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probability distribution function of a Forced Passive Tracer in the Lower Stratosphere

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Advances in Atmospheric Sciences 2007年第2期24卷 163-180页

作者：胡永云 Department of Atmospheric Sciences School of Physics Peking University

The probability distribution function （PDF） of a passive tracer, forced by a ＂mean gradient＂, is studied. First, we take two theoretical approaches, the Lagrangian and the conditional closure formalisms, to study the PDFs of such an externally forced passive tracer. Then, we carry out numerical simulations for an idealized random flow on a sphere and for European Center for Medium-Range Weather Forecasts （ECMWF） stratospheric winds to test whether the mean-gradient model can be applied to studying stratospheric tracer mixing in midlatitude surf zones, in which a weak and poleward zonal-mean gradient is maintained by tracer leakage through polar and tropical mixing barriers, and whether the PDFs of tracer fluctuations in midlatitudes are consistent with the theoretical predictions. The numerical simulations show that when diffusive dissipation is balanced by the mean-gradient forcing, the PDF in the random flow and the Southern-Hemisphere PDFs in ECMWF winds show time-invariant exponential tails, consistent with theoretical predictions. In the Northern Hemisphere, the PDFs exhibit non-Gaussian tails. However, the PDF tails are not consistent with theoretical expectations. The long-term behavior of the PDF tails of the forced tracer is compared to that of a decaying tracer. It is found that the PDF tails of the decaying tracer are time-dependent, and evolve toward flatter than exponential.

关键词： chaotic mixing probability distribution function stratosphere turbulence passive tracer

Research on the behavior of fiber orientation probability distribution function in the planar flows

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2005年第4期6卷 257-264页

作者：周锟林建忠 Department of Mechanics State Key Laboratory of Fluid Power Transmission and Control Zhejiang University

The equation of two-dimensional fiber direction vector was solved theoretically to give the fiber orientation distri- bution in simple shear flow, flow with two direction shears, extensional flow and arbitrary planar incompressible flow. The Fok- ker-Planck equation was solved numerically to validify the theoretical solutions. The stable orientation and orientation period of fiber were obtained. The results showed that the fiber orientation distribution is dependent on the relative not absolute magnitude of the matrix rate-of-strain of flow. The effect of fiber aspect ratio on the orientation distribution of fiber is insignificant in most conditions except the simple shear case. It was proved that the results for a planar flow could be generalized to the case of 3-D fiber direction vector.

关键词： Fiber suspension flow Orientation distribution probability distribution function

Dynamic Stability and Fuzzy Reliability Analysis of Toppling Perilous Rock Under Seismic Excitation

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Journal of Earth Science 2024年第1期35卷 248-262页

作者： Linfeng Wang Jixu Zhang Wanchun Xia Xiaoming Huang Guojin Tan Key Laboratory of Geological Hazards Mitigation for Mountainous Highway and Waterway Chongqing Jiaotong UniversityChongqing 400074China School of Transportation Southeast UniversityNanjing 211189China College of Transportation Jilin UniversityChangchun 130012China

To predict the occurrence of the collapse disaster in toppling perilous rock under the action of bidirectional earthquakes,the dynamic stability and fuzzy reliability calculation method of toppling perilous rock under the action of bidirectional earthquakes is ***,the mass viscoelasticity model is used to simulate two main control surfaces of toppling perilous rock,the seismic dynamic response model and motion equation of toppling perilous rock are established based on the D'Alembert principle,and the Newmark-β method is used to solve the dynamic motion ***,the instability event of toppling perilous rock is considered a fuzzy event,the membership function expression of the stability coefficient of toppling perilous rock is determined based on the fuzzy failure criterion,the calculation equations of the toppling perilous rock dynamic stability coefficient and fuzzy reliability are established,and the fuzzy reliability evaluation method based on the probability distribution of reliability is ***,the influence of different superposition modes of seismic excitation on the fuzzy reliability of toppling perilous rock is *** calculation results of toppling perilous rock in the engineering case show that the fuzzy reliability calculated after considering the fuzzy failure criterion is reduced by 10.73% to 25.66% compared with the classical *** the bidirectional seismic excitation,the fuzzy reliability of toppling perilous rock is reduced by 5.46% to 14.89%.Compared with using the acceleration peak time encounter mode to superpose the seismic excitation,the fuzzy reliability of toppling perilous rock is reduced by 3.4% when the maximum action effect time encounter mode is adopted.

