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See detailModelling the excavation damaged zone in Callovo-Oxfordian claystone with strain localization
Pardoen, Benoît ULg; Collin, Frédéric ULg; Levasseur, Séverine ULg et al

Conference (2012, October)

Gallery excavation in clayey rocks induces stress perturbations that trigger damage propagation. The excavation process creates then the so-called excavation damaged zone in which properties are modified ... [more ▼]

Gallery excavation in clayey rocks induces stress perturbations that trigger damage propagation. The excavation process creates then the so-called excavation damaged zone in which properties are modified. The prediction of the extension and especially of the fracturing structure in this zone remains a crucial issue in the context of underground storage. Since strain localization in shear band mode is frequently observed in experimental works, the excavation damaged zone can be modeled by considering the development of strain localization bands. A hydro-mechanical modelling of a gallery excavation is performed. The numerical results exhibit an excavation damaged zone extension similar to the in situ measurements and provides information about the rock state within this zone. [less ▲]

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See detailModelling the excavation damaged zone in claystone with strain localisation using coupled second gradient model and the influence of gallery ventilation
Pardoen, Benoît ULg; Levasseur, Séverine ULg; Collin, Frédéric ULg

Conference (2013, July 09)

Drilling of galleries induces stress perturbations that trigger damage propagation in the surrounding medium. The excavation process creates then the so-called excavation damaged zone around the galleries ... [more ▼]

Drilling of galleries induces stress perturbations that trigger damage propagation in the surrounding medium. The excavation process creates then the so-called excavation damaged zone around the galleries. The prediction of the extension and of the fracture structure within this zone remains nowadays a major issue especially in the context of underground storage. Since localised deformation in shear band mode is frequently observed in experimental works, the excavation damaged zone can be modelled by considering the development of shear strain localisation bands. To correctly model this behaviour, an enhanced model with a regularisation method is required. In underground structures, air ventilation inside the galleries induces a rock-atmosphere interaction that may lead to drainage and to rock desaturation close to the gallery wall. Such desaturation may influence the damage zone structure and needs to be studied. A hydro-mechanical modelling of a gallery excavation including air ventilation is thus performed and the numerical results provide information about the damaged zone extension, the strain localisation bands pattern and the influence of rock desaturation. [less ▲]

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See detailModelling the fracture generation in EDZ
Charlier, Robert ULg; Chambon, René; Al-Holo, Sama et al

in Report of the Swiss Geological Survey (2007), 2

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See detailModelling the Fringing of the FORS2 CCD
Walsh, J. R.; Kuntschner, H.; Jehin, Emmanuel ULg et al

in Kaufer, A. (Ed.) The 2007 ESO Instrument Calibration Workshop (2008)

Thinned CCD detectors display fringing which arises from the interference of multiply reflected light in the layers of the CCD. If the layer construction - the thicknesses and refractive indexes of the ... [more ▼]

Thinned CCD detectors display fringing which arises from the interference of multiply reflected light in the layers of the CCD. If the layer construction - the thicknesses and refractive indexes of the layers - is known, then the observed fringing can be accurately modelled and used to correct imaging and spectroscopic data for its effects. In practice the specifications on the actual deposited layer thicknesses may not be known to sufficient accuracy to predict the fringe behaviour. Thus calibration data, in the form of monochromatic flat fields, is required and can be modelled using the technique outlined by Malamuth et al. 2003, which has been applied to ACS CCDs. [less ▲]

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See detailModelling the general circulation of shelf seas by 3Dk-ε models
Nihoul, Jacques ULg; Deleersnijder, Eric; Djenidi, Salim ULg

in Earth-Science Reviews (1989), 26(1-3), 163-189

One examines the modifications which must be made-and the limitations which must be set-to classicalk-ε models to extend their application to the simulation of marine mesoscale, synopticscale and ... [more ▼]

One examines the modifications which must be made-and the limitations which must be set-to classicalk-ε models to extend their application to the simulation of marine mesoscale, synopticscale and macroscale processes which compose the weather-like and general circulations of the sea. The case of the general circulation—for which sub-grid scale fluctuations include such semi-organized motions as tides and storm surges-is discussed in more detail. A 3Dk-ε model appropriate to the study of the general circulation in a shallow stratified sea is presented and illustrated with the results of a simulation of the general summer circulation in the Northern Bering Sea, made in the scope of the NSF ISHTAR (“Inner Shelf Transfer and Recycling”) Program. [less ▲]

