Papers
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Particle tracking-modeling of morphologic changes in the Ria de Aveiro
Tidal currents in an estuary carry all types of dissolved, suspended or floating material. Particle tracking models constitute powerful tools in assessing the transport of this material, through the study of the particles trajectoriesand settling positions. Thus, this work aims at using a Lagrangian particle tracking model driven by hydrodynamic fields to study the impact of morphologic anthropogenic and natural changes in sediments transport at Ria de Aveiro. In fact, as many coastal systems, Ria de Aveiro is in progressive degradation associated to the lack of maintenance and to the strong currents occurring in its channels, which erode theirprotective walls. Hence, the model VELApart, which is driven by the hydrodynamic model ELCIRC (previously calibrated for this lagoon), was applied for two configurations of the Ria de Aveiro: one representing the present situation of the lagoon and another representing a scenario with the enlargement of its flooded area. According tomodel results, morphologic changes influence the sediments pathways and final position, as well as the settling time. Generally for the flooded bathymetry the sediments travel a longer distance and the preferential zones of deposition are inside the flooded area, while for the present configuration sediments settle down in the mainadjacent channels. The settling times also increase with the enlargement of the flooded area.
Year: 2011
Number Pages:
1560 - 1564.
Author(s): Picado, A.; Silva, P. A.; Fortunato, A. B.; Dias, J. M.
: Journal of Coastal Research, ICS2011 (Proceedings)
Keywords: Settling time; Sediments pathway; Sediments transport; Flooded areas
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Performance of intertidal topography video monitoring of a meso-tidal reflective beach in South Portugal
This study discusses site-specific system optimizationefforts related to the capability of a coastal videostation to monitor intertidal topography. The systemconsists of two video cameras connected to a PC, and isoperating at the meso-tidal, reflective Faro Beach (Algarvecoast, S. Portugal). Measurements from the period February4, 2009 to May 30, 2010 are discussed in this study.Shoreline detection was based on the processing of varianceimages, considering pixel intensity thresholds for featureextraction, provided by a specially trained artificial neuralnetwork (ANN). The obtained shoreline data return ratewas 83%, with an average horizontal cross-shore root meansquare error (RMSE) of 1.06 m. Several empiricalparameterizations and ANN models were tested to estimatethe elevations of shoreline contours, using wave and tidaldata. Using a manually validated shoreline set, the lowestRMSE (0.18 m) for the vertical elevation was obtainedusing an ANN while empirical parameterizations based onthe tidal elevation and wave run-up height resulted in anRMSE of 0.26 m. These errors were reduced to 0.22 m afterapplying 3-D data filtering and interpolation of thetopographic information generated for each tidal cycle.Average beach-face slope tan(
Year: 2011
Number Pages:
1521-1540pp.
Author(s): Vousdoukas, M. I.; Ferreira, P. M.; Almeida, L. P.; Dodet, G.; Psaros, F.; Andriolo, U.; Taborda, R.; Silva, A. N.
Editor: Ocean Dynamics
Keywords: Remote sensing; Nearshore; Coastal erosion; Artificial neural networks; Coastal morphodynamics; Video monitoring
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Rehabilitation and protection of Colwyn Bay beach: a case study
Colwyn Bay beach is undergoing a process of erosion. The present study aims at characterizing the beachdynamics and developing alternative solutions for beach rehabilitation and protection. The method applied tocharacterize the foreshore morphological evolution was the assessment of the shoreline evolution, the analysis ofthe foreshore 3D evolution and the analysis of cross-shore profile evolution. The sedimentologic contents of thebeach were characterized based on the analysis of superficial samples. The hydrodynamic characterization wasbased on the analysis of the wave climate at three inshore points in front of the beach and of the tidal and surgelevels. These data provided the necessary information for the characterization of the longshore transport andevaluation of the beach active zone. The first part of developing alternative solutions was the definition of theoptimum long-term recharged beach profile, which, due to the high tidal range, was calculated based on the2S-EBP method. The beach berm was designed to avoid direct wave action on the seawall existent at the beachbackshore. For that, a morphodynamic model was applied to test the beach retreat under storm events. Finally,alternative long-term solutions based on a nourishment strategy were tested with two shoreline evolution models.Two initial alternative solutions of beach recharge with different grain size sand followed by six alternativesolutions of beach recharge with sand retention structures arrangements were tested. The results, herequalitatively and qu
Year: 2011
Author(s): Oliveira, F. S. B. F.; Freire, P.; Sancho, F. E.; Vicente, C.; Clímaco, M.
: Journal of Coastal Research
Editor: Journal of Coastal Research
Volume:
Nº. 64, Vol.II.
Keywords: Beach nourishment; Beach dynamics; Erosion
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Sediment transport in nonlinear skewed oscillatory flows: Transkew experiments
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 nonlinearitiesassociated with velocity and acceleration skewness and a negative mean current, the undertow. Net transport rates were evaluated from the sedimentbalance equation and show that (1) the acceleration skewness in an oscillatory flow produces a net sediment transport in the direction of the highestacceleration; (2) the net transport in the presence of an opposing current is negative, against the direction of the highest acceleration, and reduces with anincrease in flow acceleration; and (3) velocity skewness increases the values of the net onshore transport rates.
