NCR-days 2008 : 10 years NCR: November 20-21

De verschillende subthema’s van de NCR-dagen 2008, (i) Stroomgebied en Overstromingsrisico management (ii) Hydrologie en (iii) Geomorfodynamica en Morfologie, dekken een groot gedeelte van het hedendaagse onderzoek dat in Nederland op rivierkundig gebied wordt uitgevoerd

Identifying Self-excited Vibrations with Evolutionary Computing

AbstractThis study uses differential evolution to identify the coeffic ients of second-order differentia l equations of self-e xc ited vibrations fro m a time signal. The motivation is found in the ample occurrence of this vibration type in engineering and physics, in particu lar in the real -life proble m of v ibrations of hydraulic structure gates. In the proposed method, an equation structure is assumed at the level of the ordinary differentia l equation and a population of candidate coefficient vectors undergoes evolutionary training. In this way the numerical constants of non-linear terms of various self-e xc ited vibration types were recovered fro m the time signal and the velocity value only at the initial t ime. Co mparisons are given regarding accuracy and computing time. Dependency of the test errors on the algorith m para meters is studied in a sensitivity analysis. The presented evolutionary method shows good promise for future applicat ion in engineering systems, in particular operational early -wa rning systems that recognise oscillations with negative damping before they can cause damage

The presence of supposedly primitive human tools along the upper reaches of the Kizil Irmak in Anatolia

Die ersten Angaben über Flußterrassen in Ost-Anatolien wurden vor kurzem durch Izbirak (1962) und Ketin (1962) gemacht. Die Verfasser der vorliegenden Arbeit haben eine rasche und noch oberflächliche Exploration eines Terrassensystems von fünf bis sieben verschiedenen Niveaus ausgeführt entlang dem oberen Lauf des großen Kizil Irmak (des Roten Flusses) zwischen Sivas und Kayseri in Ost-Anatolien. Teilweise ist es die von Izbirak beschriebene Gegend, größtenteils geht sie aber über diese hinaus. Die Terrassenflächen sind ziemlich gleichmäßig entwickelt entlang des genannten Teils des Flusses, verschwinden aber plötzlich weiter unterhalb. Die Verfasser meinen mit Izbirak, daß die Entstehung dieser Terrassen wahrscheinlich in erster Linie tektonisch und erst an zweiter Stelle klimatisch bedingt ist. Die dritte Terrasse (von unten an gezählt) enthielt überall eine nur geringe Zahl vermutlicher primitiver Artefakten, unter ihnen einige „pebble-tools". Diese sind in vorliegendem Aufsatz beschrieben; sie stellen vielleicht einen Beweis für die Anwesenheit von frühpleistozänen Hominiden in der Türkei dar. In einem Fall wurde in dieser dritten Terrasse ein fossiler Molar eines Hipparion in situ gefunden, teilweise bedeckt mit demselben versteinerten roten Lehm, welcher auch einige der vermutlichen Artefakten einhüllte. Das Alter der Terrassen ist noch nicht genau bekannt. Es scheint aber, daß die ältesten und höchstgelegenen Tertiär sind, die Terrasse, welche die Artefakten enthält, vielleicht dem untersten Pleistozän angehört, und die untersten Terrassen in das junge Pleistozän oder gar Holozän zu stellen sind.researc

How to Speed up Optimization? Opposite-Center Learning and Its Application to Differential Evolution

This paper introduces a new sampling technique called Opposite-Center Learning (OCL) intended for convergence speed-up of meta-heuristic optimization algorithms. It comprises an extension of Opposition-Based Learning (OBL), a simple scheme that manages to boost numerous optimization methods by considering the opposite points of candidate solutions. In contrast to OBL, OCL has a theoretical foundation-the opposite center point is defined as the optimal choice in pair-wise sampling of the search space given a random starting point. A concise analytical background is provided. Computationally the opposite center point is approximated by a lightweight Monte Carlo scheme for arbitrary dimension. Empirical results up to dimension 20 confirm that OCL outperforms OBL and random sampling: the points generated by OCL have shorter expected distances to a uniformly distributed global optimum. To further test its practical performance, OCL is applied to differential evolution (DE). This novel scheme for continuous optimization named Opposite-Center DE (OCDE) employs OCL for population initialization and generation jumping. Numerical experiments on a set of benchmark functions for dimensions 10 and 30 reveal that OCDE on average improves the convergence rates by 38% and 27% compared to the original DE and the Opposition-based DE (ODE), respectively, while remaining fully robust. Most promising are the observations that the accelerations shown by OCDE and OCL increase with problem dimensionality

Reducing cross-flow vibrations of underflow gates: experiments and numerical studies

