Research Of Nonlinear Vibration And Radiated Noise Characteristics For Ship Compartment Structures

The vibration and noise problem of ship structure increasingly serious,so the problem of ship vibration and noise needs to be solved urgently.In view of the large number of non-linear phenomena in the results of a certain ship vibration test,this paper studied the methods of nonlinear vibration analysis and the effect of nonlinear vibration on radiated noise based on the background of surface ship’s vibration reduction and noise reduction.This paper makes up for the shortcomings of the vibration and noise analysis method based on linear theory,and provides theoretical support for the accurate prediction of the mechanical noise of surface ships.The research contents of this paper are as follows:(1)In view of the problem that the nonlinear determination method can not distinguish the nonlinear characteristics of strong noise interference signals an improved surrogate data method is proposed in this paper.which integrates noise analysis,noise reduction and nonlinear vibration discrimination.Then,the full scale ship vibration experiment is carried out,and the vibration signals of the equipment and that of some positions in the cabin where the equipment are located are collected.The signal analysis is carried out according to the nonlinear judgment method proposed in this paper,and it is confirmed that the output vibration signals of the full scale ship equipment are nonlinear signal.(2)In view of the problem that the frequency-domain model superposition cannot reflect the nonlinear factor.In this paper,the time domain prediction method of full scale ship vibration and noise under nonlinear excitation load is proposed,and the application steps of time domain and frequency domain prediction methods are given.Then,considering the mesh size and the truncation size of the flow field,the real cabin and the truncated flow field are modeled,and the calculation accuracy and solution efficiency are controlled.Finally,the results of two prediction methods under nonlinear load excitation are obtained,and the results of time domain prediction method and frequency domain prediction method are compared and analyzed.(3)In order to better reflect the sound pressure distribution and transmission characteristics with or without considering nonlinear vibration,the concept of local acoustic radiation efficiency and its calculation method are proposed in this paper,and the specific calculation steps of these two prediction methods are given.Then,on the basis of the real ship cabin prediction model,the acoustic radiation efficiency nephogram of the bottom is obtained by time and frequency domain prediction methods,and the difference between the two prediction methods under nonlinear load excitation is analyzed.