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Single point velocity distributions in homogeneous isotropic turbulence

Chinese Physics B 2009年第10期18卷 4360-4365页

作者：燕秀林冉政 Shanghai Institute of Applied Mathematics and Mechanics Shanghai University

The starting point for this paper lies in the results obtained by Tatsumi （2004） for isotropic turbulence with the self-preserving hypothesis. A careful consideration of the mathematical structure of the one-point velocity distribution function equation obtained by Tatsumi （2004） leads to an exact ＂analysis of all possible cases and to all admissible solutions of the problem. This paper revisits this interesting problem from a new point of view, and obtains a new complete set of solutions. Based on these exact solutions, some physically significant consequences of recent advances in the theory of homogenous statistical solution of the Navier-Stokes equations are presented. The comparison with former theory was also made. The origin of non-Caussian character could be deduced from the above exact solutions.

关键词： isotropic turbulence probability distribution function

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Suspended sediment load estimation and the problem of inadequate data sampling: a fractal view

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EARTH SURFACE PROCESSES AND LANDFORMS 2006年第4期31卷 414-427页

作者： Sivakumar, B Univ Calif Davis Dept Land Air & Water Resources Davis CA 95616 USA

Suspended sediment load estimation at high resolutions is an extremely difficult task, because: (1) it depends on the availability of high-resolution water discharge and suspended sediment concentration measurements, which are often not available;(2) any errors in the measurements of these two components could significantly influence the accuracy of suspended sediment load estimation;and (3) direct measurements are very expensive. The purpose of this study is to approach this sampling problem from a new perspective of fractals (or scaling), which could provide important information on the transformation of suspended sediment load data from one scale to another. This is done by investigating the possible presence of fractal behaviour in the daily suspended sediment load data for the Mississippi River basin (at St. Louis, Missouri). The presence of fractal behaviour is investigated using five different methods, ranging from general to specific and from monofractal to multi-fractal: (1) autocorrelation function;(2) power spectrum;(3) probability distribution function;(4) box dimension;and (5) statistical moment scaling function. The results indicate the presence of multi-fractal behaviour in the suspended sediment load data, suggesting the possibility of transformation of data from one scale to another using a multi-dimensional model. Copyright (C) 2005 John Wiley & Sons, Ltd.

关键词： suspended sediment load high-resolution data fractals autocorrelation power spectrum probability distribution function box dimension statistical moment scaling function Mississippi River

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Stochastic RUL Calculation Enhanced With TDNN-Based IGBT Failure Modeling

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IEEE TRANSACTIONS ON RELIABILITY 2016年第2期65卷 558-573页

作者： Alghassi, Alireza Perinpanayagam, Suresh Samie, Mohammad Cranfield Univ Sch Aerosp Transport & Mfg Bedford MK43 0A1 England

Power electronics are widely used in the transport and energy sectors. Hence, the reliability of these power electronic components is critical to reducing the maintenance cost of these assets. It is vital that the health of these components is monitored for increasing the safety and availability of a system. The aim of this paper is to develop a prognostic technique for estimating the remaining useful life (RUL) of power electronic components. There is a need for an efficient prognostic algorithm that is embeddable and able to support on-board real-time decision-making. A time delay neural network (TDNN) is used in the development of failure modes for an insulated gate bipolar transistor (IGBT). Initially, the time delay neural network is constructed from training IGBTs' ageing samples. A stochastic process is performed for the estimation results to compute the probability of the health state during the degradation process. The proposed TDNN fusion with a statistical approach benefits the probability distribution function by improving the accuracy of the results of the TDDN in RUL prediction. The RUL (i.e., mean and confidence bounds) is then calculated from the simulation of the estimated degradation states. The prognostic results are evaluated using root mean square error (RMSE) and relative accuracy (RA) prognostic evaluation metrics.

关键词： Insulated gate bipolar transistor (IGBT) power electronics prognostics probability distribution function remaining useful life (RUL) time-delay neural network

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Fluctuation of mean Lyapunov exponent for Kuramoto-Sivashinsky equation

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PHYSICA A 2000年第3-4期285卷 325-331页

作者： Shibata, H Sojo Univ Dept Gen Educ Kumamoto 8600082 Japan

The statistical aspect of Lyapunov exponent for Kuramoto-Sivashinsky equation is studied. Fluctuation of mean Lyapunov exponent is given by the probability distribution function of its time coarse grained quantity, local Lyapunov exponent. The functional form of the probability distribution function is obtained. Its form is different from the one obtained from the large deviation statistics. Also, the relation between the damping constant included in Kuramoto-Sivashinsky equation and Lyapunov exponent is obtained. (C) 2000 Elsevier Science B.V. All rights reserved.

