Research On Propeller-induced Ship Hull Vibration And Underwater Radiated Noise

When ship is running in the water,different excitations will be loaded at the propeller due to non-uniform wake fluid.Such propeller excitations can be transmitted from shafting to the ship hull via bearings,causing structure vibration and underwater radiated noise which could impact the ship safety,functionality and habitability.Moreover,marine mammals can be impacted by the low-frequency part of underwater radiated noise.However,the researches of surface vessel structure mostly focus on military ship,the vibration and noise caused by main engine exciting force,the noise caused by propeller's hydrodynamics and the ship cabin noise.The study on the ship structure vibration and underwater radiated noise induced by propeller excitation is innovative.This research also has important reference significance to the vibration control and noise reduction of ship structure.The 50,000 DWT bulk carrier is selected as the research object in this paper.The properties of ship structure vibration and underwater radiated noise caused by different propeller excitations are studied,the influence laws caused by the shafting alignment conditions and ship hull deformation are analyzed at the same time,and the ship radiated noise in the finite field is calculated.Finally,an experimental model is designed and built,the correction of structure vibration property and analysis method is verified.As follows:Based on the research object,the full ship calculation model is constructed.Different excitations are applied at the propeller side.The transfer properties of propeller excitations are studied with vibration power flow method.The contribution law of vibration energy transmission at different bearings is obtained.The influence of ship structure vibration in various directions caused by the excitation,the distribution character of the structure vibration along the ship length direction and the contribution of different excitation on structure vibration response are all analyzed by finite element method.On this basis,the distribution characteristics of ship near-field and far-field underwater radiated noise in different space planes are analyzed by using boundary element method.And underwater radiated sound power level caused by different propeller excitation is compared.Considering shafting straight alignment and reasonable alignment,the transfer properties of different propeller excitations via different bearings are calculated.Based on that,the difference of hull vibration and underwater radiated noise is studied under the different state of shafting alignment by using finite element method and boundary element method.The deformation of empty ship in hydrostatic state is considered to research the change of the propeller excitations transfer properties by using vibration power flow method.The effect of ship hull deformation on the ship structure vibration and underwater radiated noise is studied with finite element method and boundary element method.The finite fluid fields with different boundary conditions are defined by considering the real condition of ship sailing and the acoustic property of bottom sediment which depend on the water location and depth.Based on the actual hull vibration,the vibratory velocities of the ship hull surface are obtained.In different finite fluid field,the radiated sound pressure of field points and structure underwater radiated sound power level are calculated by using boundary element method.Considering different bottom sediments,the underwater radiated noise characteristics of ship structure induced by different propeller excitations are discussed.The coupled shafting and ship hull experimental bench is designed and built.The exciting forces via different bearings and the vibration response on shafting and structure can be obtained by using the experimental bench.The model experiment with free boundary condition is carried out.The experimental results are compared with the numerical results.The experimental model is verified correct.Moreover,different excitations are loaded on the experimental propeller,the experiments of structure vibration response are performed.The vibration characteristics of experimental bench and transfer properties of different propeller exciting forces are studied by analyzing the exciting force at bearings and the vibration responses of reference points.The reasonability of numerical method for calculating ship structure vibration in this paper is verified by comparing the experimental results with the numerical results.