Ship collision accidents continue to occur regardless of efforts to prevent them. Ship-ship collisions involve highly nonlinear characteristics associated with structural crashworthiness, including crushing and fracture as well as buckling and plastic collapse. When applying nonlinear finite element method simulations to solve these problems, a reliable value of critical fracture strain accounting for strain-rate effects due to collision speed must be implemented. This study aims to propose a practical method to estimate the dynamic fracture strain to be used for the structural crashworthiness analysis associated with ship-ship collisions using the nonlinear finite element method. For this purpose, the strain-rate characteristics in struck ship structures were investigated by nonlinear finite element method computations, in which the striking vessel was assigned various velocities from 0.5 to 20 knots in the range of practical ship speeds. Based on the computations, an empirical formula was developed to calculate the strain rate at a collision scenario with a given collision speed, allowing for a practical estimation of the dynamic fracture strain. The formula is validated by a comparison with experimental data.

Ship-ship collision frequently occurs in shipping industry. The risks of economic losses and marine pollution have been increased by to ship-ship collisions especially involved with large oil tankers or liquefied natural gas (LNG)-fueled ships. Various type of methods are available for the purpose of safety studies in association with structural crashworthiness involving crushing and fracture in ship-ship collisions. In the perspectives of multi-physics and multi-criteria involved, however, the nonlinear finite element method is 2 certainly one of the most powerful techniques to model the problems. In a shipship collision accident where the bow of a striking ship is collided with the side of struck ship, the kinetic energy must be absorbed by both striking and struck ship structures in terms of collision damages and corresponding strain energies.As the bow structure of the striking ship is usually much stiffer than the side structure of the struck ship. It does not allow for deformation and damage.Therefore, no contribution of energy absorption is made by the striking structure. As the energy absorption characteristics of the striking ship depends on the structural arrangement of bulbous bow and flare, however, the contribution of striking ship cannot be entirely neglected. The aims of the present study are to examine the effects of a deformable striking ship structure on the structural crashworthiness of ship-ship collisions using LS-DYNA nonlinear finite element method computations. As an illustrative example in the paper, the struck ship is a VLCC class double hull oil tanker, while the struck ships are two types: a VLCC class tanker and a SUEZMAX class tanker.The relationships between collision forces versus penetration together with their energy absorption capabilities are characterized in association with the contributions of the striking ship bow where the deformable striking ship structures are compared with the rigid striking ship structures. Developed Findings and insights from the present study are summarized.