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See detailEffects of periurban structure on air pollution: coupling CA models to understand the link between urban structure and air pollution
Schindler, Mirjam UL; Caruso, Geoffrey UL

in Pinto N, Dourado J (Ed.) Proceedings of the Symposium on Cellular Automata Models of Urban and Spatial Systems (2012)

Air quality is a major concern in urban areas worldwide not only because of its severe health impacts but also due to its influence on living quality and residential behaviour. The subsequent increasing ... [more ▼]

Air quality is a major concern in urban areas worldwide not only because of its severe health impacts but also due to its influence on living quality and residential behaviour. The subsequent increasing demand for residential areas in the greener fringes of urban agglomerations fuels the discussion about sustainability in future cities. As traffic emissions are acknowledged to be the major source of pollutants in an urban environment this residential trend has triggered research to further understand the influence of urban structure on air quality. In order to meet sustainable growth, many researchers argue that in a global perspective a compact city is the desirable urban form due to less traffic distance, just in contrast to the trend towards urban sprawl. However, quantifying the link between urban structure and air pollution has only been the aim of few research studies so far. Thus, our objective is to deepen the understanding of this link by coupling a micro-economic CA urban growth model with a traffic emission model and a CA air pollution model while focussing on the impact on residential population. [less ▲]

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See detailAn efficient goal-oriented sampling strategy using reduced basis method for parametrized elastodynamic problems
Hoang, Khac Chi; Kerfriden, Pierre; Bordas, Stéphane UL et al

in Numerical Methods for Partial Differential Equations (2014)

In this paper, we study the class of linear elastodynamic problems with a ne parameter dependence using a goal-oriented approach by finite element (FE) and reduced basis (RB) methods. The main ... [more ▼]

In this paper, we study the class of linear elastodynamic problems with a ne parameter dependence using a goal-oriented approach by finite element (FE) and reduced basis (RB) methods. The main contribution of this paper is the "goal-oriented" proper orthogonal decomposition (POD)-Greedy sampling strategy within the RB approximation context. The proposed sampling strategy looks for the parameter points such that the output error approximation will be minimized by Greedy iterations. In estimating such output error approximation, the standard POD-Greedy algorithm is invoked to provide enriched RB approximations for the FE outputs. We propose a so-called "cross-validation" process to choose adaptively the dimension of the enriched RB space corresponding with the dimension of the RB space under consideration. Numerical results show that the new goal-oriented POD-Greedy sampling procedure with the cross-validation process improves signi ficantly the space-time output computations in comparison with the ones computed by the standard POD-Greedy algorithm. The method is thus ideally suited for repeated, rapid and reliable evaluations of input-output relationships in the space-time setting. [less ▲]

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See detailEfficient modeling of random heterogeneous materials with an uniform probability density function
Paladim, Daniel; Kerfriden, Pierre; Bordas, Stéphane UL

Scientific Conference (2014, July)

Homogenised constitutive laws are largely used to predict the behaviour of composite structures. Assessing the validity of such homogenised models can be done by making use of the concept of ``modelling ... [more ▼]

Homogenised constitutive laws are largely used to predict the behaviour of composite structures. Assessing the validity of such homogenised models can be done by making use of the concept of ``modelling error''. First, a microscopic ``faithful'' -and potentially intractable- model of the structure is defined. Then, one tries to quantify the effect of the homogenisation procedure on a result that would be obtained by directly using the ``faithful'' model. Such an approach requires (a) the ``faithful'' model to be more representative of the physical phenomena of interest than the homogenised model and (b) a reliable approximation of the result obtained using the "faithful" and intractable model to be available at cheap costs. We focus here on point (b), and more precisely on the extension of the techniques developed in [3][2] to estimate the error due to the homogenisation of linear, spatially random composite materials. Particularly, we will approximate the unknown probability density function by bounding its first moment. In this paper, we will present this idea in more detail, displaying the numerical efficiencies and computational costs related to the error estimation. The fact that the probability density function is uniform is exploited to greatly reduce the computational cost. We will also show some first attempts to correct the homogenised model using non-conforming, weakly intrusive microscopic patches. [less ▲]

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See detailEfficient modeling of random heterogeneous materials with an uniform probability density function (slides)
Paladim, Daniel; Kerfriden, Pierre; Moitinho de Almeida, José et al

Scientific Conference (2014)

Homogenised constitutive laws are largely used to predict the behaviour of composite structures. Assessing the validity of such homogenised models can be done by making use of the concept of “modelling ... [more ▼]

