Research On Vibration And Radiation Characteristics Of Submerged Structures

The ship structures are always in contact with water. Mainly due to the loading effect of the surrounding heavy fluid, submerged vibro-acoustic characteristics differ greatly from air vibro-acoustic characteristics. It is significant theoretically and practically to study the influence of the fluid characteristics on the vibro-acoustic characteristics of submerged structures. In this article, the following work has been completed:Based on the elasticity theory and Mindlin theory, the finite element shell models are formed. With the modal analysis theory and dynamic response theory, vibration modes and transfer functions have been obtained. The influence of former several modes to low frequency vibration and the influence of excitation location to the transfer function have been analyzed.Based on the direct boundary element method, acoustic radiation of three-dimensional problems in infinite domain is discussed. The singularity is treated by polar coordinate transformation method. The CHIEF (Combined Helmholtz Integral Equation Formulation) method is adopted for exterior acoustic radiation analysis to solve the nonuniqueness difficulty at critical frequencies.Make full use of geometric symmetry to save calculation time. A pulsating cube is involved to demonstrate the correctness. At the same time, the pressure, radiated sound power and radiation efficiency are obtained. The influence of the wave number to sound radiation is discussed.Based on the Rayleigh integral, the vibro-acoustic characteristics of plates and stiffened plates mounted in an infinite baffle is discussed. The fluid-structure interaction equation is established by added mass, which is turned into by dynamic fluid force. The effects of fluid density and compressibility on the nature frequency and mode shape are discussed. Some numerical examples are used to discuss the influence of the fluid characteristics, compressibility, excitation location, plate thickness, stiffener types, and boundary condition on the acoustic characteristics.The velocity potential is adopted to express the fluid pressure acting on the isolated submerged rectangular. The effect of the boundary conditions and the depth of submergence have been studied. Besides, the influence of aspect ratio and thickness ratio is also given.