Large ocean waves substantially threaten human's oceanic activities. It is nowadays demanded to understand the fully nonlinear hydrodynamics from their sudden appearance in open seas to their impacts on marine engineering applications. For this purpose, phase-resolved numerical simulations of random ocean waves covering large spatiotemporal scales with information of underlying hydrodynamics are required. In this study, we further improved the Enhanced Spectral Boundary Integral (ESBI) model by proposing a novel rapid method to compute the internal water particle kinematics. With the usage of Fast Fourier Transform (FFT), the internal velocity field can be reconstructed efficiently, which is useful for many purposes, e.g., calculating the wave forces and providing boundary condition for nesting with other small domain simulations. For verifications, the new model is used to simulate a fully nonlinear steady wave in deep water of wave steepness up to the breaking limit, and results are compared with Fenton's numerical solution. Good agreement is achieved indicating that the new model is accurate for reproducing the internal velocity field. In the future, the new model will be extended to simulate wave-structure interactions through coupling with other CFD-type approaches.
Human oceanic activities are confronted with significant threats posed by large ocean waves. The analysis of sea loads on ships, offshore platforms, and other marine installations relies on the input parameters derived from wave kinematics. Reliable predictions of the wave field and wave kinematics are crucial for obtaining accurate computations of wave loads. As a result, offshore and coastal engineering exhibit a continuous and strong interest in investigating the kinematics of steep ocean waves, particularly the so-called rogue waves. Currently, there is an increasing demand to comprehensively understand the entire process, starting from their sudden formation in open seas to their impacts on marine engineering applications. This can be achieved through the utilization of numerical simulations based on hydrodynamic models. Given the unpredictable nature of rogue waves, it is often required to employ phase-resolved simulations on large spatiotemporal scales. For this purpose, the Enhanced Spectral Boundary Integral (ESBI) model for three-dimensional large-scale phase-resolved ocean wave simulations has been proposed. This model is a pseudo-spectrum method based on the fully nonlinear potential flow (FNPF) theory, assuming an inviscid and irrotational fluid. It was initially introduced to solve the two-dimensional boundary value problem by estimating the horizontal derivative of the surface stream function in convolutions (Clamond & Grue, 2001). Later on Green's second theorem replaced Cauchy's residue theorem to generate the method to three dimensions and the surface normal velocity was calculated instead (Clamond et al., 2005; Clamond et al., 2007; Fructus et al. 2005; Fructus et al., 2007). The convolutions can be evaluated through applying Fast Fourier Transforms (FFTs) leading to an efficient numerical scheme. Over the past decade, the model has undergone further refinements (Wang & Ma, 2015; Wang et al., 2018), and a more efficient solver has recently been developed and extended to variable depth scenarios (Wang, 2023).
