Constructal Design of a Two Ramps Overtopping Wave Energy Converter Integrated into a Breakwater: Effect of the Vertical Distance between the Ramps over its Performance

Abstract

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.