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em Chinese Academy of Sciences Institutional Repositories Grid Portal
Resumo:
A large-eddy simulation with transitional structure function(TSF) subgrid model we previously proposed was performed to investigate the turbulent flow with thermal influence over an inhomogeneous canopy, which was represented as alternative large and small roughness elements. The aerodynamic and thermodynamic effects of the presence of a layer of large roughness elements were modelled by adding a drag term to the three-dimensional Navier-Stokes equations and a heat source/sink term to the scalar equation, respectively. The layer of small roughness elements was simply treated using the method as described in paper (Moeng 1984, J. Atmos Sci. 41, 2052-2062) for homogeneous rough surface. The horizontally averaged statistics such as mean vertical profiles of wind velocity, air temperature, et al., are in reasonable agreement with Gao et al.(1989, Boundary layer meteorol. 47, 349-377) field observation (homogeneous canopy). Not surprisingly, the calculated instantaneous velocity and temperature fields show that the roughness elements considerably changed the turbulent structure within the canopy. The adjustment of the mean vertical profiles of velocity and temperature was studied, which was found qualitatively comparable with Belcher et al. (2003, J Fluid Mech. 488, 369-398)'s theoretical results. The urban heat island(UHI) was investigated imposing heat source in the region of large roughness elements. An elevated inversion layer, a phenomenon often observed in the urban area (Sang et al., J Wind Eng. Ind. Aesodyn. 87, 243-258)'s was successfully simulated above the canopy. The cool island(CI) was also investigated imposing heat sink to simply model the evaporation of plant canopy. An inversion layer was found very stable and robust within the canopy.
Resumo:
通过在一小型流化床中进行高水分煤的燃烧与排放的试验研究，表明水分含量和空气－燃料比对于高水分煤的燃烧与排放有较大影响。随着水分增加，流化床床温下降，ＮＯｘ、ＳＯｘ排放量也下降。空气－燃料比存在一最佳值，这时床温最高，而偏离此值，床温下降，随着空气量的增加，ＮＯｘ、ＳＯｘ排放量也增加。当空气－燃料比变化时，燃烧干煤与燃烧高水分煤有着类似的试验结果。
Resumo:
本文用连续介质力学的理论分析了岩石屈服前的性状,导出了岩石介质的非线性弹性的本构方程,并与实验资料进行了比较,二者十分接近.进而用非线性弹性取代一般帽盖模型中关于弹性区的线弹性假设,导出了非线性弹性—塑性硬化的帽盖模型.
Resumo:
This book elucidates the methods of molecular gas dynamics or rarefied gas dynamics which treat the problems of gas flows when the discrete molecular effects of the gas prevail under the circumstances of low density, the emphases being stressed on the basis of the methods, the direct simulation Monte Carlo method applied to the simulation of non-equilibrium effects and the frontier subjects related to low speed microscale rarefied gas flows. It provides a solid basis for the study of molecular gas dynamics for senior students and graduates in the aerospace and mechanical engineering departments of universities and colleges. It gives a general acquaintance of modern developments of rarefied gas dynamics in various regimes and leads to the frontier topics of non-equilibrium rarefied gas dynamics and low speed microscale gas dynamics. It will be also of benefit to the scientific and technical researchers engaged in aerospace high altitude aerodynamic force and heating design and in the research on gas flow in MEMS
| [1] Molecular structure and energy states | (21) | ||
| [2] Some basic concepts of kinetic theory | (51) | ||
| [3] Interaction of molecules with solid surface | (131) | ||
| [4] Free molecular flow | (159) | ||
| [5] Continuum models | (191) | ||
| [6] Transitional regime | (231) | ||
| [7] Direct simulation Monte-Carlo (DSMC) method | (275) | ||
| [8] Microscale slow gas flows, information preservation method | (317) | ||
| [App. I] Gas properties | (367) | ||
| [App. II] Some integrals | (369) | ||
| [App. III] Sampling from a prescribed distribution | (375) | ||
| [App. IV] Program of the couette flow | (383) | ||
| Subject Index | (399) | ||
Resumo:
