5,214 research outputs found
Drag Reduction by Applying Speedstrips on Rowing Oars
No full textAbstractThe objective of this study was to determine the advantage of the application of speedstrips to rowing oars for a lightweight single sculler. The research method comprehended three steps: (1) the analysis of the rowing oar movement, (2) the determination of the change in drag and (3) the composition of a rowing model to establish the advantage that could be achieved. The parameters needed for the model: boat velocity, oar angle velocity and power delivered by the rower, were recorded on a real single sculler. The change in drag due to speedstrips on cylinders was determined by performing wind tunnel experiments. The rowing model (Matlab) simulates a race by using real stroke data of a world-class rower as input, while calculating the drag with the coefficients determined by the wind tunnel experiments. The output of the model is the final advantage by the application of speedstrips to rowing oars. Speedstrips induce a 0.1% advantage over a 2000 m race under calm wind conditions. The advantage increases up to .4% with a headwind velocity of 5 m s-1. For bigger boats, the advantage could be even more significant
Drag and Power-loss in Rowing Due to Velocity Fluctuations
No full textAbstractThe flow motions in the turbulent boundary layer between water and a rowing boat initiate a turbulent skin friction. Reducing this skin friction results in better rowing performances. A Taylor-Couette (TC) facility was used to verify the power losses due to velocity fluctuations PV′ in relation to the total power , as a function of the velocity amplitude A. It was demonstrated that an increase of the velocity fluctuations results in a tremendous decrease of the velocity efficiency eV . The velocity efficiency eV for a typical rowing velocity amplitude A of 20 – 25% was about 0.92 – 0.95%. Suppressing boat velocity fluctuations with 60% will increase boat speed with 1.6%. Riblet surfaces were applied on the inner and outer cylinder wall to indicate the drag reducing ability of such surfaces. The results of the measurements at constant velocity are identical as the results reported earlier, while the experimental configuration was different. This confirms once more the consistency of the TC-system for drag studies. The maximum drag reduction DR was 3.4% at a Reynolds number Res 4.7 × 104, which corresponds to a shear velocity in this TC-system with water of V 4.7 m/s. For typical rowing velocity fluctuations, the riblets maintain to reduce the drag with 2.8% and corresponds to a averaged velocity increase of 0.9%. The drag reducing ability of riblets is partly lost due to velocity fluctuations with high amplitudes (A > 20%). From these results, it is concluded that the friction coefficient Cf will vary within one cycle. Higher acceleration/deceleration leads to a additional level of turbulent kinetic energy
A.J. Cronin. A doctor into lifelong writer
No full textReality and fiction might be strictly coexistent in the narrative world. The author of this article, after a deep reading of A.J. Cronin’s novels, has tried to find out the right key to penetrate into the novelist’s intricate world. After many interrogatives on A.J. Cronin both as a man and writer, the author , finally, has been able to grasp from the pages of the novelist, the suffering of a man who has made of his romance the history of his own life
Computing with cables: Towards massively parallel neuro computers
No full textElectrical Engineering, Mathematics and Computer Scienc
Radio Frequency Interference Mitigation in Radio Astronomy
No full textThe next generation of radio telescopes is expected to be one to two orders of magnitude more sensitive than the current generation. Examples of such new telescopes are the Low Frequency Array (LOFAR), currently under construction in the Netherlands, and the Square Kilometer Array (SKA), currently in a concept study phase. Another trend is that technological advances in the fields of electronics and communications systems have led to a vast increase in radio communication applications and systems, and also to an increasing demand for radio spectrum. These two trends, more sensitive telescopes and a much denser spectrum use, imply that radio astronomy will become more vulnerable to interference from radio transmitters. Although protection criteria exist for radio astronomy, it becomes increasingly difficult to keep the radio astronomy frequency bands free from interference. In order to mitigate interference in radio astronomical data, filtering techniques can be used. In this thesis, modern array signal processing techniques have been applied to narrow-band multichannel interference detection and excision, and to narrow-band spatial interference filtering. By investigating the subspace structure of the telescope array output covariance matrices, new results were found, such as upper limits on interference residuals after excision and spatial filtering. The effect of bandwidth, extendedness of the interfering sources, and multipath effects on the detection and spatial filter effectiveness were studied as well. The advantage of a multichannel approach over a single telescope approach was demonstrated by using experimental data from the Westerbork Synthesis Radio Telescope (WSRT). As the performance of mitigation algorithms can be improved by calibration of the telescope gains and noise powers, calibration algorithms were developed. These algorithms were verified both for single and dual polarised arrays. Finally, a LOFAR interference mitigation strategy was developed.Electrical Engineering, Mathematics and Computer Scienc
