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See detailNumerical competencies of young children
Wantz, Marc UL; Martin, Romain UL; Schiltz, Christine UL

Scientific Conference (2007)

Numerous studies show that wide ranges of competencies in different fields are necessary to develop a good numerical competency. Our research tried to find an answer to the question, which out of various ... [more ▼]

Numerous studies show that wide ranges of competencies in different fields are necessary to develop a good numerical competency. Our research tried to find an answer to the question, which out of various factors mainly influence the numerical competencies of young children. We focused on visuospatial, perceptive and tactile skills as determinants of the quality of early numerical representations. We adopted a longitudinal research design with three periods of data collection (two data collections during the second year of kindergarten and one at the end of first grade). Our test setting for the kindergarten included tests in the three areas mentioned above. The evaluation of these results shows that the numerical competencies are influenced by visuospatial competencies and knowledge of pre-numerical facts. An importance of the perceptive and tactile skills could not be established. At the end of first grade, after formal mathematical instruction, we made a mathematical competency test. A structural equation model of the subtests shows that the numerical knowledge at this stage can be divided in two separate factors: 1. A representational numerical factor (analogical representation of quantities: Triple Code model of Dehaene) 2. A more formal knowledge of mathematics (visual Arabic representation: Triple Code model of Dehaene, 1992). Predicting these two factors from the competency profile measured in kindergarten showed that the representational numerical factor was very well predicted from a general spatio-numerical factor found in the previous year, while the formal knowledge was predicted to a lesser degree by tactile skills measured at the end of kindergarten. Implications for numerical teaching in Kindergarten will be discussed. [less ▲]

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See detailNumerical determination and experimental verification of the optimum autofrettage pressure for a complex aluminium high-pressure valve to foster crack closure
Repplinger, Christian UL; Sellen, Stephan; Kedziora, Slawomir UL et al

in Fatigue and Fracture of Engineering Materials and Structures (2020)

Detailed reference viewed: 56 (12 UL)
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See detailNumerical error for SDE: asymptotic expansion and hyperdistributions
Malliavin, Paul; Thalmaier, Anton UL

in Comptes Rendus. Mathématique (2003), 336(10), 851-856

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See detailNumerical evaluation of buckling behaviour induced by compression on patch-repaired composites
Deng, Jian; Zhou, Guangming; Bordas, Stéphane UL et al

in Composite Structures (2017), 168

A progressive damage model is proposed to predict buckling strengths and failure mechanisms for both symmetric and asymmetric patch repaired carbon-fibre reinforced laminates subjected to compression ... [more ▼]

A progressive damage model is proposed to predict buckling strengths and failure mechanisms for both symmetric and asymmetric patch repaired carbon-fibre reinforced laminates subjected to compression without lateral restrains. Solid and cohesive elements are employed to discretize composite and adhesive layers, respectively. Coupling with three dimensional strain failure criteria, an energy-based crack band model is applied to address the softening behaviour in composites with mesh dependency elimination. Both laminar and laminate scaled failure are addressed. Patch debonding is simulated by the cohesive zone model with a trapezoidal traction–separation law applied for the ductile adhesive. Geometric imperfection is introduced into the nonlinear analysis by the first order linear buckling configuration. Regarding strengths and failure patterns, the simulation demonstrates an accurate and consistent prediction compared with experimental observations. Though shearing is the main contributor to damage initiation in adhesive, stress analysis shows that lateral deformation subsequently reverses the distribution of normal stresses which stimulates patch debonding at one of the repair sides. The influence of patch dimensions on strengths and failure mechanisms can be explained by stress distributions in adhesive and lateral deformation of repairs. Comparison between symmetric and asymmetric regarding strength and failure modes shows that structural asymmetry can intensify lateral flexibility. This resulted in earlier patch debonding and negative effects on strengths. [less ▲]

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See detailNumerical evaluation of the plastic hinges developed in headed stud shear connectors in composite beams with profiled steel sheeting
Vigneri, Valentino UL; Odenbreit, Christoph UL; Braun, Matthias Volker UL

in Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures (2018)

For composite beams using novel steel sheeting, the current Eurocode 4 rules sometimes overestimate the load bearing capacity of the shear connector. This is due to the larger rib heights and the smaller ... [more ▼]

