Approach Flow Depth Influence on Nonlinear Weir Discharge Capacity

The high hydraulic efficiency and the compactness of nonlinear weirs favor their use in several rehabilitation or new dams projects. Main types of nonlinear weirs are labyrinth and piano key weirs.The purpose of this paper is to provide indications on the influence of the approach flow depth on the discharge capacity of these nonlinear weirs. To do so, a series of experimental tests have been carried out in the laboratory of Engineering Hydraulics of the Liege University. A labyrinth and a piano key weir have been tested in channel configuration (upstream flow width equal to the weir width) considering various dimensionless dam heights. A large range of discharge has been tested for each case. The results show that the dimensionless dam height increase may decrease up to 8% of the labyrinth weir discharge capacity while it has only very limited but opposite effects for the piano key weir

Experimental investigation of the effect of flip bucket splitters on plunge pool geometry

peer reviewedFlip buckets are common hydraulic structures aiming at deflecting high velocity flows to a free jet trajectory. Systematic experimental tests have been performed to assess the influence on energy dissipation and the plunge pool geometry of varied repartitions of splitters along the flip bucket width. In particular, it is shown that some configurations can create more erosion than a continuous channel without flip bucket.Ski-Sprünge sind übliche Strukturen in Wasserbau, entworfen um Wasser in eine Freiwurfflugbahn mit hoher Geschwindigkeit zu lenken. Die Splitter sind manchmal auf des Ski-Sprünge installiert um die Energiedissipation zu verbessern und damit des Gefahr des Erosion zu reduzieren. In systematischer Weise wurden experimentelle Untersuchungen durchgeführt, um den Einfluss der Strömungsteiler auf die Geometrie des Tosbeckens zu analysieren. Aufgrund der Tosbecken-Geometrie wurde eine Klassifizierung von verschiedenen Konfigurationen von Strömungsteilern durchgeführt und Empfehlungen für eine effiziente Gestaltung erarbeitet. Insbesondere wird gezeigt, dass bestimmte Strömungsteiler Geometrien erheblich mehr Erosion produzieren als ein Ski-Sprung ohne Teiler

Modélisation combinée pour améliorer l'étude des structures hydrauliques

peer reviewedaudience: researcher, professionalPhysical 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

A systematic procedure to predict flows induced by major dysfunctions on complexes or cascades of dams

peer reviewedHazard analysis of dams arranged in complex or in cascade may involve the assessment of a large number of different scenarios of combined failures. However, a tremendous computation time would be needed to perform a detailed modeling of the flows generated by all possible scenarios. Therefore, the present paper describes a rational methodology for analyzing the flows induced by the most relevant incidents occurring on a complex or in a cascade of dams and reservoirs. The methodology combines several hydrodynamic models, including the twodimensional flow solver WOLF 2D and a simplified lumped hydrodynamic model, to simulate (i) the flows induced on the dams complex, (ii) the potential breaching in cascade of other dams, as well as (iii) the propagation of the flood wave in the whole downstream valley. The application of the methodology to a practical case study involving a complex of five dams is also described

Automatic geometrical optimization by way of numerical flow models

peer reviewedThe potentialities in numerical flow modeling available today allow performing more and more representative and accurate computations of an increasing part of hydraulic engineering practical problems. In some cases, numerical simulation can be used as an alternative, or at least an efficient pre-design tool, to more classic physical modeling. In this framework, the paper presents the application of integrated numerical tools to the automatic optimization of the geometry of a guide-wall at the entrance of a channel. The simulations have been performed by using a Genetic Algorithm based optimization tool coupled to a 2D free surface flow model. This finite volume multibock flow solver, WOLF2D, solves the conservative form of the classical shallow water equations together with a depth-integrated k-ε type turbulence model. The calculations have been performed on a cluster of 12 processors to reach a satisfactory solution in less than 2.5 days (96 solutions tested). On the basis of the numerical results and of the value of the suitability indicators, the optimal solution is objectively better than the other tested geometries. This confirms the efficiency of the automatic optimization procedure

Traitements médiatiques des conflits sociaux : un cadre pour les penser.

 L'article propose d'aborder le traitement par les médias des conflits sociaux en considèrent les traces de ces traitements, non pour elles-mêmes mais en tant qu’elles révèlent des fonctionnements internes à chacun des multiples acteurs intervenant dans une prise en compte élargie de cette problématique, autant que des règles qui s’élaborent au fil des rapports entre eux.Différents auteurs sont sollicités pour monter la complémentarité d’approches se situant à des niveaux différents de cette complexité.  L'article propose d'aborder le traitement par les médias des conflits sociaux en considèrent les traces de ces traitements, non pour elles-mêmes mais en tant qu’elles révèlent des fonctionnements internes à chacun des multiples acteurs intervenant dans une prise en compte élargie de cette problématique, autant que des règles qui s’élaborent au fil des rapports entre eux.Différents auteurs sont sollicités pour monter la complémentarité d’approches se situant à des niveaux différents de cette complexité.

Geometric parameters influence on Piano Key Weir hydraulic performances

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

Experimental and numerical investigation of a meandering jet in shallow rectangular reservoirs under different hydraulic conditions

peer reviewedA central meandering jet in shallow rectangular reservoirs has been investigated numerically by the model WOLF2D, on the basis of experimental evidence of this type of flow field in two different setups at different scales. A sensitivity analysis has been conducted with respect to the main parameters of the model. The oscillation frequency of the transversal velocity and the characteristic Strouhal number have been calculated for different Froude numbers. A logarithmic relationship has been found between the Strouhal and the Froude numbers

Handling very different time scales in numerical modelling of sediment transport and morphodynamics

peer reviewedaudience: researcher, professional, studen

A modeling system handling the wide range of time scales involved in sediment transport processes

peer reviewe