慎用运动粘性系数比较流体的粘性大小

粘性是流体的一种物理性质，其大小代表了流体流动的难易程度。通常用动力粘性系数的数值衡量流体粘性的大小。而运动粘性系数与动力粘性系数有本质的区别，只能代表流体粘性的相对大小，若用来比较不同流体之间的粘性就会引起严重的错误。     

流体微团运动变形特性分析

流体微团的变形与运动互为因果.由于流体的易流动性,流体微团变形比固体复杂、多样.认识流体变形特性是分析流体宏观运动的基础,在流体力学及其工程应用中占有重要地位.在过去的研究中,由于一般都孤立地讨论流体微目的各种变形,结果难以发现这些变形之间的联系,同时也丧失了一些发现流体微团特定运动规律的机会.为弥补过去研究的不足,本文在分析流体微团各种可能变形的联系的基础上,以矢量分析为工具,导出了在特定条件下各种变形的特点.本文的主要成果在于获得了过去文献中没有提到过的流体微团运动、变形的两项特征:当流体微团在无变形条件下仅有旋转运动时,微团将像刚体一样绕基点作定轴转动;当流体微团仅有剪切变形时,两直角边将相向等连运动,正方形微目变形为一菱形.     

透平压缩机级间冷却器中具有可分凝组分气体混合物粘性系数和导热系数的计算

通过透平压缩机级间冷却器具有可分凝组分气体混合物迁移性质各种计算方法的比较、验证和选择，以及有关计算关联式较为精确的拟合，确立了合理有效的计算方法和混合法则。在相平衡计算的基础上，利用所确立的方法和FORTRAN程序对具有可分凝组分气体混合物的粘性系数和导热系数进行计算，取得了较为满意的结果。     

蜗杆—蜗轮间歇运动机构及运动系数

蜗杆──蜗轮间歇运动机构及运动系数燕山大学周玉林闻岩许立忠王灵忠齐齐哈尔第一机床厂王彦刚引言间歇运动机构种类较多，在生产实际中，特别在自动化设备中得到广泛的应用。不完全齿蜗杆──蜗轮间歇运动机构，到目前为止、据考查尚未发现有关报导。本文就蜗杆──蜗轮...     

润滑系统油泵粘性摩擦功耗测试及其应用

针对热轧机精轧机组,油膜轴承供油润滑系统存在的问题,对油泵粘性摩擦功耗进行分析,并依据系统摩擦功耗测试和粘性摩擦功耗分析结果,提出改进方案。     

单叶片推进器及其运动特性

提出了一种新型的流体推进器——单叶片推进器,通过对叶片的运动学和负载的分析,建立了该推进器的运动方程。基于ADAMS环境,建立了单叶片推进器的虚拟样机,并进行了推进器系统的动力学仿真。仿真分析表明:单叶片推进器能够在设定转速下稳定运行;有效推力是脉动变化的,但在稳定转速下,有效推力的幅值和频率是稳定的,可以产生稳定的推动效果。     

流体应力方向、运动方程、广义应力公式综述

目前流体力学教材上,关于流体中应力分量的定义、微元六面体上应力分量方向的假设方法各不相同,与此相对应,用应力表示的流体运动微分方程及广义应力公式也必须采取不同形式。若上述对应关系搞错势必得出错误结果。这种问题可能被忽视,为解决此问题,对流体中应力分量的定义、应力方向假设方法、用应力表示的流体运动微分方程及广义应力公式进行了分析和归纳总结,用具体例子加以说明。并给出如何根据应力计算结果的正负判断应力方向的方法。     

流体机械叶轮中三维粘性流动的势流边界层迭代解

本文用三维热流和三维边界层相互作用法求解叶轮中的粘性流动。在叶睡表面三维边界层计算中采用了半正交曲线坐标系,各向异性三维涡粘性的湍流模型,变换域技术和Keller分块解法。在叶轮流道及上下延伸体所组成的法语解域中的三维势流计算中,采用了直接边界元法。算例表明,本方法正确可行。     