Homogenised constitutive laws are largely used to predict the behaviour of composite structures. Assessing the validity of such homogenised models can be done by making use of the concept of “modelling error”. First, a microscopic “faithful” -and potentially intractable- model of the structure is defined. Then, one tries to quantify the effect of the homogenisation procedure on a result that would be obtained by directly using the “faithful” model. Such an approach requires (a) the “faithful” model to be more representative of the physical phenomena of interest than the homogenised model and (b) a reliable approximation of the result obtained using the ”faithful” and intractable model to be available at cheap costs. We focus here on point (b), and more precisely on the extension of the techniques devel- oped in [3] [2] to estimate the error due to the homogenisation of linear, spatially random composite materials. Particularly, we will approximate the unknown probability density function by bounding its first moment. In this paper, we will present this idea in more detail, displaying the numerical efficiencies and computational costs related to the error estimation. The fact that the probability density function is uniform is exploited to greatly reduce the computational cost. We will also show some first attempts to correct the homogenised model using non-conforming, weakly intrusive microscopic patches. [less ▲]

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See detailEfficient recovery-based error estimation for the smoothed finite element method for smooth and singular linear elasticity
González-Estrada, O. A.; Natarajan, S.; Ródenas, J. J. et al

in Computational Mechanics (2013), 52(1), 37-52

An error control technique aimed to assess the quality of smoothed finite element approximations is presented in this paper. Finite element techniques based on strain smoothing appeared in 2007 were shown ... [more ▼]

An error control technique aimed to assess the quality of smoothed finite element approximations is presented in this paper. Finite element techniques based on strain smoothing appeared in 2007 were shown to provide significant advantages compared to conventional finite element approximations. In particular, a widely cited strength of such methods is improved accuracy for the same computational cost. Yet, few attempts have been made to directly assess the quality of the results obtained during the simulation by evaluating an estimate of the discretization error. Here we propose a recovery type error estimator based on an enhanced recovery technique. The salient features of the recovery are: enforcement of local equilibrium and, for singular problems a "smooth + singular" decomposition of the recovered stress. We evaluate the proposed estimator on a number of test cases from linear elastic structural mechanics and obtain efficient error estimations whose effectivities, both at local and global levels, are improved compared to recovery procedures not implementing these features. © 2012 Springer-Verlag. [less ▲]

Detailed reference viewed: 281 (4 UL)
See detailÉischte Weltkrich: Remembering The Great War in Luxembourg - Digital Exhibition
Camarda, Sandra UL

in Bienert, Andreas; Jazbec, Rebeka (Eds.) EVA Berlin 2017 Elekronische Medien & Kunst, Kultur und Historie (2017)

Detailed reference viewed: 55 (12 UL)
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See detailThe elastic properties of composites reinforced by a transversely isotropic random fibre-network
Lin, Xiude; Zhu, Hanxing; Yuan, Xiaoli et al

in Composite Structures (2018), 208

This research stems from the idea of introducing a fibre-network structure into composites aiming to enhance the stiffness and strength of the composites. A novel new type of composites reinforced by a ... [more ▼]

This research stems from the idea of introducing a fibre-network structure into composites aiming to enhance the stiffness and strength of the composites. A novel new type of composites reinforced by a tranversely isotropic fibre-network in which the fibres are devided into continuous segments and randomly distributed has been proposed and found to have improved elastic properties compared to other conventional fibre or particle composites mainly due to the introduction of cross linkers among the fibres. Combining with the effects of Poisson’s ratio of the constituent materials, the fibre network composite can exhibit extraordinary stiffness. A simplified analytical model has also been proposed for comparison with the numerical results, showing close prediction of the stiffness of the fibre-network composites. Moreover, as a plate structure, the thickness of the fibre network composite is adjustable and can be tailored according to the dimensions and mechanical properties as demanded in industry. [less ▲]

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See detailAn element nodal force-based large increment method for elastoplasticity
Long, Danbin; Guo, Zaoyang; Liu, Xila et al

in AIP Conference Proceedings (2010), 1233(PART 1), 1401-1405

This paper presents a new method for establishing the basic equations in the novel force-based large increment method (LIM) for continuum elastoplastic problems. In LIM, unlike traditional displacement ... [more ▼]

This paper presents a new method for establishing the basic equations in the novel force-based large increment method (LIM) for continuum elastoplastic problems. In LIM, unlike traditional displacement methods, the (generalised) elemental force variables are adopted as system unknowns. The equilibrium equations can then be obtained directly at every nodal degree of freedom without physical equations (i.e., constitutive equations) involved. The generalised inverse of the non-square system of equations is employed to obtain the set of solutions of the non-square matrix equations directly. A conjugate gradient procedure is then used to find the correct solution from this set of solutions by optimising the compatibility of the solution based on the fact that the correct solution should also satisfy the constitutive equations and the compatibility equations. In this paper, the generalised elemental force variables are defined based on the element nodal forces. The LIM framework is therefore successfully applied to elements based on this definition. The efficiency and accuracy of the LIM are illustrated with a few benchmark problems and the results are compared with the analytical solution and the conventional displacement-based finite element method. [less ▲]

