Shoreface-connected sand ridges (sfcr) and tidal sand ridges (tsr) are large-scale rhythmic bedforms found on many sandy continental shelves. Previous studies have not addressed the combined impact of waves, wind and tides on the evolution of these ridges. Furthermore, they were unable to simulate sfcr with wave-topography feedbacks. The objectives of this study are to 1) simulate sfcr in the presence of these feedbacks; and 2) to quantify the combined impact of waves, wind and tide on the evolution of shelf ridges. To this end, a morphodynamic shelf model (Delft3D + SWAN) is used in a setting representative of the Belgian shelf. The model successfully simulates sfcr in the presence of wave-topography feedbacks, producing ridges with characteristics consistent with observations. Regarding 2), a mix of two types of ridges develops on the shelf, which resemble the sfcr and tsr observed on the Belgian shelf. However, a notable difference is that observed tsr are located further offshore than modelled ridges.
Collision avoidance is integrated into a Model Predictive Control (MPC) framework by incorporating track constraints into the MPC's objective function. These constraints are governed by COLREGs to make rule-compliant decisions and actions for resolving track conflicts. The predictive model employed in MPC also allows for more accurate collision risk assessments, with safety distances calculated at each prediction step to avoid ship domain conflicts. Collision scenarios are classified into 16 categories (4 by 4 matrix), considering both the relative bearings of the own ship and the target ship, to ensure consistency in the decisions made by the involved ships. A series of experimental model tests were conducted at the Towing Tank for Manoeuvres in Confined Water, Antwerp, Belgium to validate the proposed controller. Initially, scenarios involving collision avoidance with static obstacles in combination with various ship speeds were examined, with varying safety margin parameters to impose different safety requirements. The obstacles were set both physical and virtual to investigate the influence of ship-obstacle interactions. Further tests involved a dynamic obstacle, creating overtaking and meeting scenarios with different speed combinations for the own ship and the dynamic obstacle. Simulations were performed to evaluate scenarios that are impractical to replicate in the towing tank, thereby complementing experimental testing. The test results confirmed that collision avoidance can be successfully accomplished within a confined environment.
ABSTRACT In this paper, a Reynolds-averaged Navier–Stokes (RANS) equations solver, interFoam of OpenFOAM®, is validated for wave interactions with a dike, including a promenade and vertical wall, on a shallow foreshore. Such a coastal defence system is composed of both an impermeable dike and a beach in front of it, forming the shallow foreshore depth at the dike toe. This case necessitates the simulation of several processes simultaneously: wave propagation, wave breaking over the beach slope, and wave interactions with the sea dike, consisting of wave overtopping, bore interactions on the promenade, and bore impacts on the dike-mounted vertical wall at the end of the promenade (storm wall or building). The validation is done using rare large-scale experimental data. Model performance statistics are employed to quantify the ability of the numerical model to reproduce the experimental data. In the evaluation method, a repeated test is used to estimate the experimental uncertainty. The solver interFoam is shown to generally have a very good model performance rating.
Tidal channel will be affected by the intrusion of seawater, so the current and water depth in the channel will change at every moment. These changes are critical to the hydrodynamic characteristics of water intakes in tidal rivers. This paper establishes a 3D model and validates it through laboratory models, then analyzes the influences of dynamic change of flow velocity and water depth, the amplitude changes of velocity and water depth on the secondary flow in the water withdrawal process. With the increase of the main flow velocity and the decrease of the water depth, diversion width at the water intake decreases, the peak velocity increases, and the intensity of the secondary flow also increases. With the increase of the velocity of the main channel and the rate of change in water depth, the lag time of the velocity change at the water intake is also longer, and the peak velocity will be greater than the velocity of the constant flow. The influence of the water depth change is greater than that of the main channel velocity change. Combining these four factors, more sand may be washed into the inlet channel under conditions of high flow and low water depth.
Ongoing climate change is a significant threat to coastal communities. To understand potential risks during extreme storm events, detailed post-overtopping processes are investigated using DualSPHysics and SWASH with a newly developed approach. It is a calibrated-based wave generation: a target incident wave is first obtained from the validated SWASH model, and DualSPHysics creates the target incident wave by adjusting the offshore wave and bathymetry conditions. This one-way coupling process makes the DualSPHysics computation efficient enough to apply 3D simulation. With a vertical wall at the end of a room located at the end of the promenade in a mild and shallow foreshore, the present model shows a good correspondence on the wave force with the literature. After confirming the efficiency and accuracy of the present model, the 3D simulation with furniture inside the room was conducted and visualized with the state-of-the-art visualization technique. Based on the visualization, the potential risks during the extreme storm event are further discussed in this paper. The present work shows a further capability of DualSPHysics to deal with wave–object–structure interaction based on the latest developments in an efficient way. The developed model can be further used to understand the potential risks of ongoing climate change.
