Theoretical Research On Active Control Method For Low Frequency Radiated Noise Of Underwater Propeller

Underwater propeller radiated noise is the main component of ship radiated noise,with obvious line spectrum characteristics in the low frequency range.Due to the long propagation distance and small attenuation of low frequency noise signals,it has a significant impact on the acoustic stealth performance of underwater vessels.Therefore,research on noise control methods for low-frequency radiated noise of underwater propellers has practical application significance.Currently,passive noise technology can achieve good noise reduction effects for the middle and high frequency parts of propeller radiation noise,but its noise reduction effect for low-frequency noise is poor.As active noise control technology has been widely used in the field of reducing low-frequency noise,this thesis analyzes and verifies the noise reduction performance of an active noise control system on low-frequency radiated noise of propellers based on their characteristics.This thesis focuses on the analysis and characterization of the radiated noise and sound field distribution of the underwater propeller,an adaptive notch control algorithm based on frequency estimation is proposed for the time-frequency characteristics of propeller noise,and corresponding numerical simulation analysis is carried out.Firstly,the frequency spectrum characteristics of the low-frequency noise signal of the actual underwater propeller radiated noise signal have been studied and analyzed,using the signal modeling method based on unit cosine pulse signal,and the simulated underwater propeller radiated noise signal has been obtained.The noise control effect of the actual measured noise and simulated noise signals using the frequency estimation-based adaptive notch filter control algorithm has been studied and analyzed.Secondly,based on the sound generation formula FWH equation of the rotating object,this thesis innovatively proposes the equivalent modeling of the underwater propeller radiated sound field using rotating monopole source and rotating dipole source,and studies and analyzes the noise reduction effect of different noise control systems on the radiated sound field of the rotating source using active noise control method.Then,using dipole source to simulate the radiated noise of the propeller,the coupled sound field of the noise source and model structure was calculated at different frequencies with the stern structure of the ship.By using a traversal optimization method,the optimal placement scheme for secondary sound source and error sensor in the active noise control system for the sound field with the characteristics of underwater propeller radiation has been found during the active noise control process.Finally,the experimental verification of the principle of active control method for low-frequency radiated noise of underwater propeller has carried out in a sound insulation pool.The active noise control system has been built,and the effect of the control system on the radiated sound field at different frequencies has been studied and analyzed using dipole source to simulate the radiated noise of the propeller.The experimental results show that the active noise control system can effectively reduce the low-frequency spectral component of the radiated noise of the underwater propeller.