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See detailNumerical modeling of relativistic shock acceleration
Meli, Athina ULg

in Astrophysics & Space Sciences Transactions : ASTRA (2011)

The shock acceleration mechanism is invoked to explain non-thermal cosmic rays in Supernova Remnants, Active Galactic Nuclei and Gamma Ray Bursts jets. Especially, the importance of relativistic shock ... [more ▼]

The shock acceleration mechanism is invoked to explain non-thermal cosmic rays in Supernova Remnants, Active Galactic Nuclei and Gamma Ray Bursts jets. Especially, the importance of relativistic shock acceleration in extragalactic sources is a recurring theme raising a significant interest in the research community. We will briefly discuss the shock acceleration mechanism and we will address the properties of non-relativistic and relativistic shocks, particularly focusing on relativistic numerical Monte Carlo studies. [less ▲]

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See detailNumerical Modeling of Representative Cells of Ti-5553 Using Periodic Homogenization Technique
Gerday, Anne-Françoise ULg; Ben Bettaieb, Mohamed ULg; Pascon, Frédéric ULg et al

in Oñate, E.; Owen, D. R. J. (Eds.) Computational plasticity X. Fundamentals and applications (2009, September)

This article focuses on the modeling of representative cells of Ti-5553 using the periodic homogenization theory and a microscopic constitutive law.

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See detailNumerical modeling of the cardiac mechano-electric feedback within a thermo-electro-mechanical framework. Study of its consequences on arrhythmogenesis.
Collet, Arnaud ULg

Doctoral thesis (2015)

This doctoral study characterizes, for simple geometries, the cardiac autonomous electrical activity induced by the mechanical deformations of the myocardium via the mechano-electric feedback within a ... [more ▼]

This doctoral study characterizes, for simple geometries, the cardiac autonomous electrical activity induced by the mechanical deformations of the myocardium via the mechano-electric feedback within a thermo-electro-mechanical framework. The underlying fundamental mechanisms are highlighted and discussed in detail. In a healthy heart, the mechano-electric feedback acts as a regulator able to damp mechanical perturbations undergone by the heart, by appropriately modulating electrical activity shortly after these perturbations. In this way, a new healthy electromechanical situation is recovered. However, under certain conditions, this feedback can be a generator of dramatic cardiac arrhythmias by inducing local electrical depolarizations resulting from abnormal cardiac muscle tissue deformations. These local perturbations can then propagate in the whole heart and, thus, lead to global cardiac dysfunctions. The one- and two-dimensional models developed in this work to study the arrhythmogenic consequences of the mechano-electric feedback within a thermo-electro-mechanical framework account for three couplings: the excitation-contraction coupling, the mechano-electric feedback, and the thermo-electric coupling. The excitation-contraction coupling allows the mechanical contraction of cardiac muscle cells resulting from the electrical excitation of these cells, triggered by a propagating action potential initially generated by the sino-atrial node in a healthy heart. The mechano-electric feedback takes into account the influence of mechanical deformations on the electrical activity, both at the cell and the macroscopic level. The thermo-electric coupling then modulates certain electrical properties due to a temperature change. The excitation-contraction coupling is modeled in a phenomenological way by combining the Aliev-Panfilov model and the Rogers-McCulloch model. The propagation of the electrical excitation through cardiac muscle tissue is modeled by using the monodomain approach. The mechano-electric feedback is taken into account by considering two different contributions, namely the physiological contribution (physiological feedback) and the geometric contribution (geometric feedback). The physiological feedback consists in the onset of stretch-activated currents due to the deformations of the cardiac muscle tissue via specific mechanosensitive channels. Regarding the geometric feedback, it simply reflects that the propagation of the depolarization waves is altered by the deformations of the geometry. The thermo-electric coupling is modeled via a dependence with respect to the temperature which is exponential for the gating kinetics of ion channels, exponential for the kinetics of the active tension development in cardiomyocytes, and linear for the ionic conductances. This study shows that the mechano-electric feedback can be arrhythmogenic under specific conditions. In particular, this work clearly reveals that the size of the domain and the importance of stretch-activated currents are key factors in the behavior of the autonomous electrical activity induced by the mechano-electric feedback. This doctoral study also shows that temperature variations such as those undergone by the heart during therapeutic hypothermia or hyperthermia play a central role in the cardiac electromechanical behavior. Moreover, this work emphasizes the influence of the initial conditions on the electromechanical behavior of cardiac tissue. In the one-dimensional framework, an important result of this work is that the disappearance of the autonomous electrical activity induced by the deformations of the cardiac muscle can be associated with different types of bifurcation phenomena, depending on the values of the parameters. These bifurcations, which correspond in fact to different ways for the AEA to vanish, are emphasized and discussed in detail. [less ▲]

