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Antwerpen, Belgium

Brouwer R.L.,Technical University of Delft | Brouwer R.L.,Flanders Hydraulic Research | de Schipper M.A.,Technical University of Delft | Rynne P.F.,University of Miami | And 4 more authors.
Journal of Atmospheric and Oceanic Technology | Year: 2015

This study investigates the potential of rotary wing unmanned aerial vehicles (UAVs) to monitor the surfzone. This paper shows that these UAVs are extremely flexible surveying platforms that can gather near-continuous moderate spatial resolution and high temporal resolution imagery from a fixed position high above a study site. The rotary wing UAVs used in this study can fly for ~12 min with a mean loiter radius of 1-3.5 m and a mean loiter error of 0.75-4.5 m. These numbers depend on the environmental conditions, flying style, battery type, and vehicle type. The images obtained from the UAVs, and in combination with surveyed ground control points (GCPs), can be georectified to a pixel resolution between 0.01 and 1 m, and a reprojection error-that is, the difference between the surveyed GPS location of a GCP and the location of the GCP obtained from the georectified image-of O(1 m). The flexibility of rotary wing UAVs provides moderate spatial resolution and high temporal resolution imagery, which are highly suitable to quickly obtain surfzone and beach characteristics in response to storms or for day-to-day beach safety information, as well as scientific pursuits of surfzone kinematics on different spatial and temporal scales, and dispersion and advection estimates of pollutants. © 2015 American Meteorological Society. Source

Schramkowski G.P.,Flanders Hydraulic Research | De Swart H.E.,University Utrecht | Schuttelaars H.M.,Technical University of Delft
Ocean Dynamics | Year: 2010

A three-dimensional numerical model with a prognostic salinity field is used to investigate the effect of a partial slip bottom boundary condition on lateral flow and sediment distribution in a transect of a tidally dominated channel. The transect has a symmetrical Gaussian cross-channel bottom profile. For a deep, well-mixed, tidally dominated channel, partial slip decreases the relative importance of Coriolis deflection on the generation of cross-channel flow patterns. This has profound implications for the lateral distribution of residual salinity that drives the cross-channel residual circulation pattern. Transverse sediment transport, however, is always found to be governed by a balance between advection of residual sediment concentration by residual lateral flow on the one hand and cross-channel diffusion on the other hand. Hence, the changes in the cross-channel distribution of residual salinity modify the lateral sediment distribution. For no slip, a single turbidity maximum occurs. In contrast, partial slip gives a gradual transition to a symmetrical density distribution with a turbidity maximum near each bank. For a more shallow, partially mixed tidal channel that represents the James River, a single turbidity maximum at the left bank is found irrespective of the near-bed slip condition. In this case, semi-diurnal contributions to sediment distribution and lateral flow play an important role in cross-channel sediment transport. As vertical viscosity and diffusivity are increased, a second maximum at the right bank again exists for partial slip. © Springer-Verlag 2009. Source

Huijts K.M.H.,Royal Netherlands Meteorological Institute | De Swart H.E.,University Utrecht | Schramkowski G.P.,Flanders Hydraulic Research | Schuttelaars H.M.,Technical University of Delft
Ocean Dynamics | Year: 2011

An analytical and a numerical model are used to understand the response of velocity and sediment distributions over Gaussian-shaped estuarine crosssections to changes in tidal forcing and water depth. The estuaries considered here are characterized by strong mixing and a relatively weak along-channel density gradient. It is also examined under what conditions the fast, two-dimensional analytical flow model yields results that agree with those obtained with the more complex three-dimensional numerical model. The analytical model reproduces and explains the main velocity and sediment characteristics in large parts of the parameter space considered (average tidal velocity amplitude, 0.1-1 m s -1 and maximum water depth, 10-60 m). Its skills are lower for along-channel residual flows if nonlinearities are moderate to high (strong tides in deep estuaries) and for transverse flows and residual sediment concentrations if the Ekman number is small (weak tides in deep estuaries). An important new aspect of the analytical model is the incorporation of tidal variations in the across-channel density gradient, causing a double circulation pattern in the transverse flow during slack tides. The gradient also leads to a new tidally rectified residual flow component via net advection of along-channel tidal momentum by the density-induced transverse tidal flow. The component features landward currents in the channel and seaward currents over the slopes and is particularly effective in deeper water. It acts jointly with components induced by horizontal density differences, Coriolisinduced tidal rectification and Stokes discharge, resulting in different along-channel residual flow regimes. The residual across-channel density gradient is crucial for the residual transverse circulation and for the residual sediment concentration. The clockwise densityinduced circulation traps sediment in the fresher water over the left slope (looking up-estuary in the northern hemisphere). Model results are largely consistent with available field data of well-mixed estuaries. © 2011 Springer-Verlag (outside the USA). Source

Altomare C.,Flanders Hydraulic Research | Altomare C.,Ghent University | Crespo A.J.C.,University of Vigo | Dominguez J.M.,University of Vigo | And 4 more authors.
Coastal Engineering | Year: 2015

The present work describes the validation of an SPH-based technique for wave loading on coastal structures. The so-called DualSPHysics numerical model has been used for the scope. The attention is focused on wave impact on vertical structures and storm return walls. For vertical quay walls, the numerical results have been compared with analytical and semi-empirical solutions. Later on, the wave impact on storm return walls has been modelled and the results have been compared with experimental data. Regular and random waves have been simulated. Despite the model limitations (e.g. lack of an active wave absorption system), good agreement is achieved with the formulae predictions and experimental results which proves that DualSPHysics model is becoming an alternative to some classical approaches and can be used as complementary tool for the preliminary design of coastal structures. © 2014 Elsevier B.V. Source

Vanneste D.,Ghent University | Altomare C.,Ghent University | Altomare C.,Flanders Hydraulic Research | Suzuki T.,Flanders Hydraulic Research | And 2 more authors.
Proceedings of the Coastal Engineering Conference | Year: 2014

The paper discusses three different numerical models in a study of wave overtopping and impact on a sea wall. The models used are SWASH (based on the nonlinear shallow water equations), DualSPHysics and FLOW-3D (both based on the full Navier-Stokes equations). The models are validated against experimental measurements in a setup with a quay wall and berm in front of the sea wall. The two models based on the full Navier-Stokes equations provide good estimates of the wave impact on the sea wall. Moreover, reasonable agreement with experimental values of averaged overtopping discharges was found for the full test time series simulated with FLOW-3D. Notwithstanding the SWASH model provides reasonable estimates for the wave overtopping on a simple quay wall, at a significantly lower computational cost than the other two models, it clearly underrates the overtopping discharge in the case of a combination of a quay wall, berm and sea wall. Further investigation is needed to draw conclusions on the model accuracy of SWASH in such a case. Source

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