Implementation of Linear Potential-Flow Theory in the 6DOF Coupled Simulation of Ship Collision and Grounding Accidents

Abstract

Ship collisions and groundings are highly nonlinear and transient, coupled dynamic processes involving large structural deformations and fluid structure interactions. It has long been difficult to include all effects in one simulation. By taking advantage of the user defined load subroutine and the user common subroutine, this paper implements a model of hydrodynamic loads based on linear potential-flow theory into the nonlinear finite element code LS-DYNA, facilitating a fully coupled six degrees of freedom (6DOF) dynamic simulation of ship collision and grounding accidents. Potential-flow theory both with and without considering the forward speed effect is implemented for studying the speed influence. With the proposed model, transient effects of the fluid, global ship motions, impact forces and structural damage can all be predicted with high accuracy. To the authors' knowledge, this is the first time the fully coupled 6DOF collision and grounding simulations are carried out with linear hydrodynamic loads for transient conditions but without simplification of collision forces.The proposed method is applied to calculations of an offshore supply vessel colliding with a rigid plate and with a submersible platform. The results are compared with a decoupled method and discussed with emphasis on the influence of different initial velocities. The proposed method is capable of predicting both the 6DOF ship motions and structural damage simultaneously with good efficiency and accuracy; hence, it will be a very promising tool in the application to ship collision and grounding analysis.

Analysis and design of offshore tubular members against ship impacts

“…This observation agrees with the modified Wierzbicki and Suh model in eq. (5). When B is zero, the resistance given by eq.…”

“…More considerations regarding the hydrodynamic effects during ship collisions can be found in refs. [5][6][7]. The recommended deformation resistance curves for side, bow and stern impacts are given in Fig.…”

A static position-adjustment method for the motion prediction of the Flexible Floating Collision-Prevention System

“…Hence, we do not study the collision at initial instant and the deformation of the ship, but focus on studying the movement of the FFCPS during the collision process in this paper. Compared with the traditional collision, such as the ship colliding directly with piers, walls and ground [22] etc., the duration of the collision for our case is much longer and the acceleration will be very small, therefore the added mass relevant to the acceleration against the forward speed of the ship could be omitted in the simulation. That is to say, no dynamic effect has been considered.…”

A review of structural responses and design of offshore tubular structures subjected to ship impacts

“…Liu and Amdahl (2010) reformulated Stronge's 6DOF model in a local coordinate system for ship collisions, which allowed objects with three dimensional geometries and eccentricities such as icebergs to be considered. The accuracy of the external dynamics models was discussed by Tabri (2012) and Yu et al (Yu and Amdahl, 2016;Yu et al, 2016a;Yu et al, 2016b) by comparison with coupled simulations. The external dynamic models were found to be capable of predicting energy dissipation at the end of the first impact with good accuracy in general.…”

“…The coupled simulation model developed by Yu et al (Yu and Amdahl, 2016;Yu et al, 2016a;Yu et al, 2016b) is capable of capturing hydrodynamic forces, 6DOF ship motions and structural damage simultaneously but virtually does not increase computational time (the time for calculating hydrodynamic forces is negligible compared to that for structural response calculations). The ship rolled anticlockwise initially with large collision forces and bending moments and rolled back after some time under the action of the water restoring forces.…”