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See detailModelling the magnetic field of the B-type N-rich star ζ Cassiopeiae
Briquet, Maryline ULg; Neiner, Coralie

Diverse speeche and writing (2012)

Detailed reference viewed: 16 (1 ULg)
See detailModelling the Marine Environment.
Djenidi, Salim ULg

Report (1990)

Detailed reference viewed: 3 (0 ULg)
See detailModelling the medium-scale TEC structures, observed by Belgian GPS receiver network
Kutiev, Ivan; Marinov, P.; Fidanova, S. et al

Conference (2007)

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See detailModelling the Mid-latitude Ionosphere: Assessment of the NeQuick Model using GPS TEC and Ionosonde Data
Bidaine, Benoît ULg

Master of advanced studies dissertation (2007)

The ionosphere plays a crucial role in Global Navigation Satellite Systems (GNSS) accuracy. In extreme cases, this electrically charged part of the atmosphere can lead to errors in positioning exceeding ... [more ▼]

The ionosphere plays a crucial role in Global Navigation Satellite Systems (GNSS) accuracy. In extreme cases, this electrically charged part of the atmosphere can lead to errors in positioning exceeding 100 m. At first approximation, ionospheric effects depend mainly on the total content in free electrons of the ionosphere ("total electron content", TEC) defined as the integral of the electron density on the path between the satellite and the receiver. The modelling of the latter parameter reveals thus itself critical in particular for single frequency receivers, the most common ones constituting the mass market. In the framework of GALILEO, the European system in development, the NeQuick model has been chosen to this extent. Computing monthly median electron densities as a basis, it will be integrated into a global algorithm providing the users with daily updated information and allowing them to calculate TEC and thus to mitigate the ionospheric effects. In order to reach the specified correction level, the model itself and its latest evolutions as well as its use for GALILEO are investigated. Different situations have to be considered e.g. different latitude regions and the results can be compared to various data sets. As a first step in a thorough analysis, we take benefit of ionosonde and GPS TEC data from the Dourbes Geophysical Observatory (Belgium) to study the mid-latitudes. Constraining the model with ionosonde measurements, we first investigate the difference between GPS-derived vertical TEC (vTEC) for Dourbes station and corresponding values from NeQuick for the latest years (for solar maximum in 2002 and minimum in 2006). With this approach, we reach residual errors of about 20% RMS for 2002 and 30% for 2006 keeping in mind that TEC values are far lower in this low solar activity year. Through a focusing process, we identify then gradually best and worst months and days for which we observe the evolution between two versions of NeQuick. We highlight among others improvements from the latest modification in the topside formulation which appears clearly in the electron density profiles examined at the end of the assessment. [less ▲]

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See detailModelling the Middle Miocene climate with PLASIM and CARAIB
Henrot, Alexandra ULg

Scientific conference (2010, October)

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See detailModelling the migration of a mid-Pleistocene erosion wave in the Ardennes (western Europe) drainage network: approach and first implications
Beckers, Arnaud ULg; Bovy, Benoît ULg; Demoulin, Alain ULg

Poster (2011, April)

Model parameterization through adjustment to field data is a crucial step in the modelling and the understanding of the drainage network response to tectonic or climatic perturbations. Using a data set of ... [more ▼]

Model parameterization through adjustment to field data is a crucial step in the modelling and the understanding of the drainage network response to tectonic or climatic perturbations. Using a data set of 18 knickpoints that materialize the migration of a 0.7-Ma-old erosion wave in the Ourthe catchment of northern Ardennes (western Europe) as a test case, we explore the impact of various data fitting on the calibration of the detachment-limited stream power model of river incision, from which a simple knickpoint celerity equation is derived. Our results show that statistical least squares adjustments (or misfit functions) based either on the stream-wise distances between observed and modelled knickpoint positions at time t = 0.7 Ma or on differences between observed (0.7 Ma) and modelled time at the actual knickpoint locations yield significantly different values for the m (more exactly, m/n) and K parameters of the model. As there is no physical reason to prefer one or the other approach, we suggest that an intermediate least rectangles adjustment might be the best compromise. In the Ourthe case, this leads to a m/n value lower than that obtained from the classical distance adjustment (0.79 against 0.86), leading to an increase in the non linear character of the dependence of knickpoint celerity on discharge. If we now recall that m/n = c(1-b) (Whipple & Tucker, 1999, JGR 104B: 17661-17674), where c and b are the exponents of the power law relations respectively linking discharge to drainage area and channel width to discharge, we can compare the calculated m/n value with that derived from field measurements of channel width, discharge and drainage area in the presently graded sections of the rivers. Such data taken from Petit et al. (2005, BSGLg 46: 37-50) allow us to derive m/n = 0.48 at equilibrium. As c may be considered constant, the higher m=n value obtained from the knickpoint retreat modelling must be ascribed to a lower b, i.e., to a channel narrowing associated with the transient phase of knickpoint migration. [less ▲]

