Angular Vibration of Aircraft. Volume 1. Executive Summary
Final rept. Aug 1977-Apr 1979
ANAMET LABS INC SAN CARLOS CA APPLIED MECHANICS DIV
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This report describes development work in several distinct areas, all related to prediction of angular vibration of aircraft structures. Angular vibration in this context refers to dynamic rotations or changes in slope at specific points on a vibrating structure. It is of interest primarily in connection with high resolution optical and electro-optical systems. Efforts were directed at both low frequency vibration, where individual normal modes are known, as well as high frequency vibration where they are not. For low frequency predictions, improved accuracy per unit cost was sought by an evolutionary improvement to an existing finite element code. A state-of-the-art shell element, the Semi-Loof, was incorporated into NASTRAN by means of pre- and post- processors and DMAP instructions. Its accuracy is tested against both closed form solutions for simple cases and experiment for an actual fuselage. For high frequency predictions the method of Statistical Energy Analysis was pursued. A demonstration case involving two coupled plates is presented to show how SEA may be used to predict angular vibration in a situation where normal modes are too numerous to be predicted individually. Relationships between linear and angular vibration were developed for various structural forms. Theoretical error bounds are also derived for spectral measurements of angular vibration which are obtained by differencing of signals from translational sensors.