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research-article

STUDY OF WATER IMPACT AND ENTRY OF A FREE FALLING WEDGE USING CFD SIMULATIONS

[+] Author and Article Information
Arun Kamath

Post Doc Department of Civil and Transport Engineering Norwegian University of Science and Technology, NTNU Trondheim, Norway
arun.kamath@ntnu.no

Hans Bihs

Associate Professor Department of Civil and Transport Engineering Norwegian University of Science and Technology, NTNU Trondheim, Norway
hans.bihs@ntnu.no

Øivind A. Arntsen

Associate Professor Department of Civil and Transport Engineering Norwegian University of Science and Technology, NTNU Trondheim, Norway
oivind.arntsen@ntnu.no

1Corresponding author.

ASME doi:10.1115/1.4035384 History: Received August 11, 2016; Revised November 21, 2016

Abstract

Many offshore constructions and operations involve water impact problems with subsequent water entry and emergence like wave slamming on semi-submersibles, vertical members of jacket structures, crane operation of a diving bell and dropping of free fall lifeboats. Slamming involves large instantaneous impact pressures on the structure, accompanied with complex free surface deformations. which need to be studied in detail in order to obtain a better understanding of the fluid physics involved and develop safe and economical design. The water entry of a free-falling wedge into water is studied in this paper using a CFD model. 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. The open-source CFD model REEF3D is used in this study. A 5th-order conservative finite difference WENO scheme and a 3rd-order Runge-Kutta scheme are used for convection and time discretisation. The Poisson pressure equation is solved using a pre-conditioned BiCGStab algorithm. A sharp representation of the free surface is obtained using the level set method. The falling wedge is represented using the level set paradigm as well, avoiding the need for re-meshing during the simulation. Turbulence modeling is carried out using the k-w model. Computational performance of the numerical model is improved by parallel processing using the MPI library.

Copyright (c) 2016 by ASME
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