闭式水循环系统的稳定性分析

针对闭式水循环系统,采用关闭某个支路,进行网络求解,计算其他支路的流量偏离系数的方法,分析了稳定性随各种影响因素的变化规律。结果表明：减小干线阻抗,增大支路阻抗,可以提高系统的稳定性。改变动力的集中调节对系统的稳定性没有影响,改变阻力的集中调节将使系统的稳定性变差。泵的特性曲线对系统的稳定性有影响,平坦型对应的稳定性优于陡降型对应的稳定性。异程系统,离热源最远支路的稳定性最差。同程系统,网路中部的支路稳定性最差;同程系统的稳定性总体上不如异程系统。     

液压助力器稳定性方法的研究

针对液压助力器稳定性问题,提出了几种实际工程中常用的稳定性方法.首先阐述了液压助力器工作原理,分析了影响助力器稳定性的关键因素,进而提出实际工程使用的稳定性方法,并对稳定性方法的优缺点进行分析和对比,最终得出稳定方法的使用条件,可为助力器稳定性的研究提供参考.     

粘度对反气泡稳定性的影响

液压系统低压区容易产生反气泡,影响液压系统的稳定性。因此有必要了解反气泡稳定性的影响因素以避免反气泡的形成。反气泡结构稳定性较差,其稳定时间受多种因素的影响。该文侧重于溶液粘度对反气泡稳定性的影响,从理论上解释反气泡的动态稳定性以及溶液粘度对反气泡稳定性的影响机理。通过实验验证,溶液粘度有利于提高反气泡的稳定性。     

基于系统稳定性退化算法的重型湿式制动器稳定性研究

针对重型工程车辆湿式制动系统制动过程稳定性较差的问题,通过将系统稳定性退化算法引入重型湿式制动器制动稳定性评价体系,对产品零部件制造厂家和用户自身获得的制动器稳定性退化数据进行整合,并通过灵敏度分析确定对湿式制动器稳定性起主导作用的参数,在湿式制动器初始设计阶段对设计方案提出准确的稳定性评价结论,并与试验样机测试数据进行对比分析。分析结果表明,由于在设计环节对敏感参数初始稳定性偏差和退化信息进行考虑,提出一种新型依据系统稳定性退化理论的重型湿式制动器稳定性评价方法,通过此方法可以大大提高产品设计效率,对于减少设计盲目性,提高企业生产效率具有重要作用。     

微气体传感器的稳定性测试研究

测试了一组微热板式气体传感器的稳定性,着重讨论了稳定性的几种描述方法,采用统计学方法对文献中常用于描述稳定性的几种特征参数进行了比较和取舍,引入了特征参数离散度来描述气体传感器的稳定性,并使用该方法比较了预加热时间对传感器稳定性的影响。     

基于旋转稳定和尾翼稳定的弹丸飞行稳定性研究

在弹丸飞行稳定性准则的基础上,阐述了弹丸飞行稳定性的条件,并着重讨论陀螺稳定因子、动态稳定因子以及瞬间扰动对弹丸稳定性的影响.通过对摆动理论和旋转理论的分析研究,给出旋转弹和尾翼弹丸稳定性条件.研究表明：要同时满足陀螺稳定性和追随稳定性两个要求比较困难,有时甚至是矛盾的,这时需要采用合理的膛线缠度来保证.     

轴承抗汽流涡动系数的计算

针对超超临界汽轮发电机组稳定性问题,计算了某高压转子轴承稳定性系数,研究了轴承稳定对转子稳定性的影响.     

XTR6/260隧道掘进机稳定性设计计算

稳定性是评价隧道掘进机工作性能的一项重要指标,根据某公司产品XTR6/260隧道掘进机整机参数和受力情况,建立了稳定性分析模型,并进行了不同工况下的稳定性设计计算,得出最小稳定系数值,该结果表明该掘进机具有较高的稳定性,同时通过实际施工使用有效检验了整机的稳定性。     

角接触球轴承保持架兜孔形状对其稳定性的影响

保持架的兜孔形状影响保持架的稳定性,是决定球轴承稳定性的因素之一。研究角接触球轴承兜孔形状对其稳定性的影响,以方兜孔和圆兜孔保持架为例,研究其在不同轴向载荷、径向载荷、转速以及间隙比、沟曲率系数等工况参数下的稳定性,以及工况参数和结构参数对保持架-外圈引导面平均摩擦力矩的影响规律。结果表明:随着径向载荷、间隙比的增加,保持架的平均摩擦力矩减小,稳定性逐渐降低,且圆兜孔保持架的稳定性略高于方兜孔保持架;随着轴向载荷、转速的增加,保持架的平均摩擦力矩增大,稳定性增加,且方兜孔保持架的稳定性略高于圆兜孔;随着内外沟曲率系数的增大,保持架的稳定性先增大后减小,且外沟曲率对保持架稳定性的影响比内沟曲率的大。     

