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Zu den Einflüssen der klimatischen Umgebungsbedingungen auf die Eigenschaften eines selbstverdichtenden Betons Weisheit, Sandro Doctoral thesis (2010) Detailed reference viewed: 58 (1 UL)Alleviating the Mesh Burden in Computational Solid Mechanics Bordas, Stéphane ; ; et al in Proceedings of ECT2010 (2010, December 12) The goal of this chapter is to review recent avenues of investigation to alleviate meshing difficulties in computational mechanics and give a few exemplar applications. Keywords: meshing; enrichment ... [more ▼] The goal of this chapter is to review recent avenues of investigation to alleviate meshing difficulties in computational mechanics and give a few exemplar applications. Keywords: meshing; enrichment; meshfree methods; extended finite element methods; isogeometric analysis; advanced remeshing techniques. [less ▲] Detailed reference viewed: 393 (3 UL)Condition assessment of concrete structures and bridges using vibration monitoring in comparison to changes in their static properties Bungard, Volker Doctoral thesis (2010) The thesis deals with the non-destructive condition assessment of civil engineering structures made of reinforced and prestressed concrete as well as bridges and concentrates on a comparison of static and ... [more ▼] The thesis deals with the non-destructive condition assessment of civil engineering structures made of reinforced and prestressed concrete as well as bridges and concentrates on a comparison of static and dynamic investigation methods. The main questions discuss the sensitivity of changes in static as well as in dynamic properties during the mechanical lifetime of those types of structures under laboratory conditions, the sensitivity of these changes when testing in-situ and the dimension of undesired environmental influences on the dynamic properties. Therefore, a gradually loaded laboratory reinforced concrete beam (cp. chapter 7) and a reinforced as well as a prestressed concrete slab (cp. chapter 8) are investigated for changes in their static and dynamic parameters until reaching their ultimate loads. Furthermore, a successively damaged and stepwise loaded laboratory reinforced concrete slab and a prestressed concrete slab (cp. also chapter 8) are under investigation and also compared in changes in their static as well as in dynamic properties during their lifetimes. By means of static and dynamic tests on a successively damaged and stepwise loaded prestressed concrete bridge (cp. chapter 9) it was possible to investigate the amount of changes in static and dynamic properties for a real in-situ object. A long-term measurement of a composite bridge (cp. chapter 10) demonstrates the environmental influences on the static and dynamic properties of a system which have to be considered when conducting comparative non-destructive condition assessment techniques on real objects. All tests are calculated respectively simulated by the method of the integration of stress (cp. chapter 6) or the finite element method by using the softwares ANSYS and SOFISTIK. Furthermore, measured eigenfrequencies and modeshapes are used to adapt finite element models with the aim to improve the model or to locate and quantify damaged areas. The work is a contribution to the application of non-destructive static and dynamic condition assessment methods on civil engineering structures made of concrete in the sector of civil engineering. [less ▲] Detailed reference viewed: 157 (13 UL)An adaptive high-gain observer for nonlinear systems Boizot, Nicolas ; ; in Automatica (2010), 46(9), 1483-1488 In this paper the authors provide a solution to the noise sensitivity of high-gain observers. The resulting nonlinear observer possesses simultaneously 1) extended Kalman filter's good noise filtering ... [more ▼] In this paper the authors provide a solution to the noise sensitivity of high-gain observers. The resulting nonlinear observer possesses simultaneously 1) extended Kalman filter's good noise filtering properties, and 2) the reactivity of the high-gain extended Kalman filter with respect to large perturbations. The authors introduce innovation as the quantity that drives the gain adaptation. They prove a general convergence result, propose guidelines to practical implementation and show simulation results for an example. [less ▲] Detailed reference viewed: 124 (1 UL)A Comparison of Semantic Models for Noninterference ; Zhang, Chenyi 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 ▲] Detailed reference viewed: 73 (0 UL)Numerical Solution of Non-Isothermal Fluid Flows Using Local Radial Basis Functions (LRBF) Interpolation and a Velocity-Correction Method Bourantas, Georgios ; ; et al in Computer Modeling in Engineering & Sciences (2010), 64(2), 187-212 Meshfree point collocation method (MPCM) is developed, solving the velocity-vorticity formulation of Navier-Stokes equations, for two-dimensional, steady state incompressible viscous flow problems in the ... [more ▼] Meshfree point collocation method (MPCM) is developed, solving the velocity-vorticity formulation of Navier-Stokes equations, for two-dimensional, steady state incompressible viscous flow problems in the presence of heat transfer. Particular emphasis is placed on the application of the velocity-correction method, ensuring the continuity equation. The Gaussian Radial Basis Functions (GRBF) interpolation is employed to construct the shape functions in conjunction with the framework of the point collocation method. The cases of forced, natural and mixed convection in a 2D rectangular enclosure are examined. The accuracy and the sta- bility of the proposed scheme are demonstrated through three representative, well known and established benchmark problems. Results are presented for high values of the characteristics non-dimensional numbers of the flow, that is, the Reynolds, the Rayleigh and the Richardson number [less ▲] Detailed reference viewed: 72 (0 UL)Analysis and modelling of the noise generation during vibratory pile driving and determination of the optimization potential Hanus, Vincent Doctoral thesis (2010) Impact driving, pressing and vibrodriving are the three main methods to drive sheet piles. The sound level generated during vibrodriving varies almost between the very high level of an impact driving and ... [more ▼] Impact driving, pressing and vibrodriving are the three main methods to drive sheet piles. The sound level generated during vibrodriving varies almost between the very high level of an impact driving and the lowest sound level of a pressing. In the first part of this doctoral thesis, sound measurements feasibility is thoroughly studied. Particular attention is paid to the measurement conditions on construction sites and to the measurement methods (sound power level, beamforming and thermography). These methods are outlined and the provided results are compared. In addition, the different causes of noise are analysed and the influence of various parameters is quantified. In the second part, the acceleration measurements of the full-scale experiments are used to calibrate a Finite Element model. A parametric study analyses how the most important mechanical parameters influence the noise level. This research has shown that a decrease of the noise generation on construction sites can be obtained by two ways: by recommendations for installation of sheet piles at the construction site, and by requirement of constructive measures that significantly reduce the noise level. [less ▲] Detailed reference viewed: 97 (11 UL)Compatibilités et incompatibilités liants cimentaires / superplastifiants Nicolas, Edwige 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 ▲] Detailed reference viewed: 102 (4 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: 68 (4 UL)Sustainability of biomass resources for the use in decentralized biomass energy systems Konig, Stefan Doctoral thesis (2010) Detailed reference viewed: 36 (2 UL)An agenda for establishing the Ecological Footprint as communication instrument and indicator for sustainable development in small countries: Case study Luxembourg Hild, Paula ; ; et al Poster (2010, June) The Ecological Footprint methodology proposed by the Global Footprint Network (GFN) seems to be not entirely appropriate for small countries with less than one million inhabitants [Ewing et al., 2008 ... [more ▼] The Ecological Footprint methodology proposed by the Global Footprint Network (GFN) seems to be not entirely appropriate for small countries with less than one million inhabitants [Ewing et al., 2008]. This may be a reason why e.g. results for Luxembourg, a country with 470,000 inhabitants, have never been included into official country Footprint comparisons. Therefore, the methodology needs to be adapted to be used for communication purpose in Luxembourg. This contribution presents Luxembourg’s approach for illustrating the national consumption impacts to finally discuss the integration of the Ecological Footprint as an indicator for sustainable development in the national indicator system. [less ▲] Detailed reference viewed: 73 (1 UL)A cost-effective atomic force microscope for undergraduate control laboratories ; Goncalves, Jorge in IEEE Transactions on Education (2010), 53(2), 328-334 This paper presents a simple, cost-effective and robust atomic force microscope (AFM), which has been purposely designed and built for use as a