Numerical and physical hydraulic modelling of Piano Key Weirs

in Proceedings of the 4th Int. Conf. on Water Resources and Renewable Energy Development in Asia (2012, March)

During the last few years, several piano key weirs (PKWs) have been built in France by Electricité de France (EDF). Thanks to the reduced footprint and high release capacities of this new type of weir ... [more ▼]

During the last few years, several piano key weirs (PKWs) have been built in France by Electricité de France (EDF). Thanks to the reduced footprint and high release capacities of this new type of weir, making it particularly suited for concrete dams rehabilitation, lots of other projects in varied countries are under construction or study. The prototype use of PKW requires knowledge about its structural behaviour, hydraulic capacities as well as integration into dams’ environment. This paper aims at presenting numerical and physical modelling works performed at the University of Liege to address the last two points. In particular, large scale physical modelling and parametric scale models enabled to understand the hydraulic behaviour of the structure and to highlight its main geometric parameters as well as their best variation interval depending on various criteria related to the weir design (discharge efficiency, cost…). A 1D numerical model has also been developed based on these experimental investigations. It enables to predict in a few minutes, with 10% accuracy, the discharge capacity of a given PKW geometry on its usual operation head range. This model, available as a freeware on http://www.pk-weirs.ulg.ac.be, constitutes a key tool for the first design of such weirs. Finally, the scale model studies of major projects such as Raviège dam (France) for EDF and Ouldjet Mellegue Project (Algeria) for Coyne et Bellier – Tractebel Engineering enable to confront theoretical predictions with experimental results and to address the problem of PKW integration on dam crests. [less ▲]

The Taoussa project (Mali): an example of effective composite modeling

in 4th IAHR International Symposium on Hydraulic Structures (2012, February)

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. This paper presents the results of a successful application of such a composite numerical – physical study carried out by the Research Group Hydraulics in Environmental and Civil Engineering (former HACH) of the University of Liège on behalf of Coyne et Bellier (Tractebel Engineering). It concerned, at the stage of detailed draft, the hydraulic study of the Taoussa Project on the Niger River in Mali. The studies, performed in less than 6 months, focused on the flow characteristics at the scale of the reservoir and the river, using the numerical approach, as well as on hydrodynamic details in the spillway using a large scale factor physical model with boundary conditions defined on the basis of numerical modeling. [less ▲]

Dam break flow modelling with uncertainty analysis

in Proceedings of SimHydro 2012 (2012)

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 ▲]

Etude des écoulements induits par une déstabilisation du terril de la Héna

Report (2012)

On the Piano Key Weir hydraulics

in Rutschmann, Peter; Grünzner, Markus; Stephan, Hötzl (Eds.) Proceedings of 2nd IAHR Europe Congress (2012)

The Piano Key Weir (PKW) is a kind of labyrinth weir with a geometry that uses overhangs to reduce the base length. The PKW can thus be directly placed on the crest of an existing dam. Together with its ... [more ▼]

The Piano Key Weir (PKW) is a kind of labyrinth weir with a geometry that uses overhangs to reduce the base length. The PKW can thus be directly placed on the crest of an existing dam. Together with its high discharge capacity for low heads (up to four times as high as an ogee-crested weir of same length), this geometric feature makes the PKW an interesting solution for dam rehabilitation and for new dam projects with a high level of constraints (design discharge, available space, reservoir storage, ...). PKW has been initially designed in 2001 and built for the first time in 2006 by “Electricité de France (EDF)”. Even if the first experimental studies confirmed its appealing discharge capacities, the flow upstream, over and downstream of this complex structure is still poorly described. Following a 3 years intensive experimental and numerical study of PKW hydraulics, the paper presents a general description of the hydraulic behavior of the PKW. It aims to explain the influence of the large set of geometric parameters on the discharge capacity. The assumptions of the study link various phenomenons depicted in the literature about PKW and an evaluation of their relative influence on the PKW efficiency is given. The role of the crests shape, the crests submersion, the nappes interactions, the crests approach conditions, the position of the control section and the head losses are analyzed. Design advices are also given. [less ▲]

