Some selected publications by Benjamin Dewals
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See detailCan the collapse of a fly ash heap develop into an air-fluidized flow? - Reanalysis of the Jupille accident (1961)
Stilmant, Frédéric ULg; Pirotton, Michel ULg; Archambeau, Pierre ULg et al

in Geomorphology (in press)

A fly ash heap collapse occurred in Jupille (Liege, Belgium) in 1961. The subsequent flow of fly ash reached a surprisingly long runout and had catastrophic consequences. Its unprecedented degree of ... [more ▼]

A fly ash heap collapse occurred in Jupille (Liege, Belgium) in 1961. The subsequent flow of fly ash reached a surprisingly long runout and had catastrophic consequences. Its unprecedented degree of fluidization attracted scientific attention. As drillings and direct observations revealed no water-saturated zone at the base of the deposits, scientists assumed an air-fluidization mechanism, which appeared consistent with the properties of the material. In this paper, the air-fluidization assumption is tested based on two-dimensional numerical simulations. The numerical model has been developed so as to focus on the most prominent processes governing the flow, with parameters constrained by their physical interpretation. Results are compared to accurate field observations and are presented for different stages in the model enhancement, so as to provide a base for a discussion of the relative influence of pore pressure dissipation and pore pressure generation. These results show that the apparently high diffusion coefficient that characterizes the dissipation of air pore pressures is in fact sufficiently low for an important degree of fluidization to be maintained during a flow of hundreds of meters. [less ▲]

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See detailPrediction of mean and turbulent kinetic energy in rectangular shallow reservoirs
Camnasio, Erica; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Engineering Applications of Computational Fluid Mechanics (2014), 8(4),

Shallow rectangular reservoirs are common structures in urban hydraulics and river engineering. Despite their simple geometry, complex symmetric and asymmetric flow fields develop in such reservoirs ... [more ▼]

Shallow rectangular reservoirs are common structures in urban hydraulics and river engineering. Despite their simple geometry, complex symmetric and asymmetric flow fields develop in such reservoirs, depending on their expansion ratio and length-to-width ratio. The original contribution of this study is the analysis of the kinetic energy content of the mean flow, based on UVP velocity measurements carried throughout the reservoir in eleven different geometric configurations. A new relationship is derived between the specific mean kinetic energy and the reservoir shape factor. For most considered geometric configurations, leading to four different flow patterns, the experimentally observed flow fields and mean kinetic energy contents are successfully reproduced by an operational numerical model based on the depth-averaged flow equations and a two-length-scale k-e turbulence closure. The analysis also highlights the better performance of this depth-averaged k-e model compared to an algebraic turbulence model. Finally, the turbulent kinetic energy in the reservoir is derived from the experimental measurements and the corresponding numerical predictions based on the k-e model agree satisfactorily in the main jet but not in the recirculation zones. [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 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 detailHybride Modellierung deichbruchinduzierter Strömungen
Roger, Sebastian; Dewals, Benjamin ULg; Schüttrumpf, Holger

in Heimerl, S.; Meyer, H. (Eds.) Vorsorgender und nachsorgender Hochwasserschutz (2014)

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See detailDiscussion of "Two-dimensional depth-averaged finite volume model for unsteady turbulent flows"
Erpicum, Sébastien ULg; Pirotton, Michel ULg; Archambeau, Pierre ULg et al

in Journal of Hydraulic Research (2014), 52(1), 148-150

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See detailExperimental parametric study and design of Piano
Machiels, Olivier; Pirotton, Michel ULg; Archambeau, Pierre ULg et al

in Journal of Hydraulic Research (2014)

Piano Key Weirs are an effective solution for dam rehabilitation as well as new dam projects with a high level of hydraulic constraints. In order to improve the efficiency of their design, an experimental ... [more ▼]

Piano Key Weirs are an effective solution for dam rehabilitation as well as new dam projects with a high level of hydraulic constraints. In order to improve the efficiency of their design, an experimental study of the influence of the main geometric parameters has been performed. Thirty one configurations were tested for a wide range of discharges. The results of the study show the influence of the weir height, the keys widths and the overhangs lengths on the discharge capacity and flow characteristics. Based on hydraulic considerations, optimum values of the main geometric ratios are provided. An analytical formulation is developed to predict the discharge capacity of the weir as a function of its geometry. It shows an accuracy of 10% compared to the experimental results of this study and from other sources. [less ▲]