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See detailModelling the migration of contaminants through variably saturated dual-porosity, dual-permeability chalk
Brouyère, Serge ULg

in Journal of Contaminant Hydrology (2006), 82(3-4), 195-219

In the Hesbaye region in Belgium, tracer tests performed in variably saturated fissured chalk rocks presented very contrasting results in terms of transit times, according to artificially controlled water ... [more ▼]

In the Hesbaye region in Belgium, tracer tests performed in variably saturated fissured chalk rocks presented very contrasting results in terms of transit times, according to artificially controlled water recharge conditions prevailing during the experiments. Under intense recharge conditions, tracers migrated across the partially or fully saturated fissure network, at high velocity in accordance with the high hydraulic conductivity and low effective porosity (fracture porosity). At the same time, a portion of the tracer was temporarily retarded in the almost immobile water located in the matrix. Under natural infiltration conditions, the fissure network remained inactive. Tracers migrated downward through the matrix, at low velocity in relation with the low hydraulic conductivity and the large porosity of the matrix. Based on these observations, Brouyere et al. (2004a) [Brouyere, S., Dassargues, A., Hallet, V, 2004a. Migration of contaminants through the unsaturated zone overlying the Hesbaye chalky aquifer in Belgium: a field investigation, J. Contain. Hydrol., 72 (1-4), 135-164, doi: 10.1016/j.conhyd.2003.10. 009] proposed a conceptual model in order to explain the migration of solutes in variably saturated, dual-porosity, dual-permeability chalk. Here, mathematical and numerical modelling of tracer and contaminant migration in variably saturated fissured chalk is presented, considering the aforementioned conceptual model. A new mathematical formulation is proposed to represent the unsaturated properties of the fissured chalk in a more dynamic and appropriate way. At the same time, the rock water content is partitioned between mobile and immobile water phases, as a function of the water saturation of the chalk rock. The groundwater flow and contaminant transport in the variably saturated chalk is solved using the control volume finite element method. Modelling the field tracer experiments performed in the variably saturated chalk shows the adequacy and usefulness of the new conceptual, mathematical and numerical model. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 61 (14 ULg)
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See detailModelling the Neritosphere
Djenidi, Salim ULg; Nihoul, Jacques ULg

in Sanchez-Arcilla, A.; Pastor, M.; Zienkiewicz, O. C. (Eds.) et al Proceedings of the 2nd International Conference on Computer Modelling in Ocean Engineering (1991)

Detailed reference viewed: 5 (0 ULg)
See detailModelling the North Sea hydrodynamics in a management perspective
Djenidi, Salim ULg; Delhez, Eric ULg; Martin, Géraldine ULg et al

in Bulletin de la Société Royale des Sciences de Liège (1996), 65

Detailed reference viewed: 10 (5 ULg)
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See detailModelling the Phenomenon of Galloping in Overhead Lines
Lilien, Jean-Louis ULg; Ponthot, Jean-Philippe ULg

in Revue de la Société Royale Belge des Electriciens (1987), 103(12), 5-19

Detailed reference viewed: 38 (8 ULg)
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See detailModelling the plastic anisotropy of metals
Habraken, Anne ULg

in Archives of Computational Methods in Engineering (2004), 11

This work is an overview of available constitutive laws used in finite element codes to model elastoplastic metal anisotropy behaviour at a macroscopic level. It focuses on models with strong links with ... [more ▼]

This work is an overview of available constitutive laws used in finite element codes to model elastoplastic metal anisotropy behaviour at a macroscopic level. It focuses on models with strong links with the phenomena occurring at microscopic level. Starting from macroscopic well-known models such as Hill or Barlat’s laws, the limits of these macroscopic phenomenological yield loci are defined, which helps to understand the current trends to develop micro-macro laws. The characteristics of micro-macro laws, where physical behaviour at the level of grains and crystals are taken into account to provide an average macroscopic answer are described. Some basic knowledge about crystal plasticity models is given for non-specialists, so every one can understand the microscopic models used to reach macroscopic values. The assumptions defining the transition between the microscopic and macroscopic scales are summarized: full constraint or relaxed Taylor’s model, self-consistent approach, homogenisation technique. Then, the two generic families of micromacro models are presented: macroscopic laws without yield locus where computations on discrete set of crystals provide the macroscopic material behaviour and macroscopic laws with macroscopic yield locus defined by microscopic computations. The models proposed by Anand, Dawson, Miehe, Geers, Kalidindi or Nakamachi belong to the first family when proposals by Montheillet, Lequeu, Darrieulat, Arminjon, Van Houtte, Habraken enter the second family. The characteristics of all these models are presented and commented. This paper enhances interests of each model and suggests possible future developments. [less ▲]

