Engineering Prediction And Atttenuation Of Structure Borne Sound On Board Ships

With the increasing demand of power in shipping industry, thequantity and scale of maritime equipments have risen substantially inrecent years. Consequently, the impact of structure-borne sound hasincreased as well. How to reduce the noise and vibration, and improve thehabitability on board ships has became one of the hottest issues in marineindustry. Excessive vibration will lead to fatigue problems and interferewith the normal use of various kinds of equipment, which is harmful tosafety. Moreover, the noise radiated by it will also cause great trouble tocrew and passengers.In this thesis, the attenuation effect of corner structures usingnumerical and experiment method were investigated according to wavetheory. Based on that, a simplified prediction method of structure-bornesound attenuation has been proposed, and the attenuation of it in doubleshell ships has been studied. Besides, a wave blocking method, combingthe use of blocking mass and damping, has been put forward, which isvery economic. This thesis focuses on the following aspects:(1) The vibration velocity field and energy allocation of finite singlecorner structure and multi-corner structure has been studied via wavetheory. The situation of stiffened plate has also been studied. Besides,a simplified method of considering stiffened plate as orthotropic plate has been put forward.(2) Structure-borne sound attenuation in typical ship structure consistingof stiffeners reinforced plates has been studied. Displacement fieldand vibration energy transmission in reinforced multi-corner structureis deduced by wave approach. And the impact of parametersincluding thickness, length, thickness ratio, junction order, density ofstiffeners and junction forms on vibration reduction are investigatedthrough numerical computation. It can be obtained from thecomputational results that plate thickness and junction order are themain factors influencing the vibration reduction. Plate length, junctionforms, thickness ratio and stiffeners should also been taken intoconsideration in the prediction process, while junction angle can beignored. Then, an engineering formula for vibration reductionprediction in ship structure is put forward based on parameter analysis,which is also validated through the experiment on a scaled modelsimulating a hold section of a ship.(3) The energy transmission has been investigated based on theoreticalanalysis and numerical calculation, and a simplified method ofregarding the sound bridge as beam has been put forward. Thismethod can decrease the freedom degree and enhance the computingefficiency. Besides, the impact of sound bridge equivalent stiffnessand damping on double hull structure has been analyzed on basis of numerical calculation.(4) The differential equation of ship section vibration has beenestablished. Dimensionless coefficients and equivalent rigidity havebeen introduced to deduce the transmission and reflection efficiencyof incident bending wave under the impact of blocking mass anddamping. Besides, the vibration displacement field and the energydistribution density have also been studied. On the basis of that,numerical calculations have been carried out to investigate the variouskinds arrangements of blocking mass and damping. Furthermore, acomprehensive comparison has been carried out.In this thesis, comprehensive analysis has been done to investigate thestructure-borne transmission, and a simplified fast prediction formula hasbeen put forward. Besides, an optimized method for decreasing thestructure-borne sound transmission has been proposed. The resultobtained by it can provide theory basis for acoustic design, and providenew measures of reducing noise and vibration on board.