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Research Papers: Ocean Engineering

Rigid-Body Water–Surface Impact Dynamics: Experiment and Semianalytical Approximation

[+] Author and Article Information
Ravi Challa

Graduate Research Assistant

Solomon C. Yim

Glenn Willis Holcomb Professor
School of Civil and Construction Engineering,
Oregon State University,
Corvallis, OR 97330

C. P. Vendhan

Professor
Department of Ocean Engineering,
Indian Institute of Technology Madras,
Chennai 600036, India

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received September 25, 2010; final manuscript received October 5, 2013; published online November 12, 2013. Assoc. Editor: .

J. Offshore Mech. Arct. Eng 136(1), 011102 (Nov 12, 2013) (10 pages) Paper No: OMAE-10-1096; doi: 10.1115/1.4025653 History: Received September 25, 2010; Revised October 05, 2013

An experimental study of the dynamics of a generic rigid body during water impact and an equivalent-radius approximate analytical procedure is developed and calibrated in this study. The experimental tests in a wave basin covered a range of drop heights using a 1/6th-scale model of a practical water-landing object prototype for two drop mechanisms to determine the water impact and contact effects. The first mechanism involved a rope and pulley arrangement, while the second mechanism employed an electromagnetic release to drop the rigid body. Hydrodynamic parameters including peak acceleration and touchdown pressure were measured and the maximum impact/contact force was estimated for various entry speeds (corresponding to various drop heights) and weights of the rigid body. Results from the tests show that the impact acceleration and touchdown pressure increases approximately linearly with increasing drop height and the data provides conditions that keep impact accelerations under specified limits for the rigid-body prototype. The experimentally measured maximum accelerations were compared with classical von Karman and Wagner approximate closed-form solutions. In this study, an improved approximate solution procedure using an equivalent radius concept integrating experimental results with the von Karman and Wagner closed-form solutions is proposed and developed in detail. The resulting semianalytical estimates are calibrated against experimental results and found to provide close matching.

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References

Figures

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Fig. 1

Overall configuration of WLO prototype (all dimensions are in mm)

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Fig. 2

Measured data of a 5 m drop test: Acceleration time history of a sample test case

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Fig. 3

Measured data of a 5 m drop test: Pressure time history of a sample test case

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Fig. 4

Consistency of measured peak acceleration and peak pressure versus sampling rate (PC based data acquisition)

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Fig. 5

Consistency of measured peak acceleration and peak pressure versus sampling rate (oscilloscope capture)

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Fig. 6

Electromagnet with protruding strut: (a) Up-close view of the setup for drop test II and (b) WLO touchdown with water surface

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Fig. 7

Measured electromagnetic release data of a 5 m drop test: (a) Acceleration time history and (b) pressure time history

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Fig. 8

Maximum impact force versus square of impact velocity (drop tests I and II)

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Fig. 9

Maximum impact pressure versus square of normalized impact velocity (drop tests I and II)

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Fig. 10

Maximum acceleration using von Karman and Wagner solutions (drop test I)

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Fig. 11

Maximum acceleration using von Karman and Wagner solutions (drop test II)

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Fig. 12

Equivalent radius of the WLO model

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Fig. 13

Equivalent radius (r) of the WLO for different normalized velocities of impact for drop test I and drop test II using von Karman and Wagner approaches

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Fig. 14

Maximum impact accelerations calculated based on the mean equivalent radius (r*) of the WLO for different normalized velocities of impact for drop test I using von Karman and Wagner approaches

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Fig. 15

Maximum impact accelerations calculated based on the mean equivalent radius (r*) of the WLO for different normalized velocities of impact for drop test II using von Karman and Wagner approaches

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