流体阻尼器粘性发热对整星隔振的影响

在航天器发射过程中,流体粘度随温度变化而改变,流体阻尼器具有不同的阻尼比和共振频率。结合流体阻尼器在整星隔振中的应用,建立发射阶段的热动力学模型。通过数值模拟比较不同粘温系数、不同阻尼器参数下的整星隔振秒特性,并对粘性发热的作用进行了试验研究。理论分析和试验表明,随着时间的推移,阻尼器温度升高,隔振系统的共振频率发生偏移,共振峰值发生变化。     

可压缩流体流经蝶阀的流量系数的计算

从实际使用要求出发，讨论引进一个压缩修正系数来确定可压缩流体流经蝶阀的流量系数的计算，并建议采用简便的图算法，说明其具有一定的应用价值。     

基于DXF文件和图论的轴类零件相似程度比较方法

目前零件的相似程度判断问题,往往是根据已有的经验,精确性难以得到保证。针对这个问题,利用图论中的相关知识,结合图形交换文件(DXF)中的零部件数据信息,给出了一种用于存储零件二维图的数据结构,并且提出了一种针对零件二维图的存储方案,在此基础上讨论了轴类零件图的存储算法,以及基于这种存储方案的轴类零件相似程度的比较算法,为零件相似程度的比较提供了一条比较新的途径。     

思辨信息化

通过对信息化内涵的思考,提出IS^4的理念以描绘信息化蓝图;在多年来信息化实践的基础上总结并提出“天地人神鬼”是企业信息化成功的五大关键要素;笔者认为企业信息化是企业的核心竞争力,并给出企业信息化的“点、线、面、体”评价模型;现从进程说、源头探、三层论等三方面对信息化源头进行探索,并在文末提出了对信息文化不懈追求的意义。     

“精打”专业品质 “细算”办公成本——Epson Me office 1100A3＋图形设计专用打印机使用体验

对于一些中、小型的专业设计机构，用户在关注CAD工程图打印效果的同时，也非常看重打印速度、使用成本等问题。     

The significance and use of the friction coefficient

The quantity known as the friction coefficient (or ‘coefficient of friction’) has long been used in science and engineering. It is easy to define, but not easy to understand on a fundamental level. Conceptually defined as the ratio of two forces acting, respectively, perpendicular and parallel to an interface between two bodies under relative motion or impending relative motion, this dimensionless quantity turns out to be convenient for depicting the relative ease with which materials slide over one another under particular circumstances. Despite the fact that both static and kinetic friction coefficients can be measured with little difficulty under laboratory conditions, the time- and condition-dependent characteristics of friction coefficients associated with both clean and lubricated surfaces have proven exceedingly difficult to predict a priori from first principles.The shaky nature of friction's fundamental underpinnings, has not prevented investigators from compiling lists of friction coefficients and publishing them for general use. Problems often arise, however, when engineers attempt to use tabulated friction coefficients to solve specific problems in mechanical design or failure analysis. The systems-dependence of frictional behavior is sometimes ignored, leading to misapplication of published data. This is particularly true for applications in nano-technology and others that differ from typical laboratory size scales. This paper will review the measurement and use of static and kinetic friction coefficients, discuss their usefulness, and describe the sources of frictional resistances in terms of shear localization.     

精心组织项目实施,全力打造精品工程

高邮市丘陵山区农业综合开发项目于2000年正式立项实施。10年来,实施总面积1346．67hm2,项目区涉及送桥、菱塘、天山、郭集4个乡镇24个行政村（场）。项目的成功建设,加快了高邮市丘陵山区的发展,促进了农业增效、农民增收和农村繁荣。     

当心新的"信息化陷阱"——合理规划、慎重选择"信息化"切入点

信息化巳成为当今的一大热点，文章以客观的角度分析了企业信息化应用的现状，阐述了如何合理规划、选择“信息化”切入点，对待实施信息化的企业具有重要的意义。     

过零点位置比相在齿轮误差信号处理中的应用

介绍一台20世纪80年代的光栅式齿轮单面啮合检查仪的测量原理;利用最小二乘法求拟合直线,再由拟合直线求零点位置对应的x值进行比相.在虚拟仪器平台下编程实现齿轮整体误差处理虚拟仪器化,提高了原有设备的自动化、数字化水平,具有更广泛的实用性.     

