References of "Léonard, Olivier"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailA hybrid optimization technique coupling an evolutionary and a local search algorithm
Kelner, Vincent ULg; Capitanescu, Florin ULg; Léonard, Olivier ULg et al

in Journal of Computational & Applied Mathematics (2006), 215(2), 281-287

Evolutionary algorithms are robust and powerful global optimization techniques for solving large-scale problems that have many local optima. However, they require high CPU times, and they are very poor in ... [more ▼]

Evolutionary algorithms are robust and powerful global optimization techniques for solving large-scale problems that have many local optima. However, they require high CPU times, and they are very poor in terms of convergence performance. On the other hand, local search algorithms can converge in a few iterations but lack a global perspective. The combination of global and local search procedures should offer the advantages of both optimization methods while offsetting their disadvantages. This paper proposes a new hybrid optimization technique that merges a genetic algorithm with a local search strategy based on the interior point method. The efficiency of this hybrid approach is demonstrated by solving a constrained multi-objective mathematical test-case. [less ▲]

Detailed reference viewed: 40 (6 ULg)
Full Text
See detailA Quasi-One Dimensional Model for Axial Compressors
Adam, Olivier; Léonard, Olivier ULg

in Proceedings od the 17th ISABE Conference (2005, September)

The object of the present paper is to present a fast and reliable CFD tool that is able to simulate stationary and transient operations of multistage axial compressors. The computational domain is the ... [more ▼]

The object of the present paper is to present a fast and reliable CFD tool that is able to simulate stationary and transient operations of multistage axial compressors. The computational domain is the compressor flow path, using a row-by-row, quasi-one-dimensional representation of the machine at mid-span. This analysis tool is based on an adapted version of the Euler equations solved by a time-marching, finite-volume method. The basic Euler equations have been extended by including source terms expressing the blade-flow interactions. The source terms are determined using the velocity triangles for each blade row, at mid-span. The losses and deviations undergone by the fluid in each blade row are supplied by correlations. The resulting flow solver is a performance prediction tool based only on compressor geometry. It offers the possibility of exploring the entire characteristic map of a compressor before its construction. Its efficiency in terms of CPU time makes it possible to use it as a fast design tool by coupling it to an optimization algorithm. In this paper, this CFD tool (called Quads hereafter) has been applied to two test-cases. Calculated characteristic curves are presented and compared to experimental ones. A correlation tuning process is described for an undocumented family of blade profiles. [less ▲]

Detailed reference viewed: 91 (2 ULg)
Full Text
See detailMulti-Objective Optimization of a Fan Blade by Coupling a Genetic Algorithm and a Parametric Flow Solver
Kelner, Vincent ULg; Grondin, Gilles; Léonard, Olivier ULg et al

in Proceedings of EUROGEN'05 (2005, September)

Detailed reference viewed: 36 (0 ULg)
Full Text
Peer Reviewed
See detailOn-Line Transient Engine Diagnostics in a Kalman Filtering Framework
Borguet, Sébastien ULg; Dewallef, Pierre ULg; Léonard, Olivier ULg

in Proceedings of the ASME Turbo Expo 2005 (2005, June)

A common assumption made in the performance assessment of a turbine engine for aircraft propulsion consists in restricting the data processing to steady-state data. This especially holds for on-board ... [more ▼]

A common assumption made in the performance assessment of a turbine engine for aircraft propulsion consists in restricting the data processing to steady-state data. This especially holds for on-board performance monitoring of a commercial aircraft which spends up to 90% of the time in cruise flight where such conditions are satisfied. The present contribution is intended to investigate the ability of a diagnosis method to process unsteady data rather than steady-state data. The aim of this unsteady approach is to strongly reduce the time and the efforts spent to obtain a reliable diagnosis. In order to assess the improvements in terms of diagnosis efficiency and engine operability, the resulting diagnostic method is tested for different degradations that can be expected on commercial turbofans. The results are also compared to those obtained from cruise flight steady-state data in order to balance the two approaches. [less ▲]

Detailed reference viewed: 27 (7 ULg)
Full Text
Peer Reviewed
See detailA Throughflow Analysis Tool Based on the Navier-Stokes Equations
Simon, Jean-Francois; Léonard, Olivier ULg

in 6th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics - Conference Proceedings (2005, March)

This paper describes a throughlow analysis tool based on a modern ¯nite-volume approach. The numerical model is obtained by averaging the 3-D Navier-Stokes equations in the blade passage, keeping only the ... [more ▼]