An experimental study is combined with numerical modelling to investigate new ways to reduce cross-flow vibrations of hydraulic gates with underflow. A rectangular gate section placed in a flume was given freedom to vibrate in the vertical direction. Holes in the gate bottom enabled leakage flow through the gate to enter the area directly under the gate which is known to play a key role in most excitation mechanisms. For submerged discharge conditions with small gate openings the vertical dynamic support force was measured in the reduced velocity range 1.5 < Vr < 10.5 for a gate with and without holes. The leakage flow through the holes significantly reduced vibrations. This attenuation was most profound in the high stiffness region at 2 < Vr < 3.5. Two-dimensional numerical simulations were performed with the Finite Element Method to assess local velocities and pressures for both gate types. A moving mesh covering both solid and fluid domain allowed free gate movement and two-way fluid-structure interactions. Modelling assumptions and observed numerical effects are discussed and quantified. The simulated added mass in still water is shown to be close to experimental values. The spring stiffness and mass factor were varied to achieve similar response frequencies at the same dry natural frequencies as in the experiment. Although it was not possible to reproduce the vibrations dominated by impinging leading edge vortices (ILEV) at relatively low Vr, the simulations at high Vr showed strong vibrations with movement-induced excitation (MIE). For the latter case, the simulated response reduction of the ventilated gate agrees with the experimental results. The numerical modelling results suggest that the leakage flow diminishes the whipping effect of fluctuations at the trailing edge associated with the streamwise pressure drop across the gate and the body's vertical oscillatory motion.Comment: 27 pages, 15 figures, 2 table

Evolutionary Design of Numerical Methods: Generating Finite Difference and Integration Schemes by Differential Evolution

Classical and new numerical schemes are generated using evolutionary computing. Differential Evolution is used to find the coefficients of finite difference approximations of function derivatives, and of single and multi-step integration methods. The coefficients are reverse engineered based on samples from a target function and its derivative used for training. The Runge-Kutta schemes are trained using the order condition equations. An appealing feature of the evolutionary method is the low number of model parameters. The population size, termination criterion and number of training points are determined in a sensitivity analysis. Computational results show good agreement between evolved and analytical coefficients. In particular, a new fifth-order Runge-Kutta scheme is computed which adheres to the order conditions with a sum of absolute errors of order 10^-14. Execution of the evolved schemes proved the intended orders of accuracy. The outcome of this study is valuable for future developments in the design of complex numerical methods that are out of reach by conventional means.Comment: 19 pages, 7 figures, 10 tables, 4 appendice

Listening Space:An Exploratory Case Study on a Persuasive Game Designed to Enrich the Experience of Classical Music Concerts

Classical music venues in the Netherlands and throughout the world are struggling to attract new audiences. Especially younger visitors are underrepresented. Previous research emphasizes the importance of providing new, potentially interested audiences with more means to consume the music. This paper presents an exploratory case study with the persuasive game Listening Space which we developed to help attract new audiences and thus preserve Western classical music heritage. In particular, we studied to what extent this game could promote more varied ways of listening to classical music and thus enrich the experience of visiting a classical music concert. We designed and executed a controlled randomized trial with surveys before and after the experiment as well as a series of in-depth interviews with participants after the experiment. Our treatment group consisted of 139 participants (both new and existing visitors). They played our digital game at their own convenience, followed by a visit to a concert in a renowned classical music concert hall. A control group of 165 participants only visited the concerts. We measured the effects of the game – changes in the ways participants listen to classical music – through self-report in questionnaires before and after the experiment. Results show that Listening Space seems most effective for new audiences: the game promoted more varied ways of listening in the treatment group and thus enriched their experience of visiting a classical music concert. The control group of new visitors did not show an effect and also no differences were found between the treatment and control groups of regular visitors of classical music concerts We employed regression analysis to identify predictors of the game's effect on listening styles: participants’ age and their level of appreciation of the classical music genre were negatively related to the effectiveness of the game. The way in which participants experienced the game also significantly influenced the effectiveness. This case study shows the potential of using games to promote classical music concerts: games seem to be valuable in attracting new, young audiences and, therefore, represent powerful instruments to help preserve Western classical music cultural heritage

"...weil wir praktisch in 'ner verkehrten Welt leben": Schichtarbeiter und ihre Frauen erzählen

"Ich war vor kurzem mal bei meinem Schwager eingeladen. Der ist Ingenieur im öffentlichen Dienst. Und da waren mehrere Leute, die auch im öffentlichen Dienst arbeiten. Die haben mich gefragt: 'Ham Sie eigentlich auch gleitende Arbeitszeit?' - Ich sach': 'Ja, meine Woche beginnt Montagmorgen um sechs bis zwei ... und dann Sonntagabend um zehn bis annern Morgen um sechs. Und dann die nächste Woche von mittags zwei bis abends um zehn.' - Da hat man mich angeguckt, als wenn man sagen wollte, der muß irgendwie nich' ganz hundertprozentig klar im Kopf sein ... 'Wieso, die stellen doch die Öfen übers Wochenende ab?' - Ich sach: 'Was?' Ich sach: 'Ham Sie überhaupt eine Vorstellung von einem Stahlwerk', ich sach, 'wo man überhaupt arbeitet?' Ich sach: 'Bei uns werden Montagmorgen die Maschinen angeschmissen, im Dreischichtsystem', ich sach, 'und dann geht das bis Sonnabendabend um zehn Uhr ... und natürlich nachts und Sonntags auch!' - 'Och ', ham die gesagt, 'das würd' ich nur zwei Tage machen, dann wär' ich tot'. ... Das kann sich mancher Außenstehende gar nicht vorstellen, wie das ist, wenn wir da mittags zur Schicht fahren - und statt in den Garten oder zum Baden zu fahren, müssen wir zur Schicht. Das ist ..." (Jürgen Mahnke, Schichtarbeiter