No abstract

No abstract

SUMMARYInstabilities can introduce highly non-linear effects into structural problems. The instabilities, not clearly associated with a change in a parameter, result in a stochastic variation of the responses. This process variation can be distinguished from the effects of the parameter variation by mapping the response variation onto a predictable space and a residual space, where the predictable space contains the possible effects of the parameter variation, and the residual space contains the process effects. This study discusses the sources (mechanics) of the response variation in this class of problems, the use of response surfaces to distinguish between effects driven by design variable changes and bifurcations, and the visualization of unstable zones in the structure. Analytical problems, a headform impact problem, and an occupant safety study clarify the use of the proposed methodology.

Abstract. Competitive numerical simulation codes solving partial differential equations have to tap the full potential of both modern numerical methods -like multi-grid and adaptive grid refinement -and available computing resources. In general, these two are rival tasks. Typically, hierarchical data structures resulting from multigrid and adaptive grid refinement impede efficient usage of modern memory architectures on the one hand and complicate the efficient parallelization on the other hand due to scattered data for coarse-level-points and unbalanced data trees. In our previous work, we managed to bring together high performance aspects in numerics as well as in hardware usage in a very satisfying way. The key to this success was to integrate space-filling curves consequently not only in the programs flow control but also in the construction of data structures which are processed linearly even for hierarchical multilevel data. In this paper, we present first results on the second challenge, namely the efficient parallelization of algorithms working on hierarchical data. It shows that with the same algorithms as desribed above, the two main demands on good parellel programs can be fulfilled in a natural way, too: The balanced data partitioning can be done quite easily and cheaply by cutting the queue of data linearized along the space-filling curve into equal pieces. Furtheron, this partitioning is quasi-optimal regarding the amount of communication. Thus, we will end up with a code that overcomes the quandary between hierarchical data and efficient memory usage and parallelization in a very natural way by a very deep integration of space-filling-curves in the underlying algorithm.

The paper reports on a joined research project of Knorr-Bremse, Siemens Mobility and the Institute of Robotics and Mechatronics. The goal of the project was to analyse the dynamical behaviour of friction brakes for high-speed trains. It was intended to gain insight into possible vibration mechanisms and to assess the potential for lay-out and operation improvements for future light-weight designs. In particular, the frequency range up to 250 Hz has been addressed, since the corresponding excitation is unavoidable at least to some extent and has to be considered when the brake system is designed. The study includes a comprehensive multibody simulation study and its comparison to experimental results at the test rig of Knorr-Bremse in Munich. The simulation model is adapted step by step in order to clearly identify and separate the influences on the dynamical properties of the complete brake system including its mounting. Additionally a minimal model is introduced that demonstrates some characteristics of the brake system. It turned out that the underlying knowledge is essential for the mechanical lay-out, which could be demonstrated by solving a particular vibration problem in an actual high-speed project.