Response of Launch Pad Structures to Random Acoustic Excitation

Ravi N Margasahayam,Raoul E Caimi

doi:10.1155/1994/409461

Abstract

The design of launch pad structures, particularly those having a large area-to-mass ratio, is governed by launch-induced acoustics, a relatively short transient with random pressure amplitudes having a non-Gaussian distribution. The factors influencing the acoustic excitation and resulting structural responses are numerous and cannot be predicted precisely. Two solutions (probabilistic and deterministic) for the random vibration problem are presented in this article from the standpoint of their applicability to predict the response of ground structures exposed to rocket noise. Deficiencies of the probabilistic method, especially to predict response in the low-frequency range of launch transients (below 20 Hz), prompted the development of the deterministic analysis. The relationship between the two solutions is clarified for future implementation in a finite element method (FEM) code.

Highlights

One purpose of taking acoustic measurements during Space Shuttle launches is their application to structural response analysis and environmental testing
All terms of Eq (20) were defined previously except for matrix C, which contains correlated pressure distributions (CPDs) as a function of frequency in the "hidden third dimension." Practical computations are governed by the frequency array in Hm, which contains resonances of selected modes; the array in matrix C must correspond to Hm
There is a definite price for simplification: mUltiple runs must be made by varying the position of the CPD center in C(fk) in order to ensure that computed response in each mode is an absolute maximum

Summary

INTRODUCTION

One purpose of taking acoustic measurements during Space Shuttle launches is their application to structural response analysis and environmental testing. Phase relations in Nc remain the same as in e pp If the field is assumed to have white noise decay, off-diagonal elements are complex analytical functions and are given by the righthand side of Eq (2), except for the K term. Definition of both PSs and NCPSs is influenced by data processing intervals and locations of sensors relative to the plume The actual launch environment is a transient with a duration that for some frequencies (below 20 Hz) does not con-

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CONCLUSIONS