Research And Analysis On Mechanical Impedance Of Ship And Pedestal Coupling Structure

During the navigation of a ship,the vibration and radiation noise will occur due to the operation of the components.The larger vibration and noise will affect the stealth performance of the ship and the comfort of the crew.In the three major sources of noise for surface ships,mechanical noise caused by equipment is an important source of radiation noise.It seriously restricts the realization of ship's quieter target,which has always been the focus of ship noise control.The structure of engine base coupled with ship shell is an important part of acoustic radiation from mechanical equipment to the outside.The coupling mechanical impedance is very important for the research of ship's vibration and noise reduction.In recent years,the mechanical impedance method is widely used to analyze the dynamic characteristics of structures and the transmission of acoustic vibrations with the continuous development of vibration and noise reduction technology.On one hand,input impedance in structure of engine base coupled with ship shell is one of the most important parameter of vibration isolation and acoustic design.It determines the ratio of vibration power from the vibration source to the hull structure.On the other hand,the transfer impedance in structure of engine base coupled with ship shell determines the decrement in the process of vibration transmission.It is obvious that the increase of transfer and input impedance leads to the decrease of the vibration and noise of the ship.So the theoretical calculation and finite element calculation method are applied to study the mechanical impedance in structure of engine base coupled with ship shell.The main researches are as follows.Both theoretical and finite element calculation methods are applied in research of input impedance in structure of engine base coupled with ship shell.Theoretical calculation of input impedance is completed by analyzing physical model of the coupling structure.In theoretical calculation method,the calculation model is simplified by finding out equal effect physical model according to relationship between wavelength and ship structure parameters.In finite element calculation,calculation model and grid size are synthetically considered in order to balance accuracy and efficiency of calculation.A typical sample is studied in two methods mentioned above,two input impedance values obtained are compared to prove the accuracy of the two method.Both theoretical and finite element calculation methods are applied in research of transfer impedance in structure of engine base coupled with ship shell.In theoretical calculation,coupling structure are simplified as two spring in series,as their effects in transfer vibration power are equal.Then,dynamical stiffness engine base and ship structure are obtained.The dynamic stiffness of coupling structure is obtained structural series formula.Especially,in process of solving dynamic stiffness,simplification of ship structures varies from calculation frequency.In finite element calculation of coupling structure transfer impedance,a finite element model is established,boundary conditions and mesh are setted properly.In study of typical sample,transfer impedance values obtained in the two methods mentioned above are compared,the accuracy of these methods are proved.Finally,through the theoretical and finite element method,three measures which are base plate thickness,base and web with damping layer base,hull joints for laying steel loop structure are studied,their effects in increasing input and transfer impedance of coupling structures are compared in order to compare these control measures,and compare the results and application scope of the two methods.