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See detailMulti-scale detection of failure in planar masonry thin shells using computational homogenisation
Mercatoris, Benoît ULg; Bouillard, Ph; Massart, T. J.

in Engineering Fracture Mechanics (2009), 76(4), 479-499

This paper presents a computational homogenisation-based technique for localisation detection in planar masonry shells. A computational homogenisation procedure is used for the in-plane and the out-of ... [more ▼]

This paper presents a computational homogenisation-based technique for localisation detection in planar masonry shells. A computational homogenisation procedure is used for the in-plane and the out-of-plane behaviour of masonry walls taking the periodicity of the material into account. The quasi-brittle nature of the masonry constituents results in initial and damage-induced (evolving) anisotropy properties with localisation of damage at both the structural and fine scales. Using a closed-form damage model at the mesoscopic scale, it is shown that a structural scale localisation criterion based on the acoustic tensor adapted to shell kinematics allows to detect the structural scale localisation. This detection identifies average preferential cracking orientations consistent with the stacking mode of masonry for both in-plane and out-of-plane failure. This approach is illustrated by examples of bed joint and stair-case failure, and its subsequent integration in multi-scale nested computational schemes is discussed. © 2008 Elsevier Ltd. All rights reserved. [less ▲]

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See detailMulti-scale effect of landscape processes and habitat quality on newt abundance: Implications for conservation
Denoël, Mathieu ULg; Lehmann, Anthony

in Biological Conservation (2006), 130(4), 495-504

Recent studies in population dynamics suggest that landscape processes and habitat quality act at different scales on population abundances, but very few have modelled their simultaneous effects. However ... [more ▼]

Recent studies in population dynamics suggest that landscape processes and habitat quality act at different scales on population abundances, but very few have modelled their simultaneous effects. However, at a time of large declines in natural populations, it is essential to understand such multivariate components. We tested the hypothesis that natural populations of palmate newts (Triturus helveticus) are affected on three scales: breeding patch (pond), habitat complementation (terrestrial cover), and metapopulation. structure (density of ponds, surrounding populations). We conducted our survey in 130 ponds from southern France (Larzac) and analysed data with generalized additive models (GAM). Two main novel results emerge from these models: (1) the three landscape scales have significant effects on newt abundance, with more newts in deep, vegetated ponds, devoid of fish and surrounded by wooded areas and inhabited ponds; (2) the quality of the surrounding breeding patches is of primary importance in determining the abundance at core sites in a complex way: high abundances are associated positively with high densities of inhabited ponds, but negatively with the number of surrounding ponds. Deforestation, invasive species and abandonment of ponds all have negative impacts on the persistence of palmate newt populations. Future studies should encompass landscapes at different scales and incorporate the habitat quality in surrounding sites to better understand population dynamics and. provide adequate conservation measures. [less ▲]

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See detailA multi-scale flood vulnerability assessment of agricultural production in the context of environmental change: The case of the Sangkae River watershed, Battambang province
Doch, Sotheavin; Diepart, Jean-Christophe ULg; Heng, Chinda

in Diepart, Jean-Christophe (Ed.) Learning for resilience: Insights from Cambodia’s rural communities (2015)

Flooding on Cambodian land use systems is not a new phenomenon but its significance has increased in the context of global environmental changes. This study aims to assess the vulnerability of ... [more ▼]

