Search

Wave energy is a renewable source with significant amount in relation to the global demand. A good concept of a device applied to extract this type of energy is the onshore oscillating water column wave energy converter (OWC-WEC). This study shows a numerical analysis of the diameter determination of two types of turbines, Wells and Impulse, installed in an onshore OWC device subjected to a hypothetical sea state. Commercial software FLUENT®, which is based on RANS-VoF (Reynolds-Averaged Navier-Stokes equations and Volume of Fluid technique), is employed. A methodology that imposes air pressure on the chamber, considering the air compressibility effect, is used. The mathematical domain consists of a 10 m deep flume with a 10 m long and 10 m wide OWC chamber at its end (geometry is similar to that of the Pico’s plant installed in Azores islands, Portugal). On the top of the chamber, a turbine works with air exhalation and inhalation induced by the water free surface which oscillates due to the incident wave. The hypothetical sea state, represented by a group of regular waves with periods from 6 to 12 s and heights from 1.00 to 2.00 m (each wave with an occurrence frequency), is considered to show the potential of the presented methodology. Maximum efficiency (relation between the average output and incident wave powers) of 46% was obtained by using a Wells turbine with the diameter of 2.25 m, whereas the efficiency was 44% by an Impulse turbine with the diameter of 1.70 m.

The most studied device used for extracting wave energy is the Oscillating Water Column (OWC). In general, numerical simulations of these cases by means of models based on Reynolds Averaged Navier-Stokes equations adopt the Volume of Fluid method to deal with the free surface flow which is considered incompressible in both water and air. The aim of this study is to investigate the influence of the compressibility effect on the air inside the OWC chamber by the FLUENT® numerical model. A methodology is implemented, taking into account both water and air flows incompressible, but, at every instant, a pressure condition is imposed on the top boundary of the chamber to consider the compressibility effect. This pressure condition is based on an analytical equation that considers the isentropic transformation of the air and effects of Wells and impulse turbines. Results of compressible and incompressible numerical models are compared. The amplification factor, the root mean square of air pressure inside the chamber and OWC efficiency in relation to incident wave period, wave height and turbine characteristic relation are analyzed. Results show that air compressibility effects can diminish the predicted OWC efficiency up to about 20% in both Wells and impulse turbines.

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.

Although studies show high wave energy potential in several coastal regions around the world, its evaluation and detailed characterization are necessary to optimize its harvest. This study aims at numerically evaluating the power output of an Oscillating Water Column (OWC) wave energy converter installed in the southern Brazilian coast. The FLUENT® numerical model, based on the Reynolds Averaged Navier-Stokes (RANS) equations and the Volume of Fluid (VoF) technique, is used. The turbine diameter optimization (TDO) model, which considers the motion of the water surface inside the OWC chamber as a piston movement in response to the hydrodynamic forces from the incoming waves, is also employed. The OWC is equipped with a Wells turbine, with pressure control (relief valve) and regulation of the turbine rotational speed. The turbine diameter is chosen by taking into account the wave characteristics in the region where the device is installed. An OWC device 10 m wide, 10 m long, 16 m high (10 m submerged) with a front wall 2.5 m submerged reaches its optimum performance with an annual-averaged power output of 36.48 kW (efficiency of 54.6%), by using a turbine with 2.25 m diameter.

This paper describes a methodology to determine the optimal size of a Wells turbine to be used in an OWC device taking into account hydro-aerodynamic coupling, performance curves of the turbine and air pressure control by a relief valve. The proposed model, named turbine diameter optimization (TDO) model, considers the movement of the water surface inside the OWC chamber as a piston movement in response to the hydrodynamic forces from the incoming waves. The aerodynamic is based on the first law of thermodynamics applied to the air column of the chamber. The power-pressure curve of the turbine and the air pressure control by relief valve are implemented in the model to determine the turbine power output for several regular incident waves. The TDO model is initially calibrated by a numerical model based on Reynolds-Average-Navier-Stokes (RANS) equations for each wave component of an expected sea state distribution. Thereafter, the power output generated by turbines of several sizes is calculated with lower computational cost (few minutes) in comparison with RANS based models (thousands of hours) in a personal computer. This developed methodology is an important support to the process of turbine sizing for an OWC device for an expected sea state distribution.

