89 research outputs found
Lipids and inter/intramolecular interactions regulating calcium entry pathways
No full textAuthor Christina Humer BSc MScDissertation Johannes Kepler Universität Linz 2023Arbeit nach Ablauf der Sperre auf den öffentlichen PCs in den Bibliotheken der JKU+Medizin abrufba
Lipids and inter/intramolecular interactions regulating calcium entry pathways
No full textAuthor Christina Humer BSc MScDissertation Universität Linz 2023Arbeit nach Ablauf der Sperre auf den öffentlichen PCs in den Bibliotheken der JKU+Medizin abrufba
A noninvasive system‐level model order reduction scheme for flexible multibody simulation
No full textThis paper presents a novel system‐level model order reduction scheme for flexible multibody simulation, namely the system‐level affine projection (SLAP). Contrary to existing system‐level model order reduction approaches for multibody systems simulation, this methodology allows to obtain a constant reduced order basis which can be obtained in a noninvasive fashion with respect to the original flexible multibody model. It is shown that this scheme enables an automatic joint constraint elimination which can be obtained at low computational cost through exploitation of the component level modes typically employed in flexible multibody simulation. The equations of motion are derived such that the computational cost of the resulting SLAP model is independent of the original model size. This approach results in a set of ordinary differential equations with a constant mass matrix and nonlinear internal forces. This structure makes the resulting model suitable for a range of estimation, control, and design applications. The proposed approach is validated numerically on a flexible four‐bar mechanism and shows good accuracy for a very low‐order SLAP model.sponsorship: The research of Frank Naets is funded by a postdoctoral fellowship of the Fund for Scientific Research, Flanders (FWO). The Research Fund KU Leuven is gratefully acknowledged for its support. The Flanders Innovation & Entrepreneurship Agency within the IMPROVED project is gratefully acknowledged for its support. Alexander Humer and Johannes Gerstmayr acknowledge the support by the Linz Center of Mechatronics (LCM) in the framework of the Austrian COMET-K2 programme. (Fund for Scientific Research, Flanders (FWO), Research Fund KU Leuven, Flanders Innovation & Entrepreneurship Agency within the IMPROVED project, Linz Center of Mechatronics (LCM))status: Published onlin
Dancing rod problem in the context of Lagrangian mechanics
No full textDancing rod problem in the context of Lagrangian mechanics
Yury Vetyukov, Alexander Humer
In this talk we discuss the aspects of non-material modelling of a flexible structure moving between two qualitatively different domains with a configurational force, acting at the boundary. In particular, we consider the dynamics of a flexible rod, partially inserted into an inclined rigid channel with little or no friction. Initially, the rod will slide downwards because of the gravitational force. The free segment vibrates with growing frequency and decreasing amplitude as the rod is injected further. The falling will be decelerated by the longitudinal contact force, which is acting at the interface between the free segment and the part inside the channel. This configurational force is expressed in terms of the work needed to straighten the curved rod to pull it into the channel. Eventually it will outweigh gravity such, that injection will change to ejection. Under circumstances the rod will fully eject out of the opening.
The formulation of this dancing rod problem was first suggested by the authors of [1], who also performed physical experiments and provided a fascinating video of the dynamic process as supplementary material. Being restricted to the case of vanishing inertia of the rod with a concentrated mass at its tip, their mathematical model is based on the equations of Newtonian mechanics and reproduces the experimental observations. The numerical approach of the present contribution features a finite element discretization of the deformation of the free segment with respect to a normalized coordinate. The material length of the free segment is considered as an additional degree of freedom. This results into a mixed Eulerian-Lagrangian kinematic description of a sliding beam in the spirit of [2,3]: while the material particles move across the boundaries of the elements, we still manage to obtain expressions for the potential and the kinetic energy of the entire rod. Numerical experiments using both, classical Kirchhoff rod model and shear deformable Simo-Reissner theory demonstrate the existence of the critical initial length of the free segment, which, in dependence on other parameters, determines, whether the motion is quasi-periodic or the rod will completely eject out of the channel. Further investigations on the configurational force feature analytical solution of the contact problem for a flexible beam, confined in a channel with small width, which allows to consistently account for frictional interaction between the rod and the channel in the general setting.