For composite beams using novel steel sheeting, the current Eurocode 4 rules sometimes overestimate the load bearing capacity of the shear connector. This is due to the larger rib heights and the smaller rib widths in comparison with the old studies, which have been carried out to calibrate the current design equations. The RFCS Project “DISCCO” investigated this phenomena and the working group under mandate M515, CEN/TC250/SC4/SC4.T3 is enhancing this equation and working on a proposal to be taken over in the new version of Eurocode 4. The proposed new equation covers the failure behaviour of the shear connection more in detail. The test results show, that the failure consists in a combined concrete cone and stud in bending. Due to the geometry of novel steel sheeting, the load bearing capacity of the headed stud shear connector is no more limited by its shear capacity, but by its bending capacity. A 3D non-linear finite element model is developed and validated through the support of the DISCCO push-out tests. A good agreement between numerical and experimental results in terms of force-slip behaviour is achieved. Special attention of this work lies on the numerical evaluation of the number of plastic hinges ny: a stress-based procedure is presented and the results are compared to the equations presented for new Eurocode 4. The numerical simulations show that the upper plastic hinge moves up as the slip increases due to the progressive crushing of the concrete in the rib. From the parametric study, it turns out that ny is linearly proportional to the embedment depth. Compared to pre-punched hole decking, through-deck welding specimen activates less plastic hinges in the studs because of the higher stiffness provided at the base of the stud. [less ▲]

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See detailNumerical evaluation of the plastic hinges developed in headed stud shear connectors in composite beams with profiled steel sheeting
Vigneri, Valentino UL; Odenbreit, Christoph UL; Braun, Matthias Volker UL

in Structures (2019), 21

For composite beams using novel steel sheeting, the current Eurocode 4 rules sometimes overestimate the load-bearing capacity of headed stud shear connectors. This is due to the larger rib heights and the ... [more ▼]

For composite beams using novel steel sheeting, the current Eurocode 4 rules sometimes overestimate the load-bearing capacity of headed stud shear connectors. This is due to the larger rib heights and the smaller rib widths in comparison with the old studies, which have been carried out to calibrate the current design equations. The RFCS Project “DISCCO” investigated this phenomena and the working group under mandate M515, CEN/TC250/SC4/SC4.T3 is enhancing this equation and working on a proposal to be taken over in the new version of Eurocode 4. The proposed new equation covers the failure behaviour of the shear connection more in detail. The test results show, that the failure consists in a combined concrete cone and stud in bending. Due to the geometry of novel steel sheeting, the load bearing capacity of the headed stud shear connector is no more limited by its shear capacity, but by its bending capacity. A 3D non-linear finite element model is developed and validated through the support of the DISCCO push-out tests. A good agreement between numerical and experimental results in terms of force-slip behaviour is achieved. Special attention of this work lies on the numerical evaluation of the number of plastic hinges n y : a stress-based procedure is presented and the results are compared to the equations presented for new Eurocode 4. The numerical simulations show that the upper plastic hinge moves up as the slip increases due to the progressive crushing of the concrete in the rib. From the parametric study, it turns out that n y is linearly proportional to the embedment depth. Compared to pre-punched hole decking, through-deck welding specimen activates less plastic hinges in the studs because of the higher stiffness provided at the base of the stud. [less ▲]

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See detailNumerical integration over arbitrary polygonal domains based on Schwarz-Christoffel conformal mapping
Natarajan, S.; Bordas, Stéphane UL; Roy mahapatra, D.

in International Journal for Numerical Methods in Engineering (2009), 80(1), 103-134

This paper presents a new numerical integration technique on arbitrary polygonal domains. The polygonal domain is mapped conformally to the unit disk using Schwarz-Christoffel mapping and a midpoint ... [more ▼]

This paper presents a new numerical integration technique on arbitrary polygonal domains. The polygonal domain is mapped conformally to the unit disk using Schwarz-Christoffel mapping and a midpoint quadrature rule defined on this unit disk is used. This method eliminates the need for a two-level isoparametric mapping usually required. Moreover, the positivity of the Jacobian is guaranteed. Numerical results presented for a few benchmark problems in the context of polygonal finite elements show that the proposed method yields accurate results. © 2009 John Wiley & Sons, Ltd. [less ▲]

