This study addresses the non-dimensional analysis of adaptive magnetorheological energy absorbers (MREAs) for drop-induced shock mitigation. The control objective to ensure that the payload mass comes to rest at the end of the available stroke of the MREA, that is, a ‘soft landing.’ The governing equation of motion of a single-degree-of-freedom system with an MREA was derived. The Bingham number was defined and its effect on the system response was examined. A comprehensive non-dimensional analysis was conducted using non-dimensional stroke, velocity and acceleration, where Bingham number and time constant were key parameters. An optimal Bingham number - based on drop velocity, payload mass, and passive damping - minimized the drop-induced shock loads transmitted to the payload by utilizing maximum damper stroke.
A linear stroke adaptive magnetorheological energy absorber (MREA) was designed, fabricated and tested for intense impact conditions with piston velocities up to 8 m s−1. The performance of the MREA was characterized using dynamic range, which is defined as the ratio of maximum on-state MREA force to the off-state MREA force. Design optimization techniques were employed in order to maximize the dynamic range at high impact velocities such that MREA maintained good control authority. Geometrical parameters of the MREA were optimized by evaluating MREA performance on the basis of a Bingham-plastic analysis incorporating minor losses (BPM analysis). Computational fluid dynamics and magnetic FE analysis were conducted to verify the performance of passive and controllable MREA force, respectively. Subsequently, high-speed drop testing (0–4.5 m s−1 at 0 A) was conducted for quantitative comparison with the numerical simulations. Refinements to the nonlinear BPM analysis were carried out to improve prediction of MREA performance.
Optimal control of a gun recoil absorber is investigated for minimizing recoil loads and maximizing rate of fire. A multi-objective optimization problem was formulated by considering the mechanical model of the recoil absorber employing a spring and a magnetorheological (MR) damper. The damper forces are predicted by evaluating pressure drops using a nonlinear Bingham-plastic model. The optimization methodology provides multiple optimal design configurations with a trade-off between recoil load minimization and increased rate of fire. The configurations with low or high recoil loads imply low or high rate of fire, respectively. The gun recoil absorber performance is also analyzed for perturbations in the firing forces. The adaptive control of the MR damper for varying gun firing forces provides a smooth operation by returning the recoil mass to its battery position (ready to reload and fire) without incurring an end-stop impact. Furthermore, constant load transmissions are observed with respect to the recoil stroke by implementing optimal control during the simulated firing events.
Non-dimensional analysis and optimal control design of adaptive magnetorheological shock isolation (MRSI) mounts are addressed for drop-induced impacts. The governing equation of motion of a single degree-of-freedom under impact was derived, where a magnetorheological energy absorber (MREA), which has controllable stroking load and a passive linear spring, isolate the payload mass from the base that impacts the ground. During the impact event, the payload experiences both a compression and a rebound stroke. During the compression stroke, the payload descends as the MREA dissipates and the spring stores, the energy of impact. During the rebound stroke, the spring releases its stored energy under the control of the MREA. The Bingham number, defined as the ratio of the MREA yield force to its viscous force, is utilized as the control variable. A non-dimensional analysis was conducted using key parameters such as available MREA stroke and Bingham number. The first control objective was to ensure that the payload achieved a soft landing (i.e., comes to rest) at the end of the compression stroke by fully utilizing the available stroke of the MREA. The second control objective was to completely recover the available MREA stroke during rebound, with no overshoot of the equilibrium point, i.e. dead-beat control. It is shown that the optimal MRSI control strategy implies the selection of two distinct Bingham numbers, one for the compression stroke and one for the rebound stroke, which achieve the control objectives.
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