Adiabatic shear localization is a mode of failure that occurs in dynamic loading. It is characterized by thermal softening occurring over a very narrow region of a material and is usually a precursor to ductile fracture and catastrophic failure. This reference source is the first detailed study of the mechanics and modes of adiabatic shear localization in solids, and provides a systematic description of a number of aspects of adiabatic shear banding. The inclusion of the appendices which provide a quick reference section and a comprehensive collection of thermomechanical data allows rapid access and understanding of the subject and its phenomena. The concepts and techniques described in this work can usefully be applied to solve a multitude of problems encountered by those investigating fracture and damage in materials, impact dynamics, metal working and other areas. This reference book has come about in response to the pressing demand of mechanical and metallurgical engineers for a high quality summary of the knowledge gained over the last twenty years. While fulfilling this requirement, the book is also of great interest to academics and researchers into materials performance.Table of Contents
| 1 | Introduction | 1 |
| 1.1 | What is an Adiabatic Shear Band? | 1 |
| 1.2 | The Importance of Adiabatic Shear Bands | 6 |
| 1.3 | Where Adiabatic Shear Bands Occur | 10 |
| 1.4 | Historical Aspects of Shear Bands | 11 |
| 1.5 | Adiabatic Shear Bands and Fracture Maps | 14 |
| 1.6 | Scope of the Book | 20 |
| 2 | Characteristic Aspects of Adiabatic Shear Bands | 24 |
| 2.1 | General Features | 24 |
| 2.2 | Deformed Bands | 27 |
| 2.3 | Transformed Bands | 28 |
| 2.4 | Variables Relevant to Adiabatic Shear Banding | 35 |
| 2.5 | Adiabatic Shear Bands in Non-Metals | 44 |
| 3 | Fracture and Damage Related to Adiabatic Shear Bands | 54 |
| 3.1 | Adiabatic Shear Band Induced Fracture | 54 |
| 3.2 | Microscopic Damage in Adiabatic Shear Bands | 57 |
| 3.3 | Metallurgical Implications | 69 |
| 3.4 | Effects of Stress State | 73 |
| 4 | Testing Methods | 76 |
| 4.1 | General Requirements and Remarks | 76 |
| 4.2 | Dynamic Torsion Tests | 80 |
| 4.3 | Dynamic Compression Tests | 91 |
| 4.4 | Contained Cylinder Tests | 95 |
| 4.5 | Transient Measurements | 98 |
| 5 | Constitutive Equations | 104 |
| 5.1 | Effect of Strain Rate on Stress-Strain Behaviour | 104 |
| 5.2 | Strain-Rate History Effects | 110 |
| 5.3 | Effect of Temperature on Stress-Strain Behaviour | 114 |
| 5.4 | Constitutive Equations for Non-Metals | 124 |
| 6 | Occurrence of Adiabatic Shear Bands | 125 |
| 6.1 | Empirical Criteria | 125 |
| 6.2 | One-Dimensional Equations and Linear Instability Analysis | 134 |
| 6.3 | Localization Analysis | 140 |
| 6.4 | Experimental Verification | 146 |
| 7 | Formation and Evolution of Shear Bands | 155 |
| 7.1 | Post-Instability Phenomena | 156 |
| 7.2 | Scaling and Approximations | 162 |
| 7.3 | Wave Trapping and Viscous Dissipation | 167 |
| 7.4 | The Intermediate Stage and the Formation of Adiabatic Shear Bands | 171 |
| 7.5 | Late Stage Behaviour and Post-Mortem Morphology | 179 |
| 7.6 | Adiabatic Shear Bands in Multi-Dimensional Stress States | 187 |
| 8 | Numerical Studies of Adiabatic Shear Bands | 194 |
| 8.1 | Objects, Problems and Techniques Involved in Numerical Simulations | 194 |
| 8.2 | One-Dimensional Simulation of Adiabatic Shear Banding | 199 |
| 8.3 | Simulation with Adaptive Finite Element Methods | 213 |
| 8.4 | Adiabatic Shear Bands in the Plane Strain Stress State | 218 |
| 9 | Selected Topics in Impact Dynamics | 229 |
| 9.1 | Planar Impact | 230 |
| 9.2 | Fragmentation | 237 |
| 9.3 | Penetration | 244 |
| 9.4 | Erosion | 255 |
| 9.5 | Ignition of Explosives | 261 |
| 9.6 | Explosive Welding | 268 |
| 10 | Selected Topics in Metalworking | 273 |
| 10.1 | Classification of Processes | 273 |
| 10.2 | Upsetting | 276 |
| 10.3 | Metalcutting | 286 |
| 10.4 | Blanking | 293 |
| Appendices | 297 | |
| A | Quick Reference | 298 |
| B | Specific Heat and Thermal Conductivity | 301 |
| C | Thermal Softening and Related Temperature Dependence | 312 |
| D | Materials Showing Adiabatic Shear Bands | 335 |
| E | Specification of Selected Materials Showing Adiabatic Shear Bands | 341 |
| F | Conversion Factors | 357 |
| References | 358 | |
| Author Index | 369 | |
| Subject Index | 375 |
Resumo:
<正>基础研究是国家科技发展的原动力,学科的交融与渗透已经成为当今科学发展的重要趋势,促进交叉学科的健康成长是目前科学界普遍关心的问题之一。分析近百年来获得诺贝尔自然科学奖的300多项成果中,近一半的项目是多学科合作的研究成果,对170多位生理学或医学诺贝尔奖获得者及他们的原创性成果的统计研究发现,具有跨学科知识
Resumo:
The steady state ion acceleration at the front of a cold solid target by a circularly polarized flat-top laser pulse is studied with one-dimensional particle-in-cell (PIC) simulation. A model that ions are reflected by a steady laser-driven piston is used by comparing with the electrostatic shock acceleration. A stable profile with a double-flat-top structure in phase space forms after ions enter the undisturbed region of the target with a constant velocity. (C) 2007 Elsevier B.V. All rights reserved.
