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See detailSimultaneous Analysis of Strongly-Coupled Composite Energy Harvester-Circuit Systems Driven by Fluid-Structure Interaction
Zilian, Andreas UL; Ravi, Srivathsan UL

Scientific Conference (2016, July 27)

A specific class of energy harvester devices is investigated, that allow conversion of ambient fluid flow energy to electrical energy via flow-induced vibrations [1] of a piezo-ceramic composite structure ... [more ▼]

A specific class of energy harvester devices is investigated, that allow conversion of ambient fluid flow energy to electrical energy via flow-induced vibrations [1] of a piezo-ceramic composite structure positioned in the flow field. Potentially harmful flow fluctuations are harnessed to provide independent power supply to small electrical devices [2]. Such concept 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 these devices and to increase their robustness and performance, a predictive model of the complex physical system allows systematic computational investigation of the involved phenomena and coupling characteristics. A monolithic approach is proposed that provides simultaneous modelling and analysis of the harvester, which involves surface-coupled fluid-structure interaction, volume-coupled electro mechanics and a controlling energy harvesting circuit for applications in energy harvesting. A three dimensional space-time finite element approximation [3] is used for numerical solution of the weighted residual form of the governing equations of the flow-driven piezoelectric energy-harvesting device. This method enables time-domain investigation of different types of structures (plate, shells) subject to exterior/interior flow with varying cross sections, material compositions, and attached electrical circuits with respect to the electrical power output generated [4]. The space-time finite element model presented incorporates a novel method to enforce equipotentiality on the electrodes covering the piezoelectric patches, making the charge unknowns naturally appear in the formulation [5]. This enables to adapt any type of electrical circuit added to the electromechanical problem. [less ▲]

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See detailPrédiction de la résistance mécanique d’un bloc de maçonnerie sans joint par calcul numérique
Chewe Ngapeya, Gelen Gael UL; Waldmann, Danièle UL; Scholzen, Frank UL et al

Presentation (2016, July 06)

La nouvelle génération de blocs de maçonnerie montés à sec (sans joint) et muni d’éléments d’engrenages ou d’emboîtement présente des avantages substantiels tant en précision et vitesse de pose, qu’en ... [more ▼]

La nouvelle génération de blocs de maçonnerie montés à sec (sans joint) et muni d’éléments d’engrenages ou d’emboîtement présente des avantages substantiels tant en précision et vitesse de pose, qu’en résistance aux déplacements transversaux, en économie de matériaux et en facilité de démontage. La performance d’un mur en maçonnerie est étroitement liée à sa stabilité générale et à la résistance mécanique des blocs de maçonnerie qui le composent. L’un des objectifs de cette étude était de rechercher un optimum entre cinq paramètres importants dans la conception d’une maçonnerie à savoir le poids, le coût, la facilité de production, mais surtout la résistance mécanique et la résistance thermique. La conception du nouveau bloc a ainsi été entreprise par calculs numériques. [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 detailLarge-deformation lattice model for dry-woven fabrics including contact
Magliulo, Marco UL; Beex, Lars UL; Zilian, Andreas UL et al

Speeches/Talks (2016)

Short Presentation on the Quasi-continuum method

Detailed reference viewed: 257 (32 UL)
See detailStrongly-coupled modelling and analysis of energy harvesting devices
Zilian, Andreas UL

Scientific Conference (2016, March 11)

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. In this way, potentially harmful flow fluctuations are harnessed to provide independent power supply to small electri- cal 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 struc- ture 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 nu- merical model of the complex physical system is required to allow systematic computational investigation of the involved phenomena and coupling characteristics. A monolithic approach is proposed that provides simultaneous modelling and analysis of the harvester, which involves surface-coupled fluid-structure interaction, volume-coupled electro- mechanics and a controlling energy harvesting circuit for applications in energy harvesting. A space-time finite element approximation is used for numerical solution of the weighted residual form of the governing equations of the flow-driven piezoelectric energy harvesting device. This method enables time-domain investigation of different types of structures (plate, shells) subject to exterior/interior flow with varying cross sections, material compositions, and attached electrical circuits with respect to the electrical power output generated. [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 ▲]

Detailed reference viewed: 147 (22 UL)
See detailmafe - Educational Matlab framework for finite element analysis of structures.
Zilian, Andreas UL

Software (2016)