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See detailModelling the Gibraltar Strait/Western Alboran Sea ecohydrodynamics
Skliris, Nikolaos; Beckers, Jean-Marie ULg

in Ocean Dynamics (2009), 59(3), 489-508

The ecohydrodynamics of the Gibraltar Strait and the Western Alboran Sea is investigated using a 3-D, two-way nested, coupled hydrodynamic/plankton ecosystem model, exploiting the MEDATLAS climatological ... [more ▼]

The ecohydrodynamics of the Gibraltar Strait and the Western Alboran Sea is investigated using a 3-D, two-way nested, coupled hydrodynamic/plankton ecosystem model, exploiting the MEDATLAS climatological database. A high-resolution model (~1 km) of the Gibraltar/Western Alboran region embedded within a coarse-resolution model of the West Mediterranean (~5 km) is implemented. The model seasonal climatology of the 3-D circulation and the flow characteristics at the Gibraltar Strait and the Alboran Sea are discussed, and their impact on the plankton ecosystem evolution is explored. An important ecohydrodynamic feature produced by the model is a permanent upwelling zone in the northwestern part of the Alboran Sea in agreement with observations. Model results show that both horizontal and vertical current intensity of the Atlantic Jet increases progressively at the strait to obtain maximum values in the northeastern Mediterranean entrance, inducing an upward displacement of the nitracline. The nutrient-rich water transport through the strait along with the generation of cyclonic vorticity in the northwestern Alboran Sea result in the accumulation of nutrients there and thus induce a permanent fertilisation of this area. [less ▲]

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See detailModelling the glacial-interglacial changes in the continental biosphere
François, Louis ULg; Delire, Christine; Warnant, Pierre ULg et al

in Global and Planetary Change (1998), 17

A new estimate of the glacial-interglacial variations of the terrestrial carbon storage was obtained with the CARAIB biosphere model. The climatic data for the Last Glacial Maximum (LGM) necessary to ... [more ▼]

A new estimate of the glacial-interglacial variations of the terrestrial carbon storage was obtained with the CARAIB biosphere model. The climatic data for the Last Glacial Maximum (LGM) necessary to drive the biosphere model are derived from results of the ECHAM2 General Circulation Model (GCM). Six model simulations (four under typical interglacial and two under typical glacial climatic conditions) were performed to analyse the roles of different environmental changes influencing the biospheric net primary productivity (NPP) and carbon stocks. The main differences between these simulations come from the adopted CO, levels in the atmosphere, the presence or absence of crops and from changing continental boundaries. The variation of the terrestrial carbon stocks since the LGM are estimated by comparing the pre-agricultural (280 ppm of CO2, no crops, modern climate) and the full glacial simulations (200 ppm of CO2, LGM climate reconstruction). Our model predicts a global NPP increase from 38 Gt C year(-1) to 53 Gt C year(-1) during the deglaciation, a substantial part of that change being due to CO, fertilization. At the same time, the terrestrial biosphere would have fixed between 134 (neglecting CO2 fertilization effects) and 606 Gt C. The treatment of both the C-3 and C-4 photosynthetic pathways in the CARAIB model enabled us further to reconstruct the partitioning between C, and C, plants. Following our experiments, 29.7% of the total biospheric carbon stock at the LGM was C-4 material, compared to an interglacial fraction of only 19.8%. The average biospheric fractionation factor was similar to 1.5 parts per thousand less negative at LGM than it is today. Considering an atmospheric delta(13)C 0.5 +/- 0.2 parts per thousand lower at LGM than at pre-industrial times, the 606 Gt C transfer would lead to a global ocean delta(13)C shift of roughly -0.41 parts per thousand, fully consistent with currently available data. For the smaller change of 134 Gt C obtained without the CO2 fertilization effect, this shift would only be on the order of -0.10 parts per thousand. (C) 1998 Elsevier Science B,V. All rights reserved. [less ▲]

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See detailModelling the Global Riverine U Fluxes to the Oceans
Riotte, Jean; Goddéris, Yves; Chabaux, François et al

Conference (2005, May 21)

Mean U isotopic ratio of the ocean has remained roughly constant since about 600 kyrs (Henderson, 2001). This 1.14 value cannot be explained considering the present day value of the U riverine ratio (1.17 ... [more ▼]

