超声流量计阻流件影响评估软件的设计与开发

多声道超声流量计广泛应用于大口径流量测量,内部流场是影响其测量准确度的一个重要方面,在阻流件附近安装流量计需要评估复杂流场带来的附加误差。在多声道超声流量计阻流件数值模拟数据的基础上,设计与开发了一套多声道超声流量计阻流件影响评估软件,实现了各种安装条件下流量计附加误差的评估,用来指导超声流量计的安装选型与优化设计,也可以检查相应条件下安装的流量计是否工作正常。本文介绍了该评估软件的数据结构和软件构架,特别是插值算法的实现。软件数据库的信息量可以在未来不断扩展,逐渐覆盖流量计可能的安装条件。     

探头局部扰流对超声流量计测量结果影响

插入式探头安装方式会对超声流量计内部流场产生扰动,进而影响测量结果。在高压空气流量标准装置上对DN100 mm和DN200 mm的气体超声流量计进行标定,结果显示探头局部扰流对超声流量计会产生负向误差,管道口径越小,局部扰流引入的误差越大。DN100 mm超声流量计在3～27 m/s的流速范围内的测量误差在–1.5%～–3%之间,而DN200 mm的超声流量计在1.4～13 m/s的流速范围内的测量误差在–1.2%～–2.1%之间。分析不同压力、不同流速下探头局部扰流对超声流量计测量结果的影响规律,并基于流速和测量误差对实验结果进行曲线拟合,提供了拟合曲线的数学模型。     

多声道超声流量计阻流件影响数据库的建立

建立了一套基于数值流场的阻流件影响数据库,一方面可以提供不同安装条件下的阻流件附加误差,来指导超声流量计的安装选型与优化设计,另一方面可以提供特定条件下的声道速度分布,来检查相应条件下安装的流量计是否工作正常.阻流件影响数据库的建立避免了数值模拟技术实施难度大的问题.     

18声道超声流量计在DN1000三峡流道模型中的测量准确度研究

通过在开封国家水大流量计量站开展DN1000口径三峡模型流道中18声道超声流量计测量准确性实验研究,得到了复杂流场给流量计引入的测量误差,验证了18声道超声流量计即使在复杂流场中依然具有较高的测量准确性.通过分析流量计得到的流速分布图可以推断出模型管道中的流场情况.流量计在正常安装位置旋转90.后测量误差变化不大,流量...     

扰流流场对超声流量计积分误差的影响分析

对若干典型扰流流场条件下的超声流量计积分误差进行了系统推算,在分析流场结构对积分误差影响的基础上,研究了声路数量对积分误差的统计规律。流量计的积分误差与流场的复杂程度直接相关,流场越复杂积分误差也越大。在统计意义上流量计声路越多则积分误差越小,但对于某特定流场则不存在这种单调性。OWICS积分方案要优于Gauss-Jaccobi方案,尤其在声路数量受限时具有明显优势。     

三峡工程超声流量计的测量准确度评估

采用模型实验与模拟计算相结合的研究方法,评估了三峡电站安装的超声流量计的准确度.搭建了比尺为1:24的模型管路,实验结果表明三峡特殊流场将使流量计示值偏高0.3%左右;模型数值模拟分析结果与实验结果一致性很好.分析了实验结果的不确定度和流量计基本性能,流量计准确度优于1%,流量计满足三峡电站流量测量要求.     

用模型实验方法研究三峡电站流量计准确度

利用水力学相似原理,采用模型实验的方法对安装于三峡电站的超声流量计进行准确度的评估.按照三峡电站的引水钢管结构以124.8的比例设计并加工了500 mm口径的流道系统模型和模型流量计.通过对2组模型实验的结果及不确定度分析,发现由于流道形状特殊对流量计处流场产生影响,使得流量计会产生约0.3%的正向偏差,但流量计准确度水平仍能优于±1%,满足电站进行水轮机效率测量的要求.     

差压式流量计安装中压力位差对流量计量的影响

本文对差压式蒸汽流量计安装中由于压力变送器安装位差不作迁移对蒸汽流量计量带来的误差作了分析,提出了压力变送器安装位差迁移的必要性.     

旋进旋涡流量计的数值模拟研究

通过计算流体力学(CFD)的方法对50 mm口径的旋进旋涡流量计进行了数值仿真.分析了旋涡进动效应下流量计内部流场的演变情况,找出传感器最佳安装位置以减小外界振动与流体脉动噪声对旋进旋涡流量计造成的影响,并且在此基础上对旋进旋涡流量计进行改进——在旋进旋涡流量计前面加导流片.改进后的旋进旋涡流量计压力损失有了较大幅度的减少.     

动量式气体流量计内部流场特性与测量性能研究

采用数值模拟与实验验证相结合的方法,得到了动量式气体流量计内部的流场,分析了流量变化时受力元件阻力系数的变化规律,研究了受力元件的形状、安装误差对测量性能的影响。研究结果表明,动量式流量计的阻力系数在量程范围内有较大变化,必须对阻力系数随雷诺数的关系式予以拟合;长方形受力元件阻力系数的拟合公式计算误差最小,拟合结果与实验数据的最大误差为0.32%,应优先选用;安装误差引起的阻力系数误差不大于0.32%,对测量精度影响较小,动量式流量计适合在线安装。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。