Analysis of two-dimensional finite solids with microcracks

A general method is presented for solving the plane elasticity problem of finite plates with multiple microcracks. The method directly accounts for the interactions between different microcracks and the effect of outer boundary of a finite plate. Analysis is based on a superposition scheme and series expansions of the complex potentials. By using the traction-free conditions on each crack surface and resultant forces relations along outer boundary, a set of governing equations is formulated. The governing equations are solved numerically on the basis of a boundary collocation procedure. The effective Young's moduli for randomly oriented cracks and parallel cracks are evaluated for rectangular plates with microcracks. The numerical results are compared with those from various micromechanics models and experimental data. These results show that the present method provides a direct and efficient approach to deal with finite solids containing multiple microcracks.

Effect of weak Brownian motion on gravitational coagulation

The effect of a small amount of Brownian diffusion on gravitational coagulation is numerically calculated by incorporating gravitational and interparticle forces (both attractive and repulsive), as well as hydrodynamic interactions. It is found that weak Brownian diffusion, the effect of which is nonlinearly coupled with gravity, can act to decrease the coagulation rate.

Theoretical analysis for mechanical erosion of carbon-base materials in ablation

This article derives and provides a theoretical analysis for the mechanical erosion of carbon-base materials in ablation. The theory of mechanical erosion based on a nondimensional critical roughness parameter is proposed, The important parameters in this analytical method are independent of the test, The analysis accounts for the heating, pressure, and shear forces acting on material particles exposed to the boundary-layer flow. For the validity of a theoretical analytical method a computational example is given. The theoretical results agree fairly with the experimental data.

Dynamic-response of a laminated plate with friction damping

黄土丘陵沟壑区纸坊沟小流域农业生态安全态势变化的驱动力分析

以黄土丘陵沟壑区纸坊沟小流域为研究对象,利用1985—2006年调查和监测资料,综合现有研究成果,将主成分分析和通径分析方法相结合,分析可能影响农业生态安全态势变化的各因子,探讨农业生态安全态势变化的驱动力。结果表明:自然条件是影响黄土丘陵沟壑区纸坊沟小流域农业生态安全态势变化的基础,人文社会经济条件是其变化的主要驱动力,具体可归纳为经济发展、人口压力、流域产业结构调整和农业科技进步4类因子;此外,国家和区域的相关政策、农业产业链与资源量相关度对农业生态安全也有一定影响。

岷江上游景观变化及驱动力分析

岷江上游地区是我国重要的林区之一，它不但影响当地和崛江下游的农业生产、生活用水和生态环境建设，甚至影响长江上游地区生态环境改善，在长江上游生态安全格局中占有重要地位。本文在收集遥感数据、统计数据、问卷调查数据和相关图件的基础上，以GIS为技术手段研究了崛江上游地区从1974年到2000年间的景观变化，并结合统计数据和问卷调查资料·分析了景观变化的原因，旨在为该区资源的合理利用、环境保护和可持续发展提供依据。主要结论如下：①有林地是崛江上游地区主要的景观类型，也是唯一一种面积持续减少的景观类型。林地与草地面积占研究区面积的90％以上，是该区的景观基质。草地、灌木林地、经济林、耕地和居民用地等面积都有不同程度的增加，以灌木林地最多。景观变化转移量以在有林地和灌木林地、草地之间为最大；且变化多分布在干旱河谷周围和松潘高原地区。②斑块水平上的各类型的斑块数和边界密度都在增加；有林地和灌木林地的最大斑块占景观面积的比例和平均斑块面积呈减少趋势，LPI以草地增加最为明显，MPS以灌木林地增加最多，草地次之。景观水平上的斑块数、最大斑块占景观面积的比例、边界密度、散布并列指数、多样性指数和均匀度指数都在增加，而平均斑块面积和蔓延度指数在降低。各指数说明研究区的景观异质性和破碎化程度增加，连通性降低，且变化趋势有所减缓，以1974一1986年变化为最大。③导致景观变化的原因是多方面的。人口、经济和教育是该区景观变化的主要因素；并且人口和经济的驱动作用具有阶段性和发展性。参与式的问卷调查，是研究景观变化驱动力的一个有效方法。④景观变化导致了研究区的森林覆盖率下降，径流减少，草场退化，水土流失加剧，干旱河谷扩大，滑坡、泥石流等自然灾害频繁发生。建议进一步加大干旱河谷植被建设的力度，适当调整产业结构，并对资源进行合理的优化配置和规划使用，同时加强法制建设，走在保护和建设中发展，在发展中保护和建设的生态建设道路。

Stress Analysis of the Superconducting Magnet of LPT

The superconducting magnet of the LPT (Lanzhou Penning trap) consists of nine coaxial coils. The maximum magnetic field is 7 T and thus results in a large magnetic force. In order to assure the mechanical stability, it is necessary to do the stress analysis of the magnet system. The 3D Finite Element Analysis of thermal and mechanical behavior was presented in this paper. For the numerical simulation and analysis of the phenomena inside the structure, the ADINA and TOSCA code were chosen right from start. The ADINA code is commonly used for numerical simulations of the structure analysis [1] and the TOSCA code is professional software to calculate the magnetic field and Lorentz Forces. The results of the analysis were evaluated in terms of the stress and deformation.

