Publications

O Porto de Leixões, localizado na costa norte de Portugal, é um dos maiores do país, recebendo diariamentevários navios de grandes dimensões. Um dos principais postos de acostagem situa-se à entrada do porto e encontra-se sujeito à agitação marítima que é difratada pelo olhe principal de proteção do porto. Para avaliar dos movimentos induzidos no navio estacionado nesse posto de acostagem e as forças exercidas nas suas amarras e defensas pela agitação incidente, utilizou-se o modelo físico de Leixões, construído num dos tanques do LNEC. Neste modelo físico, encontra-se representada a envolvente do porto de Leixões, assim como a sua batimetria. O modelo do navio

An alternative to the energy matrix expansion, due to the increase of global electricity demand, is the renewable sea wave energy source, which has high energy potential. The Oscillating Water Column (OWC) converter is one of the most studied, although it is not yet used at commercial scale. Therefore, searching the optimal geometric configuration is fundamental to turn this device viable. This study proposes a numerical analysis of an onshore OWC for different slopes of chamber walls (from 40o to 90o) and equipped with a Wells turbine. Simulations of incompressible 2D flows are performed by means of the FLUENT® software, which is based on Reynolds-averaged Navier-Stokes (RANS) equations. The k-

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.

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 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

Atualmente, mais importante que assegurar a resistência de um aglomerado urbano a um eventual invasor, importa garantir a sobrevivência a catástrofes naturais das infraestruturas críticas que garantem a salubridade das condições de vida nesse aglomerado, a mobilidade dos habitantes e o abastecimento de bens essenciais. Em rigor, face ao carater aleatório destas solicitações, pretende-se que, uma vez terminadas essas solicitações extremas, eventuais estragos causados pelas mesmas não impeçam o restabelecimento, em tempo útil, das atividades normais da população. Nesta comunicação apresentam-se ferramentas e procedimentos para avaliação do risco associado a infraestruturas críticas com um viés para o controlo de cheias urbanas e de infraestruturas de transporte marítimo.

The current program of Systematic Observation of Maritime Works (OSOM+), under development at the National Laboratory for Civil Engineering (LNEC), is essentially applied to rubble mound breakwaters. The OSOM

HIDRALERTA is a forecast and early warning system for coastal and port regions capable of predicting emergency situations, as well as carrying out risk assessment. The system concentrates on evaluating wave overtopping and flooding scenarios. It uses offshore sea-wave and wind forecast data, as well as tide data, as input to determine wave overtopping at specific locations. The calculation of the mean overtopping discharge over a structure is made through artificial neural network (ANN) tools and/or empirical formulae, which are able to define the spatial distribution of the flow behind the structure.The HIDRALERTA system is composed of four modules developed in Open Source Web Technology, mainly using the Python Language. The Warning System can be configured and adapted for specific scenarios. The system has been successfully tested for the Port and Bay of Praia da Vitória, Terceira Island, Azores, Portugal, and is now under development and being implemented at the ports of Madalena do Pico and S. Roque do Pico.This paper describes the work carried out to date on the system and its application to these two ports in the Pico Island, Azores.

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

Mechanical constraints have a non-negligible influence in the motion of oscillating wave surge converter (OWSC) devices. The key novelty of this paper is a numerical simulation tool for OWSCs that does not neglect or significantly compromise mechanical constraints such as hydraulic power take-off (PTO) system, revolute joints and frictional contacts among components. The paper is aimed at presenting the key components of the numerical simulation tool and at validating it with laboratory data featuring an OWSC with mechanical constraints under regular and irregular waves. It is based on the implementation of the multibody solver of Project Chrono under the Smoothed Particle Hydrodynamics (SPH) model of DualSPHysics, where the SPH solver resolves the interaction between wave and flap and the multibody solver resolves the interaction between flap and mechanical constraints. Comparison between numerical results and experimental data show that the numerical simulation tool properly predicts the dynamics of the OWSC. Furthermore, in what concerns hydrodynamics of the near-flap flow, the computed and measured free-surface elevations and phase-averaged flow field show reasonable agreement. Once properly validated, the numerical simulation tool is then applied to study the influence of several mechanical constraints, PTO damping characteristics and flap inertia on the hydrodynamic of the OWSC. The viability of OWSC design solutions based on the developed numerical simulation tool is emphasised, in view of its performance in the test cases to which it was subjected.

