Effects of a deformable striking ship's bow on the structural crashworthiness in ship-ship collisions

Ship-ship collision accidents continue to occur regardless of the continuous efforts to prevent them, and they essentially involve highly nonlinear problems associated with structural crashworthiness due to crushing and fracture. The nonlinear finite-element method is one of the most powerful techniques to solve the problems. In industry practice, the bow structure of a striking ship is often modelled as a rigid body as it is usually much stiffer than the side structure of a struck ship. However, reality is that the initial kinetic energy in a ship-ship collision accident can be absorbed by the damages of not only the struck ship's side structures but also the striking ship's bow structures because the striking ship bow structure is actually deformable. The aim of the present study is to examine the effects of a deformable striking ship's bow on the structural crashworthiness in ship-ship collisions. In the present study, two scenarios are considered where the side structure of a VLCC class double hull oil tanker is collided by the bow structure of a VLCC class double hull oil tanker or a SUEZMAX class double hull oil tanker. All of the ships considered are real ships in operation. The structural crashworthiness in terms of the collision force-penetration relation and the collision energy-penetration relation is then studied with two cases in which the striking ship's bow structures are either rigid or deformable. It is concluded that the striking ship's bow may be modelled as a rigid body in minor collisions at a collision angle of about 90 degrees where the initial kinetic energy is entirely consumed before the inner hull structure is ruptured, but it should be modelled as a deformable body in a major collision accident or at an inclined collision angle where the maximum penetration can be greater than the double side breadth.