Research On Designing Quiet Structures

Through structure material change, model tailor and other methods, quiet structure design makes structure acoustic radiation to least, and then, uses optimal methods to make the structure one "Weak Radiator". As a new emerging method of noise control, the study of quiet structure faces to many difficulties.This thesis has studied three aspects of these difficulties, as follows:(1) Uses a new method------Wave superposition to calculate structure soundpower radiation.(2) Uses adding point mass to optimize shell structure sound power radiation, and discusses the amounts,positions of adding point mass to affect shell structure sound power radiation.(3) Designs and produces a device to measure structure surface acoustic impedance, and calibrates the device to make sure its performance through experiment.The main research conclusions are obtained as follows:(1) As known the radiated structure surface velocity, through calculating radiator internal source's intensity, wave superposition method can make a good estimate for structure sound power radiation. Compares with other BEM methods, wave superposition method has some benefits as below: first, it does not need to deal with the irregularity issue, so makes the computational process simplification; next, because this method forms matrix using the superficial node not the unit, so nothing to do with the unit shape, and causes the computational process simplification again.(2) As a way to structure tailor, adding point mass changes structure velocity response distribution. When the amounts and positions of adding point mass changed, the structure velocity response distribution also changed. Because the adding point mass was small in this thesis, so structure normal frequency didn't change obviously, and structure sound power radiation curves had no difference in shape, just difference in peak value size. (3) Uses experiment way to measure structure surface acoustic impedance is a complement of theory method, it can be used in achieve surface acoustic impedance of complex construction. This thesis designs and produces a device to measure structure surface acoustic impedance, and calibrates the device to make sure its performance through experiment. This device can be a base for future surface acoustic impedance measurement.