32,795 research outputs found

    Вдосконалення робочого процесу гідротурбін та систем їх регулювання

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    The paper provides the detail analysis of the causes of various types of the vortex motion of the turbulent flow in the inlet parts of the turbine and in the inter-blade channels of the runner. The causes of the appearance of large-scale vortex structures in the meridional sections of the spiral case of radial-axial hydraulic turbines with the heads of 400–500 m are shown. As a result of this phenomenon, in the section of the spiral case the flow is directed in the region of the walls to the runner. In the central part it is directed from the runner, i. e. the spiral case executing its functions of supplying the flow functions only with part of its section – the near-wall zone – where the vortex near-wall flow with increased velocity and energy losses enters to the channels of the runner. These conclusions in the work are argued by extensive experimental data. Energy losses in the spiral case reaches 3–5 % and a complex vortex structure, which enters to the runner, leads to a decrease of the energy characteristics. The flow inlet to the runner using nozzle devices located on the ring in front of the runner is considered in the paper. These nozzle devices increase the velocity by five or more times and provide low losses in the inlet (about 0,5 %) and almost uniform flow in front of the runner with a moment of quantity of motion, which provides an optimal operation of the hydraulic turbine. The improvement of the working flow and control systems is presented in this paper using new design solutions, for which more than ten patents of Ukraine for the invention were obtained. In particular, as a result of this study of the working processes of Francis-Deriaz hydraulic turbines, which allowed the use of blade turbines for the heads of more than 400–500 m up to 800–1000 m with high energy and cavitation characteristics with wide operating areas in terms of rates (powers) and heads, with an increase of 2–7 % average operating efficiency. The working process of a new type of diagonal-axial hydraulic turbine with a very wide operation range in terms of flow and pressure with a significantly increased average operating efficiency, increased operation reliability, which is illustrated by the predictive universal characteristic, is also considered. This characteristic allows the use of rotary-blade hydraulic turbines for heads up to 230–250 m. Therefore, the carried out improvement of the working process of hydraulic turbines and their control systems convincingly proves the advantage of the new scientific and technical solutions in comparison with previously used ones.В роботі проведено детальний аналіз причин виникнення різних видів завихреності турбулентного потоку в підвідних органах гідротурбіни і в міжлопатевих каналах робочого колеса. Показано причини виникнення великомасштабних вихрових структур в меридіональних перетинах спіральних камер радіально-осьових гідротурбін на напори 400–500 м. Внаслідок цього явища в перерізі спіральної камери потік спрямований в області стінок до робочого колеса, а в центральній частині від робочого колеса, тобто спіральна камера виконуючи свої функції підведення потоку функціонує лише частиною перетину – пристіночної зони, в якій завихрений пристінковий потік зі збільшеною швидкістю і втратами енергії надходить в канали робочого колеса. Ці висновки в роботі аргументовані чисельними експериментальними даними. Втрати енергії в спіральній камері досягають 3–5 % і складна вихрова структура, що надходить в робоче колесо приводить до зниження енергетичних показників. В роботі розглядається підвід потоку до робочого колеса за допомогою розташованих по кільцю перед робочим колесом соплових апаратів, що збільшують швидкість в п'ять і більше разів і забезпечують низькі втрати в підвідних органах (близько 0,5 %) практично рівномірний потік перед робочим колесом з моментом кількості руху, що забезпечує оптимальну роботу гідротурбіни. Удосконалення робочого процесу і систем регулювання представлено в цій роботі з використанням нових конструктивних рішень, на які отримані більш десяти патентів України на винахід. У тому числі в результаті дослідження робочих процесів радіально-діагональних гідротурбін, що дозволили застосовувати лопатеві турбіни на напори понад 400–500 м аж до 800–1000 м з високими енергокавітаційними показниками з широкими зонами експлуатації по витратам (потужностям) і напору, зі збільшеним на 2–7 % середньоексплуатаційним ККД. Розглянуто також робочий процес нового типу діагонально-осьової гідротурбіни з досить широким діапазоном експлуатації по витратам та напору з істотно підвищеним середньоексплуатаційним ККД, підвищеною надійністю експлуатації, що ілюструється прогнозною універсальною характеристикою, що дозволяє застосувати поворотно-лопатеві гідротурбіни на напори до 230–250 м. Таким чином, проведене вдосконалення робочого процесу гідротурбін і систем їх регулювання переконливо доводить перевагу нових науково-технічних рішень в порівнянні з раніше застосовуваними