O presente trabalho descreve a aplicação do modelo numérico COULWAVE ao estudo da propagação de ondas na zona da Praia do Lugar de Baixo, Madeira, com vista a simular as características hidrodinâmicas na zona de estudo permitindo analisar as alturas de ondas, zona de rebentação e reflexão da onda junto à costa. O objetivo final é propor soluções para a renaturalização desta zona e o melhoramento das condições de surf.

The objective of this paper is to describe and compare the use of different high-resolution survey techniques to create and analyse 3D surface models made up of point clouds, using open-source and freeware post-processing tools. Within this framework, several tests were conducted on a three-dimensional scale model of a breakwater, with surveys performed by a smartphone, the Microsoft® Kinect® sensor and a UAV camera. All the tests were conducted for a physical model placed in an empty wave tank. For this comparison, a number of post-processing software were used: the Microsoft Kinect Fusion Application, Visual SFM and MicMac, all freeware software. The clouds of points were compared using the CloudCompare freeware software and the Golden Software Surfer commercial software.In order to obtain a clear comparison between these tools (i.e., to better evaluate accuracy and associated errors), all the point clouds (with RGB colour information) were aligned with data coming from a survey used to coordinate some points in the model (Ground Control Points). All the clouds were compared with a corrected cloud based upon coordinated points painted on the concrete floor of the wave tank.The specific experimental conditions needed for using each of these methodologies were investigated and classified.

Nesta comunicação apresenta-se os novos desenvolvimentos que estão em curso no sistema SWAMS ALERT, que é um sistema previsão, alerta e avaliação de risco de eventos perigosos associados à navegação em áreas portuárias e ao comportamento dos navios amarrados.O sistema usa as características da agitação marítima previstas para determinar os seus efeitos em termos de forças em amarras e defensas, bem como de movimentos de um navio amarrado. Para isso, o sistema utiliza um conjunto de modelos numéricos. O sistema consiste em quatro módulos: I - Características da agitação marítima; II - Navegação em áreas portuárias; III - Avaliação de Risco e IV - Sistema de Alerta. A interface do sistema é através de uma plataforma web totalmente interativa e amigável.Ilustra-se a aplicação deste sistema ao porto da Praia da Vitória.

This paper presents recent new features of the Systematic Observation of Maritime Works (OSOM+) program, under development at LNEC since 1986, for using in an extensive number of maritime structures of mainland Portugal. Those functionalities are illustrated with applications to a real case scenario (the port of Ericeira) and by indicating their added-value on the existing methodology.

It is common for the local sea state in coastal waters to be a complex combination of waves due to local and recent wind (the "sea") and long period waves resulting from earlier weather systems, which have travelled many 100s of km with little attenuation of these very long waves (the "swell"). Sea and swell may have very different directions and periods.

This paper presents the validation of a wave maker with active absorption method implemented in FLUENT® RANS-VOF code for modelling long time series of waves propagating and interacting with coastal structures, more specifically, with Oscillating Water Column devices, to cancel out the reflected wave that reaches the wave maker. Verification of the numerical technique was performed in a 3D wave tank in which a technique of multiple active absorption wave makers was used. Good results were obtained in quasi-3D and fully-3D applications showing that active absorption should be used for modelling accurately the complex interaction between wave and coastal structures, in the present case, with an oscillating water column device integrated in a vertical breakwater.

