Accuracy of Taylor length scale measurements by two-point laser Doppler velocimetry: a theoretical study

The accuracy of the measurement of the Taylor length scale by two-point laser Doppler velocimetry is mainly determined by the probe volume length and the portion of the correlation curve used to fit a matching parabola. The importance of these parameters is investigated theoretically using simulated correlations. Several models are used to characterise the true autocorrelation of the fluctuating velocity. It appears clearly that the probe volume length has no significant effect on the measured integral scale however it has an important effect on the Taylor scale. The results reveal also that the relative uncertainty on the Taylor scale is governed not only by the probe volume length and the procedure of the data processing but also by the ratio of the integral to the Taylor scales, that is to say, by the Reynolds number.     

Improvement of lubrication characteristics in the reciprocating fuel pump of marine diesel engines

In this study, we apply circumferential grooves and taper shape to the plunger in order to improve the lubrication characteristics of reciprocating fuel pumps for marine diesel engines. We use the two-dimensional Reynolds equation to evaluate lubrication characteristics with variation of viscosity, clearance, groove and taper for an incompressible, unsteady state flow. Moreover, we use the equilibrium equation of moment and forces in the vertical and horizontal directions to determine the motion of the plunger. The validity of numerical model is verified through the fact that the position of wear is similar to that of minimum film thickness. We investigate the lubrication characteristics of the pump by comparing the dimensionless minimum film thickness, or film parameter. Through numerical analysis, we find that to improve the lubrication characteristics of the pump, applying both circumferential groove and taper shape to the plunger is more effective than applying just either one of them.

     

大型往复压缩机综合管理经验

针对气体往复压缩机的特点，以塔河油田输气首站2RDSA－2压缩机型为例，从投产试运、维护保养、油水润滑、备品备件管理等实际生产环节总结了综合管理经验，以提高生产设备保障水平。     

Comparison between numerical computations and measurements by LDV for fluid flow in rectangular duct systems

Fluid flows in rectangular duct systems are measured by using the laser-Doppler velocity meter and computed by commercial software of Star-CD for comparisons between flows. Three rectangular systems are investigated in this study: a rectangular duct with a 90 degree bent elbow, a rectangular duct with two branches, and a rectangular duct in the middle of which a circular cylinder is located. These investigations show that the numerical solutions satisfactorily predict design factors: for example, the K -factor for an elbowed duct, the distribution ratio of flow rates into each branch from a main duct, and the Nusselt number around the circular duct. However, there are some disagreements in the velocity profile and turbulent kinetic energy at each cross section of the duct systems.     

A procedure for evaluating the positioning accuracy of reciprocating friction drive systems

The dynamic characteristics of stick-slip motion in reciprocating friction drive systems are investigated under dry contact using a 0.45% carbon steel pair. Based on this dynamic analysis, the stick-slip motion can be eliminated under certain experimental conditions depending upon driver speed, normal load and spring constant. The effects of normal load, driver speed, and spring constant on the positioning accuracy of the reciprocating friction drive system are examined under harmonic oscillation without stick-slip motion. Results show that at very low spring constants, the slip increases with increasing driver speed such that higher normal load has better positioning accuracy or smaller slip than does lower normal load. However, at high spring constants and high normal loads, there exhibits severe wear or peak at two limit positions on the sliding region. As a result, smaller normal loads have a better positioning accuracy than larger normal loads due to severe wear at high normal loads.     

