ABSTRACT
The open source CFD library OpenFOAM is used to simulate the process of the crane lifting cargo into the water. In this paper, overset mesh strategy and the overInterDyMFoam solver are used to solve the process of two-dimensional water entry of a wedge. Firstly, the pressure coefficient distribution and free surface profile of wedges with different deadrise angles into the calm water with constant velocity or free-falling are calculated. Furthermore, water entry of a wedge into a wave was studied. The accuracy of the code is verified by comparing with the published academic data and experimental results.
With ever-increasing marine engineering construction and marine resources exploitation, the water entry problem in marine crane hoisting operations has been one of the major concerns in ocean engineering. The most critical problem is the hydrodynamic impact on the cargo during the water entry phase. In some cases, the cable breaks due to the irregular movement of the cargo, resulting in serious accidents (Driscoll, Lueck, and Nahon, 2000; Hover, Grosenbaugh, and Triantafyllou, 1994). Therefore, it is very important to realize efficient and safe deep-sea hoisting operations in complex sea conditions and to enter the water quickly and smoothly. In naval engineering and marine resources exploitation, cranes lift cargo or parts of various shapes into the water, including small fishing boats or lifeboats after maintenance. In this paper, the lifeboat is simplified into a wedge to study its entry process and verify the accuracy of the code.
In previous studies, a heave compensation system has been used to eliminate the impact of vessel motion on cargo, while precise analysis of force on payload is rarely carried out. Wu, Yang, and Wu (2018) took into account the hydrodynamic forces on the payload but simplified them for ease of calculation. A numerical model that can accurately calculate the hydrodynamic force on the payload is urgently needed to provide guidance for later control system design. Before calculating complex payload entry motion, the numerical model needs to be validated using simulations such as the water entry of a wedge.
Based upon the theory of similarity flows of an incompressible fluid, Dobrovol's (1969) obtained a self-similar solution for the wedge waterentry problem. Greenhow and Lin (1983) published the experimental results of two-dimensional high speed water entry of a wedge, and pointed out that linear theory could not accurately solve the water entry problem. Zhao and Faltinsen (1993) solved the problem of water entry of wedge with different deadrise angles using the boundary element method in the time domain. When the wedge impacts the water, the jet is developed and attached to wedge surface. Zhao and Faltinsen (1993) cut the jet off from the main flow in the calculation, while Battistin and Iafrati (2004) obtained more accurate results by using the shallow water approximation. Oblique water entry of an asymmetrical wedge is solved by combing BEM with the shallow water approximation (Xu, Duan, and Wu, 2008).