"mafe" is an educational MATLAB framework for finite element analysis of structures like rod, beams, slabs and plates that allows for (a) static linear analysis, (b) dynamic linear analysis in frequency ... [more ▼]

"mafe" is an educational MATLAB framework for finite element analysis of structures like rod, beams, slabs and plates that allows for (a) static linear analysis, (b) dynamic linear analysis in frequency and time domain. [less ▲]

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See detailStrongly-coupled modelling and analysis of energy harvesting devices
Zilian, Andreas UL; Ravi, Srivathsan UL

in Applied Mathematics and Mechanics (2016), 16

A monolithic approach is proposed that provides simultaneous modelling and analysis of the harvester, which involves surface- coupled fluid-structure interaction, volume-coupled electro- mechanics and a ... [more ▼]

A monolithic approach is proposed that provides simultaneous modelling and analysis of the harvester, which involves surface- coupled fluid-structure interaction, volume-coupled electro- mechanics and a controlling energy harvesting circuit for applica- tions in energy harvesting. A space-time finite element approximation is used for numerical solution of the weighted residual form of the governing equations of the flow-driven piezoelectric energy harvesting device. This method enables time-domain investigation of different types of structures (plate, shells) subject to exterior/interior flow with varying cross sections, material compositions, and attached electrical circuits with respect to the electrical power output generated. [less ▲]

Detailed reference viewed: 135 (27 UL)
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See detailBiomechanical properties of five different currently used implants for open-wedge high tibial osteotomy
Diffo Kaze, Arnaud UL; Maas, Stefan UL; Waldmann, Danièle UL et al

in Journal of Experimental Orthopaedics (2015), 2(14),

Background: As several new tibial osteotomy plates recently appeared on the market, the aim of the present study was to compare mechanical static and fatigue strength of three newly designed plates with ... [more ▼]

Background: As several new tibial osteotomy plates recently appeared on the market, the aim of the present study was to compare mechanical static and fatigue strength of three newly designed plates with gold standard plates for the treatment of medial knee joint osteoarthritis. Methods: Sixteen fourth-generation tibial bone composites underwent a medial open-wedge high tibial osteotomyn(HTO) according to standard techniques, using five TomoFix standard plates, five PEEKPower plates and six iBalance implants. Static compression load to failure and load-controlled cyclic fatigue failure tests were performed. Forces, horizontal and vertical displacements were measured; rotational permanent plastic deformations, maximal displacement ranges in the hysteresis loops of the cyclic loading responses and dynamic stiffness were determined. Results: Static compression load to failure tests revealed that all plates showed sufficient stability up to 2400 N without any signs of opposite cortex fracture, which occurred above this load in all constructs at different load levels. During the fatigue failure tests, screw breakage in the iBalance group and opposite cortex fractures in all constructs occurred only under physiological loading conditions (<2400 N). The highest fatigue strength in terms of maximal load and number of cycles performed prior to failure was observed for the ContourLock group followed by the iBalance implants, the TomoFix standard (std) and small stature (sm) plates. The PEEKPower group showed the lowest fatigue strength. Conclusions: All plates showed sufficient stability under static loading. Compared to the TomoFix and the PEEKPower plates, the ContourLock plate and iBalance implant showed a higher mechanical fatigue strength during cyclic fatigue testing. These data suggest that both mechanical static and fatigue strength increase with a wider proximal T-shaped plate design together with diverging proximal screws as used in the ContourLock plate or a closed-wedge construction as in the iBalance design. Mechanical strength of the bone-implant constructs decreases with a narrow T-shaped proximal end design and converging proximal screws (TomoFix) or a short vertical plate design (PEEKPower Plate). Whenever high mechanical strength is required, a ContourLock or iBalance plate should be selected. [less ▲]

Detailed reference viewed: 185 (34 UL)
See detailNumerical simulation of energy harvesting devices driven by fluid-structure interaction
Zilian, Andreas UL; Ravi, Srivathsan UL

Scientific Conference (2015, June)

A specific class of piezo-electric energy harvesting devices for renewable energy resources is investigated. The key idea is to invert the traditional intention of engineers to avoid flow-induced ... [more ▼]