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See detailClosure to “Parapet Wall Effect on Piano Key Weir Efficiency”
Erpicum, Sébastien ULg; Machiels, Olivier; Pirotton, Michel ULg et al

in Journal of Irrigation & Drainage Engineering (2014)

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See detailLocal head-loss coefficient at the rectangular transition from a free-surface channel to a conduit
Van Nam, Nguyen; Archambeau, Pierre ULg; Dewals, Benjamin ULg et al

in Journal of Hydraulic Engineering (2013), 139(12), 1318-1323

Experimental tests have been performed to observe and determine, in stationary flow conditions, the local head loss at the transition from a free surface channel to a conduit. These investigations ... [more ▼]

Experimental tests have been performed to observe and determine, in stationary flow conditions, the local head loss at the transition from a free surface channel to a conduit. These investigations considered a wide range of discharge and varied dimensions and positions of a rectangular cross section conduit connected to the downstream extremity of a rectangular free surface channel. From the head loss evaluation results, simple analytical expressions to predict the local head loss coefficient value at the rectangular transition from a channel to a conduit are proposed and validated. [less ▲]

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See detailContribution of land use changes to future flood damage along the river Meuse in the Walloon region
Beckers, Arnaud ULg; Dewals, Benjamin ULg; Erpicum, Sébastien ULg et al

in Natural Hazards & Earth System Sciences (2013), 13

Managing flood risk in Europe is a critical issue because climate change is expected to increase flood hazard in many european countries. Beside climate change, land use evolution is also a key factor ... [more ▼]

Managing flood risk in Europe is a critical issue because climate change is expected to increase flood hazard in many european countries. Beside climate change, land use evolution is also a key factor influencing future flood risk. The core contribution of this paper is a new methodology to model residential land use evolution. Based on two climate scenarios (“dry” and “wet”), the method is applied to study the evolution of flood damage by 2100 along the river Meuse. Nine urbanization scenarios were developed: three of them assume a “current trend” land use evolution, leading to a significant urban sprawl, while six others assume a dense urban development, characterized by a higher density and a higher diversity of urban functions in the urbanized areas. Using damage curves, the damage estimation was performed by combining inundation maps for the present and future 100 yr flood with present and future land use maps and specific prices. According to the dry scenario, the flood discharge is expected not to increase. In this case, land use changes increase flood damages by 1–40 %, to EUR 334–462 million in 2100. In the wet scenario, the relative increase in flood damage is 540–630 %, corresponding to total damages of EUR 2.1–2.4 billion. In this extreme scenario, the influence of climate on the overall damage is 3–8 times higher than the effect of land use change. However, for seven municipalities along the river Meuse, these two factors have a comparable influence. Consequently, in the “wet” scenario and at the level of the whole Meuse valley in the Walloon region, careful spatial planning would reduce the increase in flood damage by no more than 11–23 %; but, at the level of several municipalities, more sustainable spatial planning would reduce future flood damage to a much greater degree. [less ▲]

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See detailDam break flow modelling with uncertainty analysis
Dewals, Benjamin ULg; Erpicum, Sébastien ULg; Pirotton, Michel ULg et al

in Gourbesville, Philippe; Cunge, Jean; Caignaert, Guy (Eds.) Advances in Hydroinformatics (2013)

Handling uncertainties in dam break flow modelling is of primary interest. Therefore, a procedure is presented here to conduct systematic analysis of the uncertainties resulting from the roughness ... [more ▼]

Handling uncertainties in dam break flow modelling is of primary interest. Therefore, a procedure is presented here to conduct systematic analysis of the uncertainties resulting from the roughness coefficient, the breaching hydrograph and topographic data. The flow simulations have been conducted with the model WOLF 2D developed at the University of Liege. This two-dimensional flow model is computationally too costly to perform a high number of repeated runs, as needed for Monte Carlo simulations. Therefore, a “reduced complexity model” has been set up, in the form of multidimensional Hermite polynomials. This method, developed by Isukapalli et al. (2004) and first applied to dam break flow by Niemeyer (2007), involves a reduced number of runs of the complete model to calibrate the polynomials. This paper shows the applicability and efficiency of the methodology, but it also discusses previously unreported shortcomings of the approach, together with hints to overcome them. Results of such uncertainty analysis for dam break flow modelling disclose crucial information for practical risk management. In particular, they reveal that the uncertainty ranges on maximum water depth and time of arrival of the front are not symmetric (overestimation vs. underestimation) and very unevenly distributed in space. [less ▲]