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See detailModelling the Position Control of a Segment of the E-ELT using OOFELIE::Multiphysics Integrated FEM-based Approach
Nachtergaele, Philippe; Gamonal Rozas, Leonardo Alfredo ULg; Bruls, Olivier ULg

in Proceedings of the 13th International Conference on New Actuators (2012, June)

This paper presents the extension of a multiphysics software solution allowing to perform integrated simulation of multiphysics controlled systems. This enhancement relies on an innovative formulation of ... [more ▼]

This paper presents the extension of a multiphysics software solution allowing to perform integrated simulation of multiphysics controlled systems. This enhancement relies on an innovative formulation of time integration schemes allowing to take into account simultaneously, in an integrated FEM-based approach, the non linear structural response of a system and the controller dynamics. Interest and feasibility of this unified approach is illustrated through the Modelling of the position control of a segment of the primary mirror of the E-ELT (European Extremely Large Telescope), a highly representative application of complex multiphysics controlled systems. [less ▲]

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See detailModelling the primary production interannual variability in the Ligurian Sea due to meteorological conditions with a 1D hydrodynamic/biological model
Lacroix, Geneviève; Nival, Paul; Djenidi, Salim ULg

in EOS : Transactions, American Geophysical Union (1998), 79

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See detailModelling the propagation pathway of street-traffic noise : practical comparison of German guidelines and real-world measurements
Wetzel, Edgar; Nicolas, Jacques ULg; Andre, Philippe ULg et al

in Applied Acoustics (1999), 57(2), 97-107

In Germany, several guidelines were developed to model the noise propagation pathway. The study compares the guidelines DIN 18005, RLS-90 and VDI 2714, all of which provide some kind of sound object line ... [more ▼]

In Germany, several guidelines were developed to model the noise propagation pathway. The study compares the guidelines DIN 18005, RLS-90 and VDI 2714, all of which provide some kind of sound object line source suited to model street traffic noise. Differences between those guidelines are explained, and their effect on practical calculations is shown in a real-world situation, National Road N4, in Arlon, Belgium. Calculated results are compared to measurements made on critical points along the road. The paper emphasises the understanding of the inner workings of models. In order to avoid differences in calculated results due to software design methods applied, all calculations are made using one single commercially available simulation program. Additionally, this allows for a test of guideline sensitivity to changes in input parameters. [less ▲]

Detailed reference viewed: 56 (3 ULg)
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See detailModelling the pumping scheme associated with an impervious wall to avoid the groundwater pollution from a landfill
Dassargues, Alain ULg

in Computer Techniques in Environmental Studies IV, ENVIROSOFT 92, Southampton (1992)

Detailed reference viewed: 10 (3 ULg)
See detailModelling the risk of ecosystem disruption in Europe with a dynamic vegetation model
Dury, Marie ULg

Conference (2012, June)

With unprecedented speed and extent, the projected climate change might lead to a disruption of terrestrial plants functioning in many regions. In the framework of the EcoChange project, the process-based ... [more ▼]

With unprecedented speed and extent, the projected climate change might lead to a disruption of terrestrial plants functioning in many regions. In the framework of the EcoChange project, the process-based dynamic vegetation model, CARAIB DVM (Dury et al., 2011, iForest 4, 82-99) was used to assess the transient vegetation response to climate change and identify threatened regions across Europe. The vegetation model was driven over 1951-2100 by the outputs of 4 climate models under different SRES scenarios: the ARPEGE/Climate model and 3 regional climate models from the European Union project ENSEMBLES. European vegetation was studied at the Bioclimatic Affinity groups scale as well as the species scale. The ability of the climate models to reproduce the present-day climate was evaluated comparing the interannual climate variability simulated by the models with the observed climate variability over 1961-1990 (CRU TS 3.0 dataset). Under the combined effects of projected changes particularly in temperature and precipitations, CARAIB simulates important reductions in the annual soil water content which have large impacts notably on net primary productivity and fire risk in the Mediterranean region but also in other parts of Europe. With this background, the species and biome distributions are projected to be strongly modified. Finally a quantitative index combining some CARAIB outputs evaluates the risk of ecosystem disruption in Europe. [less ▲]

