An investigation into container constraint effects on the cavity characteristics due to high-speed projectile water entry

Diving consists of jumping into water from a platform, usually while performing acrobatics. During high diving competitions, the initial height reaches 27 m. From this height, the crossing of the water surface occurs at 85 km/h, and as such it is very technical to avoid injuries. Major risks occur due to the violent impact at the water entry and the formation and collapse of the air cavity around the diver. In this study, we investigate experimentally the dynamics of the jumper underwater and the hydrodynamic causes of injuries in high dives by monitoring dives from different heights with high-speed cameras and accelerometers in order to understand the physics underlying diving.

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All-Speed Time-Accurate Underwater Projectile Calculations Using a Preconditioning Algorithm

Journal of Fluids Engineering ◽

10.1115/1.2169816 ◽

2005 ◽

Vol 128 (2) ◽

pp. 284-296 ◽

Cited By ~ 39

Author(s):

Michael Dean Neaves ◽

Jack R. Edwards

Keyword(s):

High Speed ◽

Compressible Flows ◽

Time Derivative ◽

Water Entry ◽

Ideal Gas ◽

Projectile Motion ◽

Imaging Results ◽

Underwater Projectile ◽

Phase Water ◽

Compressibility Effects

An algorithm based on the combination of time-derivative preconditioning strategies with low-diffusion upwinding methods is developed and applied to multiphase, compressible flows characteristic of underwater projectile motion. Multiphase compressible flows are assumed to be in kinematic and thermodynamic equilibrium and are modeled using a homogeneous mixture formulation. Compressibility effects in liquid-phase water are modeled using a temperature-adjusted Tait equation, and gaseous phases (water vapor and air) are treated as an ideal gas. The algorithm is applied to subsonic and supersonic projectiles in water, general multiphase shock tubes, and a high-speed water entry problem. Low-speed solutions are presented and compared to experimental results for validation. Solutions for high-subsonic and transonic projectile flows are compared to experimental imaging results and theoretical results. Results are also presented for several multiphase shock tube calculations. Finally, calculations are presented for a high-speed axisymmetric supercavitating projectile during the important water entry phase of flight.

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Experimentally Measured Hydroelastic Effects on Impact-Induced Loads during Flat Water Entry and Related Uncertainties

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4044632 ◽

2019 ◽

pp. 1-30

Author(s):

Simon Toedter ◽

Ould el Moctar ◽

Jens Neugebauer ◽

Thomas E. Schellin

Keyword(s):

High Speed ◽

Water Entry ◽

Test Case ◽

Primary Concern ◽

Air Trapping ◽

Flat Bottom ◽

Benchmark Data ◽

Elastic Bottom ◽

Structural Deformations ◽

Two Bodies

Abstract Extensive water entry experiments were performed to identify uncertainties associated with measured impact-induced loads acting on flat bottom ship structures. Of primary concern was the influence of air trapping on elastic structural deformations. The experimental measurements supplied benchmark data suitable to validate CFD predictions. Two bodies were tested. One body was fitted with stiffened, rigid bottom plating; the other body, with thin elastic plating. A large number of 30 repetitive runs recorded bottom pressures and forces acting on the flat bottom plating and monitored impact-induced elastic bottom strains. For each test case, high-speed videos of water entry sequences were evaluated. The resulting average peak values standard deviations quantified the uncertainty of these measurements.

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Numerical investigations on the oblique water entry of high-speed projectiles

Applied Mathematics and Computation ◽

10.1016/j.amc.2019.06.061 ◽

2019 ◽

Vol 362 ◽

pp. 124547

Author(s):

Jian-Guo Gao ◽

Zhi-Hua Chen ◽

Zhen-Gui Huang ◽

Wei-Tao Wu ◽

Yu-Jie Xiao

Keyword(s):

High Speed ◽

Water Entry ◽

Numerical Investigations

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Numerical Investigation of Air Cavity Formation During the High-Speed Vertical Water Entry of Wedges

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4006760 ◽

2013 ◽

Vol 135 (1) ◽

Cited By ~ 14

Author(s):

Jingbo Wang ◽

Odd M. Faltinsen

Keyword(s):

Free Surface ◽

High Speed ◽

Nonlinear Boundary ◽

Water Entry ◽

Similarity Solutions ◽

Free Surface Flows ◽

Cavity Formation ◽

Air Cavity ◽

Numerical Instabilities ◽

Entry Velocity

In this paper, a nonlinear boundary element method (BEM) is developed for investigating air cavity formation during the high-speed water entry of wedges. A technique is proposed for dynamic re-gridding of free surface boundaries. This technique applies to both equally and nonequally spaced grids, and it is able to suppress the numerical instabilities encountered using a BEM for simulating free surface flows. The authors also develop a purely numerical method to simulate nonviscous flow separation, which occurs when the flow reaches the knuckle of the wedge. The present nonlinear BEM has been verified by comparisons with similarity solutions. We also compare numerical results with experimental results. Finally, we give a numerical prediction of the evolution of the cavity until the closure of the cavity, and the influence of the initial entry velocity, wedge mass, and deadrise angle on the characteristics of the transient cavities is investigated.

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