LDV measurements of turbulent flow behavior of droplets in a two-phase coaxial jet

Coaxial nozzles are frequently utilized for the atomization of liquids in sprays. The performance of a nozzle is generally evaluated by its atomizing characteristics, which are actually governed by the turbulence interactions of two fluids. With this point of view, this experimental study was carried out to investigate the turbulent behavior of the droplets atomized in a two-phase coaxial jet. Air and water have been used as the working fluids, and the measurements have been made by an on-line data acquisition system connected to a two-channel LDV set(DISA, 5W, Argon laser, blue: 488 nm, green: 514.5 nm). In order to generate a two-phase mixing jet, two types of coaxial nozzles (liquid column type, liquid sheet type) were used. For the investigations of the turbulent flow structure of this two-phase mixing jet, the spreading rates, mean and fluctuating components, intermittency factors and the iso-contours of joint probability densities were measured and analyzed. The results from the both types of nozzles did not show remarkable differences in mean and fluctuating velocity distributions, intermittency factors or the iso-joint probability density contours. Since the measurements were made in the fully developed turbulent mixing regions, the mean velocity distribution profiles showed good similarities and agreed well with the semi-empirical curves. The RMS values were represented as high order levels and so were the intermittency factors. The typical development trends of turbulent components ofu′ andv′ for both types were illustrated in the iso-joint probability density contours.     

On the accuracy of high impulse voltage measurements

Measurements and tests on solid dielectrics with lightning or switching impulses have received considerable attention because they are concerned in the optimal design of internal insulation for high voltage apparatus. Accuracy of measurements relating to the above phenomena is generally deemed very important. In this paper a model is proposed and an investigation is attempted regarding the accuracy of such measurements. The results are confirmed through laboratory measurements. According to the results presented, the value of the grounding resistance is a crucial parameter that affects measurement accuracy; it must never exceed the value of 0.5 Ω.     

Assessing geometrical errors of multi-axis machines by three-dimensional length measurements

In this paper a method is presented for assessing geometrical errors of multi-axis machines based on volumetric three-dimensional length measurements. A universal machine error model is proposed since a large variety of machine configurations exists. Such models can be used for software error compensation techniques in order to improve the machine’s positioning behaviour as well as for diagnostic purposes. Length measurements are chosen for the measurement of the positioning errors of a multi-axis machine because these measurements can be executed in a short period of time in a relatively simple way combined with a high accuracy. In order to get comparable results for the geometrical errors as measured with conventional techniques, i.e., laser interferometry, the design of the measurement setup as well as the formulation of the machine error model (including parameter correlation effects) appeared to be of major importance and are subject of this paper.     

Increasing of accuracy of angular measurements by using hybrid photoelectric converters

The basis sources and methods of reducing the errors of incremental photoelectric digital converters for angular measurements are analyzed. A method of constructing hybrid photoelectric converters that increase the accuracy of angular measurements is proposed. The result is achieved by simultaneous measurements of the turning angle and current radial deflections of the converter shaft axis.     

浅谈保证皮带秤应用准确度之心得

本文主要介绍在安装时如何保证皮带秤在使用中的准确度以及校准的几种方法和故障分析。     

On the accuracy of microinterferometric measurements of optical-path differences by means of the half-shade method

Using a shearing double-refracting interference microscope with a half-shade eyepiece, the accuracy of optical-path-difference measurements has been examined. For the half-shade elements, birefringent strips with phase difference equal to 180°, 110° and 20° as well as a half-wave plate with a narrow slit, cemented between two glass plates, were used. It is known that different relative intensities of the background inside and outside the half-shade strip introduce a subjective error in the correct visual assessment of the matching point of the interference image of the object under examination. Applying test objects made of thin strips of dielectric evaporated in vacuum onto glass slides, it has been demonstrated that this error depends upon the optical-path difference and image size of the object being measured, as well as upon the half-shade phase difference. For a small half-shade phase difference the error is practically imperceptible and for the half-shade strip giving half-wave retardation it attains maximum values. In the case of homogeneous objects, the images of which are as large as 1.5–2° in the field of view of the microscope, this error does not usually produce inaccuracies greater than ± λ/100 in optical-path-difference measurements. Using the half-shade strip with a diaphragm which masks the misleading background and enables an observer to see the matched image areas only, the optical-path difference can be measured with accuracy ± 0.003λ or better.     

