The present study investigates three-dimensional gap resonance between two fixed side-by-side barges under combined wave and uniform current excitation using a fully nonlinear numerical wave tank based on the Navier–Stokes equations. It examines how currents aligned with regular waves affect the gap response under head and beam seas. In beam seas, the free surface in the gap primarily exhibits a modal-type response in the form of a standing wave. The maximum gap response, consistently occurring at the midpoint of the gap, increases gradually with the current speed. Conversely, in head seas, the maximum response decreases slightly with increasing current speed, and the occurring location shifts downstream. Moreover, resonant free-surface responses along the gap in head seas manifest as propagating waves rather than modal-type standing waves, consisting of a wider spectrum of wave components around the resonant ones and traveling faster than the incident waves regardless of current speed. The wavelengths of those resonant waves tend to increase with increasing current speed. Additionally, the presence of current significantly enlarges the transverse first-harmonic and mean-drift wave forces on the barges under beam-sea conditions. The study highlights the necessity of considering current effects on three-dimensional gap resonances in marine operations at coastal and offshore locations.
Accurate prediction of wave transformation is key in the design of coastal and nearshore structures which typically depends on numerical models. Turbulent and rotational effects call for the use of Computational Fluid Dynamics (CFD) solvers of which a large range of formulations including free surface treatments exists. Physical wave flume tests of wave propagation over a submerged bar with various levels of nonlinearity, regularity, and wave-breaking, dedicated to numerical model benchmarking or validation, were carried out in the Ocean and Coastal Engineering Laboratory of Aalborg University. Three fundamentally different CFD models each widespread within their category are benchmarked against the experimental data. The CFD models are based on (i) the Volume of Fluid (VoF) based interFoam solver of OpenFOAM, (ii) the sigma-transformation solver of MIKE 3 Waves Model FM, and (iii) the weakly compressible delta-SPH solver of DualSPHysics. Accuracy of the numerical models is assessed from surface elevation time series, evaluation metrics (averaged errors on surface elevations, amplitudes, phases, and wave set-up), and spectral analyses to calculate the amplitude and phase contents of primary and higher-order components along the wave flume. Applicability is assessed from computational costs and ease-of-use factors such as the effort to configure the numerical models and achieve convergence. In general, the numerical models have high correlation to the physical tests and are as such suitable to model complex wave transformation with an accuracy sufficient for most coastal engineering applications. The VoF model performs more accurately under the turbulent conditions of breaking waves, increasing its relative accuracy in the prediction of downwave surface elevation. The sigma transformation model has simulation times one to two orders of magnitude lower than those of the VoF and SPH models.