Publications

Na sequência dos estragos causados pelo furacão Lorenzo no molhe principal do porto de Ponta Delgada, foi elaborado um projeto de reparação do mesmo, tendo havido necessidade derealização de ensaios em modelo físico tridimensional com o objetivo de avaliar a estabilidade da solução projetada.

Em 2 de outubro de 2019, o furacão Lorenzo atingiu as ilhas do Arquipélago dos Açores, provocando estragos nas infraestruturas portuárias, nomeadamente no molhe principal do porto de Ponta Delgada. No sentido de minorar este problema, foi elaborado um projeto de reparação do molhe (CONSULMAR, 2020), tendo nesse âmbito sido necessária a realização dos ensaios em modelo físico tridimensional com o objetivo de avaliar a estabilidade da solução projetada.Os ensaios foram realizados num tanque de ondas irregulares do LNEC à escala geométrica1:65 e contemplaram 6 séries de ensaios associados a 3 rumos de agitação marítima (WSW, S, SSW) e a dois níveis de maré (baixa-mar e preia-mar) associados a períodos de pico (Tp) entre 12 s e 20 s e alturas de onda significativa (Hs) variando entre 8 m e 15 m, Lemos et al. 2020.

A avaliação da estabilidade do manto resistente de quebra-mares de taludes requer, na maioria dos casos, a realização de ensaios em modelo físico. Entre os diferentes métodos de avaliação da evolução da estabilidade, destaca-se a medição do volume erodido do manto resistente por ação da agitação marítima. Este volume pode ser determinado a partir de levantamentos consecutivos da envolvente dos taludes. Melby[1] apresentou uma fórmula para previsão da evolução do dano em quebra-mares de taludes com base nas características da agitação neles incidente. No presente estudo pretendeu-se utilizar um programa de ensaiosem modelo físico bidimensional semelhante ao programa que conduziu à referida fórmula aplicado a um caso de estudo correspondente a uma secção do quebra-mar do porto de Peniche.Os ensaios realizados fazem parte do projeto BSafe4Sea que visa desenvolver, testar e comprovar o conceito de previsão do comportamento estrutural de quebra-mares de talude, que constitui a base de um sistema inovador de apoio à decisão. Os ensaios tiverem como objetivo analisar a resposta da estrutura a diferentes estados de agitação incidentes, cujos resultados são fundamentais para o desenvolvimento d e formulações empíricas de previsão da evolução do dano.

This paper studies the effects of an air bubble curtain on surface water waves. Water particle velocities and free surface elevations were measured simultaneously at two cross-shore sections downstream the air bubble curtain. Measurements were carried out for regular waves regarding different air bubble curtain configurations. Free surface elevations were measured using resistive gauges and the instantaneous velocities were acquired using an Acoustic Doppler Velocimeter (ADV). The characteristics of the free surface elevation, velocity field and turbulence are analyzed and discussed. The free surface elevation was found to be constantly attenuated by the air bubble curtain. The phase-averaged velocity profiles also depict the effect of the air bubbles in the flow field by generating milder longitudinal velocities (u) and by increasing the transverse component of the velocity (w). The increase in the turbulence intensity and the different energy spectrum produced by the air bubble curtain is also analyzed. The experimental results indicate that the thickness of the air bubble curtain and the total air flow rate affects the wave field.

An experimental study was carried out to investigate seabed-pipeline interactions with regard to soil liquefaction. For a soil with a high proportion (30 to 60%) of fine sediment, four groups of tests were configured to reproduce soil liquefaction around pipelines for different initial pipe depths, pipe densities and wave conditions (wave height and period). The study focused on verifying the theoretically computed areas of soil failure by analyzing the sinking depths of the pipelines. The main findings are that a pipe with a submerged specific weight of less than half that of the soil will move up to the mudline; that the loss of soil loading capacity is more frequently evidenced in a fluid-like behavior of the soil than by an abrupt breaking of the soil matrix; and that the pipes which are totally buried will sink more than half-buried pipes. Moreover, wave action and the specific weight of the pipes seem to play more important roles in the expected behavior of the wave

In coastal areas, overtopping events and coastal floods, resulting from the occurrence of maritime storms, can cause severe damage to infrastructure, building and equipment, can be responsible for coastal morphology changes (coastal erosion), as well as put in damage human lives, animals or the ecosystem.

SAFEPORT safety system aims to daily reports to Sines harbour administration, potencial emergency situations regarding ships operation in port areas caused by extreme weather-oceanographic conditions, that may occur in the next three. It consists of a set of numerical models and a qualitative risk assessment and forecasting. It uses forecasts provided offshore of the area under study of sea agitation, wind and tide. The characterization of the response of the free and moored ships at a berth is performed using the numerical modelswhich deals with formulations in the frequency and time domain. The system issue alerts, through danger levels associated with risk levels of exceedance of recommended values for movements and forces imposed on ship mooring systems. SAFEPORT can be adapted to any port. So far, it has been developed and adapted to three terminals of the port of Sines, where three different ships were simulated. This paper presents the developments made to date of the safety system, in terms of its implementation and validation. The numerical models run every day, in real-time mode, in a computer cluster and the system provide forecast results for the next 72 hours. The results are disseminated on a web page and a mobile application in a variety of formats.

Early warning systems are an important tool for local authorities to detect emergency situations in advance and initiate the necessary safety measure. The To-SEAlert project has the aim of increasing the efficiency, robustness and reliability of the HIDRALERTA coastal hazards early warning system. This study shows a first intent to implement the SWASH numerical model to simulate wave overtopping for the Ericeira prototype. SWASH was implemented for one breakwater profile where overtopping discharge and associated risk levelsare estimated. It was compared to the current approach used in HIDRALERTA, the neuronal network NN_OVERTOPPING2. Finally, both approaches were compared with previously analysed video images of the site. The results showed that SWASH generally overestimates overtopping and is not in good agreement with the NN_OVERTOPPING2 or the video images. A possible reason might be the wave direction, which cannot be included in one-dimensional simulations in SWASH.

No âmbito do

Extending for more 900 km with diverse geomorphologies and land-use occupation, the Portuguese coastal zone is highly vulnerable to overtopping and flooding.

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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