University of Stuttgart

About: University of Stuttgart is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Laser & Finite element method. The organization has 27715 authors who have published 56370 publications receiving 1363382 citations. The organization is also known as: Universität Stuttgart.

Effects of damping on mode-coupling instability in friction induced oscillations

Abstract: The mode-coupling instability has generally been acknowledged as one of the most prominent mechanisms leading to self-excited oscillations in sliding friction systems. The influence of structural damping on this type of instability mechanism however has not yet been fully clarified. The objective of the present work therefore is to investigate qualitative and quantitative aspects of the mode-coupling instability in the presence of structural damping, which will be assumed as linear viscous. For the sake of simplicity a two-degree-of-freedom minimal model is set up and analyzed. It is shown that under specific conditions the mode-coupling instability may be regarded as a viscous instability in the sense that an increase in structural damping may render a stable system unstable. An explanation for this behavior is given by two lines of argument: First a description and explanation is given in terms of eigenvalue-analysis. Due to the mathematical formality of this approach, the insight gained remains phenomenological. Second, a feedback-loop formalism is developed that allows a more detailed understanding of the underlying mechanical processes. Based on this formalism, necessary and in sum sufficient conditions for the onset of instability can be deduced and also the role of damping can be clarified.

The (Q,q)-Schur algebra

Abstract: In this paper we use the Hecke algebra of type which is an analogue of the has ‘generic’ basis which is independent of the choice of ring and the parameters $\mathcal S$-modules defined over any field.1991 Mathematics Subject Classification: 16G99, 20C20, 20G05.

Initiation and propagation of flame fronts in lean CH4-air mixtures by the three modes of the ignition spark

Abstract: The initiation and subsequent propagation of flame fronts by breakdown, are and glow discharge ignition devices have been investigated by time resolved interferometry in CH4-air mixtures (1/Ф=1.0, 1.11, 1.25, 1.4) at 4 bar. Based on size, effective expansion velocity, and radial temperature profiles across the flame fronts as functions of time after spark onset, it is shown that the breakdown controls the inflammation process up to ≈1 ms. The breakdown is far better suited for inflaming combustible mixtures than are or glow discharge due to very high energy transfer efficiency (≈95%), large double sided contact areas with the unburnt mixture, very steep gradients of temperature and particle density, and reignition capabilities at ≈300 μs. Thus extremely lean (1/Φ≈1.6) mixtures ignited at high flow velocities with high inflammation probabilities.