References
[1] Armanini, C., Dal Corso, F., Misseroni, D., & Bigoni, D. (2019). Configurational forces and nonlinear structural dynamics. Journal of the Mechanics and Physics of Solids, 130, 82-100.
[2] Humer, A., Steinbrecher, I., & Vu-Quoc, L. (2020). General sliding-beam formulation: A non-material description for analysis of sliding structures and axially moving beams. Journal of Sound and Vibration, 480, 115341.
[3] Vetyukov, Y. (2018). Non-material finite element modelling of large vibrations of axially moving strings and beams. Journal of Sound and Vibration, 414, 299-317
Proceedings in Applied Mathematics and Mechanics (PAMM) / Design and optimization of large‐deformation compliant mechanisms
No full textAs compared to conventional mechanisms, compliant mechanisms exploit flexible deformation rather than rigid‐body motion of its components. The key advantage of jointless or monolithic structures lies in the absence of relative motion between the links. Besides the reduction in parts required to perform a task, compliant mechanisms typically show little friction, if any, and do not require lubrication to minimize wear. On the downside, design and synthesis of compliant mechanisms become much more involved than in rigid‐body linkages. In particular, optimization of compliant mechanisms relying on (sub‐)structures subjected to large flexible deformation is a challenging task, in which diverse aspects need to be considered. First and foremost, kinematic analysis of compliant mechanisms usually requires geometric non‐linearities to be accounted for. Further, limitations in actuation forces and torques impose constraints on the design. Depending on the application, the performance of compliant mechanisms may crucially depend on the natural frequencies and their change over the range of operation. In view of the diverse aspects, one typically has to deal with multi‐objective optimization problems in comparatively high‐dimensional parameter spaces.Refereed/Peer-reviewedVersion of recor
Large deformation and stability of a shear-deformable beam with a variable length under a uniformly distributed force
No full textElliptic integral solution of the extensible elastica with a variable length under a concentrated force
No full textRegional planning: an arena of interests, institutions and relations
No full textThis special issue approaches regional planning as a contested arena of strategic planning. With this view, we transcend the idea that regional planning is purely a matter of scale and approach the complexity of regional planning from three perspectives: interests, institutions and relations. The perspective of ‘interests’ reveals the various underlying motivations connected to regional planning. The perspective of ‘institutions’ addresses the encounter of formal and informal rules, norms and discourses shaping planning and governance practices. The perspective of ‘relations’ uncovers the complex constellations of actors and processes associated with planning, involving various administrative scales, territorial entities and sectoral policies.Spatial Planning and Strateg
Energy-Momentum Conserving Time Integration of Modally Reduced Flexible Multibody Systems
No full textCeria based cathodes for CO 2 electrolysis in solid oxide cells
No full textAls alternative Treibstoffgewinnung für "Solid Oxide Fuel Cells" (SOFC) sowie zur Gewinnung von Gasen für chemische Reaktionen werden bereits "Solid Oxide Electrolyse Cells" (SOEC) eingesetzt. Diese haben den großen Vorteil kein weiteres CO2 zu produzieren, wie dies bei der Vergasung von Kohlenstoff unter einer Wasserdampfatmosphäre der Fall ist. Die Reduktion von CO2 geht jedoch mit der Möglichkeit einer Ablagerung von Kohlenstoff an den Elektroden einher. Das Ziel der Arbeit ist es die Nutzbarkeit von gemischt ionisch/elektronisch leitenden Cer0.9Gd0.1O1.95-Kathoden (GDC) auf YSZ-Elektrolyten mit LSCF-Anoden für kontinuierliche CO2-Elektrolyse zu testen. Weiters soll der Einfluss von Nickelpartikeln in den GDC-Kathoden sowie