Year: 2011
Number Pages:
72-80pp.
Author(s): Silva, P. A.; Abreu, T.; Van der A, D. A.; Sancho, F. E.; Ruessink, B. G.; Werf, J.; Ribberink, J.
: Journal of Hydraulic Research
Editor: Journal of Hydraulic Research
Keywords: Wave skewness; Wave asymmetry; Sheet flow; Sediment transport; Flow acceleration
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Short-Term Sediment Transport at a Backbarrier Beach
This article defines short-term (tidal cycle) sediment-transport patterns at a backbarrier beach based on detailed fieldstudies. Fieldwork was planned to record nonstorm, spring tide conditions that enable the definition of backgroundsediment dynamics at the study area. The experiment was set at two beach morphologies: beach face and sandbank.Current meters were deployed at both sites. Fluorescent tracer techniques were applied to determine rates and directionof transport. Topographic surveys and sediment sampling were undertaken. During the experiment, limited tracerdisplacement and small morphological changes occurred. The low magnitude changes are representative of predominant,low-energy hydrodynamic conditions. Sediment transport was primarily longshore orientated and dependent on thevelocity of tidal currents. Tidal currents had the potential for sediment transport only during a short period of the tidalcycle and had higher velocities during ebb, which results in a net sediment transport orientated towards the nearby inlet.It is suggested that there is dependence on sediment transport rate at the study site and on the variability of tidalcurrents, which are greatly influenced by the distance to, and conditions of, the nearby Anca
Year: 2011
Number Pages:
1076-1084pp.
Author(s): Carrasco, A. R.; Ferreira, Ó.; Pacheco, A.; Freire, P.
: Journal of Coastal Research
Editor: Journal of Coastal Research
Keywords: Hydrodynamic conditions; Fluorescent tracer; Sediment dynamics
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Surf hydrodynamics in front of collapsing coastal dunes
The hydrodynamics of the surf zone in front of collapsing coastal dunes are examined. The data was gatheredduring the HYDRALAB-III funded Transnational Access experiment performed at the CIEM large-scale waveflume. Here, it is presented results of the cross-shore evolution of several flow parameters at four positions. Despikedand band-pass filtered ADV velocity data were used to enable a focus on only the short-wave component.As the waves approach the shore they reduce their (velocity) skewness, but increase their vertical asymmetry.Despite the non-negligible wave reflection, the theoretical wave model of Abreu et al. (2010) was applied tosuccessfully reproduce the measured velocities. Lastly, an estimate of the bed shear stress exerted by the shortwavecomponents is presented.
Year: 2011
Number Pages:
144-148pp.
Author(s): Sancho, F. E.; Abreu, T.; D´Alessandro, F.; Tomasicchio, G.; Silva, P. A.
: Journal of Coastal Research
Editor: Journal of Coastal Research
Keywords: Non-linear waves; Velocity asymmetry; Velocity skewness; Bed shear stress
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The importance of the topo-hydrogaphy in the prediction of the short and medium-term evolution of the coastal zone
N/A
Year: 2011
Number Pages:
239-242pp.
Author(s): Oliveira, F. S. B. F.; Freire, P.; Clímaco, M.
Editor: Instituro Hidrográfico
Keywords: Beach; Shoreline; Morphodynamics; Prediction; Coastal evolution
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Waves, wind and tidal forcing on a sandpit morphodynamics
Due to the increasing demand of sand for construction and beach nourishment, offshore extraction is being considered as an alternative source. Long term morphological changes caused by such an extraction must bepredicted because they can affect the sediments budget and potentially promote coastal erosion. Numerical models are powerful tools that can help in the evaluation of environmental impacts induced by this activity.The objective of this study is to describe the morphodynamics in the area surrounding a sandpit through the use of the MORSYS2D modelling system. The sandpit under study is located offshore Vale do Lobo, an importantbeach and golf resort located on the Southern Portuguese coast. The numerical solutions of the mean flow and the wave height around the pit were obtained with MORSYS2D between March 28 and April 29, 2008 when two storm events with significant wave height (Hs) greater than 2.5 m occurred.The numerical results are analysed in terms of the sand fluxes and bathymetry changes induced by wind and tidal currents and wave orbital velocities. The results show the strong impact of storm events in the morphologic evolution of the pit and surrounding area. The value for Hs > 2.5m was also confirmed as determinant for thesediment dynamics.
Year: 2011
Number Pages:
1170 - 1174.
Author(s): Rosa, J.; Silva, P. A.; Bertin, X.; Fortunato, A. B.
: Journal of Coastal Research, ICS2011 (Proceedings)
Volume:
SI 64.
Keywords: Morphodynamic model; Continental shelf; Sand extraction
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Analytical approximate wave form for asymmetric waves
A simple analytical formulation that reproduces a skewed, nonlinear near-bed wave orbital velocity is presented. It contains four free parameters, where two are solely related to the velocity and accelerationskewnesses. The equation is compared with other models and is validated against field and laboratoryexperiments. The results reveal that it can simulate a wide range of nonlinear wave shapes, reproducing satisfactorily the measured nonlinear wave particle velocity. Also, the new expression overcomes somelimitations of the other models. The new formulation is therefore capable of being used in many engineering applications that require the use of representative wave forms.