Resumo:
设计了一种单块晶体集成的n×n纵横开关(Crossbar)网络。通过综合考虑晶体的双折射和全内双反射现象,以及晶体的电光效应,将构成n×n纵横开关网络的所有单元器件都集成到一块具有电光效应的双折射晶体上。同时,给出了该网络的控制算法,通过对开关工作状态的控制,可以实现任意输入输出通道之间的无阻塞连接。这种单块晶体集成的纵横开关网络具有能量损耗低、无阻塞、易安装、抗干扰等优点,适合于全光网络发展的需要。
Resumo:
用蒙特卡罗方法仿真了增益随机散射体中的非相干辐射，观察了非相干随机激光的特性。当抽运能量超过一定阈值时，散射体的整体辐射谱突然变窄；随着抽运能量继续增大，在光滑谱背景上会出现分离尖峰；散射体内空间某位置处频率组成不是单一的；辐射谱中某单个频率的空间方向分布和位置分布比较广。增益随机散射体中产生的非相干随机激光本质上既不同于无反馈的普通放大自发辐射，又不同于相干反馈形成的常规激光。解释了非相干随机激光辐射谱上出现分离尖峰的原因，出现这种现象是由于少数光子在增益散射体中经历较多次数散射后得到了相对充分的放大。
Resumo:
研究了两种新型芴类衍生物9，9-二(2-乙基已基)-2，7-二咔唑-9H-芴(简记为DCZF)和9，9-二(2-乙基已基)-2，7-二(2-(4-甲氧基)苯-2，1-乙烯基)芴(简记为BMOSF)在N，N-二甲基甲酰胺(DMF)中的线性吸收和单光子荧光行为，并用脉冲宽度为38ps，重复频率为10Hz的1064 nm Nd：YAG脉冲激光研究了两种化合物的三光子吸收性质．结果表明：两种新材料的最大线性吸收峰分别位于330和380nm，吸收区域覆盖了270-420nm波段．两种化合物的荧光带位于蓝-紫区，中心
Resumo:
设计了组成为0．70TeO2-(0．20-x)ZnO-xGeO2—0．05La2O3-0．025K2O-0．025Na2O-0．01Yb2O3(摩尔分数x=0,0．05，0．10，0．15和0．20)的碲酸盐激光玻璃，测试了热学性质、吸收光谱、荧光光谱和荧光寿命。计算了Yb^3+离子的吸收截面、受激发射截面、荧光有效线宽等参数。结果表明，组成为0．70TeO2-0．20GeO2-0．05La2O3-0．025K2O-0．025Na2O的玻璃具有优于著名的碲锌钠(TZN)玻璃的热稳定性，高的受激发射截面(1
Resumo:
Er3+-doped TeO2-based oxysulfide glasses have been prepared in argon atmosphere in carbon crucibles. The thermal analysis and spectroscopic properties of Er (3+) have been considered in terms of sulfide influence. As a function of composition, we have principally measured optical absorption, spontaneous emission and lifetime measurements. Judd-Ofelt theory was introduced to calculate bandwidth and emission cross-section. The results show the product FVMM x sigma(c) increase from 476.8 8 to 635.04 10(-21) cm(2) nm evidently with the addition of 10 mol% PbS into tellurite glass, which indicates a perfect effect on spectra property of Er3+ ions. (C) 2004 Elsevier B.V. All rights reserved.
Resumo:
In this paper, we present results on upconversion luminescence performed on Yb3+-doped yttrium aluminum garnets under 940 nm excitation. The upconversion luminescence was ascribed to Yb3+ cooperative luminescence and the presence of rare earth impurity ions. The cooperative luminescence spectra as a function of Yb concentration were measured and the emission intensity variation with Yb concentration was discussed. Yb3+ energy migration quenched the cooperative luminescence of Yb:YAG crystals with doping level over 15 at%. (c) 2004 Elsevier B.V. All rights reserved.
