作用于斜坡结构物上海冰荷载的三维计算

作用于斜坡结构物上的海冰荷载包括两部分：使冰板发生弯曲破坏的分力和使破裂冰块沿斜面上爬的分力。当结构物迎冰面的宽度小于冰的宽度时，冰与结构物之间的相互作用为三维问题。本文分析冰板作用于结构物时的三维破坏机理，建立一个通用的三维计算模式，并计算了给定的海冰条件作用于斜坡结构物上的冰荷载。     

用滑移线理论确定工件塑性区的一种方法

在分析了变形体和模具的接触特点和接触面金属的流动应力与应变特点的基础上,在考虑接触摩擦为最大剪应力K的情况下,绘制出接触面的滑移线场,应用滑移线理论求解出接触金属进入塑性区的极限载荷,并以此为标准来判断接触金属是否进入塑性区。     

薄壁圆筒工件抛物面型缩口成形的力学分析

应用适用于板料轴对称成形过程的应力平衡方程对薄壁圆筒工件抛物面型缩口成形中的应力进行了分析 ,得出了薄壁圆筒工件抛物面型缩口成形时的经向应力与各种参数之间的关系及缩口力的计算公式 ,从而为工艺设计人员制定此类缩口工艺提供了方便     

Large-Eddy Simulation of Coastal Upwelling Flow

Large-eddy simulations were carried out to study laboratory-scale realizations of coastal upwelling in an annular rotating tank with a sloping bottom. A two-layer stratified fluid was set into rigid body motion with the tank and then driven by the relative rotation of a solid top lid. The simulation code developed in this work was a three-dimensional incompressible Navier-Stokes solver using the message passing interface. The simulation runs were performed on a distributed memory massively parallel computer, namely, the IBM SP2. The simulation results were able to reveal the evolution of the complex upwelling structures in detail. The results were used to compare with and to complement two relevant series of coastal upwelling experiments. A Rayleigh-Taylor type of instability took place in the top inversion layer due to the unstable stratification after establishment of the upwelling front. The primary upwelling front was unstable to azimuthal perturbations and developed large amplitude baroclinic waves. The frontal wave structure consists of cyclone/anticyclone pairs. Whether cyclonic eddies containing the lower-layer fluid pinch off from the front depends on the _* value. The non-dimensional parameter _*=gh ₀/u _* f_s, which was first introduced by Narimousa and Maxworthy, combines the effects of stratification, rotation and surface stress and can be used to characterize the upwelling flow field. Our studies show that the frontal instabilities are much more intense and the upwelling front itself displays strong unsteadiness and cyclonic eddies containing the lower-layer fluid pinch off from the front when _* is significantly less than 5.8. For _*=5.8, the frontal instabilities are less intense and no pinched-off process is observed. To separate these regimes, a critical value of _* of about 5.4 is consistent with Narimousa and Maxworthy's results.     

农业土地利用变化及原因、效应分析

利用航空遥感影像结合野外调查方法 ,获取了研究区域 1 979年和 1 999年土地利用类型图 ,并分析了该时段土地利用变化情况。通过农户调查 ,探讨了土地利用变化的原因。分析表明 ,技术水平提高和投入增加是耕地产量提高的重要因素 ,提高土地经济收益是旱地土地利用结构变化的直接动力。     

高原退化湿地纳帕海植物多样性格局特征及其驱动力

对滇西北纳帕海湿地不同退化演替阶段的植物群落结构特征及多样性格局的研究结果表明:纳帕海共有植物115种,隶属38科、82属,植物群落15个,包括3个沉水植物群落、2个浮叶植物群落、6个挺水植物群落、4个草甸群落。其中原生沼泽有湿地植物25种,隶属16科、17属,3个沉水植物群落、2个浮叶植物群落;沼泽化草甸有湿地植物35种,隶属19科、26属,6个挺水植物群落;草甸有湿地植物64种,隶属28科、55属,4个草甸群落;垦后湿地仅有农作物4种,隶属4科、4属。随着原生沼泽、沼泽化草甸向草甸、垦后湿地的退化演替,植物群落伴生种增多,优势种的优势度明显下降,群落结构逐渐变得复杂;原生沼泽、沼泽化草甸植物群落分布面积萎缩,草甸、垦后湿地面积不断增大;物种丰富度与多样性指数随原生沼泽、沼泽化草甸、草甸的退化演替而逐渐增加,草甸植物物种丰富度、多样性指数最大,而垦后湿地为最低值。纳帕海植物多样性格局特征是对不同人为干扰强度与类型的响应,当前影响植物多样格局的驱动力主要是排水垦殖、无序旅游、过度放牧和周边森林的破坏等人为生产活动。     

Influences of greenhouse effect on agricultural production in China

An obvious warming in China induced by doubled carbon, dioxide as simulated by the climatic models have been found. It is also noticed that there might be drying or wetting in some parts of China induced by doubled CO2 as simulated by the general circulation models(GCMs). Agricultural productivity mainly depends on the temperature, rainfall and soil moisture in China. The changes of agricultural productivity in the different parts of China induced by doubled CO2 have been estimated in this paper. It is shown that the greenhouse effect might cause increasing production in some parts of China and decreasing production in other parts of China.     

一种新型直流旋风分离器

针对普通旋风分离器结构上存在有内旋流和混流区会卷走尘粒而降低分离效率的问题 ,总结了原直流旋风分离器生产设计经验 ,开发设计出了一种新型直流旋风分离器 ,没有普通旋风分离器存在的两个问题 ,而且能克服普通旋风分离器流动路线长的缺陷 ,在同一工作条件下 ,分离粒径比原直流旋风分离器减小了 6～ 8μm。在此介绍了分离机理 ,提出了一套设计计算方法 ,给出了计算实例 ,总结出新型直流旋风分离器的特点及适用场合     

苏州市非农用地扩展的驱动因素时空变化研究

利用1984—2003年间4个时段的TM影像解译获得该时期苏州市非农用地扩张变化规律,并结合大量的社会经济资料,定量分析了过去20 a间苏州市非农用地扩张与社会经济因素的关系,筛选出非农用地高速增长的主导驱动因素,揭示了主导驱动力在不同时期的时空变化规律。结果表明,非农用地扩张的社会经济驱动因素随社会经济发展的不同阶段而显著变化,GDP、上海对苏州的经济辐射作用和人口增长是过去20 a间苏州市非农用地急剧扩张的3个主要驱动力。     

混凝沉淀技术及其在纺织印染废水处理中的应用前景

本文对纺织印染污水处理中采用的几种混凝剂进行小结与评价，并开展一些技术讨论，从而确定了混凝沉淀技术在纺织工业污水处理中的应用前景。