Year: 2010
Number Pages:
13p.
Author(s): Abreu, T.; Silva, P. A.; Sancho, F. E.; Temperville, A.
: Coastal Engineering
Volume:
57, 7.
Keywords: Orbital velocity; Acceleration skewness; Wave asymmetry; Wave skewness
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Application of empirical models to bay shaped beaches in Portugal
Three models were applied to analyse the planform of bay-shaped Portuguese beaches. They are based on empirical mathematical functions: the logarithmic spiral bay equation, the hyperbolic tangent bay equation, and the parabolic bay equation. These models were applied to analyse the fitting to the beach planform of 42 beaches on the Portuguese Atlantic coast which was calculated through the validation against the waterline extracted from rectified aerial photographs. The logarithmic spiral model fits well the curved zone of the beaches, in particular small beaches with two headlands. Despite the good fitting of the hyperbolic tangent model for one headland beach, its process of approximation to the solution was less intuitive than the processes of the other two models, therefore its application was more exhaustive. A comparative analysis between the logarithmic spiral model and the hyperbolic tangent model revealed the best fit of the first. The application of the parabolic model allowed to conclude that despite the majority of the beaches analysed being in dynamic equilibrium condition due to the high energy wave regime of the Portuguese Atlantic coast, their planform was very close to the planform in static equilibrium condition due to the high dynamics of the coastal environment
Year: 2010
Number Pages:
pp. 124-131.
Author(s): Oliveira, F. S. B. F.; Barreiro, O. M.
: Coastal Engineering
Volume:
Vol. 57, No. 2.
Keywords: Portuguese bay beaches; Headland bay beach; Shoreline modelling; Beach planform
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Comunicação
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The Tagus estuary
The estuary of the Tagus river is one of the largest estuaries in Europe covering an area of about 320 km2. It is located in the Portuguese west coast, in the metropolitan area of Lisbon, and due to its social and economic context and environmental characteristics it is the Portuguese most relevant estuary. The estuary comprises along its margins 11 municipalities with about 1.6million inhabitants (Tavares et al., 2015). It hosts the Port of Lisbon, the national leader in the movement of vessels (in number and in GT), and the Tagus Estuary Natural Reserve considered one of the most important sanctuaries for birds in Europe.
Year: 2019
Number Pages:
54-56pp..
Author(s): Freire, P.
: Collection of Papers. 6th Biennal Conference Particles in Europe, PiE-2018. Lisbon, Portugal, 14-17 October 2018
Editor: -
Keywords: Tagus; Estuary
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Tidal influence on the phytoplankton community of Tagus estuary
Estuaries are highly variable systems and the most productive ecosystems in the world.Phytoplankton is a major contributor to the high productivity, rapidly responding to changes inthe environment
Year: 2019
Number Pages:
1p.
Author(s): Cereja, R.; Cruz, J.; Brito, A.; Rodrigues, M.; Brotas, V.
Editor: EEF 2019
Keywords: Tagus; Tidal influence
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Topo-bathymetric monitoring south of the Mondego river mouth after the extension of the north jetty
This work evaluates the morphological evolution of the coastal frontage south of Figueira da Foz (west coast of Portugal) after the extension of the north jetty based on the analysis of topo-bathymetric surveys located in twelve equidistant transepts in the study site. The results show that the study site has large inter-annual morphological variations and the complex morphological behaviour shows an erosive tendency of the beach face downdrift of the structures.
Year: 2019
Number Pages:
19-20pp.
Author(s): Oliveira, J. N.; Oliveira , F.; Teixeira, A.
: 5ª Conferência sobre Morfodinâmica Estuarina e Costeira - Livro de Resumos
Editor: Faculdade de Ciências da Universidade de Lisboa
Keywords: Figueira da Foz.; Erosion; Beach morphodynamics; Hydro-topographic profiles; Nearshore monitoring
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Towards an operational hydrodynamics and biogeochemical model of the Tagus estuary
Climate change and the predicted increase of human activities in estuaries may increase the hazards inthese systems. Water observatories can support both the daily and the long-term management of estuarineecosystems. Although in the past water observatories were mostly based on observations, these tools haveevolved to account for forecasts, scenarios analysis and indicators
Year: 2019
Number Pages:
1p.
Author(s): Rodrigues, M.; Santos, D.; Rogeiro, J.; Fortunato, A. B.; Teixeira, J.; Oliveira, A.; Martins, R.
Editor: International Society for Ecological Modelling / Elsevier
Keywords: Estuary; Tagus
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Using HPC to enable coastal waters observatories
Coastal systems are among the most productive ecosystems in the world, providing multipleresources and guaranteeing the resilience of the coastal communities. Climate change (e.g.,sea level rise) represents a major threat to the world
Year: 2019
Number Pages:
1p.
Author(s): Rodrigues, M.; Oliveira, A.; Martins, R.; Rogeiro, J.; Santos, D.; Fortunato, A. B.; Azevedo, A.
Editor: Ibergrid 2019
Keywords: Waters; HPC
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Water observatories as supporting tools to climate change adaptation in coastal ecosystems
Climate change, such as sea level rise, represents a major threat to the world
Year: 2019
Number Pages:
1p.
