Global design of hydraulic structures optimised with physically based flow solvers on multiblock structured grids

peer reviewedThis paper presents the numerical studies lead by the Laboratory of Applied Hydrodynamics and Hydraulic Constructions of the University of Liège (HACH) for the rehabilitation of the 21-meter high Nisramont dam in Belgium. After determination of the up-to-date 1000-year return flood using the hydrological runoff model WOLFHYDRO on the global 74,000 ha watershed real topography coupled with statistical analyzes, and after validation on the existing situation and for extreme observed events, the 2D finite volume multiblock flow solver WOLF2D has been applied to the design of the new stilling basin and to the bottom outlet rehabilitation impact study. The multiblock solver possibilities allow mesh refinement close to interesting areas, such as dam spillway and stilling pool, without leading to prohibitive CPU times, while suitable shallow water equations formulation allows the computation of the flows on the strongly vertically curved bottom of the spillway. In the described simulation, 270,000 structured finite volumes, from .25 to 1 meters long, are used to simulate as a whole the flows in the upstream reservoir, dam, spillway, stilling basin and downstream river, this on a real topography

Large scale 2D numerical modelling of reservoirs sedimentation and flushing operations

peer reviewedaudience: researcherThe quasi-3D flow solver WOLF has been developed at the University of Liege for almost a decade. It has been used to carry out the simulation of silting processes in large reservoirs and to predict the efficiency of flushing operations. Besides briefly depicting the mathematical and numerical model, the present paper demonstrates its applicability on the case of a large hydropower project in India. The silting process of the reservoir has been simulated by means of the quasi-3D flow model with a quasi-steady approach. For simulating flushing events, both the topography changes and their interactions with the flow have been carefully handled in a strongly coupled approach. This narrow coupling has required the development of a suitable upwind numerical scheme. Results are presented with 2D- and 3D-views, completed by cross-sections and curves of the variation of key variables. The numerous observations based on those results lead to a global assessment of the silting mechanism and of the flushing efficiency

Similarity matrices for colored graphs

In this paper, we extend the notion of similarity matrix, which has been used to define similarity between nodes of two graphs, to the case of colored graphs, where the coloring is either on the nodes or on the edges of both graphs. The proposed method tries to find the optimal matching between the nodes or edges of both graphs but only performs the comparison when their colors are the same. The proposed cost function nevertheless uses the connectivity between all nodes and edges of both graphs. We then also show how to extend this to the notion of low rank similarity matrix, by defining it as a constrained optimization problem

Graph matching with type constraints on nodes and edges

In this paper, we consider two particular problems of directed graph matching. The first problem concerns graphs with nodes that have been subdivided into classes of different type. The second problem treats graphs with edges of different types. In the two cases, the matching process is based on a constrained projection of the nodes and of the edges of both graphs in a lower dimensional space. The procedures are formulated as non-convex optimization problems. The objective functions use the adjacency matrices and the constraints on the problem impose the isometry of the so-called projections. Iterative algorithms are proposed to solve the optimization problems. As illustration, we give an example of graph matching for graphs with two types of nodes and graphs with two types of edges

Modelling of the wave propagation, the coastal currents and the induced topographic changes

peer reviewedThis paper models the sea bottom evolution. This model is built up on three main parts. The first one describes the wave propagation, taking simultaneously into account the refraction, the diffraction and the reflection but also the energy dissipation caused by wave breaking. This model is solved by the numerical method of the finite volumes, using an iterative resolution (the GMRES method). Several validations of this model have been carried out on many examples such as harbors of various geometries and depths, beaches,… The wave induced currents are computed in the second part based on the concept of the radiation stresses describing the excess of the flux momentum caused by the waves. A model based on the complete Navier-Stokes equations integrated on the depth and associated with appropriated forcing and friction terms is used. This model is computed as an update of WOLF software (HACH, ULg) and is applied to some examples such as beaches with or without coastal structures. Finally, the third part is about the sediment transport. It exhibits the topographic modifications of the coastal sea bottom caused by the waves and their currents. A loop execution of these three models ends this work. It gives us an operational tool to describe the topographic evolution of the coastal areas caused by the incident waves, the induced currents and then the resulting sediment transport, fulfilling the objectives of this paper

Accompagner des enseignants ingénieurs dans un processus de changement

International audienceL’Ecole Polytechnique de Louvain (EPL) dans ses conduites de changement et ses prises de décision, propose des modes collaboratifs. Les enseignants sont invités à participer au changement dès le début du processus et sont accompagnés dans ceux-ci par la cellule pédagogique de l’EPL présidée par le doyen, via des actions de types : journées pédagogiques, workshops, réunion de coordination et suivi. Nous analysons particulièrement ici le processus d’accompagnement collaboratif dans un cas pratique dont l’objectif est la redéfinition des acquis d’apprentissage transversaux des quatre projets proposés aux étudiants du programme de bachelier, qui fait suite à une réforme de ce programme. Suite à l’analyse des étapes du processus et plus précisément en regardant les actions d’accompagnement proposées, nous constatons un besoin patent de créer une équipe composée d’acteurs divers qui sont responsabilisés et ce, dès le début du processus. Ce besoin se manifeste par un sentiment de confusion des rôles des différentes équipes. Nous observons aussi la nécessité de définir un processus du changement a priori pour le mener à bien. Nous pensons que capitaliser les bonnes pratiques de conduite de changement pourrait parfaire l’amélioration continue, et ce, même si nos pratiques actuelles permettent très clairement que le changement aboutisse

Scale modelling and similarity laws for the study of an under pressure settling structure

peer reviewedThis paper presents the scale model studies of a complex under pressure settling structure, carried out at the Laboratory of Hydraulic Constructions of the University of Liège. Made up of fourteen identical settling chambers placed side by side and the bottom of which is divided into pyramidal hoppers, the structure, totally under pressure, is fed by a vertical shaft. Downstream, the settling chambers discharge into a collector, which ensures the clean water feeding of four penstocks through a free surface basin. Finally, a pipes network, under the chambers, ensures the downstream evacuation of the sand trapped in the hoppers. Using adapted and theoretically justified similarity laws coupled with realistic scales for the models, the hydrodynamic behavior and solid transport phenomena in this complex system have been studied. Special care has been taken to evaluate the trap efficiency, the evacuation system working and the global discharge repartition between the fourteen chambers. Sawdust, plastic balls or very small sand particles have been used to model real sediments. A total of three models, from only one hopper to the full settling structure, have been built, with scales from 1/18.5 to 1/100. According to the results of the studies, the length of the settling chambers has been shortened of up to 38 meters, i.e. 2 hoppers, and best use instructions have been suggested for the sediment evacuation system