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A study on compressive shock wave propagation in metallic foams

Science china(Physics,mechanics & Astronomy) 2010年第2期53卷 279-287页

作者： WANG ZhiHua1,2.ZHANG YiFen2.REN HuiLan1 & ZHAO LongMao2.1 State Key Laboratory of Explosion Science and Technology,beijing Institute of Technology,beijing 100081,{2. 2.Institute of Applied mechanics and Biomedical engineering,Taiyuan University of Technology,Taiyuan 03002.,{2. 1. State Key Laboratory of Explosion Science and Technology Beijing Institute of Technology Beijing 100081 China2. Institute of Applied Mechanics and Biomedical Engineering Taiyuan University of Technology Taiyuan 030024 China

Metallic foam can dissipate a large amount of energy due to its relatively long stress plateau,which makes it widely applicable in the design of structural crashworthiness. However,in some experimental studies,stress enhancement has been observed when the specimens are subjected to intense impact loads,leading to severe damage to the objects being protected. This paper studies this phenomenon on a 2. mass-spring-bar model. With the model,a constitutive relationship of metal foam and corresponding loading and unloading criteria are presented; a nonlinear kinematics equilibrium equation is derived,where an explicit integra-tion algorithm is used to calculate the characteristic of the compressive shock wave propagation within the metallic foam; the effect of heterogeneous distribution of foam microstructures on the shock wave features is also included. The results reveal that under low impact pulses,considerable energy is dissipated during the progressive collapse of foam cells,which then reduces the crush of objects. When the pulse is sufficiently high,on the other hand,stress enhancement may take place,especially in the heterogeneous foams,where high peak stresses usually occur. The characteristics of compressive shock wave propagation in the foam and the magnitude and location of the peak stress produced are strongly dependent on the mechanical properties of the foam material,amplitude and period of the pulse,as well as the homogeneity of the microstructures. This research provides valuable insight into the reliability of the metallic foams used as a protective structure.

关键词： aluminum foam heterogeneous intensive pulse loading stress enhancement

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On the definition of fractional derivatives in rheology

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Theoretical & Applied mechanics Letters 2011年第1期1卷 62-65页

作者： Fan Yang~(1,2.a)) and Ke-Qin Zhu~(1,b)) 1)Department of engineering mechanics,Tsinghua University,{2. 100084,china 2.Department of Physics,the Chinese University of Hong Kong,Hong Kong,china Department of Physics the Chinese University of Hong Kong Hong Kong China

During the last two decades fractional calculus has been increasingly applied to physics, especially to *** is well known that there are obivious differences between Riemann-Liouville (R-L) definition and Caputo definition,which are the two most commonly used definitions of fractional *** multiple definitions of fractional derivatives have hindered the application of fractional calculus in *** this paper,we clarify that the R-L definition and Caputo definition are both Theologically unreasonable with the help of the mechanical analogues of the fractional element *** also find that to make them more reasonable Theologically,the lower terminals of both definitions should be put to—∞.We further prove that the R-L definition with lower terminal—∞and the Caputo definition with lower terminal—∞are equivalent in the differentiation of functions that are smooth enough and functions that have finite number of singular *** we can define the fractional derivatives in rheology as the R-L derivatives with lower terminal—∞(or,equivalently,the Caputo derivatives with lower terminal—∞) not only for steady-state processes,but also for transient processes.

关键词： fractional derivative Caputo definition Riemann-Liouville definition Scott-Blair model

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The influence of thermal radiation on MHD station-point flow past a stretching sheet with heat generation

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Acta Mechanica Sinica 2011年第4期27卷 502-509页

作者： Jing Zhu.Lian-Cun Zheng.Xin-Xin Zhang Department of Mathematics and mechanics,University of Science and Technology beijing,100083 beijing,china Thermal engineering Department,University of Science and Technology beijing,100083 beijing,china Zheng Department of Mathematics and mechanics University of Science and Technology Beijing Beijing China Thermal engineering Department University of Science and Technology Beijing Beijing China

This letter is concerned with the plane and axisymmetric stagnation-point flows and heat transfer of an electrically-conducting fluid past a stretching sheet in the presence of the thermal radiation and heat generation or absorption. The analytical solutions for the velocity distribution and dimensionless temperature profiles are obtained for the various values of the ratio of free stream velocity and stretching velocity, heat source parameter, Prandtl number, thermal radiation parameter, the suction and injection velocity parameter and magnetic parameter and dimensionality index in the series form with the help of homotopy analysis method （HAM）. Convergence of the series is explicitly dis- cussed. In addition, shear stress and heat flux at the surface are calculated.

