Defect and Diffusion Forum Vol. 396

Abstract: Wave energy studies have increased by a large amount in the last years. Basically, the studies are divides either at describing the wave characteristics of the study region, either to develop and optimize wave energy converters (WEC’s). This study aims to characterize in part the wave potential of the brazilian coast, and after that, calculate how much energy would be generate by a point-absorber type WEC in a set of different locations. It was found that Rio Grande do Sul alongside Santa Catarina state presented the higher potentials amongst all the brazlian coast. Mean while, at Rio Grande do Norte state, the variability of the waves were lower when compared to the south region of Brazil. This study aims to serve as indicator to interest regions with wave power capabilities in the alongside the brazilian shore.

Abstract: This paper presents the application of the OpenFOAM^® software package, using the IHFoam/OlaFlow solver, in the simulation of the water waves and air flow in an OWC-WEC located on a breakwater, the Mutriku power station in the north of Spain. The numerical code solves the transient Reynolds averaged Navier-Stokes (RANS) equations, using the Volume of Fluid (VoF) technique to identify the free surface. The standard k-ε turbulence model was used evaluate the Reynold stresses. Two geometries were considered: one with the pneumatic chamber completely open to the atmosphere; and other with the chamber connected to the turbine duct. The solutions obtained by OpenFOAM^® are compared with those obtained by the commercial code Fluent.

Abstract: This paper presents a biphasic two-dimensional numerical study of sea wave energy converters with operating principle being Oscillating Water Column (CAO) devices with two couples chambers. For the study of the geometric optimization, the Constructal Design method is applied in association with the exhaustive search method to determine the geometric arrangement that leads to the greatest hydropneumatic power available. The objective function is the maximization of hydropneumatic power converted by the device. The constraints of the problem are the inflow volumes of the hydropneumatic chamber (V_E1, V_E2), the total volumes (V_T1, V_T2) and the thicknesses of the device columns (e₁, e₃). The degrees of freedom analyzed were H₁/L₁ (ratio between height and length of the hydropneumatic chamber of the first device), H₂/L₂ (ratio between height and length of the hydropneumatic chamber of the second device), H₂ (height of the column dividing the two devices) and e₂ (thickness of the column dividing the devices). In the present work the degree of freedom H₆ (depth of immersion of the device) is kept constant and equal to H₆ = 9.86 m. The Finite Volume Method (FVM) was used in the numerical solution of the equations employed. For the treatment of the interaction between the air and water phases, the Volume of Fluid (VOF) method was applied. The results show that the maximum hydropneumatic power available was 5715.2 W obtained for degrees of freedom H₁/L₁ = H₂/L₂ = 0.2613 and e₂ = 2.22 m. The case of lower performance has a power value equal to 4818.5 W with degrees of freedom equal to H₁/L₁ = H₂/L₂ = 0.2613 and e₂ = 0.1 m.

Abstract: A set of scale-model tests carried out to enlarge the range of wave steepness values analysed in run-up, overtopping and armour layer stability studies, focusing on oblique extreme wave conditions and on their effects on a gentler slope breakwater’s trunk armour and roundhead, is presented in this paper. A stretch of a rubble mound breakwater (head and part of the adjoining trunk, with a slope of 1(V):2(H)) was built in a wave basin at the Leibniz University Hannover to assess, under extreme wave conditions (wave steepness of 0.055) with different incident wave angles (from 40º to 90º), the structure behaviour in what concerns wave run-up, wave overtopping and damage progression of the armour layer. Two types of armour elements (rock and Antifer cubes) were tested. Non-intrusive methodologies including a new application of laser scanning technique for the assessment of both armour layer damage and wave run-up and overtopping were used. It is expected that such work will contribute also with data to improve empirical formulas as well as to validate complex numerical model for wave-structure interaction.

Abstract: In this work a computational model is presented in order to simulate the trajectory of objects near the Ilhabela island region, in São Paulo coastline, Brazil. The MOHID platform (MOdelagem HIDrodinâmica - Hydrodynamics Modelling) was used with the downscalling technique used to obtain local hydrodynamic currents at local scale. Two different applications are tested, the first is the hypothetical trajectory of a dead cetacean specimen drifting that could have happened in fact if it was not arrested to a more adequate spot near Ilhabela island in November, 2017, and the second is the simulation for the drift of floating objects that resulted from an accidental release of containers at the Port of Santos in August, 2017. The use of these technologies has great potential for researchers interested to simulate different drift occurrences near the Brazilian costal region.

