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A note on hydrodynamics from dissipative particle dynamics

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Applied Mathematics and Mechanics(English Edition) 2018年第1期39卷 63-82页

作者： X. BIAN z. li N.A. ADAMS Department of Mechanical Engineering Technical University of Munich Munchen 85748 Germany Division of Applied Mathematics Brown University Rhode Island 02912 U. S. A.

We calculate current correlation functions （CCFs） of dissipative particle dy- namics （DPD） and compare them with results of molecular dynamics （MD） and solutions of lineariz.d hydrodynamic equations. In particular, we consider three versions of DPD, the empirical/classical DPD, coarse-grained （CG） DPD with radial-direction interactions only and full （radial, transversal, and rotational） interactions between particles. To fa- cilitate quantitative discussions, we consider specifically a star-polymer melt system at a moderate density. For bonded molecules, it is straightforward to define the CG variables and to further derive CG force fields for DPD within the framework of the Mori-z.anz.g formalism. For both transversal and longitudinal current correlation functions （TCCFs and LCCFs）, we observe that results of MD, DPD, and hydrodynamic solutions agree with each other at the continuum limit. Below the continuum limit to certain length scales, results of MD deviate significantly from hydrodynamic solutions, whereas results of both empirical and CG DPD resemble those of MD. This indicates that the DPD method with Markovian force laws possibly has a larger applicability than the continuum description of a Newtonian fluid. This is worth being explored further to represent gen- eraliz.d hydrodynamics.

关键词： dissipative particle dynamics (DPD) fluctuating hydrodynamics molec-ular dynamics (MD) coarse-graining Mori-z.anz.g projection

MODEliNG OF STRAIN-INDUCED PRECIPITATION KINETICS IN Nb MICROALLOYED STEELS

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Acta Metallurgica Sinica(English Letters) 2006年第5期19卷 385-390页

作者： X. G. z.ou z. Y. liu D. Wu z. li C.M. li State Key Lab. of Rolling and Automation Northeastern University Shenyang 110004 China Baoshan Iron ＆ Steel Co. Ltd. Shanghai 201900 China Engineering ＆ Research Incorporation limited WISDRI （Wuhan Iron ＆ Steel Design and

On the basis of the thermodynamic calculation of precipitation and considering the effect of strain on the precipitation behavior and chemical composition （Si and Mn）, the kinetics of precipitation from austenite has been investigated for different temperatures and strains. Nucleation theory and the solubility product of niobium, carbon, and nitrogen in austenite have been used to derive equations for the start time of precipitation as a function of temperature and composition. The value of n in Avrami equation was determined using the available experimental data from the published reports, which indicated that n is a constant independent of temperature and the end time of precipitation is a function of n and the start time of precipitation. The values of the start time and end time of precipitation predicted by the new model are compared with the experimental values and a good agreement was obtained between both.

关键词： strain-induced precipitation start time of precipitation end time ofprecipitation precipitation kinetics

Preface： theory, methods, and applications of mesoscopic modeling

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Applied Mathematics and Mechanics(English Edition) 2018年第1期39卷 1-2页

作者： z. li Guohui HU G.E. KARNIADAKIS Division of Applied Mathematics Brown UniversityProvidenceRhode Island 02912U.S.A. Shanghai Institute of Applied Mathematics and Mechanics Shanghai UniversityShanghai 200072China

With increasing attention to complex fluids and soft matter, we have witnessed a fast- growing research in mesoscopic modeling and simulation in the past decades. The development of mesoscopic methods offers many potential opportunities as well as challenges in modeling of complex materials for diverse applications. Despite significant progress in the past decade, mesoscopic methods are still under development. New formulation in the models, novel theo- retical interpretations, and innovative numerical algorithms often appear in literature. These mesoscopic methods have been already applied to a large number of problems, including poly- mer and colloidal suspensions, multiphase fluids, biological materials, and blood rheology. New applications of mesoscopic modeling in different areas are still emerging.