Asymptotic spectra of large matrices coming from the symmetrization of Toeplitz structure functions and applications to preconditioning
No full textThe singular value distribution of the matrix-sequence {YnTn[f]}n, with Tn[f] generated by (Formula presented.), was shown in [J. Pestana and A.J. Wathen, SIAM J Matrix Anal Appl. 2015;36(1):273-288]. The results on the spectral distribution of {YnTn[f]}n were obtained independently in [M. Mazza and J. Pestana, BIT, 59(2):463-482, 2019] and [P. Ferrari, I. Furci, S. Hon, M.A. Mursaleen, and S. Serra-Capizzano, SIAM J. Matrix Anal. Appl., 40(3):1066-1086, 2019]. In the latter reference, the authors prove that {YnTn[f]}n is distributed in the eigenvalue sense as (Formula presented.) under the assumptions that f belongs to (Formula presented.) and has real Fourier coefficients. The purpose of this paper is to extend the latter result to matrix-sequences of the form {h(Tn[f])}n, where h is an analytic function. In particular, we provide the singular value distribution of the sequence {h(Tn[f])}n, the eigenvalue distribution of the sequence {Ynh(Tn[f])}n, and the conditions on f and h for these distributions to hold. Finally, the implications of our findings are discussed, in terms of preconditioning and of fast solution methods for the related linear systems
Set Functionals in Stochastic Geometry
No full textElectrical Engineering, Mathematics and Computer Scienc
Afsluiting Veersegat VIII: Ontgrondingen ten gevolge van het plaatsen van doorlaatcaissons: Rapport modelonderzoek
No full textNa het gereedkomen van het wintersluitgat in de Veerse Gatdam werd de bodem ten zuidoosten van het sluitgat achter de bezinking plaatselijk uitgeschuurd tot een diepte van N.A.P. - 36 m. Deze ontgronding was een gevolg van de wervelstraat die bij vloed van het landhoofd aan de Noordbevelandse zijde binnenwaarts trok. Door het plaatsen van de doorlaatcaissons zouden, zeker wanneer, zoals aanvankelijk in de bedoeling lag, de laatst geplaatste en de helft van de voordien geplaatste caisson gasloten zouden, blijven wervelstraten worden geïntroduceerd. Daarom is het modelonderzoek betreffende de afsluiting van het Veerse Gat voortgezet met een onderzoek naar de ontgrondingen, die in de omgeving van het sluitgat ten gevolge van het plaatsen van de doorlaatcaissons zouden kunnen optreden. In het prototype kon de ontwikkeling van de ontgrondingen, dank zij de wekelijkse peilingen die door Rijkswaterstaat werden verricht, op de voet worden gevolgd. Daardoor deed zich de gelegenheid voor de ontgrondingen in het model te vergelijken met die in het prototype. Eet bleek, dat de ontgrondingen in het samengetrokken model M 586 beter werden gereproduceerd dan in het niet samengetrokken model M 588. In een nota van het Waterloopkundig Laboratorium betreffende de afwijkingen tussen model en prototype in verband met de vormgeving van het wintersluitgat wordt als verklaring hiervoor aangegeven, dat het model M 588 in zijn geheel te ruw is en daardoor het stroombeeld niet voldoende juist weergeeft. Het onderhavige onderzoek is dan ook verricht in het samengetrokken model M 586 (schalen 150/50). Vanwege de korte tijd die beschikbaar was, zijn slechts de belangrijkste fasen uit de sluitingsperiode onderzocht.Deltawerken, Veerse Ga
Modern Medival Monasteries: Two Modern Dutch Monasteries compared to the Benedictine Ideal
No full textIn the 19th century the interest in monasteries and monastic life returned, leading to the design of the Abbey of Egmond by architect A.J. Kropholler in 1929 and the design of St. Benedictusberg in Vaals by architect Dom Hans van der Laan.This research investigates how the architects A.J. Kropholler and Dom Hans van der Laan incorporated the Benedictine Rule into their modern abbeys. Specifically, it examines the historical context of the Dutch abbeys and the development of monastic architecture, drawing on Wolfgang Braunfels’ Monasteries of Western Europe as a foundation for contextualizing the St. Gall Utopia. Additionally, it explores the design principles and philosophies that influenced the layout and construction of the Dutch abbeys under investigation, through an analysis of the floor plans and layouts of the abbeys, as well as interviews with a current monk or an employee at both Dutch abbeys.The thesis is structured into four chapters, beginning with an examination of the Benedictine Rule and Utopia of St. Gall, followed by separate analyses of St. Adalbert’s Abbey in Egmond by A.J. Kropholler and the St. Benedictusberg Abbey in Vaals by Dom Hans van der Laan. The final chapter compares the two Dutch abbeys with each other and the Utopia of St. Gall. The study is limited by the scope of the two Dutch abbeys chosen for analysis, but it offers insights into how the architects of the abbeys incorporated the Benedictine Rule into their designs, and sheds light on the role of monasteries in modern society.The spaces for the three main pillars of the Benedictine Rule are integrated in both Dutch Abbeys. However this research shows that the role in society for Monasteries has changed. The essential elements of the St. Gall Utopia can still be recognized in both floor plans, however the size and clustering of several functions changed.ABSTRACTAR2A011Architectural History ThesisArchitecture, Urbanism and Building Science
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