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See detailCombining demand management and merge control in an equilibrium network model
Viti, Francesco UL; Huang, Wei; Smith, Mike J.

Scientific Conference (2013)

Equilibrium models under congested traffic conditions, and especially those addressing blocking back, are very useful to estimate the demand conditions that ITS policies should be able to manage, for ... [more ▼]

Equilibrium models under congested traffic conditions, and especially those addressing blocking back, are very useful to estimate the demand conditions that ITS policies should be able to manage, for instance to maintain congestion within controlled areas and avoiding that they further spillback and cause more serious and/or less controllable congestion states. The objective of this paper is to supplement the equilibrium model, developed by the authors in recent research, with a more thorough analysis of merge behaviour, especially in cases of blocked nodes. Regulating the merger behaviour together with the demand pattern can lead to certain desired stationary states. It has a great practical significance when congestion is inevitable, while demand management and merge control are able to retain queues and spill-backs within the local area. [less ▲]

Detailed reference viewed: 132 (2 UL)
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See detailA comparative study of task assignment and path planning methods for multi-UGV missions
Thunberg, Johan UL; Anisi, D.; Ögren, P.

in Optimization and Cooperative Control Strategies (2009)

Many important problems involving a group of unmanned ground vehicles (UGVs) are closely related to the multi traviling salesman problem (m-TSP). This paper comprises a comparative study of a number of ... [more ▼]

Many important problems involving a group of unmanned ground vehicles (UGVs) are closely related to the multi traviling salesman problem (m-TSP). This paper comprises a comparative study of a number of algorithms proposed in the litterature to solve m-TSPs occuring in robotics. The investigated algoritms include two mixed integer linear programming (MILP) formulations, a market based approach (MA), a Voronoi partition step (VP) combined with the local search used in MA, and a deterministic and a stocastic version of the granular tabu search (GTS). To evaluate the algoritms, an m-TSP is derived from a planar environment with polygonal obstacles and uniformly distributed targets and vehicle positions. The results of the comparison indicate that out of the decentralized approaches, the MA yield good solutions but requires long computation times, while VP is fast but not as good. The two MILP approaches suffer from long computation times, and poor results due to the decomposition of the assignment and path planning steps. Finally, the two GTS algorithms yield good results in short times with inputs from MA as well as the much faster VP. Thus the best performing centralized approach is the GTS in combination with the VP. [less ▲]

Detailed reference viewed: 86 (0 UL)
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See detailA comparison between conventional Earth Observation Satellites and CubeSats; Requirements, Capabilities and Data Quality
Backes, Dietmar UL; Hassani, Saif Alislam UL; Teferle, Felix Norman UL et al

Scientific Conference (2019, September 11)

From its early beginning as an educational tool in 1999, cubesats have evolved into a popular platform for technology demonstrations and scientific instruments. Ideas and innovations sparked from an ... [more ▼]

From its early beginning as an educational tool in 1999, cubesats have evolved into a popular platform for technology demonstrations and scientific instruments. Ideas and innovations sparked from an enthusiastic community led to the development of new Earth Observation (EO) technology concepts based on large constellations of satellites with high-resolution optical imagers previously considered as infeasible. Probably the most significant constellation today is deployed by Planet who are currently operating a fleet larger than 120 3U Dove satellites, which provide an imaging service with up to 3m Ground Sample Distance (GSD). The number of low-cost EO Cubesat systems is constantly increasing. However, for a number of reasons there still seems to be a reluctance to use such data for many EO applications. A better understanding of the capabilities of the current generation of small Cubesats compared to the traditional well-established bigger operational missions of high and medium resolution EO satellites is required. What are the critical capabilities and quality indicators? Due to the limited size and weight of Cubesats, critical system components, e.g. for navigation and communication, always compete with operational payloads such as optical camera/sensor systems. A functional EO system requires balanced payload, which provides adequate navigational capabilities, that match the requirements of the optical imagers (camera) deployed with the system. This study reviews the current performance and capabilities of Cubesats for optical EO and compares them to the capabilities of conventional, dedicated high and medium resolution EO systems. We summarise key performance parameters and quality indicators to evaluate the difference between the systems. An empirical study compares recent very high-resolution (VHR) imagery from big EO satellite missions with available images from Cubesats for the use case in disaster monitoring. Small and agile Nanosatellites or Cubesats already show remarkable performance. Although it is not expected that their performance and capability will match those of current bigger EO satellite missions, they are expected to provide a valuable tool for EO and remote sensing, in particular for downstream industry applications. [less ▲]

