Papers
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Analysis of forces on a submarine outfall by a RANS-VoF numerical wave tank
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-
Year: 2019
Number Pages:
50-59pp.
Author(s): Didier, E.; Neves, M. G.; Teixeira, P.
: Defect and Diffusion Forum
Editor: Trans Tech Publications Ltd, Switzerland
Volume:
Vol. 396.
Keywords: Numerical wave tank; RANS-VoF; Forces; Submarine outfalls
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Damage progression in rubble-mound breakwaters scale model tests, under a climate change storm sequence
This paper describes the two-dimensional (2D) physical model tests of a rock armor breakwater, performed at LNEC´s experimental facilities, under the framework of the HYDRALAB+ project. The aim of the present work was to evaluate damage evolution under future climate change scenarios, by using different damage evaluation techniques. The tested wave conditions simulated a storm sequence where two water levels (low water and high water) were considered, as well as an increase of the wave height. The water levels and the wave heights were chosen to simulate extreme events forecasted on climate change scenarios. Damage evaluation was based on the traditional counting method and on stereo-photogrammetric techniques. Test results are presented in terms of the damage parameter S and in terms of the percentage of removed armor units. The analysis is focused on the damage progression during the scale model tests, for the imposed storm sequence. The damage presents an oscillating behavior with two main damage areas corresponding to the active zones for each level, due to the variation of the water level between low-water and high-water. This behavior differs significantly from that found for the common storm sequences usually tested, where the water level does not change. Both measuring techniques lead to an intermediate damage of the cross-section breakwater. However, the damage parameter assessment with the stereo-photogrammetric technique allows a more versatile evaluation, since it is possible to characterize damage in representative zones of the cross-section
Year: 2019
Author(s): Fortes, C. J. E. M.; Lemos, R.; Mendonça, A. C.; Reis, M. T. L. G. V.
: Journal of Research on Engineering Structures and Materials (RESM)
Editor: MIM Research Group
Volume:
Vol. 5 Iss. 4.
Keywords: Stereo-photogrammetric techniques; Climate change; Rubble-mound breakwaters; Damage progression
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Experimental investigation on the power capture of an oscillating wave surge converter in unidirectional waves
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.
Year: 2019
Number Pages:
975-992pp.
Author(s): Brito, M.; Ferreira, R. L.; Teixeira, L; Neves, M. G.; R. Canelas
: Renewable Energy
Editor: Elsevier
Volume:
Volume 151.
Keywords: Power take-off: PTO damping; Response amplitude operator: RAO; Capture width ratio: CWR; Oscillating wave surge converter: OWSC; Wave energy
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Measuring wave run-up, overtopping and damage of rubble-mound breakwaters in scale model tests
A set of scale-model tests was carried out at the wave basin of the Leibniz University Hannover to extend 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
Year: 2019
Number Pages:
118-129pp.
Author(s): Santos, J. A.; Lemos, R.; Weimper, J.; Gronz, O.; Hofland, B.; Sande, J.; Pinheiro, L.; Spans, J.H.; Peña, E.; Reis, M. T. L. G. V.; Fortes, C. J. E. M.; Figuero, A.; Laiño, E.; Bornschein, A.; Kerpen
Editor: Hydralab+
Keywords: Rubble-mound breakwaters; Model tests; Overtopping; Wave run-up
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Numerical analysis of the interference between two elastically mounted cylinders in tandem subject to flows at low Reynolds numbers
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.
Year: 2019
Number Pages:
11p.
Author(s): Teixeira, P.; Rechsteiner, P.; Didier, E.
: Journal of the Brazilian Society of Mechanical Sciences and Engineering
Editor: Springer
Volume:
Vol. 41.
Keywords: Finite element method; Vortex-induced vibration; Wake interference; Tandem arrangement; Circular cylinders
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Observação e monitorização de obras marítimas com a nova metodologia OSOM+
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
Year: 2019
Number Pages:
22p.
Author(s): Fortes, C. J. E. M.; Capitão, R.; Henriques, M. J.; Lemos, R.; Neves, M. G.; Reis, M. T. L. G. V.; Silva, L. G.
: Revista Mundi, Engenharia, Tecnologia e Gestão
Editor: Instituto Federal do Paraná
Volume:
v.4, n.2.
Keywords: Ericeira
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A methodology to determine the optimal size of a wells turbine in an oscillating water column device by using coupled hydro-aerodynamic models
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.
Year: 2018
Number Pages:
9-18pp.
Author(s): Torres, F.; Teixeira, P.; Didier, E.
: Revista Renewable Energy
Editor: Elsevier
Volume:
Vol. 121.
Keywords: Air pressure control; Turbine sizing; Oscillating water column; Wave energy
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An integrated tool for modelling oscillating water column (OWC) wave energy converters (WEC) in vertical breakwaters
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.
Year: 2018
Number Pages:
198
Author(s): Mendonça, A. C.; Dias, J.; Didier, E.; Fortes, C. J. E. M.; Neves, M. G.; Reis, M. T. L. G. V.; Conde, J. M.; Poseiro, P.; Teixeira, P. R. F.
: Journal of Hydro-environment Research
Editor: Elsevier
Volume:
Vol. 19.
Keywords: Wave power; SWAN-URANS models; Nonlinear numerical modelling; Physical modelling; Wave-structure interaction; Oscillating water column (OWC) wave energy converter (WEC)
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Asymmetric copula
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
Year: 2018
Number Pages:
304-334pp.
Author(s): Fazeres-Ferradosa, T.; Taveira-Pinto, F.; Vanem, E.; Reis, M. T. L. G. V.; Neves, L.
: Wind Engineering
Editor: Sage
Volume:
Vol. 42, No. 4.
Keywords: Asymmetry; Crámer
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Characterization of ship motions induced by wake waves
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
Year: 2018
Number Pages:
547-555pp.
Author(s): Pedro, F.; Pinheiro, L.; Fortes, C. J. E. M.; Santos, J. A.; Hinostroza , M.
: Progress in Maritime Technology and Engineering
Editor: Taylor & Francis
Keywords: Wake waves; SWAMS; Ship motions
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