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ORBi

Machine learning techniques for atmospheric pollutant monitoring Sainlez, Matthieu ; Poster (2012, January 27) Detailed reference viewed: 22 (0 UL)Maintenance location routing for rolling stock under line and fleet planning uncertainty Arts, Joachim ; ; in Transportation Science (in press) Detailed reference viewed: 201 (22 UL)Management of product characteristics uncertainty based on Formal Logic and Characteristics Properties Model ; Qureshi, Ahmed Jawad ; et al in CIRP Annals - Manufacturing Technology (2013), 62(1), Uncertainty in product characteristics is ubiquitous in any engineering system at all the stages of product life-cycle. Considering uncertainty from different sources during the product design phase is ... [more ▼] Uncertainty in product characteristics is ubiquitous in any engineering system at all the stages of product life-cycle. Considering uncertainty from different sources during the product design phase is critical to its reliable performance. This paper presents a framework integrating the uncertainty propagation through different product characteristics and its effect on product properties. The framework consists of three main parts: a descriptive model based on formal logic and characteristics properties model; a mathematical implementation through set theory and probabilistic approach; and an algorithm for design space evaluation and tolerancing. The application of framework is demonstrated through an industrial case study. [less ▲] Detailed reference viewed: 102 (5 UL)A Markov Chain dynamic model for trip generation and distribution based on CDR Di Donna, Simone Aniello ; Cantelmo, Guido ; Viti, Francesco in Proceedings of the MT-ITS Conference (2015, June) Detailed reference viewed: 90 (6 UL)A Markov chain dynamic model for trip generation and distribution based on CDR Viti, Francesco ; Cantelmo, Guido in Periodica Polytechnica (2015) Detailed reference viewed: 92 (14 UL)A Markov Chain Mote Carlo Approach for Estimating Daily Activity Patterns Scheffer, Ariane Hélène Marie ; ; et al Poster (2019, January) Determining the purpose of trips brings is a fundamental information to evaluate travel demand during the day and to predict longer-term impacts on the population’s travel behavior. The concept of tours ... [more ▼] Determining the purpose of trips brings is a fundamental information to evaluate travel demand during the day and to predict longer-term impacts on the population’s travel behavior. The concept of tours is the most suited to consider the value of a daily scheduling of individuals and travel interdependencies. However, the meticulous care required for both collecting data of high quality and interpret results of advanced demand models are frequently considered as major drawbacks. The objective of this study is to incorporate into a standard trip-based model some inherent concepts of activity-based models in order to enhance the representation of travel behavior. The main focus of this work is to infer, employing utility theory, the trip purpose of a population, at a zonal level. Making use of Markov Chain Monte Carlo, a set of parameters is estimated in order to retrieve tour-based primitives of the demand. The main advantage of this methodology is the low requirements in terms of data, as no individual information are used, and the good interpretation of the model. Estimated parameters of the priors set a utility-based probability function for departure time, which allows to have a dynamic overview of the demand. In order to account for the tour consistency of travel decisions, a duration constraint is added to the model. The proposed model is applied to the region of Luxembourg city and the results show the potential of the methodologies for dividing an observed demand based on the activity at destination. [less ▲] Detailed reference viewed: 40 (1 UL)A mass conservative Kalman filter algorithm for thermo-computational fluid dynamics ; Baroli, Davide ; et al in Materials (ISSN 1996-1944) (n.d.) Computational fluid-dynamics (CFD) is of wide relevance in engineering and science, due to its capability of simulating the three-dimensional flow at various scales. However, the suitability of a given ... [more ▼] Computational fluid-dynamics (CFD) is of wide relevance in engineering and science, due to its capability of simulating the three-dimensional flow at various scales. However, the suitability of a given model depends on the actual scenarios which are encountered in practice. This challenge of model suitability and calibration could be overcome by a dynamic integration of measured data into the simulation. This paradigm is known as data-driven assimilation (DDA). In this paper, the study is devoted to Kalman filtering, a Bayesian approach, applied to Reynolds-Averaged Navier-Stokes (RANS) equations for turbulent flow. The integration of the Kalman estimator into the PISO segregated scheme was recently investigated by (1). In this work, this approach is extended to the PIMPLE segregated method and to the ther- modynamic analysis of turbulent flow, with the addition of a sub-stepping procedure that ensures mass conservation at each time