teaching aid in undergraduate controls labs. The guiding ... [more ▼] This paper presents a simple, cost-effective and robust atomic force microscope (AFM), which has been purposely designed and built for use as a teaching aid in undergraduate controls labs. The guiding design principle is to have all components be open and visible to the students, so the inner functioning of the microscope has been made clear to see. All of the parts but one are off the shelf, and assembly time is generally less than two days, which makes the microscope a robust instrument that is readily handled by the students with little chance of damage. While the scanning resolution is nowhere near that of a commercial instrument, it is more than sufficient to take interesting scans of micrometer-scale objects. A survey of students after their having used the AFM resulted in a generally good response, with 80% agreeing that they had a positive learning experience. [less ▲] Detailed reference viewed: 131 (0 UL)Adaptive high-gain extended kalman filter and applications Boizot, Nicolas Doctoral thesis (2010) The work concerns the ``observability problem” --- the reconstruction of a dynamic process's full state from a partially measured state--- for nonlinear dynamic systems. The Extended Kalman Filter (EKF ... [more ▼] The work concerns the ``observability problem” --- the reconstruction of a dynamic process's full state from a partially measured state--- for nonlinear dynamic systems. The Extended Kalman Filter (EKF) is a widely-used observer for such nonlinear systems. However it suffers from a lack of theoretical justifications and displays poor performance when the estimated state is far from the real state, e.g. due to large perturbations, a poor initial state estimate, etc… We propose a solution to these problems, the Adaptive High-Gain (EKF). Observability theory reveals the existence of special representations characterizing nonlinear systems having the observability property. Such representations are called observability normal forms. A EKF variant based on the usage of a single scalar parameter, combined with an observability normal form, leads to an observer, the High-Gain EKF, with improved performance when the estimated state is far from the actual state. Its convergence for any initial estimated state is proven. Unfortunately, and contrary to the EKF, this latter observer is very sensitive to measurement noise. Our observer combines the behaviors of the EKF and of the high-gain EKF. Our aim is to take advantage of both efficiency with respect to noise smoothing and reactivity to large estimation errors. In order to achieve this, the parameter that is the heart of the high-gain technique is made adaptive. \textit{Voila}, the Adaptive High-Gain EKF. A measure of the quality of the estimation is needed in order to drive the adaptation. We propose such an index and prove the relevance of its usage. We provide a proof of convergence for the resulting observer, and the final algorithm is demonstrated via both simulations and a real-time implementation. Finally, extensions to multiple output and to continuous-discrete systems are given. [less ▲] Detailed reference viewed: 107 (9 UL)Meshfree Point Collocation Schemes for 2D Steady State Incompressible Navier-Stokes Equations in Velocity-Vorticity Formulation for High Values of Reynolds Number Bourantas, Georgios ; ; et al in Computer Modeling in Engineering & Sciences (2010), 59(1), 31-63 A meshfree point collocation method has been developed for the velocity- vorticity formulation of two-dimensional, steady state incompressible Navier-Stokes equations. Particular emphasis was placed on ... [more ▼] A meshfree point collocation method has been developed for the velocity- vorticity formulation of two-dimensional, steady state incompressible Navier-Stokes equations. Particular emphasis was placed on the application of the velocity-correc- tion method, ensuring the continuity equation. The Moving Least Squares (MLS) approximation is employed for the construction of the shape functions, in conjunc- tion with the general framework of the point collocation method. Computations are obtained for regular and irregular nodal distributions, stressing the positivity con- ditions that make the matrix of the system stable and convergent. The accuracy and the stability of the proposed scheme are demonstrated through two representative, well-known, and established benchmark problems. The numerical scheme was also applied to a case with irregular geometry for marginally high Reynolds numbers [less ▲] Detailed reference viewed: 128 (7 UL)LINEAR BUCKLING ANALYSIS OF CRACKED ISOTROPIC PLATES USING THE EXTENDED FINITE ELEMENT METHOD ; ; et al Scientific