关键词： theory methods mesoscopic modeling

Revealing the high-frequency attenuation mechanism of polyurea-matrix composites

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Acta Mechanica Sinica 2020年第1期36卷 130-142页

作者： J.Cheng z.L.liu C.C.Luo T.li z.J.li Y.Kang z.z.uang Applied Mechanics Laboratory School of Aerospace EngineeringTsinghua UniversityBeijing100084China Key Laboratory of Advanced Materials of Ministry of Education Department of Chemical EngineeringTsinghua UniversityBeijing100084China School of Materials Science and Engineering Tsinghua UniversityBeijing100084China

In this paper,a method for analyz.ng the high-frequency attenuation property of polyurea-matrix composites is developed by combining experimental,computational and theoretical ***,the ultrasonic experimental platform is established by solving the difficulties of high-frequency ultrasonic testing as high-frequency signal distortion,insufficient driving voltage and sampling rate failure,to study the dynamic mechanical properties(1-5 MHz.of pure polyurea and polyurea-matrix ***,the influences of composite parameters including the siz. and volume fraction of inclusions on wave attenuation performance under different frequencies are obtained and further verified by numerical ***,the contribution of inclusions to the wave attenuation performance is also theoretically *** is found that the increase of inclusion volume fraction and inclusion diameter will increase the attenuation coefficient of the *** the attenuation of composites with the inclusions of a 150-μm diameter and 30%as volume fraction can be 82%higher than pure *** amplifying attenuation effect of inclusions is mainly attributed to the scattering effect,which is verified by comparing numerical and theoretical results.

关键词： Polyurea Viscoelastic Dynamic mechanical properties Ultrasound

High Temperature Oxidation as a Production Route for Electronic Materials

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中国腐蚀与防护学报 2009年第4期29卷 248-252页

作者： W. GAO z. W. li Department of Chemical and Materials Engineering The University of Auckland Private Bag 92019 Auckland New Zealand BRANz.Ltd Judgeford Porirua 5381 Private Bag 50908 New Zealand

Oxidation of metallic components often results in degradation and structural failure,prevention is therefore an important *** the other hand,oxidation process creates new products such as metal oxides,can be used as a production route.A well-known process in semiconductor industry is that oxidation in dry or wet atmosphere is a popular way for growth of multi-functional SiO_2 films on Si wafers. Recently,oxidation processes under controlled conditions(atmosphere,temperature,and time) are used to prepare various oxides,carbides,or nitrides with micro-/nano-struetures,well-defined composition,dimension, shape and *** use of oxidation now includes thin film and nano-/micro-siz.d devices, and porous oxides for sensing and catalysis *** paper introduces the research activities in the authors' group on applications of oxidation as a tool for synthesis of functional materials.

关键词：金属腐蚀保护氧化

Nonlinear mechanics of a ring structure subjected to multi-pairs of evenly distributed equal radial forces

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Acta Mechanica Sinica 2017年第5期33卷 942-953页

作者： Q. Chen F. Sun z. Y. li L. Taxis N. Pugno Biomechanics Laboratory School of Biological Science and Medical Engineering Southeast University State Key Laboratory of Mechanics and Control of Mechanical Structures Nanjing University of Aeronautics and Astronautics School of Chemistry Physics and Mechanical EngineeringQueensland University of Technology (QUT) Laboratory of Bio-Inspired and Graphene Nanomechanics Department of Civil Environmental and Mechanical Engineering University of Trento School of Engineering and Materials Science Queen Mary University of London Ket Lab Italian Space Agency Via del Politecnico snc

Combining the elastica theory, finite element (FE) analysis, and a geometrical topological experiment, we studied the mechanical behavior of a ring subjected to multi-pairs of evenly distributed equal radial forces by looking at its seven distinct states. The results showed that the theoretical predictions of the ring deformation and strain energy matched the FE results very well, and that the ring deformations were comparable to the topological experiment. Moreover, no matter whether the ring was compressed or tensioned by N-pairs of forces, the ring always tended to be regular polygons with 2N sides as the force increased, and a proper compressive force deformed the ring into exquisite flower-like patterns. The present study solves a basic mechanical problem of a ring subjected to lateral forces, which can be useful for studying the relevant mechanical behavior of ring structures from the nano- to the macro-scale.

