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Modeling and analysis of rigid multibody systems with driving constraints and frictional translation joints

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Acta Mechanica Sinica 2014年第3期30卷 437-446页

作者： fang-fang Zhuang Qi Wang Beihang University

An approach is proposed for modeling and anal- yses of rigid multibody systems with frictional translation joints and driving constraints. The geometric constraints of translational joints with small clearance are treated as bilat- eral constraints by neglecting the impact between sliders and guides. Firstly, the normal forces acting on sliders, the driv- ing constraint forces （or moments） and the constraint forces of smooth revolute joints are all described by complementary conditions. The frictional contacts are characterized by a set- valued force law of Coulomb＇s dry friction. Combined with the theory of the horizontal linear complementarity problem （HLCP）, an event-driven scheme is used to detect the transi- tions of the contact situation between sliders and guides, and the stick-slip transitions of sliders, respectively. And then, all constraint forces in the system can be computed easily. Secondly, the dynamic equations of multibody systems are written at the acceleration-force level by the Lagrange multiplier technique, and the Baumgarte stabilization method is used to reduce the constraint drift. Finally, a numerical example is given to show some non-smooth dynamical behaviors of the studied system. The obtained results validate the feasibility of algorithm and the effect of constraint stabilization.

关键词： Multibody systems Lagrange multipliers Driving constraints Coulomb's friction Horizontal linearcomplementarity problem (HLCP)

Line-primitive Linear Spaces with fang-Li Parameter gcd（k,r） at Most 12

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Acta Mathematica Sinica,English Series 2011年第4期27卷 657-670页

作者： Sheng Lin ZHOU Yan Bo MA Wei Dong fang Department of Mathematics South China University of Technology Guangzhou 510641 P. R. China Department of Mathematics and Information Technology Hanshan Normal University Chaozhou 521041 P. R. China

Let G be a subgroup of the automorphism group of a non-trivial finite linear space $. In this paper we prove that if G is line-primitive with fang-Li parameter gcd（k, r） = 11 and 12, then G is also point-primitive. This extends the results of fang and Li （1993） and Li and Liu （2001） which combined gives the result for gcd（k,r） ≤ 10.

关键词： Finite linear spaces line-primitive point-imprimitive

Non-equilibrium turbulent phenomena in transitional flat plate boundary-layer flows

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Applied Mathematics and Mechanics(English Edition) 2021年第4期42卷 567-582页

作者： Feng LIU Le fang Jian fang School of Energy and Power Engineering North University of ChinaTaiyuan 030051China Laboratory of Mathematics and Physics Ecole Centrale de P′ekinBeihang UniversityBeijing 100191China Scientific Computing Department STFC Daresbury LaboratoryWarrington WA44ADU.K.

Many recent laboratory experiments and numerical simulations support a non-equilibrium dissipation scaling in decaying turbulence before it reaches an equilibrium *** analyzing a direct numerical simulation(DNS)database of a transitional boundary-layer flow,we show that the transition region and the non-equilibrium turbulence region,which are located in different streamwise zones,present different non-equilibrium ***,in the wall-normal direction,the viscous sublayer,log layer,and outer layer show different non-equilibrium phenomena which differ from those in grid-generated turbulence and transitional channel *** findings are expected to shed light on the modelling of various types of non-equilibrium turbulent flows.

关键词： non-equilibrium turbulence flat plate boundary layer turbulence model

Embedding laser-generated CdTe nanocrystals into ultrathin ZnIn_(2)S_(4) nanosheets with sulfur vacancies for boosted photocatalytic H_(2) evolution

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Journal of Materials Science & Technology 2023年第35期166卷 113-122页

作者： Z.G.Tai G.T.Sun x.H.Zhang x.B.Yang T.Wang Z.Y.fang Q.Ye L.C.Jia H.Q.Wang State Key Laboratory of Solidification Processing Center for Nano Energy MaterialsSchool of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi’an 710072China Research&Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen 518063China School of Materials Science and Engineering Shaanxi Normal UniversityXi’an 710119China

To suppress the inner charge recombination and inject vast electrons,CdTe nanocrystals are embedded into ultrathin ZnIn_(2)S_(4) nanosheets to construct ZnIn_(2)S_(4)/CdTe heterostructures,where the nanocrystals are generated by a laser irradiation *** optimal ZnIn_(2)S_(4)/CdTe heterojunction exhibits an excellent catalytic activity of 24.3 mmol/h/g,which is relatively high among the ZnIn_(2)S_(4)-based photocatalysts with-out noble *** enhancement is ascribed to a win-win mechanism of nanoscale heterojunctions and sulfur *** strong electron coupling effect,which is verified by density functional the-ory(DFT)calculations,impels the photo-generated electrons transfer from CdTe to ZnIn_(2)S_(4),boosting the charge ***,the sulfur vacancies existing in ZnIn_(2)S_(4) can capture photoelectrons and act as active sites,facilitating the H_(2) generation *** addition,the ZnIn_(2)S_(4) base and the ZnIn_(2)S_(4)/CdTe heterojunction also possess an evident photothermal effect and renewable cycle phenomena,enhancing the photocatalytic *** research provides new insights into the regulation of charge transfer through embedding nanocrystals.