step and the com- patibility among the unknowns involved. The accuracy of the algorithm is verified with respect to the heated lid-driven cavity benchmark, incorporat- ing also temperature observations, comparing the augmented prediction of the Kalman filter with the CFD solution obtained on a very fine grid. [less ▲] Detailed reference viewed: 71 (4 UL)Mathematical Modelling of Flux Decline due to Concentration Polarisation and Cake Layer Formation in Crossflow Filtration Systems Hale, Jack ; ; et al Scientific Conference (2007, May) Crossflow membrane filtration is an effective way of removing both colloidal and dissolved organic matter from contaminated water supplies. Two phenomena domimate solute flux in crossflow systems ... [more ▼] Crossflow membrane filtration is an effective way of removing both colloidal and dissolved organic matter from contaminated water supplies. Two phenomena domimate solute flux in crossflow systems; concentration polarization and cake layer formation. Many innovative mathematical models for predicting both flux decline and quasi-steady state flux have been produced in the literature. However, limited regime applicability and conflicting physical predictions have made choosing optimal performance parameters in design a challenging process. An overview of the current field of models was undertaken, including an assessment of mathematical assumptions, numerical computation workload and number and complexity of system constants. A new model incorporating viscosity dependence on concentration is developed for the concentration polarization regime. Preliminary results will also be presented from a Monte Carlo based molecular dynamics simulation of volume packing fraction in the cake layer regime. The novel aspects of these models will be compared with existing models and the experimental results of our collaborators. Laboratory ultrafiltration tests were undertaken using varying concentrations of Dextran. An outline of future model directions and refinements will be presented. [less ▲] Detailed reference viewed: 38 (1 UL)Mathematical models of circadian Ca2+ oscillations ; Goncalves, Jorge ; in Proceedings of the eighth International Conference on Systems Biology (2007) In the model plant Arabidopsis thaliana, the concentration of cytosolic-free Ca2+ ([Ca2+]cyt) oscillates with a circadian rhythm. We are investigating the regulation and role of these oscillations both ... [more ▼] In the model plant Arabidopsis thaliana, the concentration of cytosolic-free Ca2+ ([Ca2+]cyt) oscillates with a circadian rhythm. We are investigating the regulation and role of these oscillations both experimentally and mathematically. Through systems identification, we have developed simple mathematical models from a single experiment measuring [Ca2+]cyt and the promoter activity of CIRCADIAN CLOCK ASSOCIATED 1 (CCA1). Through validation with 4 contrasting datasets, including a clock-arrhythmic transgenic line (CCA1 overexpressor), we demonstrate the necessity for a light input pathway to regulate basal [Ca2+]cyt levels. [less ▲] Detailed reference viewed: 23 (2 UL)Mathematical relationships between representations of structure in linear interconnected dynamical systems ; Goncalves, Jorge ; et al in The proceedings of the 2011 American Control Conference (ACC) (2011) A dynamical system can exhibit structure on multiple levels. Different system representations can capture different elements of a dynamical system's structure. We consider LTI input-output dynamical ... [more ▼] A dynamical system can exhibit structure on multiple levels. Different system representations can capture different elements of a dynamical system's structure. We consider LTI input-output dynamical systems and present four representations of structure: complete computational structure, subsystem structure, signal structure, and input output sparsity structure. We then explore some of the mathematical relation ships that relate these different representations of structure. In particular, we show that signal and subsystem structure are fundamentally different ways of representing system structure. A signal structure does not always specify a unique subsystem structure nor does subsystem structure always specify a unique signal structure. We illustrate these concepts with a numerical example. [less ▲] Detailed reference viewed: 64 (2 UL)Maximum-Entropy Meshfree Method for the Reissner-Mindlin Plate Problem based on a Stabilised Mixed Weak Form Hale, Jack ; Scientific Conference (2012) Meshless methods, such as the Element Free Galerkin (EFG) method, hold various advantages over mesh-based techniques such as robustness in large-deformation problems and high continuity. The Reissner ... [more ▼] Meshless methods, such as the Element Free Galerkin (EFG) method, hold various advantages over mesh-based techniques such as robustness in large-deformation problems and high continuity. The Reissner-Mindlin plate model is a particularly popular choice for simulating thin structures. It is well known in the Finite Element and Meshless literature that the simplest numerical treatments of the Reissner-Mindlin model lead to shear-locking which in turn produces erroneous