The Study On Modulation Feature Detection Of Ship-radiated Noise

Ship radiated noise mainly consists of mechanical noise,propeller noise and hydrodynamic noise.The radiated noise consists of a single-frequency line spectrum and superposition of broadband continuous spectrum.The line spectral components mainly include mechanical noise and shaft frequency and blade frequency are generated by propeller blade resonance,and are mainly distributed in the frequency range below 1000 Hz,and the line spectral composition ratio Continuum has higher energy and stability,and is often used as the basis for detecting the type and speed of a ship.However,propeller shaft noise and blade frequency modulation characteristics cannot be directly extracted from the radiated noise power spectrum because propeller noise has amplitude modulation on continuous components such as cavitation noise.The traditional DEMON spectrum analysis method is used to extract the modulation feature line spectrum,but in the extraction process,the bandpass filter square wave detection is selected,and then the power spectrum analysis is used to extract the line spectrum information,so that the line spectrum is extracted and the effect is unsatisfactory,there are shortcomings such as poor noise suppression capability and insignificant harmonic characteristics after extraction.Based on the research of higher-order statistics and empirical mode decomposition,this paper improves the traditional DEMON spectrum analysis method,mainly including the following points:1.Research on the basic characteristics of ocean environment noise and ship radiation noise,discuss the various components of ship radiation noise in detail,and conduct modeling and simulation.2.Research on the basic principles of higher-order statistics are studied and bispectrum and 1(1/2)spectra are discussed in depth.Applying 1(1/2)-dimensional spectrum to DEMON spectrum analysis,a method for extracting ship radiated noise modulation feature information based on 1(1/2)-dimensional spectrum is obtained,and the principle of the method is described and the measured data is simulated.Analyze the extracted line spectrum information.Compared with the traditional DEMON spectrum analysis method,the extracted line spectrum have clear fundamental frequency and obvious harmonic information.3.Research on empirieal mode decomposion basic principles,nature and advantages.The empirical mode decomposition is applied to the DEMON spectrum analysis,and combined with 1(1/2)-dimensional spectrum analysis to obtain a ship radiated noise modulation feature extraction method based on EMD-1(1/2)spectrum,and the method is The principle is explained and the measured data is simulated and analyzed to extract the line spectrum information.Compared with the traditional DEMON spectrum analysis method,the feasibility and advantages of this method are emerged.