Conference (2010, March) The behaviour of plate structures under compressive loads has been of great concern for engineering applications, especially in aeronautical and aerospace structures in which the demanding design of ... [more ▼] The behaviour of plate structures under compressive loads has been of great concern for engineering applications, especially in aeronautical and aerospace structures in which the demanding design of weight critical applications usually leads to stability problems. In this paper, the linear buckling problem of cracked isotropic plates is studied using the extended finite element method (XFEM). The mixed interpolation technique of the well-established MITC4 quadrilateral finite element with 12 standard degrees of freedom per element is used. The critical buckling load and mode shapes of simply supported square plates are computed as a function of crack length. [less ▲] Detailed reference viewed: 199 (0 UL)An internal version of epistemic logic Aucher, Guillaume in Studia Logica (2010), 94(1), 1-22 Representing an epistemic situation involving several agents obviously depends on the modeling point of view one takes. We start by identifying the types of modeling points of view which are logically ... [more ▼] Representing an epistemic situation involving several agents obviously depends on the modeling point of view one takes. We start by identifying the types of modeling points of view which are logically possible. We call the one traditionally followed by epistemic logic the perfect external approach, because there the modeler is assumed to be an omniscient and external observer of the epistemic situation. In the rest of the paper we focus on what we call the internal approach, where the modeler is one of the agents involved in the situation. For this approach we propose and axiomatize a logical formalism based on epistemic logic. This leads us to formalize some intuitions about the internal approach and about its connections with the external ones. Finally, we show that our internal logic is decidable and PSPACE-complete. [less ▲] Detailed reference viewed: 67 (0 UL)Robust Traffic Anomaly Detection with Principal Component Pursuit ; ; Wang, Wei et al in Proceedings of the ACM CoNEXT Student Workshop (2010) Principal component analysis (PCA) is a statistical technique that has been used for data analysis and dimensionality reduction. It was introduced as a network traffic anomaly detection technique firstly ... [more ▼] Principal component analysis (PCA) is a statistical technique that has been used for data analysis and dimensionality reduction. It was introduced as a network traffic anomaly detection technique firstly in [1]. Since then, a lot of research attention has been received, which results in an extensive analysis and several extensions. In [2], the sensitivity of PCA to its tuning parameters, such as the dimension of the low-rank subspace and the detection threshold, on traffic anomaly detection was indicated. However, no explanation on the underlying reasons of the problem was given in [2]. In [3], further investigation on the PCA sensitivity was conducted and it was found that the PCA sensitivity comes from the inability of PCA to detect temporal correlations. Based on this finding, an extension of PCA to Kalman-Loeve expansion (KLE) was proposed in [3]. While KLE shows slight improvement, it still exhibits similar sensitivity issue since a new tuning parameter called temporal correlation range was introduced. Recently, in [4], additional effort was paid to illustrate the PCA-poisoning problem. To underline this problem, an evading strategy called Boiled-Frog was proposed which adds a high fraction of outliers to the traffic. To defend against this, the authors employed a more robust version of PCA called PCA-GRID. While PCA-GRID shows performance improvement regarding the robustness to the outliers, it experiences a high sensitivity to the threshold estimate and the k-dimensional subspace that maximizes the dispersion of the data. The purpose of this work is to consider another technique to address the PCA poisoning problems to provide robust traffic anomaly detection: The Principal Component Pursuit. [less ▲] Detailed reference viewed: 97 (1 UL)FM Discriminator for AIS Satellite Detection Jurado Gallardo, Maria De Los Angeles ; in Personal Satellite Services (2010) The Automatic Identification System (AIS) is a tracking system used on ships for several decades to improve traffic monitoring and safety at sea in a short range. The modulation technique used is Gaussian ... [more ▼] The Automatic Identification System (AIS) is a tracking system used on ships for several decades to improve traffic monitoring and safety