• Energy Research

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.

A two-dimensional numerical study about the influence of a vertical distance between two ramps of an Overtopping Device Wave Energy Converter (OTD-WEC) integrated into a breakwater in the city of São José do Norte, Rio Grande do Sul, Brazil was analyzed. The main purpose was to evaluate the influence of the vertical distance between the two ramps (Hg) of OTD-WEC, on the average overtopping dimensionless flow () using the Constructal Design for the geometric evaluation defining: 1) degree of freedom, (Hg), and 2) constraints, horizontal distance between the ramps (Lg), ratio between the height and length of the ramps (H1/L1 and H2/L2), area as a function of the wave parameters (Awave), areas of the ramps (Ar,i), maximum ramp height (fixed as half of the significant wave height (HS/2) at the MWL) and area fractions of the ramps (φi). The equations of conservation of mass, momentum, and an equation for the transport of volumetric fraction were solved using the Finite Volume Method (FVM). The multiphase model Volume of Fluid (VOF) was applied for the air-water interaction. The results showed that, in general, lower values of the vertical distance between the ramps (Hg) led to higher values of the average overtopping dimensionless flow (). Moreover, the geometric evaluation of the degree of freedom Hg through the Constructal Design method proved to be an important tool because some configuration of the ramps of the overtopping device facilitated the flow of water to the reservoir of the device, and others made it difficult. The maximum value of the average overtopping dimensionless flow was max = 0.044, with a difference of 2.23% for the value obtained with empirical equation found in the literature, for the vertical distance equal to Hg = 0.10.

O dispositivo de galgamento é um conversor de energia das ondas em energia elétrica. Seu princípio de funcionamento consiste no galgamento de ondas do mar através de uma rampa, a água então é acumulada no reservatório do dispositivo escoando por uma turbina de baixa queda ligada a um gerador, convertendo a energia potencial da água em energia elétrica. O presente trabalho aborda a simulação numérica de um dispositivo de galgamento de ondas, anteriormente estudado na literatura. O principal objetivo foi avaliar a influência do emprego de diferentes parâmetros e métodos numéricos disponíveis no software FLUENT sobre o comportamento transiente do galgamento. Para todos os casos testados foram empregados os seguintes parâmetros e/ou métodos: discretização da pressão foi utilizado o método PRESTO, acoplamento pressão-velocidade foram utilizados os métodos PISO e SIMPLEC, reconstrução geométrica, Geo-Reconstruct e Modified HRIC, e por fim, os esquemas advectivos Upwind de primeira ordem, Upwind de segunda ordem, Upwind de terceira ordem e Power Law foram empregados. Os resultados mostraram que o comportamento da altura de superfície livre da onda em função do tempo foi o mesmo para os diferentes esquemas de advecção, acoplamento pressão-velocidade e reconstrução geométrica. Com relação ao galgamento foi observado que os esquemas Upwind de primeira ordem e Power Law podem ser empregados para a determinação da massa total de água que entra no reservatório. Entretanto, em comparação com esquemas de ordem superior (segunda e terceira ordens), o esquema Upwind apresentou um comportamento com maior amortecimento nos picos de vazão mássica instantânea. Palavras-chave - Dispositivo de galgamento, simulação numérica, esquemas de advecção.

The present work investigates the influence of rectangular deflectors on the performance of a Savonius turbine mounted in an L-shaped channel, which represents a geometry like that found in one oscillating water column (OWC) device. It also performs a geometric investigation of the entrance region of the channel. More precisely, it investigates the effect of the height/length ratio (H1/L1) of the entering region of the channel on the system performance for three different configurations: (1) without the use of deflectors, (2) with just one deflector upstream the turbine, and (3) with one deflector upstream and another downstream the turbine. The geometric investigation is performed based on the constructal design method, and the entering channel area (A1) is the problem constraint. The performance indicators are the mechanical power in the Savonius turbine and the available power in the device. For all cases, it is considered turbulent airflow in the domain, being solved by the unsteady Reynolds Averaged Navier–Stokes mass and momentum equations. The numerical solution was obtained with the finite-volume method using the Ansys FLUENT software (version 2021 R1). The k-ω shear stress transport turbulence closure model is used. The results demonstrated that the mechanical and available powers depend on the H1/L1 ratio, regardless of the usage of deflectors. For instance, differences of up to 16.35% in mechanical power and 7.25% in available power were observed between the best and worst performance configurations in the case without deflectors. The use of deflectors resulted in increases of two and three times in available and mechanical powers, respectively, when the cases with one and two deflectors are compared with those without deflectors. This demonstrates that the enclosed domain and the insertion of the deflectors can enhance the performance of the Savonius turbine.

In this work, a 2D numerical study was performed on the effect of the ramp geometry on the performance of an onshore overtopping device in real scale employing constructal design. More precisely, it evaluates the effect of ratio between height and length of the ramp (H 1/L 1) over the mass of water (m) entering the reservoir for two different depths (S = 5.0 m and 6.0 m). For all simulations, the ramp device area is maintained constant. A computational model based on the finite volume method and volume of fluid to tackle with the mixture of water/air was employed. The once maximized mass entering reservoir (m m) increases with S, as expected. However, the best geometries changed with the device depth (S), showing that there is no universal shape that maximizes the performance of the wave energy converter device. The submergence also presented a strong influence over the transient behavior of the mass flow rate of water entering the reservoir of the overtopping device.

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.