Mean U isotopic ratio of the ocean has remained roughly constant since about 600 kyrs (Henderson, 2001). This 1.14 value cannot be explained considering the present day value of the U riverine ratio (1.17, Chabaux et al., 2001). However, the mean riverine ratio was calculated on half of the total continental runoff. Is this partial mean value really representative of the mean value? If yes, might this value have changed over a glacial-interglacial cycle ? We build up a numerical model calculating the flux of U transfer to the ocean through weathering. The spatial resolution of the model reaches 0.5°lat x0.5°long. Lithology is modified from Amiotte-Suchet et al. (2003). Weathering fluxes are estimated from simple parametric laws, calculating the flux of total dissolved solids from mean annual temperature and runoff. Soil PCO2 is used to estimate carbonate dissolution rates, and is calculated from a simulation of the Caraib model. Uranium fluxes are estimated proportional to the TDS flux, weighted by its abundance in the source rock. CO2 consumption through weathering is simultaneously computed. The 234U/238U ratio of the river is calculated according to a correlation existing between the measured 234U/238U and runoff, showing a decrease of this ratio with increasing runoff. The model is first validated over several large watersheds, including the Amazon, the Ganges-Brahmapoutra, the Mississippi, and the Congo rivers. Global runs are then performed, showing that the modelled mean global value is close to the measured partial mean of 1.17. We explore then possible variations of the modelled ratio at the last glacial maximum. Temperature and runoff fields are taken from LGM simulations of the ECHAM GCM. Extension of ice sheets is assumed to cut off part of the weathering fluxes, producing possible fluctuations in the riverine U isotopic ratio, as well as changes in the regional runoff pattern. [less ▲]

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See detailModelling the habitat suitability of cetaceans:Example of the sperm whale in the northwestern Mediterranean Sea
Praca, Emilie; Gannier, Alexandre; Das, Krishna ULg et al

in Deep-Sea Research Part I, Oceanographic Research Papers (2009), (56), 648657

Cetaceans are mobile and spend long periods underwater. Because of this, modelling their habitat could be subject to a serious problem of false absence. Furthermore, extensive surveys at sea are time and ... [more ▼]

Cetaceans are mobile and spend long periods underwater. Because of this, modelling their habitat could be subject to a serious problem of false absence. Furthermore, extensive surveys at sea are time and money consuming, and presence–absence data are difficult to apply. This study compares the ability of two presence–absence and two presence-only habitat modelling methods and uses the example of the sperm whale (Physeter macrocephalus) in the northwestern Mediterranean Sea. The data consist of summer visual and acoustical detections of sperm whales, compiled between 1998 and 2005. Habitat maps were computed using topographical and hydrological eco-geographical variables. Four methods were compared: principal component analysis (PCA), ecological niche factor analysis (ENFA), generalized linear model (GLM) and multivariate adaptive regression splines (MARS). The evaluation of the models was achieved by calculating the receiver operating characteristic (ROC) of the models and their respective area under the curve (AUC). Presence–absence methods (GLM, AUC=0.70, and MARS, AUC=0.79) presented better AUC than presence-only methods (PCA, AUC=0.58, and ENFA, AUC=0.66), but this difference was not statistically significant, except between the MARS and the PCA models. The four models showed an influence of both topographical and hydrological factors, but the resulting habitat suitability maps differed. The core habitat on the continental slope was well highlighted by the four models, while GLM and MARS maps also showed a suitable habitat in the offshore waters. Presence–absence methods are therefore recommended for modelling the habitat suitability of cetaceans, as they seem more accurate to highlight complex habitat. However, the use of presence-only techniques, in particular ENFA, could be very useful for a first model of the habitat range or when important surveys at sea are not possible. [less ▲]

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See detailModelling the Holocene migrational dynamics of Fagus sylvatica L. and Picea abies (L.) H. Karst
Lehsten, Lehsten; Dullinger, Stefan; Hülber, Karl et al

in Global Ecology and Biogeography (2014)

Aim: Vegetation dynamics and the competitive interactions involved are assumed to restrict the ability of species to migrate. But in most migration modelling approaches disturbance-driven succession and ... [more ▼]