Author(s): Rodrigues, M.; Cravo, A.; Fortunato, A. B.; Oliveira, A.; Martins, R.; Jacob, J.; Rogeiro, J.; Rosa, A.; Santos, D.; Freire, P.; Azevedo, A.
Editor: ECCA 2019
Keywords: Coastal; Water
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Bound and free infragravity waves over a bar
This study aims to investigate the changes in the infragravity wave energy under partialshort-wave breaking conditions induced by a longshore bar. Field observations of near-bottompressure records on a cross-shore array were analysed for such purpose. The bispectrum wasemployed to detect the phase-coupling between short and infragravity wave frequencies. This allowedto separate the infragravity wave energy in bound and free energy components.The bar crest induced a decrease on the short-wave energy due to depth-induced breaking. At thesame location, a damping on the bound infragravity wave energy was observed. This dampingcoincides with a negative value of the short-wave radiation stress cross-shore gradient. This providesevidence that bound infragravity wave energy decreases with a reduction in the forcing.
Year: 2018
Number Pages:
198-201pp..
Author(s): Mendes, D.; Pires Silva, A.; Pinto, J.; Fortunato, A. B.
Editor: Instituto Hidrogrâfico
Keywords: S. Jacinto; Field observations; Bispectral analysis; Infragravity waves
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Dinâmica sedimentar e evolução a longo prazo do porto da Praia, ilha de Santiago, Cabo Verde
Resumo: Os processos de evolução costeira em Cabo Verde, resultantes de fatores naturais e deatividades humanas, são ainda pouco conhecidos. Analisa-se neste trabalho a evolução morfológica dabaía do porto da Praia, na ilha de Santiago, com base em levantamentos hidrográficos de 1882 a 2016,fotografia aérea, imagens de satélite e cartografia histórica. Recorre-se também à modelaçãomatemática de processos hidrodinâmicos e morfodinâmicos, considerando a interação ondascorrentes,para interpretar as condições locais. Os elementos analisados sugerem uma tendência deacumulação sedimentar, com uma taxa média de avanço da praia, a longo prazo, da ordem de 1 m/ano.Estima-se que o caudal sólido transportado episodicamente pelas ribeiras afluentes seja uma fontesedimentar importante. Embora a recente expansão do porto tenha diminuído a influência da ação dasondas, as condições mais favoráveis à remobilização e à circulação sedimentar no interior da baíapermanecem associadas aos períodos de agitação marítima mais energética
Year: 2018
Number Pages:
245-248pp..
Author(s): Portela, L. I.
Editor: Instituto Hidrogrâfico
Keywords: Morfodinâmica; Modelação; Cartografia hidrográfica; Acreção; Cabo Verde
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Evolução da praia da Nazaré após a construção do porto de pesca
Evolution of Nazaré beach after the construction of the fishing harbour
Year: 2018
Number Pages:
321-322pp..
Author(s): Portela, L. I.; Teixeira, S.; Sancho, F. E.
Editor: Departamento de Ciências da Terra da Universidade de Coimbr
Keywords: Morphodynamics; Linear regression; Beach; Accretion; Nazaré; GIS; EPR
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Monitoring the implementation of a dredging plan in the Óbidos Lagoon (Portugal)
The Óbidos lagoon (central west coast of Portugal) is a small coastal system exposed tointense wave action. Because its inlet is highly dynamic and closes occasionally, frequent interventionshave been carried out by local and national authorities. However, their results have been ephemeral, andthe interventions
Year: 2018
Number Pages:
273-276pp..
Author(s): Freire, P.; Fortunato, A. B.; Portela, L. I.; Azevedo, A.
Editor: Instituto Hidrogrâfico
Keywords: Dredging; Monitoring; Hydrodynamics; Morphologic evolution; Tidal inlet
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Books
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MEC2011 - Conferência sobre Morfodinâmica Estuarina e Costeira
N/A
Year: 2011
Author(s): Fortunato, A. B.; Freire, P.; Oliveira, A.
Editor: Laboratório Nacional de Engenharia Civil
Volume:
CD Room.
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Capítulo de Livro
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Evaluating the geomorphologic stability of an estuarine sandy beach. Integrated Coastal Zone Management
The hydrodynamics and sediment dynamics of a low energy estuarine beach was analysed. The beach is subjected to local wind waves generated in an area of restricted fetch, wake waves generated by catamarans and a semi diurnal meso-tidal regime. Only storm events of short duration modify the beach profile, which, once the normal hydrodynamic conditions are restored, naturally recovers its initial shape. The beach is characterised by having a steep upper slope until mean sea level, followed, seaward, by a low gradient terrace, and a bimodal sediment distribution. To investigate the hydro sedimentologic beach behaviour, wind, topo-hydrographic and sedimentologic data were used as input and validation of process based numerical modelling. Wave generation and transformation in an area of restricted fetch, nearshore circulation, sediment transport and morphological evolution were simulated for average annual conditions and storm conditions. The statistical analysis of a six-year wind data series allowed to derive the average wind regime, based on which, the average annual wave regime and the average annual longshore sediment budget, 14.5x103 m3year-1, were calculated. The contribution of the individual components of the representative wave regime, discretised by directional sector and height class of incidence, was evaluated as well as the spatial distribution of the longshore sediment transport in the active part of the beach profile. The characteristics of the wave groups generated by the passage of catamarans at different speeds were estimated and their action on the beach morphology was simulated. Although when the catamarans travel at 20 knots speed the average annual wake wave energy dissipated at the beach is 2.5 times higher than the average annual wind wave energy, the erosion effect on the beach profile is still not relevant for the present traffic. In opposition, short duration storm events generate the formation of an erosion scarp at the upper part of the beach face. The numerical modelling of this phenomenon allowed to acknowledge on the protective effect that the low gradient terrace has on the beach face.