Flooding on Cambodian land use systems is not a new phenomenon but its significance has increased in the context of global environmental changes. This study aims to assess the vulnerability of agricultural production to floods in the Sangkae River watershed in Battambang province, Northwestern Cambodia. The study was conducted in conjunction with the provincial spatial planning team hosted by the Provincial Department of Land Management and can be viewed as a first step toward a flood management decision-making tool for provincial authorities. The assessments rest on specific dimensions of vulnerability (exposure, sensitivity and adaptive capacity) at different levels in a multi-scale framework: spatial scale (watershed, commune and household); temporal scale (decade, year and season); and institutional scale (national policy, provincial operating rules and communal agencies). The analysis rests on triangulation of qualitative and quantitative data (time-series rainfall data, land use systems, participatory flood mapping, commune workshops (n=31), social-economic statistical databases, in-depth interviews with relevant institutions (n=5) and household surveys (n=162). Intensification of rainfall since the 1920s has increased the risk of flooding in the Sangkae River watershed during the late rainy season, particularly in the upstream area. Using an indicator-based approach, we discovered that the vulnerability of communes is highly dependent on the agro-ecology of land use systems. The household assessment reveals the variability of adaptive capacity between households according to their food security status and income portfolio. Agricultural innovation and structural adaptation to flood are scarce; the households mostly cope with flood through credit, external aid and de-capitalization (sale of household assets). These coping mechanisms adopted by farmers do not reduce vulnerability but reinforce it.The application of this assessment methodology provides nested pictures of vulnerability at different levels and scales and we argue that a dialogue between these levels and scales is necessary to understand the nature of the vulnerability and to act to reduce it. Using these different typologies of vulnerability, this approach enables recommendations to be formulated to reduce vulnerability through better horizontal and vertical integration of institutions and agencies, and effective collective action. [less ▲]

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See detailA multi-scale magnetotail reconnection event at Saturn and associated flows: Cassini/UVIS auroral observations
Radioti, Aikaterini ULg; Grodent, Denis ULg; Jia, X. et al

Conference (2015)

We present high-resolution Cassini/UVIS (Ultraviolet Imaging Spectrograph) observations of Saturn's aurora during May 2013 (DOY 140-141). The observations reveal an enhanced auroral activity in the ... [more ▼]

We present high-resolution Cassini/UVIS (Ultraviolet Imaging Spectrograph) observations of Saturn's aurora during May 2013 (DOY 140-141). The observations reveal an enhanced auroral activity in the midnight-dawn quadrant in an extended local time sector (~02 to 05 LT), which rotates with an average velocity of ~ 45% of rigid corotation. The auroral dawn enhancement reported here, given its observed location and brightness, is most probably due to hot tenuous plasma carried inward in fast moving flux tubes returning from a tail reconnection site to the dayside. These flux tubes could generate intense field-aligned currents that would cause aurora to brighten. However, the origin of tail reconnection (solar wind or internally driven) is uncertain. Based mainly on the flux variations, which do not demonstrate flux closure, we suggest that the most plausible scenario is that of internally driven tail reconnection which operates on closed field lines. The observations also reveal multiple intensifications within the enhanced region suggesting an x-line in the tail, which extends from 02 to 05 LT. The localised enhancements evolve in arc and spot-like small scale features, which resemble vortices mainly in the beginning of the sequence. These auroral features could be related to plasma flows enhanced from reconnection which diverge into multiple narrow channels then spread azimuthally and radially. We suggest that the evolution of tail reconnection at Saturn may be pictured by an ensemble of numerous narrow current wedges or that inward transport initiated in the reconnection region could be explained by multiple localised flow burst events. The formation of vortical-like structures could then be related to field-aligned currents, building up in vortical flows in the tail. An alternative, but less plausible, scenario could be that the small scale auroral structures are related to viscous interactions involving small-scale reconnection. [less ▲]

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See detailMulti-scale model of the cardiovascular system
Kosta, Sarah ULg; Pironet, Antoine ULg; Negroni, Jorge et al

Poster (2014)

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See detailMulti-scale model of the cardiovascular system
Kosta, Sarah ULg; Pironet, Antoine ULg; Negroni, Jorge et al

in 13th Belgian National Day on Biomedical Engineering (2014)

Detailed reference viewed: 22 (2 ULg)
See detailMulti-Scale Modeling of Crash & Failure of Reinforced Plastics Parts with Digimat to LS-DYNA interface
Adam, Laurent; Depouhon, Alexandre ULg; Assaker, Roger

in Proceedings of the 7th European LS-DYNA Conference (2009)