Aim: Vegetation dynamics and the competitive interactions involved are assumed to restrict the ability of species to migrate. But in most migration modelling approaches disturbance-driven succession and competition processes are reduced to simple assumptions or are even missing. The aim of this study was to test a combination of a migration model and a dynamic vegetation model to estimate the migration of tree species controlled by climate, environment and local species dynamics such as succession and competition. Location: Europe. Methods: To estimate the effect of vegetation dynamics on the migration of European beech and Norway spruce, we developed a post-process migration tool (LPJ-CATS). This tool integrates outputs of the migration model CATS and the dynamic vegetation model LPJ-GUESS. The model LPJ-CATS relies on a linear dependency between the dispersal kernel and migration rate and is based on the assumption that competition reduces fecundity. Results: Simulating potential migration rates with the CATS model, which does not account for competition and disturbance, resulted in mean Holocene migra- tion rates of 435 ± 55 and 330 ± 95 m year−1 for the two species Picea abies and Fagus sylvatica, respectively. With LPJ-CATS, these mean migration rates were reduced to 250 ± 75 and 170 ± 60 m year−1 for spruce and beech, respectively. Moreover, LPJ-CATS simulated migration pathways of these two species that gen- erally comply well with those documented in the palaeo-records. Main conclusions: Our ‘hybrid’ modelling approach allowed for the simulation of generally realistic Holocene migration rates and pathways of the two study species on a continental scale. It suggests that competition can considerably modify spread rates, but also the magnitude of its effect depends on how close climate conditions are to the niche requirements of a particular species. [less ▲]

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See detailModelling the huge, Herschel-resolved debris ring around HD 207129
Löhne, T.; Augereau, J.-C.; Ertel, S. et al

in Astronomy and Astrophysics (2012), 537

Debris disks, which are inferred from the observed infrared excess to be ensembles of dust, rocks, and probably planetesimals, are common features of stellar systems. As the mechanisms of their formation ... [more ▼]

Debris disks, which are inferred from the observed infrared excess to be ensembles of dust, rocks, and probably planetesimals, are common features of stellar systems. As the mechanisms of their formation and evolution are linked to those of planetary bodies, they provide valuable information. The few well-resolved debris disks are even more valuable because they can serve as modelling benchmarks and help resolve degeneracies in modelling aspects such as typical grain sizes and distances. Here, we present an analysis of the HD 207129 debris disk, based on its well-covered spectral energy distribution and Herschel/PACS images obtained in the framework of the DUNES (DUst around NEarby Stars) programme. We use an empirical power-law approach to the distribution of dust and we then model the production and removal of dust by means of collisions, direct radiation pressure, and drag forces. The resulting best-fit model contains a total of nearly 10[SUP]-2[/SUP] Earth masses in dust, with typical grain sizes in the planetesimal belt ranging from 4 to 7 μm. We constrain the dynamical excitation to be low, which results in very long collisional lifetimes and a drag that notably fills the inner gap, especially at 70 μm. The radial distribution stretches from well within 100 AU in an unusual, outward-rising slope towards a rather sharp outer edge at about 170-190 AU. The inner edge is therefore smoother than that reported for Fomalhaut, but the contribution from the extended halo of barely bound grains is similarly small. Both slowly self-stirring and planetary perturbations could potentially have formed and shaped this disk. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. [less ▲]

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See detailModelling the hydrodispersive behaviour of variably saturated chalk
Brouyère, Serge ULg

Conference (2003, April 02)

The presentation dscribes the mathematical and numerical modelling of solute tracer experiments in variably saturated chalk

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See detailModelling the hydrogeological environment for disposal of wastes in low permeability sediments
Dassargues, Alain ULg

Scientific conference (1996, November 07)

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See detailModelling the hydrological response of an urban watershed Diachronic analysis of the effects of land use changes on storm runoff generation in the Upper Bukit Timah basin, Singapore
Cesar, Emilie ULg

Master's dissertation (2011)

This work consisted in the modelling of the rainfall-runoff relationships in the Upper Bukit Timah catchment in Singapore, in order to highlight the impacts of urbanisation on hydrology. The SWMM model, a ... [more ▼]

This work consisted in the modelling of the rainfall-runoff relationships in the Upper Bukit Timah catchment in Singapore, in order to highlight the impacts of urbanisation on hydrology. The SWMM model, a one-dimensional physically based model especially developed for urban areas, was mainly used. The parameters encoded into the model were determined by different means and several methods were used for their determination in order to assess their influence on the modelling.Using the final adjustment of the SWMM model, a diachronic analysis was performed in order to present the effects of urbanisation on runoff. [less ▲]

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See detailModelling the impact of benthic filter-feeders on the composition and biomass of river plankton
Descy, Jean-Pierre; Everbecq, Etienne ULg; Gosselain, Véronique ULg et al

in Freshwater Biology (2003), 48(3), 404-417

1. The POTAMON model [Everbecq E. et al. (2001) Water Research, 35, 901] has been used to simulate the effect of benthic bivalves (mainly Dreissena polymorpha ) on the phytoplankton and zooplankton in a ... [more ▼]

