Sound Radiation Prediction For Underwater Flat Composite Plates

Composite rectangular plate is the basic element of ships and submarines.It's a fundamental issue to study the underwater radiation for the sake of marine vessel's acoustic stealthy technology.According to the structural and functional differences,four different types of panels are investigated in this paper:free-damping-layer composite plate,constrained-damping-layer composite plate(sandwich plate),thermal-viscous sandwich plate,fiber-reinforced laminated plate.The former two are typical damping structure,so a more efficient with higher accuracy method compared to the traditional one is put forward here.For the rest two newly-developed composite structures,few studies have been conducted before,so it's necessary to understand its radiation characteristics and establish a corresponding forecast method.The main researches of this essay are given as following:Sound radiation of baffled and unbaffled rectangular plate is studied,a method for rapid calculation modal sound radiated impedance is proposed,which also provided research foundation for composite plate sound radiation.By comparing the sound radiation in different frequency band,it provided theoretical support for using plate sound radiation to instead cylindrical shell in high frequency.Proposed a simple method for calculating the free damping layer plate sound radiation,the method described base plate by Kirchhoff theory and described coat by Mindlin theory.Combined with Hamilton's principle,the motion equation is obtained.By comparing the 3D elastical theory,quasi-fluid theory,the advantage of this algorithm for composite plate sound radiation was pointed out.Proposed a simplified discrete layer theory for sandwich plate sound radiation,which uses the displacement and stress transfer matrix to simplify the traditional theory.Then combined the Hamilton's principle,the motion equation is obtained.Studies have shown that the theory has high accuracy and computing speed.Based on this theory,an equivalent thin plate for sandwich plate sound radiation is given,studies have shown that the result was in good agreement with exact solution in low and middle frequency.The sound radiation model was established of thermal-visco sandwich plate,combing the basic theory of thermal viscous fluid,and a first order asymptotic expansion,the system motion equation is established,the equivalent loss factor was obtained,which is not changing by frequency and temperature.And it is more convenient than viscoelastic sandwich plate.It is found that the thickness and shear viscosity coefficient is the key factor for system damping and sound radiation.The simplified third order shear deformation theory is proposed for composite laminates underwater sound radiation,nonlinear strain and displacement distribution is applied,which is more realistic.The advantage in calculating thick plate in high frequency is obtained by comparing with FSDT and CLPT.Followed by an analysis of the impact of the elastic modulus,ply thickness,fiber laying angle on sound radiation,a theoretical basis for the composite laminates low noise design is provided.