Research On Semi-active Dynamic Vibration Absorbers For Thrust Bearing Pedestal Based On Magneto-rheological Elastomers

The bending vibration of the hull,caused by the longitudinal pulsating force of the propeller which is transmitted to the hull through the thrust bearing base,is the main cause of the pulsating force.The control of the longitudinal pulsating force and the vibration generated is very important to improve the stealth performance of the ship.Among them,the installation of dynamic vibration absorber is one of the effective means of longitudinal vibration control,and has received extensive attention and research.The magnetorheological elastomer(MRE)has the property of controlling the mechanical properties by external magnetic field,and overcomes the shortcomings of the magnetorheological fluid,such as easy settling,easy leaking and bad stability.It also has many goof characteristics of fast response,good reversibility and good controllability.It can be used as variable-stiffness components in the design of tuned dynamic vibration absorber(TDVA)among engineering applications and thus becomes the current research focus.In this paper,a tunable semi-active vibration absorber(MRE-SDVA)is designed based on the MRE,s magnetostrictive stiffness characteristics.Considering the limitation of installation space and additional mass on the ship's shafting,a new thought of mounting the dynamic vibration absorber to the thrust bearing base is proposed.Firstly,the coupled dynamic model of the paddle-shaft-bearing base-dynamic vibration absorber is established,considering the damping of oil film and the bearing base structure.Based on the four-pole parameter method,the amplitude ratio of the base is solved analytically.The influence of design parameters of vibration absorber on the effect of vibration control is studied numerically using MATLAB software.It is shown that the semi-active vibration absorber has vibration-absorbing effect on the vibration caused by the first two modes of the shaft and the base.Then,the structural design and optimization of the MRE-SDVA are mainly focused on the magnetic field,temperature rise and frequency shift performance.Electromagnetic field,thermal field and structural field are analyzed by ANSYS software.Finally,the frequency-shifting performance and the vibration-absorbing effect of the vibration absorber are validated by experiments.The results show that the frequency range of the vibration absorber is 43.09-56.88HZ,and the frequency-shift bandwidth is 13.79HZ.The vibration-absorbing effect is gradually improved with the excitation frequency approaching the natural frequency of the system,and the vibration attenuation can reach 1.5dB near 59.5HZ.