Detailed reference viewed: 301 (47 UL)
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See detailComparison of Machine Learning techniques for atmospheric pollutant monitoring in a Kraft pulp mill
Sainlez, Matthieu UL; Heyen, Georges

Scientific Conference (2011, November)

In this paper, machine learning techniques are compared to predict nitrogen oxide (NOx) pollutant emission from the recovery boiler of a Kraft pulp mill. Starting from a large database of raw process data ... [more ▼]

In this paper, machine learning techniques are compared to predict nitrogen oxide (NOx) pollutant emission from the recovery boiler of a Kraft pulp mill. Starting from a large database of raw process data related to a Kraft recovery boiler, we consider a regression problem in which we are trying to predict the value of a continuous variable. Generalization is done on the worst case configuration possible to make sure the model is adequate: the training period concerns stationary operations while test periods mainly focus on NOx emissions during transient operations. This comparison involves neural network techniques (i.e., static multilayer perceptron and dynamic NARX network), tree-based methods and multiple linear regression. We illustrate the potential of a dynamic neural approach compared to the others in this prediction task. [less ▲]

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See detailComparison of metadata quality in open data portals using the Analytic Hierarchy Process
Kubler, sylvain; Robert, Jérémy UL; Neumaier, Sebastian et al

in Government Information Quarterly (2018)

Detailed reference viewed: 131 (3 UL)
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See detailA Comparison of Network Reconstruction Methods for Chemical Reaction Networks
Ward, C.; Yeung, E.; Brown, T. et al

in The proceedings of the Third International Conference on Foundations of Systems Biology in Engineering (FOSBE 2009) (2009)

Chemical reaction networks model biological interactions that regulate the functional properties of a cell; these networks characterize the chemical pathways that result in a particular phenotype. One ... [more ▼]

Chemical reaction networks model biological interactions that regulate the functional properties of a cell; these networks characterize the chemical pathways that result in a particular phenotype. One goal of systems biology is to understand the structure of these networks given concentration measurements of various species in the system. Previous work has shown that this network reconstruction problem is fundamentally impossible, even for simplified linear models, unless a particular experiment design is followed. Nevertheless, reconstruction algorithms have been developed that attempt to approximate a solution using sparsity or similar heuristics. This work compares, in silico, the results of three of these methods in situations where the necessary experiment design has been followed, and it illustrates the degradation of each method as increasing noise levels are added to the data. [less ▲]

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See detailComparison of recently developed recovery type discretization error estimators for the extended finite element method
Ródenas, J. J.; Duflot, Marc; Bordas, Stéphane UL et al

in Schrefler, B A; Perego, U (Eds.) 8th World Congress on Computational Mechanics (WCCM8). 5th.European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2008) (2008)

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See detailA Comparison of Semantic Models for Noninterference
van der Meyden, R.; Zhang, Chenyi UL

in Theoretical Computer Science (2010), 411(47), 41234147

The literature on definitions of security based on causality-like notions such as noninterference has used several distinct semantic models for systems. Early work was based on state machine and trace-set ... [more ▼]

The literature on definitions of security based on causality-like notions such as noninterference has used several distinct semantic models for systems. Early work was based on state machine and trace-set definitions; more recent work has dealt with definitions of security in two distinct process algebraic settings. Comparisons between the definitions has been carried out mainly within semantic frameworks. This paper studies the relationship between semantic frameworks, by defining mappings between a number of semantic models and studying the relationship between notions of noninterference under these mappings. [less ▲]

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See detailComparison of Several RANS Modelling for the Pavia TRIGA Mark II Research Reactor
Introini, Carolina; Baroli, Davide UL; Peters, Bernhard UL

Poster (2017)

In this study, a detailed analysis of the turbulent regime within the core of the Pavia TRIGA Mark II reactor is perfomed by means of an in-depth comparison of the RAS (Reynolds-Averaged Simulation ... [more ▼]

In this study, a detailed analysis of the turbulent regime within the core of the Pavia TRIGA Mark II reactor is perfomed by means of an in-depth comparison of the RAS (Reynolds-Averaged Simulation) turbulence models implemented in OpenFOAM. Aim of this analysis is to give some important information with respect to the flow regime within the core. The performance of the various models is tested against a LES (Large Eddy Simulation) of the innermost channel. [less ▲]

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See detailComparison of Several RANS Modelling for the Pavia TRIGA Mark II Research Reactor
Introini, Carolina; Cammi, Antonio; Lorenzi, Stefano et al

in Journal of Nuclear Engineering and Radiation Science (2018)

