裂齿矩形翅片板翅式换热器优化设计的分析

对裂齿矩形翅片板翅式换热器中的裂齿矩形翅片的传热效率作了分析,并以单位质量材耗的换热能力最大为目标函数,分析研究了在不同雷诺数(Re)的操作条件下裂齿矩形翅片间角度、翅片厚、长度、宽度及极厚之间的关系。结果表明:在气体换热的场合下,当Re在某一范围时翅片可有效地起到强化传热的作用。当板厚为5mm,翅片厚为3mm,翅片间夹角为45°～70°,Re为2×10~3～8×10~3,最佳翅片纵向间距与翅片长度和翅片厚度乘积的平方根的比为1.5～2.5,最佳翅片尺寸系数为3～5时,传热强化效果较好。     

Structural transformation of FePt nanocomposite films during annealing and its effects on magnetic properties

Fe100-xPtx(x=30at.%-60at.% ) nanocomposite films were deposited on natural-oxidized Si(100) substrates by magnetron sputtering. The as-deposited films were annealed between 373 and 1073 K. In situ X-ray diffraction shows that the FePt nanocomposite films undergo a phase transformation from a disordered FCC phase to an ordered L10 phase between 673 and 773 K. The coercivity is 306 kA·m-1 whiles the average grain sizes is about 10 nm in the optimized FePt alloy film sample annealed at 673K. The adjustable coercivity and fine grain size suggest that this FePt nanocomposites system is suitable as recording media at extremely high areal density.     

Effects of Seismically Induced Pounding at Expansion Joints of Concrete Bridges

This paper presents the result of a study on the effect of pounding at expansion joints on concrete bridge response to earthquake ground motions. An engineering approach, rather than continuum mechanics approach, is emphasized. First, the dynamic behavior of a damped multidegree-of-freedom bridge system separated by an expansion joint involving an impact is examined by means of the finite element method. Second, the sensitivity analysis of the stiffness in gap elements is performed. Third, usefulness of the analysis method for simulation of pounding phenomena is demonstrated and the effect of pounding on the ductility demands measured in terms of the rotation of column ends is investigated. Two-dimensional finite element analysis using a bilinear hysterestic model for bridge substructure joints and a nonlinear gap element for the expansion joint is performed on a realistic bridge with an expansion joint. The effects of the primary factors on the ductility demand such as gap sizes and characteristics of earthquake ground motion are investigated through a parametric study. The major conclusions are (1) the effect of impact most directly depends on the size of momentum (or pounding magnitude); and (2) the pounding effect is generally found to be negligible on the ductility demand for wide practical ranges of gap size and peak ground acceleration, but is potentially significant at the locations of impact.     

连铸钢坯质量的原位统计分布分析研究

采用原位统计分布分析技术得到与样品原位置相对应的数以万计原始信号并对其进行系统解析，实现不同质量连铸钢坯试样的疏松度、均匀度以及夹杂物含量的定量表征。准确计算了连铸钢坯试样疏松度、碳元素的最大偏析度。提出铸坯各原位置成分含量的权重比率方法用以表征材料的均匀度，并提供了统计分布允许差范围内（C0±R）所占权重比率以及权重比率为95%置信度时，中位值置信扩展率（K）等2种判断模式。该方法以测量信息的原始性、原位性及统计性为特征，反映了连铸钢坯较大尺度范围内各化学组成及其形态的定量统计分布规律。采用上述方法可以     

高可靠性烧结金属丝网防爆元件的应用研究

烧结金属多孔元件作为隔爆元件的应用，很好地满足了火焰过滤元件的性能要求，进一步拓宽了烧结金属多孔元件的应用领域，章在论述其性能特点、结构类型的同时，对其在微孔结构设计上的差异也进行了描述。     

具有随机输入的混合复合动态系统的稳定性判据

本文给出了如图1所示的具有随机输入的混合复合动态系统的稳定性分析,所讨论的系统由一个算子L和一个随机微分方程描述的方块组成。对于这样的系统,我们建立了随机吸引性、随机渐近稳定性、随机有界性、大范围随机渐近稳定性、p吸引性、渐近p稳定性、一致p有界性和大范围渐近p稳定性的判据。这些判据包含了一些假设,这些假设描述了算子L和整个系统的定性I/O性质和表示了由随机微分方程描述的子系统的性质。     

关于重力坝坝内细部构造设计的几个问题

重力坝常采用横，纵缝将坝体分为柱状体施工。为此，横缝须设置止水，纵缝则待坝体冷却后灌浆，将柱状坝块连成整体。此外坝体内部还须设置坝面排水管以消除坝内渗透压力。关于坝内这些细部构造，设计规范仅有原则性要求，一般专业书列举不多，目前有些工程往往参照已建工程的设计图采用，常由于施工详图不祥易发生施工质量问题。根据丹江口重力坝设计经验，对接缝灌浆中的键槽，止浆片，灌浆管道，出浆盒，排气槽及排气管，基岩陡坡     

A CONSTITUTIVE MODEL FOR ELASTIC-PLASTIC DEFORMATION UNDER CYCLIC MULTIAXIAL STRAINING

Abstract— The yield criterion is interpreted as defining the metric of the stress space. Hydrostatic stresses correspond to null geodesies. The plastic strain increment represents a normal projection of the increment undergone by a certain scalar function (hardening function) which depends only on the distance between stress points. This establishes a flow rule formally equivalent to the Prandtl-Reuss equations. Consideration of un-loading processes leads to the analysis of equivalent paths and to the definition of a generalized length or separation which provides a new representation of kinematic hardening.     

硼酸铝钕(NAB)晶体光学均匀性的测量

NAB晶体是一种综合性能较好的新型激光工作物质,有希望做成高效的小型固体激光器。本文介绍一种测量这种晶体光学均匀性的方法。 一般都采用在干涉仪上观测干涉图样来判定激光棒的光学均匀性。NAB晶体的吸收光谱曲线显示出其在可见光光谱区内有多个吸收峰。我们注意到:通常用做激光干涉仪光源的He-Ne激光器发射的632.8nm谱线正位于NAB晶体的一个吸收峰,并用输出约为45mW