A Method for Sizing Noise Protective Unit Design Features

The purpose of this paper is to develop a sizing method to decide the best design features of a noise protective unit (NPU). The method of “inverse matrix” was used to assess the local acoustic pressure drop when a wave goes through the multi-layer shell of the NPU. Solutions of the wave equations were used in each of the layers taking into account: 1) the incidence angle of the sound waves and the layer loss factor; 2) the input boundary conditions establishing the equality of the normal components of particle velocity and acoustic pressure at medium borders; 3) the system of algebraic complex equations and corresponding matrix equations. The telemetric information obtained during a real launch was processed by means of specially developed software. A novel method of sizing the best design features for a noise protective unit makes it possible to reduce vibroacoustic loads on spacecraft to acceptable levels. The comparison of the data calculated using this method and the experimental data showed their good agreement. The devised method appears to have considerable promise when developing new launch vehicles able to protect spacecraft from noise and vibration. At critical frequencies the levels of acoustic pressure decreased by half to two thirds.