Year: 2009
Number Pages:
pp. 35-49.
Author(s): Oliveira, F. S. B. F.; Vargas, C.
Editor: Wiley-Blackwell Publishing
Volume:
Integrated Coastal Zone Management.
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Tese de Doutoramento
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Three-dimensional modelling of cohesive sediment transport in estuarine environments
N/A
Year: 1995
Author(s): Costa, R.
Editor: ******
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A Two-Dimensional Hydrodynamic Model Using a Finite-Volume Approach
A two-dimensional model of wind-driven circulation in a closed basin was developed using a finite-volume technique for generalized curvilinear grids and applying some of the recent developments in hydrodynamic modeling. The terms in the Navier¬Stokes equations were treated separately according to the fractional step method and the propagation step, including the continuity equation and the pressure and stress terms in the momentum equations, was solved using a conjugate gradient method.The model was then applied to a number of test cases to examine the feasibility of the approach used by comparing with results obtained with the two-dimensional version of the three-dimensional model CH3D. These included a square basin with constant slope and with a V-shaped bottom and Lake Okeechobee, in South Florida. To evaluate the long-term numerical stability of the model, a ten-day model simu¬lation with varying wind was also run for Lake Okeechobee.
Year: 1989
Author(s): Capitao, J.
Editor: ******
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Flow-Fine Sediment Hysteresis in Sediment-Stratified Coastal Waters
An examination of the causes for generation and dynamics of turbidity maxima in estuaries reveals the critical role of sediment tidal pumping phenomenon and, to a lesser extent, of the well-known effect of residual gravitational circulation due to salt water penetration. Both phenomena depend on the vertical sediment concentration profile and, consequently, on the magnitude of the vertical mass transport fluxes. Where high concentration suspensions occur regularly, the erosion/deposition fluxes can be drastically modified by sediment stratification, consequently influencing sus¬pended sediment response to currents and wave action. This influence is inherent in flow-sediment hysteresis, which therefore reflects the role of vertical mass transport in the estuarine and coastal suspended fine sediment regime.A vertical transport numerical model was used to investigate the influence of several key parameters describing sediment settling, bed properties and stabilized diffusion on the concentration profile. The model was also applied to simulate the influence of the same parameters on the time-lagged sediment response to flow variations, reflected in the characteristics of flow-sediment hysteresis loops.Field data obtained in Hangzhou Bay (People´s Republic of China), a high concentration environment, showed typical features of flow-sediment hysteresis and confirmed the importance of the vertical mass fluxes in contributing to sediment transport in the bay. A qualitative simulation provided by the numerical model, using settling parameters corresponding to local sediment, while confirming the importance of the hysteresis phenomenon, also revealed the critical need to use algorithms describing adequately stabilized diffusion and bed fluxes.Additional evidence of hysteresis was obtained through analysis of microscale variables, such as the Reynolds stresses and the variances of the velocity components resulting from combined effects of wave action and turbulence. Spectral analysis of the measured random variations did not support the commonly accepted hypothesis of similarity between the responses to turbulent flow of sediment concentration and temperature. The normalized turbulent intensities for all the measured veloc¬ity components showed their highest values during the period of lowest sediment concentration; this result is consistent with the hypothesis of turbulent intensity damping by suspended sediment.
Year: 1989
Author(s): Costa, R.
Editor: ******
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Alimentação artificial de praias
A contribution to increased use and development of the method of artificial nourishment of beaches is the main objective of this thesis. It also aims at being a guide for the design of the reconsctrution or outright creation of beaches.In the first chapter, the subject is introduced and the objectives of the thesis are outlined. The second chapter cover´s some general considerations on littoral dynamics, beach equilibrium and sediment budget.Since the theoretical foundations of the artificial nourishment of beaches still leave much to be desired, a description of this method and its principles are presented in the third chapter. Important technical and economic aspects are included, such as: sampling, analysis and characterization of native and borrow material; selection Of nourishment sources; extraction and transport of borrow sand; and characteristics of the theoretical final beach profile. Such problems as the integration of ecological aspects, and cost-benefit analysis are also treated.in the fourth chapter, the Portuguese experience in this domain is described. The experience of such countries as France and the U.S., where this method has frequently been used is also mentioned. In this way a considerable amount of hitherto scattered information is presented in a unified way.The fifth chapter, treats briefly the problem of coastal model similitude, both as a support for the experimental work: which was carried out and to help engineers in the design of a coastal physical model or in merely assessing the possibilities of such a model.In the sixth chapter, an experimental study is described of the influence of both the grain size of borrow material and the nourishment method on the redistribution of sediments after the nourishment. The obtained results are compared with existing theoretical methods and some prototype results.Finally, in the last chapter the main conclusions and recomendations of the thesis are presented.
