Research On The Radiated Noise Separation Method For The Ship Propellers

Recently, researches on ship vibration noise are almost focused on aspects such as theprinciples and transfer paths of sound radiations subject to shell vibrations excited bymechanical equipments, inherent structural characteristics of vibration noises of thepropulsion shafting, as well as the theoretical predictions and model tests of propeller noisesand so on. However, studies on noise separation of propellers from the general radiated noisesof ships under service conditions, and separation methods for direct radiated noises ofpropellers from their sound radiations excited by shell vibrations are still relatively rare.Therefore, developing researches on noise separation methods of ship propellers shall have animportant significance for further lowering the radiated noise level of ships, as well as thenoise evaluation of their propellers.In this paper, issues on noise evaluation of propellers and separation methods for directradiated noises of propellers from their sound radiations excited by shell vibrations areresearched, where the spectrum characteristics of direct radiated noises of propellers and theirchange laws with the rotating speed, and the spectrum characteristics of vibration noises ofshells excited by propellers through the propulsion shafting are discussed, a set of noiseseparation method for propellers from the general radiated noises of ships under serviceconditions is established successfully, as well as a method for separating direct radiated noisesof propellers and the sound radiations excited by shell vibrations; further more, by means of aseries of test analysis, the effectiveness and the correctness of corresponding results of theseparation methods for ship noises are verified. Details are as follows:General acoustic characteristics of direct radiated noises of propellers are researchedfirstly based on the analysis of acoustic characteristics of dipole sound sources, where discretespectrums of direct radiated noises of propellers and the change laws of continuous spectrumsof different frequency bands along with the increasing rotating speed are analyzed in depth,providing a theoretical basis for researches on the propeller noise separation method and thegeneral radiated noises of ships, as well as a method for separating direct radiated noises ofpropellers and the sound radiations excited by shell vibrations.By means of theoretical studies and simulation analysis, the basic physical processes andmain transfer paths of propeller’s exciting forces acting on submarine bodies for generatingvibration noises are described, the acoustic model and information model of them are studied,and the spectrum characteristics of vibration radiated noises of shells excited by propellers are analyzed. Works mentioned above together have provided necessary supports such as basicgrounds and information sources for the research of separation methods for direct radiatednoises of propellers and sound radiations excited by shell vibrations.By means of analyzing the spectrum characteristics of vibration radiated noises of shellsexcited by mechanical equipments and the vibration sound radiations of shells excited bycurrent, and making clear their differences between the spectrum characteristic of propellernoises, the mathematical conversion model of propeller’s direct radiated noise of differentfrequency bands and different rotating speeds is established properly; and finally, a set ofpropeller noise separation method from the general radiated noises of ships, and the methodfor separating direct radiated noises of propellers and secondary sound radiations excited byshell vibrations are provided.To apply the propeller noise separation method on ships, basic requirements ofcomprehensive tests of noises and vibrations are analyzed, and corresponding proceedingmethods for test data are studied in depth; by means of test data processing, the change lawsof spectrum characteristic of propellers’ direct radiated noises with rotating speeds areverified, as well as theoretical analysis results of spectrum characteristic of vibration soundradiations of shells by excited the propeller. On the basis of which, the effectiveness of thepropeller noise separation method from general radiated noises of ships and the practicabilityof the separation method for direct radiated noises of propellers from the vibration soundradiations of shells excited by propellers are proved; further more, the correctness of theseparation method for ship propeller is verified by means of comparative analysis on directradiated noise separation results of ship propulsion and relevant model test results.