共查询到18条相似文献，搜索用时 109 毫秒
1.
一体化电子式电流电压互感器研究 总被引：7，自引：1，他引：7
A high-performance current and voltage measurement system has been developed in power system.The system is composed of two parts:one current measurement element and one voltage measurement element.A Rogowski coil and a capacitive voltage divider are used respectively for the line current and voltage measurements.Active electronic components are used to modulate signal,and power supply for these components is drawn from power line via an auxiliary current transformer,Measurement signal is transmitted y optical fibers,which is resistant to electromagnetic induction and noise,With careful design and the use of digital signal processing technology,the whole system can meet 0.5% accuracy for metering and provides large dynamic range coupled with good accuracy for protective relaying use. 相似文献
2.
Modified surface tension model for free surface flow with single-phase lattice Boltzmann method 总被引：1，自引：0，他引：1
A single-phase lattice Boltzmann model with modified surface tension is developed in this paper to solve the problem of high-density-ratio free surface flow.The computational efficiency and accuracy are both enhanced.The restriction to the relaxation factor （which needs to be smaller than 1） is circumvented by the new surface tension algebra,due to its rational physical nature compared with the treatment of Xing,Buther and Yang in their paper （Comp.Mater.Sci.,2007,39（2）：282-290）.The proposed stable surface tension scheme is applied to simulate the free deformation of a square droplet with surface tension effect and the process of a droplet impinging on a liquid film.The numerical solution for free deformation of a droplet agrees well with thermodynamic principles,and also achieves high accuracy in comparison with Xing,et al.＇s model.Three typical impinging modes are successfully obtained with the new scheme,and another particular mode found by Wang and Chen is also successfully simulated.The evolutions of liquid crown agree well with the power law related to time. 相似文献
3.
The design methods of anode and cathode are proposed for precision profile grinding.Based on the electrolytic machining theory, electrolytic equilibrium condition and Faraday‘s law of electrolysis are applied to establishing the mathematical model of profile diamond dressing processes. A finite element method (FEM) program is developed to solve the inverse boundary problem of Laplace‘s equation. Desired anode contour or cathode shape is determined by computing the distribution of electric potential layer by layer. Electrolytic machining experiment is carried out to verify the simulated anode shape. The research result shows that shape deviation between designed cathode and profile wheel increases with the value of angle between feed rate and the normal to anode surface. The shape of simulated anode is consistent with the contour of metal-bonded diamond profile wheel for a given cathode. Based on the anode contour, cathode shape can also be designed accurately. 相似文献
4.
A novel light scattering technique for mapping metal surface corrosion is presented and its results on copper exposed to atmosphere are reported. The front end of the instrument is made up of a sensor module comprising a thin beam light emitting diode （LED） illuminating a small spot on the metal surface, and a matched pair of photodetectors, one for capturing the reflected light and the other for sampling the scattered light. The analog photocurrent signals are digitized and processed online by a per- sonal computer （PC） to determine the corrosion factor defined in terms of the two current values. By scanning the sample surface using the light beam and by computing the corrosion factor values simultaneously, a three dimensional graph and a two dimensional contour map are generated in the PC using Matlab tools. The values of the corrosion factor measured in different durations of exposure to atmosphere, which obey a bilogarithmic law, testify to the validity of our mathematical model. 相似文献
5.
Parameters optimization and nonlinearity analysis of grating eddy current displacement sensor using neural network and genetic algorithm 总被引：1，自引：0，他引：1
A grating eddy current displacement sensor （GECDS） can be used in a watertight electronic transducer to realize long range displacement or position measurement with high accuracy in difficult industry conditions. The parameters optimization of the sensor is essential for economic and efficient production. This paper proposes a method to combine an artificial neural network （ANN） and a genetic algorithm （GA） for the sensor parameters optimization. A neural network model is developed to map the complex relationship between design parameters and the nonlinearity error of the GECDS, and then a GA is used in the optimization process to determine the design parameter values, resulting in a desired minimal nonlinearity error of about 0.11%. The calculated nonlinearity error is 0.25%. These results show that the proposed method performs well for the parameters optimization of the GECDS. 相似文献
6.