关键词： Thermal radiation MHD Laminar boundarylayers - Homotopy analysis method

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The Numerical Simulation of the Flow with Contact Lines

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Communications in Nonlinear Science and Numerical Simulation 1996年第3期1卷 50-56页

作者： Zuowei LU Guixiang CUI Zhaoshun ZHANG(Department of engineering mechanics, Tsinghua University,{2., P. R. china )E-mail: demzzs@*** Department of engineering mechanics Tsinghua University Beijing 100084 P. R. China

The paper proposes a physical model for tracking the motion of the contactline and the gas-liquid interface. The local motion of the contact line at the solid wall isassumed and the interface between gas and liquid is trared by a level function. The finitevolume method and staggered grids are used to solve the governing equation numericallyThe motion of the water column in a vertical pipe is computed and the results are comparedwith experimental data in good agreement.

关键词： numerical simulation motion of contact line interface tracking

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Entropy product measure for multipartite pure states

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Science china(Physics,mechanics & Astronomy) 2006年第5期49卷 606-615页

作者： CAO Wancang1,2. LIU Dan2. PAN feng3 & LONG Guilu2.4 1. Department of Physics, Chifeng College, Chifeng 02.001, china 2. Key Laboratory for Quantum Information and Measurements, Department of Physics, Tsinghua University, beijing 100084, china 3. Department of Physics, Liaoning Normal University, Dalian 11602., china 4. Key Laboratory for Atomic and Molecular Nano-Sciences, Tsinghua University, beijing 100084, china Correspondence should be addressed to Long Guilu Department of Physics Chifeng College Chifeng 024001 China Key Laboratory for Quantum Information Measurements Department of Physics Tsinghua University Beijing 100084 China Department of Physics Liaoning Normal University Dalian 116029 China Key Laboratory for Atomic Molecular Nano-Sciences Tsinghua University Beijing 100084 China

An entanglement measure for multipartite pure states is formulated using the product of the von Neumann entropy of the reduced density matrices of the constituents. Based on this new measure, all possible ways of the maximal entanglement of the triqubit pure states are studied in detail and all types of the maximal entanglement have been compared with the result of ‘the average entropy’. The new measure can be used to calculate the degree of entanglement, and an improvement is given in the area near the zero entropy.

关键词： multipartite pure state von Neumann entropy entanglement measure

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Tailoring chaotic motion of microcavity photons in ray and wave dynamics by tuning the curvature of space

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Science china(Physics,mechanics & Astronomy) 2024年第7期67卷 107-112页

作者： Wei Lin Yechun Ding Yongsheng Wang Peng Li Yanpeng Zhang feng Yun feng Li Key Laboratory for Physical Electronics and Devices of the Ministry of Education Shaanxi Key Lab of Information Photonic TechniqueSchool of Electronic Science and EngineeringFaculty of Electronic and Information EngineeringXi’an Jiaotong UniversityXi’an 710049China Department of Electrical and Photonics engineering Technical University of DenmarkKgs.Lyngby 2800Denmark Center for Regenerative and Reconstructive Medicine Med-X InstituteThe First Affiliated Hospital of Xi’an Jiaotong UniversityXi’an 710061China Solid-State Lighting engineering Research Center Xi’an Jiaotong UniversityXi’an 710049China

Microcavity photon dynamics in curved space is an emerging interesting area at the crossing point of nanophotonics,chaotic science,and non-Euclidean *** report the sharp difference between the regular and chaotic motions of cavity photons subjected to the varying space *** the island modes of regular motion rise in the phase diagram in the curved space,the chaotic modes show special mechanisms to adapt to the space curvature,including the fast diffusion of ray dynamics,and the localization and hybridization of the Husimi wavepackets among different periodic *** observations are unique effects enabled by the combination of the chaotic trajectory,the wave nature of light,and the non-Euclidean orbital motion,and therefore make the system a versatile optical simulator for chaotic science under quantum mechanics in curved space-time.