This paper describes the preliminary developments of an innovative integrated tool for the numerical modelling of oscillating water column (OWC) wave energy converters (WEC) integrated in vertical breakwaters. The main purpose of the tool is the numerical modelling of wave propagation from offshore to nearshore, wave-structure interaction, and the complex nonlinear hydrodynamic and aerodynamic phenomena that occur in OWC-WECs. The tool development and validation were supported by experimental data from physical model tests carried out in a wave flume at the Portuguese National Laboratory for Civil Engineering (LNEC). Prototype data were also available for the Pico OWC-WEC in the Azores, Portugal, monitored by the Portuguese Wave Energy Centre since 2005. Application of the tool for sea-wave characterization at the Azores archipelago and calculation of the corresponding wave power for a period of 10 years at various points around each island show that, in winter, there is good availability of wave energy in most quadrants of each island. In summer, the resource exploitation is only worthwhile on the north-west coasts of the islands. Physical and numerical modelling results for an OWC with a fully open chamber show good agreement between experimental data and numerical values for several incident wave conditions. The analysed results include the time series of the free-surface elevation at different locations, the time series of the mean free surface inside the water chamber, the amplification factors, the phase angles and the velocity vectors at the highest and the lowest positions of the mean free surface inside the chamber. The tool showed its potential to be useful in supporting ocean and coastal engineering projects due to its capacity to effectively reproduce the main phenomena involved in these types of studies.

This paper presents the validation of active and passive, made by a dissipation beach, numerical absorbing methods implemented in RANS-VOF FLUENT® code for modelling long time series of wave propagation interacting with coastal structures. Verification of both numerical techniques was performed in 2D – wave flume, and 3D – wave tank, this one using a multiple active absorption wave makers. The active absorption wave maker allows maintaining the incident wave generation and the mean water level along the time. Good results were obtained for 2D and 3D applications for active absorption wave maker at the generation boundary and both numerical beach and active absorption at the end of the flume/tank.

Wave energy extraction in coastal regions may be an excellent alternative due to the increase in global demand for renewable energy. The viability study of this extraction depends on the evaluation of the wave energy potential that is higher in regions located in high latitudes. Therefore, this study shows evaluation and characterization of wave energy in the south of Brazil. Numerical simulations were carried out by the Mike 21 SW spectral model which was calibrated and validated in the region measurement campaigns. Annual, seasonal and monthly means and the temporal variability of the wave energy potential in a 10-year wave hindcast were analyzed offshore and nearshore. Annual mean fluxes in three points nearshore had similar values; the highest one was 6.7 kW/m, while the wave energy flux offshore was 22.3 kW/m. The refraction and the bottom friction dissipation were responsible for the wave attenuation from offshore to nearshore and, consequently, for the decrease in wave energy. The annual, seasonal and monthly variabilities of wave energy fluxes were moderate offshore and high nearshore. A directional analysis showed that the dominant wave directions were S and NE offshore whereas they were SSE and E nearshore.

Fluid-dynamic interference among cylindrical structures in arrays, frequently used in engineering, is of fundamental and practical interests since it may considerably change fluid–structure interactions and produce large fluctuating forces on structures that cause vibrations, lock-in and important motions. This paper aims to study the mutual interference between two circular cylinders in tandem arrangement, which is considered the simplest configuration of one array cylinders, elastically mounted in transversal direction and subject to a bi-dimensional uniform laminar flow at low Reynolds numbers. Both cylinders have the same diameter D, and the center-to-center spacing is equal to L = 5.25D which corresponds to co-shedding regime. The academic numerical model Ifeinco, which is based on the finite element method and uses a partitioned scheme that considers two-way interaction of fluid flow and structure, has been employed to the analysis. Combinations of upstream and downstream stationary and elastically mounted cylinders are investigated for Reynolds number range from 90 to 140. Differences of flow behaviors drag and lift forces and resonance between single cylinder and cylinders in tandem arrangement were found. Mutual and respective influences of upstream cylinder motion on the downstream cylinder and vice versa are analyzed. Results show that, in some engineering studies, the consideration of the flexibility of cylindrical structures in arrays is fundamental since it influences significantly the interference between cylinders, mainly the magnitude and direction of forces and characteristics of the resonance range, and, consequently, structural and dynamical behaviors.