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See detailNumerical integration over arbitrary surfaces in partition of unity finite elements
Natarajan, Sundararajan; dal Pont, Stefano; Hung, Nguyen-Xuan et al

Scientific Conference (2009, September)

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See detailNumerical investigation into the blasting-induced damage characteristics of rocks considering the role of in-situ stresses and discontinuity persistence
Jayasinghe, Laddu Bhagya UL; Shang, J.; Zhao, Z. et al

in Computers and Geotechnics (2019), 116

This paper presents a 3D coupled Smoothed Particle Hydrodynamics (SPH) and Finite Element Method (FEM) model, which was developed to investigate the extent of damage zone and fracture patterns in rock due ... [more ▼]

This paper presents a 3D coupled Smoothed Particle Hydrodynamics (SPH) and Finite Element Method (FEM) model, which was developed to investigate the extent of damage zone and fracture patterns in rock due to blasting. The RHT material model was used to simulate the blasting-induced damage in rock. The effects of discontinuity persistence and high in-situ stresses on the evolution of blasting-induced damage were investigated. Results of this study indicate that discontinuity persistence and spatial distribution of rock bridges have a significant influence on the evolution of blasting-induced damage. Furthermore, high in-situ stresses also have a significant influence on the propagation of blasting-induced fractures, as well as the patterns of fracture networks. It is also shown that the blasting-induced cracks are often induced along the direction of the applied high initial stresses. Moreover, additional cracks are normally generated at the edges of the rock bridges probably due to the relatively high stress concentration. � 2019 Elsevier Ltd [less ▲]

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See detailNumerical Investigation into the Primary Breakup of Liquid Jets and Sheets
Kannan, Kumar UL

Doctoral thesis (2012)

Detailed reference viewed: 136 (5 UL)
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See detailNumerical investigation of bridges with the aim of condition assessment in applying the Deformation Area Difference method (DAD-method) and selecting appropriate measurement techniques
Erdenebat, Dolgion UL; Waldmann, Danièle UL; Teferle, Felix Norman UL

in 5th International Symposium on Life-Cycle Civil Engineering (IALCCE 2016), Delft (2016, October)

Condition assessment of existing road bridges gains ever increasing importance today as bridges are getting older and the inflow of heavy traffic is constantly increasing. The further development of ... [more ▼]

Condition assessment of existing road bridges gains ever increasing importance today as bridges are getting older and the inflow of heavy traffic is constantly increasing. The further development of recognized techniques and the development of new methods for early and accurate detection of damage to the structure are made possible by means of innovative technological progress. In this contribution, the principles of Defor-mation Area Difference Method (DAD-Method) for condition assessment of bridges are presented. This method is based on the further processing of measured and computed deformation values. The application of the DAD-Method requires a precise recording of the deflection of a load-deflection test. On the basis of theoretical cal-culations, this method has allowed to identify as well as to localise damage to a structure. The DAD-Method is independent of a reference measurement and insensitive to global influences such as temperature fluctuations. For precise detection of deformations, the most modern measuring instruments and methods like photogram-metry, total stations, displacement sensors, strain gauges and levelling are compared to each other. In collabo-ration with the appropriate measurement technology, the localisation of damage in bridges becomes possible. [less ▲]

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See detailNumerical investigation of insulation glass units with undercut point fittings
Tibolt, Mike UL; Odenbreit, Christoph UL; Hechler, Oliver UL

in European COST Action TU0905 - Book (2013, April)

The highest transparency in glass façades is obtained with point fitted glass units. Point fitted insulating glass units minimize thermal bridging and lead to glass façades with better energy efficiency ... [more ▼]

The highest transparency in glass façades is obtained with point fitted glass units. Point fitted insulating glass units minimize thermal bridging and lead to glass façades with better energy efficiency. Though, insufficient knowledge is present to offer a design method for point fittings in insulating glass. Therefore research has been carried out to extend the existing SLG-design-method of Beyer for point fitted single and laminated glass to insulation glass units. This paper presents first results of this research campaign. Load bearing tests on point fittings in single glazing have been conducted. An FEA-model of the point fitting is calibrated by the test data according to the method of Kasper. By means of this verified FEA-model, the influence on the stress peak at the borehole of the edge distance of the point fitting as well as the edge bond is investigated. In addition, the size of the so called “local area” is adjusted for insulation glass units. [less ▲]

