Research On The Calculation Method Of Vibration And Acoustic Radiation Of Cylindrical Shells With Interior Structures

As an important part of submarine structure,vibro-acoustic characteristics of cylindrical shells are directly related to the acoustic stealth performance of a submarine.There are ring ribs,bulkheads,pedestals,floating rafts and other structures inside the hull.If only cylindrical shells are used to evaluate vibration and acoustic characteristics,while interior structures are neglected,it will inevitably deviate from the real situation.Although the finite element method(FEM)and the boundary element method(BEM)can be adopted to analyze vibro-acoustic characteristics of complex structures,some inherent disadvantages in efficiency,storage space and mechanism do exist.Under these circumstances,developing an efficient method to quantitatively predict vibro-acoustic performance of cylindrical shells with interior structures is of great academic value and military significance.First of all,an approach is presented to analyze vibro-acoustic behavior of cylindrical shells subjected to arbitrary boundary conditions.The cylindrical shell is divided into shell segments according to axial positions of excitations.Based on the displacement continuity and force balance conditions at the junctions of adjacent segments,as well as boundary conditions at the two shell ends,governing equations of cylindrical shells are established.The axisymmetric boundary element method is used to describe the sound field because of the axisymmetric feature of cylindrical shells.The Helmholtz boundary integral equation is converted to the line integral along the generatrix of shell,which greatly improves computational efficiency.After obtaining the relationship between the surface velocity and the pressure of shells,a fluid sound pressure correction term is introduced in the force balance condition at junctions of adjacent segments and governing equations of underwater cylindrical shells are established.Present method has been verified and effects of boundary conditions on vibro-acoustic characteristics are investigated.When it comes to the ring-stiffened cylindrical shell with multi-cabin,it is divided into shell segments,circular plate(bulkhead)and annular plate(ring).According to the displacement continuity and force balance conditions at the junctions of adjacent sub-structures,governing equations of the ring-stiffened cylindrical shell with multi-cabin are established.Research shows that the rings can effectively improve the natural frequency of shells.However,as for the beam vibration of shells,ring ribs and bulkheads not only do not increase the corresponding natural frequency,but also reduce the natural frequency.A hybrid analytical/numerical approach is developed to investigate vibro-acoustic characteristics of cylindrical shells with complex interior structures,which combines the fastness of acoustic-structure coupling analysis of analytical method with the versatility of FEM for dealing with complex structures.Interior structures are coupled to the shell through the artificial spring technique.By allowing appropriate spring stiffness constants,elastic and rigid coupling conditions between the shell and interior structures can be easily simulated.On the other hand,the two moments which can't be directly applied on the shell are converted to equivalent couples,and 6-degree-of-freedom(DOF)coupling conditions between the shell and interior structures are achieved,which has higher computational accuracy than 3-DOF or 4-DOF couplings in some literature.Finally,based on MATLAB GUI,a vibro-acoustic behavior prediction system for cylindrical shells with interior structures is designed,and it is friendly and easy for users to operate.