关键词： Photocatalysis Hydrogen evolution Laser irradiation Heterostructure Sulfur vacancies

Automatic search for topological materials shifts paradigm

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National Science Review 2019年第2期6卷 204-206页

作者： Chen fang Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences CAS Centre for Excellence in Topological Quantum Computation Kavli Institute for Theoretical Sciences Chinese Academy of Sciences Physical Science Laboratory Huairou National Comprehensive Science Center Songshan Lake Materials Laboratory

Topological materials are known for their exotic properties. Topological insulators have gapless modes on their surfaces despite having perfectly insulating bulk, and these surface modes cannot be gapped or localized as long as time-reversal symmetry is preserved [1]; topological semimetals host ‘Fermi arcs’ on their surfaces and exhibit quantum anomalies in their bulk [2]. The physical quantity underlying these distinct properties is the topological invariant, the defining quantum number of any topological material.

关键词： Automatic search for topological materials shifts paradigm

Reciprocal Screw Theory Based Singularity Analysis of a Novel 3-DOF Parallel Manipulator

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Chinese Journal of Mechanical Engineering 2012年第4期25卷 647-653页

作者： fang Hairong fang Yuefa ZHANG Ketao School of Mechanical Electronic and Control engineering Beijing Jiaotong University Beijing 100044 China

Singularity analysis is an essential issue for the development and application of parallel *** of the existing researches focus on the singularity of parallel manipulators are carried out based on the study of Jacobian matrices.A 3-DOF parallel manipulator with symmetrical structure is *** novel parallel manipulator employs only revolute joints and consists of four closed-loop subchains connecting to both base and platform via revolute *** closed-loop subchain in each chain-leg is a spherical 6R *** motion characteristics of the output link in the spherical 6R linkage with symmetrical structure are analyzed based on the interrelationships between screw *** constraints that are exerted on the platform by each chain-leg are investigated applying the concept of generalized kinematic pair in terms of equivalent screw *** the geometric characteristics of the parallel manipulator,the singularity criteria of the parallel manipulator corresponding to different configurations are revealed based on the dependency of screw system and line *** existing conditions of certain configuration that a singularity must occur are *** paper presents a new way of singularity analysis based on disposition of constraint forces on the geometrically identified constraint plane and the proposed approach is capable of avoiding the complexity in solving the Jacobian matrices.

关键词： parallel manipulator singularity screw theory grassmann line geometry

STRESS ANALYSIS OF THE APERTURE IN COMPOUND PIPELINE BY FEM

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Acta Metallurgica Sinica(English Letters) 2007年第5期20卷 385-390页

作者： J.G. Yang H.Y. fang C.L. Fan Z. Luo x.Z. Hou State Key Laboratory of Advanced Welding Production Technology Harbin Institute of Technology Harbin 150001 China School of Material Science and Engineering Tianjin University Tianjin 300072 China Daqing Oil-Ghem-Wdding Institute Daqing 163712 China

There is a cyclical aperture at a certain part of the fiberglass reinforced plastic compound pipeline with a stainless steel pipe as a liner, which becomes the weakness of the conduit. The field of stress and strain of the aperture was investigated using the nonliner finite element code Marc. The results of the finite element analysis showed that there were concentrations of stress and strain in the layer of stainless steel at the part of the pipeline where the aperture existed. The method to solve these problems was also discussed.

关键词： compound pipeline stress software Marc

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高温下HMx热分解反应分子动力学模拟

原子与分子物理学报 2025年第2期42卷 105-110页

作者：陈芳贾方硕陈瑶李天浩郭国琦董羚中北大学化学与化工学院太原030051

本文采用ReaxFF-lg反应分子动力学方法研究了奥克托金(HMx)在六种不同温度下的初始反应热分解过程,验证了ReaxFF-lg势函数对HMx体系的适用性,计算了不同温度下HMx体系势能、总物种演化趋势、初始反应产物以及指前因子和活化能.结果表明,... 详细信息

本文采用ReaxFF-lg反应分子动力学方法研究了奥克托金(HMx)在六种不同温度下的初始反应热分解过程,验证了ReaxFF-lg势函数对HMx体系的适用性,计算了不同温度下HMx体系势能、总物种演化趋势、初始反应产物以及指前因子和活化能.结果表明,HMx热分解过程主要有三种初始分解机理:N-NO_(2)键的断裂,HONO的解离和主环上C-N键的断裂,计算得到的初始分解阶段活化能Ea和指前因子ln(A),与实验值相吻合.

关键词： HMx 反应分子动力学(RMD) ReaxFF-lg 热分解温度

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Preparation and corrosion resistance of rare earth-silane composite conversion coatings on magnesium-lithium alloy surface

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Rare Metals 2023年第3期42卷 1011-1017页

作者： fang-fang xu Yong Zhao Yue xu School of Chemistry and Environment Beihang UniversityBeijing 100191China

The poor corrosion resistance of magnesiumlithium alloy surface works against its application in aerospace,automobile,electronics,*** this research,some kinds of non-toxic and non-polluting rare earth and silane(RE-Si)composite conversion coatings were built up on Mg-Li alloy surface,and formation process of coatings was *** parameters for coating preparation were determined,including immersion time and temperature,pH value of conversion solution and curing *** optimized technological parameters for preparation of RE-Si composite coating were finally *** influence of doping nanoparticles on RE-Si composite coating was also discussed,and the microstructure of coatings shows that the addition of nanoparticles can effectively improve the compactness and uniformity of composite *** corrosion resistance of specimens with RE-Si composite conversion coating is improved to a great extent compared with those of substrate or specimens with single rare earth(RE)conversion coating or with silane *** result also indicates that corrosion resistance of RE-Si composite coating doping with nanoparticles is further *** of the composite coatings was analyzed,and the effect of RE elements and silane on coating formation process was *** resistance mechanism of composite coatings on Mg-Li alloy surface was discussed.

关键词： Magnesium-lithium alloy Rare earth-silane composite coating Nanoparticles Corrosion resistance