关键词： toppling perilous rock bidirectional earthquake fuzzy failure criterion dynamic stability fuzzy reliability Newmark-βmethod probability distribution function

Monte Carlo method for evaluation of surface emission rate measurement uncertainty

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Nuclear Science and Techniques 2024年第7期35卷 126-136页

作者： Yuan-Qiao Li Min Lin Li-Jun Xu Rui Luo Yu-He Zhang Qian-Xi Ni Yun-Tao Liu China Institute of Atomic Energy Beijing102413China National Key Laboratory for Metrology and Calibration Techniques Beijing102413China Department of Radiation Oncology Hunan Cancer HospitalChangsha410031China The Affiliated Cancer Hospital of Xiangya School of Medicine Central South UniversityChangsha410031China

The aim of this study is to evaluate the uncertainty of 2πα and 2πβ surface emission rates using the windowless multiwire proportional counter *** study used the Monte Carlo method (MCM) to validate the conventional Guide to the Expression of Uncertainty in Measurement (GUM) method.A dead time measurement model for the two-source method was established based on the characteristics of a single-channel measurement system,and the voltage threshold correction factor measurement function was indirectly obtained by fitting the threshold correction *** uncertainty in the surface emission rate was calculated using the GUM method and the law of propagation of *** MCM provided clear definitions for each input quantity and its uncertainty distribution,and the simulation training was realized with a complete and complex mathematical *** results of the surface emission rate uncertainty evaluation for four radioactive plane sources using both methods showed the uncertainty’s consistency E_(n)<0.070 for the comparison of each source,and the uncertainty results of the GUM were all lower than those of the ***,the MCM has a more objective evaluation process and can serve as a validation tool for GUM results.

关键词： Surface emission rate Monte Carlo method Metrology probability distribution function Dead time Low-energy loss correction Least-squares method

Wind energy feasibility and wind turbine selection studies for the city Surat, India

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CLEAN ENERGY 2024年第3期8卷 166-173页

作者： Banu, Arshi P. S. Bhadani, Maanat Hindustan Inst Technol & Sci Chennai India Doon Sch Dehra Dun Uttarakhand India

Wind energy represents a clean, abundant and cost-effective power source, fostering job growth and environmental mitigation. Although wind energy harnesses several gigawatts today, its availability hinges on diverse factors, with geographical location standing out. Commercial turbines, with varying capacity ranges, saturate the market. Locating site-specific suitability and matching the appropriate turbine to meet specific requirements are of paramount importance. This study aims to assess the feasibility of wind energy in Surat, Gujarat, India and select an optimal small commercial turbine for residential use. The research involves Rayleigh and Weibull probability distribution functions based on yearlong velocity data. These distributions are fitted with actual data, revealing the most probable velocity (vmf = 3 m/s) and velocity at maximum power (vpmax = 5 m/s). The power availability of the site has been assessed as 42.6 W/m2 using both graphical and analytical methods. Several commercial turbines have been shortlisted based on on-site power criteria and their specifications are evaluated against site power availability. A comparative analysis culminates in identifying the most suitable turbine for the location. The best suitable turbine for the site with an annual energy yield of 8 MW has been suggested amongst selected turbines for small-scale residential applications. The feasibility of wind energy in Surat, Gujarat, India is assessed by selecting an optimal small commercial turbine for residential use. Rayleigh and Weibull probability distribution functions of wind velocity are fitted with yearlong data, revealing the most probable velocity and velocity at maximum power. Graphical Abstract

关键词： site feasibility wind energy commercial wind turbine probability distribution function rated power

Establishment Method of a Mixture Model and Its Practical Application for Transmission Gears in an Engineering Vehicle

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Chinese Journal of Mechanical Engineering 2012年第5期25卷 1001-1010页

