This paper proposed a minimum transmitted load (MTL) control method for drop-induced shock isolation mounts (SIM) with magnetorheological energy absorbers (MREAs). MTL control method consists of two parts of maximum damping force (MDF) control and one part of constant acceleration (CA) control, which can make the payload stop after fully utilize MREA stroke (soft landing) with minimum transmitted load. The control algorithm of MTL control method is derived in a single-degree-of-freedom (SDOF) system. The relationship between the controllable velocity range of MTL control method and parameters of shock isolation mounts is also derived. An optimal control method selection criterion between Bingham number (BN) control method and MTL control method is developed. The performance of MTL control method and selection criterion are shown by applying to the SIM system with variable drop velocities and system parameters. Results shows that MTL control method has the minimum transmitted load and the selection criterion is feasible.
This research presents a minimal maximum deceleration (MMD) control method which can be used in the shock mitigation system with magnetorheological energy absorbers (MREAs). The proposed control method can make the payload stop at the end of the available MREA stroke with the lowest maximum deceleration, which does not exceed the deceleration threshold value and lead to the lowest occupant injury probability. The shock mitigation system controlled by MMD will experience constant deceleration control stage and maximum damping force control stage while making full use of the available MREA stroke. The comparative performance of the MMD control method with Bingham number (BN) control, constant deceleration (CD) control and minimum duration deceleration exposure (MDDE) control is shown. Then, the controllable drop velocity range and the required maximum MREA controllable damping force range of MMD control method is calculated. Subsequently, the optimal control method selection criterion among BN control method, CD control method and MMD control method is developed. Finally, the optimal selection criterion is applied to the drop induced shock mitigation system with varying payload velocity, payload mass (occupant type) and the maximum controllable damping force of MREA.
Magnetorheological (MR) dampers are widely used for vibration isolation and the dynamic range is a key index to evaluate its performance. According to the vibration isolation theory, it is essential for the damper to maximize the damping force in resonance region and minimize the damping force in high-frequency excitation. However, for single-path MR dampers, achieving the goals of low field-off force and large dynamic range has conflicting requirements on the structural parameters. In this research, a dual paths MR damper has been proposed to overcome this problem. The proposed MR damper has two coaxial paths and the magnetic field strength in each path can be controlled separately. According to the flow state of the MR fluid, the working modes of the dual paths MR damper are divided into three kinds and the corresponding mathematical models are driven. Based on the mathematical models, the effect of structural parameters on the dynamic range, maximum and minimum damping force is investigated. It is concluded that increasing the piston rod radius and piston length is an effective method to expand the dynamic range while maintain a small field-off damping force. The experimental results show that the proposed MR damper working mode can be controlled by the applied currents, the minimum force is obtained in the dual path flow state while the maximum force is obtained in the inner path flow state. In particular, the dynamic range of the proposed MR damper is significantly improved to 93.3 and the filed-off damping force remains small compared to the previously reported MR damper.
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