1. The POTAMON model [Everbecq E. et al. (2001) Water Research, 35, 901] has been used to simulate the effect of benthic bivalves (mainly Dreissena polymorpha ) on the phytoplankton and zooplankton in a lowland Western European river (the Moselle). Here we use a modified version of the POTAMON model with five categories of phytoplankton (Stephanodiscus, Cyclotella -like, large diatoms, Skeletonema and non-siliceous algae) to model filter-feeding effects of benthic bivalves in the Moselle. Zooplankton has been represented in the model by two categories, Brachionus -like and Keratella -like rotifers. 2. According to density estimates from field surveys (Bachmann V. et al. (1995) Hydroecologie Appliquee, 7, 185, Bachmann V. & Usseglio-Polatera P. (1999) Hydrobiologia, 410, 39), zebra mussel density varied among river stretches, and increased through the year to a maximum in summer. Dreissena filtration rates from the literature were used, and mussels have been assumed to feed on different phytoplankton categories (but less on large and filamentous diatoms) as well as on rotifers. 3. The simulations suggest a significant impact of benthic filter-feeders on potamoplankton and water quality in those stretches where the mussels are abundant, their impact being maximal in summer. Consequently, different plankton groups were not affected to the same extent, depending on their period of development and on indirect effects, such as predation by mussels on herbivorous zooplankton. 4. A daily carbon balance for a typical summer shows the effect of benthic filter-feeders on planktonic and benthic processes: the flux of organic matter to the bottom is greatly enhanced at high mussel density; conversely, production and breakdown of organic carbon in the water column are reduced. Mussel removal would drive the carbon balance of the river toward autotrophy only in the downstream stretches. [less ▲]

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See detailModelling the impact of wind turbines on the visual attractivity of landscapes at a regional scale
Van Rompaey, A.; Vanderheyden, V.; Schmitz, Serge ULg

in European Wind Energy Conference & Exhibition : Brussels Expo 31 March-3 April 2008 (2008)

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See detailModelling the influence of activation-induced apoptosis of CD4+ and CD8+ T-cells on the immune system response of a HIV-infected patient
Stan, Guy-Bart; Belmudes, Florence ULg; Fonteneau, Raphaël ULg et al

in IET Systems Biology (2008), 2(2), 94-102

On the basis of the human immunodeficiency virus (HIV) infection dynamics model proposed by Adams, the authors propose an extended model that aims at incorporating the influence of activation-induced ... [more ▼]

On the basis of the human immunodeficiency virus (HIV) infection dynamics model proposed by Adams, the authors propose an extended model that aims at incorporating the influence of activation-induced apoptosis of CD4+ and CD8+ T-cells on the immune system response of HIV-infected patients. Through this model, the authors study the influence of this phenomenon on the time evolution of specific cell populations such as plasma concentrations of HIV copies, or blood concentrations of CD4+ and CD8+ T-cells. In particular, this study shows that depending on its intensity, the apoptosis phenomenon can either favour or mitigate the long-term evolution of the HIV infection. [less ▲]

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See detailModelling the Influence of Climate on Black Grouse Population Dynamics in Lüneburger Heide (North Germany)
Loneux, Michèle ULg; Lütkepohl, Manfred; Wübbenhorst, Jann et al

in PLUMMER, Ron (Ed.) European Conference Black Grouse Endangered species (2005, December)

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See detailModelling the injection of a tracer in a well: a new mathematical and numerical approach.
Brouyère, Serge ULg

in Dassargues, Alain (Ed.) Tracers and Modelling in Hydrogeology (2000)

A new mathematical approach is proposed to model the injection of a tracer in a well for field tracer tests. It is based on the water and tracer mass budget integrated over the injection well, for the ... [more ▼]

A new mathematical approach is proposed to model the injection of a tracer in a well for field tracer tests. It is based on the water and tracer mass budget integrated over the injection well, for the different injection steps (tracer injection, water flush and tracer behaviour after the injection). This physical approach deals with well-bore mixing and dilution effects, local distortion of the flow field around the injection well, back-diffusion of the tracer in the injection well after the injection, and tracer capture in the well bore. A numerical solution (finite differences over time) is proposed and implemented in a three-dimensional finite element flow and transport simulator (SUFT3D). A radially converging tracer test is computed to illustrate the adequacy and usefulness of this new mathematical concept to model field results. [less ▲]

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