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A method for improved accuracy in three dimensions for determining wheel/rail contact points

VEHICLE SYSTEM DYNAMICS 2015年第11期53卷 1620-1640页

作者： Yang, Xinwen Gu, Shaojie Zhou, Shunhua Zhou, Yu Lian, Songliang Tongji Univ Key Lab Rd & Traff Engn Minist Educ Shanghai 201804 Peoples R China

Searching for the contact points between wheels and rails is important because these points represent the points of exerted contact forces. In order to obtain an accurate contact point and an in-depth description of the wheel/rail contact behaviours on a curved track or in a turnout, a method with improved accuracy in three dimensions is proposed to determine the contact points and the contact patches between the wheel and the rail when considering the effect of the yaw angle and the roll angle on the motion of the wheel set. The proposed method, with no need of the curve fitting of the wheel and rail profiles, can accurately, directly, and comprehensively determine the contact interface distances between the wheel and the rail. The range iteration algorithm is used to improve the computation efficiency and reduce the calculation required. The present computation method is applied for the analysis of the contact of rails of CHINA (CHN) 75 kg/m and wheel sets of wearing type tread of China's freight cars. In addition, it can be proved that the results of the proposed method are consistent with that of Kalker's program CONTACT, and the maximum deviation from the wheel/rail contact patch area of this two methods is approximately 5%. The proposed method, can also be used to investigate static wheel/rail contact. Some wheel/rail contact points and contact patch distributions are discussed and assessed, wheel and rail non-worn and worn profiles included.

关键词： computation method multi-point contact wheel/rail interaction iteration algorithm

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Efficient algorithms for solving condition number-constrained matrix minimization problems

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LINEAR ALGEBRA AND ITS APPLICATIONS 2020年 607卷 190-230页

作者： Li, Jiao-fen Li, Wen Vong, Seak-Weng Guilin Univ Elect Technol Guangxi Coll & Univ Key Lab Data Anal & Computat Sch Math & Comp Sci Guilin Peoples R China South China Normal Univ Sch Math Sci Guangzhou Peoples R China Univ Macau Dept Math Macau Peoples R China

Well-conditioned matrices are often required in science and engineering, such as signal processing and finance. Problem to find the nearest positive definite matrix by explicitly imposing a constraint on the condition number are considered in this paper. A new algorithm based on geometric perspective is proposed for getting the required well-conditioned matrix. Based on these, a condition number-constrained matrix minimization problem is further considered, where the constraints are imposed for avoiding degenerate solutions in which parameter matrices become rank deficient. An inexact version of alternating direction method with truly implementable inexactness criteria is proposed for solving this problem. Numerical experiments, including comparison with some existing methods, are performed to illustrate the efficiency of the proposed algorithms. (C) 2020 Elsevier Inc. All rights reserved.

关键词： Matrix nearness problem Condition number Well-conditioned matrix Alternating direction method iteration algorithm

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A two-step neutron spectrum unfolding method for fission reactors based on artificial neural network

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ANNALS OF NUCLEAR ENERGY 2020年 139卷 107219-107219页

作者： Cao, Chenglong Gan, Quan Song, Jing Long, Pengcheng Wu, Bin Wu, Yican Chinese Acad Sci Inst Nucl Energy Safety Technol Key Lab Neutron & Radiat Safety Hefei 230031 Anhui Peoples R China Univ Sci & Technol China Hefei 230027 Anhui Peoples R China

Comprehensive knowledge of neutron spectrum is significant in reactor design. Online wide-range neutron spectrum unfolding technology still requires improvement in accuracy and efficiency. In the work, a "two-step" neutron spectrum unfolding method based on artificial neural network (ANN) was developed to unfold spectrum with wide energy range. First, a default spectrum was reconstructed by using the ANN model which had been trained with a large amount of neutron spectra generated from Monte Carlo transport calculation. Second, the default spectrum was optimized by using iteration algorithm. The two-step method was verified with a thermal neutron reactor VENUS-3 and a fast neutron reactor BN-600. Comparison of mean square error (MSE) between this method and the traditional unfolding method showed reduction of 83.4% and 85.6% on VENUS-3 and BN-600 respectively, and average relative deviation (ARD) reduction of 89.3% and 86.1% respectively. Also, comparison of spectrum quality (Qs) showed reduction of 83.4% and 86.0% respectively for the two cases. This work demonstrated that the developed two-step method could obtain the better accuracy than traditional method. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Neutron spectrum unfolding Two-step method Artificial neural network iteration algorithm