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See detailMulti-scale modeling of mycosubtilin lipopeptides at the air/water interface: structure and optical second harmonic generation
Loison, Claire; Nasir, Mehmet Nail ULg; Benichou, Emmanuel et al

in Physical Chemistry Chemical Physics [=PCCP] (2014), 16

Monolayers of the lipopeptide mycosubtilin are studied at the air/water interface. Their structure is investigated using molecular dynamics simulations. All-atom models suggest that the lipopeptide is ... [more ▼]

Monolayers of the lipopeptide mycosubtilin are studied at the air/water interface. Their structure is investigated using molecular dynamics simulations. All-atom models suggest that the lipopeptide is flexible and aggregates at the interface. To achieve simulation times of several microseconds, a coarse-grained (CG) model based on the MARTINI force field was also used. These CG simulations describe the formation of half-micelles at the interface for surface densities up to 1 lipopeptide per nm2. In these aggregates, the tyrosine side chain orientation is found to be constrained: on average, its main axis, as defined along the C–OH bond, aligns along the interface normal and points towards the air side. The origin of the optical second harmonic generation (SHG) from mycosubtilin monolayers at the air/water interface is also investigated. The molecular hyperpolarizability of the lipopeptide is obtained from quantum chemistry calculations. The tyrosine side chain contribution to the hyperpolarizability is found to be dominant. The orientation distribution of tyrosine, associated with a dominant hyperpolarizability component along the C–OH bond of the tyrosine, yields a ratio of the susceptibility elements χ(2)ZZZ/χ(2)ZXX consistent with the experimental measurements recently reported by M. N. Nasir et al. [Phys. Chem. Chem. Phys., 2013, 15, 19919]. [less ▲]

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See detailMulti-Scale Modelisation of the Optical Second Harmonic Generation of Tyrosine-Containing Iturinic Antimicrobial Lipopeptides
Loison, Claire; Nasir, Mehmet Nail ULg; Benichou, Emmanuel et al

Poster (2013)

The optical Second Harmonic Generation (SHG) of Mycosubtilin Langmuir Layers at the air/water interface are modeled. In this tyrosine-containing lipopepeptide, the environment of the tyrosine residue is ... [more ▼]

The optical Second Harmonic Generation (SHG) of Mycosubtilin Langmuir Layers at the air/water interface are modeled. In this tyrosine-containing lipopepeptide, the environment of the tyrosine residue is critical in defining the SHG response. To propose reasonable the structure of Mycosubtilin aggregates at the air-water interface, molecular dynamics simulations (all-atom and coarse-grained) are performed. Molecular hyperpolarizability of the lipopeptide are obtained by Quantum Chemistry calculations. Finally, the SHG susceptibilities of the interface are calculated using a simple additive model. The molecular dynamics simulations suggest that lipopeptides aggregate at the interface into half-micelles, and that this phenomena is the origin of a constraint on Tyrosine orientation. In particular the C-OH bond of the Tyrosine residue has a preferential orientation along the interface normal, pointing towards the air. This inhomogneneous orientation distribution, associated with a dominant hyperpolarizability component along the C-OH bond of the Tyrosine, yields a characteristic SHG response. Comparison with experimental data gathered in our lab are proposed. [less ▲]

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See detailMulti-scale modelling
Noels, Ludovic ULg; Becker, Gauthier; Mulay, Shantanu Shashikant ULg et al

Scientific conference (2013, March 11)

Detailed reference viewed: 42 (13 ULg)
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See detailMulti-scale modelling of failure in heterogeneous periodic thin shells
Mercatoris, Benoît ULg; Massart, Thierry J.

