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DEFECT ASSESSMENT PROCEDURE BASED ON DUCTILE TEARING PROCESS

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Acta Mechanica Sinica 1987年第4期3卷 344-353页

作者： Yang Wei department of engineering mechanics,Tsinghua {3. department of engineering mechanics Tsinghua University Tsinghua China

Strain hardening,crack growth resistance and nonuniform load distribution have significanteffects on the ductile tearing process.A defect assessment procedure incorporating with the above features isproposed in the pr... 详细信息

关键词： defect assessment strain hardening crack growth ductile tearing process theoretical resistance curves nonuniform strain distribution design curve

NUMERICAL DISSIPATION FOR THREE-POINT DIFFERENCE SCHEMES TO HYPERBOLIC EQUATIONS WITH UneVEN MESHES

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Journal of Computational Mathematics 2003年第4期21卷 519-534页

作者： Zi-niu Wu(department of engineering mechanics, Tsinghua {3., Beijing 100084, China) department of engineering mechanics Tsinghua University 北京 100084

The widely used locally adaptive Cartesian grid methods involve a series of abruptly refined interfaces. The numerical dissipation due to these interfaces is studied here for three-point difference approximations of a hyperbolic equation. It will be shown that if the wave moves in the fine-to-coarse direction then the dissipation is positive (stabilizing), and if the wave moves in the coarse-to-fine direction then the dissipation is negative (destabilizing).

关键词： Refined interfaces Numerical dissipation Three-point difference approxima-tion Hyperbolic equation.

Nonlinear Rupture of Thin Free LiquidSheets

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Communications in Nonlinear Science and Numerical Simulation 1999年第3期4卷 3-5页

作者： Zhi LI and N. R. SIBGATULLIN(department of mechanics & engineering Sciences, Peking {3., Beijing 100871,China)(department of mechanics & Mathematics, Moscow State {3., Moscow 119899,Russia) department of mechanics & engineering Sciences Peking University Beijing 100871 China department of mechanics & Mathematics Moscow State University Moscow 119899 Russia

Introductionfleeliquidsheet,orplaneliquidjet,isacontinuousfareroffluidboundedbytwointerfaCesbetweenliquidandgasorliquidandtwootherliquids,anditmovesalmostinaconsta***... 详细信息

Introductionfleeliquidsheet,orplaneliquidjet,isacontinuousfareroffluidboundedbytwointerfaCesbetweenliquidandgasorliquidandtwootherliquids,anditmovesalmostinaconsta***...

关键词： thin free liquid sheet

WATER ENTRY OF A WEDGE BASED ON SPH MODEL WITH AN IMPROVED BOUNDARY TREATMENT

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Journal of Hydrodynamics 2009年第6期21卷 750-757页

作者： GONG Kai LIU Hua WANG Ben-long department of engineering mechanics Shanghai Jiao Tong University Shanghai 200240 China State Key Laboratory of Ocean engineering Shanghai Jiao Tong University Shanghai 200240 China

The hydrodynamic problem of a two-dimensional wedge entering water is studied based on Smoothed Particle Hydrodynamics （SPH） model. A non-reflection boundary treatment for SPH method is proposed to reduce the reflection of sound waves. The boundary pressure is obtained using an improved coupling boundary treatment approach, which is validated by comparing the simulation results with experimental and analytical results in literature. A series of cases with different initial entering velocities are simulated. The maximum force on the wedge and the corresponding time required to reach it for the different cases of initial entering velocities of the wedge are obained and fitted into formulas against the initial entering velocity of the wedge. The maximum drag coefficients of the wedge for the different cases with Froude number greater than 2 are all near the value of 0.91.

关键词： water entry Smoothed Particle Hydrodynamics (SPH) non-reflection boundary

Multiple time step molecular dynamics simulation for interaction between dislocations and grain boundaries

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Acta Mechanica Sinica 2005年第4期21卷 371-379页

作者： X.Y.Li W.Yang department of engineering mechanics,Tsinghua {3.,Beijing 100084.China department of engineering mechanics Tsinghua University Beijing China

A multiple time step algorithm, called reversible reference system propagator algorithm, is introduced for the long time molecular dynamics simulation. In contrast to the conventional algorithms, the multiple time method has better convergence, stability and efficiency. The method is validated by simulating free relaxation and the hypervelocity impact of nano-clusters. The time efficiency of the multiple time step method enables us to investigate the long time interaction between lattice dislocations and low-angle grain boundaries.

关键词： Multiple time step Molecular dynamics ,Dislocation Grain boundary

A land surface model incorporated with soil freeze/thaw and its application in GAME/Tibet

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Science China Earth Sciences 2006年第12期49卷 1311-1322页

作者： HU Heping1, YE Baisheng2, ZHOU Yuhua3.& TIAN Fuqiang1 1. department of Hydraulic engineering, Tsinghua university, Beijing 100084, China 2. Cold and Arid Regions Environmental and engineering Research Institute, Chinese Academy of Sciences, Lanzhou 73.000, China 3. department of Civil engineering, Massachusetts Institute of Technology, usa department of Hydraulic engineering Tsinghua University Beijing China Cold and Arid Regions Environmental and engineering Research Institute Chinese Academy of Sciences Lanzhou China department of Civil engineering Massachusetts Institute of Technology USA