提高辊道秤计量系统准确性的初探

本文对提高辊道秤计量系统的准确性进行了初步探讨,通过下述几方面努力可以达到快捷、自动称量、准确计量的目的.1.计量辊道的改进及要求;2.称重传感器、限位装置的选择与配合;3.开发角差数字调校和自动静态称量.     

Estimation of surface area and length with the orientator

The orientator is a new technique for the estimation of length and surface density and other stereological parameters using isotropic sections. It is an unbiased, design-based approach to the quantitative study of anisotropic structures such as muscle, myocardium, bone and cartilage. A simple method for the practical generation of such isotropic planes in biological specimens is described. No special technical equipment is necessary. Knowledge of an axis of anisotropy can be exploited to optimize the efficiency. To randomize directions in space, points are selected with uniform probability in a square using various combinations of simple random, stratified random, and systematic random sampling. The point patterns thus produced are mapped onto the surface of a hemisphere. The mapped points define directions of sectional planes in space. The mapping algorithm ensures that these planes arc isotropic, hence unbiased estimates of surface and length density can be obtained via the classical stereological formulae. Various implementations of the orientator are outlined: the prototype version, the orientator-gencrated ortrip, two systematic versions, and the smooth version. Orientator sections can be generated without difficulty in large specimens; we investigated human skeletal muscle, myocardium, placenta, and gut tissue. Slight practical modifications extend the applicability of the method to smaller organs like rat hearts. At the ultrastructural level, a correction procedure for the loss of anisotropic mitochondrial membranes due to oblique orientation relative to the electron beam is suggested. Other potential applications of the orientator in anisotropic structures include the estimation of individual particle surface area with isotropic nucleators, the determination of the connectivity of branching networks with isotropic disectors, and generation of isotropic sections for second-order stereology (three-dimensional pattern analysis).     

基于高准确度汽车衡仪表的特色化应用

本文结合XK3190-D18系列高准确度汽车衡仪表的软硬件特色,以两个典型应用方案为例,重点介绍了该仪表在网络化和流程管理方面的特色化应用,帮助广大系统应用领域的工作人员充分了解该仪表,有助于提高相关领域招投标项目的成功率以及系统集成的完成质量和效率.     

Life and wear of frictional couplings and improved compression measurements in internal combustion engines

Analysis of the restoration of piston engines demonstrates the influence of the shape of surfaces in the frictional pair on the life and wear of the frictional coupling. The variation in gas pressure within the cylinders is established. The method of measuring the compression ratio is improved.     

影响电子秤准确度的因素及其对策

本文介绍了影响电子衡器--电子计价准确度的主要5种因素:重物冲击;附加物;振动和风力;环境温度;环境湿度和酸、碱物体.同时也介绍了选择电子计价秤注意事项和定期检定以保证电子计价秤的准确度.     

提高液压钢卷秤准确度的实践

武钢股份有限公司冷轧硅钢片厂PA2是一条半自动化包装机组.主要对硅钢成品进行称重和包装,其产品的附加值高,售价也高,因此,电子衡器的准确性就显得格外重要.在半自动生产线上安装液压升降平台秤具有快速、高效的特点.但设计时往往容易忽视液压钢卷秤的结构与包装机组有效的结合,本文通过PA2液压钢卷秤的改造,对液压钢卷秤的称量精度和工作效率等问题进行了论证.     

Improving the accuracy of single radioactive particle technique for flow velocity measurements

An original method of flow velocity estimation for a radioactive particle technique is presented. It is based on exchanging measured pulses into cumulative signals, and determination of time delay as time difference of occurrences of inflection points of cumulative curves. To determine the inflection points, a suitable algorithm is proposed. The preliminary results show that the proposed method is especially more precise than the classical cross-correlation approach. The preliminary results show that this method can be successfully applied in a laminar flow with any type of fluid, and can without limitation be applied for different types of radioactive detectors.     

关于提升装载机电子秤检定结果测量准确度的探讨

装载机电子秤广泛应用于货场、建筑工地,如何使检定结果准确可靠,本文对自动衡器检定装置标准器量值的管理方法进行了一些探讨。