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See detailNumerical methods for fracture/cutting of heterogeneous materials
Sutula, Danas UL; Agathos, Konstantinos UL; Ziaei Rad, Vahid UL et al

Presentation (2016, December)

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See detailNumerical model for tsunami generation by subaerial landslides
Pasenow, Frithjof; Zilian, Andreas UL; Dinkler, Dieter

in PAMM (2008), 8(1), 10519--10520

A discretization method based on stabilized space–time finite elements is presented for the numerical analysis of three–fluid flows of immiscible and incompressible fluids. Signed distance functions are ... [more ▼]

A discretization method based on stabilized space–time finite elements is presented for the numerical analysis of three–fluid flows of immiscible and incompressible fluids. Signed distance functions are used to assign the material properties to each spatial point in the domain. The motion and the change in topology of fluid–fluid interfaces are implicitly described by the level–set method. Strong and weak discontinuities in the fields of the physical state variables are captured by locally enriched approximations based on the partition–of–unity concept. An interior penalty method enforces interfacial conservation of mass and momentum. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [less ▲]

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See detailNumerical Modeling of air-gap membrane distillation
Cramer, Kerstin Julia UL

Doctoral thesis (2019)

Fresh water supply is a problem in large parts of the world and present on every continent. Many countries facing physical water scarcity, however, have access to the sea and lie in arid zones of the ... [more ▼]

Fresh water supply is a problem in large parts of the world and present on every continent. Many countries facing physical water scarcity, however, have access to the sea and lie in arid zones of the earth where solar energy is plentiful available. Membrane distillation (MD) describes an emerging desalination technology which has advantages when driven by solar energy or waste heat. In MD, seawater is thermally desalinated by generating a temperature gradient between hot salt water and produced fresh water which are separated by a membrane. In air-gap membrane distillation (AGMD) an insulating air-gap is introduced between membrane and distillate in order to minimize conductive losses. Despite its advantages, the permeate stream needs to be increased for large-scale application. To improve performance and energy efficiency, a detailed understanding of the highly coupled heat and mass transfer is crucial. However, for AGMD not many models exist and the existing models simplify the heat and mass transfer processes. The goal of this thesis is therefore to increase the understanding of the AGMD process and the predictive power of numerical models. A three-dimensional (3D) macro-scale model is developed with emphasis on the heat and mass transfer. It integrates aspects from multiphase flow modeling namely energy conservation over phase-change interfaces and the thermodynamic concept of moist air in the air-gap. Thereby, it computes the condensation mass flow independently from the evaporation mass flow, allowing to study the influence of convection on the heat and mass transfer in the air-gap. The model is accelerated for computation on graphical processing units (GPU). Employing the macro-scale model, a comparative analysis of the effects of module orientation on module performance and efficiency is performed. Vortexes in the air-gap are observed when using a module configuration where the hot feed flows below air-gap and membrane and the temperature gradient is opposing gravity. These vortexes lead to a significantly increased energy utilization also at low feed velocities. As the main advantage of AGMD is the reduction of heat losses, this configuration could bring further improvement. Furthermore, membrane transport properties are determined from high-resolution 3D membrane imaging combined with Lattice-Boltzmann simulation. Thereby, the 3D structure of membrane samples is obtained and porosity, tortuosity and permeability values are computed for the investigated membranes. Following the findings in the papers, further studies are suggested employing the modeling approaches developed in this thesis. [less ▲]

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See detailNumerical Modeling of Flow-Driven Piezoelectric Energy Harvesters
Ravi, Srivathsan UL; Zilian, Andreas UL

Scientific Conference (2016, June 09)

A specific class of energy harvester devices for renewable energy resources is investigated, that allow conversion of ambient fluid flow energy to electrical energy via flow-induced vibrations of a piezo ... [more ▼]