The main objective of this study is to investigate differences of random incident waves from regular ones in performance of wave energy converters (WEC). A numerical analysis of an onshore oscillating water column (OWC) WEC is carried out by means of the FLUENT® software, which is based on Reynolds-Averaged Navier-Stokes equations. Analyses of the efficiency of an onshore OWC device with similar characteristics of the Pico’s plant and equipped with a Wells-type turbine, located at a 10 m deep flume, subjected to random waves with TMA spectrum and regular waves are shown. The resonance occurs at an energy period T = 8.6 s with an efficiency of 62% for a root mean square wave height Hrms = 1 m in random waves, while it is observed at T = 7.1 s with 84% of efficiency for H = 1.00 m in regular waves. Differences between efficiencies of regular and random waves are significant up to around the resonant period. This study showed that the use of random incident waves is fundamental to obtain more real results of analyses of onshore OWC device performance, even considering their requirement of high simulation time.

Despite the simplicity of the geometry of the circular cylinders, the uniform flow around them is complex, since it may induce unsteady forces on structures associated with vortex shedding. This paper describes the study of two circular cylinders (the downstream one is elastically mounted in transversal direction) in tandem arrangement subject to bi-dimensional uniform laminar flows at low Reynolds numbers. The academic numerical model Ifeinco, which is based on the finite element method and uses a partitioned scheme that considers two-way interaction of fluid flow and structure, has been employed to the analysis. Firstly, both stationary cylinders in tandem arrangement for Re = 100 are analysed for center to center distance between the cylinders, L/D, from 1.5 to 6.0. Results of lift and drag coefficients and Strouhal number are compared with other numerical results and good agreement is found. Secondly, numerical results for L/D = 5.25, considering downstream elastically mounted cylinder, are analysed for Reynolds numbers ranging from 100 to 140. It shows that the resonance occurs for Reynolds numbers between 115 and 120 and the maximum dimensionless amplitude of oscillation is 0.721 for Re = 118.

The availability of clean energy of wind waves is enough to meet current demand of the world, attracting researches to find devices with good performance to extract this type of energy. The oscillating water column converter is a type of device that has been extensively studied for this purpose. This paper describes a numerical analysis of an onshore oscillating water column device taking into account hydrodynamic and aerodynamic coupling, performance curves of the turbine and air pressure control by a relief valve. The numerical analyses are carried out by the Fluinco model, based on slightly compressible flow method to solve the Navier–Stokes equations, and employing the two-step semi-implicit Taylor–Galerkin method. The aerodynamic model is based on the first law of thermodynamics applied to the air column inside the chamber and on turbines similar to Pico's. The turbine power output with air pressure control inside the chamber due to a relief valve is compared to the one without control. A significant increase in the power output by using the pressure control in comparison with that without control is observed. The analysis of the turbine power output considers different turbine diameters and ranges of rotational speeds.

This paper presents the application and the validation of the SPH numerical model SPHyCE, based on a standard Smoothed Particle Hydrodynamics formulation, for modeling an onshore oscillating water chamber, comparing results of amplification factor and phase lag with those obtained by a mesh-based RANS model. Firstly, an analysis of the results for different resolutions (i.e. particle dimension) showed the independence of results with refinement. Secondly, the amplification factor of mean free surface elevation inside the oscillating water chamber and the phase lag between time series of free surface elevation outside and inside the water chamber were analysed. A good agreement was achieved between the mesh free SPHyCE model and the mesh-based RANS model. SPHyCE model was finally applied to analyse the hydrodynamic fluid flow inside and outside the water chamber and to quantify the forces on the vertical wall and the amplification factor for different incident wave heights for a rough sea state with complex wave breaking, impact loads and overtopping, contributing to the future applications of SPH models for development and studies of OWC devices.