The first synthesis of a water-soluble alpha-cyclodextrin/C-60 supramolecular complex using anionic C-60 as a building block

A novel supramolecular inclusion complex of alpha-CD/C-60 was synthesized using anionic C-60. The reaction progress was monitored in situ by visible and near-IR spectroscopy. The obtained complex was characterized by UV-vis, C-13 NMR, MALDI-TOF, and cyclic voltammetry. The induction and dispersion forces are considered to be the major driving forces for the formation of a resulting alpha-CD/C-60(.-) inclusion complex.

Complex aggregates of spherical colloids via modified micromolding in capillaries

This paper describes a simple approach to fabricate aggregates composed of monodispersed silica microspheres by modified micromolding in capillaries (MIMIC). Two different kinds of contact modes, namely, conformal contact and non-conformal contact, between the poly(dimethylsiloxane) (PDMS) mold and the underlying prepatterned substrate, can be controlled during the micromolding, which result in the formation of different aggregates under the influence of template confinement and capillary forces. These aggregates, including woodpile structure, discoid, conoid and rectangular clusters, possess well-controlled sizes and orientation. The possible mechanisms for the formation of different aggregates are discussed in detail.

Modern changes of tidal troughs among the radial sand ridges in northern Jiangsu coastal zone

Using satellite images taken on different dates, GIS analysis of aerial photos, bathymetric maps and other field survey data, tidal troughs and major sand ridges in the northern Jiangsu coastal area were contrasted. The results show that there have been three types of movement or migration of tidal trough in this area: (1) Periodic and restricted, this type of trough usually developed along the beaches with immobile gully head as a result of the artificial dams and the swing range increased from gully head to the low reaches, so they have been obviously impacted by human activity and have longer swing periods; (2) Periodic and actively, this kind of trough, which swung with a fast rate and moved periodically on sand ridges, were mainly controlled by the swings of the host tidal troughs and hydrodynamic forces upon tidal sand ridge and influenced slightly by human constructions; (3) Steadily and slowly, they are the main tidal troughs with large scale and a steady orientation in this area and have slow lateral movement. The differences in migration mode of tidal trough shift result in different rates of migration and impact upon tidal sand ridges. Lateral accumulation on current tidal trough and deposition on abandoned tidal troughs are the two types of sedimentation of the tidal sand ridges formation. The whole radial sand ridge was generally prone to division and retreat although sand ridges fluctuated by the analysis of changes in talwegs of tidal troughs and shorelines of sand ridges.

基于解耦控制的SCARA机器人轨迹跟踪控制器设计

SCARA型机器人的控制问题由于其动力学模型中没有重力矩项的作用而得以简化,由于在实际应用中经常要求其高速运动,则对具有强耦合的哥氏力与向心力的控制就成为制约其系统性能的重要问题。提出通过线性变换对机器人系统解耦,将高阶系统转化为解耦的低阶系统进行控制的方法,并且应用极点配置对解耦的系统求解机器人控制器。该方法无需测量关节速度和加速度,只需要测量关节位置信号。所提出的控制器既能保证闭环系统全局渐进稳定,又能通过对线性化系统闭环极点的配置来获得期望的闭环系统响应性能。仿真实验证明了所提出的控制器设计方法的可行性。

3自由度并联柔索驱动变刚度操作臂的刚度控制

利用柔索的弹性及驱动冗余性构造了一种3自由度并联柔索驱动变刚度操作臂,在静力学与刚度分析的基础上,进行刚度控制研究。首先,将柔索驱动力映射到关节空间,并分析等效关节力与柔索张力和外力的关系, 提出该操作臂的三维力矢量闭合原理。根据微分变换原理进行刚度分析,得到关节刚度矩阵及操作手刚度矩阵, 并进行数值算例分析,结果表明:刚度与柔索的张力有关,调节柔索张力可以改变系统刚度。最后,采用位置与张力混合控制的策略,对该变刚度操作臂进行了刚度控制,并进行了仿真验证。

7000米载人潜水器推进器故障容错控制分配研究

介绍了7000米载人潜水器推进系统的组成和推进器布置,描述了潜水器控制分配问题,对推进器推力和期望控制量进行了归一化处理.根据载人潜水器的推进器布置,建立了系统的控制分配模型,设计了推进器故障容错处理策略,研究了基于推力最小二范数的载人潜水器控制分配求解方法.采用基于伪逆矩阵与定点分配的混合控制分配求解算法,在半物理仿真平台上实验验证了控制分配求解算法的正确性和有效性.