This paper describes a throughlow analysis tool based on a modern ¯nite-volume approach. The numerical model is obtained by averaging the 3-D Navier-Stokes equations in the blade passage, keeping only the axisymmetric part of the equations. The averaging reduces the spatial dimension of the problem but introduces additional terms, the blade forces, which have to be modeled. In the present viscous through°ow model, the 2-D annulus endwall °ow is captured by the resolution of the Navier-Stokes equations coupled to a simple mixing-length turbulence model. This allows to simulate high energy interactions and high losses near the endwalls. However, 3-D features such as tip or corner °ows cannot be predicted in axisymmetric computations. In the present contribution, these 3-D e®ects are modeled using empirical correlations from the literature. They are introduced into the equations, together with the pro¯le losses, by the so-called distributed loss model. Two test-cases, a high subsonic single stage compressor and a low speed three stage compressor, show the potential of the method. [less ▲]

Detailed reference viewed: 62 (2 ULg)
See detailRobust Design of a Fan Blade by Coupling Multi Objective Genetic Optimization and Flow Parameterization
Kelner, Vincent ULg; Grondin, Gilles; Léonard, Olivier ULg et al

in Proccedings od the International Congress on Fluid Dynamics Applications in Ground Transportation (2005)

Detailed reference viewed: 28 (1 ULg)
Full Text
Peer Reviewed
See detailApplication of genetic algorithms to lubrication pump stacking design
Kelner, Vincent ULg; Léonard, Olivier ULg

in Journal of Computational & Applied Mathematics (2004), 168(1-févr Sp. Iss. SI), 255-265

Sizing a pump stacking used in an aircraft lubrication system is a challenging task. The combination of several pumps, in parallel and in a single casing, must deliver specified oil flow rates, on a ... [more ▼]

Sizing a pump stacking used in an aircraft lubrication system is a challenging task. The combination of several pumps, in parallel and in a single casing, must deliver specified oil flow rates, on a variable number of circuits, and under given flight conditions. Furthermore, the optimal assembly has to minimize overall dimensions, weight and cost. This optimization problem involves a large space search, continuous and discrete variables and multi-objectives. Genetic Algorithms (GA)-stochastic search methods that mimic the metaphor of natural biological evolution-seem well suited to solve that kind of problems. A new GA is proposed. The efficiency of this GA is first demonstrated in solving various mathematical test-cases and then applied to the industrial problem. (C) 2003 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 8 (2 ULg)
Full Text
Peer Reviewed
See detailCombining classification techniques with Kalman filters for aircraft engine diagnostics
Dewallef, Pierre ULg; Léonard, Olivier ULg; Mathioudakis, Kostas et al

in Proceedings of the ASME Turbo Expo 2004 (2004, June)

Detailed reference viewed: 13 (2 ULg)
Full Text
Peer Reviewed
See detailOn-Line Aircraft Engine Diagnostic Using a Soft-Constrained Kalman Filter
Dewallef, Pierre ULg; Léonard, Olivier ULg; Mathioudakis, Kostas

in Proceedings of the ASME Turbo Expo 2004 (2004, June)

Detailed reference viewed: 149 (0 ULg)
Full Text
See detailHealth Monitoring of Gas Turbine Engines
Léonard, Olivier ULg

Scientific conference (2004, March 26)

Detailed reference viewed: 24 (5 ULg)
Full Text
Peer Reviewed
See detailOn-Line Performance Monitoring and Engine Diagnostic Using Robust Kalman Filtering Techniques
Dewallef, Pierre ULg; Léonard, Olivier ULg

in Proceedings of the ASME Turbo Expo 2003 (2003, June)

In this contribution, an on-line engine performance monitoring is carried out through an engine health parameter estimation based on several gas path measurements. This health parameter estimation makes ... [more ▼]

In this contribution, an on-line engine performance monitoring is carried out through an engine health parameter estimation based on several gas path measurements. This health parameter estimation makes use of the analytical redundancy of an engine model and therefore implies the knowledge of the engine state. As the latter is a priori not known the second task is therefore an engine state variable estimation. State variables here designate working conditions such as inlet temperature, pressure, Mach number, rotational speeds, . . . Estimation of the state variables constitutes a general application of the Extended Kalman Filter theory, while the health parameter estimation is a classical recurrent regression problem. Recent advances in stochastic methods [1] show that both problems can be solved by two Kalman filters working jointly. Such filters are usually named Dual Kalman Filters. The present contribution aims at using a dual Kalman filter modified to provide robustness. This procedure should be able to cope with as much as 20 to 30% of faulty data. The resulting online method is applied to a turbofan model developed in the frame of the OBIDICOTE 1 project. Several tests are carried out to check the performance monitoring capability and the robustness that can be achieved. [less ▲]

