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Solutions for a Mode Ⅲ Growing Crack in a Piezoelectric Plane Under Two Kinds of Electric Boundary Conditions ＊

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Chinese Physics Letters 2003年第11期20卷 2036-2038页

作者：张兴武刘凯欣 departmentofmechanicsandengineeringscience PekingUniversityBeijing100871

The solutions for a mode III crack growing along an arbitrary propagation path in a piezoelectric plane are studied under the impermeable surface condition and the electrical contact surface condition respectively. According to the two kinds of electric boundary conditions, the Hilbert and Riemann boundary value problems in a half-plane including opening smooth arc are obtained from the theoretical analysis. Moreover, the equipollence of the solution formed under these two electric boundaries is proved, and unified solutions for the stress and electric displacement distribution in the crack-tipfield of the piezoelectric plane are achieved.

关键词： Boundary value problems

Fronts of Stress Waves in Anisotropic Piezoelectric Media

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Chinese Physics Letters 2004年第1期21卷 194-196页

作者：刘颖刘凯欣高凌天 departmentofmechanicsandengineeringscience PekingUniversityBeijing100871

The characteristic of wave fronts in anisotropic piezoelectric media is analysed by adopting the generalized characteristic theory. Analytical expressions for wave velocities and wave fronts are formulated. Apart from the ordinary characteristics, a new phenomenon, energy velocity funnel, is formed on the wave fronts of quasi-transverse waves in anisotropic piezoelectric materials. A three-dimensional representation of wave fronts in anisotropic piezoelectric materials is given for a better understanding of the new phenomena.

关键词： Condensed matter: electrical magnetic and optical

THE RELATIONS BETWEEN MODEL PARAMETERS AND CERTAIN PHENOMENA IN TRAFFIC FLOW

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Journal of Hydrodynamics 2004年第4期16卷 423-430页

作者： OUZhong-hui TAOMing-de WUZheng departmentofmechanicsandengineeringscience FudanUniversityShanghai200433China

Based on the dimensionless dynamic model of traffic flow, the modelparameters were compared with numerically simulating solutions, and the effects of the former on thelatter was investigated. Some relations between the parameters were obtained. Investigation severalidealized results from dimensionless dynamic model of traffic flow were concluded.

关键词： traffic flow dynamic model dimensionless parameter

MACROSCOPIC STRAIN POTENTIALS IN NONLINEAR POROUS MATERIALS

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Acta Mechanica Sinica 2003年第1期19卷 52-58页

作者：刘熠黄筑平 departmentofmechanicsandengineeringscience PekingUniversityBeijing100871China

By taking a hollow sphere as a representative volume element (RVE), the macroscopic strain potentials of porous materials with power-law incompressible matrix are studied in this *** to the principles of the minimum potential energy in nonlinear elasticity and the variational procedure, static admissible stress fields and kinematic admissible displacement fields are constructed,and hence the upper and the lower bounds of the macroscopic strain potential are obtained. The bounds given in the present paper differ so slightly that they both provide perfect approximations of the exact strain potential of the studied porous materials. It is also found that the upper bound proposed by previous authors is much higher than the present one, and the lower bounds given by Cocks is much lower. Moreover, the present calculation is also compared with the variational lower bound of Ponte Castafneda for statistically isotropic porous materials. Finally, the validity of the hollow spherical RVE for the studied nonlinear porous material is discussed by the difference between the present numerical results and the Cocks bound.

关键词： strain potential porous material upper and lower bounds power-law material

Swarm Dynamics of a Group of Mobile Autonomous Agents

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Chinese Physics Letters 2005年第1期22卷 254-257页

作者：刘波楚天广王龙王占峰 IntelligenceControlLaboratory CentreforSystemsandControlDepartmentofMechanicsandEngineeringSciencePekingUniversityBeijing100871

We propose a simple swarm model to study collective behaviour of a group ofmobile autonomous agents interacting through a long range attraction and short range repulsionfunction. It is shown that the individuals (agents) will aggregate and eventually form a cohesivecluster of finite size around the swarm centre in a finite time, and the size depends only on theparameters of the swarm model. Furthermore, it is also shown that all the individuals will convergeto equilibrium positions of the swarm model, and thus the configuration of the swarm converges to aconstant constellation. Numerical simulations are also worked out to illustrate the analyticalresults.

