Study On The Propeller-Induced Pressure Fluctuation And Vibro-Acoustic Characteristics Induced By Propeller

With the development of large-scale and high-speed ships,the power of the main engine and propeller is increasing,resulting in excessive vibration and noise level that beyond criteria.The propeller is one of main vibration sources of a ship and causes 70% of the total vibration of ship stern.In order to avoid harmful vibration and excessive cabin noise,it is necessary to explore the propeller fluctuating pressure and vibration and ship noise induced by it at the design stage.This thesis mainly focuses on the research of the propeller fluctuating pressure and induced vibration and noise.Several sections as follows are presented:(1)Firstly,this thesis introduces the reasons for strong vibration of ship stern induced by propeller,Analyzes and summarizes present research situation of theories,simulations,model tests and real ship tests for fluctuating pressure and cabin noise in domestic and abroad.Also,theoretical methods and empirical formulas for calculating the fluctuating pressure are presented.(2)Then,basic theory and numerical simulation of CFD method are detailed and utilized to study characteristics of fluctuating pressure induced by propeller for river-sea-through ship.As the result,propeller fluctuating pressure is obtained via numerical self-propulsion test of a ship with propeller,with values and distribution law of it achieved by arrangement of monitoring points.The effect of ship speed and propeller speed on fluctuating pressure is studied.(3)In consideration of virtual added mass and weight stowage,natural frequencies of first three orders of global vibration of the ship are calculated under two cases: full load departure case and ballast departure case.By considering pulsating pressure of all monitoring points extracted as excitation input,frequency response of this ship and its characteristics are analyzed.(4)Based on the basic idea of the numerical calculation of acceleration level of acoustic vibration of finite element energy flow model,with displacement response and velocity response gained in chapter four,the overall acceleration level of the plate in zone of action is obtained.Finally,cabin noise is predicted by referring to aforementioned acceleration level as excitation of propeller and contrasted with its counterpart of empirical method.In this thesis,propeller excitation and induced vibro-acoustic characteristics of ship are researched by CFD,FE and SEA method.This provides a new way to calculate vibration and cabin noise of ships.