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A low frequency piezoelectric power harvester using a spiral-shaped bimorph

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Science China(Physics,mechanics & Astronomy) 2006年第6期49卷 649-659页

作者： HU Yuantai1,2,HU Hongping2 & YANG Jiashi3.1. Institute of mechanics and Sensing Technology,Central South university,Changsha 410083.China 2. department of mechanics,Huazhong university of Science and Technology,Wuhan 43.074,China 3. department of engineering mechanics,university of nebraska,lincoln,ne 68588-052.,usa 1. Institute of mechanics and Sensing Technology Central South University Changsha 410083 China 2. department of mechanics Huazhong University of Science and Technology Wuhan 430074 China 3. department of engineering mechanics University of Nebraska Lincoln NE 68588-0526 USA

We propose a spiral-shaped piezoelectric bimorph power harvester operating with coupled flexural and extensional vibration modes for applications to low frequency energy sources. A theoretical analysis is performed and the computational results show that the spiral structure has relatively low operating frequency compared to beam power harvesters of the same size. It is found that to optimize the performance of a piezoelectric spiral-shaped harvester careful design is needed.

关键词： spiral-shaped bimorph,piezoelectric harvester,power density.

Analysis on cohesive crack opening displacement considering the strain softening effect

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Science China(Physics,mechanics & Astronomy) 2006年第1期49卷 88-101页

作者： WANG Limin1, XU Shilang2 & ZHAO Xiqiang3.1. mechanics department, Shandong university of Technology, Zibo 255049, China 2. Civil {3. department, Dalian university of Technology, Dalian 116024, China 3. Mathematics department, Ocean university of China, Qingdao 266071, China mechanics department Shandong University of Technology Zibo 255049 China Civil engineering department Dalian University of Technology Dalian 116024 China Mathematics department Ocean University of China Qingdao 266071 China

In order to investigate the crack propagation in quasi-brittle materials like rock, ceramic and concrete, Hillerborg and his co-researchers abstracted the fracture process zone in front of a stress free crack in terms of a “fictitious crack zone”. On the fictitious crack zone, cohesive stresses distribute following a given softening relationship of stress vs. crack opening. Based on the polynomial or power series expression of cohesive crack opening displacement, the relationship of the cohesive stress vs. the crack opening displacement is established using elastic theory and integral equation, and some unknown physics variables are obtained using variation approach. The calculation results gained in this paper are close to the experimentally test ones.

关键词： cohesive crack, softening, dissipation work, variation approach.

Development of SOM combustion model for Reynolds-averaged and large-eddy simulation of turbulent combustion and its validation by DNS

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Science China(Technological Sciences) 2008年第8期51卷 1073-1086页

作者： ZHOU LiXing department of engineering mechanics, Tsinghua {3., Beijing 100084, China department of engineering mechanics Tsinghua University Beijing 100084 China

The derivation and closure methods of the second-order moment (SOM) combus- tion model are proposed. The application of this model to Reynolds averaged (RANS) and large-eddy simulation (LES) of turbulent swirling diffusion combustion, jet diffusion combustion, and bluff-body stabilized premixed combustion is sum- marized. It is indicated that the SOM model is much better than the eddy-beak-up (EBU) and presumed PDF models widely used in commercial software and engi- neering. The SOM modeling results are close to those obtained using the most accurate but much more complex PDF equation model. Moreover, it can save much more computation time than the PDF equation model. Finally, the SOM model is validated by the direct numerical simulation (DNS) of turbulent reacting channel flows.

关键词： turbulent combustion second-order moment model Reynolds averaged simulation large-eddy simulation

On the Time Scale of TCP-Friendly Admission Control Protocols

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On the Time Scale of TCP-Friendly Admission Control Protocol...

