A simultaneous space-time discretization approach to the inverse dynamics of geometrically exact strings

A continuous space-time Galerkin method is newly proposed for the numerical solution of inverse dynamics problems. The proposed space-time finite element method is combined with servo-constraints to partially prescribe the motion of the underlying mechanical system. The new approach to the feedforward control of infinite-dimensional mechanical systems is motivated by the classical method of characteristics. In particular, it is shown that the simultaneous space-time discretization is much better suited to solve the inverse dynamics problem than the semi-discretization approach commonly applied in structural dynamics. Representative numerical examples dealing with elastic strings undergoing large deformations demonstrate the capabilities of the newly devised space-time finite element method

An Enhanced Tire Model for Dynamic Simulation based on Geometrically Exact Shells

In the present work, a tire model is derived based on geometrically exact shells. The discretization is done with the help of isoparametric quadrilateral finite elements. The interpolation is performed with bilinear Lagrangian polynomials for the midsurface as well as for the director field. As time stepping method for the resulting differential algebraic equation a backward differentiation formula is chosen. A multilayer material model for geometrically exact shells is introduced, to describe the anisotropic behavior of the tire material. To handle the interaction with a rigid road surface, a unilateral frictional contact formulation is introduced. Therein a special surface to surface contact element is developed, which rebuilds the shape of the tire

The world from a cat's perspective - statistics of natural videos

Abstract.: The mammalian visual system is one of the most intensively investigated sensory systems. However, our knowledge of the typical input it is operating on is surprisingly limited. To address this issue, we seek to learn about the natural visual environment and the world as seen by a cat. With a CCD camera attached to their head, cats explore several outdoor environments and videos of natural stimuli are recorded from the animals' perspective. The statistical analysis of these videos reveals several remarkable properties. First, we find an anisotropy of oriented contours with an enhanced occurrence of horizontal orientations, earlier described in the "oblique effect” as a predominance of the two cardinal orientations. Second, contrast is not elevated in the center of the images, suggesting different mechanisms of fixation point selection as compared to humans. Third, analyzing a sequence of images we find that the precise position of contours varies faster than their orientation. Finally, collinear contours prevail over parallel shifted contours, matching recent physiological and anatomical results. These findings demonstrate the rich structure of natural visual stimuli and its direct relation to extensively studied anatomical and physiological issue

An energy-momentum consistent time integration scheme based on a mixed framework for non-linear electro-elastodynamics

The objective of the present work is the introduction of new mixed variational principles for EM time integrators in electromechanics, hence bridging the gap between the previous work presented by the authors in References [11] and [1], opening up the possibility to a variety of new Finite Element implementations

Social Influence, Risk and Benefit Perceptions, and the Acceptability of Risky Energy Technologies:An Explanatory Model of Nuclear Power Versus Shale Gas

Risky energy technologies are often controversial and debates around them are polarized; in such debates public acceptability is key. Research on public acceptability has emphasized the importance of intrapersonal factors but has largely neglected the influence of interpersonal factors. In an online survey (N = 948) with a representative sample of the United Kingdom, we therefore integrate interpersonal factors (i.e., social influence as measured by social networks) with two risky energy technologies that differ in familiarity (nuclear power vs. shale gas) to examine how these factors explain risk and benefit perceptions and public acceptability. Findings show that benefit perceptions are key in explaining acceptability judgments. However, risk perceptions are more important when people are less familiar with the energy technology. Social network factors affect perceived risks and benefits associated with risky energy technology, hereby indirectly helping to form one's acceptability judgment toward the technology. This effect seems to be present regardless of the perceived familiarity with the energy technology. By integrating interpersonal with intrapersonal factors in an explanatory model, we show how the current "risk-benefit acceptability" model used in risk research can be further developed to advance the current understanding of acceptability formation

Konzepte der Numerik endlicher Rotationen

Algorithmen zur Berechnung endlicher Rotation, die typischer Weise bei Finite Element Simulationen Anwendung finden, können in zwei allgemeine Kategorien unterteilt werden: Im Rahmen der ersten Kategorie werden iterative Rotationsfreiheitsgrade betrachtet, wohingegen der zweiten Kategorie totale Rotationsfreiheitsgrade zugrunde liegen. Diese Freiheitsgrade konnen auf drei unterschiedliche Konfigurationen bezogen werden: Den letzten Iterationsschritt, den letzten inkrementellen Lastschritt  oder den unrotierten Ausgangszustand. Unabhänging von der gew¨ahlten Parametrisierung endlicher Rotationen  weisen diese Formulierungen unterschiedliche numerische Eigenschaften in Bezug auf Robustheit und Stabilität sowie den erforderlichen zus ¨atzlichen Speicherplatzbedarf auf. Diese allgemein zu klassifizierenden Merkmale werden in diesem Beitrag diskutiert