Research On Characteristics Of Vibration And Acoustic Radiation Of Damaged Stiffened Plate In Water

Since ship structure is in multi-excitation condition, it is very important to research the characteristics of vibration and acoustics to improve the warship's vitality and combat capacity.The characteristics of structure vibration and acoustic radiation have been focused on in engineering area. There are theoretical method and numerical method for resolving the problems. Former is applicable to the regular elastic structures with simple geometry, simple material characteristic and simple boundary conditions and the latter is applicable to the complicated elastic structures.Damage is inevitable for structures during the process of bearing all kinds of loads and damaged structures have different mechanics characteristics compared with health structures. The changes of mechanics characteristics will bring the changes of acoustic radiation characteristics as well. Base on dynamical changes, damages of structures can be identified and be evaluated. The changes can also be used to forecast damaged structures' life and remained intension and to research variances of acoustic radiations. In this paper, the stiffened plates which are common structures in navel and ocean engineering are chosen as research objects.Base on the theory of dynamics and acoustic radiation and choosing the stiffened plate as example, the characteristics of natural frequency, static response, exited vibration, power of radiation and directivity of sound are researched respectively. Using the Mindlin theory, the four-node finite element shell modal of healthy and damaged structure is formed; Using Green Function theory, the fluid around the structure is considered to be inviscid, irrotational and incompressible, and then the effect of fluid to structure is translated to the added mass matrix compared with global mass matrix using BEM. As for isotropic damage element, the isotropic global weakening of stiffness is used; as for anisotropic damage element, the reduction coefficient of elasticity damage in x and y directions based on Kachanov's theory is used to form stiffening matrix. Sound pressure of structure radiating outwards can be calculated through Rayleigh's integral formula, and then the radiated power and directivity can be obtained.