In this paper, we present a fully coupled computational fluid dynamic (CFD) and discrete module beam (DMB) method for the numerical prediction of nonlinear hydroelastic responses of a ship advancing in regular and focused wave conditions. A two-way data communication scheme is applied between two solvers, whereby the external fluid pressure exported from the CFD simulation is used to derive the structural responses in the DMB solver, and the structural deformations are fed back into the CFD solver to deform the mesh. We first conduct a series of verification and validation studies by using the present CFD–DMB method to investigate the global ship motion, vertical bending moments (VBMs), and green water phenomenon of the ship in different regular wave conditions. The numerical results agreed favourably with the CFD–FEA model and experimental measurements. Then, the extreme ship motions are studied in focused wave conditions to represent extreme sea conditions that a ship may experience in a real sea state. According to the conclusion drawn from the numerical simulations, it is founded that the focused wave case will lead to the increase of the longitudinal responses of the hull compared to regular wave condition, i.e., the heave, pitch, and total VBMs rise about 25%, 20% and 9%, respectively. In focused wave conditions, intensive ship responses and severe waves cause stronger slamming phenomena. It is found that the instantaneous impact pressure from the focused wave is higher and sharper compared to the regular waves and comes along with the obvious green-water-on-deck phenomena.

Commercial vessels have recently shown a common trend in increasing their sizes to meet the growing demand for transportation and operations. This trend may however result in more flexible or ‘softer’ hulls. The flexible hull structure reduces the ship natural frequency close to the wave encounter frequency, increasing the probability of resonance or high-frequency vibrations. Meanwhile, the resulting structural deformations from flexible hull could significantly affect the flow field and the hydrodynamic loads cannot be estimated accurately. Hence, it is important to treat a flexible hull and its surrounding flow field as an interacting system to predict a ship’s dynamic behaviour based on the hydroelastic theory. In this study, a novel fluid-structure interactions coupling scheme using the “preCICE” library to communicate with the fluid solver “OpenFOAM” and structure solver “calculiX” was first proposed to study the hydroelastic behavior of a container ship with a forward speed in regular waves. With the advantage of this numerical model, the flexible behaviour of this ship, such as its vertical bending displacement and corresponding bending moment can be quantified, and the “springing” and “whipping” responses can be calculated. It is believed that the present FSI model will exhibit more advantages over the traditional rigid-body methods currently used in the ship seakeeping field.

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