Strongly-coupled modelling and analysis of energy harvesting devices

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 ▲]

Biomechanical properties of five different currently used implants for open-wedge high tibial osteotomy

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 ▲]

Numerical simulation of energy harvesting devices driven by fluid-structure interaction

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 ▲]

Modelling of Fluid-Structure Interaction – Effects of Added Mass, Damping and Stiffness

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 ▲]

Entwicklung und Einsatz eines numerischen Modells zur systematischen Untersuchung wirkungsgradrelevanter hydraulischer Phänomene und Sensitivitäten bei Hochleistungswasserrädern. Abschlussbericht an die DFG

Report (2014)

A short course on The Extended Finite Element Method

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

Extended space-time finite elements for landslide dynamics

in International Journal for Numerical Methods in Engineering (2013), 93(3), 329-354

The paper introduces a methodology for numerical simulation of landslides experiencing considerable deformations and topological changes. Within an interface capturing approach, all interfaces are ... [more ▼]

The paper introduces a methodology for numerical simulation of landslides experiencing considerable deformations and topological changes. Within an interface capturing approach, all interfaces are implicitly described by specifically defined level-set functions allowing arbitrarily evolving complex topologies. The transient interface evolution is obtained by solving the level-set equation driven by the physical velocity field for all three level-set functions in a block Jacobi approach. The three boundary-coupled fluid-like continua involved are modeled as incompressible, governed by a generalized non-Newtonian material law taking into account capillary pressure at moving fluid-fluid interfaces. The weighted residual formulation of the level-set equations and the fluid equations is discretized with finite elements in space and time using velocity and pressure as unknown variables. Non-smooth solution characteristics are represented by enriched approximations to fluid velocity (weak discontinuity) and fluid pressure (strong discontinuity). Special attention is given to the construction of enriched approximations for elements containing evolving triple junctions. Numerical examples of three-fluid tank sloshing and air-water-liquefied soil landslides demonstrate the potential and applicability of the method in geotechnical investigations. © 2012 John Wiley & Sons, Ltd. [less ▲]

Numerical Modelling of Piezoelectric Energy Harvesting Devices

Scientific Conference (2013)

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

Numerical analysis of free-surface flow through rotating machines

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 ▲]

Design concept for point fitting of insulation glass units

in VI International Congress on Architectural Envelopes - Book (2012, June)

The façade significantly influences the energy efficiency of the building. However, in addition to high insulating properties, modern architecture demands a high transparency for natural illumination and ... [more ▼]

The façade significantly influences the energy efficiency of the building. However, in addition to high insulating properties, modern architecture demands a high transparency for natural illumination and the compliance with inner comfort criteria in the building. The increasing use of glass can be seen as the architectural intention to combine those well-being and energetic principles. The highest transparency can be achieved with point-fitted glass units. Though, insufficient knowledge is present to use point fittings for insulation glass units, which are required to comply with the demand for energy-efficiency. Therefore, research has been carried out to investigate in the load bearing mechanism of different point-fitted insulating glass units in order to find an innovative point fitting connection system for insulating glass units to the steel substructures. This paper presents results of this research campaign and provides information on how to design point-fitted insulating glass units. [less ▲]