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Experimental Study Of The Random Vibrations Of An Aircraft Structure Excited By Jet Noise

Report Number: WADD TR 61-70
Author: Clarkson, B. L.
Author: Ford, R. D.
Corporate Author: University Of Southampton
Laboratory: Materials Central
Date of Publication: 1961-03
Pages: 36
Contract: AF 61(052)-332
Project: 7351 - Metallic Materials
Task: 73521
AD Number: AD0258591

Recordings have been made of the strains induced in a full scale rear fuselage test structure of the Caravelle airliner when one jet engine is running at maximum take-off thrust. The structure is a conventional sheet-stringer combination attached to pressed out frames.

The analysis has been concentrated on the strains in the centres of panels. Correlation measurements have indicated that the lower frequencies (up to 500 c.p.s.) are associated with overall vibration modes and have low strain amplitude. The larger panel strains occur at higher frequencies with the frames acting as boundaries. In these measurements the main resonance peak in each panel occurs at about 600-700 c.p.s. and has been identified with the fundamental stringer twisting mode (i.e., adjacent panels 180° out of phase). There are generally two smaller peaks in the 800-1000 c.p.s. range but the modes of vibration have not been completely identified due to lack of information.

An attempt has been made to calculate the panel resonant frequencies theoretically, assuming that the frames act as boundaries. Although this work appears promising it has not yet progressed far enough for any definite conclusions to be drawn from it.

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