Abstract: Knowledge of forces due to the action of waves on submarine outfalls composed by a pipe and stabilizing concrete weights, considering the wave propagation direction to the outfalls, is essential to their design. 3D numerical models based on RANS-VoF (Reynolds-Average-Navier-Stokes Volume-of-Fluid) are able to estimate forces on the pipe and weights. The present study aims to simulate a submarine outfall with stabilizing concrete weights at 1:15 scale which was previously tested in the 3D Shallow Water Basin at the Danish Hydraulics Institute (DHI) to analyse the influence of the direction of the incident wave and the distance from the pipe to the bottom on the outfall forces. In this study, numerical results are compared with experimental ones for waves with four different amplitudes and with wave incidence perpendicular to the outfall. The use of k-ω SST turbulence model led to good agreement between numerical drag and lift forces and experimental ones, with a mean difference of 8.9 and 7.6%, respectively.

Abstract: This paper describes the physical model, experimental setup and tests performed at the Portuguese Civil Engineering Laboratory (LNEC), to study the motions and forces of a moored ship at the Leixões port, for different sea states in irregular waves. The tests were carried out at one of the wave tanks of LNEC, where the Leixões port layout was implemented at scale 1:80 with the detailed model similar to the prototype bathymetry and surrounding structures. The moored ship is a 3.43 m long scale model of the well-known “Esso Osaka” tanker and is moored to the pier A of the oil terminal at 0.135 m draft. Several types of measurements were recorded in this study. The free-surface elevation and wave direction were measured with a set of resistive wave gauges. The wave velocities at the entrance of the harbour were measured with an acoustic Doppler velocimeter. Motions of the moored ship were measured with the OptiTrackTM motion capture system whereas forces on fenders and mooring lines were measured with load cells attached to a complex spring system developed at LNEC. Several tests were carried out for a number of incident sea states characterized by a JONSWAP spectrum, with different significant wave heights and peak periods. The measurement, analysis and results obtained for the incident wave conditions characterized by a significant wave height of 6 m and a peak wave period of 14 s are presented and discussed in this paper.

Abstract: Energy is a fundamental element for the development of societies, with energy transformation from renewable sources a challenging theme throughout the world. In Brazil, the energy matrix is composed mainly of non-renewable sources such as petroleum and its derivatives, but the transformation for electricity supply is carried out mainly by hydroelectric plants. This paper presents data from the National Energy Balance between the years 2011 to 2016, regarding the internal supply of energy, as well as the sectors that use it as their main source of electricity, allowing a better visualization of the national scenario. In view of the problem, the main objective is to present possibilities for the production of energy by ocean waves, a concept already studied in developed countries. For example, three tested converter devices are considered: one in Norway and two in Denmark. Considering this possibility from the power of the ocean waves in the world, as well as the climatic, geographical and wave characteristics of Brazil, this work indicates the possibility of a significant increase in the Brazilian energy matrix through the use of the energy of the ocean waves. However, there is a growing need to foster research and development projects in this area, so that this alternative source of energy will become viable.

Abstract: The Advection-Diffusion Multilayer Method (ADMM) emerged to address the solution of advection-diffusion equations with variable coefficients in the context of pollutant dispersion modeling. The ADMM is based on the piecewise-constant approximation of the variable coefficients and the application of the Laplace transform. Applications of ADMM in other areas are potentially relevant for modeling the behavior of heterogeneous media. However, if such heterogeneity is characterized by rapidly oscillating coefficients, the direct application of the ADMM would increase the computational effort needed, as it would require a very fine discretization of the domain. In order to overcome such a drawback, in this contribution, an alternative approach combining the ADMM with the Asymptotic Homogenization Method (AHM) is presented. The ADMM-AHM integrated approach is compared to the direct application of the ADMM in order to assess the accuracy of the estimations of the solution of the original problem, and the computational efficiency.