Structural Design And Damping Performance Analysis Of Displacement-dependent Magnetorheological Grease Damper

Magnetorheological(MR)dampers have become an important direction in the development of dampers due to their many advantages,such as fast damping response,wide range of adjustable damping,real-time controllability,and low energy consumption.They have been widely applied in devices such as automotive suspensions,aircraft landing gears,bridge dampers,and prosthetic knee joints.However,the large density difference between the dispersed phase particles and the base fluid in MR fluids leads to the problem of particle sedimentation,resulting in the deterioration of the control characteristics of the dampers.Additionally,MR fluids are prone to leakage after multiple uses,which necessitates complex design of the sealing components and limits the long-term serviceability of the dampers.To address the limitations of MR fluids,this thesis adopts a new type of MR grease material that is resistant to sedimentation and leakage.However,the majority of MR greases suffer from drawbacks such as poor flowability,high viscosity,and insufficient adjustability of yield stress,which result in excessive initial damping force and a limited range of adjustable damping for MR grease dampers,significantly restricting their application scenarios and development prospects.In order to further improve the dynamic performance of MR grease dampers,this thesis proposes and designs a novel displacement-related MR grease damper,where the output damping force is correlated with the displacement of the piston assembly.The designed damper is subjected to sequential theoretical analysis,numerical simulation,optimization design,and experimental analysis.The main research contents of this thesis are as follows:(1)A displacement-dependent magnetorheological grease damper is proposed and designed,and the structural form and operating principle of the damper are analyzed.Selection of materials for each part of the damper,preliminary determination of the structural dimensions of each part and calibration of key structural dimensions.The magnetic circuit of the damper was also designed and the number of turns of the excitation coil was calculated based on the ohm’s law of the magnetic circuit.Finally,the designed magnetic circuit is verified by magnetic field simulation with COMSOL software.(2)Based on the theory of fluid dynamics,Bingham’s intrinsic structure model is used to analyze the flow of magneto-rheological grease in each flow channel based on the structural characteristics of each flow channel in the damper piston assembly,and to establish the output damping force calculation model.At the same time,the dynamic performance of the damper was simulated in MATLAB software to obtain the dynamic characteristic curve of the damper,and the resulting dynamic characteristics of the damper were analyzed.(3)A multi-objective optimization design of the structural dimensions of the initially designed displacement-dependent magnetorheological grease damper using an improved non-dominated genetic algorithm(NSGA-II)with the professional optimization software mode FRONTIER,with the minimum output damping force of the damper and the maximum output damping force of 3000 N as the optimization objectives;The dynamic performance of the damper before and after optimization was compared and analyzed to verify the effectiveness of the optimized design,and the new damper obtained from the optimized design was verified by electromagnetic field simulation.(4)Two sets of displacement-dependent magnetorheological grease damper principle prototypes were machined and fabricated according to the optimized front and rear damper structure dimensions,respectively.Referring to QC/T545-1999 "Automotive cartridge damper bench test method",the damping performance test was conducted on an electric servo-sine dynamometer with a fixed vibration amplitude,and by changing the input current and the movement velocity of the damper,the indicator curve and velocity characteristic curve of the damper were obtained under different working conditions.The rationality of the structural design and the feasibility of the optimized design were further verified.