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Research Papers: CFD and VIV

Study of Water Impact and Entry of a Free Falling Wedge Using Computational Fluid Dynamics Simulations

[+] Author and Article Information
Arun Kamath

Department of Civil and Transport Engineering,
Norwegian University of Science
and Technology (NTNU),
Trondheim 7491, Norway
e-mail: arun.kamath@ntnu.no

Hans Bihs

Associate Professor
Department of Civil and Transport Engineering,
Norwegian University of Science
and Technology (NTNU),
Trondheim 7491, Norway

Øivind A. Arntsen

Associate Professor
Department of Civil and Transport Engineering,
Norwegian University of Science
and Technology (NTNU),
Trondheim 7491, Norway
e-mail: oivind.arntsen@ntnu.no

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received August 11, 2016; final manuscript received November 21, 2016; published online March 28, 2017. Assoc. Editor: Celso P. Pesce.

J. Offshore Mech. Arct. Eng 139(3), 031802 (Mar 28, 2017) (6 pages) Paper No: OMAE-16-1092; doi: 10.1115/1.4035384 History: Received August 11, 2016; Revised November 21, 2016

Many offshore constructions and operations involve water impact problems such as water slamming onto a structure or free fall of objects with subsequent water entry and emergence. Wave slamming on semisubmersibles, vertical members of jacket structures, crane operation of a diving bell, and dropping of free fall lifeboats are some notable examples. The slamming and water entry problems lead to large instantaneous impact pressures on the structure, accompanied with complex free surface deformations. These need to be studied in detail in order to obtain a better understanding of the fluid physics involved and develop safe and economical design. Numerical modeling of a free falling body into water involves several complex hydrodynamic features after its free fall such as water entry, submergence into water and resurfacing. The water entry and submergence lead to formation of water jets and air cavities in the water resulting in large impact forces on the object. In order to evaluate the forces and hydrodynamics involved, the numerical model should be able to account for the complex free surface features and the instantaneous pressure changes. The water entry of a free falling wedge into water is studied in this paper using the open source computational fluid dynamics (CFD) model REEF3D. The vertical velocity of the wedge during the process of free fall and water impact are calculated for different cases and the free surface deformations are captured in detail. Numerical results are compared with experimental data and a good agreement is seen.

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References

Figures

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Fig. 1

Illustration of the wedge used for free fall wedge simulations in this study

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Fig. 2

Grid convergence studies for a free falling wedge: (a) vertical position of the free falling wedge and (b) vertical velocity of the free falling wedge

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Fig. 3

Effect of grid resolution on the free surface features during the impact of the wedge: (a) t = 1.11 s, dx = 0.05 m and (b) t = 1.11 s, dx = 0.02 m

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Fig. 4

Comparison to numerical results to experimental data from Ref. [12]: (a) vertical position of the free falling wedge and (b) vertical velocity of the free falling wedge

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Fig. 5

Numerical results for vertical position and velocity of the free falling wedge for different densities of the wedge: (a) vertical position of the free falling wedge and (b) vertical velocity of the free falling wedge

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Fig. 8

Three-dimensional (3D) simulation of freely falling wedge impacting still water

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Fig. 7

Free surface around the wedge during maximum penetration into water for the wedges with the maximum and minimum density in this study with velocity magnitude contours: (a) t = 1.21 s for ρwedge=900.0 kg/m3 and (b) t = 1.13 s for ρwedge=466.7 kg/m3

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Fig. 6

Simulation of free fall of the wedge with ρwedge=600.0 kg/ m3 and water impact with velocity magnitude contours: (a) t = 0.0 s, (b) t = 0.72 s, (c) t = 0.74 s, (d) t = 0.77 s, (e) t = 0.79 s, (f) t = 0.90 s, (g) t = 1.20 s, and (h) t = 1.89 s

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