Research On Hysteretic Dynamics Of Magnetorheological Dampers

Magnetorheological (MR) dampers are the typical MR devices that produce large damping force but only require small power source and can respond to outside loading extremely fast. The configuration of MR devices is simple and the damping force can be continually controlled. Such unique features have great advantages in applications of semi-active control systems. However, because of the hysteretic effect of MR phenomenon involved in the dynamic behaviour of MR dampers, the force-velocity curves demonstrate a one-two relationship. Modeling these kinds of hysteretic behaviours accurately is the basis of relative applications. In order to control MR dampers precisely and widely implement them into really applications, a model that is suitable for system analysis and control is indispensable.The current paper begins with the physic properties of MR fluids, and then the rheology mechanism is studied. When external magnetic field is applied, MR fluids that consist of magnetized chains is viewed as a solid phase, and MR fluids that flow in two opposite directions perpendicular to the magnetic fields are viewed as two symmetric fluid phases. Based on a non-convex constitute relationship, the dynamic behaviour of MR fluids in external magnetic field can be modeled successfully by mimicking the switch of MR fluids between three phases.The paper is divided into six chapters; the primary contents of research for each chapter are as follows:In the first chapter, the background and the meaning of this study and the current research situation of MR damper are briefly presented; main contents of this study and unique characteristics and creative points are proposed.In the second chapter, the nonlinear dynamics of MR fluids and comparisons of two constitutive laws are discussed, then the major working models are investigated in detail.In the third chapter, the rheology mechanism of MR fluids is studied from a phase-transition viewpoint, and then a differential equation model is proposed. According the experimental data, parameters of the proposed model are estimated using Nelder-Mead nonlinear optimization algorithm, and it is verified that with appropriate system coefficients the proposed differential equation model is able to precisely mimic the hysteretic dynamics of MR dampers.In chapter four, the frequency dependency of the proposed model is investigated. It is verified by experiments that coefficients of the proposed model would not change when external loading changes, provided the input current of MR dampers is the same.In chapter five, hysteretic dynamics of MR dampers are investigated by experiments. At the beginning, the experimental devices are briefly described, and then comparisons of dynamics of MR dampers for different combinations of external loading frequency and input current are presented. Various influencing factors are discussed in detail at the end of this chapter.In chapter six, a conclusion of this study is presented and the new trend of MR damping technology is discussed.In the current paper, a differential equation model is proposed by theoretic and experimental investigations that are able to precisely mimic the hysteretic behaviour of MR dampers and suitable for system analysis and control, which is the basis of relative engineer applications.