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

An investigation of the applicability of the SWASH model for wave overtopping estimation of a porous structure with a recurved wall was carried out. The results demonstrate the capability of SWASH to predict with good accuracy the mean overtopping discharges when compared to data from physical model tests. Also, detailed validation of the instantaneous wave overtopping shows a reasonable agreement.Whilst free surface is well represented without considering several parametrizations, even for one-layer mode, wave overtopping is very sensitive to any variation in numerical and physical parameters. Wave overtopping simulations are very sensitive to the non-linear Forchheimer coefficient,

This paper focus on the study of different methodologies for surveying two-dimensional scale models of a rubble mound breakwaters.Tests were conducted in one of the LNEC

Este artigo descreve os mais recentes desenvolvimentos do sistema SWAMS ALERT. 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. O sistema está a ser desenvolvido e implementado numa plataforma web totalmente interativa e amigável.O sistema SWAMS ALERT usa as características da agitação marítima medidas ou previstas para determinar os seus efeitos em termos de movimento vertical excessivo de uma embarcação em manobras que entra ou sai de uma bacia portuária ou 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. A comparação dos valores calculados das variáveis relevantes com valores máximos pré-definidos permite a avaliação em tempo real de possíveis situações de emergência ou quando a segurança das operações portuárias estiver em risco e emitir avisos às autoridades competentes; e ainda a construção de mapas de risco, considerando longas séries temporais de ondas de mar medidas ou previstas ou cenários predefinidos associados a alterações climáticas ou eventos extremos.Ilustra-se a aplicação deste sistema ao porto da Praia da Vitória.

The design of certain seawalls / breakwaters has often been required to achieve very low target overtopping discharges when these structures protect vulnerable infrastructure or activities. The balance between economically viable protection and performance requirements is often difficult to achieve without good knowledge on low overtopping. The paucity of data in this space and the high uncertainties associated with existing methods, increase the challenge. The occurrence of a low number of overtopping waves has the consequence that any test results are substantially more affected by the inherent variation of random waves, therefore more uncertain. The physical model test results presented hereafter were successful in obtaining low to very low overtopping discharge data. For low / very low overtopping, these test data present considerable scatter relative to the latest empirical prediction. A number of repetitions was performed for conditions giving very low overtopping discharges, which illustrated the inherent uncertainty associated with low overtopping.

Rubble mound breakwaters (RMB) are the most common maritime structures in Portugal. Their main goal is to reduce the action of waves on the sheltered area of the structure to achieve safety conditions for ships, people and harbour activities.To account and define the need for maintenance or repair works on such structures, it is necessary to evaluate its evolution along its expected lifetime. To predict damages that may occur in those structures and evaluate its importance in terms of structural safety and functionality, it is therefore of utmost importance to follow a monitoring program on such structures. For that purpose, a monitoring mobile tool to be used onsite by the observer would be very useful, adding in this way more efficiency to the existing traditional monitoring techniques used nowadays at LNEC, where visual, systematic, observations are made to attain relevant qualitative evaluation of those structures.Hence, a responsive WebGIS system was developed (Maia et al., 2017) for assisting the observation campaigns, enabling the introduction of photos and videos, their accurate georeferencing, the automatic evaluation of the current, and evolutive, structural state of the structure, and also the checking of physical characteristics of the structure and materials.Besides briefly describing the monitoring tool, this paper focuses primarily on demonstrating its application to a real case scenario of an inspection campaign to the RMB of Ericeira,Portugal, on the 20th of April 2017.

O LNEC tem implementado, desde 1986, um programa designado por OSOM (Observação Sistemática de Obras Marítimas) para quebra-mares de talude localizados em Portugal continental. Para armazenamento, consulta e análise da informação que vai sendo recolhida sobre os diferentes quebramares no programa OSOM, desenvolveu-se no LNEC a aplicação ANOSOM (Análise de Observação Sistemática de Obras Marítimas), a qual tem vindo a ser alvo de diversas atualizações, inclusivamente o manuseamento de nuvens de pontos provenientes de levantamentos dos quebra-mares com sistema de sondador multifeixe e/ou com a ajuda de UAV. Presentemente está em desenvolvimento uma aplicação Web a, ANOSOM_SIG, a qual virá a ser utilizada como interface da base de dados ANOSOM que inclui as funcionalidades de um Sistema de Informação Geográfica (SIG), transformando-se assim, numa ferramenta de gestão de risco em estruturas de proteção costeira e portuária.O objetivo desta comunicação é descrever a aplicação ANOSOM_SIG, bem como as suas funcionalidades até agora implementadas, apresentando alguns exemplos de aplicação.

