Abstract
This article describes a method to determine locations of noise sources that minimize modal coupling in complex acoustic volumes. Using the acoustic source scattering capabilities of the boundary element method, predictions are made of mode shape and pressure levels due to various source locations. Combining knowledge of the pressure field with a multivariable function minimization technique, the source location generating minimum pressure levels can be determined. The analysis also allows for an objective comparison of “best/worst” locations. The technique was implemented on a personal computer for the U.S. Space Station, predicting 5–10 dB noise reduction using optimum source locations.
Highlights
Equipment within enclosed volumes excites acoustic resonances that may exceed acceptable limits
Acoustic resonances may excite structural modes resulting in excessive vibration
A consequence of this behavior is that a point source will always generate a significant modal pressure field amplitude. This characteristic is different than for structural modes where only local direct forces affect the structure response, and is one reason why using only intuition for source placement optimization may not result in expected results for acoustic problems
Summary
Equipment within enclosed volumes excites acoustic resonances that may exceed acceptable limits. In the case of the US Space Station, acoustic levels can excite equipment vibrations that can exceed payload microgravity limitations This is true especially in the frequency range below 100 Hz, where strong isolated resonances exist. Finite element method (FEM) and boundary element method (BEM) assessments are commonly used to predict acoustic or vibration modes, especially for the low frequency ranges where modal frequencies are not closely spaced. These analysis methods can provide narrow band frequency response level predictions caused by acoustic and/or mechanical forces. This article presents a method that automatically locates low frequency sources so that the source-acoustic volume coupling efficiency is minimized This results in a pressure field minimized for predetermined receiver locations. Another advantage of this approach is that noise reduction is accomplished without the added cost and complexity of absorption or damping materials or active control equipment
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