Composite modeling to enhance hydraulic structures studies

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 ▲]

Modelling sediment transport over partially non-erodible bottoms

in International Journal for Numerical Methods in Fluids (2012), 70(2), 186-199

In depth- and cross section-averaged morphodynamic models, based on explicit time integration, it may happen that the computed bed level becomes lower than the top level of a non-erodible layer (e.g ... [more ▼]

In depth- and cross section-averaged morphodynamic models, based on explicit time integration, it may happen that the computed bed level becomes lower than the top level of a non-erodible layer (e.g. concrete, bedrock or armoured layer). This is a standard pitfall which has been addressed in different ways. In this paper, we present an original approach for avoiding computation of non-physical bed levels, using an iterative procedure to correct the outward sediment fluxes. The procedure is shown to be computationally efficient while it achieves a high accuracy in terms of mass conservation. We compare our original approach with the existing Struiksma’s method and with a reformulation of the problem in terms of mathematical optimization of a linear or non-linear objective function under linear constraints. The new procedure has been incorporated into an existing finite volume morphodynamic model. It has been validated with several 1D benchmarks leading to configurations with sediment transport over non-erodible bottom. The computation time has been verified not to increase by more than 15% compared to runs without non-erodible bottom. [less ▲]

Transboundary assessment of the effect of climate change on river Meuse: flood wave selection for hydraulic modelling from Ampsin (B) to Maaseik (NL)

in Water - infinitely deformable but still limited (2012)

This paper addresses high resolution inundation modelling in a transboundary context. In particular, flood wave propagation and inundation characteristics are simulated over a stretch of almost 100 km of ... [more ▼]

This paper addresses high resolution inundation modelling in a transboundary context. In particular, flood wave propagation and inundation characteristics are simulated over a stretch of almost 100 km of river Meuse across the Belgian-Dutch border, using 2D fully dynamic modelling. This transboundary hydraulic simulation requires inflow hydrographs to be prescribed as upstream boundary conditions. However, existing procedures for generating flood wave hydrographs differ between the concerned regions. Therefore, we review the main characteristics of the existing regional procedures and compare the resulting synthetic hydrographs. Besides, transnational hydrological scenarios have been developed to investigate the impact of climate change on flood risk along river Meuse in both countries. [less ▲]

On the advantage of using risk curves to assess flood protection measures

in Mambretti, Stefano (Ed.) Environmental Risk (2012)

Modern flood management approaches require the quantification of flood risk, accounting for the hazard component (flood frequency and inundation intensity) as well as the vulnerability of the floodplains ... [more ▼]

Modern flood management approaches require the quantification of flood risk, accounting for the hazard component (flood frequency and inundation intensity) as well as the vulnerability of the floodplains (exposure, value and susceptibility). In this chapter, we present a detailed flood risk model, in which flow computation, monetary valuation of the assets and damage calculation are conducted at the scale of individual buildings or facilities. To avoid the shortcoming of focusing on economic damage, psycho-social impacts of floods are also included in the analysis. The model has been applied to evaluate three flood protection measures on a river reach in the Meuse basin (Belgium). The resulting risk curves show that such a micro-scale risk analysis provides important insights into the relative influence of the different flood protection measures. This could neither be evaluated through a more standard hydraulic analysis nor through the quantification of flood risk by only a single number. [less ▲]

Dike-break induced flows: a simplified model

Conference (2011, November)

A simplified model for the prediction of the steady-state outflow through 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 outflow through 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 into account the main characteristics of the flow and thus to compensate for the extreme simplification of the space discretisation of the model. At the breach, a relation derived from the shallow-water equations is used to determine the directions of the flow. Developments have been guided by numerical simulations and results have been compared to experimental data. Both the precision and the application domain of the simplified model are found satisfactory. [less ▲]