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Research Papers

Drop-Induced Shock Mitigation Using Adaptive Magnetorheological Energy Absorbers Incorporating a Time Lag

[+] Author and Article Information
Young-Tai Choi

Department of Aerospace Engineering,
University of Maryland,
College Park, MD 20742
e-mail: nicechoi@umd.edu

Norman M. Wereley

Fellow ASME
Department of Aerospace Engineering,
University of Maryland,
College Park, MD 20742
e-mail: wereley@umd.edu

1Corresponding author.

Contributed by the Technical Committee on Vibration and Sound of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received April 6, 2014; final manuscript received October 3, 2014; published online November 12, 2014. Assoc. Editor: Eugenio Dragoni.

J. Vib. Acoust 137(1), 011010 (Feb 01, 2015) (7 pages) Paper No: VIB-14-1127; doi: 10.1115/1.4028747 History: Received April 06, 2014; Revised October 03, 2014; Online November 12, 2014

This study addresses the nondimensional analysis of drop-induced shock mitigated using magnetorheological energy absorbers (MREAs) incorporating a time lag. This time lag arises from two sources: (1) the time required to generate magnetic field in the electromagnet once current has been applied and (2) the time required for the particles in the magnetorheological fluid to form chains. To this end, the governing equations of motion for a single degree-of-freedom (SDOF) system using an MREA with a time lag were derived. Based on these equations, nondimensional stroke, velocity, and acceleration of the payload were derived, where the MREA with a time lag was used to control payload deceleration after the impact. It is established that there exists an optimal Bingham number that allows the payload mass to achieve a soft landing, that is, the payload comes to rest after utilizing the available stroke of the MREA. Finally, the shock mitigation performance when using this optimal Bingham number control strategy is analyzed, and the effects of time lag are quantified.

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References

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Figures

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Fig. 1

Configuration of MREAs for drop-induced shock mitigation

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Fig. 2

The block diagram of the optimal Bingham number control

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Fig. 3

Comparison of the exact and approximated optimal Bingham numbers for no time lag case with respect to the initial drop velocity

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Fig. 4

Comparison of the exact and approximated optimal Bingham numbers under different time lags versus the initial drop velocity. (a) With a time lag of τ¯ = 0.3 and (b) with a time lag of τ¯ = 0.7.

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Fig. 5

The identified coefficients and the curve-fitting functions

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Fig. 6

The nondimensional time response of an MREA with a time lag of τ¯ = 0.3 for drop-induced shock mitigation at different initial drop velocities. (a) At initial drop velocity of 5 m/s and (b) at initial drop velocity of 10 m/s.

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Fig. 7

The nondimensional time response of an MREA with a time lag of τ¯ = 0.7 for drop-induced shock mitigation at different initial drop velocities. (a) At initial drop velocity of 5 m/s and (b) at initial drop velocity of 10 m/s.

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