results. This is due to the inability of the approximation functions to satisfy the Kirchoff constraint in the thin-plate limit. A recent advance in the area of meshless approximation schemes are Maximum-Entropy (MaxEnt) approximants. MaxEnt schemes provide a weak Kronecker-delta property on convex node sets which allows the direct imposition of Dirichlet (essential) boundary conditions. In this work, we derive a shear-locking free meshless method using MaxEnt approximants by consider- ing a stabilised mixed weak form. We include a scalar parameter which splits the energy from the shear bilinear form into two parts; the first is formed from the displacement fields only and the second from the independently interpolated shear strain field and the displacement fields. This splitting greatly eases the satisfaction of the LBB stability condition. We then eliminate the independently interpolated shear strain field using a localised projection operator, related to the “volume-averaged pressure” technique, which produces a final system of equations in the original displacement unknowns only. We show the good performance of the method for a variety of test problems. [less ▲] Detailed reference viewed: 46 (2 UL)Measure and Failure Cost Analysis: Selecting Risk Treatment Strategies Gericke, Kilian ; ; Blessing, Lucienne in Proceedings of the 17th International Conference on Engineering Design (2009) Project Risk Management is used to prevent projects to fail. Despite its proven use, barriers still exist that hinder implementation and use by inexperienced persons. One barrier is the additional effort ... [more ▼] Project Risk Management is used to prevent projects to fail. Despite its proven use, barriers still exist that hinder implementation and use by inexperienced persons. One barrier is the additional effort required by the process of Project Risk Management itself. An additional barrier is the lack of systematic support of important steps like the selection of an appropriate risk treatment strategy. The decision which strategy to select is a challenging task due to the uncertain character of the addressed issue. The trade-off of the perceived additional efforts caused by a method must be addressed by an enhancement of the cost-benefit ratio of the applied methods and implemented risk treatment measures. Decision making using the proposed Measure and Failure Cost Analysis (MFCA) method enables the Risk Manager to compare the arising costs of different risk treatment strategies caused by an occurring risk and risk treatment measures. It is based on a de-escalation principle which analyzes the course of the impact of an event. The method compares the reaction rate of different strategies and proposes the favorite one. [less ▲] Detailed reference viewed: 47 (0 UL)Mechanical failure in microstructural heterogeneous materials Bordas, Stéphane ; ; in Lecture Notes in Computer Science (2007), 4310 LNCS Various heterogeneous materials with multiple scales and multiple phases in the microstructure have been produced in the recent years. We consider a mechanical failure due to the initiation and ... [more ▼] Various heterogeneous materials with multiple scales and multiple phases in the microstructure have been produced in the recent years. We consider a mechanical failure due to the initiation and propagation of cracks in places of high pore density in the microstructures. A multi-scale method based on the asymptotic homogenization theory together with the mesh superposition method (s-version of FEM) is presented for modeling of cracks. The homogenization approach is used on the global domain excluding the vicinity of the crack where the periodicity of the microstructures is lost and this approach fails. The multiple scale method relies on efficient combination of both macroscopic and microscopic models. The mesh superposition method uses two independent (global and local) finite element meshes and the concept of superposing the local mesh onto the global continuous mesh in such a way that both meshes not necessarily coincide. The homogenized material model is considered on the global mesh while the crack is analyzed in the local domain (patch) which allows to have an arbitrary geometry with respect to the underlying global finite elements. Numerical experiments for biomorphic cellular ceramics with porous microstructures produced from natural wood are presented. [less ▲] Detailed reference viewed: 43 (2 UL)The mechanical reliability of an electronic textile investigated using the virtual-power-based quasicontinuum method Beex, Lars ; ; et al in Mechanics of Materials (2015), 80 The quasicontinuum (QC) method is a multiscale method for the solution of lattice models that combines coarse-grained regions and fully resolved regions with individual lattice events. QC methodologies ... [more ▼] The quasicontinuum (QC) method is a multiscale method for the solution of lattice models that combines coarse-grained regions and fully resolved regions with individual lattice events. QC methodologies are mainly used to reduce the computational costs of conservative atomistic lattice computations. Recently, a virtual-power-based variant has been proposed that enables