• Energy Research

The ocean wave energy conversion into electricity has been increasingly researched in the last years. There are several proposed converters, among them the Oscillating Water Column (OWC) device has been widely studied. The present paper presents a two-dimensional numerical investigation about the fluid dynamics behavior of an OWC Wave Energy Converter (WEC) into electrical energy. The main goal of this work was to numerically analyze the optimized geometric shape obtained in previous work under incident waves with different heights. To do so, the OWC geometric shape was kept constant while the incident wave height was varied. For the numerical solution it was used the Computational Fluid Dynamic (CFD) commercial code FLUENT®, based on the Finite Volume Method (FVM). The multiphasic Volume of Fluid (VOF) model was applied to tackle with the water-air interaction. The computational domain is represented by the OWC device coupled with the wave tank. This work allowed to check the influence of the incident wave height on the hydropneumatic power and the amplification factor of the OWC converter. It was possible to identify that the amplification factor increases as the wave period increases, thereby improving the OWC performance. It is worth to highlight that in the real phenomenon the incident waves on the OWC device have periods, lengths and height variables.

The present study aims to evaluate the difference in the fluid-dynamic behavior of an overtopping wave energy converter under the incidence of irregular waves based on a realistic sea state when compared to the incidence of regular waves, representative of this sea state. Thus, the sea data of three regions from the Rio Grande do Sul coast, Brazil, were considered. Fluent software was employed for the computational modeling, which is based on the finite volume method (FVM). The numerical generation of waves occurred through the imposition of the velocity boundary conditions using transient discrete values through the WaveMIMO methodology. The volume of fluid (VOF) multiphase model was applied to treat the water–air interaction. The results for the water amount accumulated in the device reservoir showed that the fluid-dynamic behavior of the overtopping converter has significant differences when comparing the two proposed approaches. Differences up to 240% were found for the water mass accumulated in the overtopping device reservoir, showing evidence that the results can be overestimated when the overtopping device is analyzed under the incidence of the representative regular waves. Furthermore, for all studied cases, it was possible to approximate the water volume accumulated over time in the overtopping reservoir through a first-degree polynomial function.

This research conducts a numerical study of a wave energy converter (WEC) device with five coupled hydropneumatic chambers, operating based on the principle of an oscillating water column (OWC). A turbine was not included, only considering the tube without it. The computational domain was defined by a wave channel housing an OWC device subjected to regular incident waves. The central objective was to assess the impact of chamber geometry on maximizing the total hydropneumatic power in energy conversion. The numerical simulations consider the pressure, mass flow rate, and total hydropneumatic power, with the latter being the performance indicator. To determine the geometries to be analyzed, the Constructal Design method was employed in conjunction with the exhaustive search optimization method to maximize the performance indicator. The degrees of freedom defined were the ratios between the height (Hn) and the length (Ln) of the hydropneumatic chambers (Hn/Ln, where n varies from one to five). Based on the results of the mass flow rate and pressure, their influence on power was evaluated. It was observed that the influence of the degrees of freedom on the pressure difference, mass flow rate, and hydrodynamic power was quite similar, displaying an increase for low ratios of Hn/Ln up to a maximum magnitude and followed by a decrease in magnitude. The best performance was achieved for the geometric configuration with Hn/Ln = 0.2613 (Hn = 5.0625 m and Ln = 15.8219 m), representing an improvement of 98.6% compared to the worst case analyzed.

Abstract Current work aims to study the geometry of an overtopping wave energy converter in real scale using Constructal Design. Problem studied here is submitted to two constraints (areas of wave tank and overtopping ramp) and two degrees of freedom: ratio between the height and length of ramp (H1/L1) (or ramp slope, β) and distance between the bottom of wave tank and the device (S). The effect of H1/L1 and S over dimensionless device available power (Pd) is evaluated for three different ramp area fractions (ϕ) and two different monochromatic waves. Conservation equations of mass, momentum and one equation for the transport of water volume fraction are solved with the finite volume method. To tackle with water-air mixture, multiphase model Volume of Fluid is used. Results showed the applicability of Constructal Design for improvement of device performance. For fixed magnitudes of S, the highest magnitudes of Pd are achieved for the lowest possible ratio of H1/L1. For smaller construction areas of the ramp, intermediate magnitudes of S led to the highest magnitudes of Pd, i.e., the sinking of device does not led necessarily to the best performance. Moreover, optimal shapes are not universal (the same) for the two wave conditions studied.

A numerical study was performed in the present work about an Overtopping Device Wave Energy Converter (OTD-WEC) with one and two ramps incorporated in a real breakwater. The Constructal Design method was applied to evaluate the effects on the average dimensionless overtopping flow of the degrees of freedom of the device with one and two ramps. In addition, a comparison was carried out among the different geometry configurations of the OTD-WEC to determine which one presents the best hydrodynamic performance. The work used the JONSWAP spectrum and the multiphase Volume of Fluid model. It also solved the conservation equations for mass, momentum, and an equation for the transport of the volume fraction using the Finite Volume Method. Results showed that a device with a two-ramps configuration presented an average dimensionless overtopping flow 6.48% higher than those obtained for the one ramp. Present results obtained using Constructal Design theoretical recommendations about the influence of a complex configuration with four degrees of freedom over the performance of an OTD-WEC integrated into the east breakwater of the city of São José do Norte, State of Rio Grande do Sul (RS), Brazil.

