The Research Of Vibro-acoustic Characteristics Of The Typical Stiffened Plate Of Ship Structure

Reducing the vibration and sound radiation of the structure is of great significance to improve the acoustic performance of the ship.The stiffened plate structure is widely used in the ship field for its light weight and good mechanical performance.In this paper,focusing on the stiffened plate structures,the vibro-acoustic characteristics of four different kinds of infinite stiffened plates including the one or two sets of parallel periodically stiffened plates,the orthogonal stiffened plate,double-stiffened plate are systematically theoretical researched and analyzed.And the relevant vibration experiments are carried out.The references of ship stiffened plate structure for acoustic design can be provided.The main research contents of this thesis are as follows:On the basis of the spatial harmonic expansion theory,with the consideration of the torsional motion equations of the stiffeners,the structural dynamic model of the infinite plates periodically stiffened by one or two sets of parallel stiffeners are established.The spatial domain is transformed into the spatial wave field by Fourier transform method.Considering the application constructors,Poisson equation and the properties of periodic function,the analytical solution of the displacement vibration equations of typical periodic stiffened plate is derived and calculated.Using the stationary phase method,the far field sound radiatation pressure can be present.The vibration and acoustic formulations of the infinite orthogonal stiffened plate are deduced by the infinite series method.The numerical solution is obtained through the series truncation method in the wave number domain.With the consideration of the plate-plate couple of up and down plate between panel and floor,the structural dynamic model of double deck stiffened plate is established.The Fourier transforms method is utilized to transform the spatial domain into space wave number domain.And the numerical solution is calculated by using the series truncation method in the wave number domain.The influences of the excitation types,the excitation locations,thickness of the plate,the periodicity spacing and parameters of the stiffeners on the vibro-acoustic characteristic of four different models of periodic stiffened plates are numerically quantified and discussed.The results show that the torque of the stiffener has less effect on the structural vibration characteristics,from the point of view of engineering calculation,the effect of aggregate torque on the plate can be neglected.The excitation loading on the strong artifacts could effectively weaken the vibration.The periodicity spacing and parameters of the stiffeners have obvious effects on structural vibration characteristics.The local vibration can be caused but the overall vibration can be reduced for the existence of aggregate.The effect of damping on structural vibration and acoustic radiation is obvious.Increase the thickness of the upper and lower panels of the double deck frame,and the thickness of the ribs is helpful to reduce the vibration of the double-layer stiffened plate structure.Based on the Ritz method,the vibration formulations of the finite orthogonal stiffened plates are deduced.Combining with engineering practice,considering the simplified model of stiffened plate,two kinds of simplified methods which are orthotropic plate theory and equivalent thickness method are proposed.The analytical formulations of natural frequency of three stiffened plate models are obtained and discussed.Through the research above,it is shown that the analytical natural frequencies are in good agreements with those from simulation results.The acoustic radiation characteristics of three stiffened plate models in the water,as well as in the air,are calculated.The two simplified methods are proposed for the vibration and low frequency acoustic radiation problem of orthogonal stiffened plate.At last,the experimental study of the vibration characteristics of three kinds of stiffened plate test models of single layer stiffened plate,double layer plate and double reinforced plate is conducted.The natural frequency,mode and frequency response function of the three models are compared by theoretical simulation.There is a good agreement between the theoretical simulation results and the experimental analysis in the low frequency band,and the reliability of the theoretical simulation is verified.The vibration response of single layer,double layer and double layer stiffened plate is compared and analyzed,which shows that the double layer can suppress the transmission of vibration compared with single layer board.The reasonable configuration of the aggregate in the double-layer stiffened plate can effectively reduce the vibration transmission of the double-layer board and achieve the effect of vibration reduction.