Year: 1987
Author(s): Clímaco, M.
Editor: ******
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Solution of Advection-Dominated Transport by Eulerian-Lagrangian Methods Using Backwards Method of Characteristics
We provide a systematic analysis of the consistency, stability, convergence and accuracy of the numerical solution of the transport equation by a general Eulerian-Lagrangian Method (ELM). The method involvesthree basic steps: the backwards tracking of characteristic lines following the flow, the interpolation of concentrations at the feet of these lines, and the solution of dispersion taking such concentrations as initial conditions. The first two steps constitute the Backwards Method of Characteristics (BMC); the third step involves a time-discretization along the characteristic lines, and a spatial discretization of the dispersion operator, both based on conventional techniques (e.g.. Euler or Crank¬Nicholson for time; finite-elements or finite-differences for space).The choice of the spatial interpolator is shown to impact the consistency, stability and convergence, as well as the accuracy of the BMC. Most interpolators ensure consistency, but only a few ensure stability, hence convergence; stability criteria are derived from a newly developed generalized Fourier analysis, which can account for non-linearities introduced by quadratic grids. The comparison of formally derived propagation and truncation errors, complemented by numerical experimentation, provides a reference for the choice of the interpolator, given a specific transport problem characterized by prevailing concentration gradients.The BMC potentiates the use of large time-steps, well above Courant number of order one. In the limiting case of pure advection, optimal accuracy would be obtained for a At close to the total time of interest; the presence of dispersion constrains, however, the size of At, especially in the case of non-uniform flows. The comparison of the truncation errors for the three basic steps of ELM provides a reference to select At. as a function of Ax, of the spatial interpolators and time-discretization schemes, and of the gradients of flow and concentrations.
Year: 1987
Author(s): Melo Baptista, A.
Editor: ******
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Accurate Numerical Modeling of Advection-Dominated Transport of Passive Scalars. A Contribution
Apresenta-se um estudo sistemático, baseado simultaneamente em análises formais e em experimentação numérica, da precisão e estabilidade da solução da equação de transporte por um método Euleriana-Lagrangeana (MEL). 0 método decompõe a equação de transporte em equações separadas de advecção e de difusão, resolvendo a primeira pelo método das características regressivas no tempo (MCR), e a segundo por um método de elementos finitos, do tipo Galerkin.Mostra-se que as interpolações no espaço requeridas pelo MCR são um factor limitativo da precisão global do MEL, e comparam-se diversas técnicas alternativas de interpolação, algumas das quais originais. A combinação de esquemas compactos e não-compactos de interpolação, baseados em polinómios de Lagrange, é apontada como uma potencial solução óptima.Demonstra-se que, para uma adequada escolha do esquema de interpolação, o MCR é consistente, estável e convergente e tem boas características de precisão. Escolhas inadequadas do esquema de interpolação podem, no entanto, causar instabilidade e inconsistência.Estabelece-se a dependência da precisão do MCR no passo de cálculo, mostrando-se que essa precisão aumenta, em geral (para um tempo total fixo), quando se reduz o número de passos de cálculo, isto é, quando se aumenta o passo de cálculo (uma propriedade simultaneamente pouco habitual e muito conveniente). No entanto, na gama de valores muito pequenos do Número de Courant, a precisão é praticamente independente do passo de cálculo, o que evita que o método se torne divergente.Analisa-se brevemente o efeito de malhas irregulares e pluridimensionais sobre a aplicabilidade e precisão do MCR. Apesar de sensível à irregularidade da malha, o método mantém boas características de precisão desde que as distorções geométricas não sejam excessivas. Malhas pluri-dimensionais, quando simultaneamente irregulares, levantam problemas específicos de aplicabilidade de esquemas não-compactos de interpolação; esses problemas poderão se resolvidos através da utilização conjugada de esquemas compactos e não-compactos, para um mesmo problema. Investigação adicional a ainda requerida nestas áreas.Mostra-se ainda que a presença de mecanismos físicos de difusão beneficia tanta a precisão da solução da equação de advecção como a precisão global do MEL.Finalmente, demonstra-se a eficácia da aplicação do MEL (numa forma particular, restricta a esquemas de interpolação compactos) à simulação do transporte de poluentes em águas costeiras. 0 método permite, em particular, realizar simulações longas (várias marés) a custos moderados, mesma para malhas irregulares com elevado número de nós, e, também, evitar a necessidade do uso de difusividades artificiais como garante de estabilidade; em geral, e nestes dois aspectos em particular, o método revela-se superior a métodos Eulerianos, mais convencionais (por exemplo, métodos de elementos finitos, do tipo Galrkin ou Petrov-Galerkin, aplicados à equação de transporte indivisa).
Year: 1986
Author(s): Melo Baptista, A.