基于线性规划的工件稳定性建模及其应用

工件在实现定位后,在加工过程中将要受到工件重力和切削力等外力的作用。为使工件保持定位精度与生产安全性,必须保证工件在整个加工过程中具有稳定性。系统地讨论了工件稳定性建模及其求解方法,在摩擦锥线性近似以及变量非负转换的基础上,提出了工件稳定性的定量判断准则;利用线性规划方法对工件稳定性模型进行分析。结果表明,稳定性模型不仅能够验证工件的稳定性,而且还能够分析夹紧力大小、作用点以及夹紧顺序的合理性。这种方法既适用于夹具夹持稳定性分析,也适用于机械手的抓取稳定性分析。     

EXPERIMENTAL RESEARCH AND DESIGN ON HEAT TRANSFER OF EVAPORATOR USED IN THE LARGE QUICK FREEZE PLANT

The evaporator is the main part of a quick-freeze equipment. There are many factors influencing the heat transfer coefficient of an evaporator. The most important factors among them are the fin shape, tube diameter, distance of fin space, frost, and velocity of air flow etc. They mainly influence the thermal efficiency of an evaporator, and therefore its thermal efficiency has direct relationship with the whole efficiency of the quick freeze plant. Evaporators with different structural types have different heat transfer efficiency. In order to obtain high efficiency structure of evaporator, 8 evaporator models with different fin shape, tube diameter and tube arrangement are analyzed and compared. The calculation results show that the integral waved fins, equilateral-triangle arranged small diameter tubes and varying fin-spacing has the highest heat transfer coefficient. The experimental result also shows that the evaporator with this type of structure has better thermal efficiency. The experimental result is in good agreement with the calculation result. It can instruct engineering design for usual designer. A real quick-freeze equipment is designed and put into production. The result shows that, compared with traditional domestic quick-freeze equipments, this equipment decreases by 40% in size and by 20% in energy consumption.     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

The use of chemiluminescence in determining the thermal and oxidative stability of motor oils

Chemiluminescence is reviewed as a method of characterising different behaviour of lubricating oils. This includes mineral oils containing additives such as zinc dialkyl-dithiophosphates, sulphonates, succinamides. alkylphenols and polymers. Using a chemiluminescence apparatus and manometric apparatus, various lubricant oil fractions blended with additives were examined. The basic emitters of chemiluminescence are excited carbonyl compounds, and results are presented showing the measurement of chemiluminescence at elevated temperatures.     

GENERATE ROUGH TOOL-PATHS FROM UNORGANIZED POINT-CLOUD DIRECTLY

An approach is presented to generate rough interference-free tool-paths directly from massive unorganized data in rough machining that is performed by machining volumes of material in a slice-by-slice manner. Unorganized point-cloud is firstly converted to cross-section data. Then a robust data-structure named tool-path net is constructed to save tool-path data. Optimal algorithms for partitioning sub-cut-areas and computing interference-free cutter-locations are put forward. Finally the tool-paths are linked in a zigzag milling mode, which can be transformed into a traveling sales man problem. The experiment indicates optimal tool paths can be acquired, and high computation efficiency can be obtained and interference can be avoided successfully.     

PHENOMENON OF CARVED DRIVING WHEELS

A newly found phenomenon of carved driving wheels of a rear-wheel-drive tractor used in an airport is discussed. The circum of every driving wheel is damaged at three regions,which distribute regularly and uniformly. Everyday,the tractor tows a trailer which are times heavier than the tractor,and moves on the same road in the airport. The phenomenon is explained by the torsional self-excited vibration system of the powertrain. The simplified torsional vibration system is discribed by a 2-order ordinary differential equation,which has a limit circle. Experiments and numerical simulations show the followings: Because of the heavy trailer,the slip ratio of the tractor’s driving wheels is very large. Therefore,there is severe torsional self-excited vibration in the tractor’s drivetrain,and the self-excited vibration results in severe and regular fluctuations of the rear wheel’s velocity. The severe fluctuations in velocity fastens the damage of the driving wheels. At the same time,the time interval in which an arbitrary point in the circum of the driving wheel contacts with the road twice is two times more than the period of the torsional self-excited vibration,and this times explained the existence of three damaged regions. At last,it points out that the phenomenon can be avoided when the torsional damping is large enough.     