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See detailParapet wall effect on Piano Key Weirs efficiency
Machiels, Olivier; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Journal of Irrigation & Drainage Engineering (2013), 139(6), 506-511

Piano Key Weir is a cost effective solution for rehabilitation as well as for new dam projects with a high level of constraints (limited space, high specific flood discharge, small reservoir level ... [more ▼]

Piano Key Weir is a cost effective solution for rehabilitation as well as for new dam projects with a high level of constraints (limited space, high specific flood discharge, small reservoir level variation). While the higher efficiency of the Piano Key Weir compared to standard linear weirs has already been demonstrated, its optimal geometry is still poorly defined. In order to improve the design of the complex geometry of this structure, the use of parapet walls has been tested. They consist of vertical extensions placed over the weir crest. Following a former study of the influence of the weir height on its discharge capacity, this paper presents the results of an experimental campaign dedicated to investigating the effect of parapet walls to increase weir height while reducing bottom slopes and keeping the weir height constant. These results indicate the relative influences of the alveoli bottom slopes and of the weir height on the Piano Key Weir release capacity. Comparisons with former experimental results as well as design guidelines are also provided. [less ▲]

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See detailModélisation numérique hydrosédimentaire au service de la gestion durable des sédiments
Dewals, Benjamin ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Recyclage et Valorisation (2013), 41

La gestion des sédiments revêt une importance croissante pour l’exploitation des voies navigables et nombre de projets de construction de barrages et de complexes hydroélectriques. L’impact des apports en ... [more ▼]

La gestion des sédiments revêt une importance croissante pour l’exploitation des voies navigables et nombre de projets de construction de barrages et de complexes hydroélectriques. L’impact des apports en matériaux solides se manifeste tant par des effets à long terme, telle la réduction de la capacité du réservoir, que par des conséquences à plus court terme, telle l’usure prématurée des turbines. L’étude détaillée des effets sédimentaires s’impose donc de plus en plus tôt dans la conception de nouveaux aménagements. Elle est aussi un objectif tout au long de l’exploitation des ouvrages, dans une perspective de gestion sécuritaire et durable. [less ▲]

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See detailDike-break induced flows: a simplified model
Stilmant, Frédéric ULg; Pirotton, Michel ULg; Archambeau, Pierre ULg et al

in Environmental Fluid Mechanics (2013), 13(1), 89-100

A simplified model for the prediction of the steady-state outflowthrough a breach in an inland dike is presented. It consists in the application of the mass and momentum conservation principles to a ... [more ▼]

A simplified model for the prediction of the steady-state outflowthrough a breach in an inland dike is presented. It consists in the application of the mass and momentum conservation principles to a macroscopic control volume. A proper definition of the shape of the control volume enables to take the main characteristics of the flow into account and thus to compensate for the extreme simplification of the spatial representation of the model. At the breach, a relation derived from the shallow-water equations is used to determine the direction of the flow. Developments have been guided by numerical simulations and results have been compared to experimental data. Both the accuracy and the domain of validity of the simplified model are found satisfactory. [less ▲]

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See detailCoupling between flow and sediment deposition in rectangular shallow reservoirs
Camnasio, Erica; Erpicum, Sébastien ULg; Orsi, Enrico et al

in Journal of Hydraulic Research (2013), 51(5), 535-547

Flow velocity and sedimentation patterns were investigated experimentally and numerically in shallow rectangular reservoirs with different asymmetric locations of the inlet and outlet channels. Velocity ... [more ▼]

Flow velocity and sedimentation patterns were investigated experimentally and numerically in shallow rectangular reservoirs with different asymmetric locations of the inlet and outlet channels. Velocity fields were measured in the entire reservoir, both for clear water flow and with suspended sediments. Thickness of sediment deposits were mapped in the whole reservoir by means of a laser light method. In one of the studied geometric configurations, injection of suspended sediments led to a complete change in the observed flow field. Experimental results were compared with numerical simulations performed with the depth-averaged flow model WOLF 2D, using a depth-averaged k-e turbulence model. The simulations lead to accurate predictions of the velocity profiles and the change in flow pattern as a result of sediment deposits was successfully reproduced. [less ▲]