at sea in a short range. The modulation technique used is Gaussian Minimum Shift Keying (GMSK). Recently, the idea of receiving AIS signals from space arose. This presents mainly two challenges. The first one is that received signals present a large Doppler range due to the satellite speed. The second one is the simultaneous reception of signals from ships because of the broad satellite coverage. In this paper, a novel non-coherent GMSK demodulator is proposed to handle the large Doppler shift problem based on several FM discriminators in parallel. A frame collision detection algorithm is presented but the collision problem is not addressed. In addition, computer simulated and real signals are used to study the receiver performance on an AWGN channel. [less ▲] Detailed reference viewed: 174 (0 UL)Entwicklungsmethodik nach Pahl und Beitz und Design thinking. Vergleich und Einordnung Gericke, Kilian ; ; et al in Proceedings of 19th Symposium Design for X (2010) Die Konstruktionsforschung strebt danach die Entwicklungspraxis zu unterstützen indem Methodiken, Methoden, Tools und Empfehlungen erarbeitet werden, welche die Arbeit der Entwickler erleichtern sollen ... [more ▼] Die Konstruktionsforschung strebt danach die Entwicklungspraxis zu unterstützen indem Methodiken, Methoden, Tools und Empfehlungen erarbeitet werden, welche die Arbeit der Entwickler erleichtern sollen, mit dem Ziel bessere Produkte zu entwickeln. Das Umfeld der Entwicklungspraxis ist dabei gekennzeichnet durch Komplexität, Wettbewerb auf globalen Märkten, Dynamik und sich ständig ändernden Kundenwünschen und -bedürfnissen. Die daraus erwachsenden Herausforderungen nehmen fortlaufend zu und tangieren alle Entwicklungsprozesse unabhängig davon ob eine Maschine, eine Software, ein Service oder ein andere Produktform entwickelt wird. Neben den genannten Aspekten stellt auch das veränderte Konsumentenverhalten eine Herausforderung für die Produktentwicklung dar. Das Internet ermöglicht eine nie dagewesene Auswahl- und Vergleichsmöglichkeit von Produkten, wodurch wesentlich selektiver konsumiert wird und infolge dessen Produkte immer differenzierter und tärker an die Kundenwünsche und –bedürfnisse angepasst werden müssen. Abhängig von Entwicklungsgegenstand, Marktsegment, Branche und weiteren Faktoren sind die existierenden methodischen Hilfsmittel unterschiedlich gut geeignet, die Arbeit des Entwicklers zu erleichtern und die Entwicklung besserer Produkte zu unterstützen. Dies bedeutet, dass methodische Ansätze Kontext-abhängig ausgewählt bzw. adaptiert werden müssen. In jüngster Zeit hält Design Thinking, ein neuer Ansatz zur methodischen Produktentwicklung, Einzug in verschiedenste Branchen. Im nachfolgenden Artikel wird Design Thinking kurz beschrieben und exemplarisch mit dem methodischen Vorgehen nach Pahl und Beitz verglichen. Der Vergleich beinhaltet den Prozessumfang (welche Phasen des Entwicklungsprozesses werden abgebildet) und ausgewählte Kontext-Aspekte (für welche Art von Entwicklungsvorhaben ist der Ansatz anwendbar). Anhand dieser Aspekte wird diskutiert, welche wesentlichen Unterschiede zwischen den Ansätzen bestehen, wo Überschneidungen existieren und welches Potential die Kombination beider Ansätze in sich birgt. [less ▲] Detailed reference viewed: 189 (1 UL)PANEL: Position-based Aggregator Node Election in Wireless Sensor Networks ; Schaffer, Peter in International Journal of Distributed Sensor Networks (2010), 2010 We introduce PANEL a position-based aggregator node election protocol for wireless sensor networks. The novelty of PANEL with respect to other aggregator node election protocols is that it supports ... [more ▼] We introduce PANEL a position-based aggregator node election protocol for wireless sensor networks. The novelty of PANEL with respect to other aggregator node election protocols is that it supports asynchronous sensor network applications where the sensor readings are fetched by the base stations after some delay. In particular, the motivation for the design of PANEL was to support reliable and persistent data storage applications, such as TinyPEDS; see the study by Girao et al. (2007). PANEL ensures load balancing, and it supports intra and intercluster routing allowing sensor-to-aggregator, aggregator-to-aggregator, base station-to-aggregator, and aggregator to-base station communications. We also compare PANEL with HEED; see the study by Younis and Fahmy (2004) in the simulation environment provided by TOSSIM, and show that, on one hand, PANEL creates more cohesive clusters than HEED, and, on the other hand, that PANEL is more energy efficient than HEED. [less ▲] Detailed reference viewed: 185 (0 UL) |
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