Stromules and the dynamic nature of plastid morphology

Investigation of plastids via green fluorescent protein (GFP) has led to the rediscovery of tubular extensions of the plastid membrane, termed stromules, for stroma‐filled tubules. These unique structures are challenging our understanding of plastid structure and function. Stromules are highly dynamic, branching and elongating across the plant cell. Recent experiments indicate that cytoplasmic microtubules and microfilaments control the shape and motility of stromules. Whether stromule formation involves plastid‐specific structural systems, such as the plastid division machinery, remains open to debate. Fluorescence photobleaching experiments have revealed that GFP can traffic between plastids joined by stromules. As a result, interest has grown in whether other macromolecules can also travel through these connections. Although the function of stromules is unknown, several aspects of their biology suggest they play a role in molecular exchange between plastids and other organelles.     

A microscope diffusion chamber for the determination of the equilibrium and non-equilibrium osmotic response of individual cells

A microscope diffusion chamber has been developed which allows direct observation of the dynamic osmotic response of individual cells in micro-volume suspensions. Continuous observation of stationary cells is possible including short experimental times while the extracellular chemical composition is changed. Multiple changes of solute type or concentration are easily imposed upon a single sample volume. Response times are a function of chamber configuration but response times as low as 1–10 s are possible with negligible solute concentration gradients within the sample region. The chamber is simple and economical to construct and use. It is the size of an ordinary glass microslide and it can be adapted easily to any common laboratory microscope. All standard optical techniques may be used with the chamber. Construction details and operating characteristics including important limitations are discussed. Example photomicrographs and osmotic data are included.     

VOLUME DEFECT FATIGUE FAILURE OF CERAMIC BALLS UNDER ROLLING CONDITION

A newly developed pure rolling fatigue test rig with three contact points is used to test the rolling contact fatigue properties of silicon nitride ceramic balls. Ball surfaces are examined after failure with optical microscopy and scanning electron microscopy. The failure cause,fatigue phenomenon and mechanics are analyzed. The research shows that subsurface cracks play a dominant role in the formation of spalling failure. These cracks originated from volume defects of the material and propagate,to form elliptical fatigue spalls under the action of principal tensile stresses. The principal tensile stress increases with increasing contact load,causing spall formation and reduction of rolling contact life. The greater the principal tensile stress is,the more severe the peeling of near surface is. Under the same condition,the closer volume defects are to the surface,the more likely failure occurs,the shorter the rolling contact life is.     

气化炉三维扫描测量与数据处理

以德士古气化炉耐火砖的内壁蚀损检测设备为基础,对采集到的点云数据做了进一步处理.通过对数据的筛选和剔除,实现了数据点的平滑降噪细化和精简.然后利用点云对整、网格划分和分色显示等方法,最终完成了内壁腐蚀情况的三维建模.重点讨论了点云数据的预处理及后处理的方法,并根据内壁耐火砖的腐蚀阈值,提出了一种气化炉内壁腐蚀区域的识别与分割方法.对耐火砖的腐蚀分析、气化炉的生产与维修提供了可靠依据,并在工程应用中获得了一致认可.     

Multiple-tapped-delay-line hardware-linearisation technique based on wire load regulation

This article describes designing, implementation and tuning processes of multiple-tapped-delay-line (MTDL). Obtained MTDL can be implemented in various field-programmable-logic-devices (FPGA) devices and applied for time-to-digital-converters (TDC) construction. The task of tuning process is the tapped-delay-line (TDL) linearisation, and consists of two stages. The first stage depends on selecting an appropriate configurable-logic-block (CLB) for particular delay-segment realization and selecting proper connection between these blocks. The second tuning stage, that is essential from this article viewpoint, depends on inter CLBs connecting wires delay regulation realized directly by load regulation. The Load regulation depends on connecting an appropriate number of unused three-state-buffers or CLB inputs to the wire which delay is adjusted. Depending on the number of inputs connected to the wire its capacitance changes that influences its time-constant and finally changes its time-delay.The MTDL mathematical model, obtained characteristics and results of time-interval (TI) measurements are also presented. The derived TDL model provides information about how the particular wire delay should be changed and in which order the changes should be executed. This makes the designing process predictable and easy to carry out. Presented characteristics confirm the proper operation of presented linearisation technique. The proper operation of the whole measuring module is confirmed by obtained TIs histograms presentation.