A fully nonlinear wave interaction with a fixed surface piercing body is studied using a two-dimensional numerical wave tank (NWT) based on potential flow theory. Nonlinear waves are modeled using a mixed Eulerian and Lagrangian (MEL) technique. In this framework, the boundary value problem governing water wave mechanics is solved in the Eulerian frame of reference using a higher-order boundary element method (HOBEM) to calculate free surface velocity components, which are then used to solve the fully nonlinear free surface equations in the Lagrangian frame of reference. The updated free surface position and velocity potential are obtained because of Lagrangian particle tracking. Diffraction forces and moments are calculated over the body using an acceleration potential method with a mode decomposition technique. The ability to model wave propagation in the presence of the following current and opposing current is tested and validated. Wave body interaction in uniform current is carried out for different current speeds and depth-to-draft ratios in regular waves. This work also investigates the effect of current and varying depth on the higher harmonic component of wave forces and moments.
In recent years, it has become increasingly necessary to understand the effect of operating conditions on the response of ocean structures such as floating platforms, ships, FPSOs, fixed structures, etc. When referring to operating conditions it is generally understood that it refers to the sea state, that being the wave height and period. Various researchers have carried out nonlinear wave modelling to study the effect of operating conditions on the behaviour of ocean structures.
Longuet-Higgins & Cokelet (1976)) pioneered the fully nonlinear potential flow model with their mixed Eulerian and Lagrangian techniques. Cointe (1990) later adopted the scheme and laid the foundation for a modern numerical wave tank with features that include an inlet, an artificial damping scheme at the outlet, numerical treatments at the corners, and so on. In the following years MEL found many useful applications in modelling overturning waves (Grilli et al., 2001), wave-current interactions (Ryu et al., 2003), wave-structure interactions (Koo & Kim, 2004, 2007b; Tanizawa et al., 1999) etc. Out of these applications, numerical modelling of the combined effect of waves and uniform current has been modelled before in the frequency domain in the works of Zhao & Faltinsen (1988). The linearized time domain models, such as Isaacson & Cheung (1993) and could not simulate the wave run-up at the vicinity of the body accurately under the assumption of linearization, especially when the current speed is increased, Ferrant (2001). Ryu et al. (2003) implemented wave current modelling using a nonlinear potential flow-based numerical wave tank and validated their results with a multilayer Boussinesq model. Subsequently, Koo & Kim (2007) implemented wave current interaction for fixed and floating bodies using a potential flow-based nonlinear numerical wave tank. In this article, we focus on the numerical modeling of a single surface-piercing barge-like structure in two dimensions. A fully nonlinear potential flow-based two-dimensional numerical wave tank is developed to model wave and fixed body interaction in the presence and absence of uniform current. The mixed Eulerian and Lagrangian (MEL) technique is adopted in the developed numerical wave tank code based on the higher-order boundary element method (HOBEM). The capability to model water waves and wave propagation in the presence of uniform current is tested and validated. A fixed surface piercing barge is modelled, and the numerical wave tank is used to model the regular wave-body interaction. Forces and moment are calculated using an acceleration potential method and validated with the existing results in the literature.