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A minimization problem of the risk probability in first passage semi-Markov decision processes with loss rates

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Science China Mathematics 2015年第9期58卷 1923-1938页

作者： HUANG XiangXiang ZOU XiaoLong GUO XianPing School of Mathematics and Computational Science Sun Yat-Sen University

This paper is the first attempt to investigate the risk probability criterion in semi-Markov decision processes with loss rates. The goal is to find an optimal policy with the minimum risk probability that the total loss incurred during a first passage time to some target set exceeds a loss level. First, we establish the optimality equation via a successive approximation technique, and show that the value function is the unique solution to the optimality equation. Second, we give suitable conditions, under which we prove the existence of optimal policies and develop an algorithm for computing ?-optimal policies. Finally, we apply our main results to a business system.

关键词： semi-Markov decision processes loss rate risk probability first passage time optimal policy iteration algorithm

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Admission Control of Double-Sided Queues With Multiple Customer Types

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IEEE TRANSACTIONS ON AUTOMATIC CONTROL 2024年第3期69卷 1960-1966页

作者： Su, Yan Li, Junping Nanjing Univ Posts & Telecommun Sch Management Nanjing 210003 Peoples R China Guangdong Univ Sci & Technol Dongguan 523083 Peoples R China

In this technical note, we study a finite double-sided queue with multiple customer types, where two-sided arrivals follow independent Poisson processes. Customers arrive to one side and match with queued customers on the opposite side. A gatekeeper who has complete knowledge of the number of customers decides to accept or reject each arrival. The difference between customer types is defined by the customer's profit to the gatekeeper. Assuming no matching time between the two-sided customers, we show that the optimal admission control policy for maximizing the long-run average profit per unit time has a threshold structure. Furthermore, we also explore more selective (bias) optimal policies when the average optimal policy is not unique. Finally, using the abovementioned results, we provide an efficient iterative algorithm to produce the optimal control policy.

关键词： Logic gates Costs Admission control Process control Optimal control Markov processes Telecommunications Double-sided queue iteration algorithm Markov decision processes threshold

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Investigation of Dual Polarization Reflectometry for Determination of Plasma Density and Magnetic Field in a Spherical Tokamak

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JOURNAL OF FUSION ENERGY 2017年第1期36卷 1-8页

作者： Grekov, D. L. Tretiak, K. K. Kharkiv Inst Phys & Technol Natl Sci Ctr Inst Plasma Phys Kharkov Ukraine Kharkov Natl Univ Kharkov Ukraine

The paper deals with dual polarization reflectometry as a method for determination of plasma density and poloidal magnetic field profile in low aspect ratio tokamaks. A numerical iteration algorithm is developed and solutions for integral equations for O- and X-modes are presented. The numerical calculations confirm the use of the iterative algorithm for effective reconstruction of the density and magnetic field profile.

关键词： Spherical tokamak Dual polarization reflectometry iteration algorithm Poloidal magnetic field

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Solving singularity problems in unbounded domains by coupling of natural BEM and composite grid FEM

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APPLIED NUMERICAL MATHEMATICS 2001年第1-2期37卷 127-143页

作者： Hu, QY Yu, DH Chinese Acad Sci Acad Math & Syst Sci Inst Computat Math & Sci Engn Comp Beijing 100080 Peoples R China

In this paper, based on the natural boundary reduction method advanced by Feng and Yu, we discuss a coupled FEM-BEM for Dirichlet exterior problems. In this method, the finite element grids consist of fine and coarse grids (i.e., composite grids), so that the singularity at the corner points can be handled conveniently by the fast adaptive composite grid method (FAC). We prove that the corresponding approximation has optimal error estimates. To solve the coupled system efficiently, we propose an iteration that combines FAC with classical steepest descent. We, show that this method converges with a rate that is bounded independent of the mesh sizes, (C) 2001 IMACS. Published by Elsevier Science B.V. All rights reserved.

