Study On Acoustic Scattering For Numerical And Experimental Of Plate And Shell Structures

With development of scientific technology, acoustic scattering by object has been a topic of interest over the past few decades. The importance of studying the acoustic scattering by objects lies in the fact that many physical objects can at least be approximated by one of the aforementioned geometries or non-destructive detection. The object acoustic scattering characteristic is the basic of target identification that is so significance to study. This dissertation addresses a detailed of studying on numerical and experimental of plane and shell acoustic scattering characteristics for ship and offshore structure. The major contributions and conclusions are as follows:A new shallow water Green's function for sea bottom with impedance boundary condition is derived. The interaction of acoustic wave with the scattering ellipsoids object in an ocean wave-guide was examined by using BEM. The effect of impedance boundary on the scattering characteristics of the acoustic wave by an obstacle was considered and the results show that the scattering characteristic of ellipsoids in shallow water is different from that of in infinite field. The scattering pressure made by ellipsoids is not only similar but also lower than that of sphere when the ellipsoids scale is appropriate. The scattering characteristic of ellipsoids in shallow water with impedance boundary condition is different from that of rigid sea bottom. The impedance boundary condition affects both the horizontal propagation and vertical propagation greatly. The scattering pressure will greatly increase if the object is close to sea bottom or the impedance is large. The effect of impedance boundary condition on scattering characteristic by an obstacle in shallow water wave-guide is prominent Design the dimension scale of underwater structures reasonable and control its scattering characteristics will be further developed.The acoustic scattering characteristics of a three-dimensional finite plate with multi-cracks considering both soft and rigid surface conditions are studied by using BEM. The effect of the cracked position and the shape of the crack on scattering pressure are considered. It is can be concluded the sound pressure decrease as the cracks increasing and the diversification of sound pressure and directivity of pattern are greatly effect by the hard plane and the soft surface plate with cracks. The correlation acoustic scattering and transmission experiments of 13 freedom plates of different cracks and an intact freedom plate have been investigated by using advanced acoustical experiment system. Insertion loss is used as diagnose index and experimental show that insertion loss is sensitive to the crack position and it will be decreasing with the length, the depth and the number of cracks. Insertion loss can be considered as an easy new diagnose index for non-destructive detection.The correlation acoustic scattering and transmission experiment of damped finite plate has been investigated in this paper by using advanced acoustical experiment system that the sphere source is changed to plane sound beam. Experiment results show that the insertion loss increases greatly as the distance between sound source and finite plate becomes closer. The insertion loss made by the damped plate is higher than that made by non-damped plate and the effect of sound insulation made by soft surface plate facing to source is better than the non-damped plate. It can be concluded that the damped layer and soft surface have a better effect on acoustic isolation and enhance transmission loss if the damped layer or soft surface is placed inside of the cabin of the ship. Besides, study the acoustic scattering and sound transmission is especially important for the prediction of vibration and noise and the design of sound-absorbing layer and the safety of submarines.