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See detailAn experimental and numerical investigation on the influence of external gas recirculation on the HCCI autoignition process in an engine: Thermal, diluting, and chemical effects
Machrafi, Hatim ULg; Cavadias, Simeon; Guibert, Philippe

in Combustion & Flame (2008), 155(3), 476-489

In order to contribute to the solution of controlling the autoignition in a homogeneous charge compression ignition (HCCI) engine, parameters linked to external gas recirculation (EGR) seem to be of ... [more ▼]

In order to contribute to the solution of controlling the autoignition in a homogeneous charge compression ignition (HCCI) engine, parameters linked to external gas recirculation (EGR) seem to be of particular interest. Experiments performed with EGR present some difficulties in interpreting results using only the diluting and thermal aspect of EGR. Lately, the chemical aspect of EGR is taken more into consideration, because this aspect causes a complex interaction with the dilution and thermal aspects of EGR. This paper studies the influence of EGR on the autoignition process and particularly the chemical aspect of EGR. The diluents present in EGR are stimulated by N-2 and CO2, with dilution factors going from 0 to 46 vol%. For the chemically active species that could be present in EGR, the species 0 and 170 ppm, while that of CH2O alters between 0 and 1400 ppm. For the investigation of the effect of the chemical species on the autoignition, a fixed dilution factor of 23 vol% and a fixed EGR temperature of 70 degrees C are maintained. The inlet temperature is held at 70 degrees C, the equivalence ratios between 0.29 and 0.41, and the compression ratio at 10.2. The fuels used for the autoignition are n-heptane and PRF40. It appeared that CO, in the investigated domain, did not influence the ignition delays, while NO had two different effects. At concentrations up until 45 ppm, NO advanced that ignition delays for the PRF40 and at higher concentrations, the ignition delayed. The influence of NO on the autoignition of n-heptane seemed to be insignificant, probably due to the higher burn rate of n-heptane. CH2O seemed to delay the ignition. The results suggested that especially the formation of OH radicals or their consumption by the chemical additives determines how the reactivity of the autoignition changed. (C) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved. [less ▲]

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See detailExperimental and numerical investigations for I-girders in bending and shear stiffened by closed trapezoidal stiffeners
Boissonnade, N.; Degée, Hervé ULg; Naumes, J. et al

in Proceedings of the ICMS Conference (2006)

The paper investigates the shear resistance of I-girders longitudinally stiffened by closed trape-zoidal stiffeners. It first reports on 4 full-scale tests performed at RWTH Aachen, on stiffened panels ... [more ▼]

The paper investigates the shear resistance of I-girders longitudinally stiffened by closed trape-zoidal stiffeners. It first reports on 4 full-scale tests performed at RWTH Aachen, on stiffened panels with strong closed stiffeners. As expected, failure in the subpanels has been governing. A devoted FEA shell model is then described and validated towards these results and other experimental sources. Parametric stud-ies led with the numerical tool help pointing out several aspects where the Eurocode 3 Part 1.5 recommenda-tions on stiffened panels in bending and shear may be improved. [less ▲]

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See detailExperimental and numerical investigations for I-girders in bending and shear stiffened by closed trapezoidal stiffeners for use in steel bridges
Feldmann, M.; Naumes, J.; Oppe, M. et al

in Proceedings of the IABSE Symposium "Improving infrastructures..." (2007)

The paper summarizes the investigations on shear resistance of I-girders longitudinally stiffened by closed trapezoidal stiffeners, performed in the frame of a European RFCS project (RFS-CR-03018 ... [more ▼]

The paper summarizes the investigations on shear resistance of I-girders longitudinally stiffened by closed trapezoidal stiffeners, performed in the frame of a European RFCS project (RFS-CR-03018) designated as “ComBri” (Competitive Steel and Composite Bridges by improved Steel Plated Structures), with configurations typical of what may be expected in the design of modern steel bridges. It first reports on four full-scale tests performed at RWTH Aachen, on stiffened panels with strong closed stiffeners where the deformations have been measured with photogrammetric devices. As expected, failure in the subpanels has been governing. A devoted FEA shell model is then described and validated towards these results and other experimental sources. The numerical simulations demonstrate a very good agreement with the test-results. Parametric studies performed with a sophisticated numerical tool help pointing out several aspects where the recommendations of EN 1993-1-5 [1] on stiffened panels in bending and shear may be improved. [less ▲]

