Noise Prediction And Optimization Of Cabins In Large LNG Carriers

There are many kinds and quantities of mechanical equipment in large LNG carriers,which produce great noise when working.In order to improve the comfort of LNG carriers,noise prediction and optimization are needed in the cabin of LNG carriers.Based on the statistical energy method,this study takes a 20,000-square-meter large LNG ship as the research object,and uses VA One analysis software to forecast the noise of the whole ship.In this thesis,two kinds of methods commonly used in noise prediction are systematically introduced,in which the principle of statistical energy method is studied emphatically,the energy conservation equation is established according to the energy conservation principle,the balance equation between subsystems is obtained,and the three assumptions of statistical energy method are derived.Noise control technology can be divided into active control technology and passive control technology according to whether it adds external input energy.At present,the common passive control technology in the industry includes sound isolation technology,sound absorption technology and vibration isolation technology.The commonly used active control technology includes active vibration absorption technology and active vibration isolation technology.The main noise reduction measures adopted in this calculation include sound absorption and isolation technology,vibration isolation technology and noise elimination technology.The preliminary modeling and parameter setting include establishing the finite element model,establishing the subsystem model,calculating the noise source spectrum according to the empirical formula,and setting the excitation in the noise source cabin.The calculation is mainly divided into four parts.In the first part,the naked ship noise prediction is carried out to provide reference for the subsequent calculation results.The results of the naked ship prediction show that the noise of most cabin is above 90 d B,so it is very necessary to deal with noise reduction.In the second part,the noise level after adding muffler,vibration isolator and initial sound absorption and isolation scheme is calculated successively,and the results of each calculation are compared with the results of the previous one.The comparison shows that the noise reduction effect of noise reduction technology,vibration isolation technology and sound absorption technology on the cabin of liquefied natural gas ship is significant.In the third part,targeted optimization was carried out for the cabin exceeding the standard after the initial noise reduction treatment.Finally,all the cabins in the superstructure have met the noise limit requirements.The fourth part studies the influence of different damping structures on the noise reduction effect and finds that the constrained damping structure is better than the free damping.In this thesis,a set of systematic noise prediction method is obtained by combining theoretical calculation with numerical calculation,which has practical engineering value.