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Dive into the research topics where Tiago Abreu is active.

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Featured researches published by Tiago Abreu.


Journal of Geophysical Research | 2011

Observations of velocities, sand concentrations, and fluxes under velocity‐asymmetric oscillatory flows

B.G. Ruessink; Hervé Michallet; Tiago Abreu; Francisco Sancho; J. van der Werf; Paulo A. Silva

[1] U‐tube measurements of instantaneous velocities, concentrations, and fluxes for a well‐sorted, medium‐sized sand in oscillatory sheet flow are analyzed. The experiments involved two velocity‐asymmetric flows, the same two flows with an opposing current of 0.4 m/s, and a mixed skewed‐asymmetric flow, all with a velocity amplitude of 1.2 m/s and flow period of 7 s. We find that the net positive transport rate beneath velocity‐ asymmetric oscillatory flow results from large, but opposing sand fluxes during the positive and negative flow phase. With an increase in velocity asymmetry and, in particular, velocity skewness, the difference in the magnitude of the fluxes in the two half cycles increases, leading to larger net transport rates. This trend is consistent with the observed increase in skewness of the oscillatory bed shear stress. Phase‐lag effects, whereby sand stirred during the negative flow phase has not settled by the time of the negative‐to‐positive flow reversal and is subsequently transported during the positive flow phase, are notable but of minor importance to the net transport rate compared to earlier experiments with finer sands. In the vertical, the oscillatory flux is positive above the no‐ flow bed. Within the sheet flow pick‐up layer, the oscillatory flux is negative and similar in magnitude to the positive flux induced by the residual flow. The 0.4 m/s opposing current causes more sand to be picked up during the negative than during the positive flow phase. Above the no‐flow bed the resulting negative oscillatory flux is comparable in magnitude to the current‐related flux.


Journal of Hydraulic Research | 2011

Sediment transport in nonlinear skewed oscillatory flows: Transkew experiments

Paulo A. Silva; Tiago Abreu; Dominic A. van der A; Francisco Sancho; B.G. Ruessink; Jebbe J. van der Werf; Jan S. Ribberink

New experiments under sheet flow conditions were conducted in an oscillating water tunnel to study the effects of flow acceleration on sand transport. The simulated hydrodynamic conditions considered flow patterns that drive cross-shore sediment transport in the nearshore zone: the wave nonlinearities associated with velocity and acceleration skewness and a negative mean current, the undertow. Net transport rates were evaluated from the sediment balance equation and show that (1) the acceleration skewness in an oscillatory flow produces a net sediment transport in the direction of the highest acceleration; (2) the net transport in the presence of an opposing current is negative, against the direction of the highest acceleration, and reduces with an increase in flow acceleration; and (3) velocity skewness increases the values of the net onshore transport rates.


Archive | 2016

Parameterizations of wave nonlinearity from local wave parameters: a comparison with field data

Mariana Vieira Lima Matias da Rocha; Paulo A. Silva; Hervé Michallet; Tiago Abreu; Delminda Moura; Juana Fortes

ABSTRACT Rocha, M.V.L., Silva, P.A., Michallet, H., Abreu, T., Moura, D., Fortes, C.J., 2013. Parameterizations of wave nonlinearity from local wave parameters: a comparison with field data Three different parameterizations of wave nonlinearity from local wave parameters are applied to field data (free-surface elevation and flow velocities) gathered in different beaches along the Portuguese coast, under diverse wave conditions. The hydrodynamics of the various sites are analyzed, together with the performance of each formulation. The data considered extend the range of the data previously used by the authors of the parameterizations, including longer wave lengths and higher Ursell numbers. A comparison is done, based on skill and agreement index values, to understand the performance and applicability of each parameterization and what could be changed to improve such formulations.


Visualization, Imaging and Image Processing / 783: Modelling and Simulation / 784: Wireless Communications | 2012

Modelling Horizontal Velcocities within the Wave Bottom Boundary Layer

Tiago Abreu; Paulo A. Silva; Francisco Sancho; Hervé Michallet; Luís Vasconcelos

As waves travel and shoal towards a beach, their surface elevation becomes peaky (sharp crests) and asymmetric relative to the vertical, differing from the sinusoidal profile of linear waves. Below the surface, the passage of the progressive waves induces fluid velocities, showing similar (time) asymmetries. These nonlinearities are inextricably linked to sediment transport, but the processes involved are not well understood. This work analyses the data collected during a recent experimental project under skewed oscillatory flows. It validates a simple method based on the defect law to reproduce the horizontal velocities within the wave bottom boundary layer. Results indicate a good agreement between the measured and modeled velocities using this methodology.