作者： WANG Jixin WANG Zhenyu YU Xiangjun YAO Mingyao YAO Zongwei ZHANG Erping College ofMechanicalScience andEngineering Jilin University Changchun 130022 China School of Automatic Control and Mechanical Engineering Kunming University Kunming 650214 China Guangxi Liugong Machinery Co. Ltd. Liuzhou 545007 China

Highly versatile machines, such as wheel loaders, forklifts, and mining haulers, are subject to many kinds of working conditions, as well as indefinite factors that lead to the complexity of the load. The load probability distribution function （PDF） of transmission gears has many distributions centers; thus, its PDF cannot be well represented by just a single-peak function. For the purpose of representing the distribution characteristics of the complicated phenomenon accurately, this paper proposes a novel method to establish a mixture model. Based on linear regression models and correlation coefficients, the proposed method can be used to automatically select the best-fitting function in the mixture model. Coefficient of determination, the mean square error, and the maximum deviation are chosen and then used as judging criteria to describe the fitting precision between the theoretical distribution and the corresponding histogram of the available load data. The applicability of this modeling method is illustrated by the field testing data of a wheel loader. Meanwhile, the load spectra based on the mixture model are compiled. The comparison results show that the mixture model is more suitable for the description of the load-distribution characteristics. The proposed research improves the flexibility and intelligence of modeling, reduces the statistical error and enhances the fitting accuracy, and the load spectra complied by this method can better reflect the actual load characteristic of the gear component.

关键词： mixture distribution model probability distribution function correlation coefficient load spectra wheel loader

Single point velocity distributions in homogeneous isotropic turbulence

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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

Coverage of communication-based sensor nodes deployed location and energy efficient clustering algorithm in WSN

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Journal of Systems Engineering and Electronics 2010年第4期21卷 698-704页

作者： Xiang Gao Yintang Yang Duan Zhou College of Microelectronics Xidian University Xi' an 710071 P. R. China College of Computer Science and Technology Xidian University Xi'an 710071 E R. China

An effective algorithm based on signal coverage of effective communication and local energy-consumption saving strategy is proposed for the application in wireless sensor *** algorithm consists of two *** is the multi-hop partition subspaces clustering algorithm for ensuring local energybalanced consumption ascribed to the deployment from another algorithm of distributed locating deployment based on efficient communication coverage probability（DLD-ECCP）.DLD-ECCP makes use of the characteristics of Markov chain and probabilistic optimization to obtain the optimum topology and number of sensor *** simulation,the relative data demonstrate the advantages of the proposed approaches on saving hardware resources and energy consumption of networks.

关键词： wireless sensor network probability distribution function Markov chain received signal strength indicator Gaussian distribution.

An Experimental Study on the Void Fraction for Gas-Liquid Two-Phase Flows in a Horizontal Pipe

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Fluid Dynamics & Materials Processing 2021年第6期17卷 1037-1048页

作者： Li Lei Jun An Fushun Liang Cheng Cheng Naixiang Zhou Yanhong Ning Jingzhi Zhang School of Energy and Power Engineering Shandong UniversityJinan250061China Shandong Urban and Rural Planning and Design Institute JinanChina China National Petroleum Corporation Jichai Power Co. Ltd.JinanChina Shenzhen Research Institute of Shandong University ShenzhenChina

The flow patterns and the void fraction related to a gas-liquid two-phase flow in a small channel are experimentally *** test channel is a transparent quartz glass circular channel with an inner diameter of 6.68 *** working fluids are air and water and their superficial velocities range from 0.014 to 8.127 m/s and from 0.0238 to 0.556 m/s,*** void fraction is determined using the flow pattern images captured by a high-speed camera,while quick closing valves are used for *** flow patterns are analyzed in experiments:slug flow,bubbly flow,annular flow and stratified *** intermittent flows(bubbly flow and slug flow),the cross-sectional void fraction is in a borderline condition while its probability distribution function(PDF)image displays a bimodal *** continuous flows(annular flow and stratified flow)the cross-sectional void fraction behaves as a fluctuating continuous curve while the(PDF)image displays a single peak *** volumetric void fraction data are also compared with available predictive formulas,and the results show that the agreement is very *** effort is also provided to improve the so-called Gregory and Scott model using the available data.

关键词： Gas-liquid two-phase flow small channel flow regime map probability distribution function void fraction