Conference (2010)

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See detailMulti-scale modelling of heterogeneous shell structures
Massart, T. J.; Mercatoris, Benoît ULg; Piezel, B. et al

in Computer Assisted Mechanics and Engineering Sciences [=CAMES] (2011), 18(1-2), 53-71

This paper reviews multi-scale computational homogenisation frameworks for the non-linear behaviour of heterogeneous thin planar shells. Based on a review of some of the currently available methods, a ... [more ▼]

This paper reviews multi-scale computational homogenisation frameworks for the non-linear behaviour of heterogeneous thin planar shells. Based on a review of some of the currently available methods, a computational homogenisation scheme for shells is applied on to representative volume elements for plain weave composites. The effect of flexural loading on the potential failure modes of such materials is analysed, focusing on the reinforcement-matrix delamination mechanism. The attention is next shifted toward failure localisation in masonry unit cells. Subsequently, a recently developed computational FE 2 solution scheme accounting for damage localisation at structural scales based on RVE computations is applied. Copyright © 2011 by Institute of Fundamental Technological Research, Polish Academy of Sciences. [less ▲]

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See detailMulti-scale modelling of permeability evolution in the excavation damaged zone around tunnels
Levasseur, Séverine ULg; Collin, Frédéric ULg; Charlier, Robert ULg et al

in PROCEEDINGS OF THE 2nd INTERNATIONAL SYMPOSIUM ON COMPUTATIONAL GEOMECHANICS (COMGEO I ) (2011)

A zone with significant irreversible deformations and significant changes in flow and transport properties is expected to be formed in indurated clay around underground excavations. The stress perturbation ... [more ▼]

A zone with significant irreversible deformations and significant changes in flow and transport properties is expected to be formed in indurated clay around underground excavations. The stress perturbation around the excavation could lead to a significant increase of the permeability, related to diffuse and/or localized crack propagation in the material. The main objective of the study is to model these processes at large scale with a micromechanical damage approach, based on the Ponte-Castaneda and Willis approximation (PCW) in the presence of initial stress, in order to assess the crack impacts on the performance of radioactive waste geological repositories. Combined with this model, permeability tensor is described as a function of micromechanical damage that is generated during the excavation. Advantages and drawbacks of this approach are described thanks to the results on Opalinus Clay and of the Selfrac long term dilatometer experiment. [less ▲]

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See detailMulti-scale modelling of sediment transport
Dewals, Benjamin ULg

Conference (2010, January 07)

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See detailMulti-scale modelling of shell failure for periodic quasi-brittle materials
Mercatoris, Benoît ULg; Massart, Thierry J.

in Fifth International Conference on Multiscale Material Modeling (MMM2010) (2010)

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See detailMulti-scale modelling of shell failure for periodic quasi-brittle materials
Mercatoris, Benoît ULg

Doctoral thesis (2010)

In a context of restoration of historical masonry structures, it is crucial to properly estimate the residual strength and the potential structural failure modes in order to assess the safety of buildings ... [more ▼]

