References of "Dewals, Benjamin"
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See detailFlow and turbulence characterization as an onset for assessing the stability of gravel beds
Duma, Diana ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in 7th International Conference on Fluvial Hydraulics (2014, September)

The flow characteristics, such as velocity profiles and turbulence intensities, are of high practical relevance in the assessment of riverbed stability. So far, the Shields diagram remains the most widely ... [more ▼]

The flow characteristics, such as velocity profiles and turbulence intensities, are of high practical relevance in the assessment of riverbed stability. So far, the Shields diagram remains the most widely accepted approach for defining the initiation of sediment motion. However, it faces a number of shortcomings. In principle, it is only valid for uniform flow conditions and, under non-uniform flow conditions, it fails to account properly for the influence of turbulence in sediment entrainment. In this paper, we focus on a more detailed description of quasi-uniform and non-uniform flow characteristics in the vicinity of the critical flow conditions for inception of motion of gravel beds. Laboratory experiments were designed, involving two configurations. First, the entire bottom of the flume was paved with stones of uniform diameter (8 or 15 mm), leading to quasi-uniform flow conditions. Second, the flume bottom was smooth upstream of the zone of measurement while the downstream part was covered with gravels, leading to a sudden smooth-to-rough transition. The flow velocity was obtained by acoustic measurements and the turbulence intensity was calculated for both configurations. By fitting the velocity profile to a modified logarithmic law, the shear velocity was estimated. Standard approaches for predicting the threshold of motion, initially developed for uniform flows, were compared to other methods, based on depth-averaged turbulence kinetic energy, recently proposed in literature for non-uniform flow conditions. [less ▲]

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See detailTowards enhanced estimates of future water demand in the Meuse basin: literature review
De Cuyper, Anaïs; Bruwier, Martin ULg; Archambeau, Pierre ULg et al

Report (2014)

With respect to water management in the Meuse basin, the hydrological consequences of climate change have been taken into account in several studies so far; but this is not the case of many other ... [more ▼]

With respect to water management in the Meuse basin, the hydrological consequences of climate change have been taken into account in several studies so far; but this is not the case of many other environmental and socio-economic changes, including trends in future water demand. The objective of this report is to serve as an onset for the development of a first approach to estimate at a relatively large-scale future water demand in the Meuse basin. Based on a review of recent literature, this report discusses the key drivers which influence water demand, with the aim of identifying the most suitable methods to implement in a subsequence more detailed analysis, as well as to highlight the data needs. [less ▲]

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See detailLa Meuse au fil des crues
Devuyst, Paul; Dewals, Benjamin ULg; Archambeau, Pierre ULg et al

Article for general public (2014)

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See detailHow to simulate quickly and efficiently a flow over a spillway ?
Goffin, Louis ULg; Erpicum, Sébastien ULg; Dewals, Benjamin ULg et al

Conference (2014, August)

Flows over hydraulic structures, such as weirs or spillways, can be modelled using different techniques. New models such as SPH or PFEM are becoming more and more popular. These models are particle and/or ... [more ▼]

Flows over hydraulic structures, such as weirs or spillways, can be modelled using different techniques. New models such as SPH or PFEM are becoming more and more popular. These models are particle and/or meshless and consequently require a lot of computational power. Other methods such as VOF also require a lot of computational time. In the frame of 2-D vertical flows, other techniques use much less computation time. For irrotationnal flows, solving the Laplace equation can be done very efficiently. The difficulty of this method lies in the definition of boundary conditions. The free-surface, which is naturally determined when using Lagrangian methods, needs a heavy iterative solving due to its non-linear nature when expressed in the frame of the Laplace equation. This paper will present an original technique that allows a quicker and easier determination of the free-surface. An irregular mesh for boundaries is used and discussed. The method is validated with analytical solutions and experimental measurements. [less ▲]

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See detailGeometric parameters influence on Piano Key Weir hydraulic performances
Erpicum, Sébastien ULg; Archambeau, Pierre ULg; Pirotton, Michel ULg et al

in Chanson, Hubert; Toombes, Luke (Eds.) Hydraulic Structures and Society – Engineering Challenges (2014, June)

The Piano Key Weir is a recent evolution of the traditional labyrinth weir. Thanks to a reduced foot print, this nonlinear weir can be placed on the top of gravity dams. The Piano Key Weir geometry ... [more ▼]

The Piano Key Weir is a recent evolution of the traditional labyrinth weir. Thanks to a reduced foot print, this nonlinear weir can be placed on the top of gravity dams. The Piano Key Weir geometry involves a large number of geometric parameters. Several experimental studies have been carried out to investigate the main geometric parameters influencing the weir hydraulic efficiency and to define their optimal value. In this paper, the experimental data gathered at the University of Liege are re-examined to show how the weir height, the keys widths and the overhangs positions influence, for a given crest length magnification ratio, the weir discharge capacity. The theoretical rating curve of a standard linear weir is considered for comparison. The analysis highlights that the keys widths and overhangs lengths ratios influence significantly the Piano Key Weir efficiency, but less than the weir height. Considering the above mentioned results, a cost efficient design proposed in the literature is also proved to be close to the hydraulic optimum. [less ▲]