its use for non-conservative lattice computations. In this contribution the virtual-power-based QC approach is adopted in combination with a recently proposed mesostructural lattice model for electronic textile in order to investigate its mechanical behaviour. The interactions of the lattice model for electronic textile are modelled elastoplastically and hence, regular conservative QC approaches are not adequate. This article incorporates a modification of a previously defined exact summation rule for QC methods –by sampling the lattice interactions directly instead of via the lattice nodes. This leads to a significant reduction of the computational cost, whereas the accuracy of the summation rule remains unaffected. The presented methodology is used to efficiently investigate the failure envelope of an electronic textile – a woven fabric with embedded electronic components and conductive wires. The dependence of the failure envelope on the locations of the conductive wires and the stiffness of the weft yarns is investigated as well. [less ▲] Detailed reference viewed: 172 (8 UL)Mechanische und thermische Untersuchungen zur Entwicklung eines Wärmedämmsteines aus Leichtbeton Leufgens, Nadine Doctoral thesis (2010) The current discussion about the necessity of sustainable reduction of primary energy for heating of housing structures and of CO2 – emissions led the University of Luxembourg to issue a project to ... [more ▼] The current discussion about the necessity of sustainable reduction of primary energy for heating of housing structures and of CO2 – emissions led the University of Luxembourg to issue a project to develop hybrid light-weight concrete blocks with high heat-insulating properties. Therefore, the demand for wall constructions limiting the heat flow through the outer wall was steadily growing. Because of the progressing standard of national and European Energy Saving Regulations for housing structures and office buildings in the past years, most of the producers of bricks and concrete masonry blocks were forced to develop new, innovative wall materials and constructions. For assessing the real actual state of the art of masonry blocks, 15 different bricks and blocks were taken from European free market as samples. It was shown, that especially for highly-heat insulating masonry lightweight concrete blocks (e.g. Vbl SW 2) with dry densities below 800 kg/m3 an optimization potential still exists. A relevant aspect for a critical estimation of a wall construction is the knowledge of mechanical and thermal lightweight aggregate concrete (LAC) parameters. The present work describes investigations for determining design limit values of the thermal and mechanical properties of LAC. Based on this, a mathematical approach to describe the strength, the thermal conductivity and for e.g. the stress-strain-relationship linked to the dry density in a range between 500 and 2000 kg/m3 was derived. For studying the material behavior of LAC, specimens were produced in laboratory tests as well as in the production line by fabricating solid lightweight concrete blocks without inner air holes. Due to the unsatisfying results of the market study, further investigations had to be done to determine the influence of size and slenderness effects on the strength of solid specimen and masonry blocks with inner air holes made of LAC. Additionally, combined influencing factors were studied on block sections cut out of hollow and solid masonry blocks. In the following, the experimental results were verified by simulations with the Finite-Element-Method using the commercial software ANSYS© for modeling different LAC-specimen geometries and the influence of the kind of load applications by a contact zone between steel plates and specimen. Subsequently, the results of these investigations and the achieved knowledge of the influencing factors on the load carrying capacity of the block structures lead to an analytical model approach for design purpose of masonry blocks based on the elasticity theory. This model allows quantitative predictions of the load bearing strength of hollow and solid masonry blocks with inner air holes arranged in a grid system. The analytical model is verified by comparison of experimental results of different block geometries. Finally, the knowledge of the load carrying behavior of different LAC specimen geometries achieved by various experimental and numerical results contribute to the construction of new prototypes of heat insulating masonry blocks made of LAC. Based on the results of the market study and numerical parameter studies, it is revealed that it is suggestive to separate the load bearing from the thermal function of the block by developing 3-layered Sandwich and composite blocks made of an insulating and load bearing part. [less ▲] Detailed reference viewed: 60 (4 UL)Médias et médiations culturelles au Luxembourg Colas-Blaise, Marion ; Tore, Gian Maria Book published by Binsfeld (2011) Detailed reference viewed: 75 (4 UL)Merging DEMs from VHR Optical Imagery with Drone Data - A High-resolution DEM for Tristan da Cunha Backes, Dietmar ; Teferle, Felix Norman Scientific Conference (2018, December 12) The extraction of