Detailed reference viewed: 70 (0 UL)
See detailEmbracing diversity in the digital transformation of primary healthcare
Lygidakis, Charilaos UL

Scientific Conference (2017, June 30)

The use of information and communication technologies for health constitutes a strategic ally to the sustainable development goals and attaining universal health coverage through enabling equitable access ... [more ▼]

The use of information and communication technologies for health constitutes a strategic ally to the sustainable development goals and attaining universal health coverage through enabling equitable access to high quality and affordable health care services. The omnipresence of mobile devices and sensors, the increasing availability of data and computational power, and the breakthroughs in imaging and genomics, are creating a perfect storm that is bound to transform health care profoundly. At the population level, the coordination of disease control and prevention programmes is facilitated, cost-effective interventions are implemented, and ultimately the quality of life of our communities is enhanced. EHealth also plays a significant role in the delivery of people-centred and integrated health services, empowers individuals to make informed decisions and self-manage their health needs. For the first time in history, the individual is placed at the centre, has timely and affordable access to data, knowledge and tools, and health care is tailored for his/her diverse background, context and needs. A second perspective to the digital revolution is how our own discipline is transformed. As technology is a catalyst for sustainable, large scale social change, health care has the opportunity to invest in inter-professional collaboration, and leverage a diverse range of expertise, stakeholders and resources to expand its horizons and tackle old and future challenges. [less ▲]

Detailed reference viewed: 81 (0 UL)
See detailThe emergence of leapfrogging in an urban growth model combining an economic approach and cellular automata
Frankhauser, Pierre; Caruso, Geoffrey UL; Peeters, Dominique et al

Scientific Conference (2009)

Detailed reference viewed: 36 (1 UL)
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See detailEmpirical Cognitive Study on Abstract Argumentation Semantics
Cramer, Marcos UL; Guillaume, Mathieu UL

in Frontiers in Artificial Intelligence and Applications (2018)

In abstract argumentation theory, multiple argumentation semantics have been proposed that allow to select sets of jointly acceptable arguments from a given set of arguments based on the attack relation ... [more ▼]

In abstract argumentation theory, multiple argumentation semantics have been proposed that allow to select sets of jointly acceptable arguments from a given set of arguments based on the attack relation between arguments. The existence of multiple argumentation semantics raises the question which of these semantics predicts best how humans evaluate arguments, possibly depending on the thematic con- text of the arguments. In this study we report on an empirical cognitive study in which we tested how humans evaluate sets of arguments de- pending on the abstract structure of the attack relation between them. Two pilot studies were performed to validate the intended link between argumentation frameworks and sets of natural language arguments. The main experiment involved a group deliberation phase and made use of three different thematic contexts of the argument sets involved. The data strongly suggest that independently of the thematic contexts that we have considered, strong acceptance and strong rejection according to the CF2 and preferred semantics are a better predictor for human argument acceptance than the grounded semantics (which is identical to strong acceptance/rejection with respect to complete semantics). Furthermore, the data suggest that CF2 semantics predicts human argument acceptance better than preferred semantics, but the data for this comparison is limited to a single thematic context. [less ▲]

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See detailEnergieaudit Schul -und Sportkomplex Roodt/Syre
Scheuren, Jean-Jacques UL; Scholzen, Frank UL

in Revue Technique Luxembourgeoise (2008), Heft 2-2008

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See detailEnergieeffizienz neuer Schul-und Bürogebäude in Luxemburg basierend auf Verbrauchsdaten und Simulationen
Thewes, Andreas UL

Doctoral thesis (2011)

In Luxemburg, energy consumption in the building and housing sector has been significantly increasing over the last years. An assessment of the energy saving potential of buildings requires a ... [more ▼]