A specific class of energy harvester devices for renewable energy resources is investigated, that allow conversion of ambient fluid flow energy to electrical energy via flow-induced vibrations of a piezo-ceramic composite structure positioned in the flow field [3,4]. In this way, potentially harmful flow fluctuations are harnessed to provide independent power supply to small electrical devices. In order to harvest energy from fluid flows by means of piezoelectric materials the kinetic energy of the fluid first has to be transformed to cyclic straining energy of the piezoelectric material which is then transformed to electrical energy under the presence of an attached electrical circuit representing the powered electrical device or charged battery. This energy converter technology simultaneously involves the interaction of a composite structure and a surrounding fluid, the electric charge accumulated in the piezo-ceramic material and a controlling electrical circuit. In order to predict the efficiency and operational properties of such future devices and to increase their robustness and performance, a mathematical and numerical model of the complex physical system is required to allow systematic computational investigation of the involved phenomena and coupling characteristics. The research is devoted to introducing a monolithic approach that provides simultaneous modeling and analysis of the coupled energy harvester, which involves surface-coupled fluid-structure interaction, volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for applications in energy harvesting. The weak form of the governing equations is discretized by the space-time finite element method based on a mixed velocity-stress/rate form of the potential-dielectric displacement framework. The space-time finite element [2,3] model incorporates a novel method to enforce equipotentiality on the electrodes covering the piezoelectric patches, making the charge unknowns naturally appear in the formulation. This enables to adapt any type of electrical circuit added to the electromechanical problem. To validate the formulation, the case of piezoelectric triple layer EHD driven by base excitations, as described in [1] is chosen. The closed-form solution from [1] is compared to numerical solution proposed in this work. The variation of the electric potential through the thickness of the piezoelectric patch, assumed to be linear in many closed-form solutions, is shown to be quadratic in nature. The research contributes to the mathematical modeling and numerical discretization of complex multi- physics system in an efficient way which facilitates an ideal basis for precise and transient coupling. This may lead to improved convergence and numerical efficiency in comparison with portioned approaches. This methodology also provides new insights and in-depth understanding on design requirements on such energy harvesting devices in terms of their robustness and efficiency. [less ▲]

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See detailNumerical Modeling of Flow-Driven Piezoelectric Energy Harvesting Devices
Ravi, Srivathsan UL; Zilian, Andreas UL

in Ibrahimbegovic, Adnan (Ed.) Computational Methods for Solids and Fluids (2016)

The present work proposes uniform and simultaneous computational analysis of smart, low power energy harvesting devices targeting flow-induced vibrations in order to enable reliable sensitivity ... [more ▼]

The present work proposes uniform and simultaneous computational analysis of smart, low power energy harvesting devices targeting flow-induced vibrations in order to enable reliable sensitivity, robustness and efficiency studies of the associated nonlinear system involving fluid, structure, piezo-ceramics and electric circuit. The article introduces a monolithic approach that provides simultaneous modeling and analysis of the coupled energy harvester, which involves surface-coupled fluid-structure interaction, volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for applications in energy harvesting. A space-time finite element approximation is used for the numerical solution of the governing equations of the flow-driven piezoelectric energy harvesting device. This method enables modeling of different types of structures (plate, shells) with varying cross sections and material compositions, and different types of simple and advanced harvesting circuits. [less ▲]

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See detailNumerical modelling of electrified particle layer formation on the surface of filtration fabric.
Peters, Bernhard UL; Dzuigys, A.

in Environmental Engineering (2001), 4

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See detailNumerical Modelling of Piezoelectric Energy Harvesting Devices
Ravi, Srivathsan UL; Zilian, Andreas UL

in 2nd ECCOMAS Young Investigators Conference (YIC 2013) (2013)

This paper introduces a monolithic approach that provides simultaneous solution to the coupled system which involves volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for ... [more ▼]

This paper introduces a monolithic approach that provides simultaneous solution to the coupled system which involves volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for applications in energy harvesting. The weak form of the governing equations is discretized by space-time nite element method based on mixed velocity-stress/ rate of potential-dielectric displacement setting. The results will be compared to the simple cases with closed-form solution available from literature. [less ▲]

Detailed reference viewed: 103 (17 UL)