Publications

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-

The aim of this paper is the experimental characterization of the capture width ratio (CWR) and response amplitude operator (RAO) of a 1:10 physical model of an oscillating wave surge converter (OWSC), under unidirectional regular and irregular waves. The effects of hydraulic power take-off (PTO) system are explicitly taken in consideration. A mathematical model is proposed to describe the PTO damping as a function of the angular velocity of the flap. The harmonic decomposition of free-surface elevation, angular velocity of the flap and pressure in the PTO system demonstrates that these signals are dominated by their linear component. However, the signals also present some important higher-order frequency components. To predict the CWR of the OWSC under irregular waves the nonlinear output frequency response functions are considered as the extension of the RAO to the nonlinear case. It is shown and discussed that the PTO system, wave frequency and height have a significant influence on the CWR and RAO. The RAO curve for irregular waves does not exhibit a well-defined peak, showing a limited variation in a broadband. A weak correlation between CWR and RAO was found, i.e., the maximum CWR does not occur for the maximum value of RAO.

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 influence 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.

This paper describes a programme under the responsibility of the National Laboratory for Civil Engineering (LNEC), Portugal for the systematic observation and monitoring of maritime works, termed OSOM+, which has been applied to an extensive number of maritime structures on the Portuguese mainland coast and abroad. The OSOM+ programme comprises the following four main components for each structure: a) Periodic visual inspections by a trained technician; b) Periodic aerial inspections using a UAV/drone; c) The ANOSOM-GIS database, to store and/or query obtained information, as well as to diagnose present, evolution and risk conditions; and d) A mobile, portable, application, for real-time input and visualization of the ANOSOM-GIS database information.This recently updated methodology encompasses a number of tools whose functionalities are illustrated in this paper with an application to a case study: the Ericeira

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.

Joint statistical models for long-term wave climate are a key aspect of offshore wind engineering design. However, to find a joint model for sea-state characteristics is often difficult due to the complex nature of the wave climate and the physical constraints of seastates phenomena. The available records of wave heights and periods are often very asymmetric in their nature. This article presents a copula-based approach to obtain the joint cumulative distribution function of the significant wave heights and the up-crossing mean period. This study is based on 124-month hindcast data concerning Horns Rev 3 offshore wind farm. The extra-parametrization technique of symmetric copulas is implemented to account for the asymmetry present in the data. The analysis of the total sea, the wind-sea and primary swell components is performed separately. The results show that the extra-parametrization technique with pairwise copulas consistently provided a better goodness-of-fit when compared to symmetric copulas. Moreover, it is demonstrated that the separation of the total sea into its components does not always improve the extra-parametrized copula

This paper analyses the hydrodynamic interaction between two ships, one stationary and the other navigating nearby, using physical and numerical modelling. The passing ship is a self-propelled scale model of the

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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