Technical Brief

Inversion of a Capsule Impacting Water: Flip by Resurge Jet

[+] Author and Article Information
Ralph D. Lorenz

Johns Hopkins University Applied Physics Laboratory,
11100 Johns Hopkins Road,
Laurel, MD 20723
e-mail: ralph.lorenz@jhuapl.edu

Michael V. Paul, David W. Olds

Applied Research Laboratory,
Pennsylvania State University,
College Park, PA 16802

Justin Walsh

Applied Research Laboratory,
Pennsylvania State University,
College Park, PA 16802

Edward B. Bierhaus

Lockheed Martin Space Systems Company,
Littleton, CO 80127

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received July 5, 2014; final manuscript received March 20, 2015; published online April 17, 2015. Assoc. Editor: Solomon Yim. The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States Government purposes.

J. Offshore Mech. Arct. Eng 137(4), 044501 (Aug 01, 2015) (6 pages) Paper No: OMAE-14-1074; doi: 10.1115/1.4030289 History: Received July 05, 2014; Revised March 20, 2015; Online April 17, 2015

A scale-model blunt-cone capsule intended for ocean splashdown was projected into a water pool to evaluate impact loads and postimpact behavior. In a small region of the speed/angle parameter space, the capsule would reproducibly capsize, flipping forward (pitch-down), despite a pitch-up motion induced at impact. Inspection of high-speed video shows that the resurging central jet of the impact cavity is responsible. Capsize occurs when this jet is energetic enough (for which we develop a simple criterion), and is timed to lift the trailing edge of the vehicle. The same phenomenon was observed on the Apollo capsules, and may be relevant for lifeboat deployment from ships and offshore platforms.

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Grahic Jump Location
Fig. 1

Cross section of the test article. The center of mass (black dot) is 48 mm below the deck, somewhat above the waterline which roughly coincides with the lip. The attachment fitting and transparent lid are seen at top; instrumentation boxes indicated by shading.

Grahic Jump Location
Fig. 2

Scenes from the test campaign. (a) Installing the model on the carriage that allowed adjustment of the vehicle pitch at release. (b) The carriage is hoisted to the top of the launch rail that could be tilted to impart a horizontal as well as vertical velocity at impact (c) at the bottom of the launch rail, the pin holding the model is retracted by a cam, releasing the model for a brief free-flight before impact on the water surface (d).

Grahic Jump Location
Fig. 3

Screengrabs from a high-speed video camera. In free flight the capsule has a slightly pitch-down attitude (a). At impact (b), an impulsive pitch-up acceleration is introduced such that in frames ((c) and (d)) the capsule has positive pitch–the ejecta ring around the transient cavity is clearly seen here. In (e) the vehicle has dramatically pitched down and a jet of water behind the capsule is seen. In (f), (g), (h), and (i), the capsule continues, now more slowly, to pitch-down and forward, becoming inverted ((j)–(l)).

Grahic Jump Location
Fig. 4

High-speed side view of the test in Fig. 2. Frames are ∼0.03 s apart. The upper surface of the vehicle is not in fact submerged, even though the vehicle penetrates below the undisturbed waterline in frames ((d)–(h)). Note that the vehicle pitches up (anticlockwise in this view) at the instant of impact, but subsequently pitches down (or forward, clockwise in this view) later in the event due to the resurging central jet of the transient cavity–this interaction on the underside of the capsule is seen in frames ((j)–(n)). The interaction flips the vehicle onto its side, from which it slowly topples forward and becomes inverted (outside the frame).

Grahic Jump Location
Fig. 5

Pitch rate history for a capsizing impact at 7.13 m/s, recorded by a solid-state gyro on the model, sampled at 512 samples/s. Despite the impulsive pitch-up at impact, a pitch-down rate builds up over the next 0.5 s, causing the capsule to tip forward.

Grahic Jump Location
Fig. 6

Summary plot of results from the three test series (points randomly displaced ∼0.1 m/s to show duplicates.) The vertical line is the resurge timing criterion from Ref. [2], namely VH > R/t (see text): the horizontal solid line shows the energy criterion developed in Eq. (1) with parameter γ empirically determined to be 0.85.

Grahic Jump Location
Fig. 7

Schematic of capsize conditions by the mechanism discussed in this paper



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