Due to both its geographic location and maritime importance, Portugal is equipped with a large number of port infrastructures, the majority of which built for goals such as to guarantee the tranquility of the sheltered areas of the harbour basins, to help controlling sedimentation by guiding the currents, to protect water taken from thermoelectric plants, amongst others. In Portugal, the most common of these structures is the rubblemound breakwater. Due to its characteristics, maintenance or repair works are common throughout its lifetime. However, the need for these repair works should be evaluated in advance, in order to avoid significant costs associated to those works or, even worse, the collapse of the structure. It is therefore quite important to evaluate the Present Condition of the structure, as well its Evolution and Risk Conditions. The Present Condition is periodically checked on-site and all relevant data gathered is recorded, by filling in inspection forms, in order to perform further comparisons and analyses with previous inspections of the structure, as to eventually characterize Evolution and Risk conditions. To expedite all this process and prevent likely occurrence of errors in data collection, a monitoring tool, supported through a map-based online geographic information system (WebGIS) was developed, enabling the georeferencing of the structures concerned. This system adapts to the location of the user

The air entrainment effect on wave breaking is of the highest importance for the wave energy dissipation. Wave breaking is a complex phenomenon with several physical processes, making it difficult to quantify the contribution of the air in the energy dissipation process. This study presents a different approach where the wave propagation is exposed to air injected in the bottom of a wave flume. The experiment allows studying in a controlled environment the direct effect of the air bubbles in the wave propagation. The measurements show the free surface elevations and velocity profiles at two sections of the wave flume. The turbulence effect of the air injection on the wave propagation was evaluated. The results show differences for the three types of air injection that were tested. The air injection rate of each orifice is an important factor for the wave dissipation. The wave heights were found to decrease due to the air injection. The Turbulent Kinetic Energy shows an increase along the water column and on the downstream direction of the flume.

Apresenta-se nesta comunicação uma técnica baseada em análise de imagem para a medição e caraterização da concentração de ar produzida no processo de rebentação de onda. Para este efeito, realizaram-se filmagens dos ensaios num canal de ondas no Laboratório Nacional de Engenharia Civil (LNEC), que reproduzem dois tipos de rebentação de onda, progressiva e mergulhante. A validação da técnica de análise de imagem é feita por dois métodos, o primeiro com recurso à injeção de bolhas de ar através de uma bomba de ar e o segundo com a medição pontual da concentração de ar com uma sonda de deteção de bolhas de ar. Os resultados, relativos aos dois tipos de rebentação de onda, mostram as concentrações de ar e a distribuição da pluma de bolhas de ar. As medições realizadas permitem quantificar e caracterizar o ar emulsionado no processo de rebentação de onda.

Um dispositivo de aproveitamento da energia das ondas de tipo coluna de água oscilante (CAO) near-shore (que pode se assimilar a um cilindro vertical oco com a sua parte inferior aberta e a parte superior equipada com uma turbina Wells) implementada em profundidade intermédia pequena é estudado numericamente recorrendo a um modelo RANS-VOF 3D. O modelo numérico integra técnicas de geração e absorção das ondas por batedores múltiplos que permite dispor de um tanque de onda eficiente, eliminando as ondas reflectidas e difractadas. O dispositivo de CAO near-shore é um dispositivo alternativo ao clássico dispositivo integrado em quebra-mar ou na linha de costa e ao dispositivo off-shore (assimilado a um cilindro vertical oco estabilizado por um sistema de ancoragem por cabos) e tem duas vantagens: a resposta do dispositivo é independente da direcção das ondas e pode ser facilmente afundado no fundo do mar já que o dispositivo é desenhado para ser implementado em profundida pequena (~20 m). No entanto, a proximidade do fundo e a interacção complexa onda-estrutura resultante podem interferir em termo hidrodinâmico e energético na resposta do dispositivo CAO near-shore, comparativamente a um dispositivo off-shore. O artigo apresenta os primeiros resultados deste projecto através da análise pormenorizada de um caso de agitação marítima. Também, permite evidenciar e prever respostas diferentes do dispositivo CAO near-shore de um dispositivo clássico off-shore através da analise das series temporais de elevação de superfície livre, do caudal na turbina, da pressão na câmara-de-ar da CAO, da potência pneumática e dos vectores e campos de velocidade e de vorticidade ao redor e dentro do dispositivo.

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