Telematik für Österreichs Verkehrssystem

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Telematik für ?sterreichs Verkehrssystem     

Finding alternatives and reduced formulations for process-based models

This paper addresses the problem of model complexity commonly arising in constructing and using process-based models with intricate interactions. Apart from complex process details the dynamic behavior of such systems is often limited to a discrete number of typical states. Thus, models reproducing the system's processes in all details are often too complex and over-parameterized. In order to reduce simulation times and to get a better impression of the important mechanisms, simplified formulations are desirable. In this work a data adaptive model reduction scheme that automatically builds simple models from complex ones is proposed. The method can be applied to the transformation and reduction of systems of ordinary differential equations. It consists of a multistep approach using a low dimensional projection of the model data followed by a Genetic Programming/Genetic Algorithm hybrid to evolve new model systems. As the resulting models again consist of differential equations, their process-based interpretation in terms of new state variables becomes possible. Transformations of two simple models with oscillatory dynamics, simulating a mathematical pendulum and predator-prey interactions respectively, serve as introductory examples of the method's application. The resulting equations of force indicate the predator-prey system's equivalence to a nonlinear oscillator. In contrast to the simple pendulum it contains driving and damping forces that produce a stable limit cycle.     

Mass-selective vibrational spectroscopy of vanadium oxide cluster ions

A corner stone in the study of the size-dependent properties of cluster ions in the gas phase is their structural characterization. Over the last 10 years, significant progress has been in this research field because of significant advances in the gas phase vibrational spectroscopy of mass-selected ions. Using a combination of modern experimental and quantum chemical approaches, it is now in most cases possible to uniquely identify the geometric structure of cluster ions, based on the comparison of the experimental and simulated infrared spectra. In this article, we highlight the progress made in this research area by reviewing recent infrared photodissociation (IR-PD) experiments on small and medium sized (up to 30 atoms) vanadium oxide ions.     

Knobology in use: an experimental evaluation of ergonomics recommendations

The scientific basis for ergonomics recommendations for controls has usually not been related to active goal-directed use. The present experiment tests how different knob sizes and torques affect operator performance. The task employed is to control a pointer by the use of a control knob, and is as such an experimentally defined goal-directed task relevant to machine systems in general. Duration of use, error associated with use (overshooting of the goal area) and movement reproduction were used as performance measures. Significant differences between knob sizes were found for movement reproduction. High torques led to less overshooting as opposed to low torques. The results from duration of use showed a tendency that the differences between knob sizes were reduced from the first iteration to the second iteration. The present results indicate that the ergonomically recommended ranges of knob sizes might differently affect operator performance.     

A fixed-point iteration scheme for real-time model predictive control

A simple model predictive control (MPC) concept for nonlinear systems under input constraints is considered. The presented algorithm takes advantage of an MPC formulation without terminal constraints in order to solve the optimality conditions by a fixed-point iteration scheme that is easy to implement and of algorithmic simplicity. Sufficient conditions for the contraction of the fixed-point iterations are derived. To allow for a real-time implementation within an MPC scheme, a constant number of fixed-point iterations is used in each sampling step and sufficient conditions for asymptotic stability and incremental reduction of the suboptimality are presented.     

Superconvergent Patch Recovery for plate problems using statically admissible stress resultant fields

In this paper, we study an approach for recovery of an improved stress resultant field for plate bending problems, which then is used for a posteriori error estimation of the finite element solution. The new recovery procedure can be classified as Superconvergent Patch Recovery (SPR) enhanced with approximate satisfaction of interior equilibrium and natural boundary conditions. The interior equilibrium is satisfied a priori over each nodal patch by selecting polynomial basis functions that fulfil the point‐wise equilibrium equations. The natural boundary conditions are accounted for in a discrete least‐squares manner. The performance of the developed recovery procedure is illustrated by analysing two plate bending problems with known analytical solutions. Compared to the original SPR‐method, which usually underestimates the true error, the present approach gives a more conservative error estimate. Copyright © 1999 John Wiley & Sons, Ltd.     

The influence of dynamic ice formation on hydraulic heterogeneity in steep streams

During winter, different types of ice formation are commonly observed in northern boreal stream systems. Although largely overlooked today, river ice has profound effects on in‐stream hydraulics and therefore ice processes should be considered in freshwater stream management and assessment. In particular, limited knowledge exists about the impacts of dynamic ice formation on stream environments. Results presented from the changes of in‐stream heterogeneity in three steep stream environments caused by dynamic ice formation demonstrate that the formation of anchor ice and anchor ice dams may induce significant backwater effects by increasing wetted areas (maximum 43%) and water depths (maximum 241%) and reducing water velocities (maximum 70%); independent of minimal changes in discharge. Consequently, stream environments are transformed from fast‐flow to slow‐flow areas, even on a short temporal scale (<12 h). Furthermore, the anchor ice build‐up initiated static (surface) ice formation due to reduced local water velocities upstream ice dams. Thus, dynamic ice formation plays a key role in the balanced ice regime in steep stream environments and contributes largely to stable static ice cover in these environments. Observations from the present study suggest that the current paradigm emphasizing the role of discharge as the main controller of in‐stream heterogeneity may call for a modification in steep streams that experience seasonal ice formation. This is particularly important if future hydraulic‐/habitat models and assessment tools are to be implemented in freshwater management to realistically characterize steep stream environments in cold climate regions on a seasonal scale. Copyright © 2009 John Wiley & Sons, Ltd.     

High temperature behaviour of NiCrAlY coatings made by laser cladding

The oxidation behaviour of NiCrAlY coatings made by laser cladding on Hastelloy X is presented in this study. Laser cladding is an alternative method to thermal spraying for the production of bond coats. Comparable dense layers with approximately zero porosity should improve the oxidation behaviour. The oxidation behaviour of the coated specimens was assessed by air furnace oxidation tests at 1100 °C for up to 450 h. The coatings were analysed by means of light and electron microscopy techniques, microprobe analysis and X-ray diffraction analysis. The analysis was performed before and after the oxidation tests. The as-clad coating had a columnar dendritic structure and it did not show the presence of the relevant defects. After the oxidation tests an oxide scale was present which consisted of two distinct layers. The layers consisted of an outer layer of mixed spinel-type oxides and an inner continuous layer, in which alumina was present. The obtained results suggested that up to 450 h the system was able to form a continuous alumina layer that could protect the substrate from oxygen diffusion.     

State and potentials of the “Virtual Forming Press”

This article summarizes the state of the model-based analyzing methods. Furthermore, it depicts the application potentials of the so-called “Virtual Press” in fields of press design and development. Continuative applications in manufacturing and operational use of presses are presented. Moreover, the model fundamentals, developed in Wiemer (Stand und Möglichkeiten der Systemsimulation von mechanischen Pressmaschinen für die Blechumformung. Ph. D. Thesis, Technische Universität Dresden 2004), are briefly explained. The paper concludes with application examples for the “Virtual Press” like for dimensioning of the drive systems of a six-ram press with offset in the crank angles, for simulation of reversal clearance at joint of the crank gear and for work piece specific press selection.     

Walk-through animation in three-dimensional scenes on massively parallel systems

This paper presents a new method for distributed walk-through animation in threedimensional scenes on arbitrary networks on a multiprocessor system (Supercluster) that can be scaled to an almost unlimited number of nodes. We show how a threedimensional scene is distributed over the network and calculated in parallel so that all processors work simultaneously and the idle time of all nodes is minimized. A special self-adapting load-balancing scheme is applied to preserve optimal performance.