Une approche unifiée pour la modélisation d'écoulements à surface libre, de leur effet érosif sur une structure et de leur interaction avec divers constituants

La thèse constitue une juxtaposition de plusieurs contributions originales à l’élaboration et l’analyse de modèles numériques capables de décrire une vaste gamme d’écoulements à surface libre ainsi que les phénomènes de transport associés. Deux axes principaux sous-tendent les recherches entreprises. Il s’agit, d’une part, d’une contribution à l’étude de modèles visant à reproduire adéquatement les interactions du fluide avec divers constituants transportés, tels que de l’air entraîné, un polluant ou des sédiments. Cette phase du travail inclut également la caractérisation et la prédiction du comportement de l’écoulement en présence d’une topographie mobile ou érodable, y compris dans le cas d’un barrage en remblai subissant une surverse. D’autre part, partant du constat qu’une modélisation fidèle des processus de transport, notamment hydrosédimentaires, passe inévitablement par un raffinement du calcul hydrodynamique proprement dit, une partie des travaux effectués dans le cadre de cette thèse est spécifiquement orientée vers un enrichissement de la connaissance des champs hydrodynamiques au sein du modèle

Malignant catarrhal fever induced by Alcelaphine herpesvirus 1 is characterized by an expansion of activated CD3+CD8+CD4- T cells expressing a cytotoxic phenotype in both lymphoid and non-lymphoid tissues

Alcelaphine herpesvirus 1 (AlHV-1) is carried by wildebeest asymptomatically. It causes a fatal lymphoproliferative disease named wildebeest-derived malignant catarrhal fever (WD-MCF) when cross-species transmitted to a variety of susceptible species of the Artiodactyla order. WD-MCF can be reproduced experimentally in rabbits. In a previous report, we demonstrated that WD-MCF induced by AlHV-1 is associated with a severe proliferation of CD8+ T cells in the lymphoid tissues. Here, we further studied the mononuclear leukocytic populations in both the lymphoid (throughout the infection and at time of euthanasia) and non-lymphoid (at time of euthanasia) organs during WD-MCF induced experimentally in rabbits. To reach that goal, we performed multi-colour flow cytometry stainings. The results obtained demonstrate that the development of WD-MCF correlates in peripheral blood with a severe increase of CD8+ cell percentages; and that CD3+CD8+CD4- T cells were the predominant cell type in both lymphoid and non-lymphoid organs at time of euthanasia. Further characterization of the mononuclear leukocytes isolated from both lymphoid and non-lymphoid tissues revealed that the CD8+ T cells express high levels of the activation markers CD25 and CD44, produce high amount of gamma-interferon (IFN-γ) and perforin, and showed a reduction of interleukin-2 (IL-2) gene expression. These data demonstrate that the development of WD-MCF is associated with the expansion and infiltration of activated and cytotoxic CD3+CD8+CD4- T cells secreting high amount of IFN-γ but low IL-2

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

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

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

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