Editor: ******
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Sobre a Avaliação de Parâmetros de Qualidade de Água por Detecção Remota: Suspensões
No âmbito de um projecto de investigação intitulado caracterizarão de Formações Estuárias e do Meio Marítimo Litoral Por Técnicas de Detecção Remota , insere-se o estu¬do da avaliação de suspensões na água do mar com recurso à aplicação de técnicas de detecção remota como meio de caracterização de parâmetros de qualidade de água. 0 trabalho que se apresenta foi desenvolvido com os seguintes objectivos:1- Desenvolvimento de metodologias de análise e quantificação de suspensões na água do mar a partir de dados de satélite;2- Implementação sob forma de programas para computador de modelos de quantificação de suspensões orgânicas e inorgânicas na água do mar, a aplicar aos dados do radiómetro CZCS do satélite NIMBUS-7;3- Aplicação e verificação do modelo ao litoral português.Corn vista à consecussão destes objectivos, começa-se por apresentar uma extensa análise das formas de abordagem do problema, enumerando-se os diversos métodos actualmente seguidos, nomeadamente o Empírico, o Teórico e, neste, os métodos microscópico e macroscópico.Com base nesta análise, propõe-se um modelo numérico de quantificção das suspensões a partir dos dados do radiómetro CZCS do satélite NIMBUS-7, o qual, embora empírico na sua formulação como a maioria dos actualmente existentes, se apoia no comportamento radiomótrico da água do mar e dos seus constituintes típicos, cujas características se apresentam também.A implementação prática do modelo exige a filtragem da componente atmosférica presente nos dados rediométricos. Com este objectivo, apresenta-se um modelo baseado na metodo¬logia correntemente utilizada. Consiste na consideração da difusão simples, causada pelos constituintes básicos da atmosfera (moléculas gasosas, aerosóis e ozono) na gama de comprimentos de onda considerada (440, 520, 550 e 670nm). Esta metodologia conduz, porém, a um sistema de equações indeterminado e que é resolvido pela consideração de uma equação ´exterior´ ao processo de transferência radiativa que tem lugar na atmasfera. Para este efeito, utilizou-se a equação de Smith e Wilson por ser a mais divulgada, ressalvando-se, contudo, a necessidade de verificação da sua efectiva aplicação às águas do litoral português, o oqe não foi possível concretizar dada a inexistência de dados.
Year: 1986
Author(s): Oliveira, E. M.
Editor: ******
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Eulerian-Lagrangian Analysis of Pollutant Transport in Shallow Water
A numerical method for the solution of the two-dimensional, unsteady, transport equation is formulated, and its accuracy is tested.The method uses a Eulerian-Lagrangian approach, in which the transport equation is divided into a diffusion equation (solved by a finite element method) and a convection equation (solved by the method of characteristics). This approach leads to results that are free of spurious oscillations and excessive numerical damping, even in the case where advection strongly dominates diffusion. For pure diffusion problems, optimal accuracy is approached as the time-step, At, goes to zero; conversely, for pure-convection problems, accuracy improves with increasing At; for convection-diffusion problems the At leading to optimal accuracy depends on the characteristics of the spatial discretization and on the relative importance of convection and diffusion.The method is cost-effective in modeling pollutant transport in coastal waters, as demonstrated by an illustrative application to a case study (sludge dumping in Massachusetts Bay). Numerical diffusion is eliminated or greatly reduced, raising the need for realistic estimation of dispersion coefficients. Costs (based on CPU time) should not exceed those of conventional Eulerian methods and, in some cases (e.g., problems involving predictions over several tidal cycles), considerable savings may even be achieved.
Year: 1984
Author(s): Melo Baptista, A.
Editor: ******
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Sobre a Propagação de Ondas do Mar em Regiões Costeiras. Análise pelo Método dos Elementos Finitos
0 principal objectivo desta tese é mostrar a habilidade do métodos dos elementos finitos e do método dos elementos de fronteira na modelação das ondas gravíticas de superfície.Na análise linear, as equações reduzidas do movimento ondulatório são resolvidas pelo método dos elementos finitos, levando em linha de conta a reflexão parcial, a radiação e o atrito de fundo. A modelação da radiação é feita com elementos infinitos ou com elementos de radiação, sendo estes encarados como um caso particular dos elementos de reflexão. 0 atrito de fundo é introduzido após a discretização e é levado a efeito através de um coeficiente empírico que se pode relacionar com o coeficiente de Chezy.Quer o modelo determinístico quer o modelo estocástico, obtido do primeiro com base na noção do estimador natural, permitem a realização de ensaios de ressonância ou de agitação. Nos ensaios de ressonância de uma bacia portuária tem particular interesse o conhecimento do espectro de resposta ao ruído bran¬co de banda limitada.A título de exemplo de aplicação mostram-se alguns aspectos do estudo das condições de ressonância do porto de Leixões.Logo que não sejam válidas as hipóteses simplificativas que permitem uma abordagem linear das ondas gravíticas de superfície, são resolvidas as equações não lineares do movimento ondulatório com superfície livre, pelo método dos elementos de fronteira. As suas peculiaridades permitem, sem qualquer dúvida, considerar o método dos elementos de fronteira como o mais vocacionado para este tipo de análise.Os programas de cálculo automático para o estudo da análise não linear estão ainda em fase de teste, pelo que não se apresentam exemplos de aplicação.
Year: 1982
Author(s): Portela, A.