high-resolution, Digital Elevation Models (DEM) from very high-resolution (VHR) optical satellite imagery, as well as low altitude drone images by Photogrammetric methods or modern ... [more ▼] The extraction of high-resolution, Digital Elevation Models (DEM) from very high-resolution (VHR) optical satellite imagery, as well as low altitude drone images by Photogrammetric methods or modern Structure from Motion (SFM) engines, has rapidly matured. Today both data sources are representing cost-effective alternatives to dedicated airborne sensors, especially for remote and difficult to access regions. Ever-growing archives of high-resolution Satellite imagery, are providing a rich data source which covers even the most remote locations with high-resolution imagery up to 0.30m ground sample distance multiple times enabling the generation of high-resolution DEMS. Furthermore, low-cost, low weight and easy to use drones can easily be deployed in remote regions and capture limited areas with very high resolution. Dense point clouds derived from this method provide an invaluable data source to fill the gap between globally available low-resolution DEMs and highly accurate terrestrial surveys. The presented case study investigates the use of VHR archive imagery as well as low-cost drone imagery to generate high-quality DEMs using photogrammetric tools over a remote region which is difficult to access by manned airborne platforms. We highlight the potential and limitations of both data sources to provide high resolution, accurate elevation data. [less ▲] Detailed reference viewed: 38 (2 UL)Mesh adaptivity driven by goal-oriented locally equilibrated superconvergent patch recovery ; ; et al in Computational Mechanics (2013) Goal-oriented error estimates (GOEE) have become popular tools to quantify and control the local error in quantities of interest (QoI), which are often more pertinent than local errors in energy for ... [more ▼] Goal-oriented error estimates (GOEE) have become popular tools to quantify and control the local error in quantities of interest (QoI), which are often more pertinent than local errors in energy for design purposes (e.g. the mean stress or mean displacement in a particular area, the stress intensity factor for fracture problems). These GOEE are one of the key unsolved problems of advanced engineering applications in, for example, the aerospace industry. This work presents a simple recovery-based error estimation technique for QoIs whose main characteristic is the use of an enhanced version of the Superconvergent Patch Recovery (SPR) technique previously used for error estimation in the energy norm. This enhanced SPR technique is used to recover both the primal and dual solutions. It provides a nearly statically admissible stress field that results in accurate estimations of the local contributions to the discretisation error in the QoI and, therefore, in an accurate estimation of this magnitude. This approach leads to a technique with a reasonable computational cost that could easily be implemented into already available finite element codes, or as an independent postprocessing tool. © 2013 Springer-Verlag Berlin Heidelberg. [less ▲] Detailed reference viewed: 125 (2 UL)Meshfree methods for shear-deformable structures based on mixed weak forms Hale, Jack Scientific Conference (2014, July 24) Similarly to the finite element method, meshfree methods must be carefully designed to overcome the shear-locking problem when discretising the shear-deformable structural theories. Many successful ... [more ▼] Similarly to the finite element method, meshfree methods must be carefully designed to overcome the shear-locking problem when discretising the shear-deformable structural theories. Many successful treatments of shear-locking in the finite element literature are constructed through the application of a mixed variational form, where the shear stress is treated as an independent variational quantity in addition to the usual displacements. Because of its sound mathematical underpinnings this is the methodology I have chosen to solve the shear-locking problem when using meshfree basis functions. In this talk I will discuss the mathematical origins of the shear-locking problem and the applicability of the celebrated LBB stability condition for designing well-behaved mixed meshfree approximation schemes. I will show results from two new formulations that demonstrate the effectiveness of this approach. The first method is a meshfree formulation for the Timoshenko beam problem that converges to a classic inf-sup stable finite element method when using Maximum- Entropy basis functions. The second method is a generalised displacement meshfree method for the Reissner- Mindlin problem where the shear stress is eliminated prior to the solution of the linear system using a local patch-projection technique, resulting in a linear system expressed in terms of the original displacement unknowns only. Stability is ensured by using a stabilised weak form which is necessary due to the loss of kernel coercivity for the Reissner-Mindlin problem. [less ▲] Detailed reference viewed: 62 (7 UL) |
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