Land surface process is of great importance in global climate change, moisture and heat exchange in the interface of the earth and atmosphere, human impacts on the environment and eco- system, etc. Soil freeze/thaw plays an important role in cold land surface processes. In this work the diurnal freeze/thaw effects on energy partition in the context of GAME/Tibet are studied. A sophisti- cated land surface model is developed, the particular aspect of which is its physical consideration of soil freeze/thaw and vapor flux. The simultaneous water and heat transfer soil sub-model not only reflects the water flow from unfrozen zone to frozen fringe in freezing/thawing soil, but also demon- strates the change of moisture and temperature field induced by vapor flux from high temperature zone to low temperature zone, which makes the model applicable for various circumstances. The modified Picard numerical method is employed to help with the water balance and convergence of the numerical scheme. Finally, the model is applied to analyze the diurnal energy and water cycle char- acteristics over the Tibetan Plateau using the Game/Tibet datasets observed in May and July of 1998. Heat and energy transfer simulation shows that: (i) There exists a negative feedback mechanism between soil freeze/thaw and soil temperature/ground heat flux; (ii) during freezing period all three heat fluxes do not vary apparently, in spite of the fact that the negative soil temperature is higher than that not considering soil freeze; (iii) during thawing period, ground heat flux increases, and sensible heat flux decreases, but latent heat flux does not change much; and (iv) during freezing period, soil temperature decreases, though ground heat flux increases.

关键词： land surface model,soil freeze/thaw,GAME/Tibet,simultaneous liquid,vapor and heat transfer.

Stability of core-annular flow of power-law fluids in the presence of interfacial surfactant

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Science China(Physics,mechanics & Astronomy) 2010年第5期53卷 933-943页

作者： SUN XueWei,PENG Jie & ZHU KeQin department of engineering mechanics,Tsinghua {3.,Beijing 100084,China department of engineering mechanics Tsinghua University Beijing China

The shear-thinning influence on the core-annular flow stability of two immiscible power-law fluids is considered by making a linear stability *** flow is driven by an axial pressure gradient in a straight pipe with the interface between the two fluids occupied by an insoluble *** the basic flow for this core-annular arrangement,the analytical solution is obtained with respect to the power-law fluid *** linearized equations for the evolution of infinitesimal disturbances are derived and the stability problem is formulated as a generalized matrix eigenvalue problem,which is solved by using the software package Matlab based on the QZ *** shear-thinning property is found to have marked influence on the power-law fluid core-annular flow stability,which is reflected in various ***,the capillary instability is magnified by the shear-thinning property,which may lead to an essential difference between power-law and newtonian fluid *** when the interface is close to the pipe wall,the power-law fluid flow may be unstable while the newtonian fluid flow is ***,under disturbances to the interface a velocity discontinuity at the interface appears which is destabilizing to the *** magnitude of this velocity discontinuity is affected by the power-law index and the flow stability is influenced ***,the shear-thinning property may induce new stability modes which do not appear in the newtonian fluid *** flow stability shows much dependence on the interface location,the role of which was neglected in most previous *** shear-thinning fluid flow is more unstable to long wave disturbances when the interface is close to the pipe wall,while the newtonian fluid flow is more unstable when the interface is close to the pipe *** this trend is changed by the addition of interfacial surfactant,for which the power-law fluid flow is more stable no matter where the interface is loca

关键词： core-annular flow power-law fluid interfacial surfactant linear stability analysis

A STUDY ON THE WEIGHT FUNCTION OF THE MOVING LEAST SQUARE APPROXIMATION IN THE LOCAL BOUNDARY INTEGRAL EQUATION METHOD

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Acta Mechanica Solida Sinica 2003年第3期16卷 276-282页

作者： Long Shuyao Hu De’an (department of engineering mechanics,Hunan {3.,Changsha 410082,China) department of engineering mechanics Hunan University Changsha 410082 China

The meshless method is a new numerical technique presented in recent *** uses the moving least square(MLS)approximation as a shape *** smoothness of the MLS approximation is determined by that of the basic function and of the weight function,and is mainly determined by that of the weight ***,the weight function greatly affects the accuracy of results *** kinds of weight functions,such as the spline function, the Gauss function and so on,are proposed recently by many *** the present work,the features of various weight functions are illustrated through solving elasto-static problems using the local boundary integral equation *** effect of various weight functions on the accuracy, convergence and stability of results obtained is also *** show that the weight function proposed by Zhou Weiyuan and Gauss and the quartic spline weight function are better than the others if parameters c and α in Gauss and exponential weight functions are in the range of reasonable values,respectively,and the higher the smoothness of the weight function,the better the features of the solutions.

关键词： weight function meshless methods local boundary integral equation method moving least square approximation

Mathematic Expression of Kinetic Compensation Effect and Relationship between the Exothermic Decomposition Temperature and Critical Temperature of Thermal Explosion of Eighty-six Energetic Materials

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含能材料 2001年第1期9卷 8-9页

作者： HU Rong zu 1, YANG De suo 2, ZHANG Jiao qiang 3. (1. department of Chemistry,Northwest university, Xi′an 710065, China 2. department of Chemistry and Chemical {3., Baoji College of Arts and Science, Baoji 721007, China 3. department of 西北大学陕西西安 710065 宝鸡文理学院陕西 721007 西北工业大学陕西西安 710072

Two relationships are established using the least squares method,between the kinetic parameters (the apparent activation energy and pre exponential constant),and the exothermic decomposition temperature and ther... 详细信息

关键词： critical temperature of thermal explosion decomposition temperature DSC energetic materials.