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See detailMeandering flows in rectangular shallow reservoirs
Peltier, Yann ULg; Erpicum, Sébastien ULg; Dewals, Benjamin ULg

Report (2014)

During this research, previously unexplored meandering flows in free-surface rectangular shallow reservoirs were investigated theoretically, experimentally and numerically. For the first time, a complete ... [more ▼]

During this research, previously unexplored meandering flows in free-surface rectangular shallow reservoirs were investigated theoretically, experimentally and numerically. For the first time, a complete description of the hydrodynamics of the meandering flows was obtained from laboratory experiments. An innovative procedure for the characterisation of the physics of the flow was developed based on several techniques, including Large Scale Particle Image Velocimetry (LSPIV), Proper Orthogonal Decomposition (POD) and a new topology algorithm. This research provides new insights into these fascinating meandering flows, of high practical relevance in civil and environmental engineering. Six papers were written and, so far, five of them have been accepted for publication (two in international journals and three in peer-reviewed international conference proceedings). [less ▲]

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See detailMeandering jets in shallow rectangular reservoirs: POD analysis and identification of coherent structures
Peltier, Yann ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Experiments in Fluids (2014), 55

The effect of the shallowness on meandering jets in a shallow rectangular reservoir is investigated. Four meandering flows were investigated in an experimental shallow rectangular reservoir. Their ... [more ▼]

The effect of the shallowness on meandering jets in a shallow rectangular reservoir is investigated. Four meandering flows were investigated in an experimental shallow rectangular reservoir. Their boundary conditions were chosen to cover a large range of friction numbers (defined with the sudden expansion width). Due to the unsteady characteristics of the flows, a Proper Orthogonal Decomposition of the fluctu-ating part of the surface velocity fields measured using LSPIV was used for discriminating the flow struc-tures responsible for the meandering of the jet. Less than 1 % of the calculated POD modes significantly contribute to the meandering of the jet and two types of instability are in competition in such a flow con-figuration. The sinuous mode is the dominant mode in the flow and it induces the meandering of the flow, while the varicose mode is a source of local mixing and weakly participates to the flow. The fluctuating velocity fields were then reconstructed using the POD modes corresponding to 80% of the total mean fluctuating kinetic energy and the coherent structures were identified using the residual vorticity, their centres being localised using a topology algorithm. The trajectories of the structures centres emphasize that at high friction number the coherent structures are small and laterally paired in the near, middle and far fields of the jet, while with decreasing friction number the structures merge into large horizontal vortices in the far-field of the jet, their trajectories showing more variability in space and time. The analysis of the stability regime finally reveals that the sinuous mode is convectively unstable and may become absolutely unstable at the end of the reservoir when the friction number is small. [less ▲]

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See detailLanduse change and future flood risk: the influence of micro-scale spatial patterns (FloodLand) - 1st progress report
Dewals, Benjamin ULg; Bruwier, Martin ULg; El Saeid Mustafa, Ahmed Mohamed ULg et al

Report (2014)

The goal of the project FloodLand is to investigate the complex interactions between landuse change and future flood risk. Landuse change is assumed to be mainly driven by population growth and socio ... [more ▼]

The goal of the project FloodLand is to investigate the complex interactions between landuse change and future flood risk. Landuse change is assumed to be mainly driven by population growth and socio-economic factors. It affects future flood risk by altering catchment hydrology as well as vulnerability in the floodplains; but the feedback effect of (the perception of) changes in flood hazard on landuse evolution is also considered. The research is based on a chain of modelling tools, which represent parts of the natural and human systems, including: landuse change modelling, transportation modelling as an onset for the estimation of indirect flood damage, continuous hydrological modelling (forced by precipitation and temperature data disturbed according to climate change scenarios), as well as efficient hydraulic modelling of inundation flow in the floodplains. Besides reproducing a broad spectrum of processes, the modelling approach spans over multiple scales, from the regional or catchment level down to the floodplain and building levels. This distinctive feature is reflected both within the individual models and through their combination involving fine-scale detailed analyses (or data) embedded within coarser models at a broader level. [less ▲]

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See detailContributions to transnational flood risk management in the Meuse basin
Dewals, Benjamin ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in European Symposium on Flood Frequency Estimation and Implications for Risk Management (2014, March)

Experience in transboundary river basins emphasizes the need for more cooperative transnational water management. In this respect, the Interreg IVB project AMICE aims at developing a shared adaptation ... [more ▼]

