Simulation And Experimental Study On Dynamic Characteristics Of Water-lubricated Bearing Based On Squeeze Magnetorheological Fluid Damping

Water-lubricated bearings have been widely used in ship propulsion shaft systems.Under severe operating conditions,the bearing interface between shaft and bearing is prone to local contact friction,and the resulting vibration is transmitted to the hull through the bearing and base components,thus reducing the quality of navigation and the equipment life.Improving the vibration isolation capacity of water-lubricated bearings is an effective measure to reduce the impact of vibration in the shaft system,and it is difficult to adjust the bearing damping actively by material improvement and structural optimization of bearing liners.To this end,a water-lubricated bearing scheme based on squeeze magnetorheological fluid damping(SMFD)is proposed,which can actively adjust the damping effect and improve the vibration isolation capability of the bearing.The simulations and experimental studies of the SMFD water-lubricated bearing are carried out on shafting test bench.The specific work is as followed:(1)The SMFD water-lubricated bearing structure scheme and magnetic circuit scheme were designed,and the structure with the best vibration damping performance was selected by the shaft system vibration comparison test,and the 3S scheme has the best vibration damping effect in both horizontal and vertical directions.The finite element simulation calculation of the bearing and electromagnet was carried out to determine the inherent frequency of the bearing and analyze the static stiffness of the SMFD bearing,the magnitude and variation law of magnetic induction strength and the coupling effect between the magnetic fields of the electromagnet group.(2)The two DOF dynamics model of SMFD water-lubricated bearing is established.The method of solving the dynamic characteristic coefficients of the water film under small disturbance is analyzed.Based on the squeezing working mode of the magnetorheological fluid(MF),the calculation formula of the squeezing damping force with magnetic field or not is derived by applying the plain plate model,in which the biviscous constitutive model is chosen under magnetic field and the Newtonian constitutive model is chosen without magnetic field.(3)The influencing factors of water film dynamic characteristics of bearing interface and the SMFD force are analyzed,and the simulation results show that: the water film dynamic characteristics change significantly with the speed and the magnitude and direction of load.With the increase of rotational speed,the direct stiffness and direct damping are decreasing.When vertical and horizontal loads are applied respectively,the direct stiffness of corresponding directions are significantly increased.Under the zero-field viscosity,the SMFD force is stable.Under the magnetic field,the SMFD force increases with the increase of viscosity and extrusion speed,the increase is more obvious with the decrease of gap value,and tends to decrease with the increase of yield zone ratio.(4)The SMFD bearing test shows that the magnetic flux density is attenuated from the surface of the electromagnet to the inner surface of the bushing.Under the excitation of dynamic load,the shaft moves slightly,showing a forward progress.Rotational speed and offset load affect the direct stiffness of the vertical and horizontal directions.As the voltage of the electromagnet group increases,the vibration amplitude decreases at each acceleration measurement point of the bearing base.When the voltage is higher than 20 V,the vibration amplitude begins to increase,and the vibration suppression effect is gradually lost,even the opposite.