Welding processes on plates involve complex physical and chemical phenomena which make mathematical modeling difficult. Although coupled thermal-mechanical-metallurgical effects are important, good results can usually be found when numerical models based on heat transfer equation and governing equations of the structural behavior are used. In this paper, a numerical analysis of multi-pass single V-groove weld in butt joint (three passes) of AISI 304L stainless steel, using the conventional MIG/MAG process is presented. The plates are 9.6 mm thick, 200 mm long and 50 mm wide. The numerical simulations were performed by ANSYS® Multiphysics software, considering a moving heat source with Gaussian type distribution, convection and radiation heat transfer on the surfaces and temperature-dependent material properties, for both mechanical and thermal simulations. The von Mises yield criterion and associated flow rule are used together with kinematic hardening and a bilinear representation of the stress–strain curve. The element birth and death technique is employed to consider an appropriate analysis of the welding processes with material deposition. The fusion zone shape, thermal cycles and final distortion of the plates obtained from the experiments developed in the laboratory of research in welding engineering (LAPES–FURG), located in Rio Grande, RS, Brazil, are compared with numerical results. In general, both thermal and mechanical results obtained by numerical simulation are in good agreement with experimental ones. Analysis of the influence of each pass on the plate distortion is discussed.

In this study, a numerical analysis of the performance of two Oscillating Water Column (OWC) wave energy converters, at different front and back wall slopes, was carried out. The first device had vertical front and back walls and the second one had its wall slopes of 40° in relation to the horizontal plane. The FLUENT® numerical model, which is based on the Reynolds-Averaged Navier-Stokes (RANS) equations, was used. The Volume of Fluid (VoF) method was employed to take into account free surface flows. The case study comprised a 10 m deep flume with an onshore OWC at its end, equipped with a Wells turbine. A 2D hydrodynamic mathematical model was employed and a 3D air pressure effect inside the OWC air-chamber was considered. Analyses of the hydrodynamics behavior, fluid-structure interaction outside (run-up/down, reflected waves) and inside the chamber (free surface elevation, sloshing) and energy distribution (pneumatic extracted energy, reflected wave energy and energy losses) were conducted. Results showed that the device with inclined walls had the best efficiency in comparison with the other one. However, the latter showed lower variation in efficiency in the wave period range than the former.

The technique of weaving by magnetic arc deflection was developed a few years ago to enable the oscillation of the weld pool, thus, causing grain refinement and improving the properties on the welded joint. This paper aims to propose two heat source models that include effects of magnetic arc deflection on a bead-on-plate GTAW process in numerical simulations by using the finite element method. Two cases are studied. In the first case, non-deflected arc and straigth magnectic deflected arc along the torch movement are carried out and compared to numerical simulations. Temperatures at three different points on the backside of the plates (two away from the welding center line and one in its center) and weld pools of SAE 1020 3.2 mm and 6 mm thick steel plates are analyzed. Results obtained by numerical simulations are close to the experimental ones. In the second case, welding with weaving (frequency of 1Hz) on 3 mm thick steel plates is analyzed. The bead width and its visual presentation are compared to experimental results, which show good agreement with both proposed models. Resumo A técnica de tecimento por deflexão magnética do arco foi desenvolvida há alguns anos para permitir a oscilação da poça fundida, causando o refinamento de grão e melhorando as propriedades da junta soldada. Este artigo tem como objetivo propor dois modelos de fontes de calor que inclui os efeitos de deflexão magnética do arco em um processo GTAW sobre chapa nas simulações numéricas pelo uso do método dos elementos finitos. Dois casos são estudados. No primeiro, são comparadas as simulações numéricas para o arco sem deflexão e para o arco com deflexão magnética fixa ao longo do movimento da tocha. São analisadas as temperaturas em três pontos na parte inferior da chapa (dois afastados da linha de centro de soldagem e outro no centro) e poças de fusão para chapas de aço SAE 1020 e espessuras de 3,2 e 6 mm. Os resultados obtidos pelas simulações numéricas estão muito próximos aos experimentais. No segundo caso, é analisada a soldagem com tecimento (frequência de 1Hz) em chapas de aço de 3 mm de espessura. São comparadas as larguras do cordão e sua forma geométrica com os resultados experimentais, que mostram a boa concordância obtida pelos dois modelos propostos.