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See detailNumerical modeling of the deep Black Sea ecosystem functioning during the late 80’s (eutrophication phase)
Grégoire, Marilaure ULg; Raick, Caroline ULg; Soetaert, Karline

in Progress in Oceanography (2008), 76(9), 286-333

A one-dimensional coupled physical–biogeochemical model has been developed to simulate the ecosystem of the central Black Sea at the end of the 1980s when eutrophication and invasion by gelatinous ... [more ▼]

A one-dimensional coupled physical–biogeochemical model has been developed to simulate the ecosystem of the central Black Sea at the end of the 1980s when eutrophication and invasion by gelatinous organisms seriously affected the stability and dynamics of the system. The physical model is the General Ocean Turbulence Model (GOTM) and the biogeochemical model describes the foodweb from bacteria to gelatinous carnivores through 24 state variables including three groups of phytoplankton: diatoms, small phototrophic flagellates and dinoflagellates, two zooplankton groups: micro- and mesozooplankton, two groups of gelatinous zooplankton: the omnivorous and carnivorous forms, an explicit representation of the bacterial loop: bacteria, labile and semi-labile dissolved organic matter, particulate organic matter. The model simulates oxygen, nitrogen, silicate and carbon cycling. In addition, an innovation of this model is that it explicitly represents processes in the anoxic layer. Biogeochemical processes in anaerobic conditions have been represented using an approach similar to that used in the modeling of diagenetic processes in the sediments lumping together all the reduced substances in one state variable [Soetaert, K., Herman, P., 1996. A model of early diagenetic processes from the shelf to abyssal depths. Geochimica et Cosmochimica Acta 60 (6) 1019–1040]. In this way, processes in the upper oxygenated layer are fully coupled with anaerobic processes in the deep waters, allowing to perform longterm simulations. The mathematical modeling of phytoplankton and zooplankton dynamics, detritus and the microbial loop is based on the model developed by Van den Meersche et al. [Van den Meersche, K., Middelburg, J., Soetaert, K., van Rijswijk P.H.B., Heip, C., 2004. Carbon–nitrogen coupling and algal–bacterial interactions during an experimental bloom: Modeling a 13c tracer experiment. Limnology and Oceanography 49 (3), 862–878] and tested in the modeling of mesocosm experiments and of the Ligurian sea ecosystem [Raick, C., Delhez, E., Soetaert, K., Gregoire, M., 2005. Study of the seasonal cycle of the biogeochemical processes in the Ligurian sea using an 1D interdisciplinary model. Journal of Marine Systems 55 (3–4) 177–203]. This model has been extended to simulate the development of top predators, the aggregation of detritus as well as the degradation and chemical processes in suboxic/anoxic conditions (e.g. denitrification, anoxic remineralization, redox reactions). The coupled model extends down to the sediments (’2000 m depth) and is forced at the air–sea interface by the 6 hourly ERA-40 reanalysis of ECMWF data. The model has been calibrated and validated using a large set of data available in the Black Sea TU Ocean Base. The biogeochemical model involves some hundred parameters which are first calibrated by hand using published values. Then, an identifiability analysis has been performed in order to determine a subset of identifiable parameters (i.e. ensemble of parameters that can be together estimated from the amount of data we have at our disposal, see later in the text). Also a subset of 10 identifiable parameters was isolated and an automatic calibration subroutine (Levenberg Marquart) has been used to fine tune these parameters. Additionally, in order to assess the sensitivity of model results to the parameterization of the two gelatinous groups, Monte Carlo simulations were performed perturbing all the parameters governing their dynamics. In order to calibrate the particle dynamics and export, the chemical model was run off-line with the particle and microbial loop model in order to check its capacity of simulating anoxic waters. After a 104 year run, the model simulated NH4 and H2S profiles similar to observations but steady state was not reached suggesting that the Black Sea deep waters are not at steady state. The fully coupled model was then used to simulate the period 1988–1992 of the Black Sea ecosystem. The model solution exhibits a complex dynamics with several years of transient adjustment. This complexity is imparted by the explicit modeling of top predators. The integrated chlorophyll and phytoplankton biomasses, the maximum concentration and depth of maximum, mesozooplankton biomass, depth of oxycline, primary production, bacterial production, surface concentrations of nutrients and plankton simulated by the model and obtained from available data analysis were compared and showed a satisfactory agreement. Also, as in the data, the model shows a continuous development of phytoplankton throughout the year, with an intense spring bloom dominated by diatoms and a fall bloom dominated by dinoflagellates. Dinoflagellates dominate from summer until late fall while small phototrophic flagellates are never dominant in terms of biomass, but are present almost throughout the year except in winter. The model simulates an intense silicate removal associated to increased diatoms blooms which were promoted by increased nutrient conditions, and by the presence of gelatinous zooplankton. This silicate pumping leads to silicate limitation of diatoms development in summer allowing the development of dinoflagellates. [less ▲]

