Iñigo Bidaguren

Breakwater-integrated Oscillating Water Column (BOWC) performance depends strongly on incident-wave frequency and Power Take-Off (PTO) aerodynamic damping, making experimental validation important for assessing CFD predictions. This study investigates the hydrodynamic and energetic performance of the Mutriku BOWC chamber and validates a Computational Fluid Dynamics (CFD) model against experimental measurements. An isolated 1:36 scale chamber was tested in a controlled wave flume under regular wave conditions. The experimental campaign varied wave period and PTO aerodynamic damping using orifice plates as passive loads. Experimental results showed higher Response Amplitude Operator (RAO) values at longer periods. For Capture Width Ratio (CWR), low-damping configurations with larger orifices (16 mm) improved performance at a specific wave condition (kh = 0.61) but reduced efficiency under other conditions. In contrast, intermediate damping (12 mm) maintained comparatively high CWR values over a broader range of wave conditions. The CFD simulations showed good agreement with experimental measurements, with Normalized Root Mean Square Error (NRMSE) values ranging from 4.19% to 11.31%. These results support the use of the CFD model as a complementary tool to experimental and operational studies at the Mutriku plant, providing a validated framework for assessing chamber hydrodynamics, pneumatic energy capture, and the effects of PTO aerodynamic damping.

This paper presents an extensive experimental study on the hydrodynamic behavior of vertical cylinders representative of the structural elements of offshore floating photovoltaic (OFPV) platforms under both wave and steady-current conditions. The objectives are to determine reliable hydrodynamic coefficients for Morison-type formulations and to analyze the wake effects between cylinders for modular floating configurations. Tests under regular waves are conducted in a 25 m long wave flume at the Energy Engineering Department of the Bilbao School of Engineering. The obtained inertia and drag coefficients follow the expected trends for a wide range of Keulegan–Carpenter (KC) numbers, aligning well with classical experimental studies. Steady-current experiments are conducted in the same flume using a towing tank method. Again, the obtained drag coefficients align well with previous studies. As for the wake provoked by the first cylinder on the second cylinder located downstream at one of four different distances, in the wave cases, the wake attenuation is minimal and rapid recovery of the flow is observed for a wide range of KC values, while in the steady-current cases, the wake is stronger and affects the forces acting on the second cylinder.

The Basque Energy Agency commissioned the Mutriku Wave Power Plant, using an Oscillating Water Column technology in 2011, and although the cumulative total power has been over 3 GW/h until 2023, the initial expectations of efficiency and LCoE have not been accomplished. This paper proposes a series of modifications to the breakwater and chamber geometry of the plant to increase energy production and efficiency. These proposed improvements were tested in experimental campaigns in the modular wave flume in the Energy Engineering Department at the University of the Basque Country, using a mock-up of the original installation. Some results also came from validated numerical simulations, showing that the response amplitude operator and the capture width ratio values were better than those in the original L-shaped power plant. The best configurations appear to be U-shaped and when harbor walls are used. In conclusion, this paper reports the proper configurations and localizations for new wave power plants that could be commercially competitive.

Time efficiency is a critical concern in Computational Fluid Dynamics (CFD) simulations of industrial applications. Despite the extensive research to improve the underlying numerical schemes to reduce the processing time, many CFD applications still need to improve on this issue. Reduced-Order Models (ROM) appeared as a promising alternative for significantly enhancing cost-effectiveness. The dimension of the initial problem is reduced significantly while keeping an acceptable level of accuracy. Proper Orthogonal Decomposition (POD), a data analysis technique, is widely used to construct a ROM to solve Euler and Navier-Stokes equations in CFD. Many aspects, however, need to be improved. In this paper, first, a general upper-bound error formula is derived, and second, a mesh-adaptivity based algorithm for snapshot locations in parameter space is provided (a sensitive step for POD-based ROM) in the context of Partial Differential Equations (PDE). The method’s efficiency is demonstrated through numerical tests by comparison to exact solutions and numerical results of a finite volume scheme on inviscid flow over a NACA0012.

Wave overtopping occurring in offshore wind renewable energy structures such as tension leg platforms (TLPs) or semi-submersible platforms is a phenomenon that is worth studying and preventing in order to extend the remaining useful life of the corresponding facilities. The behaviour of this phenomenon has been extensively reported for linear coastal defences like seawalls. However, no referenced study has treated the case of cylindrical structures typical of these applications to a similar extent. The aim of the present study is to define an empirical expression that portrays the relative overtopping rate over a vertical cylinder including a variety of bull-nose type mitigation structures to reduce the overtopping rate in the same fashion as for the linear structures characteristic of shoreline defences. Hydrodynamic interaction was studied by means of an experimentally validated numerical model applied to a non-impulsive regular wave regime and the results were compared with the case of a plain cylinder to evaluate the expected improvement in the overtopping performance. Four different types of parapets were added to the crest of the base cylinder, with different parapet height and horizontal extension, to see the influence of the geometry on the mitigation efficiency. Computational results confirmed the effectivity of the proposed solution in the overtopping reduction, though the singularity of each parapet geometry did not lead to an outstanding difference between the analysed options. Consequently, the resulting overtopping decrease in all the proposed geometries could be modelled by a unique specific Weibull-type function of the relative freeboard, which governed the phenomenon, showing a net reduction in comparison with the cylinder without the geometric modifications. In addition, the relationship between the reduced relative overtopping rate and the mean flow thickness over the vertical cylinder crest was studied as an alternative methodology to assess the potential damage caused by overtopping in real structures without complex volumetric measurements. The collection of computational results was fitted to a useful function, allowing for the definition of the overtopping discharge once the mean flow thickness was known.