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

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

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

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

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An exact Riemann Solver and Godunov Scheme for Simulating Highly Transient Mixed Flows

AbstractThe current research aims at deriving a one-dimensional numerical model for describing highly transient mixed flows. In particular, this paper focuses on the development and assessment of a unified numerical scheme adapted to describe free-surface flow, pressurized flow and mixed flow (characterized by the simultaneous occurrence of free-surface and pressurized flows). The methodology includes three steps. First, the authors derived a unified mathematical model based on the Preissmann slot model. Second, a first-order explicit finite volume Godunov-type scheme is used to solve the set of equations. Third, the numerical model is assessed by comparison with analytical, experimental and numerical results. The key results of the paper are the development of an original negative Preissmann slot for simulating sub-atmospheric pressurized flow and the derivation of an exact Riemann solver for the Saint-Venant equations coupled with the Preissmann slot

Modelling sediment transport over partially non-erodible bottoms

peer reviewedIn 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