Aim of this work is the comparison of different turbulent models based on the Reynolds Averaged Navier-Stokes (RANS) equations in order to find out which model is the most suitable for the study of the ... [more ▼]

Aim of this work is the comparison of different turbulent models based on the Reynolds Averaged Navier-Stokes (RANS) equations in order to find out which model is the most suitable for the study of the channel thermal-hydraulics of the TRIGA Mark II reactor. Only the steady state behaviour (i.e. the full power stationary operational conditions) of the reactor has been considered. To this end, the RAS (Reynolds-Averaged Simulation) models available in the open source CFD software OpenFOAM have been applied to the most internal channel of the TRIGA and assessed against a Large Eddy Simulation (LES) model. The results of the latter approach, expressed in terms of axial velocity, turbulent viscosity, turbulent kinetic energy, and temperature have been compared with the results obtained by the RAS models available in OpenFOAM (k − ε, k − ω and Reynolds Stress Transport). Heat transfer is taken into account as well by means of the turbulent energy diffusivity parameter. The simulation results demonstrate how, amongst the RAS models, the k − ω SST is the one whose results are closer to the LES simulation. This model seems to be the best one for the treatment of turbulent flow within the TRIGA subchannel, offering a good compromise between accuracy and computational requirements. Since it is much less expensive than an LES model, it can be applied even to full core calculation, in order to obtain accurate results with less computational effort. [less ▲]

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See detailA comparison of two meso-models for dry-woven fabrics and their multiscale equivalents
Beex, Lars UL; Duflot, Marc; Adam, Laurent

Scientific Conference (2016, April)

In this presentation, an X-braced spring mesomodel will be compared to a mesomodel in which the diagonal springs are replaced by rotational springs. The results are signi cantly di fferent, but some ... [more ▼]

In this presentation, an X-braced spring mesomodel will be compared to a mesomodel in which the diagonal springs are replaced by rotational springs. The results are signi cantly di fferent, but some disadvantages of the use of rotational springs will also be mentioned. A substantial part of the presentation will furthermore be dedicated to the multiscale quasicontinuum method to upscale the mesomodels in order to achieve e fficient macroscale computations. macroscale computations [less ▲]

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See detailComparisons of design methodologies and process models across disciplines: A literature review
Gericke, Kilian UL; Blessing, Lucienne UL

in Proceedings of the 18th International Conference on Engineering Design (2011)

Challenges resulting from an environment characterised by complexity, competition on global markets, dynamics and ever-changing user wants and needs are increasing and affect all design processes ... [more ▼]

Challenges resulting from an environment characterised by complexity, competition on global markets, dynamics and ever-changing user wants and needs are increasing and affect all design processes, irrespective of whether the product or system designed is a machine, a building, software, service, etc.. These challenges require collaboration between disciplines, but current design processes of large systems, such as aircraft, essentially show separate development strands for each discipline. Research into methods is ongoing, but the original design methodologies have not been adapted accordingly. Based on a literature study this paper consolidates findings from different comparisons of design methodologies and process models across disciplines. A consensus can be found that at least on an abstract level design process models have a generic core of common stages. On a detailed level the picture is different. The extent to which design approaches appear similar depends on the perspective of the analyses. The literature study provides an overview of shortcomings of existing design methodologies which may serve as starting points for further research and development of design methodologies. [less ▲]

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See detailCompatibilités et incompatibilités liants cimentaires / superplastifiants
Nicolas, Edwige UL

Doctoral thesis (2010)

Currently required concrete strength imposes a lower water/cement ratio and use of superplasticizer to make easier the fresh material implementation. Polycarboxylate type products are very effective in ... [more ▼]

Currently required concrete strength imposes a lower water/cement ratio and use of superplasticizer to make easier the fresh material implementation. Polycarboxylate type products are very effective in the short term but can lead to a fast loss of workability in case of binder/superplasticizer incompatibility. The object of this work is the identification of cementitous phases involved in these rheological variations. Initially, flow of various superplasticized pastes is evaluated by a rheometer fitted with a ball measuring system. Compatible combinations flow like a Bingham’s fluid. An incompatibility results in an increase of yield stress and plastic viscosity or rheological properties evolution into Herschel-Bulkley’s fluid. Then, cement/superplasticizer combinations are characterized by rheological tests. Stiffening assessment of pastes and chemical characterisation of hydrated cements show that consistency is associated with amount and microstructure of formed ettringite. These parameters depend on initially present aluminate phase and calcium sulphates. Finally, study of synthetic cementitous systems states that calcium sulphates solubility, in presence of superplasticizer, is increased probably because Ca2+ ions complexation by polycarboxylates. As for the orthorhombic variety of aluminate phase, more reactive than cubic variety, it leads to a large amount of needle-shaped ettringite. [less ▲]