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See detailNumerical modeling of the hydro-mechanical behaviour of a large slope movement: the Triesenberg landslide
François, Bertrand ULg; Bonnard, Christophe; Laloui, Lyesse et al

in Zimmermann, T.; Truty, A. (Eds.) Numerics in geotechnics and structures (2006)

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See detailNumerical modeling of the long term behavior of Municipal Solid Waste in a landfill
Hubert, Julien ULg; Collin, Frédéric ULg

Scientific conference (2015, January 30)

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See detailNumerical Modeling of Tribological Devices Using Various Contact Algorithms
CHABRAND, P.; DUBOIS, F.; GRAILLET, D. et al

in Proceedings of “NUMIFORM’98, Simulation of Materials Processing: Theory, Methods and Applications (1998, June)

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See detailNumerical Modelisation of Contact with friction phenomena by the FEM
Charlier, Robert ULg

in Proc. of the Euromech Colloquium 248: Non Linear Soil-Structure Interaction (1989, April)

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See detailNumerical Modelisation of Contact with Friction Phenomena by the Finite Element Method
Charlier, Robert ULg; Habraken, Anne ULg

in Computers & Geotechnics (1990), 9(n°1&2), 59-72

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See detailNumerical modelling and experimental validation of steel deep drawing processes - Part I. Material characterization
Garcia, Claudio; Celentano, Diego; Flores, F. et al

in Journal of Materials Processing Technology (2006), 172(3), 451-460

This work presents an experimental characterization of the mechanical behaviour of the EK4 deep drawing steel. The experimental procedure encompasses spectrometry, rnetalography, tension testing and ... [more ▼]

This work presents an experimental characterization of the mechanical behaviour of the EK4 deep drawing steel. The experimental procedure encompasses spectrometry, rnetalography, tension testing and hardness measurements. Special attention is devoted to the derivation of the elastic and plastic parameters involved in the assumed constitutive model based on the anisotropic Hill-48 yield criterion. The simulation of the deformation process during the whole tensile test is subsequently performed with the aim of assessing the adequateness of the proposed methodology. It should be mentioned that the material parameters obtained with this procedure are the basic data for the modelling and experimental validation of different deep drawing applications presented in Part II of this work. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailNumerical modelling and experimental validation of steel deep drawing processes - Part II. Applications
Garcia, Claudio; Celentano, Diego; Flores, Fernando et al

in Journal of Materials Processing Technology (2006), 172(3), 461-471

This paper presents the modelling and experimental validation of three different deep drawing applications: the Erichsen test, a cylindrical cup test and an industrial sheet metal forming process. The ... [more ▼]

This paper presents the modelling and experimental validation of three different deep drawing applications: the Erichsen test, a cylindrical cup test and an industrial sheet metal forming process. The sheet forrning material considered in the study is the EK4 steel characterized in Part I of this work. A finite element analysis of the deformation process is performed with a large strain hyperelastic shell formulation including the Hill-48 associate plasticity model. The experimental validation of the results provided by the simulation encompasses the punch force evolution together with the in-plane principal deformations and thickness distributions of the final deformed part. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailNumerical modelling and seasonal investigations of the Northwest African Upwelling
Elmoussaoui, Abdellali; Djenidi, Salim ULg; Beckers, Jean-Marie ULg

Conference (2003)

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See detailNumerical modelling and theoretical analysis of geometrically-controlled flow instabilities in rectangular basins
Dewals, Benjamin ULg; Erpicum, Sébastien ULg; Pirotton, Michel ULg

in Proceedings of the 4th International Conference on Advanced Computational Methods in Engineering (2008)

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See detailNumerical modelling in TIMODAZ: developments and achievements
Charlier, Robert ULg; Collin, Frédéric ULg; Levasseur, Séverine ULg

in Post-TIMODAZ International Workshop THM effects in clay host rocks for radioactive waste repositories (2012)

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See detailNumerical modelling of a rock cutting process
Wang, X. C.; Charlier, Robert ULg; Pierry, J.

in Proc. of the 8th Int. Congress on Rock Mechanics (1995, September)

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See detailNumerical modelling of a single storey industrial building at elevated temperature - comparison between the 2D and 3D analyses
de Souza Junior, Valdenir; Creus, G. J.; Franssen, Jean-Marc ULg

in Proceedings of the First South-American Congress on Computational Mechanics (2002)

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See detailNumerical modelling of an in situ ventilation test in Callovo-Oxfordian claystone
Pardoen, Benoît ULg; Talandier, J.; Charlier, Robert ULg et al

Poster (2012, October)

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