关键词： Ring structures Mechanical properties Shape Strain energy

Computer Aided Modeling and Deign of a New Magnetic Sealing Mechanism in Engineering Applications

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Engineering（科研） 2010年第1期2卷 22-27页

作者： z. li 不详

This article introduces a new type of magnetic sealing mechanism that reduces the lubrication oil pollution and media gaseous leakage in general reciprocating machinery including air compressors and refrigerators. The feasible function and reliable performance of this new sealing mechanism are introduced and analyz.d in this paper. The computer aided design, modeling and analysis are being used to study this new sealing mechanism, and the prototype of this sealing mechanism is being tested. The study indicated the proper function of this sealing mechanism. The major advantages of this sealing mechanism include: improved sealing capacity to prevent the gaseous leakage and oil leakage, simple and compact in structure, lower precision requirement on surfaces of reciprocating pistons and shafts in production and manufacturing, and longer services in sealing life span. Also there is almost no frictional loss during the reciprocating motion of piston or shaft.

关键词： Magnetic Sealing Magnetic Flux Reciprocating Machinery Self-Lubricated System

An Efficient Cationic Cycliz.tion Approach for the Construction of Labdane Diterpenoid Decalin Ring Skeleton

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Chinese Chemical Letters 2005年第4期16卷 433-436页

作者： Jin Hui YANG, Wei Dong z. li* State Key Laboratory of Applied Organic Chemistry, Lanz.ou University, Lanz.ou 730000 State Key Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou 730000 China

An effective approach for the construction of the decalin ring skeleton of labdane diterpenoids was developed based on a key biomimetic cationic polyene cycliz.tion of an epoxy allylsilane precursor. The synthetic approach demonstrated here would be useful in the enantioselective and diastereoselective total synthesis of natural labdane diterpenoids in general.

关键词： Allylsilane labdane skeleton cationic cycliz.tion biomimetic synthesis.

Nonlinear Transient Response of Functionally Graded Material Sandwich Doubly Curved Shallow Shell Using New Displacement Field

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Acta Mechanica Solida Sinica 2018年第1期31卷 108-126页

作者： z.N.li Y.X.Hao W.z.ang J.H.z.ang College of Mechanical Engineering Beijing Information Science and Technology University College of Mechanical Engineering Beijing University of Technology

In this paper, the nonlinear transient dynamic response of functionally graded material （FGM） sandwich doubly curved shell with homogenous isotropic material core and functionally graded face sheet is analyz.d using a new displacement field on the basis of Reddy＇s third-order shear theory for the first time. The equivalent material properties for the FGM face sheet are assumed to obey the rule of simple power law function in the thickness direction. Based on Reddy＇s theory of higher shear deformation, a new displacement field is developed by introducing the secant function into transverse displacement. Four coupled nonlinear differential equations are obtained by applying Hamilton＇s principle and Galerkin method. It is assumed that the FGM sandwich doubly curved shell is subjected to step loading, air-blast loading, triangular loading, and sinusoidal loading, respectively. On the basis of double-precision variable- coefficient ordinary differential equation solver, a new program code in FORTRAN software is developed to solve the nonlinear transient dynamics of the system. The influences of core thickness, volume fraction, core-to-face sheet thickness ratio, width-to-thickness ratio and blast type on the transient response of the shell are discussed in detail through numerical simulation.

关键词： New displacement fields Functionally graded materials Sandwich doubly curvedshell Blast load Nonlinear transient response