Some variational principles in electroelastic media under finite deformation

2008 IEEE International Conference on Communications(ICC 2008)

作者： Jie Feng and Lisong Xu department of Computer Science and engineering university of nebraska-{3. {3.,ne 68588-0115 usa

The definition of TCP friendliness has been evolved over time from the traditional one for congestion control protocols to the recent ones for admission control *** of them can effectively prevent the Internet from congestion collapse and TCP starvation,while enabling a wide variety of traffic control protocols other than ***,the current TCP-friendly admission control protocols are designed to be TCP friendly only on fairly long time *** is,it is likely that a group of TCP users all experience persistent poor performance during their transmission,which then leads to dissatisfaction of TCP *** this paper,we first present a new definition of TCP friendliness,called Stochastic TCP Friendliness,with which we study the time scale of TCP-friendly admission control ***,we develop a new traffic control protocol,called Stochastically TCPFriendly Admission Control (STFAC),which is stochastically TCP friendly not only on a long time scale but also on a short time ***,we present very encouraging simulation results showing that STFAC can considerably improve the performance of UDP users and TCP users on both a long time scale and a short time scale,when compared with the traditional TCPfriendly congestion control protocols.

关键词： UDP On the Time Scale of TCP-Friendly Admission Control Protocols Internet

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Science China(Physics,mechanics & Astronomy) 2008年第9期51卷 1390-1402页

作者： KUANG ZhenBang department of engineering mechanics,Shanghai Jiaotong {3.,Shanghai 200240,China department of engineering mechanics Shanghai Jiaotong University Shanghai 200240 China

It is proposed that the universal thermodynamic energy variational principle is in-cluded in the first law of thermodynamics. Some variational principles in the elec-troelastic media under finite deformation are derived from this universal thermo-dynamic variational principle. It is suggested that in the general electroelastic analysis the environment should be considered together with the discussed elec-troelastic medium. For the variational principle of nonlinear electroelastic media the variation of the electric potential is coupled with the virtual displacement,and the variation of the initial volume should be considered. The Maxwell stress in the initial configuration is naturally derived from this variational principle and it is unique in the second order precision.

关键词： first law of thermodynamics variational principle the electroelastic media the governing equation

AN EXACT SYMPLECTIC SOLUTION FOR THE DYNAMIC ANALYSIS OF SHEAR DEFORMABLE ANTISYMMETRIC ANGLE-PLY LAMINATED PLATES

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Acta Mechanica Solida Sinica 1996年第3期9卷 263-273页

作者： Zou Guiping (department of engineering mechanics,Tongji {3.,Shanghai 200092) TONGJI UNIV DEPT MECH ENGN SHANGHAI 200092 PEOPLES R CHINA

From the mixed variational principle, by the selection of the state variables and its dual variables, the Hamiltonian canonical equation for the dynamic analysis of shear deformable antisymmetric angle-ply laminated plates is derived, leading to the mathematical frame of symplectic geometry and algorithms, and the exact solution for the arbitrary boundary conditions is also derived by the adjoint orthonormalized symplectic expansion method. Numerical results are presented with the emphasis on the effects of length/thickness ratio, arbitrary boundary conditions, degrees of anisotropy, number of layers, ply-angles and the corrected coefficients of transverse shear.

关键词： Hamilton canonical equation symplectic free vibration analysis antisymmetric angle-ply laminated plates

Damage and progressive failure of concrete structures using non-local peridynamic modeling

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Science China(Technological Sciences) 2011年第3期54卷 591-596页

作者： HUANG Dan1,2, ZHANG Qing1,2 & QIAO PiZhong1,3.1 State Key Laboratory of Hydrology-Water Resources and Hydraulic engineering, Hohai university, Nanjing 210098, China 2 department of engineering mechanics, Hohai university, Nanjing 210098, China 3.department of Civil and Environmental engineering, Washington State university, Pullman, WA 99164-2910, usa 1. State Key Laboratory of Hydrology-Water Resources and Hydraulic engineering Hohai University Nanjing 210098 China2. Department of Engineering Mechanics Hohai University Nanjing 210098 China3. Department of Civil and Environmental Engineering Washington State University Pullman WA 99164-2910 USA