A facile method to compare EFTEM maps obtained from materials changing composition over time

Energy Filtered Transmission Electron Microscopy (EFTEM) is an analytical tool that has been successfully and widely employed in the last two decades for obtaining fast elemental maps in TEM mode. Several studies and efforts have been addressed to investigate limitations and advantages of such technique, as well as to improve the spatial resolution of compositional maps. Usually, EFTEM maps undergo post‐acquisition treatments by changing brightness and contrast levels, either via dedicated software or via human elaboration, in order to maximize their signal‐to‐noise ratio and render them as visible as possible. However, elemental maps forming a single set of EFTEM images are usually subjected to independent map‐by‐map image treatment. This post‐acquisition step becomes crucial when analyzing materials that change composition over time as a consequence of an external stimulus, because the map‐by‐map approach doesn't take into account how the chemical features of the imaged materials actually progress, in particular when the investigated elements exhibit very low signals. In this article, we present a facile procedure applicable to whole sets of EFTEM maps acquired on a sample that is evolving over time. The main aim is to find a common method to treat the images features, in order to make them as comparable as possible without affecting the information there contained. Microsc. Res. Tech. 78:1090–1097, 2015. © 2015 Wiley Periodicals, Inc.     

Use of low-temperature scanning electron microscopy to compare and characterize three classes of snow cover

This study, which uses low-temperature scanning electron microscopy (LTSEM), systematically sampled and characterized snow crystals that were collected from three unique classes of snow cover: prairie, taiga, and alpine. These classes, which were defined in previous field studies, result from exposure to unique climatic variables relating to wind, precipitation, and air temperature. Snow samples were taken at 10 cm depth intervals from the walls of freshly excavated snow pits. The depth of the snow pits for the prairie, taiga, and alpine covers were 28, 81, and 110 cm, respectively. Visual examination revealed that the prairie snow cover consisted of two distinct layers whereas the taiga and alpine covers had four distinct layers. Visual measurements were able to establish the range of crystal sizes that occurred in each layer, the temperature within the pit, and the snow density. The LTSEM observations revealed the detailed structures of the types of crystals that occurred in the snow covers, and documented the metamorphosis that transpired in the descending layers. Briefly, the top layers from two of the snow covers consisted of freshly fallen snow crystals that could be readily distinguished as plates and columns (prairie) or graupel (taiga). Alternatively, the top layer in the alpine cover consisted of older dendritic crystal fragments that had undergone early metamorphosis, that is, they had lost their sharp edges and had begun to show signs of joining or bonding with neighboring crystals. A unique layer, known as sun crust, was found in the prairie snow cover; however, successive samplings from all three snow covers showed similar stages of metamorphism that led to the formation of depth hoar crystals. These changes included the gradual development of large, three-dimensional crystals having clearly defined flat faces, sharp edges, internal depressions, and facets. The study, which indicates that LTSEM can be used to enhance visual data by systematically characterizing snow crystals that are collected at remote locations, is important for understanding the physics of snowpacks and the metamorphosis that leads to potential avalanche situations. In addition, the metamorphosis of snow crystals must be considered when microwave radiometry is used to estimate the snow water equivalent in the winter snowpack, because large snow crystals more effectively scatter passive microwave radiation than small crystals.     

Simple apparatus to measure Seebeck coefficient up to 900 K

An apparatus for measuring Seebeck coefficient (S) has been designed that allows measurement of S from room temperature to 900 K. It is constructed from readily available equipment and instrumentation with parts that can be easily fabricated. The details of instrument fabrication, sources of errors, method of calibration, typical measurement in test sample are described. We report the Seebeck coefficient measurement of Ca-cobaltite (Ca₃Co₄O₉) a p-type thermoelectric material. The obtained results from the fabricated setup are well matched with the reported and standard instrument data with standard deviation of ±3%.