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See detailComplex Networks in Manufacturing - Suitability and Interpretation
Omar, Yamila UL

Doctoral thesis (2021)

The fourth industrial revolution, and the associated digitization of the manufacturing industry, has resulted in increased data generation. Industry leaders aim to leverage this data to enhance ... [more ▼]

The fourth industrial revolution, and the associated digitization of the manufacturing industry, has resulted in increased data generation. Industry leaders aim to leverage this data to enhance productivity, boost innovation and generate new manners of competition. In this work, out of the many domains within the manufacturing sector, production will be explored. To this end, the mathematical tools of network science are utilized to characterize and evaluate production networks in terms of complex networks. In a manufacturing complex network, nodes represent workstations, and directed edges abstract the material flow that occurs among pairs of workstations. These types of complex networks are known as "material flow networks" and are used to study issues associated with manufacturing systems in the domain of production at the intra-enterprise level. While some research on the subject exists, this work will demonstrate that the use of complex networks to describe and evaluate manufacturing systems constitutes a nascent research field. In fact, the limited existing literature tackles a vast number of issues raising more questions than providing answers. This work aims to answer a number of those open questions. Firstly, which complex network metrics are suitable in the context of manufacturing networks will be determined. As a consequence, unsuitable metrics will be identified as well. To accomplish this, the flow underlying assumptions of popular complex network metrics is studied and compared to those of manufacturing networks. Furthermore, other existing complex network metrics with more appropriate underlying assumptions, but not yet explored in the context of manufacturing, are proposed and evaluated. Then, the appropriate interpretation of suitable complex network metrics in terms of Operations Research is provided. Finally, shortcomings of these metrics are highlighted to caution practitioners regarding their use in industrial settings. [less ▲]

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See detailComputational heuristics for simplifying a biological model
Petre, Ion; Mizera, Andrzej UL; Back, Ralph-Johan

in Lecture Notes in Computer Science (2009), 5635

Detailed reference viewed: 167 (0 UL)
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See detailA computational library for multiscale modeling of material failure
Talebi, H.; Silani, M.; Bordas, Stéphane UL et al

in Computational Mechanics (2013)

We present an open-source software framework called PERMIX for multiscale modeling and simulation of fracture in solids. The framework is an object oriented open-source effort written primarily in Fortran ... [more ▼]

We present an open-source software framework called PERMIX for multiscale modeling and simulation of fracture in solids. The framework is an object oriented open-source effort written primarily in Fortran 2003 standard with Fortran/C++ interfaces to a number of other libraries such as LAMMPS, ABAQUS, LS-DYNA and GMSH. Fracture on the continuum level is modeled by the extended finite element method (XFEM). Using several novel or state of the art methods, the piece software handles semi-concurrent multiscale methods as well as concurrent multiscale methods for fracture, coupling two continuum domains or atomistic domains to continuum domains, respectively. The efficiency of our open-source software is shown through several simulations including a 3D crack modeling in clay nanocomposites, a semi-concurrent FE-FE coupling, a 3D Arlequin multiscale example and an MD-XFEM coupling for dynamic crack propagation. © 2013 Springer-Verlag Berlin Heidelberg. [less ▲]

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See detailComputational Mechanics Lab Report 2013-2014
Bordas, Stéphane UL

Report (2015)

This is the report of the Computational Mechanics Lab led by Prof. Stéphane Bordas

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See detailComputational mechanics of interfaces
Bordas, Stéphane UL

Presentation (2016, May 22)

The course will present an overview of recent developments, which will enable students to make informed choices in terms of discretization and model selection in solving numerical problems in mechanics ... [more ▼]

The course will present an overview of recent developments, which will enable students to make informed choices in terms of discretization and model selection in solving numerical problems in mechanics. We will cover discretization strategies ranging from the standard finite element method, the smoothed finite element method, the extended finite element method, polygonal and virtual element methods, meshfree methods. The applications range between fracture of heterogeneous materials and biomedical simulations. The intended learning outcomes of the course are such that the students will be: - able to critically assess discretization schemes in mechanics - able to implement simple error estimators for finite element methods - familiar with basic multi-scale methods for fracture and their limitations - able to follow basic literature in model error and model selection, in particular based on Bayesian inference Course participants will learn these topics through lectures and hands-on numerical experiments. [less ▲]

Detailed reference viewed: 414 (16 UL)