A specific class of piezo-electric energy harvesting devices for renewable energy resources is investigated. The key idea is to invert the traditional intention of engineers to avoid flow-induced excitation of structures such, that flow-induced vibrations can successfully be controlled and utilised in order to provide independent power supply to small-scale electrical devices. Possible application are e.g. micro electro-mechanical systems, monitoring sensors at remote locations or even in-vivo medical devices with the advantage of increased independence on local energy storage and reduced maintenance effort. This energy converter technology involves transient boundary-coupled fluid-structure interaction, volume-coupled piezo-electric-mechanics as well as a controlling electric circuit simultaneously. In order to understand the phenomenology and to increase robustness and performance of such devices, a mathematical and numerical model of the transient strongly-coupled non-linear multi-physics system is developed for systematic computational analyses. On basis of numerical investigations of the overall system optimal designs of the flow-induced vibrating piezo-electric energy harvester shall be identified with respect to electric power supply under varying exterior conditions. Vortex-induced excitations of a cantilever piezo-electric plate are exemplarily considered for studies on robustness and efficiency. [less ▲]

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See detailComputational Modeling of FSI Energy Harvesting Devices
Ravi, Srivathsan UL; Zilian, Andreas UL

Scientific Conference (2015, June)

This paper introduces a monolithic approach that provides simultaneous modeling and analysis of a coupled energy harvester, which involves surface-coupled fluid-structure interaction, volume-coupled ... [more ▼]

This paper introduces a monolithic approach that provides simultaneous modeling and analysis of a 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 results will be compared to test cases with closed-form solution available from literature. [less ▲]

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See detailEnergy harvesting
Zilian, Andreas UL

in Science and Technology (2015), 15

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See detailModelling of Fluid-Structure Interaction – Effects of Added Mass, Damping and Stiffness
Zilian, Andreas UL

in Irschik, Hans; Belyaev, Alexander K. (Eds.) Dynamics of Mechanical Systems with Variable Mass (2014)

Fluid-flow around mechanical structures can sometimes lead to catastrophic failures. Improved modelling of fluid/structure interaction is required for safety and mechanical considerations. In this ... [more ▼]

Fluid-flow around mechanical structures can sometimes lead to catastrophic failures. Improved modelling of fluid/structure interaction is required for safety and mechanical considerations. In this contribution, concepts for modelling the interaction of structures and fluids are presented. Starting from excitation mechanisms and associated classifications, various model depth approaches are compared. Among them, the use of added coefficients for quasi-steady problems is discussed. On the basis of potential flow theory, different approaches for determining fluid-induced additional mass are established and illustrated using an analytical example. Given the limitations of simplifying the engineering models, the second part of the paper provides a brief overview on computational methods for fluid-structure interaction and presents a monolithic modelling approach using space-time finite elements for discretisation of both fluid and structure. Applications from aero- and hydro-elasticity show the applicability of computational methods for problems involving flow-induced added mass, damping, and stiffness. [less ▲]

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See detailMethodenentwicklung zur numerischen Strömungsanalyse von Freispiegelströmungen bei Schaufelwasserrädern
Schippke, Henning; Seidel, Christian; Dinkler, Dieter et al

Scientific Conference (2014, March)

Der Ausbau der Wasserkraft gewinnt im Kontext der Energiewende weltweit an Bedeutung. Neben der Turbinentechnologie erweisen sich Wasserräder im Hinblick auf ihre hohe ökologische Verträglichkeit und ihr ... [more ▼]

Der Ausbau der Wasserkraft gewinnt im Kontext der Energiewende weltweit an Bedeutung. Neben der Turbinentechnologie erweisen sich Wasserräder im Hinblick auf ihre hohe ökologische Verträglichkeit und ihr hohes ganzjähriges Arbeitsvermögen als besonders geeignet. Das sich drehende Wasserrad, umgeben von Wasser und Luft, stellt mechanisch ein gekoppeltes Drei- Feld-System bestehend aus einer Struktur und zwei Fluiden dar. Hinreichend genau ist es möglich, die Wasserradstruktur als Starrkörper zu beschreiben, während Luft und Wasser mit Hilfe der inkom- pressiblen Navier-Stokes Gleichungen gut modelliert werden können. Durch Anwendung der Raum-Zeit-Finite-Elemente-Methode zur Diskretisierung der inkompressiblen Navier-Stokes Gleichungen wird die Grenzfläche zwischen dem Starrkörper und den Fluiden explizit beschrieben und stets automatisch korrekt erfasst. Die Beschreibung der freien Wasseroberfläche als Grenzfläche zwischen den beiden Fluiden erfolgt implizit mit Hilfe der Level-Set Methode. Die Netzknoten der Fluid-Struktur-Grenzfläche verändern ihre Position infolge der Wasserraddrehung mit der Zeit, so dass ein Netzbewegungsalgorithmus notwendig ist. Die shear-slip mesh update method (SSMUM) ermöglicht als diskontinuierliches Netzbewegungsverfahren eine durchgehende Berechnung des Gesamtsystems, ohne dass das gesamte Gebiet neu vernetzt werden muss. Anhand verschiedener Testbeispiele wird die Güte der entwickelten numerischen Methode im Hinblick auf Ihre Erhaltungseigenschaften untersucht. Besonderes Augenmerk wird auf die Lösungsübertragung am shear-slip layer sowie auf die Abbildung der implizit beschriebenen freien Wasseroberfläche gelegt. [less ▲]