This paper ilustrates lhe application of a non-linear shallow water numerical model, AMAZON, to study Oscillating Water Column Wave Energy Converters (OWC-WEC) inregrated in vertical breakwaters. This application has been performed within the scope of the research project DITOWEC - Development of an Integrated Tool for Numerical Modelling of Oscillating Water Cohumn Wave Energy Converters Integrated in Vertical Breakwaters. The main objective of DITOWEC is the development of an innovative integrated tool for numerical modeling of wave propagation from offshore to nearshore, of wave-structure interaction and of the complex nonlinear hydrodynamic and aerodynamic phenomena that occur in an OWC-WEC. This development is supported by field data from PICO power plant (Azores) and from two-dimensional experimental data, from physical model tests carried out at LNEC, which are used here for AMAZON calibration/validation. A sensitivity analysis on AMAZON parameters (grid resolution and momentum adjustment factor at vertical barrier) is presented and discussed, centered on wave height obtained near and inside lhe water chamber, amplification factor and phase lag. The obtained AMAZON results are encouraging though more tests are required for different water depths, vertical openings and incoming wave periods, allowing further calibration and validation of the momentum adjustment factor.

Com base em 10 anos de dados de temporais medidos na boía ondógrafo de Sines entre os anos 2001 e 2010, analisaram-se as características de diversos parâmetros da agitação, entre as quais as alturas de onda (significativa e máxima), o período médio e a direção de agitação. Em particular estudou-se a relação entre alturas de onda máxima e alturas de onda significativa durante condições de temporal, compararam-se as relações encontradas com as propostas na literatura e usualmente aplicadas no dimensionamento de quebra-mares verticais, e analisou-se a sua influência na estabilidade dessas estruturas. Verificou-se que os coeficientes de segurança calculados com base em valores de altura máxima registada são inferiores aos calculados com a relação proposta na literatura.

O dispositivo de aproveitamento de energia das ondas de tipo coluna de água oscilante (CAO) é um sistema que foi desenvolvido há já algumas décadas. Em condições de agitação marítima forte, pode ocorrer entrada de ar na câmara-de-ar do dispositivo, pela abertura submersa, comprometendo assim o seu rendimento. A colocação de uma parede vertical submersa, em frente ao dispositivo (UCAO), permite evitar este problema, mas altera o seu desempenho. Neste artigo, o modelo SPH é utilizado para uma primeira análise comparativa da hidrodinâmica dos dois dispositivos. Verifica-se que o factor de amplificação é fortemente condicionado pela dimensão da abertura submersa, reduzindo-se para uma abertura pequena, particularmente para os períodos de onda mais baixos. A amplitude da cava, na câmara de água e em frente ao dispositivo, é menor na configuração de UCAO que na CAO. É, assim, evidente que a UCAO reduz fortemente o risco de sucção de ar na câmara, embora reduza o factor de amplificação, quando comparada com a CAO.

The phenomenon of scour in the vicinity of coastal and harbour protection structures, wind farms, offshore platforms and marine outfalls is one of the causes associated with its collapse. During the design of such structures, the prediction of the maximum erosion depth located in the vicinity of the structure is of utmost importance, requiring, frequently, a validation by scale-model tests. The objective of this study is to validate the use of stereo photogrammetry in such tests. To accomplish this goal, two sets of tests were conducted: A stereo photogrammetric survey of a well-known shape molded in a sand box was carried out in order to infer on the accuracy of the technique when applied to a sand bed. The second set of tests consisted on the survey of the scour around a pile, using the stereo photogrammetric method as well as a bed profiler in order to compare the results obtained with both methods.

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