Investigation On Longitudinal Vibration Control Method Of The Shafting System Based On Dynamic Antiresonance Vibration Isolator

As the improvement of the naval ships,it is desirable to minimize the vibroacoustic responses of the maritime vessels.In the low frequency area,structure borne noise generated by the submarine is mainly caused by the propellershafting system.In order to minimize the vibro-acoustic responses of the submarine in this frequency range,it is necessary to investigate the methods to control the longitudinal vibration of the shafting system.The most frequently used method to prevent the longitudinal force from the propeller to the foundation are the vibration isolation and the absorption.Aiming at solving the current problems of controlling the longitudinal vibration of the shafting system,such as that isolation method will reduce the effective stiffness of the shafting system and the absorption method need a relatively large mass and will add the degree freedom of the system,this paper uses the dynamic antiresonance vibration isolator(DAVI)to control the longitudinal vibration and the sound radiation induced by the propeller through theoretical study and a series of carefully designed experimental study.The specific research contents and contributions are outlined as below:(1)The coupled finite element/boundary element and the substructure synthesis method is applied to investigate the longitudinal vibration characteristics of the propeller-shafting system with attached-water taken into consideration.According to the results within 100 Hz,the longitudinal vibration of the shafting system is mainly comprised of the propeller's first vibration mode and the shaft's first vibration mode.Then the finite element model and the semi-analytical model of the propeller-shaft-hull system with attached-water are established.The coupled vibro-acoustic effect between the shafting system and the hull is investigated.Combined with the in-house identified propeller-induced axial force spectral,the isolation frequency is given.(2)In order to control the axial vibration of the shafting system,firstly,a resonance changer(RC)is put in series with the thrust bearing to control the vibration.The semi-analytical model of the shafting system with RC is established and parametric optimization model with the force transmissibility and power flow serving as the objective function are established.From the investigation,it can be found that this scheme will reduce the effective stiffness of the thrust bearing system and it may influence the manipulating property of the shafting system.Then the DAVI is put in parallel with the thrust bearing to isolate the axial vibration transmitted to the foundation from the propeller.The theoretical model of the DAVI and the semi-analytical model of the shafting system with DAVI are established.Sensitive study of the lever ratio of the isolator on the isolation performance of the DAVI is conducted.The results show that the DAVI can effectively reduce the force transmitted to the foundation at the designed frequency with the effective stiffness of the shafting system unchanged.(3)Considering the difficulty in manufacturing the existing hydraulic leveraged DAVI and the unadjustability of its parameters,a new type of hydraulic leveraged DAVI is proposed with the same principle.Due to the current model of the isolator cannot predict its isolation performance,a new model is proposed and its correctness and effectiveness is validated.Based on this model,a parametric study of the isolator on its isolation performance is conducted.(4)A scaling model of 1:4 shafting system is built up.The finite element method and testing method are used to investigate its longitudinal vibration properties.A scheme to put the hydraulic leveraged DAVI in parallel with the thrust bearing is proposed without affecting the shaft rotary.Through the experimental method the effectiveness of the scheme is verified.The test results show that using the proposed method,the hydraulic leveraged DAVI only uses 1.6 kg which is about 1.8% of the shaft mass.Additionally,the acceleration amplitude of the foundation at the designed frequency can be reduced about 2.5 d B with 7 Hz bandwidth.The research results presented in this paper will provide a solid theoretical basis on the dynamic anti-resonance vibration isolator applied to suppress the low-frequency vibro-acoustic responses of propulsion systems.