Antonio Moñino

SCALE EFFECTS IN RUBBLE MOUND BREAKWATERS CONSIDERING WAVE ENERGY BALANCE

Scale effects in rubble mound breakwaters physical modeling are analyzed through the results of new laboratory tests. The Reynolds number disparity between model and prototype becomes crucial in the wave flow through the pores of the mound breakwater, affecting the flow dissipation inside the mound and consequently the flow reflection and transmission. Several tests have been carried out on a rectangular porous structure and a new approach has been used to analyze the data, considering the wave height inside the porous media as a function of two terms. In this paper one of those terms is analyzed. The results show that, similarly to the Darcy-Weissbach diagram, a friction diagram for the wave height envelope decay inside the porous media can be obtained as a function of the incident wave height, nominal diameter of the grains and wave number. The most important conclusion is that, due to the dimensionless variables involved in the diagram, scaling a model with it does not imply any scale effects.

Effects of Seabed Morphology on Oscillating Water Column Wave Energy Converter Performance

This chapter presents a numerical model to analyse the effects of changes in the bedforms morphology on Oscillating Water Column (OWC) wave energy devices. The model was developed in FLUENT\(^{\circledR }\) and based on the Actuator Disk Model theory to simulate the turbine performance. The seabed forms were reproduced with the morphodynamic model XBeach-G for a series of characteristic sea states in Playa Granada (southern Spain). These bedforms were used as input bed geometries in FLUENT\(^{\circledR }\) and compared with a hypothetical flat seabed to analyse the effects of changes in bed level on the OWC performance. Results of the simulated sea states reveal the influence of the seabed morphology in the power take–off performance, affecting the relationship between pressure drop and air flow rate through the turbine. Energy dissipation was found to be directly dependent on the bedforms unit volume. This lead to lower mean efficiencies for the cases with evolved morphologies (up to \(15\%\)) compared to those obtained for the hypothetical flat cases (\(19\%\)). The effects of seabed formations on the power take–off performance presented in this chapter can be of interest in planning control strategies for OWC devices.

Thermodynamics of an Oscillating Water Column Containing Real Gas

Oscillating Water Column (OWC) devices are usually modelled as simple systems containing ideal, dry air. However, high humidity levels are likely to occur in a prototype device open to the sea, particularly in warm climates such as prevail in the lower latitudes. In this chapter, a real gas model is implemented to take into account humidity variations inside an OWC chamber. Using a modified adiabatic index, theoretical expressions are derived for the thermodynamic state variables including enthalpy, entropy and specific heat. The model is validated against experimental data, and shown to provide better agreement than obtained using the ideal gas assumption. By calculating real air flow in an OWC it is shown that the mechanical efficiency reduces and the flow phase alters with respect to the ideal gas case. Accurate prediction of efficiency is essential for the optimal design and management of OWC wave energy converters.

A Real Gas Model for Oscillating Water Column Performance

Oscillating Water Column (OWC) are devices for wave energy extraction equipped with turbines for energy conversion. The purpose of the present chapter is to study the thermodynamic of a real gas flow through the turbine and its differences with respect to the ideal gas hypothesis, with the final goal to be applied to OWC systems. The effect of moisture in the air chamber of the OWC entails variations on the atmospheric conditions near the turbine, modifying its performance and efficiency. In this chapter the influence of humid air in the performance of the turbine is studied. Experimental work is carried out and a real gas model is asserted, in order to take a first approach to quantify the extent of influence of the air-water vapour mixture in the turbine performance. The application of a real gas model and the experimental study confirmed the deviations of the turbine performance from the expected values depending on flow rate, moisture and temperature.

The Role of Wave Energy Converter Farms in Coastal Protection

Many worldwide coasts are under erosion with climate projections indicating that damages will rise in future decades. Specifically, deltaic coasts are highly vulnerable systems due to their low-lying characteristics. This chapter investigates the role of wave energy converter (WEC) farms on the protection of an eroding gravel-dominated deltaic coast (Guadalfeo, southern Spain). Eight scenarios with different alongshore locations of the wave farm were defined and results were compared with the present (no farm) configuration of the coast. Assuming that storm conditions drive the main destruction to the coast, we analysed the impact of the most energetic storm conditions and quantified the effects of the location of the farm. Significant wave heights in the lee of the farm were calculated by means of a calibrated wave propagation model (Delft3D-Wave); whereas wave run-up and morphological changes in eight beach profiles were quantified by means of a calibrated morphodynamic model (XBeach-G). The farm induces average reductions in significant wave heights at 10 m water depth and wave run-up on the coast down to 18.3% and 10.6%, respectively, in the stretch of beach most affected by erosion problems (Playa Granada). Furthermore, the erosion of the beach reduces by 44.5% in Playa Granada and 23.3% in the entire deltaic coast. Combining these results with previous works at the study site allowed selecting the best alternative of wave farm location based not only on coastal protection but also on energetic performance criteria. This chapter, whose methodology is feasibly extensible to other coasts worldwide, provides insights into the role of the alongshore location of WEC farms on wave propagation, run-up and morphological storm response of deltaic coasts.

Steady flow regime for free overfall spillways. Influence of the ascending

This paper presents a study on the influence of the upstream quadrant of the spillway crest section, designed with equal geometry as that of the lower surface profile of a free flow over a sharp crested weir, on the discharge characteristics of a free overfall spillway. Geometrical deviations of the upstream quadrant from the standard design criteria as proposed by the U.S. Bureau of Reclamation, lead to variations in the flow discharge efficiency and on the upstream free surface elevations, i.e. on the reservoir free surface level. Starting with an analytical description of the weir problem, governing equations are derived, yielding the identification of three weir operation regimes, say, deep, intermediate or shallow weir; the first of them is the condition standing for many dam spillways. Experiments on the spillway crest profile under deep-weir operation conditions have been conducted, testing an evolution sequence of upstream quadrants ranging among simple geometrical shapes, with the standard design profile as one of them. As a result, a new upstream quadrant consisting of a 1:1 slope chamfer is proposed, since the hydraulic performance is found to be equal to or slightly better than the standard crest profile. An experimental program has also been carried out in order to determine safety limits regarding negative pressures on the spillway surface. From the standpoint of design, the suggested upstream geometry is easier to define, and cost-effective in terms of construction. A wider range of experimental set-ups, referred to model scales and flow conditions, should be conducted with the presented results as a starting point, in order to verify the adequate performance of the proposed design.