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See detailExperimental and numerical investigations for I-Girders in bending and shear stiffened by trapezoidal stiffeners
Boissonnade, N.; Degée, Hervé ULg; Naumes, J. et al

in Advanced Steel Construction (2008), 4(1), 1-13

The paper investigates the shear resistance of I-girders longitudinally stiffened by trapezoidal stiffeners. It first reports on 4 full-scale tests performed at RWTH Aachen, on stiffened panels with ... [more ▼]

The paper investigates the shear resistance of I-girders longitudinally stiffened by trapezoidal stiffeners. It first reports on 4 full-scale tests performed at RWTH Aachen, on stiffened panels with strong closed stiffeners. As expected, failure in the subpanels has been governing. A devoted FEA shell model is then described and validated towards these results and other experimental sources. Parametric studies led with the numerical tool help pointing out several aspects where the Eurocode 3 Part 1.5 recommendations on stiffened panels in bending and shear may be improved. [less ▲]

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See detailExperimental and numerical investigations of dike-break induced flows
Roger, Sebastian; Dewals, Benjamin ULg; Erpicum, Sébastien ULg et al

in Journal of Hydraulic Research (2009), 47(3), 349-359

Experimental model data are compared with numerical computations of dike-break induced flows, focusing on the final steady state. An idealised scale model was designed reproducing the specific boundary ... [more ▼]

Experimental model data are compared with numerical computations of dike-break induced flows, focusing on the final steady state. An idealised scale model was designed reproducing the specific boundary conditions of dike breaks. Discharges, water levels and depth profiles of horizontal velocities were recorded and validated by numerical modeling. The latter was performed by two different models solving the two-dimensional depth-averaged shallow water equations, namely a total variation diminishing Runge-Kutta dis¬continuous Galerkin finite element method, and a finite volume scheme involving a flux vector splitting ap¬proach. The results confirmed convergence and general applicability of both methods for dike-break prob¬lems. As regards their accuracy, the basic flow pattern was satisfactorily reproduced yet with differences compared to the measurements. Hence, additional simulations by a finite volume model were performed con¬sidering various turbulence closures, wall-roughnesses as well as non-uniform Boussinesq coefficients. [less ▲]

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See detailExperimental and Numerical Investigations of the Aeroelastic Stability of Bluff Structures
Andrianne, Thomas ULg

Doctoral thesis (2012)

The study of the dynamic interactions between the wind and civil engineering structures has become increasingly important over the last few decades. Most of these structures are aerodynamically "bluff ... [more ▼]

The study of the dynamic interactions between the wind and civil engineering structures has become increasingly important over the last few decades. Most of these structures are aerodynamically "bluff" and are becoming more flexible. Bluff-body aeroelasticity is a very challenging research area due to the unsteadiness and nonlinearity of the aerodynamic loading. This thesis presents the investigation of three aeroelastic phenomena affecting bluff-bodies: Vortex Induced Vibration (VIV), Galloping and Torsional Flutter. For each instability, extensive experimental studies are carried out in the wind tunnel. Innovative analysis, based on the Common-base Proper Orthogonal Decomposition (CPOD) method is used to study the flow visualization data. The VIV phenomenon is studied on a flexible tube with a circular cross-section, supported from its midpoint. A CPOD-based input-output model is developed to describe the system. The galloping instability is studied on a generic bridge section. A complete analysis of the aeroelastic behaviour of the structure is presented and a new polynomial empirical model is developed, which reflects accurately the nonlinear nature of the system. The torsional flutter phenomenon is extensively studied for two different structures: a generic bridge deck and a rectangular cylinder. The Motion Induced Vortex is identified as the fundamental cause of this aeroelastic phenomenon, on the basis of the analysis of the flow around the oscillating rectangle. In addition, it is demonstrated that the quasi-steady theory is not adapted to estimate the onset velocity of torsional flutter. Finally, a 2D aeroelastic simulation code, based on the Discrete Vortex Method (DVM) is developed. The non-linear aerodynamics around the body are well reproduced, allowing the simulation of all the aeroelastic instabilities investigated experimentally. [less ▲]