Detailed reference viewed: 48 (0 ULg)
Full Text
Peer Reviewed
See detailOn-Line Measurement Validation and Performance Monitoring Using Robust Kalman Filtering Techniques
Dewallef, Pierre ULg; Léonard, Olivier ULg

in 5th European Conference on Turbomachinery - Fluid Dynamics and Thermodynamics - Conference Proceedings (2003, March)

In an on-line engine performance monitoring, two tasks must be simultaneously carried out: an on-line engine health parameter estimation and an on-line engine state variables estimation. Estimation of the ... [more ▼]

In an on-line engine performance monitoring, two tasks must be simultaneously carried out: an on-line engine health parameter estimation and an on-line engine state variables estimation. Estimation of the state variables constitutes a general application of the Extended Kalman Filter theory, while the health parameter estimation is a classical recurrent regression problem. Recent advances show that both problems can be solved by two Kalman filters working jointly. Such filters are usually named Dual Kalman Filters. The present contribution aims at using a modified dual Kalman filter to provide robustness. This procedure should be able to cope with as much as 20 to 30% of faulty data. The resulting on-line validation method has been applied to a turbofan model developed in the frame of the OBIDICOTE 1 project. Several tests have been carried out to check the performance monitoring capability and the robustness that can be achieved [less ▲]

Detailed reference viewed: 23 (1 ULg)
Full Text
See detailOptimal Pump Scheduling for Water Supply Using Genetic Algorithms
Kelner, Vincent ULg; Léonard, Olivier ULg

in Proceedings od Eurogen'03 (2003, March)

Detailed reference viewed: 78 (1 ULg)
See detailImplicit high-order geometrically conservative scheme for the solution of flow problems on moving unstructured grids
Lepot, Ingrid; Vigneron, Didier ULg; Essers, Jean-André ULg et al

Conference (2003, March)

This paper presents a finite volume solver for the computation of three-dimensional unsteady flows of inviscid compressible perfect gases on moving unstructured meshes. This solver, based on a cell ... [more ▼]

This paper presents a finite volume solver for the computation of three-dimensional unsteady flows of inviscid compressible perfect gases on moving unstructured meshes. This solver, based on a cell-centered approach for arbitrary polyhedral cells, provides unconditional second-order space and time truncation error. A new way of satisfying the Discrete Geometric Conservation Law (DGCL) adapted to this scheme is proposed. Preliminary results are presented. [less ▲]

Detailed reference viewed: 56 (9 ULg)
Full Text
See detailRapport sur la numérisation et l’avenir des bibliothèques de l’Université de Liège
Bouquegneau, Jean-Marie ULg; Denooz, Joseph ULg; Gathon, Henry-Jean ULg et al

Report (2003)

Les missions confiées par le Recteur de l'Université de Liège au groupe de travail chargé de rédiger ce rapport étaient : • Organiser le mieux et le plus rapidement possible le développement du ... [more ▼]

Les missions confiées par le Recteur de l'Université de Liège au groupe de travail chargé de rédiger ce rapport étaient : • Organiser le mieux et le plus rapidement possible le développement du numérique dans les bibliothèques ; • Apporter des solutions aux problèmes d’essaimage des budgets et des ressources humaines. Pour répondre à ces objectifs, le Groupe de travail a commencé par relever les principaux jalons de l’évolution historique de l’informatisation dans les bibliothèques de l’Université. Il s’est ensuite attaché à évaluer l’état actuel de la numérisation dans le réseau des bibliothèques de l’Université par rapport aux développements numériques du secteur. Face à cet état des lieux, il présente des pistes pour accélérer et renforcer la numérisation des bibliothèques. Enfin, pour permettre la mise en œuvre de ce projet, il propose en conclusion des mesures à prendre au niveau de la réorganisation des bibliothèques en termes de locaux et de personnel. [less ▲]

Detailed reference viewed: 38 (18 ULg)
Full Text
Peer Reviewed
See detailExplicit Thermodynamic Properties Using Radial Basis Functions Neural Networks
Adam, Olivier; Léonard, Olivier ULg

in Proceedings of the second SIAM international Conference on Data Mining (2002)

Gas turbine design, development, monitoring and maintenance are widely based on numerical simulations of the steady and transient engine performance. Most of the equations that are solved in the ... [more ▼]

