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In this research, a new type of magnetorheological damper for a small-sized aircraft landing gear system is proposed and its performance is evaluated with respect to design parameters of the magnetic core. As a first step, a new configuration of magnetorheological damper for the landing gear system, which consists of orifices, recoil valve, and magnetic circuits, is introduced with working principles. After formulating the governing equations of motion, six different models of magnetorheological damper featuring different number of magnetic core and different pole length are chosen to investigate both the landing stability and the efficiency. Subsequently, the distribution of the magnetic field intensity of each model is analyzed through the finite element method, followed by the calculation of the field-dependent damping force to be used for the landing simulation, which is undertaken by adopting the dynamic model of a half airplane landing gear system. In order to identify the significance of the magnetic core parameters, the landing stability is judged from the sign of the minimum force and the landing efficiency is determined from the energy dissipation during the vertical drop motion.

In this study, a new class of magnetorheological (MR) damper, which can realize desired damping force at both low and high speeds of vehicle suspension systems, is proposed and its salient characteristics are shown through computer simulations. Unlike conventional MR dampers, the proposed MR damper has a specific pole shape function and therefore the damping coefficient is changed by varying the effective area of the main orifice. In addition, by controlling the opening or closing the bypass orifice, the drastic change of the damping coefficient is realizable. After briefly describing the operating principle, a mathematical modeling is performed considering the pole shape function which is a key feature of the proposed MR damper. Then, the field-dependent damping force and piston velocity-dependent characteristics are presented followed by an example on how to achieve desired damping force characteristics by changing the damping coefficient and slope breaking point which represents the bilinear damping property.

This paper proposes a mathematical model of the cavitation behaviour to occur in a single-ended magnetorheological damper (MRD), and the effectiveness of the model is validated through the comparison with experimental results. Several causes of the cavitation behaviour of MRD are discussed with different conditions of the initial pressure of the gas chamber and the piston stroke speed. The model to capture the cavitation behaviour is then formulated considering differential equations for gas volume, internal pressure, ideal gas law and bulk modulus of MR fluid. In order to calculate the flow rate, which is difficult to solve from the differential equations, the model is approximated as a nondimensional equation the parameters of the yield stress and pole length. Subsequently, the field-dependent damping force of MRD is computed using gaseous cavitation model and nondimensional equation. To validate the proposed cavitation model, a single-ended MRD is designed, manufactured and tested. It is firstly observed that the damping force characteristics under cavitation are revealed to be much different from those under normal operation without cavitation. More specifically, it is hard to calculate the dissipation energy and hysteretic damping due to highly nonlinear characteristics with respect to the stroke and velocity. However, the proposed model can fairly capture the cavitation behaviour showing an excellent agreement between simulation and experiment. In this work, to confirm the internal influence of MRD by the cavitation, which is difficult to experimentally confirm, the changes of the pressure distribution and the gas-to-liquid volume ratio are analyzed through the simulation of the nondimensional equation. In addition, the bubbles representing the cavitation behaviour are visually observed from the lower chamber of

A small-sized brake generating the torque less than 0.5 Nm is very attractive to achieve desired dynamic motions in many different fields such as medical haptic and auto door closure. In this work, a controllable compact-sized brake utilizing a magnetorheological fluid (MRF) is proposed and its effectiveness is validated through simulation and experiment. Unlike conventional shear mode magnetorheological brake (MRB), a mixed mode MRB (M-MRB) featuring both the flow and shear mode operations is designed to obtain high torque efficiency in which both the key shape and ring shape structures play the significant role. Through these structures, the proposed M-MRB can provide higher torque with the relatively less amount of MRF than conventional shear mode MRB. The key shape structure is fixed to the rotor and shaft of MRB and rotates in same direction. Then, MRF on the front and back of the barrier is subjected to the pressure difference resulting in the field-dependent torque generation. To demonstrate the effectiveness of the proposed design concept, a small-sized M-MRB is designed and manufactured considering the required torque level and space constraint of auto door closure applicable to autonomous vehicle systems. It is identified through a reasonable comparison between the proposed M-MRB and conventional MRB that the proposed one can improve controllable torque range up to 325% with less MR fluid than conventional MRB.