Key Technology Study Of A Magnetorheological Shock Absorber With Individually Controlled Multi Coils Under Impact Loadings

The application of magnetorheological(MR)anti-impact technology into the gun recoil system shows great value and broad prospects.With the increasing requirements brought forward by the modern warfare,the gun recoil system is expected to exhibit good firing stability,rapid response and high mobility.Therefore,the MR buffer systems for the gun recoil are suffering from strong impact strength,causing more and more impact issues,which should be paid more attention to.Based on the engineering background of a gun recoil system,this dissertation focuses on the deep investigations about the current key issues of MR shock absorbers under impact loadings.The theoretical modelling analysis,numerical simulation and experimental validation were employed and the main contributions are concluded as the followings:(1)The differential equations of the MR gun recoil movement was established and the shock absorbing goal was proposed according to the high firing stability.After the analysis of the typical dynamic response of the MR buffer system under impact loadings,the shock absorbing process was classified by four stages and a modified Bingham-Plastic-Inertia(MBPI)model which takes minor loss,fluid inertia and quasi-static yield stress,etc.into account was proposed.The experimental results show that the MBPI model can successfully reflect the dynamic response of each stage under impact loadings,especially the two peaks of damping force.However,the nonlinear transient characteristics still cannot be fully captured and it is thought to be related with the multi-physics coupling effects formed by the magnetism,high-speed fluid flow and temperature.(2)Based on the shock absorbing goal,a novel MR shock absorber with individually controlled multi coils was proposed and designed.After that,an equivalent parallel circuit model of four electromagnetic coils was developed and the numerical relationship between the yield stress of MR fluid upon each effective area within the annular gap and the individual excitation currents was established by using finite element(FE)method.In addition,by summarizing partial differential equations of the electromagnetics,fluid dynamics and heat transfer respectively,a magneto-flow-thermal multi-physics model was proposed based on the inverse Jiles-Atherton(J-A)hysteresis model.It is shown that the proposed multi-physics model can visually and directly reflect the multi-physics transient coupling mechanism inside the MR shock absorber,such as the phenomenon of induced eddy current,the temperature rise due to the core loss and conjugate heat transfer,the nonlinear hysteresis relationship between the applied step or sinusoidal excitation currents and output damping force under impact loadings,etc.(3)An electromagnetic response model of multi magnetic coils and a driving circuit response model with a current controller were developed respectively.Based on the above theoretical analysis,the time delay of the coulomb damping force generated by the MR buffer system under impact loadings was tested and two delay correction methods including serial leading correction circuit and PID correction controller were proposed respectively.The experimental results indicate that the influential factors causing the overall time delay of the MR buffer system under impact loadings can be attributed to two parts,that is,the electronic devices such as the current controller,etc.and hysteresis characteristic of magnetic materials along with the mechanical delay part.Furthermore,the two proposed correction methods can significantly improve the dynamic response performance of the MR buffer system.(4)According to designed the experimental scheme of the impact dynamic tests,the effects of the various working modes of the novel MR shock absorber on the dynamic characteristics of the damping force,including the peak magnitude and corresponding occurrence time were investigated to verify the proposed magneto-flow-thermal multi-physics model and the vector operation of four magnetic fields along the annular gap.It is shown that the simulation results agree with corresponding experimental data well and the dynamic characteristics of the peak damping force are significantly affected by the distribution of the magnetic fields in the form of permutations and combinations along the annular gap and thus the impact efficiency can be improved effectively by adjusting different working modes of the proposed MR shock absorber.Moreover,to achieve the shock absorbing goal,an open-loop cascade control manner was proposed and realized by controlling two dimensions,namely the time and axial direction simultaneously.Compared with the traditional method of unified excitation currents,the proposed control manner can obtain smaller peak damping force and larger corresponding occurrence time.This dissertation systematically studies the current key issues of the MR buffer system under impact loadings and provides a theoretical guidance for the development of the MR anti-impact technology under high impact loadings,demonstrating great significances in the application of national economy,especially the field of national defense.