Gas turbine design, development, monitoring and maintenance are widely based on numerical simulations of the steady and transient engine performance. Most of the equations that are solved in the simulation programs involve the thermodynamic properties of the fluid flowing through the engine. These properties depend on temperature, pressure, humidity and fuel dosage. As the solution of chemical equilibrium is not compatible with real-time computations, a chemical solver is used off-line to generate a large database which neural networks are trained on. These networks are built on radial basis functions such as multiquadrics. A forward selection approach is used to select data points from the training set as the centers of the transfer functions. The selection stops when the prediction error starts growing. The resulting networks for specific heat and enthalpy of the gas mixture are 3 orders of magnitude faster than the chemical solver. In order to further increase the efficiency and the generalization capabilities of the model, an external optimization solver has been used to tune the shape of the transfer functions. Several solutions are proposed and preliminary results are presented. [less ▲]

Detailed reference viewed: 24 (1 ULg)
Full Text
Peer Reviewed
See detailRobust Validation of Measurements on jet Engines
Dewallef, Pierre ULg; Léonard, Olivier ULg

in European Journal of Mechanical and Environmental Engineering (2001), 46(4), 237-242

Nowadays, most of turbine engine tests are processed using an open loop, i.e. the measurements are verified and treated a posteriori, sometimes weeks or months after the end of the test. The scope of the ... [more ▼]

Nowadays, most of turbine engine tests are processed using an open loop, i.e. the measurements are verified and treated a posteriori, sometimes weeks or months after the end of the test. The scope of the present project is to develop a new methodology which enables real time detection of faulty measurements and the suppression of the source of these faults during the test. This implies the development of a method which is sufficiently robust to cope with a lot of faulty data (up to 20 to 30 % of the measurements). Most of the existing methods make use of a least square approach so that a set of parameters is sought which minimizes the RMS error between the measurements and the values provided by a numerical model of the installation. This type of approach is efficient in finding whether a set of measurements is valid but cannot locate the fault(s). In this paper an alternative is proposed based on a distribution of the measurement noise introduced by Huber. This so-called robust validation method has been tested on a single spool, single flow and variable geometry nozzle turbojet. Both the least square and Huber's function approaches have been tested and compared in terms of efficiency. The robust estimator based on Huber's error function has shown to be much more powerful for both finding an invalid set of measurements and locating the faulty measurements. [less ▲]

Detailed reference viewed: 18 (4 ULg)
Full Text
See detailOn-Line Validation of Measurements on Jet Engines Using Automatic Learning Methods
Dewallef, Pierre ULg; Léonard, Olivier ULg

in Proceedings od the 15th ISABE Conference (2001)

Nowadays, turbine engine tests are processed using an open loop, i.e. the measurements are verified and treated a posteriori, sometimes weeks or months after the end of the test. The purpose of the ... [more ▼]

Nowadays, turbine engine tests are processed using an open loop, i.e. the measurements are verified and treated a posteriori, sometimes weeks or months after the end of the test. The purpose of the present project is to develop a new methodology which enables real time detection of faulty measurements and the suppression of the source of these faults during the test. The validation of the measurements is achieved by a “robust” parameter identification [1]. Such a method is called robust in the sense that it can cope with 20 to 30% of faulty measurements. The robustness is insured by a distribution of the measurement noise, as introduced by Huber [7, 8], that takes into account the possibility of faults. The purpose of a parameter identification is to find the set of parameters which has most likely generated the measurements observed on the process. This leads to an optimisation problem that has to be solved for the parameters. The measurements are linked to the parameters through a non-linear model, leading to a large system of equations for modern jet engines. If no physical model of the process can be made available or if this model is too complex to allow real time validation, automatic learning methods may provide a solution: • either a mathematical representation is generated, directly based on the measurements (online learning), • or a database is first generated, based on the existing (but expensive) physical model, the database being subsequently used to build a statistical model (off-line learning). Neural networks seem to be very suitable for modeling the behavior of turbojets, avoiding the resolution of a time-consuming non-linear system. In this paper neural networks are tested to generate a mathematical representation of a single flow, single spool and variable geometry nozzle turbojet, from a data base of “measurements” generated by a physical model of the engine. Only the off-line learning approach is considered. [less ▲]

Detailed reference viewed: 22 (2 ULg)
See detailModelization, Development and Testing of a Variable Geometry Nozzle
Mignon, Anthony; Léonard, Olivier ULg

in Proceedings of the 5th Belgian National Congress on Theoretical and Applied Mechanics (2000)

Detailed reference viewed: 18 (1 ULg)