Journal of Waterway Port Coastal and Ocean Engineering-asce | 2016

Longshore Transport Estimation on Ofir Beach in Northwest Portugal: Sand-Tracer Experiment

Sandra Fernández-Fernández; Paulo Baptista; Virgínia Martins; Paulo A. Silva; Tiago Abreu; Joaquim Pais-Barbosa; Cristina Bernardes; Paulo Miranda; Mariana Vieira Lima Matias da Rocha; Fábio Alves dos Santos; Ana M. Bernabeu; Daniel Rey

AbstractThis work aims to shed some light on longshore sediment transport (LST) in the highly energetic northwest coast of Portugal. Data achieved through a sand-tracer experiment are compared with data obtained from the original and the new re-evaluated longshore sediment transport formulas (USACE Waterways Experiment Station’s Coastal Engineering and Research Center, Kamphuis, and Bayram bulk formulas) to assess their performance. The field experiment with dyed sand was held at Ofir Beach during one tidal cycle under medium wave-energy conditions. Local hydrodynamic conditions and beach topography were recorded. The tracer was driven southward in response to the local swell and wind- and wave-induced currents (Hsb=0.75m, Tp=11.5s, θb=8−12°). The LST was estimated by using a linear sediment transport flux approach. The obtained value (2.3×10−3m3⋅s−1) approached the estimation provided by the original Bayram formula (2.5×10−3m3⋅s−1). The other formulas overestimated the transport, but the estimations resu...


Archive | 2016

Use of the velocity defect law to assess sand transport rates

Tiago Abreu; Paulo A. Silva; Francisco Sancho; Hervé Michallet

ABSTRACT Abreu, T., Silva, P.A., Sancho, F. and Michallet, H., 2013. Use of the velocity defect law to assess sand transport rates. This work uses a simple method based on the defect law that is able to reproduce the horizontal velocities within the wave bottom boundary layer, using a limited number of parameters. The theory is checked against the measured velocity profiles gathered with a high resolution Acoustic Doppler Velocity Profiler. The velocities were collected during an experimental project performed at the Large Oscillating Water Tunnel of Deltares under flat-bed/sheet flow conditions, allowing the analysis of the effects of wave nonlinearities and of a net current on the sediment transport processes. The velocity estimates are used to infer the time-varying bed shear stress, using the momentum-integral method. Secondly, the bed shear stresses are incorporated in a quasi-steady bed load formulation and the transport rate predictions are compared with the net transport rate measurements obtained in the same facility. The results show that the methodology presented in this work provides a suitable estimation of the horizontal near-bed sediment transport rates under non-linear oscillatory flows.


Revista de Gestão Costeira Integrada - Journal of Integrated Coastal Zone Management | 2011

Ondas assimétricas em praias com barra

Tiago Abreu; Francisco Sancho; Paulo A. Silva

Natural beaches often present a breaker bar that significantly affect physical phenomena like, for example, wave transformation, wave refle...


Coastal Engineering | 2010

Analytical approximate wave form for asymmetric waves

Tiago Abreu; Paulo A. Silva; Francisco Sancho; André Temperville


Coastal Engineering | 2013

Bed shear stress under skewed and asymmetric oscillatory flows

Tiago Abreu; Hervé Michallet; Paulo A. Silva; Francisco Sancho; Dominic A. van der A; B.G. Ruessink


HYDRALAB IV Joint User Meeting, Lisbon, July 2014 | 2014

GLOBEX: Wave dynamics on a shallow sloping beach

Hervé Michallet; Gerben Ruessink; Mariana Vieira Lima Matias da Rocha; Anouk de Bakker; Dominic A. van der A; Andrea Ruju; Paulo A. Silva; Nadia Senechal; Vincent Marieu; Marion Tissier; Rafael Almar; Tiago Abreu; Florent Birrien; Laure Vignal; Eric Barthélemy; Dominique Mouazé; Rodrigo Cienfuegos; Peter Wellens

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Francisco Sancho

Laboratório Nacional de Engenharia Civil

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Hervé Michallet

Centre national de la recherche scientifique

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Eric Barthélemy

Centre national de la recherche scientifique

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