Urko Izquierdo

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.

With the growing concern for environmental issues, progress has been made recently in the promotion of new technologies in the field of renewable energies. This article studies a new wave energy converter that uses the heel generated by the mechanical energy of the waves to transform it into electrical energy by means of a mobile mass, coupled to an electrical generator, which moves from port to starboard and vice versa. The advantage of this converter is that it is capable of incorporating the energy conversion unit inside the converter, as well as allowing the placement of a set of several devices within the same collector, and of modifying the roll period to adapt it to the wave conditions of the installation area. To do this, on one side, two models of wave energy converters were compared by varying the beam to check whether it is better to have a smaller or larger beam by carrying out roll decay tests and simulations for different waves. Moreover, the maximum power available in the moving mass of the power take-off was calculated theoretically for two situations of different transverse metacentric height to check which is more efficient, reaching 2 MW for some waves.

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.

The effectiveness and sustainability of water utilities depend on minimizing water losses, with apparent losses due to metering inaccuracies having the greatest impact on revenue, billing accuracy, utility management, and resource planning. Ball valves are commonly used upstream and downstream of water meters, and in modern buildings, water meter rooms house meters arranged in a battery arrangement. Each meter is equipped with an upstream valve to shut off mains water and a downstream valve to prevent draining during replacement. Consumers often partially close the upstream valve to conserve water, particularly in areas with sufficient pressure. This study examines the effects of valve positioning and closure percentage on the behaviour of ultrasonic water meters, which are increasingly popular in the domestic market. Analysing meter behaviour under different closure percentages reveals that a 75% valve closure stops water volume registration, resulting in significant errors. These findings underscore the importance of carefully considering valve positioning and closure percentage to ensure accurate measurements, precise billing, revenue generation, resource optimization, and customer satisfaction.

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.

In recent years, the interest in capturing wave energy has increased notably due to the immense potential available and the need to deepen and diversify the use of renewable energies. Oscillating Water Column (OWC) technology is one of the most technologically developed, with the world's first grid-connected demonstration plant located in Mutriku. However, the efficiency of this technology is still insufficient for its consolidation in the energy mix. Therefore, the present work presents an advance in the increase in the extraction of energy from the incident waves through the installation of a frontal ramp that directs the wave flow towards the vertical chamber of the oscillating column. The improvement achieved will be determined by means of a CFD (Computational Fluid Dynamics) 2D scaled model, which represents the interaction of the structure with different incident wave states. Different geometric options of the ramp are analyzed in comparison with the usual vertical wall option where the phenomenon of pure reflection occurs. This work aims to contribute to improving the efficiency of OWC technology, favoring the use of wave energy as a renewable energy source. Keywords: Oscillating Water Column (OWC), wave energy converter (WEC), Response Amplitude Operator (RAO), Computational Fluid Dynamics (CFD), wave energy

The implementation of hydrogen as a fuel in industrial applications is an upward trend, and poses a challenge for the design of furnace burners. This article aims to advance in the knowledge of hydrogen combustion, through numerical simulation using SIEMENS STAR-CCM+ code. Several simulations have been carried out with the geometry of a 2.5 MW burner of the current SIDENOR furnace. The fuel burning there, is natural gas. Using the same geometry and the same mesh, a comparison is made between current temperatures and those that would arise when burning hydrogen, as well as mass fractions of other elements such as NOx. Maintaining the power of 2.5 MW and taking into account the lower heating value of methane and hydrogen, the inlet boundary conditions are calculated for the different fuel compositions. In this way it can be seen, qualitatively, the amount of hydrogen needed to meet the necessary temperatures in the billets, without excessive NOx production. Key Words: Hydrogen, burners, Computational Fluid Dynamics, NOx