关键词： PARTICLES SYSTEM MOTION

SHEAR WAVE SCATTERING FROM A PARTIALLY DEBONDED PIEZOELECTRIC CYLINDRICAL INCLUSION

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Acta Mechanica Solida Sinica 2004年第3期17卷 258-269页

作者： FengWenjie WangLiqun JiangZhiqing ZhaoYongmao departmentofmechanicsandengineeringscience ShijiazhuangRailwayInstituteShijiazhuang050043China

The scattering of SH wave by a cylindrical piezoelectric inclusion partially debonded from its surrounding piezoelectric material is investigated using the wave function expansion method and singular integral equation technique. The debonding regions are modeled as mul- tiple arc-shaped interface cracks with non-contacting faces. By expressing the scattered ?elds as wave function expansions with unknown coe?cients, the mixed boundary value problem is ?rstly reduced to a set of simultaneous dual series equations. Then dislocation density functions are introduced as unknowns to transform these dual series equations into Cauchy singular integral equations of the ?rst type, which can be numerically solved easily. The solution is valid for arbi- trary number and size of the debonds. Finally, numerical results of the dynamic stress intensity factors are presented for the cases of one debond and two debonds. The e?ects of incidence direc- tion, crack con?guration and various material parameters on the dynamic stress intensity factors are respectively discussed. The solution of this problem is expected to ?nd applications in the investigation of dynamic fracture properties of piezoelectric materials with cracks.

关键词： arc-shaped crack piezoelectric material wave scattering singular integral equation dynamic stress intensity factor

AUTOMATIC MESH GENERATION OF 3—D GEOMETRIC MODELS

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Acta Mechanica Sinica 2003年第3期19卷 285-288页

作者：刘剑飞 departmentofmechanicsandengineeringscience PekingUniversityBeijing100871China

In this paper the presentation of the ball-packing method is reviewed,and a scheme to generate mesh for complex 3-D geometric models is given,which consists of 4 steps:(1)create nodes in 3-D models by ball-packing method,(2)connect nodes to generate mesh by 3-D Delaunay triangulation,(3)retrieve the boundary of the model after Delaunay triangulation,(4)improve the mesh.

关键词： FEM mesh generation 3D model ball-packing method

An exact solution for a normal point source problem

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Chinese Science Bulletin 2004年第7期49卷 653-657页

作者： LIUKaixin LIUGuangyu departmentofmechanicsandengineeringscience PekingUniversityBeijing100871China

This paper presents an exact algebraic solution for a normal point source problem on elastic half-space due to impact pulse by adopting the Cagniard-Hoop method and improving Pekeris’ partial fraction decomposition m... 详细信息

关键词： Cagniard-Hoop 弹性波传播精确解正规点源碰撞脉冲 Lamb问题局部片段分解方法

VOID GROWTH AND CAVITATION IN NONLINEAR VISCOELASTIC SOLIDS

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Acta Mechanica Sinica 2003年第4期19卷 380-384页

作者：张赟黄筑平 departmentofmechanicsandengineeringscience PekingUniversityBeijing100871China

This paper discusses the growth of a pre-existing void in a nonlinear viscoelastic material subjected to remote hydrostatic tensions with different loading rates. The constitutive relation of this viscoelastic material is the one recently proposed by the present authors, which may be considered as a generalization of the non-Gaussian statistical theory in rubber elasticity. As the first order approximation, the above constitutive relation can be reduced to the "neo-Hookean" type viscoelastic *** of the influences of the material viscosity and the loading rate on the void growth, or on the cavitation are carried out. It is found that: (1) for generalized "inverse Langevin approximation"nonlinear viscoelastic materials, the cavitation limit does not exist, but there is a certain (remote)stress level at which the void will grow rapidly; (2) for generalized "Gaussian statistics" (neo-Hookean type) viscoelastic materials, the cavitation limit exists, and is an increasing function of the loading *** present discussions may be of importance in understanding the material failure process under high triaxial stress.

关键词： void growth cavitation viscoelastic non-Gaussian statistical theory inverse Langevin approximation