Dynamic Characteristics And Controllability Analysis Of Magnetorheological Shock Absorber With Individually Controlled Multi Coils Under Impact Loadings

The magnetorheological(MR)anti-impact technology applied in the gun recoil system shows great research value and broad application prospects.Although the passive recoil mechanism has been widely used in the gun recoil system,it cannot meet the weapon development requirements which are more powerful,lightweight and high mobility,due to the passive recoil mechanism is unable to real-time adjust for variable impact loading.With the development of smart material science,the damping force of MR shock absorbers can be controlled by the current applied in the coils.Meanwhile,due to the advantages of larger output damping force,wide dynamic range,rapid response and low power supply,MR shock absorbers have brought out new challenges for development of the receoil mechanism and the vibration stability control of weapon system.Based on the engineering background of the gun recoil system,this dissertation focuses on the deep investigations on the dynamic characteristics and controllability of MR shock absorber under impact loadings from the aspect of material-device-system.The theoretical modelling analysis,numerical simulation and experimental validation were employed and the main contributions of this dissertation are as the followings:(1)According to the impact application background of MR shock absorber and the flow state of MR fluid,the Hershcel-Bulkley constitutive model was adopted to describe the shear thinning phenomenon of MR fluid at high shear rate.The test scheme of rheological properties of MR fluid at high shear rate was proposed,and the searle-type magnetorheometer was designed.The actual constitutive relation of MR fluid was obtained by parameter identification of the test results.Combined with the unsteady movement factor of MR fluid,a dynamic model of MR shock absorber was established.The experimental results show that the established model can successfully reflect the dynamic response under impact loadings.However,the nonlinear transient characteristics still cannot be fully captured.(2)A novel long-stroke MR shock absorber with multistage parallel coils connection configuration was designed for the gun recoil system based on the limitations of the traditional MR shock absorber with series coils connection configuration which cannot generate the flexible magnetic field distribution.A parallel magnetic circuit model of four electromagnetic coils was developed and the magnetic field distribution was measured with single working coil to validate the effect of circuit model.Based on the established Hershcel-Bulkley model and physical field theory,magnetic-flow coupling simulation model was built by using finite element(FE)method.By coupling simulation,the effects of various coil combinations on damper performance were discussed.The results show that the magnetic field spatial distribution can affect the output damping force.In order to determine the degree of influence factors of the magnetorheological shock absorber output performance,the orthogonal simulation test was designed.It indicates that the dominant factor is the number of working coils,followed by current magnitude,magnetic field distribution and the piston movement speed,respectively.(3)In view of the structure features of the novel MR shock absorber,the experimental scheme of impact dynamic tests were proposed to study the dynamic response characteristics of MR shock absorber under different working modes,including conventional unified control mode,separate control mode and timing control mode.The influence of magnetic field spatial distribution in the damping channel dimension on the output damping force of MR shock absorber was analyzed by conducting the conventional unified control mode and separate control mode tests.By comparing the experimental results and magnetic-flow coupling simulation results,it can be found that the output damping force can increase when the magnetic field distribution is close to the entrance of flow chamel.In addition,the relationship between the magnetic field distribution in the time dimension and the output damping force of MR shock absorber was discussed by timing control mode test.(4)From the perspective of the gun recoil system,the dynamics equations of MR shock absorber during gun recoil process were established,and then the stability conditions of gun system during firing were obtained.Based on the application requirements of stationary artillery and field artillery,the "platform effect" and "piecewise linear" recoil force curve were used as their optimization recoil goals respectively.In order to evaluate the controllability of MR shock absorber applied in recoil system quantificationally,the tacking degree concept was defined and adopted.Combined with the impact test results of MR shock absorber and the optimization recoil goals,the controllability of MR shock absorber in the stationary artillery and the field artillery recoil system were investigated.It is shown that although the novel MR shock absorber fails to achieve ideal damping force during the whole recoil stroke process,to some extent,through the ON-OFF open-loop control strategy,the recoil performance of the designed MR shock absorber can be improved.