Study On The Active Noise Control Based On Generalized Lorenz System

The acoustic stealth of ships has always been the most concerned issue in marine military field.Reducing the ship radiation noise is the main research topic of acoustic stealth.The radiation noise is mainly low-frequency line spectrum.Traditional passive noise control can not achieve the optimize control effect for low frequency noise,however active control can overcome this disadvantage.Therefore,the research on active noise control has become a hot topic in recent years.This dissertation suppresses the ship radiation noise by adding active signal,researching the active noise control method based on the generalized Lorenz system.The Lorenz system is derived based on fluid N-S equation to describe turbulent flow.This is a basic model of hydrodynamic system.The ship radiate noise suppression effect is studied through a Generalized Lorenz system.In this system time-delay feedback control and the external excitation as an acoustic source are integrated with the classical Lorenz system.The effect of different parameters and building methods in the system on suppression are simulated using chaotic dynamics method.In the simulation,trajectory,bifurcation diagram and Lyapunov exponent are discussed.The Generalized Lorenz system is used to analysis the effect of parameters on the system output states.The system output states are quasi-periodic state,periodic state,or chaotic state.Parameters are amplitude and frequency parameters,harmonic number of external excitation and delay parameter.The amplitude parameter of external excitation decides chaotic state.It reveals that Generalized Lorenz system can realize noise suppression.The theoretical model of ship radiation noise is provided and the feedback module is used as a sound source controller to suppress the noise.The spectrum and energy of the Generalized Lorenz system is studied through Fourier transform.The noise suppression effect is characterized by the change of power spectrum and acoustic energy.In this dissertation,we discuss the underwater acoustic energy control by using chaos theory for the first time.The research shows that the change of Lorenz system's parameters can control the instability of fluid and the control system is chaotic.The active control method combined feedback and excitation.The noise suppression effect is characterized by the change of power spectrum and acoustic energy.The Generalized Lorenz system can realize the optimize noise suppression effect through selecting appropriate excitation parameters,and the acoustic energy can be reduced by 26.67 d B.These appropriate excitation parameters are small amplitude parameter,high frequency parameter and phase.And the phase is as same as the phase of noise.Multiple excitations may realize optimize noise suppression effect.