Detailed reference viewed: 14 (1 ULg)
See detailModelling the risk of ecosystem disruption in Europe with a dynamic vegetation model
Dury, Marie ULg; Hambuckers, Alain ULg; Warnant, Pierre et al

Conference (2012, April)

What will be the European ecosystem responses to future climate? With unprecedented speed and extent, the projected climate change might lead to a disruption of terrestrial plants functioning in many ... [more ▼]

What will be the European ecosystem responses to future climate? With unprecedented speed and extent, the projected climate change might lead to a disruption of terrestrial plants functioning in many regions. In the framework of the EcoChange project, transient projections over the 1901-2100 period have been performed with a process-based dynamic vegetation model, CARAIB DVM (Dury et al., 2011, iForest 4: 82, 99). The vegetation model was driven by the outputs of four climate models under the SRES A1B scenario: the ARPEGE/Climate model and three regional climate models (KNMI-RACMO2 , DMI-HIRHAM5 and HC-HadRM3Q0 RCMs) from the European Union project ENSEMBLES. DVMs are appropriate tools to apprehend potential climate change impacts on ecosystems and identify threatened regions over Europe. CARAIB outputs (soil moisture, runoff, net primary productivity, fire, etc.) were used to characterize the ecosystem evolution. To assess consequences on biodiversity, the evolution of 100 natural common European species (47 herbs, 12 shrubs and 41 trees) has been studied year-to-year over the 1901-2100 period. Under the combined effects of projected changes particularly in temperature and precipitations, CARAIB simulates important reductions in the annual soil water content. The species productivities vary strongly from year to year reaching during the driest years values much lower than present-day average productivity. According to CARAIB, a lot of species might go beyond their water tolerance very frequently, particularly after 2050, due to more intense summer droughts. In the northern part of Europe and in the Alps, with reduced temperature variability and positive soil water anomalies, NPP variability tends to decrease. Regions with more severe droughts might also be affected by an increase of the frequency and intensity of wildfires. With this background, the species distributions might be strongly modified. 15% of tree species and 30% of herb and shrub species (respectively 30% and 60% if the CO2 fertilization effect on species is not taken into account) might experience a loss of 30% or more of their current distribution. Proportions of new species appearance at the end of the century were also studied. Southern Europe might suffer important species extinction while the more suitable climate conditions in northern Europe might lead to a gain in species diversity. [less ▲]

Detailed reference viewed: 31 (11 ULg)
See detailModelling the sediment transport in a Belgian coastal area
Djenidi, Salim ULg

in Vreughdenil, C. B. (Ed.) Mathematical modelling of sediment transport and morphology (Euromech 177 Colloquium) (1984)

Detailed reference viewed: 10 (5 ULg)
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See detailModelling the short-term and long-term aggregate response of multiple loads fed through a sub-transmission network
Van Cutsem, Thierry ULg; Renoy, Quentin; Lefebvre, Daniel

(2006, November)

This paper addresses the problem of representing the aggregate response to voltage changes of a set of loads fed through distribution transformers connected by a subtransmission network. A simple, while ... [more ▼]

This paper addresses the problem of representing the aggregate response to voltage changes of a set of loads fed through distribution transformers connected by a subtransmission network. A simple, while accurate equivalent is proposed. The latter involves standard network components and includes a single internal bus. This equivalent matches both the short-term and the long-term response of the original system, the long-term dynamics coming from the load tap changers that control the distribution voltages. A procedure to identify its parameters from step responses of the unreduced system is detailed. The method is illustrated and validated on a large subtransmission-distribution system of Hydro-Québec. [less ▲]

Detailed reference viewed: 47 (2 ULg)
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See detailModelling the sound transmission through separation walls using a diffusion model
Billon, Alexis ULg; Foy, Cédric; Valeau, Vincent et al

Conference (2007, September)

The diffusion model has been used successfully to evaluate the acoustic behaviour of a system of coupled rooms connected through a coupling aperture. In this paper, an extension of this model is proposed ... [more ▼]

The diffusion model has been used successfully to evaluate the acoustic behaviour of a system of coupled rooms connected through a coupling aperture. In this paper, an extension of this model is proposed to deal with the propagation of sound energy through a partition wall. The diffusion model can be considered as an extension of the statistical theory to none diffuse sound fields. Numerical comparisons with the statistical theory are then carried out. The following parameters are varied: its transmission loss of the separation wall, its surface, the coupled room’s absorption coefficient and the coupled room’s volume. The agreement between the statistical theory and the diffusion model is very good. [less ▲]

Detailed reference viewed: 27 (1 ULg)