This study concentrates on numerically evaluating the behavior of a floating body with a box format. Although research on floating objects has been conducted, the numerical modeling of Wave Energy Converter (WEC) devices, considering the effects of fluctuations, remains underexplored. Therefore, this research intends to facilitate the analysis of floating devices. First, the experimental data served as a benchmark for evaluating the motion paths of the floating box’s centroid. Second, the effects of various wave periods and heights on the floating body’s movement were analyzed. The Volume of Fluid (VOF) multiphase model was applied to simulate the interactions between phases. The computational model involved solving governing equations of mass conservation, volumetric fraction transport, and momentum, employing the Finite Volume Method (FVM). The validation demonstrated that the Normalized Root Mean Square Error (NRMSE) for the x/h ratio was 3.3% for a wave height of 0.04 m and 4.4% for a wave height of 0.1 m. Moreover, the NRMSE for the z-coordinate to the depth of water (z/h) was higher, at 5% for a wave height of 0.04 m and 5.8% for a wave height of 0.1 m. The overall NRMSE remained within acceptable ranges, indicating the reliability of the numerical solutions. Additionally, the analysis of horizontal and vertical velocities at different wave periods and heights showed that for H = 0.04 m, the wave periods had a minimal impact on the amplitude, but the oscillation frequency varied. At H = 0.1 m, both velocities exhibited significantly larger amplitudes, especially for T = 1.2 s and T = 2.0 s, indicating stronger motion with higher wave heights.

In this work, we conducted a numerical analysis of an oscillating water column (OWC) wave energy converter (WEC) device. The main objective of this research was to conduct a geometric evaluation of the device by defining an optimal configuration that maximized its available hydrodynamic power while employing realistic sea data. To achieve this objective, the WaveMIMO methodology was used. This is characterized by the conversion of realistic sea data into time series of the free surface elevation. These time series were processed and transformed into water velocity components, enabling transient velocity data to be used as boundary conditions for the generation of numerical irregular waves in the Fluent 2019 R2 software. Regular waves representative of the sea data were also generated in order to evaluate the hydrodynamic performance of the device in comparison to the realistic irregular waves. For the geometric analysis, the constructal design method was utilized. The hydropneumatic chamber volume and the total volume of the device were adopted as geometric constraints and remained constant. Three degrees of freedom (DOF) were used for this study: H1/L is the ratio between the height and length of the hydropneumatic chamber, whose values were varied, and H2/l (ratio between height and length of the turbine duct) and H3 (submergence depth of hydropneumatic chamber) were kept constant. The best performance was observed for the device geometry with H1/L= 0.1985, which presented an available hydropneumatic power Phyd of 29.63 W. This value was 4.34 times higher than the power generated by the worst geometry performance, which was 6.83 W, obtained with an H1/L value of 2.2789, and 2.49 times higher than the power obtained by the device with the same dimensions as those from the one on Pico island, which was 11.89 W. When the optimal geometry was subjected to regular waves, a Phyd of 30.50 W was encountered.

The present database shows experimental and numerical results for instantaneous laboratory wave flow and discharge of water in a reservoir of a ramp with a reservoir, obtaining recommendations about the influence of the design of the ramp on the performance of an overtopping wave energy conversion device. The geometrical investigation is based on the Constructal Design method. Results for the instantaneous water surface, instantaneous water accumulated in the device reservoir for different height/length ratios of the ramp in the range (0.39 <= H1/L1 <= 0.80), and for water depth h1 = 0.392 m, are obtained. Results indicated that the smaller ratios of H1/L1 conducted to the higher magnitudes of water accumulated in the reservoir. Moreover, the experimental database allowed a validation of a computational model based on the finite volume method for reproduction of instantaneous wave behavior and overtopping discharges.

Studies regarding renewable energy sources have gained attention over recent years. One example is wave energy converters, which harvest energy from sea waves using different operational principles such as oscillating water columns, oscillating bodies, and overtopping devices. In the present paper, a numerical study is carried out, and a geometrical investigation of a full-scale overtopping device with a coupled structure mounted on the seabed is performed using the Constructal Design method. The main purpose is to investigate the influence of the design over the available power of the device. The areas of the overtopping ramp (Ar) and the trapezoidal seabed structure (At) are the problem constraints. Two degrees of freedom are studied, the ratio between the height and length of the ramp (H3/L3) and the ratio between the upper and lower basis of the trapezoidal obstacle (L1/L2). The device submersion is kept constant (H1 = 3.5 m). The equations of continuity, momentum, and the transport of volume fraction are solved with the Finite Volume Method, while the water–air mixture is treated with the multiphase model Volume of Fluid. Results showed that the ratio H3/L3 presented a higher sensibility than the ratio L1/L2 over the accumulated water in the reservoir. Despite that, the association of a structure coupled to the ramp of an overtopping device improved the performance of the converter by 30% compared to a conventional condition without the structure.