References of "Zilian, Andreas 50003363"
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See detailIsogeometric analysis of thin Reissner-Mindlin plates and shells: Locking phenomena and generalized local B-bar method
Hu, Qingyuan UL; Xia, Yang; Natarajan, Sundararajan et al

E-print/Working paper (2017)

We propose a generalized local $\bar{B}$ framework, addressing locking in degenerated Reissner-Mindlin plate and shell formulations in the context of isogeometric analysis. Parasitic strain components are ... [more ▼]

We propose a generalized local $\bar{B}$ framework, addressing locking in degenerated Reissner-Mindlin plate and shell formulations in the context of isogeometric analysis. Parasitic strain components are projected onto the physical space locally, i.e. at the element level, using a least-squares approach. The formulation is general and allows the flexible utilization of basis functions of different order as the projection bases. The present formulation is much cheaper computationally than the global $\bar{B}$ method. Through numerical examples, we show the consistency of the scheme, although the method is not Hu-Washizu variationally consistent. The numerical examples show that the proposed formulation alleviates locking and yields good accuracy for various thicknesses, even for slenderness ratios of $1 \times 10^5$, and has the ability to capture deformations of thin shells using relatively coarse meshes. From the detailed numerical study, it can be opined that the proposed method is less sensitive to locking and mesh distortion. [less ▲]

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See detailNumerical prediction of the rheological properties of fresh self-compacting concrete
Huang, Haiqin UL; Zilian, Andreas UL

Scientific Conference (2017, July 14)

Self-Compacting Concrete (SCC) is a high-performance construction material that can simplify classical handling on concrete construction by avoiding the need for additional vibrational compaction ... [more ▼]

Self-Compacting Concrete (SCC) is a high-performance construction material that can simplify classical handling on concrete construction by avoiding the need for additional vibrational compaction. Challenges in the use of SCC lie in ensuring optimal operation of the material in terms of properly filled castings in presence of complex reinforcement arrangements, reduction of entrained gas bubbles and limitation of aggregate separation. A major factor influencing the aforementioned aspects is the rheological properties of SCC mixtures under varying conditions (e.g. content composition, mechanical impact, temperature, moisture). This contribution aims at unified constitutive modelling of SCC in the setting stage. Concrete setting describes the transition from fluid-like fresh concrete, which -in presence of time- dependent transport-reaction processes- develops a porous cementitious structure, to hardened concrete showing solid-like behaviour. The constitutive model is implemented using the open-source finite element framework FENICS and applied to a number of benchmark problems. [less ▲]

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See detailTime and frequency domain analysis of piezoelectric energy harvesters by monolithic finite element modeling
Ravi, Srivathsan UL; Zilian, Andreas UL

in International Journal for Numerical Methods in Engineering (2017)

The successful design of piezoelectric energy harvesting devices relies upon the identification of optimal geometrical and material configurations to maximize the power output for a specific band of ... [more ▼]

The successful design of piezoelectric energy harvesting devices relies upon the identification of optimal geometrical and material configurations to maximize the power output for a specific band of excitation frequencies. Extendable predictive models and associated approximate solution methods are essential for analysis of a wide variety of future advanced energy harvesting devices involving more complex geometries and material distributions. Based on a holistic continuum mechanics modeling approach to the multi-physics energy harvesting problem, this article proposes a monolithic numerical solution scheme using a mixed-hybrid 3-dimensional finite element formulation of the coupled governing equations for analysis in time and frequency domain. The weak form of the electromechanical/circuit system uses velocities and potential rate within the piezoelectric structure, free boundary charge on the electrodes, and potential at the level of the generic electric circuit as global degrees of freedom. The approximation of stress and dielectric displacement follows the work by Pian, Sze, and Pan. Results obtained with the proposed model are compared with analytical results for the reduced-order model of a cantilevered bimorph harvester with tip mass reported in the literature. The flexibility of the method is demonstrated by studying the influence of partial electrode coverage on the generated power output. [less ▲]

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See detailMonolithic modeling and finite element analysis of piezoelectric energy harvesters
Ravi, Srivathsan UL; Zilian, Andreas UL

in Acta Mechanica (2017), 228(6), 2251-2267

This paper is devoted to monolithic modeling of piezoelectric energy harvesting devices. From a modeling perspective, piezoelectric energy harvesting is a strongly coupled phenomenon with two-way coupling ... [more ▼]

This paper is devoted to monolithic modeling of piezoelectric energy harvesting devices. From a modeling perspective, piezoelectric energy harvesting is a strongly coupled phenomenon with two-way coupling between the electromechanical effect of the piezoelectric material and the harvesting circuit. Even in applications related to shunt damping, where the attached electrical circuit is passive, accurate modeling of the strong coupling is crucial for proper evaluation of the relevant parameters. The article proposes a monolithic mixed-hybrid finite element formulation for the predictive modeling and simulation of piezoelectric energy harvesting devices. The governing equations of the coupled electromechanical problem are converted into a single integral form with six independent unknown fields. Such a holistic approach provides consistent solution to the coupled field equations which involve structural dynamics, electromechanical effect of the piezoelectric patches and the dynamics of the attached harvesting circuit. This allows accurate computation of the eigenvalues and corresponding mode shapes of a harvester for any finite resistive load coupled to the harvester. The fully three-dimensional mixed-hybrid formulation is capable of analyzing structures with non-uniform geometry and varying material properties. The results of the finite element model are verified against the analytical results of a bimorph harvester with tip mass reported in the literature. [less ▲]

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See detailMultiphysics applications and computational challenges
Zilian, Andreas UL

Scientific Conference (2017, January 24)

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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 ▲]

Detailed reference viewed: 129 (20 UL)
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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: 274 (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: 174 (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: 152 (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: 201 (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 detailEnergy harvesting
Zilian, Andreas UL

in Science and Technology (2015), 15

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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 ▲]

Detailed reference viewed: 171 (17 UL)