关键词： mean Lyapunov exponent local Lyapunov exponent Kuramoto-Sivashinsky equation probability distribution function

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FLOW REGIME IDENTIFICATION IN CRYOGENIC GAS-LIQUID FLOW-THROUGH VERTICAL TUBES

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CRYOGENICS 1995年第6期35卷 393-398页

作者： DAS, R PATTANAYAK, S Cryogenic Engineering Centre Indian Institute of Technology Kharagpur-721302 India

A method of identifying flow regimes in gas-liquid two-phase flow of cryogenic fluids through vertical tubes has been developed. In this method a small capacitor is used to sense the local void fraction of the flowing mixture. The capacitor is connected to a multivibrator whose pulse width is modulated in response to the changing void fraction. The pulse width is digitized after deducting its stray portion. It is seen that the probability distribution function (PDF) of the digitized pulse width data shows some unique features in different flow regimes. This technique has been used principally to overcome difficulties in detecting the fractional change of a very small capacitance of the void fraction sensor used in monitoring gas-liquid two-phase flow of nitrogen.

关键词： 2-PHASE FLOW FLOW REGIMES CAPACITANCE SENSOR PULSE WIDTH MODULATION probability distribution function

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Waves plus currents crossing at a right angle: near-bed velocity statistics

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JOURNAL OF HYDRAULIC RESEARCH 2018年第4期56卷 464-481页

作者： Faraci, C. Scandura, P. Musumeci, R. E. Foti, E. Univ Messina Dept Engn I-98166 S Agata ME Italy Univ Catania Dept Civil Engn & Architecture Vle A Doria 6 I-95125 Catania Italy

Wave-current flow over a bottom covered with different roughness elements was analysed to provide new insights into the statistical properties of the near-bed velocity. Experimental data of three different experimental campaigns, with orthogonal waves and currents over a sandy bed, a gravel bed and a rippled bed were used. Velocity profiles were acquired by means of a micro-ADV. The paper focuses on the effects that the waves have on the statistics of the velocity in the current direction. In particular, in the case of a steady current only, the near-bed velocities closely follow a Gaussian distribution. When waves are added, the distribution becomes double-peaked. In order to get single-peaked velocity distributions the total velocity events in the current direction were split in two classes according to the sign of the wave directed velocities. The nature of the distribution functions is influenced by the mass conservation principle and, in the rippled bed case, by the vorticity dynamics.

关键词： Bed roughness higher-order statistics probability distribution function ripples wave boundary layer wave-current interaction

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Optimal wind energy penetration in power systems: An approach based on spatial distribution of wind speed

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ENERGY CONVERSION AND MANAGEMENT 2016年 118卷 387-398页

作者： Zolfaghari, Saeed Riahy, Gholam H. Abedi, Mehrdad Golshannavaz, Sajjad Amirkabir Univ Technol Dept Elect Engn Tehran Iran Urmia Univ Dept Elect Engn Orumiyeh Iran

Contributing in power system expansions, the present study establishes an efficient scheme for optimal integration of wind energy resources. The proposed approach highly concerns the spatial distribution of wind speed at different points of a wind farm. In mathematical statements, a suitable probability distribution function (PDF) is well-designed for representing such uncertainties. In such conditions, it is likely to have dissimilar output powers for individual and identical wind turbines. Thus, the overall aggregated PDF of a wind farm remarkably influences the critical parameters including the expected power and energy, capacity factor, and the reliability metrics such as loss of load expectation (LOLE) and expected energy not supplied (EENS). Furthermore, the proposed approach is deployed for optimal allocation of wind energy in bulk power systems. Hence, two typical test systems are numerically analyzed to interrogate the performance of the proposed approach. The conducted survey discloses an over/underestimation of harvestable wind energy in the case of overlooking spatial distributions. Thus, inaccurate amounts of wind farm's capacity factor, output power, energy and reliability indices might be estimated. Meanwhile, the number of wind turbines may be misjudged to be installed. However, the proposed approach yields in a fair judgment regarding the overall performance of the wind farm. Consequently, a reliable penetration level of wind energy to the power system is assured. Extra discussions are provided to deeply assess the promising merits of the founded approach. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Spatial distribution of wind speed Wind farm's output power probability distribution function Reliability indices Optimal expansion planning

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A Parametric Assessment Approach to Solving Facility-Location Problems with Fuzzy Demands

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IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING 2014年第5期9卷 484-493页

作者： Lin, Pei-Chun Watada, Junzo Wu, Berlin Waseda Univ Grad Sch Informat Prod & Syst Wakamatsu Ku Kitakyushu Fukuoka 8080135 Japan Natl Chengchi Univ Dept Math Sci Taipei 11605 Taiwan