In a context of restoration of historical masonry structures, it is crucial to properly estimate the residual strength and the potential structural failure modes in order to assess the safety of buildings. Due to its mesostructure and the quasi-brittle nature of its constituents, masonry presents preferential damage orientations, strongly localised failure modes and damage-induced anisotropy, which are complex to incorporate in structural computations. Furthermore, masonry structures are generally subjected to complex loading processes including both in-plane and out- of-plane loads which considerably influence the potential failure mechanisms. As a consequence, both the membrane and the flexural behaviours of masonry walls have to be taken into account for a proper estimation of the structural stability. Macrosopic models used in structural computations are based on phenomenological laws including a set of parameters which characterises the average behaviour of the material. These parameters need to be identified through experimental tests, which can become costly due to the complexity of the behaviour particularly when cracks appear. The existing macroscopic models are consequently restricted to particular assumptions. Other models based on a detailed mesoscopic description are used to estimate the strength of masonry and its behaviour with failure. This is motivated by the fact that the behaviour of each constituent is a priori easier to identify than the global structural response. These mesoscopic models can however rapidly become unaffordable in terms of computational cost for the case of large-scale three-dimensional structures. In order to keep the accuracy of the mesoscopic modelling with a more affordable computa- tional effort for large-scale structures, a multi-scale framework using computational homogeni- sation is developed to extract the macroscopic constitutive material response from computa- tions performed on a sample of the mesostructure, thereby allowing to bridge the gap between macroscopic and mesoscopic representations. Coarse graining methodologies for the failure of quasi-brittle heterogeneous materials have started to emerge for in-plane problems but remain largely unexplored for shell descriptions. The purpose of this study is to propose a new periodic homogenisation-based multi-scale approach for quasi-brittle thin shell failure. For the numerical treatment of damage localisation at the structural scale, an embedded strong discontinuity approach is used to represent the collective behaviour of fine-scale cracks using average cohesive zones including mixed cracking modes and presenting evolving orientation related to fine-scale damage evolutions. A first originality of this research work is the definition and analysis of a criterion based on the homogenisation of a fine-scale modelling to detect localisation in a shell description and determine its evolving orientation. Secondly, an enhanced continuous-discontinuous scale tran- sition incorporating strong embedded discontinuities driven by the damaging mesostructure is proposed for the case of in-plane loaded structures. Finally, this continuous-discontinuous ho- mogenisation scheme is extended to a shell description in order to model the localised behaviour of out-of-plane loaded structures. These multi-scale approaches for failure are applied on typical masonry wall tests and verified against three-dimensional full fine-scale computations in which all the bricks and the joints are discretised. [less ▲]

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See detailMulti-scale optimal interpolation: application to DINEOF analysis spiced with a local optimal interpolation
Beckers, Jean-Marie ULg; Barth, Alexander ULg; Tomazic, Igor ULg et al

in Ocean Science Discussions (2014), 11

We present a method in which the optimal interpolation of multi-scale processes can be untangled into a succession of simpler interpolations. First, we prove how the optimal analysis of a superposition of ... [more ▼]

We present a method in which the optimal interpolation of multi-scale processes can be untangled into a succession of simpler interpolations. First, we prove how the optimal analysis of a superposition of two processes can be obtained by different mathematical formulations involving iterations and analysis focusing on a single process. From the 5 different mathematical equivalent formulations we then select the most efficient ones by analyzing the behavior of the different possibilities in a simple and well controlled test case. The clear guidelines deduced from this experiment are then applied in a real situation in which we combine large-scale analysis of hourly SEVIRI satellite images using DINEOF with a local optimal interpolation using a Gaussian covariance. It is 10 shown that the optimal combination indeed provides the best reconstruction and can therefore be exploited to extract the maximum amount of useful information from the original data [less ▲]

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See detailMulti-Scale Simulation of the Simian Immunodeficiency Virus Fusion Peptide.
Crowet, Jean-Marc ULg; Parton, Daniel L.; Hall, Benjamin A. et al

in Journal of Physical Chemistry B (2012)

Fusion peptides of type I fusion glycoproteins are structural elements of several enveloped viruses which enable the fusion between host and virus membranes. It is generally suggested that these peptides ... [more ▼]

Fusion peptides of type I fusion glycoproteins are structural elements of several enveloped viruses which enable the fusion between host and virus membranes. It is generally suggested that these peptides can promote the early fusion steps by inducing membrane curvature and that they adopt a tilted helical conformation in membranes. Although this property has been the subject of several experimental and in silico studies, an extensive sampling of the membrane peptide interaction has not yet been done. In this study, we performed coarse-grained molecular dynamic simulations in which the lipid bilayer self-assembles around the peptide. The simulations indicate that the SIV fusion peptide can adopt two different orientations in a DPPC bilayer, a major population which adopts a tilted interfacial orientation and a minor population which is perpendicular to the bilayer. The simulations also indicate that for the SIV mutant that does not induce fusion in vitro the tilt is abolished. [less ▲]

Detailed reference viewed: 57 (17 ULg)