Study of water impact and entry of a free falling wedge using computational fluid dynamics simulations

Abstract

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.