In real-world applications, sometimes randomness and fuzziness may coexist. In facility-location problems, the data expressed in natural language may contain vague information. We discuss the uncertainty included in demands in facility-location problems. The uncertain demand is called fuzzy demand in this paper. In the facility-location model, the parameters of fuzzy demand are determined by calculating the estimated expected value of the fuzzy demand, which is obtained by using the estimated parameters of the underlying probability distribution function of the fuzzy data. Moreover, we propose a defuzzification formula of the fuzzy demand called the realization of fuzzy demand. The defuzzification formula of fuzzy demand comprises the upper bound and the lower bound of the fuzzy demand. Moreover, the error of the fuzzy demand is assessed as the mean absolute percentage error of the fuzzy demand. Empirical studies show that we can solve real-life location problems by using the defuzzification formula of fuzzy demand and get higher profit in our facility-location model than by using conventional methods. (C) 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

关键词： fuzzy data uncertain demand probability distribution function fuzzy statistic location decision

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Probabilistic analysis of stress concentration factors in tubular KT-joints reinforced with internal ring stiffeners under in-plane bending loads

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THIN-WALLED STRUCTURES 2016年 99卷 58-75页

作者： Ahmadi, Hamid Yeganeh, Ali Mohammadi, Amir Hossain Zavvar, Esmaeil Univ Tabriz Fac Civil Engn Tabriz *** Iran Sharif Univ Technol Dept Civil Engn Tehran Iran

In the present research, results from the finite element (FE) stress analysis of 108 models, validated using test data obtained from the experimental investigation, was used to propose probability distribution models for stress concentration factors (SCFs) in internally ring-stiffened tubular KT-joints under four types of in-plane bending (IPB) loads. The SCF is one of the crucial parameters in the fatigue reliability analysis of tubular joints. It exhibits considerable scatter which calls for greater emphasis in accurate derivation of its governing probability function. According to the knowledge of the authors, no comprehensive research has been carried out on the probability distribution of SCF5 especially in stiffened tubular joints commonly found in offshore structures. What has been used so far as the probability distribution of SCFs in the reliability analysis of this type of joints is mainly based on assumptions and limited observations, especially in terms of distribution parameters. Based on a FE parametric study, a set of sample databases was prepared for the maximum central- and outer-brace SCF5;and density histograms were generated for these samples. Nine different probability density functions (PDFs) were fitted to these histograms. The maximum likelihood method was used to compute the parameters of fitted distributions. In each case, using a developed computer code, Kolmogorov-Smirnov and chi-squared tests were applied to evaluate the goodness of fit. Finally, the best-fitted distributions were selected and after substituting the values of estimated parameters for each distribution, six fully defined PDFs were developed for the maximum weld-toe SCF5 of central and outer braces in internally ring-stiffened tubular KT-joints subjected to four different types of IPB loading. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： Ring-stiffened tubular KT-joint In-plane bending (IPB) Stress concentration factor (SCF) probability distribution function Kolmogorov-Smirnov test Chi-squared goodness-of-fit test

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A tool for determining urban emission characteristics to be used in exposure assessment

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ENVIRONMENT INTERNATIONAL 2010年第3期36卷 281-289页

作者： Kassomenos, P. Lykoudis, S. Chaloulakou, A. Univ Ioannina Dept Phys GR-45110 Ioannina Greece Inst Environm Res & Sustainable Dev Natl Observ Athens GR-15236 Athens Greece Natl Tech Univ Athens Sch Chem Engn GR-15780 Athens Greece

The exposure of citizens to elevated air pollution concentrations is one of the major factors leading to the deterioration of the quality of life and possibly to health problems in urban areas. The concentration of air pollutants depends largely on pollutant emission levels. If the statistical probability distribution function of the concentration of an air pollutant is known, it is possible to estimate how many times this concentration exceeds the air quality standards, or estimate changes in the emission levels in an area. It can be also used to estimate the long term exposure of population to certain pollutants. In this paper fifteen theoretical probability distribution functions, were used to fit the actual concentration frequency distributions of CO, NO(2), O(3). SO(2), and Black Smoke (BS) in Athens, Greece for a 23-year period. The results showed that the theoretical distribution type best describing the distribution of the pollutants is Inverse Gaussian followed by the Extreme value distribution. The number of exceedances of air quality limits was used to validate the performance of the theoretical distributions that were best fitted to the observed ones. The temporal evolution of emission strength was estimated through the temporal evolution of the parameters of the probability distribution functions. Missing periods were accounted for by estimating the respective distribution functions through interpolation or extrapolation from the existing ones. The derived variation of emission levels consistently represents the emission reduction strategies enforced over the years, as well as the escalating growth of the passenger car fleet volume, and could be a useful tool for the design and assessment of emission control strategies. (C) 2009 Elsevier Ltd. All rights reserved.

关键词： Air pollution probability distribution function Exposure assessment Emission reduction Exceedances

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