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See detailExperimental and numerical investigations of the torsional flutter oscillations of a 4:1 rectangular cylinder
Andrianne, Thomas ULg; Dimitriadis, Grigorios ULg

in Journal of Fluids & Structures (2013), 41

The torsional flutter oscillations of a 4:1 rectangular cylinder around its pitching axis are investigated through wind tunnel experiments and numerical simulations. The rectangle’s responses to different ... [more ▼]

The torsional flutter oscillations of a 4:1 rectangular cylinder around its pitching axis are investigated through wind tunnel experiments and numerical simulations. The rectangle’s responses to different initial conditions and turbulence excitations at various wind tunnel airspeeds are recorded. Timeresolved Particle Image Velocimetry measurements are taken at two different airspeeds, when the rectangle undergoes Limit Cycle Oscillations. Aeroelastic simulations are carried out using the Discrete Vortex Method and the resulting responses are compared to the experimental measurements. The Common-base Proper Orthogonal Decomposition method is used to analyse and compare the measured and simulated unsteady flow fields around the rectangle. A discussion of the participation of each mode in the different states of the flow-field is presented, at two different amplitudes of oscillation. The Motion Induced Vortex (MIV) is identified as the fundamental cause of the torsional flutter phenomenon and its role over a complete cycle is studied. MIV-induced oscillations can be started either by a suitable initial disturbance or by a second, nearly linear self-excited instability that causes negative aerodynamic damping. The combination of these two instabilities results in a complete description of the torsional flutter of the rectangle. [less ▲]

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See detailExperimental and numerical investigations on iron columns reinforced by FRP under axial compression
Ly, Dong Phuong Lam ULg; Jaspart, Jean-Pierre ULg; Demonceau, Jean-François ULg et al

in Camelbeeck, Th.; Degée, Hervé; Degrande, G. (Eds.) et al Seismic risk (2008, September 11)

This paper presents experimental and numerical investigations on iron columns under axial compression, strengthened with high modulus carbon fibre reinforced polymer (FRP) sheets. It is shown that the ... [more ▼]

This paper presents experimental and numerical investigations on iron columns under axial compression, strengthened with high modulus carbon fibre reinforced polymer (FRP) sheets. It is shown that the resistance and stiffness of iron columns can be increased significantly with the use of longitudinal FRP sheets as a result of the reduction of the column slenderness, but also that transverse FRP sheets should be used to prevent any local buckling of the longitudinal FRP sheets. [less ▲]

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See detailExperimental and numerical investigations to assess and mitigate sedimentation problems: application to a large dam in India
Erpicum, Sébastien ULg; Dewals, Benjamin ULg; Archambeau, Pierre ULg et al

in Proceedings of the 7th National Congress on theoretical and applied Mechanics (2006)

In the global framework of river management, sedimentation problems in dam reservoirs and adjacent structures are multiple and of major interest for designers as well as dam owners or managers. Before dam ... [more ▼]

In the global framework of river management, sedimentation problems in dam reservoirs and adjacent structures are multiple and of major interest for designers as well as dam owners or managers. Before dam construction, these problems can be assessed by several techniques. In this paper, the experimental and numerical sedimentation studies realized at the Laboratory of Applied Hydrodynamics and Hydraulic Constructions (HACH) of the University of Liège on a large hydropower plant project in India are presented. Three main issues related to sedimentation problems are analyzed in details. [less ▲]

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See detailExperimental and numerical study of an AlMgSc sheet formed by an incremental process
Bouffioux, Chantal ULg; Lequesne, Cédric ULg; Vanhove, H. et al

in Journal of Materials Processing Technology (2011), 211(11), 1684-1693

A recently developed AlMgSc alloy is studied since this material, which is well adapted to the aeronautic domain, is poorly known. The first objective is to reach a better knowledge of this alloy to ... [more ▼]

