Modeling of a reververation chamber and acoustic control

During a rocket launch a spacecraft is, among other loads, exposed to a potentially damaging acoustic load. Prior to space flight, ground tests are performed to determinewhether a spacecraft, or a specific part thereof, can withstand the acoustic load. These tests take place in a reverberation chamber. An acoustic feedback control algorithm shapes the sound field to specified third octave band levels which, are characteristic to individual launch vehicles. When applying feedback control, one faces two challenges. For one, the reverberant room introduces a large time constant resulting in slow transient behaviour, i.e. slow test start-ups. Furthermore amplitude fluctuations are introduced when analysing white noise with third octave band analysis due to its stochastic nature. This causes a lack of precision in steady state operation. This thesis studies acoustic phenomena taking place in a reverberation chamber. These include non linear sound propagation. The presence and significance of this non linearity will be evaluated. Subsequently, it is aimed to derive an input-output relation, describing the acoustic room response. To extend this relation, the third octave bandpass filters will be studied. After a physical model is formulated, different feedforward control algorithms are studied to improve both the build-up time of the sound field and the accuracy of the sound field after the steady state is reached. These will first be applied to a single third octave. Thereafter the control system will be extended to multiple third octave bands.Mechanical, Maritime and Materials EngineeringPrecision and Microsystems Engineering (PME