Peridynamics (PD), a recently developed theory of solid mechanics, which employs a non-local model of force interaction and makes use of integral formulation rather than the spatial partial differential equations used in the classical continuum mechanics theory, has shown effectiveness and promise in solving discontinuous problems at both macro and micro scales. In this paper, the peridynamics theory is used to analyze damage and progressive failure of concrete structures. A non-local peridynamic model for a rectangular concrete plate is developed, and a central pairwise force function is introduced to describe the interior interactions between particles within some definite distance. Damage initiation, evolution and crack propagation in the concrete model subject to in-plane uni-axial tension, in-plane uni-axial compression and out-of-plane impact load are investigated respectively. The numerical results show that discontinuities appear and grow spontaneously as part of the solution to the peridynamic equations of motion, and no special failure criteria or re-meshing techniques are required, which proves the potential of peridynamic modeling as a promising technique for analyzing the progressive failure of concrete materials and structures.

关键词： concrete damage progressive failure peridynamic model discontinuities

Application and Comparison of Two SGS Models in Large Eddy Simulation of FreeTurbulent Jet Flow

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Communications in Nonlinear Science and Numerical Simulation 1999年第1期4卷 12-19页

作者： Hong YAN and Mingde SU (department of engineering mechanics, Tsinghua {3., Beijing 100084, China) department of engineering mechanics Tsinghua University Beijing 100084 China

Large eddy simulations of spatially evolved turbulent round jets were presented. The two SGS models called the standard Smagorinsky’s eddy viscosity model and the non-eddy viscosity stimulated small scale(SSS) model developed by Shah & Ferziger were applied. The Reynolds number of the flow was taken as 10000 based on the orifice diameter and the axial velocity in the orifice. The comparison between these two models showed that the standard Smagorinsky’s viscosity model with Smagorinsky’s constant of 0.1 underestimated the turbulent intensity, while the SSS model showed a better agreement with the experiment. Also the SSS model was used to investigate the development of vortex. The convective boundary condition at the outflow boundary was adopted to ensure less effect of noise on the upstream.

关键词： stimulated small scale model smagorinsky’s eddy viscosity model Round jet, Large eddy simulation

Influence of moisture content and time on the mechanical behavior of polymer material

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Science China(Technological Sciences) 2004年第5期47卷 595-607页

作者： ZHENG Gaofei1, 2, KANG Yilan1, SHENG Jing3. QIN Qinghua1, WANG Huaiwen1 & FU Donghui1 1. department of mechanics, Tianjin university, Tianjin 3.0072, China 2. department of mechanics, Tianjin Polytechnic university, Tianjin 3.0160, China 3. department of Material engineering, Tianjin university, Tianjin 3.0072, China Correspondence should be addressed to Kang Yilan 1. department of mechanics Tianjin University 300072 Tianjin China 2. department of mechanics Tianjin Polytechnic University 300160 Tianjin China 3. department of Material engineering Tianjin University 300072 Tianjin China

The effects of moisture content and time on mechanical behavior of polymer materials are investigated both theoretically and experimentally in this paper. An equivalence relationship between time intervals and the moisture content for polymer nylon-6 has been established by way of experimental observation and measured results. The relationship shows that there exists equivalence between moisture and service time in affecting mechanical properties. In other words, an increase in moisture can be replaced by prolonging acting time in producing the same effect on material properties. Consequently, a moisture-time superposition principle is presented based on the experimental results and the analogy of temperature-time superposition principle. Numerical results such as stress-strain curves with different moisture contents are presented to verify the applicability and correctness. The proposed method appears very promising in study on the effect of moisture content on mechanical behavior of polymer materials.

关键词： equivalence relationship of moisture-time, moisture content, mechanical properties, shift function.