Editor: ******
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Numerical simulation of the tidal flow in homogeneous estuaries
Este trabalho é dirigido principalmente para o uso da simulação numérica dos escoamentos em estuários como uma ferramenta pa¬ra estudos de engenharia. Fazem-se algumas considerações gerais sobre a definição e classificação de estuários seguidas por uma descrição sumária da hidrodinâmica dos estuários. Descrevem-se e comparam-se as várias técnicas utilizadas na solução de problemas de hidradinâmica de stuários.Faz-se a dedução formal de um modelo matemático do escoamento em estuários homogéneos e integram-se verticalmente as suas e¬quações, obtendo-se as conhecidas equações do escoamento em águas pouco profundas ("shallow water equations"). Estas equações são discretizadas utilizando os métodos dos elementos finitos e das diferenças finitas, respectivamente no espaço e no tempo.Faz-se a descrição de um sistema de cálculo para determinar a solução do modelo matemático discretizado e tecem-se várias considerações acerca do seu desenvolvimento e uso.Finalmente apresentam-se os resultados de alguns testes utilizados para verificar o funcionamento do sistema de cálculo.
Year: 1981
Author(s): Figueira, P.
Editor: ******
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Relatório Científico
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Extracção de areias na plataforma Continental Portuguesa: Impactos e evolução morfodinâmica - Evolução da linha de costa
N/A
Year: 2010
Number Pages:
51pp.
Author(s): Proença, B.; Oliveira, F. S. B. F.
Editor: LNEC
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Impacte das alterações climáticas na embocadura da Lagoa de Óbidos - Relatório de actividades do Doutor Nicolas Bruneau no projecto G-CAST
N/A
Year: 2010
Number Pages:
27pp.
Author(s): Bruneau, N.; Fortunato, A. B.; Oliveira, A.
Editor: LNEC
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Madycos
N/A
Year: 2010
Number Pages:
51pp.
Author(s): Oliveira, A.
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Madycos
N/A
Year: 2010
Number Pages:
50pp.
Author(s): Oliveira, A.
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MADYCOS
N/A
Year: 2010
Number Pages:
46pp.
Author(s): Freire, P.
Editor: LNEC
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Caracterização hidrodinâmica e sedimentar do Esteiro dos Frades, Ria de Aveiro - Observações em 2009
N/A
Year: 2009
Number Pages:
31pp.
Author(s): Portela, L. I.; Freire, P.
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Coluna de sedimentação - Velocidade de queda de sedimentos do Esteiro dos Frades, Ria de Aveiro
N/A
Year: 2009
Number Pages:
31pp.
Author(s): Portela, L. I.; Brito, F.
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Modelação numérica de praias encaixadas
O objectivo do presente trabalho é o melhoramento da simulação do equilíbrio depraias encaixadas através da adaptação de um modelo de evolução de linhas decosta. Foram aperfeiçoadas as componentes do modelo que simulam a difracção emsaliências fixas e os seus efeitos sobre a movimentação das areias e morfologia dapraia.Com vista a aferir as melhorias obtidas recorreu-se à comparação dos resultados damodelação com a formulação semi-empírica de previsão da morfologia de praiasparabólicas e com casos reais de praias encaixadas da costa portuguesa.
Year: 2009
Number Pages:
39pp.
Author(s): Vicente, C.; Pisco, V.
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MODELAÇÃO NUMÉRICA DE QUEBRA-MARES DESTACADOS
A crescente utilização internacional de quebra-mares destacados na estabilização deorlas costeiras levou à sua inclusão no modelo de evolução de linha de costa,Litmod, desenvolvido pelo LNEC.Foi introduzido no modelo este tipo de obras e simulados os efeitos da difracção eda variação da altura ao longo da linha de rebentação sobre a intensidade dotransporte das areias.Foram efectuados testes de desenvolvimento de salientes e formação de tômbolostendo-se verificado uma boa concordância entre os resultados obtidos e osprovenientes de dados da natureza e de modelos físicos, apresentados pordiferentes autores.
Year: 2009
Number Pages:
69pp.
Author(s): Vicente, C.; Clímaco, M.; Pisco, V.
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HIDRODINÂMICA E DINÂMICA SEDIMENTAR DA ORLA COSTEIRA
O presente relatório refere-se ao estudo de investigação Hidrodinâmica e Dinâmica Sedimentar daOrla Costeira do projecto de investigação Morfodinâmica de Praias, enquadrado na área temática doDepartamento de Hidráulica e Ambiente (DHA) Hidrodinâmica e Dinâmica Sedimentar em Sistemasde Águas Superficiais e na área temática do Laboratório Nacional de Engenharia Civil (LNEC)Ambiente e Sustentabilidade, do Plano de Investigação Programada (PIP) do LNEC para 2005-2008.
Year: 2008
Number Pages:
115pp.
Author(s): Oliveira, F. S. B. F.; Freire, P.; Sancho, F. E.; Clímaco, M.; Trovisco, L.
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Outro
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Estuarine and coastal morphodynamics
N/A
Year: 2015
Author(s): Fortunato, A. B.; Bertin, X.; Coco , G.; Concejo, A.; Dias, J. M.; Fernandes, E.; Larson, M.; Matias, A.; Oliveira, A.; Silva, P. A.; Dias, J. A.; Azeiteiro, U.; Costa , M.; Boski, T.
Keywords: coastal; Estuarine
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