Mechanical Self-noise Forecast Method Research Based On Equivalent Excitation Spectrum Analysis In Sonar

Sonar is a kind of electronic equipment using the propagation characteristics of underwater acoustic waves through the conversion between electricity and sound, which was been widely applied in navigation, ranging, and so on. With the development of various technologies on the ship, the performance of the sonar has been demanded to become higher and higher and the importance of sonar is becoming more and more obvious. Mechanical self-noise in sonar is the important factor influencing the sonar performance, so the analysis of mechanical self-noise forecast method has the profound significance on the sonar detection performance, at the same time, it plays a positive role to the safe navigation on the ships.The theory modeling of transmission channel was established in this paper, and the transfer characteristics from the vibration source device to the sonar platform area are researched and analyzed. The influence rule of the incentive at the sonar platform area was analyzed and summarized from acoustic channel of the hull-interface device at the platform area-the sonar array cavity. According to the rules, it was summarized that the mechanical self-noise forecast method based on equivalent excitation spectrum estimation in this paper.Firstly, the transmission channel of the mechanical self-noise was described using the admittance, the transmission channel was simplified to three parts-the hull vibration motivation, the connecting interface of hull and sonar platform area and the receptor structure made up of sonar platform area and cavity. The three parts were contacted using admittance relationship and the admittance model of the transmission channel was established.Secondly, the influence rule of the incentive at the sonar platform area was analyzed because of the different stiffness relatively of the acoustic channel of hull-interface device at the platform area-the sonar array cavity and the inherent frequency of the acoustic channel of the hull and the sonar array cavity. It is proved that excitation spectrum of the platform area was mainly affected by the intrinsic mode of the acoustic channel in the case of the low stiffness of the interface device of platform area which was in the weak-coupling case, the impedance characteristic of the sonar array cavity had a little influenced on the spectrum. The estimation of equivalent excitation spectrum of the plate and shell structure was deduced according to the actual measurement of vibration response in theory. The feasibility and estimation precision were analyzed through the example of rectangular thin plate simply supported on four edges including the determination of main impact modal and the choice of the number and location of measured points and so on.Lastly, the general theoretical model constituting of three parts of the hull vibration motivation, the connecting interface of hull and sonar platform area and the receptor structure made up of sonar platform area and cavity. The systematic theory simulation was proceed using the method of the theory and finite element in order to further verify the reliability of the above theory. It provided systematic theoretical guidance for the mechanical self-noise forecast in sonar.