关键词： microcavity chaotic motion curved space

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A constitutive model of frozen soil with damage and numerical simulation for the coupled problem

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Science china(Physics,mechanics & Astronomy) 2010年第4期53卷 699-711页

作者： ZHU ZhiWu, NING JianGuo& MA Wei 1 School of mechanics and engineering, Southwest Jiaotong University, Chengdu 610031,{2. 2.State Key Laboratory of Explosion Science and Technology, beijing Institute of Technology, beijing 100081,{2. 3 Key Laboratory of Frozen Soil engineering, CAREERI, CAS, Lanzhou 730000,{2. 1. School of mechanics and engineering Southwest Jiaotong University Chengdu 610031 China2. State Key Laboratory of Explosion Science and Technology Beijing Institute of Technology Beijing 100081 China3. Key Laboratory of Frozen Soil Engineering CAREERI CAS Lanzhou 730000 China

Based on the microcosmic mechanics of composite materials, an elastic constitutive model for frozen soil with damage is presented. For frozen sandy soil with a range of ice contents and under a range of temperature conditions, quantitative results determined by this constitutive model agree with practically measured stress-strain curves. After numerically simulating the coupled water, temperature and stress fields of channel frozen and frozen roadbed using a self-developed finite-element routine, more accurate and practical calculation results for the temperature field coupled with stress, displacement and strain fields are obtained; the results match predictions and tests undertaken by earlier researchers. Our results support the reliability of our routine for calculating interdependent physical quantities of frozen soil and for describing the relationships between them. Our program can offer necessary constraints for engineering design and construction in permafrost regions.

关键词： frozen soil microcosmic mechanics roadbed coupling stress field

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Development and application of a GIS database for the Miyun Reservoir water quality protection

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Journal of Environmental Sciences 1999年第4期11卷 485-491页

作者： JIA Hai\|feng, CHENG Sheng\|tong, XIAO Yang (Department of Environmental Sciences and engineering, Tsinghua University,{2.,china) 清华大学环境科学与工程系北京

A high quality database is the starting point for any GIS application. For the Miyun Reservoir, a large amount of spatial data has been accumulated by numerous studies. This paper introduces a GIS database development in support of these studies. And some applications of the GIS database, include integration with GPS, view and management of data, and integration with WASP5 model, are also introduced.

关键词： GIS database ARC/INFO Arcview Miyun Reservoir water quality

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Molecular　Dynamics　Simulation　on　Thermodynamic　Properties　and　Transport　Coefficients

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Journal of Thermal Science 1996年第3期5卷 196-200页

作者： D.X. Xiong Y.S. Xu, Z.Y. Guo (Department of engineering mechanics, Tsinghua University,{2., china) Department of engineering mechanics Tsinghua University Beijing China

Molecular dynamics simulation (MDS) is used to study the thermodynamic properties and transport coefficients of an argon system with Lennend-Jones potential. The results on the velocity distribution,mean free path, mean collision time, specific heat and self-diffusion coefficient agree well with the existing theoretical/ experimental data. It shows that molecular dynamics method is another bridge to connect microworld and macroworld.

关键词： molecular dynamics simulation thermodynamic property transport coefficient

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Intersection theory rules symbology

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Science china(Physics,mechanics & Astronomy) 2024年第2期67卷 93-104页

作者： Jiaqi Chen Bo feng Lilin Yang beijing Computational Science Research Center Beijing 100084China Zhejiang Institute of Modern Physics School of PhysicsZhejiang UniversityHangzhou 310027China Peng Huanwu Center for Fundamental Theory Hefei 230026China

We propose a novel method to determine the structure of symbols for any family of polylogarithmic Feynman *** the d log-bases and simple formulas for the leading order and next-to-leading contributions to the intersection numbers,we give a streamlined procedure to compute the entries in the coefficient matrices of canonical differential equations,including the symbol letters and the rational *** also provide a selection rule to decide whether a given matrix element must be *** symbol letters are deeply related to the poles of the integrands and also have interesting connections to the geometry of Newton *** method can be applied to many cutting-edge multi-loop *** simplicity of our results also hints at the possible underlying structure in perturbative quantum field theories.

关键词： scattering amplitude Feynman integral symbology

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