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

Nowadays, renewable energy is a topic widely discussed in scientific community. Specifically wave energy attracts attention because it has a high energy potential distributed throughout the planet. Oscillating Water Column (OWC) wave energy converter is one of the most studied devices that have promising perspectives to be installed commercially. This study aims investigating the influence of chamber sizes and turbine characteristics dimensions of an OWC device located at the southern Brazilian coast is carried out. Numerical simulations for incident waves with period T = 7 s and 10 s and height H = 1.5 m, by using the FLUENT® model, based on the finite volume method (VFM) are carried out. Efficiencies for different chamber sizes and Wells turbine characteristic relations (kt) in each incident wave are determined. The highest efficiencies were obtained by a chamber with 5 x 5 m and kt = 530 Pa.s/m³ in the case of an incident wave with T = 7s (52%), and 30 x 30 m and kt = 15 Pa.s/m³ at T = 10s (65%).

Port terminals downtimes lead to large economic losses and largely affect the port

This paper describes the physical model, experimental setup and tests performed to study the motions and forces of a ship moored to the pier A at the Leixões oil terminal, following the breakwater

HIDRALERTA is a forecast, early warning and risk assessment system for port and coastal areas that uses measurements and estimates of sea-waves and water levels to evaluate overtopping/flooding events. The calculation of the mean overtopping discharge over a maritime structure is performed through artificial neural network-based tools and/or empirical formulae. The system is developed in open source software, mainly using the Python language. This paper presents the application of HIDRALERTA system to reproduce the hurricane Lorenzo conditions and impacts at Lajes das Flores port on October 2nd 2019, the most affected port in Azores. This hurricane was regarded as the strongest storm to hit Azores in 20 years. The system predicted the expected results for the hurricane wave characteristics, as well as overtopping discharge volumes. Further validation still need to be improved with the collaboration of the local authorities and the use of historical data.

Numerical models are useful tools to predict the effects of storms in coastal areas. The objective of this work was to simulate the effects of storms in São Pedro de Moel beach by using XBeach. The nearshore sea state was obtained by propagating offshore conditions using the SWAN model. The XBeach model was divided into two setups to analyse overtopping events and coastal evolution. Sensibility tests, calibration, and validation, using information from different storms, were performed for the different setups. The results from the overtopping simulation were compared against results from an empirical formula. The comparison showed lower values obtained with the empirical formula. The coastal evolution run point out to the necessity of having better field data before and after storms to improve the model setting and accuracy.

The assessment of damage evolution in scale model tests of rubble-mound breakwaters can be achieved by comparing eroded depths and volumes between consecutive surveys. This paper focuses on damage evolution of a model of a rubble-mound breakwater and on the novelty of the non-intrusive survey methodologies such as laser scanning and Time of Flight (ToF) techniques, based on point clouds, enabling the extraction of profiles and the calculation of eroded depths and eroded volumes. The final objective of this work is to evaluate the applicability of the estimation the number of displaced armour units, using a non-dimensional damage parameter based on the calculated eroded volume.The paper will also describe the experiments conducted under the RODBreak, a project sponsored by the HYDRALAB+ Transnational Access Program, in which a stretch of a rubble-mound breakwater was built at the wave-current basin of the Leibniz University Hannover (LUH) to assess the structure behavior. Four scan surveys were conducted using a Faro Focus 3D laser scan, as well as a ToF sensor. Those surveys were carried out before and after two test series, in order to evaluate the eroded volume and profile evolution.

Neste trabalho é efetuada a validação do protótipo To-SEAlert para o porto da Ericeira. Para a validação dos resultados do modelo SWAN foram utilizados os dados de duas boias situadas ao largo da Nazaré e para a validação das previsões do sistema de cálculo do grau de risco foram simuladas as depressões Elsa e Fabien (ocorridas em dezembro de 2019) e que foram responsáveis por fortes danos na cabeça do molhe do porto da Ericeira. Verificou-se uma boa concordância entre os dados das boias e os resultados do modelo SWAN, tendo no entanto o modelo reproduzido melhor a direção média e a altura significativa do que o período de pico. Relativamente aos valores de galgamento, os resultados obtidos na simulação das depressões Elsa e Fabien estiveram em concordância com os valores referidos na literatura como causadores de danos nas estruturas.

This work aims to determine the exploitable wave energy resource at six potential sites, located in the Azores, Madeira and Sines breakwater city harbours. For that purpose, the thirdgeneration wave model SWAN is used to estimate the sea-wave conditions over the last 40 years. Boundary conditions of the sea states and wind fields are provided by the climate reanalysis datasets (ERA5). Using those results as inputs to the SWAN model, the sea-states were propagated shoreward, in order to estimate and analyse the wave climate conditions in the regions of interest. By combining the average energy flux per unit-length of wave front and the probability of occurrence of each sea state, the average exploitable annual energy per unit length of wave crest can be computed. The variability of this energy flux is described, since it is of fundamental importance for the efficiency of the Wave Energy Converters (WEC).

Former investigations on wave run-up and overtopping of (impermeable and permeable) coastal structures aimed at quantifying the influence of oblique waves on mean overtopping discharge, water layer thickness and velocities by developing empirical formulas of a reduction factor for wave obliquity,

In 2017, the RODBreak experiment was conducted. The experiment aimed at characterizing wave run-up, overtopping and damage in rubble-mound breakwaters. The reason for these experiments was the huge impact that climate can have on maritime structures, particularly in rubble mound breakwaters. In fact, the forecast sea level rise associated with more frequent and severe storms will have consequences either on the increase of wave runup, wave overtopping or on damage on existent structures since they were not design for those extreme values. However, for those climate change scenarios, little is known about the actual failure probability of such structures.Within this framework, a stretch of a rubble-mound breakwater was built in a wave basin. Under extreme wave conditions, with different incident wave angles (from 40° to 90°), a total of 49 tests were performed. Each test had different testing parameters, such as significant wave height (Hs), peak period (Tp) and wave direction. Also, for each test, different types of measurements were considered. Incident sea waves were measured with 3 arrays of 6 acoustic wave probes each as well as with isolated acoustic wave probes and 5 Acoustic Doppler Velocimeters (ADV

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