The Prediction And Optimal Design For Underwater Noise Of Ship

With the development of global shipping business,military and economy,there comes a request for higher level comprehensive performance for ships,which also results in the study of ship noise more and more attractive to researchers.The ship noise is regarded to have multiply threats to the ship system,which includes resulting in a structure material fatigue failure,interference to ship instruments and a threat to crews' health.At the same time,the noise is regarded to have negative effects on the behavior in concealment,safety,living and availability.The technology of chamber acoustic prediction and the research of control technique during the designing period could obviously save the budget,shorten the construction period,and also,improve the engineering efficiency.As the result,they are regarded to be essential and valuable.A study of underwater radiative noise prediction and control technique is introduced with finite element method(FEM)and boundary element method(BEM).The study is processed with separated analysis on hydrodynamic noise,propeller noise and mechanic noise.The analysis on hydrodynamic noise began with a modeling of ship sonar platform and processed with a numerical simulation method.The analysis on propeller noise without bubbles began with a modeling and analysis on the propeller flow field by Star ccm+ to acquire the propeller hydrodynamic performance.The results were processed a numerical calculation and analysis to the noise distribution with the application of FW-H method.The model of ship sonar platform is established,with the introduction of FEM software Star ccm+,the calculation of the coupled vibration of ship structure and external fluid is processed and finished with the displacement response to the coupled vibration.After the conversion from displacement response data to velocity response data,the acoustic analysis software Virtual lab is introduced to calculate the mean square acoustic pressure to the sonar platform.This method is regarded to be valid on the prediction of hydrodynamic noise.The analysis on ship mechanic noise began with the calculation of noise radiation under the case with a coupling of acoustic and vibration by applying an extra excitation on suspension point.The results allowed the calculation of the transfer function between the force and field point acoustic pressure on the suspension point.The analysis to the engine was processed to acquire the transfer function between the engine loads and the force on suspension point.The calculation from both steps were combined together to provide the transfer function of the whole system.The three kinds of noise sources are simulated on the same ship,and the characteristics of the radiated noise of the ship are obtained by the comprehensive analysis of the three kinds of noise.A simulation with the noise control technique which based on the acoustic insulation technology was processed to study the noise reduction on a due-layer steel plate configuration and the chamber wall.The effect and characteristics of this technique were acquired to help to provide an effective method on noise reduction.The study shows the above method on noise prediction and control technique is valid.The propeller noise without bubbles increased with the increasing of feed speed.With the same feed speed level,the noise decreased with an increasing distance from the center of the shaft.The ship hydrodynamic noise,the maximum occurred in the front part of bulbous bow,and increases with the increase of speed.The combined transfer function between the engine loads and field point acoustic pressure is acquired from the simulation,which is a powerful tool to study the mechanic noise from the engine.This allows the direct study on the vibration response and noise radiation resulted from an excitation on the engine load.As the sound insulation device,the space of rib increase,and the sound insulation increases.However,the increase of sound insulation is small,but after the rib is encrypted,the stffness of the outer plate of the ship will be increased,and the vibration should be reduced.So in the premise condition of hull structure and stability,can be considered for ship plate design specification of intercostal distance of the local optimum is reduced,so as to guarantee the ship stealth.