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See detailThree‐phase Bi‐layer Model for Simulating Mixed Flows
Kerger, François ULg; Archambeau, Pierre ULg; Dewals, Benjamin ULg et al

in Journal of Hydraulic Research (2012), 50(3), 312-319

Mixed flows characterized by a simultaneous occurrence of free surface and pressurized flows are often encountered in hydraulic engineering. Numerous researches have been dedicated to unify the ... [more ▼]

Mixed flows characterized by a simultaneous occurrence of free surface and pressurized flows are often encountered in hydraulic engineering. Numerous researches have been dedicated to unify the mathematical description of both flows. Herein, shock-capturing models succeed in giving a unique set of equations. However, no method accounts for both air-entrapment and air-entrainment. This study proposes an original model to simulate air–water interactions in mixed flows. The new approach relies on the area-integration of a three-phase model over two layers. The applicability of this free surface model is extended to pressurized flows by a modified pressure term accounting for the dispersed air. The derived modelling system WOLF IMPack is then validated. The code successfully simulates open channel flows, mixed flows and water hammer in a unified framework, including air–water interactions, in structures like the drainage network. [less ▲]

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See detailFlow patterns and sediment deposition in rectangular shallow reservoirs
Dufresne, Matthieu; Dewals, Benjamin ULg; Erpicum, Sébastien ULg et al

in Water & Environment Journal (2012), 26(4), 504-510

This work involves the experimental investigation of flow patterns, preferential regions of deposition and trapping efficiency in rectangular shallow reservoirs. The main flow patterns that can be ... [more ▼]

This work involves the experimental investigation of flow patterns, preferential regions of deposition and trapping efficiency in rectangular shallow reservoirs. The main flow patterns that can be encountered in rectangular shallow reservoirs are described: symmetrical flows without any reattachment point (S0), asymmetrical flows with one reattachment point (A1), and asymmetrical flows with two reattachment points (A2). The influence of geometrical and hydraulic parameters on reattachment lengths is intensively investigated. A shape parameter is introduced to classify symmetrical and asymmetrical flows. For each flow pattern, the preferential regions of deposition are studied. To conclude, a number of practical recommendations are given. Reservoirs with a shape parameter lower than 6.2 limit sediment deposition. Reservoirs with a shape parameter greater than 6.8 are favourable for sediment deposition. Finally, perspectives for maximizing and minimizing deposition are given, respectively by exploiting the great trapping potential of the flow pattern A1 and the poor trapping potential of the flow pattern S0. [less ▲]

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See detailComposite modeling to enhance hydraulic structures studies
Erpicum, Sébastien ULg; Dewals, Benjamin ULg; Archambeau, Pierre ULg et al

in Houille Blanche (2012), 6

Physical modeling and numerical modeling are two efficient analysis approaches in hydraulic engineering. The interactive application of both methods is obviously the more effective response to most flow ... [more ▼]

Physical modeling and numerical modeling are two efficient analysis approaches in hydraulic engineering. The interactive application of both methods is obviously the more effective response to most flow problems analyses. Indeed, it enables combining the inherent advantages of both approaches, which are complementary, while being beneficial to the delays as well as the quality of the analysis. The paper presents the way composite modeling is applied for years at the HECE - Laboratory of Engineering Hydraulics (University of Liege) to enhance hydraulic structures studies. Besides numerical model validation for which experimental benchmarks constitute the first reliable data source, simultaneous application of both modeling approaches may be envisaged in three different ways. Composite modeling may be used to increase the scale factor of physical models by reducing the layout of the real structure to be modeled, to provide a better answer to specific problems than a single approach study or to maximize the efficiency of experimental tests by reducing the range of variation of the unknown parameters to be tested. For each of these three issues depicted in the paper, several examples show how the combined use of efficient numerical solvers together with physical scale models enables to increase the overall quality and scope of the analyses while decreasing the delays and possibly the costs. [less ▲]

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