der Zusammenhang zwischen der inneren Oberfläche der porösen Elektroden und der Dünnschichtelektroden bestimmt werden. Die porösen Elektroden wurden auf polykristallinem YSZ-Substrat mit LSCF-Anoden mittels Siebdruckverfahren hergestellt und über Platinpartikel kontaktiert. Für die Dünnfilmelektroden wurde ein Einkristall-YSZ (100) als Substrat verwendet, die Arbeitselektrode mittels "Pulsed Laser Deposition" (PLD) aufgetragen und die Gegenelektrode über Siebdruck appliziert und gesintert. Über eine impedanzspektroskopische Charakterisierung der Dünnschichtelektroden stellte sich ein erheblich verringerter Polarisationswiderstand aufgrund einer Beschichtung mittels Nickelpartikeln auf der Oberfläche heraus. Dieser wurde später auch bei porösen Elektroden beobachtet. Durch Einzelmessungen der jeweiligen Elektrolysezellen wurde die Funktionalität der GDC- sowie Ni/GDC-Kathoden getestet und ein Leistungsvergleich der einzelnen Zellen durchgeführt. An der reinen GDC-Kathode mit einer Schichtdicke von 6,9m, wurde eine maximale Stromdichte von 1,5mA/cm2 bei 2V gemessen. Durch eine Dotierung von 10% Nickel und einer Schichtdicke von 4,8m konnte die Stromdichte auf 3,7mA/cm2 gesteigert werden, wodurch sich mehr als eine Verdoppelung ergab. Der Kohlenstoffmonoxid Produktionsstrom verhielt sich dabei dem elektrischen Strom entsprechend. Undotierte GDC-Kathoden lieferten einen CO-Volumenstrom von 0,32cm3/min während die 10% Nickel dotierten 0,65 cm3/min ergaben. Der Vergleich zwischen Dünnfilm und porösen Elektroden ergab einen deutlichen Unterschied der Stromdichten. Bei reinem GDC Dünnfilm konnten sehr hohe Ströme von 283 mA/cm2 gemessen werden. Gründe hierfür könnten in Degradationen der porösen Elektrode durch Verunreinigung liegen.Solid oxide electrolysis cells are used for the creation of fuels for solid oxide fuel cells (SOFC) as well as gases for chemical reactions. The big advantage of the fuel production through fuel cells is the CO2 neutrality during the creation instead of the use of coal gasification with steam. A main problem we face here is the deposition of carbon on the electrodes, which has to be prevented to maintain the usability of the cell. The goal of this work is to test the usability of mixed ionic/electronic conducting Ce0.9Gd0.1O1.95 cathodes (GDC) on YSZ-electrolyte with LSCF-anodes for CO2 electrolysis. Furthermore, the influence of nickel particles in GDC cathodes was tested and the performance of porous electrodes and thin film electrodes were compared. Porous electrodes have been screen printed on polycrystalline YSZ substrates with LSCF as counter electrodes and platinum particles as connecting elements. The thin film electrodes are on yttrium stabilized zirconia single crystal (100) electrolytes. The GDC electrodes are applied by pulsed laser deposition (PLD) and the counter electrodes (LSCF) are screen-printed and sintered. By impedance spectroscopy, the polarisation resistances of all samples could be obtained. The introduction of nickel reduced the polarisation resistances for all samples. The functionality of the cells was tested by applying direct voltage on the cells. The performances of the cells were compared through the amount of gas produced as well as by the current applied during the measurement. For pure porous GDC-cathodes with a film thickness of 6,9m at a voltage of 2V, a maximum current density of 1,5mA/cm2 was obtained. The nickel doping of 10% increased the current density of the GDC layer (film thickness: 4,8m) at the same conditions to 3,75mA/cm2. The CO flow corresponds to the current density. In the process pure GDC produced 0,32 cm3/min of CO per minute while doped GDC generated 0,65 cm3/min. Both had a Faraday efficiency of about 87% during the measurement. The cells with thin film electrodes showed much better performance with current densities up to 283mA/cm2. Reasons for their better performance are possibly poisoning effects due to impurities in the porous electrodes
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