A recently developed AlMgSc alloy is studied since this material, which is well adapted to the aeronautic domain, is poorly known. The first objective is to reach a better knowledge of this alloy to provide the missing useful information to the aeronautic industry and to help research institutes who want to simulate sheet forming processes by Finite Element (FE) simulations. A set of experimental tests has been performed on the as-received sheets, material laws have been chosen and the corresponding material parameters have been adjusted to correctly describe the material behaviour. The second objective is to study the applicability of the Single Point Incremental Forming process (SPIF) on this material. Truncated cones with different geometries were formed and the maximum forming angle was determined. A numerical model was developed and proved to be able to predict both the force evolution during the process and the final geometrical shape. Moreover, the model helps reaching a better understanding of the process. The characterisation method described in this research and applied on the AlMgSc alloy can be extended to other alloys. In addition, the numerical simplified model, able to accurately describe the SPIF process with a reduced computation time, can be used to study more complex geometries. [less ▲]

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See detailExperimental and numerical study of flange class 3 cross-section members
Boissonnade, N.; Jaspart, Jean-Pierre ULg

in Proceedings of the International Conference on Stability and Ductility of Steel Structures (2006)

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See detailExperimental and numerical study of fracture healing in a murine fracture model
Geris, Liesbet ULg; Gerisch, A.; Maes, C. et al

Poster (2005)

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See detailExperimental and numerical study of TA-6V mechanical behavior in different monotonic loading conditions at room temperature
Gilles, Gaëtan ULg; Cazacu, Oana; Hammami, Walid ULg et al

in Procedia IUTAM (2012), 3

This paper presents an experimental characterization of the quasi-static mechanical response of a TA-6V titanium alloy in sheet form. Monotonic tests, such as uniaxial tension and compression, plane ... [more ▼]

This paper presents an experimental characterization of the quasi-static mechanical response of a TA-6V titanium alloy in sheet form. Monotonic tests, such as uniaxial tension and compression, plane strain and simple shear, were conducted along several orientations in the plane of the sheet in order to investigate the plastic anisotropy and the tension-compression asymmetry displayed by the material at the macroscopic scale. It was observed a moderate anisotropy in yielding while the anisotropy in r-ratios is very pronounced. Initial yielding is described using criteria that account for both plastic anisotropy and strength differential effects. Comparison between experimental data and FE simulation results illustrates the ability of the model to predict the mechanical response of TA-6V. [less ▲]

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See detailExperimental and numerical study of TA6V mechanical behavior under different quasi-static strain paths at room temperature
Gilles, Gaëtan ULg; Habraken, Anne ULg; Cazacu, Oana et al

in AIP Conference Proceedings (2013), 1532

This paper presents an experimental study of the quasi-static mechanical behavior of TA6V titanium alloy. Different monotonic tests were carried out in several orientations in the plane of the sheet in ... [more ▼]

This paper presents an experimental study of the quasi-static mechanical behavior of TA6V titanium alloy. Different monotonic tests were carried out in several orientations in the plane of the sheet in order to characterize the anisotropy and the tension-compression asymmetry exhibited by the material. Initial yielding is modeled by the phenomenological CPB06 criterion and Voce's isotropic hardening is used to describe its evolution. The simulation of a deep-drawing process is performed using the proposed constitutive modeling and compared with experimental data. [less ▲]

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See detailExperimental and numerical study of the breaching of an embankment dam
Dupont, E.; Dewals, Benjamin ULg; Archambeau, Pierre ULg et al

in Proceedings of the 32nd IAHR Biennial Congress - Harmonizing the demands from art and nature (2007)

In the framework of the study of the collapse of an embankment dam following its overtopping, an experimental study of the progressive breaching of such a dam has been performed. The present laboratory ... [more ▼]

In the framework of the study of the collapse of an embankment dam following its overtopping, an experimental study of the progressive breaching of such a dam has been performed. The present laboratory tests enable to validate and to complete a numerical approach previously studied by the authors. The two-dimensional analysis of the breaching is carried out on a scale model in a flume. A cross-section of a dam is scaled according to proper similarity rules, both for the flow and for the solid transport. The originality of the approach lies in the interaction between the experimental and numerical work. The experiments on the scale model are filmed in order to determine the time evolution of the dam profiles. The cross sections are extracted from the films and analyzed by an image-processing algorithm specifically developed for this application. These results are integrated into the hydrodynamic model WOLF2D, which computes the flow generated by the given transient topography and eventually supplies the relevant hydraulic parameters characterizing the dam breaching. [less ▲]

