Research And Simulation On Active Noise Control Algorithm For Space Capsule

As one of the important environmental factors of capsules,noise directly affectsed the astronauts' long-term safety and health.Noise that exceeded the exposure limits severely affects affected the hearing and voice calls of the crew,which in turn reduced work efficiency and decreases decreased work capacity.Therefore,it is of great significance to ensure the physical and mental health of the occupants by reducing cabin noise and improving the comfort of living in the cabin.Passive noise reduction technologies that relied on materials,structures,and other means to dissipate noise energy have had a very significant inhibitory effect on high-frequency noise.For more harmful low-frequency noise,passive noise reduction technology has had little effect due to factors such as space and wavelength.Therefore,this paper to use active noise reduction technology to reduce noise,in order to control the low frequency noise exposure and improve the cabin environment comfort.Based on the traditional adaptive noise reduction algorithm,a Filtered X Least Mean Square FXLMS(Filtered X Least Mean Square)algorithm based on wavelet transform domain is was proposed.The algorithm passed through the wavelet decomposition and reconstruction of the noise signal.The least mean square error adaptive algorithm was used to continuously update the pre-stage signal and achieve real-time noise reduction.The main work of the thesis was as follows:First,based on the theory of sonic interference,the theory of active noise reduction was studied,and the mathematical expression of the closed space sound field was deduced.The main secondary sound source position of the active noise control system was optimized.The traditional update algorithm was improved,the complexity of the algorithm was reduced,and the convergence and stability of the system were improved.Secondly,an on-line identification method was proposed to identify the secondary sound source in the active noise reduction system.By updating the algorithm,the signals at the front and rear moments can be updated in real time,and the purpose of real-time noise reduction can be achieved.Thirdly,taking into account the high cost and long cycle of space capsule active noise reduction experiments,this paper combined the characteristics of enclosed space sound field,established a simplified model to simulate cabin noise environment,and used acoustic simulation software Virtual.Lab to perform acoustic fields in the cabin.Based on the simplified model,the FXLMS algorithm based on wavelet transform domain was proposed to reduce noise.The noise signal was decomposed by wavelet to separate the high and low frequency signal components in the noise.Then the high frequency signal was filtered out by the FXLMS algorithm to achieve low frequency.Finally,an experimental environment for active noise reduction in space capsule was built,and the proposed noise reduction algorithm was tested and verified.The test results showed that for low-frequency bands such as 100 Hz,200Hz,300 Hz,and 500 Hz,the sound pressure level were reduced by an average of 15%,which verified the effectiveness of the algorithm.