Further experimentation is needed in order to properly calculate the edgewise frequencies and estimate mode shapes.

Subject Categories:

  • Radiofrequency Wave Propagation
  • Structural Engineering and Building Technology

Distribution Statement:

APPROVED FOR PUBLIC RELEASE