In Luxemburg, energy consumption in the building and housing sector has been significantly increasing over the last years. An assessment of the energy saving potential of buildings requires a comprehensive data basis with real consumption figures that are not yet available. One focus of this study was to create a priori a detailed energy consumption database for new “School and Administrative Buildings” for Luxembourg. These are both groups cover a major part of the building and housing sector in Luxembourg besides residential buildings. Based on the samples collected, it was able to expand the figures to the entire country using mathematical methods and the medium heat and electricity consumption of these two types of buildings could determined. After collecting some details about each object, it was able to analyze the influence of different parameters, such as building age, size, type, glass fraction etc., on energy consumption using multivariate statistical methods. A posteriori, the results from the database were verified using parameter studies to existing objects and one object still under construction. Based on this, important key parameters relevant for both energy savings and thermal comfort could be found. This knowledge are necessary to understand energy flows within buildings better and, based on this, to be able meeting the nearly zero energy buildings requirements as set out by the EU Directive in the years to come. As conclusion, the central-European climatic zone provides opportunities to design energy-saving office and school buildings (primary energy consumption < 100 kWh/m2a) without mechanical cooling and ventilation systems that still guarantee appropriate degrees of thermal comfort. Unfortunately, the real average primary energy consumption figures of new school (187 kWh/m2a) and office buildings (677 kWh/m2a) in Luxemburg are still significantly higher. [less ▲]

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See detailEnergy harvesting
Zilian, Andreas UL

in Science and Technology (2015), 15

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See detailEnergy minimising multi-crack growth in linear-elastic materials using the extended finite element method with application to Smart-CutTM silicon wafer splitting
Sutula, Danas UL

Doctoral thesis (2016)

We investigate multiple crack evolution under quasi-static conditions in an isotropic linear-elastic solid based on the principle of minimum total energy, i.e. the sum of the potential and fracture ... [more ▼]

We investigate multiple crack evolution under quasi-static conditions in an isotropic linear-elastic solid based on the principle of minimum total energy, i.e. the sum of the potential and fracture energies, which stems directly from the Griffith’s theory of cracks. The technique, which has been implemented within the extended finite element method, enables minimisation of the total energy of the mechanical system with respect to the crack extension directions. This is achieved by finding the orientations of the discrete crack-tip extensions that yield vanishing rotational energy release rates about their roots. In addition, the proposed energy minimisation technique can be used to resolve competing crack growth problems. Comparisons of the fracture paths obtained by the maximum tension (hoop-stress) criterion and the energy minimisation approach via a multitude of numerical case studies show that both criteria converge to virtually the same fracture solutions albeit from opposite directions. In other words, it is found that the converged fracture path lies in between those obtained by each criterion on coarser numerical discretisations. Upon further investigation of the energy minimisation approach within the discrete framework, a modified crack growth direction criterion is proposed that assumes the average direction of the directions obtained by the maximum hoop stress and the minimum energy criteria. The numerical results show significant improvements in accuracy (especially on coarse discretisations) and convergence rates of the fracture paths. The XFEM implementation is subsequently applied to model an industry relevant problem of silicon wafer cutting based on the physical process of Smart-CutTM technology where wafer splitting is the result of the coalescence of multiple pressure-driven micro-crack growth within a narrow layer of the prevailing micro-crack distribution. A parametric study is carried out to assess the influence of some of the Smart-CutTM process parameters on the post-split fracture surface roughness. The parameters that have been investigated, include: mean depth of micro-crack distribution, distribution of micro-cracks about the mean depth, damage (isotropic) in the region of micro-crack distribution, and the influence of the depth of the buried-oxide layer (a layer of reduced stiffness) beneath the micro-crack distribution. Numerical results agree acceptably well with experimental observations. [less ▲]

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See detailEnergy performance assessment of an existing double-skin façade: measurements and simulation
Carton, Julien UL; Scholzen, Frank UL; Thomas, Sébastien et al

in Energy Forum - Solar Building Skins, 06 - 07 December 2012, Italy (2012, December)

An existing office building with an active double skin façade in Luxembourg has been analyzed. In the first step in-situ measurements have been performed. For this purpose outside, inside and cavity ... [more ▼]

An existing office building with an active double skin façade in Luxembourg has been analyzed. In the first step in-situ measurements have been performed. For this purpose outside, inside and cavity conditions have been measured for representative summer and winter conditions. In a second step, a thermal simulation using TRNSYS was performed. The simulation model has been compared to the time limited series of measurements and thus has been validated for some of the annual meteorological conditions. Then the model has been extrapolated to a whole year in order to assess the energy performance of the given façade. Further a parametric study of alternative façades has been carried out based on the validated simulation model to assess their own performances. For the given case study building, the double skin concept energetically performs well compared to other concepts with non outside (non weather exposed) solar protection, but worse than an external solar protection. The thermal comfort level in the rooms has also been determined by simulation - the calculated room averaged comfort level is quite optimal, but further investigations regarding the local comfort close to the glazed façades still have to be achieved. [less ▲]

Detailed reference viewed: 155 (16 UL)