13,484 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
A parallel nodal-based evolutionary structural optimization algorithm
No full textThis paper is concerned with the minimum weight design of structures using Finite Element Analysis (FEA). A new evolutionary structural optimization (ESO) algorithm is presented. This method departs from previous studies of ESO in that it exploits the movements of the nodes in an unstructured finite element mesh in an appropriate way. An attractive feature of the scheme presented is that it carries out topology optimization in the interior of the domain concurrently with shape optimization of the exterior of the domain. Circular cavities are inserted into the interior of the domain from which the internal topology is then revealed by migration of the cavity edge nodes. Due to the complexity of the resulting cavity geometry the FE mesh tends to be refined internally. A scheme for maintaining a roughly uniform density unstructured finite element mesh throughout the optimization in a two-dimensional domain is presented. The designs produced posses smooth internal and external boundaries. The method uses iterative finite element analysis and re-meshing to correct for any element distortion. The benchmark "Michell Arch" problem is used to demonstrate the approach
Set Functionals in Stochastic Geometry
No full textElectrical Engineering, Mathematics and Computer Scienc
Regional comparative study of motorcycle accidents with special reference to licensing requirements
No full textA.J. McLean, P.C.Y. Chen, T.W. Wong and T. Uka
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