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See detailExperimental and numerical study of the factors influencing the performances of magnetic screens made of high temperature superconductors
Fagnard, Jean-François ULg

Doctoral thesis (2011)

In this thesis, we investigate in details the magnetic shielding processes in high temperature superconductors. We aim at predicting and measuring the influence of the parameters governing the ... [more ▼]

In this thesis, we investigate in details the magnetic shielding processes in high temperature superconductors. We aim at predicting and measuring the influence of the parameters governing the superconducting behaviour (e.g., the critical current density Jc and its field dependence) on the magnetic flux penetration inside hollow cylinders. Three objectives are pursued. The first objective is to characterize the performances of cylindrical magnetic shields made of various high temperature superconductors (Bi-2223, Bi-2212, Y-123) for several external parameters that can be directly controlled in the experiments. These include the temperature, the geometry of the magnetic screen, the amplitude of the applied magnetic field, its orientation (H // or ⊥ cylinder axis) and its frequency (in the case of an AC excitation). The focus has been put on the effect of the sweep rate of the applied magnetic field, dBapp/dt, on the threshold magnetic flux density, Blim, above which the magnetic shielding is no longer efficient. We show that the curve of dBapp/dt vs. Blim can be directly related to the E(J) constitutive law and we explain how the field dependence of the critical current density affects the relationship between both curves. A wide range of electric field levels is investigated in this thesis thanks to the use of a number of experimental techniques. The experimental set-ups required for these investigations are described in a separate chapter where the performances and limitations of each set-up is put forward. The second objective of the thesis is to confront experimental data and numerical simulations using models of increasing complexity. We present two numerical models that take into account the strongly non-linear E(J) relationship characterizing the superconducting behaviour. The first numerical model is based on the Brandt algorithm. This model is able to describe magnetic shielding experiments which involve time-varying magnetic fields on (i) infinite samples subjected to transverse magnetic fields or on (ii) samples of finite size in axisymmetric geometries subjected to axial magnetic fields. The second model is based on a finite element method (using the GetDP software). This model can be used for both axisymmetric 2D modelling and full 3D modelling. In the latter case, it provides extremely useful information for understanding configurations where the applied magnetic field and the hollow cylinder do not present a particular symmetry. Both 2D and 3D models are able to provide current and field distributions in the superconductor. The confrontation between experimental and modelling results allows us to better understand how physical properties (critical temperature Tc, critical current density Jc, ...) and geometry affect the magnetic shielding performances (shielding factor SF, threshold induction Blim). Conversely, we present three different practical procedures using either the analytical Bean model or a 2D numerical model in order to determine the constitutive law parameters of the superconducting materials from data measured on hollow cylinders. As a third objective, we aim at investigating how the different types of HTS magnetic screens of moderate dimensions (a few cubic centimetres) could be scaled up in order to provide larger shielded volumes. Three methods are explored. The first method to build larger magnetic screens (typically ten(s) of centimetres) is to find means to assemble several (pieces of) superconducting hollow cylinders to obtain a large shielding enclosure. Experiments are carried out on superconducting cylinders cut either along or perpendicular to their axis. The influence of the cut width and the angle of the applied magnetic field with respect to the cut plane are studied. Modellings are carried out on shorter cylinders in order to understand how the presence of the cut modifies the current distribution and thus the magnetic shielding properties. The second method consist in characterizing the magnetic shielding of several hollow cylinders made with the same superconducting material but having different sizes. This helps us in determining whether the manufacturing process is able to provide large cylinders with good magnetic shielding performances. In a last method, we investigate an architecture of superconducting magnetic screens that differs from those based on bulk hollow cylinders. The idea is to exploit the high Jc-performances of superconducting tapes (based on thin film technology) to build magnetic shielding structures which can be easily scalable. The measurement results obtained on such structures are promising as the actual limitation seems to be geometrical. Using more superconducting tapes in order to achieve a higher aspect ratio should give magnetic shields which are as efficient as bulk cylinders. [less ▲]

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