Experience in transboundary river basins emphasizes the need for more cooperative transnational water management. In this respect, the Interreg IVB project AMICE aims at developing a shared adaptation strategy of the basin of the river Meuse to the hydrological impacts of climate change. The basin covers parts of France, Belgium, Germany and the Netherlands. The project combines scientific research with innovative natural and structural water retention measures, as well as enhanced transnational crisis management. In this framework, common climate and hydrological scenarios were derived for the time horizons 2021-2050 and 2071-2100. A “coordinated” procedure was set up to conduct the first hydraulic modelling of the entire river Meuse, from its spring to its mouth. For the considered climate scenarios, the increases in future flood levels were found about twice higher in the central part of the Meuse basin compared to the upper and lower parts. This distinctive spatial pattern results from the morphology of the valley. The characteristics of the hydraulic models used for this “coordinated” analysis differed significantly from one region to the other (e.g., 1D vs. 2D, steady vs. unsteady). Therefore, a more refined analysis was undertaken on a 100 km long stretch of the Meuse, crossing the border between Belgium and the Netherlands, using very similar (“harmonized”) models for the whole computation (2D unsteady models). As a result, the influence of using different interconnected models could be appreciated. The results of hydraulic modelling were used to conduct damage assessment based on a common methodology throughout the Meuse basin and combined with landuse change scenarios in the floodplains (change in vulnerability of the floodplains). In turn, several adaptation measures were tested, including upstream water retention, dredging as well as upgrade of flood defences and mobile weirs. Hydrological and hydraulic modelling was also performed for a sub-basin of the river Meuse, partly controlled by two large reservoirs. A detailed model of the operation rules of these reservoirs was implemented. This enabled to investigate the impact of the considered climate change scenarios on the performance of these multi-purpose reservoirs as well as to investigate possible enhancements in the operation rules, which may serve as adaptation measures to compensate for the detrimental effects of climate change. [less ▲]

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See detailExperimental investigation of meandering jets in shallow reservoirs
Peltier, Yann ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Environmental Fluid Mechanics (2014)

Meandering flows in rectangular shallow reservoirs were experimentally investi- gated. The characteristic frequency, the longitudinal wave length and the mean lateral exten- sion of the meandering jet ... [more ▼]

Meandering flows in rectangular shallow reservoirs were experimentally investi- gated. The characteristic frequency, the longitudinal wave length and the mean lateral exten- sion of the meandering jet were extracted from the first paired modes, obtained by a proper orthogonal decomposition of the surface velocity field measured by large scale PIV. The depth-normalised characteristic lengths and the Strouhal number were then compared to the main dimensionless numbers characterizing the experiments: Froude number, friction num- ber and reservoir shape factor. The normalised wave length and mean lateral extension of the meandering jet are neither correlated with the Froude number nor with the reservoir shape factor; but a clear relationship is found with the friction number. Similarly, the Strouhal num- ber is found proportional to a negative power of the friction number. In contrast, the Froude number and the reservoir shape factor enable to predict the occurrence of a meandering flow pattern: meandering jets occur for Froude number greater than 0.21 and for a shape factor smaller than 6.2. [less ▲]

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See detailComparative analysis of the energy dissipation on a stepped spillway downstream of a Piano Key Weir
Silvestri, Aurélien ULg; Archambeau, Pierre ULg; Pirotton, Michel ULg et al

in Erpicum, Sébastien; Laugier, Frédéric; Pfister, Michael (Eds.) et al Labyrinth and Piano Key Weirs II - PKW 2013 (2014)

A systematic experimental study has been carried out to compare the residual energy at the toe of a stepped spillway of varied length considering a classical ogee-crested weir (OCW) or two different piano ... [more ▼]

A systematic experimental study has been carried out to compare the residual energy at the toe of a stepped spillway of varied length considering a classical ogee-crested weir (OCW) or two different piano key weirs (PKW) at the top of the structure. Four spillway lengths have been considered on a wide range of discharge. An indirect method has been used to compute the residual flow energy at the spillway toe from water depth measurements in a horizontal channel downstream. The results indicate that uniform flow conditions, i.e. flow energy at the spillway toe independent of the spillway length, are reached on significantly shorter spillways downstream of a PKW than downstream of an OCW. However, the uniform flow energy at constant discharge on the spillway is found to vary depending on the weir type. In particular, it is smaller downstream of the OCW than downstream of the PKWs. [less ▲]

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See detailAn analytical approach for Piano Key weir hydraulic design
Machiels, Olivier; Dewals, Benjamin ULg; Archambeau, Pierre ULg et al

in Erpicum, Sébastien; Laugier, Frédéric; Pfister, Michael (Eds.) et al Labyrinth and Piano Key weirs II - PKW 2013 (2014)

A hydraulic design equation for Piano Key Weirs is set up using the results of a large experimental parametric study. Comparison of the analytical formulation with experi-mental data from various physical ... [more ▼]

A hydraulic design equation for Piano Key Weirs is set up using the results of a large experimental parametric study. Comparison of the analytical formulation with experi-mental data from various physical modeling studies, considering idealized as well as real projects Piano Key Weirs configurations, shows a 15% accuracy in unit discharge prediction on a large range of geometric parameters values. Comparison of the proposed formulation to two other recently proposed equations highlights the importance to consider such analytical approaches inside the range of parameter values for which they have been validated. [less ▲]

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