Monopiles are commonly adopted in marine structures and subject to combined loading from waves and currents. The nature of superposition of wave and current loads needs to be known during the design stage. In the present paper, combined hydrodynamic loading induced by nonlinear waves and uniform currents on a cylinder is experimentally investigated. The current is represented by towing the cylinder along the flume. By this, nonlinear wave–current interactions are excluded physically, but the loading of a proportional current following or opposing a wave group is captured and analyzed. It is argued that towing makes provision for analyzing the nature of superposition of wave and current loads using Morison theory (which is not applicable to true combined wave–current fields) and also facilitates experimentation of a wide range of nonlinear wave and uniform current loading combinations onto the structure. Accordingly, regular, steep non-breaking and breaking focused waves interacting with the cylinder towed along and in opposition to the wave-field at different speeds have been investigated. The non-breaking wave–structure interactions have been analyzed within the framework of Morison theory using Fully Nonlinear Potential Theory (FNPT) based kinematics. Breaking wave–cylinder interactions have been analyzed through a spectral approach. The experiments demonstrate that wave and locally-acting current loads on the structure can be linearly superimposed, irrespective of the nature of waves and towing speed. Hence, provided wave–current interactions are excluded, steep breaking wave and uniform current loads can be linearly superimposed, despite focused wave generation itself being inherently nonlinear.

In this paper, the comparative study carried out for focused wave interaction with a moving cylinder in ISOPE-2020 is reported. The fixed cylinder cases are reported in the companion paper as Part A (Sriram, Agarwal, Yan et al., 2021). The paper discusses qualitative and quantitative comparison between four different numerical solvers that participated in this comparative study. This is a challenging problem, as the cylinder moves over 40 m and interacts with the focusing waves. The performance of various solvers is compared for two different moving cylinder speeds. Both weakly coupled models and full Navier–Stokes (NS) solvers with different strategies for modeling the cylinder motion were adopted by the participants. In particular, different methods available for numerically simulating the forward speed problem emerge from this paper. The qualitative comparison based on the wave probe and pressure probe time histories between laminar and turbulent solvers is presented. Furthermore, the quantitative error analysis for individual solvers shows deviations up to 30% for moving wave probes and 50% for pressure time history. The reliability of each method is discussed based on all the wave probe and pressure probe discrepancies against experiments. The deviations for higher speed shown by all solvers indicate that further improvements in the modeling capabilities are required.

In this paper, a new set of experiments on the focused wave (using the second-order wavemaker theory) and current interactions with cylinders is being carried out. To represent a uniform current in laboratory, a cylinder is towed with a velocity opposite to the wave propagation directions. This paper discusses the experimental setup and test cases that were released for the comparative study at the ISOPE-2020 meeting. To obtain good correlation with different runs, the repeatability of the experiments is confirmed by comparing the surface elevation measurements at the fixed wave gauge location near the wave paddle, and an uncertainty analysis was carried out. The details on different test cases with varying frequency bandwidths of the focusing waves, speeds of the cylinder, and the locations of focusing are reported in this paper. Furthermore, a comparison of the dynamic pressure on the cylinder is reported between experiments with focusing waves with but without the towing condition. The present experimental campaign can be used as a validation case for state-of-theart numerical models.

In this paper, a new set of experiments on the focused wave (using the 2nd order wavemaker theory) and current interactions with cylinder is being carried out. In order to represent a uniform current in laboratory, cylinder is towed with a velocity opposite to the wave propagation directions. This paper discusses about the experimental setup and test cases that was released for the comparative study in the ISOPE 2020. In order to obtain good correlation with different runs, the repeatability of the experiments is confirmed by comparing the surface elevation measurements at the fixed wave gauge location near the wave paddle and uncertainty analysis was carried out. Different test cases with varying frequency bandwidth of the focusing waves, speed of the cylinder and the locations of focusing are investigated and will be reported in this paper. Further, a comparison for the dynamic pressure on cylinder is reported between experiments with wave and wave with uniform current.

Over recent years, many coastal engineering projects have employed the use of soft solutions as these are generally less environmentally damaging than hard solutions. However, in some cases, local conditions hinder the use of soft solutions, meaning that hard solutions have to be adopted or, sometimes, a combination of hard and soft measures is seen as optimal. This research reviews the use of hard coastal structures on the foreshore (groynes, breakwaters and jetties) and onshore (seawalls and dikes). The purpose, functioning and local conditions for which these structures are most suitable are outlined. A description is provided on the negative effects that these structures may have on morphological, hydrodynamic and ecological conditions. To reduce or mitigate these negative impacts, or to create new ecosystem services, the following nature-based adaptations are proposed and discussed: (1) applying soft solutions complementary to hard solutions, (2) mitigating morphological and hydrodynamic changes and (3) ecologically enhancing hard coastal structures. The selection and also the success of these potential adaptations are highly dependent on local conditions, such as hydrodynamic forcing, spatial requirements and socioeconomic factors. The overview provided in this paper aims to offer an interdisciplinary understanding, by giving general guidance on which type of solution is suitable for given characteristics, taking into consideration all aspects that are key for environmentally sensitive coastal designs. Overall, this study aims to provide guidance at the interdisciplinary design stage of nature-based coastal defence structures.