    A contrasting look at self-organization in the Internet and next-generation communication networks

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    This article examines contrasting notions of self-organization in the Internet and next-generation communication networks, by reviewing in some detail recent evidence regarding several of the more popular attempts to explain prominent features of Internet structure and behavior as "emergent phenomena." In these examples, what might appear to the nonexpert as "emergent self-organization" in the Internet actually results from well conceived (albeit perhaps ad hoc) design, with explanations that are mathematically rigorous, in agreement with engineering reality, and fully consistent with network measurements. These examples serve as concrete starting points from which networking researchers can assess whether or not explanations involving self-organization are relevant or appropriate in the context of next-generation communication networks, while also highlighting the main differences between approaches to self-organization that are rooted in engineering design vs. those inspired by statistical physics

    Computationally Efficient and Robust BIC-Based Speaker Segmentation

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    An algorithm for automatic speaker segmentation based on the Bayesian information criterion (BIC) is presented. BIC tests are not performed for every window shift, as previously, but when a speaker change is most probable to occur. This is done by estimating the next probable change point thanks to a model of utterance durations. It is found that the inverse Gaussian fits best the distribution of utterance durations. As a result, less BIC tests are needed, making the proposed system less computationally demanding in time and memory, and considerably more efficient with respect to missed speaker change points. A feature selection algorithm based on branch and bound search strategy is applied in order to identify the most efficient features for speaker segmentation. Furthermore, a new theoretical formulation of BIC is derived by applying centering and simultaneous diagonalization. This formulation is considerably more computationally efficient than the standard BIC, when the covariance matrices are estimated by other estimators than the usual maximum-likelihood ones. Two commonly used pairs of figures of merit are employed and their relationship is established. Computational efficiency is achieved through the speaker utterance modeling, whereas robustness is achieved by feature selection and application of BIC tests at appropriately selected time instants. Experimental results indicate that the proposed modifications yield a superior performance compared to existing approaches

    Distribution pattern-driven development of service architectures

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    Distributed systems are being constructed by composing a number of discrete components. This practice is particularly prevalent within the Web service domain in the form of service process orchestration and choreography. Often, enterprise systems are built from many existing discrete applications such as legacy applications exposed using Web service interfaces. There are a number of architectural configurations or distribution patterns, which express how a composed system is to be deployed in a distributed environment. However, the amount of code required to realise these distribution patterns is considerable. In this paper, we propose a distribution pattern-driven approach to service composition and architecting. We develop, based on a catalog of patterns, a UML-compliant framework, which takes existing Web service interfaces as its input and generates executable Web service compositions based on a distribution pattern chosen by the software architect

    The utility of twins in developmental cognitive neuroscience research: How twins strengthen the ABCD research design

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    The ABCD twin study will elucidate the genetic and environmental contributions to a wide range of mental and physical health outcomes in children, including substance use, brain and behavioral development, and their interrelationship. Comparisons within and between monozygotic and dizygotic twin pairs, further powered by multiple assessments, provide information about genetic and environmental contributions to developmental associations, and enable stronger tests of causal hypotheses, than do comparisons involving unrelated children. Thus a sub-study of 800 pairs of same-sex twins was embedded within the overall Adolescent Brain and Cognitive Development (ABCD) design. The ABCD Twin Hub comprises four leading centers for twin research in Minnesota, Colorado, Virginia, and Missouri. Each site is enrolling 200 twin pairs, as well as singletons. The twins are recruited from registries of all twin births in each State during 2006–2008. Singletons at each site are recruited following the same school-based procedures as the rest of the ABCD study. This paper describes the background and rationale for the ABCD twin study, the ascertainment of twin pairs and implementation strategy at each site, and the details of the proposed analytic strategies to quantify genetic and environmental influences and test hypotheses critical to the aims of the ABCD study. Keywords: Twins, Heritability, Environment, Substance use, Brain structure, Brain functio
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