| Magnetorheological(MR)fluids are known as one of the field-induced smart materials,and tunable rheological performances,such as the yield stress or apparent viscosity in macroscopic,are possible under the control of an external magnetic field.Based on this property,MR fluids-based actuators are widely investigated in academic and applied in engineering,such as structure protection or vibration control(MR damper,MR mount),hydraulic power transmission(MR clutch,MR brake),polishing and medical equipment(MR haptic master,MR prosthetics).However,on contrary with the engrossing developments in engineering application,the basic properties of MR fluids or their mechanism are not thoroughly understood.Specifically,for the behavior of MR fluids,especially the complicated and fickle one under squeeze mode,a universal structural evolution to interpret these behavior is lacked.Moreover,the nonlinear behavior of MR fluids-based actuators arising from the inherent nonlinear property of MR fluids and the coupling with fraction and compressibility of fluids makes it difficult to develop a precise mathematical model.Sequentially,it would be hard to realize an accurate,fast and efficient semi-active control.Hence,in order to get the mechanism of MR fluids,to broaden the engineering application,and finally to realize the effective control,a further investigation on the behavior of MR fluids and an accurate modeling of the MR fluids actuators are necessarily needed from the view of both academic and engineering.Consequently,focusing on the behavior of MR fluids in squeeze mode and hysteresis modeling,a further research is carried out in this dissertation.Specifically,a MTS basedtest system on a self-developed squeeze structure is established,and this squeeze structure featuring constant volume effectively eliminates the influence from cavitation effect,hence the inherent properties of MR fluids under quasi-static and oscillatory squeeze modes can be fully displayed.The experimental results and theoretical analysis,on one hand,reveal the mechanism of MR fluids in high frequency oscillatory squeeze modes,and on the other hand,inspire an equilibrium between the magnetic field interaction and hydrodynamic interaction to interpret the velocity-dependent mechanical property.Moreover,from the macroscopic view,the efforts to improve the accuracy and simplicity of hysteresis modeling are carried out.A restructured model from phenomenological model is proposed for MR damper,and a memory mechanism and shape function-based approach for hysteresis model designing is presented for specific Duhem hysteresis.With these fundamental researches,a MR fluids mount feathering squeeze mode is proposed.The gap-dependent hysteresis behavior is modeled by the mentioned hysteresis model,and a model-based feedforward control strategy is applied for the force tracking control.The major research and innovations in this dissertation are summarized as follows:1)Experimental setup to evaluate the behavior of MR fluids in squeeze mode.A MTSbased test system on a self-developed squeeze structure is established,and compared with conventional open-type squeeze structures,the cavitation effect is effective avoided by the feature of constant volume.It means that under certain excitation the macroscopic deformation of MR fluids is determined,then the intrinsic property of MR fluids under quasi-static and oscillatory squeeze modes can be fully presented,which makes it possible to analyze the mechanism of MR fluids in squeeze mode.2)Mechanism analysis of MR fluids in squeeze mode.Extinguish behavior is presented under quasi-static and oscillatory squeeze modes,and correspondingly,different approaches are applied to reveal the behavior under different excitation.On one hand,an assumption that MR fluids as Bingham fluids following the continuum media theory is made when under high frequency excitation,and then according to the steady flow between parallel plates and constructive Bingham model,a mathematical model is established.The damping force comparison between the model and experimental tests indicates that in high-frequency oscillatory squeeze mode,structural evolution of MR fluids in compression and tension is consistent,following the continuum media theory.On the other hand,an exciting velocity-dependent characteristic of the compressive and tensile stress is presented.Then a new concept taking account of both the hydrodynamic interaction and the magnetic field interaction is proposed and discussed.Two separate models for these two interactions are derived by applying Darcy filtration law and dipole mode.It is demonstrated that MR mechanism in valve or squeeze mode is developed on a balance between the magnetic field and hydrodynamic interactions,in which the hydraulic force is the main power propelling the deformation of the chains,and meanwhile the restoring force resulting from the deformation of the chains makes the reaction on the relative motion.As a result,a macroscopic exciting velocity-dependent characteristic of MR fluids is presented.3)Hysteresis modeling of MR fluids actuators.According to the tested hysteresis phenomenon and definition of hysteresis,an investigation on hysteresis modeling are carried out at two different levels.At the level of MR fluids actuators hysteresis behavior,a Restructured model is proposed for MR damper.From a view of rate-independency of hysteresis,the experimental test confirms that the force-displacement curve of MR fluids actuators more satisfied the definition of hysteresis.With the analysis of the hysteresis in MR fluids actuators and the parameter analysis of Spencer’s phenomenological model,a Restructured model with compact structure and simple expression is presented,and the performance of this model is validated through the damping force identification.At a further level of the hysteresis occurring in MR fluids,electrorheological(ER)fluids,piezoelectric materials and friction force,and the corresponding Bouc-Wen,Dahl and LuGre hysteresis models,a new approach for hysteresis modeling based on shape function and memory mechanism is presented.The memory mechanism originating from the charging and discharging processes of the resistor-capacitor(RC)circuit is constructed by adopting a virtual displacement variable and updating laws for the reference points.The shape function is achieved and generalized from analytical solutions of the simple semi-linear Duhem model.Using the proposed approach,the memory mechanism reveals the essence of specific Duhem model and the general shape function provides a direct and clear means to fit the hysteresis loop.4)Application of MR fluids mount.Based on the aforementioned work,a MR fluids mount featuring squeeze mode is designed for power train mounting system.Experimental tests of a prototype indicate that rationally utilizing the fluids inertia and the tunability of MR fluids allows this mount charactering a large range of dynamic stiffness and a lower field-off dynamic stiffness,which makes it possible to realize the force transmissibility and vibration displacement control.To precisely describe the controllable damping force,the aforementioned hysteresis model is applied,and a feedforward control strategy is adapted for the force tracking control. |
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