关键词： natural boundary reduction composite grid error estimate iteration algorithm convergence rate

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Calculation of hydraulic parameters of copper crystallizers with a complex connection of channels

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RUSSIAN JOURNAL OF NON-FERROUS METALS 2015年第6期56卷 648-653页

作者： Larina, T. P. Vdovin, K. N. Yachikov, I. M. Magnitogorsk State Tech Univ Magnitogorsk 455000 Russia

A mathematical model and algorithm of the hydraulic calculation of a crystallization wall with a complex connection of a periodically repeated system of horizontal and vertical channels are considered. A computer program allowing one to perform the hydraulic calculation of the crystallizer plate having an arbitrary number of channels of various forms and sizes is created based on the developed mathematical model. The possibilities of this software product in the design of copper crystallizers to select their geometric parameters and rational regimes of hydraulic operation are shown.

关键词： copper crystallizer hydraulic pressure pressure losses cylindrical channel mathematical model iteration algorithm

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Wind-induced internal pressure fluctuations of structure with single windward opening

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2006年第3期7卷 415-423页

作者：余世策楼文娟孙炳楠 Department of Civil Engineering Zhejiang University Hangzhou 310027 China Department of Civil Engineering Zhejiang University Hangzhou 310027 China Department of Architecture Engineering Ningbo College of Technology Zhejiang University Ningbo 315100 China

A frequency domain method for estimating wind-induced fluctuating internal pressure of structure with single windward opening is presented in this paper and wind tunnel tests were carried out to verify the theory. The nonlinear differential equation of internal pressure dynamics and iteration algorithm were applied to calculate fluctuating internal pressure and time domain analysis was used to verify the accuracy of the proposed method. A simplified estimation method is also provided and its scope of application is clarified. The mechanism of internal pressure fluctuation is obtained by using the proposed method in the frequency domain and a new equivalent opening ratio is defined to evaluate internal pressure fluctuation. A series of low-rise building models with various openings and internal volumes were designed for wind tunnel tests with results agreeing well with analytical results. It is shown that the proposed frequency domain method based on Gaussian distribution of internal pressure fluctuations can be applied to predict the RMS internal pressure coefficient with adequate accuracy for any opening dimensions, while the simplified method can only be used for structure with single dominant opening. Helmholtz resonance is likely to occur when the equivalent opening ratio is adequately high, and controlling individual opening dimension is an effective strategy for avoiding Helmholtz resonance in engineering.

关键词： Single windward opening Internal pressure iteration algorithm Equivalent opening ratio Wind tunnel test

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Performance Analysis for Controlled Semi-Markov Systems with Application to Maintenance

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JOURNAL OF OPTIMIZATION THEORY AND APPLICATIONS 2011年第2期150卷 395-415页

作者： Huang, Yonghui Guo, Xianping Song, Xinyuan Sun Yat Sen Univ Sch Math & Computat Sci Guangzhou 510275 Guangdong Peoples R China Guangdong Prov Key Lab Computat Sci Guangzhou 510275 Guangdong Peoples R China Chinese Univ Hong Kong Dept Stat Hong Kong Hong Kong Peoples R China

This paper concerns with the performance analysis for controlled semi-Markov systems in Borel state and action spaces. The performability of the system is defined as the probability that the system reaches a prescribed reward level during a first passage time to some target set. Under mild conditions, we develop a value iteration algorithm for computing the optimal value, and establish the existence of optimal policies with the maximal performability. Our main results are applied to a maintenance problem.

关键词： Controlled semi-Markov processes Target set Optimal value function iteration algorithm Optimal policy

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