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See detailA short course on The Extended Finite Element Method
Fries, Thomas-Peter; Zilian, Andreas UL

Book published by CES University of Luxembourg - 1 (2013)

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See detailMethodenentwicklung zur numerischen Strömungsanalyse von Schaufelwasserrädern
Schippke, Henning; Zilian, Andreas UL; Seidel, Christian et al

in PAMM (2013)

Es wird ein Berechnungsmodell vorgestellt, mit dem eine numerischen Analyse der Strömungsvorgänge innerhalb von Schau- felwasserrädern möglich ist. Der Arbeitsschwerpunkt liegt dabei auf der ... [more ▼]

Es wird ein Berechnungsmodell vorgestellt, mit dem eine numerischen Analyse der Strömungsvorgänge innerhalb von Schau- felwasserrädern möglich ist. Der Arbeitsschwerpunkt liegt dabei auf der strömungsmechanischen Optimierung von Hochleis- tungswasserrädern der Weiterentwickelten Wasserradtechnologie. In dem Berechnungsmodell werden die inkompressiblen Navier-Stokes-Gleichungen in den unabhängigen Variablen Geschwindigkeiten und Druck mit Hilfe der zeit-diskontinuierlichen Raum-Zeit-Finite-Elemente-Methode diskretisiert und die auftretende Gebietsveränderung infolge der sich drehenden Struk- tur mit der Shear-Slip Mesh Update Methode als diskontinuierlichem Netzbewegungsverfahren erfasst. [less ▲]

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See detailNumerical analysis of free-surface flow through rotating machines
Schippke, Henning; Zilian, Andreas UL

Presentation (2013)

In the context of the transformation process currently taking place in the energy production sector, energy gained from renewable power sources shall replace the present mixture, which mostly relies on ... [more ▼]

In the context of the transformation process currently taking place in the energy production sector, energy gained from renewable power sources shall replace the present mixture, which mostly relies on fossil burnings. Therefore, in the future most of the energy shall be gained by harvesting power from sun, wind or water, geothermal heat or biomass. In case of converting energy from wind into electrical power wind turbines are used in general, while hydropower turbines are the state-of-the-art machinery to derive energy from running water. In order to convert the potential energy from running water as well water wheels pose the method of choice. Turbines in air or water represent mechanically a two-field system, in which the structure of the turbine is surrounded by a streaming fluid. Due to the elasticity of the rotor blades the stresses of the fluid onto the structure deform the blades, which in return yield a time-dependent flow domain. Therefore turbines in a streaming fluid represent a typical example of fluid-structure interaction. Furthermore, in case of water wheels the surrounding air as third field and additional fluid phase comes into play introducing a free surface. In this contribution the governing equations of incompressible fluid flow are presented using primal variables and discretised via the space-time finite element method [3]. The discretised model equations of the fluid are stabilised using an SUPG/PSPG approach. Shape and test functions are continuous within the space-time slabs, while across the space- time slabs the shape and test functions are continuous only in space, but discontinuous in time yielding a time-discontinuous Galerkin approach. Due to the moving rotor blades a mesh moving technique needs to be incorporated into the computational set-up. Considering the occurring large but regular displacements of the flow boundary arising from the rotating rotor blades the shear-slip mesh update method (SSMUM) [1] as discontinuous mesh moving technique is applied. In case of water wheels the free surface is described implicitly via a Level-Set function [2] yielding a single fluid phase with almost discontinuous density and viscosity. The verification and validation of the developed numerical scheme is carried out with the help of computing classical benchmark problems as well as via a comparison to existing experimental data. [less ▲]

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