20,824 research outputs found

    Recurrent flow analysis in spatiotemporally chaotic 2-dimensional Kolmogorov flow

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    Motivated by recent success in the dynamical systems approach to transitional flow, we study the efficiency and effectiveness of extracting simple invariant sets (recurrent flows) directly from chaotic/turbulent flows and the potential of these sets for providing predictions of certain statistics of the flow. Two-dimensional Kolmogorov flow (the 2D Navier-Stokes equations with a sinusoidal body force) is studied both over a square [0, 2{\pi}]2 torus and a rectangular torus extended in the forcing direction. In the former case, an order of magnitude more recurrent flows are found than previously (Chandler & Kerswell 2013) and shown to give improved predictions for the dissipation and energy pdfs of the chaos via periodic orbit theory. Over the extended torus at low forcing amplitudes, some extracted states mimick the statistics of the spatially-localised chaos present surprisingly well recalling the striking finding of Kawahara & Kida (2001) in low-Reynolds-number plane Couette flow. At higher forcing amplitudes, however, success is limited highlighting the increased dimensionality of the chaos and the need for larger data sets. Algorithmic developments to improve the extraction procedure are discussed

    A robust design methodology suitable for application to one-off products

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    Robust design is an activity of fundamental importance when designing large, complex, one-off engineering products. Work is described which is concerned with the application of the theory of design of experiments and stochastic optimization methods to explore and optimize at the concept design stage. The discussion begins with a description of state-of-the-art stochastic techniques and their application to robust design. The content then focuses on a generic methodology which is capable of manipulating design algorithms that can be used to describe a design concept. An example is presented, demonstrating the use of the system for the robust design of a catamaran with respect to seakeeping

    The expulsion of the Moriscos from the Catalan Countries: ideology and history

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    The expulsion of the Moriscos from the Catalan Countries, particularly from the Valencian Country, has been interpreted in various ways. Historians who have dealt with the subject have tended towards one or two main positions that can be termed Moriscophile and Moriscophobic. The former considered that the expulsion of a very active Islamic minority brought about a serious check to the process of capitalist development. The latter, taking for granted that the Morisco minority was not so economically important, believed their expulsion did not have such an influence, and even that if they did have an influence, it was in the opposite direction. Both interpretations were heavily charged with ideological presuppositions. The present article attempts to settle the question more objectively by analysing the changes that took place in the population structure in the wake of the expulsion, the evolution of agricultural production during the entire Modern Age, and the changes in the structure of land ownership. The results seem to endorse what we have called Moriscophobic interpretation. This is because the population structure, the evolution of agricultural production, and changes in the structure of ownership seem to point to an acceleration in growth of the capitalistic economy after the expulsion

    Per la religió, el rei i la pàtria

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    A radial mode ultrasonic horn for the inactivation of <i>Escherichia coli</i> K12

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    Tuned cylindrical radial mode ultrasonic horns offer advantages over ultrasonic probes in the design of flow-through devices for bacterial inactivation. This study presents a comparison of the effectiveness of a radial horn and probe in the inactivation of Escherichia coli K12. The radial horn is designed using finite element analysis and the predicted modal parameters are validated using experimental modal analysis. A validated finite element model of the probe is also presented. Visual studies of the cavitation fields produced by the radial horn and probe are carried out using luminol and also backlighting to demonstrate the advantages of radial horns in producing a more focused cavitation field with widely dispersed streamers. Microbiological studies show that, for the same power density, better inactivation of E. coli K12 is achieved using the radial horn and, also, the radial horn offers greater achievable power density resulting in further improvements in bacterial inactivation. The radial horn is shown to be more effective than the probe device and offers opportunities to design in-line flow-through devices for processing applications
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