| The longitudinal vibration of the ship's propulsion shafting has seriously threatened the stealth performance of the submarine.The low-band radiation noise caused by it is one of the important sources of submarine radiation noise.Based on this,research on resonance changer came into being.However,the current research method is still mainly experimental,which is not only time-consuming but also requires a lot of work.Based on the finite element method,the longitudinal vibration modes and harmonic responses of the propulsion shafting are calculated.Then it also discusses the effects of stiffness and damping on the vibration isolation rate.At the same time,the research on the resonance changer is to explain its vibration damping theory,propound an equivalent model,derive the applicable conditions,determine the simplified structure,and establish a calculation model.Afterwards,the accuracy of the model is verified by the existing experimental conclusions.What's more,the acoustic calculation of the model further demonstrates its noise reduction effect on the submarine.Now it will be explained separately.(1)The modal analysis of the thrust bearing housing shows that the first-order resonance frequency is 1271 Hz,which cannot be excited under the excitation of the propeller,and it can be considered that resonance does not occur.However,in the process of modal calculation and harmonic response analysis of the propulsion shafting,the first-order longitudinal vibration frequency is found to be 33 Hz.This frequency is in the frequency range of several times the propeller rotation speed.It is easy to excite the longitudinal vibration mode.The vibration isolation rate analysis shows that as the damping increases,the promotion of damping effect is gradually slowed down.(2)A dual mass model which is equivalent to the resonance changer is propounded.And then its vibration equation is derived.The result shows that the dual mass system can simulate the resonance changer well when the mass ratio is greater than 5 and the stiffness ratio is approximately equal to 0.Based on the dual mass model,the C-M-C(CBUSH-MASS-CBUSH)model is propounded.The broadband vibration reduction analysis is carried out for the C-M-C model.It is found that the amplitude response curve has a fixed point.Through further calculations,it is found that the broadband vibration reduction performance can be satisfied even under the condition of applicability.(3)It discusses the effect of changing the mass ratio u and damping value c of the resonance changer on the longitudinal vibration damping of the shafting,and analyzes the applicability of the C-M-C model from the simulation point of view.Then,the acceleration frequency response curves with the changing of mass ratio and the damping value are obtained respectively.The results show that the C-M-C model can well reflect the characteristics of the resonance changer and is basically consistent with the experimental results.(4)In Virtual.Lab,the sound pressure level under no weighting and A weighted is calculated for the presence or absence of the resonance changer.The results show that the model with C-M-C as the damping unit can reflect the noise reduction effect well.By using the direct boundary element method,the sound pressure level of the tail of the submarine is calculated to be only 108 dB.A little sound absorbing material can reduce it below the ocean background noise.The use of the C-M-C model provides an effective simulation analysis method for frequency modulation and vibration reduction of longitudinal vibration of the shafting.At the same time,the C-M-C model also has good adaptability to acoustic simulation. |
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