We developed a measuring instrument that had wide range, high precision, small measuring touch force. The instrument for three-dimensional （3D） surface topography measurement was composed of a high precision displacement sensor based on the Michelson interference principle, a 3D platform based on vertical scanning, a measuring and control circuit, and an industrial control computer. It was a closed loop control system, which changed the traditional moving stylus scanning style into a moving platform scanning style. When the workpiece was measured, the lever of the displacement sensor returned to the balanced position in every sample interval according to the zero offset of the displacement sensor. The non-linear error caused by the rotation of the lever was, therefore, very small even if the measuring range was wide. The instrument can measure the roughness and the profile size of a curved surface. 相似文献
7.
Due to the complex nature of multi-source geological data, it is difficult to rebuild every geological struc-ture through a single 3D modeling method. The multi-source data interpretation method put forward in this analysis is based on a database-driven pattern and focuses on the discrete and irregular features of geological data. The geological data from a variety of sources covering a range of accuracy, resolution, quantity and quality are classified and inte-grated according to their reliability and consistency for 3D modeling. The new interpolation-approximation fitting construction algorithm of geological surfaces with the non-uniform rational B-spline （NURBS） technique is then pre-sented. The NURBS technique can retain the balance among the requirements for accuracy, surface continuity and data storage of geological structures. Finally, four alternative 3D modeling approaches are demonstrated with reference to some examples, which are selected according to the data quantity and accuracy specification. The proposed approaches offer flexible modeling patterns for different practical engineering demands. 相似文献
8.
We prepared an SbSn intermetallic compound powder with a mixture of equal molar amounts of antimony （Sb） and tin （Sn） by melt-annealing and high-energy ball milling, and characterized the obtained substance with XRD （X-ray diffraction）, DSC （differential scanning calorimetry）, SEM （scanning electron microscopy）, and XPS （X-ray photoelectron spectroscopy）. The prepared SbSn has a hexagonal structure with a melting point of 425 ℃. The particles have a dendritic appearance in micromorphology images. More Sb atoms are enriched on the surface than Sn atoms. A desulfurization efficiency of up to 33.92% can be obtained when applying this powder as a medium in the electric desulfurization of crude oil under the following conditions an emulsion with a volumetric ratio of water to oil at 20：80, a surfactant mass fraction in the emulsion of 0.18%, a processing time of 17 h, and a voltage of 9.68 V. SbSn could be a promising catalyst for desulfurizing crude oil. The desulfurization performance is ascribed to the electron cavities formed by current induction. 相似文献
9.
平面磨削工件的热变形及加工误差的实用计算方法 总被引：3，自引：0，他引：3
The paper submits a method to calculate thermal deformation and manufacture error in surface grinding.The author established a simplified temperature field model.and derived the thermal deformaiton of the ground workpiece,It is found that there exists not only a upwarp thermal deformation,but also a parallel expansion thermal deformation.A upwarp thermal deformation causes a concave shape error on the profile of the workpiece,and a parallel expansion thermal deformation causes a dimension error in height.The calculations of examples are given and compared with presented experiment data. 相似文献
10.
A method of medical image segmentation based on support vector machine （SVM） for density estimation is presented. We used this estimator to construct a prior model of the image intensity and curvature profile of the structure from training images. When segmenting a novel image similar to the training images, the technique of narrow level set method is used. The higher dimensional surface evolution metric is defined by the prior model instead of by energy minimization function. This method offers several advantages. First, SVM for density estimation is consistent and its solution is sparse. Second, compared to the traditional level set methods, this method incorporates shape information on the object to be segmented into the segmentation process. Segmentation results are demonstrated on synthetic images, MR images and ultrasonic images. 相似文献
11.
INTRODUCTION Oil and water well is an important basic estab- lishment in oilfields. In many oilfields, there are many different damages in the well’s casing walls after its development for a period of time. They will affect the normal production of damaged wells and adversely influence the neighbouring wells and the block, and threaten steady production. There are different kinds of damages due to multiple problems in the casing walls, for example, corrosion, perforation, decreased diame… 相似文献
12.
对一类分形插值曲面和它的截线进行探讨．根据生成分形插值曲面的迭代函数系,导出了其截线的迭代函数系,证明了它的不变集（即分形插值曲面的截线）是具有间断点的分形插值函数的图像,并通过计算得到分形插值曲面的盒维数与其截线的盒维数之间的关系． 相似文献
13.
利用分形维数定量表征催化剂的形状不规则程度 ,对其中进行的气 -固相催化反应进行了分析计算 .计算结果表明 ,催化剂的形状越不规则 ,催化剂的外表面分形维数越高 ,在相同反应条件下 ,催化剂的利用率越高 .同时给出了适用于形状不规则催化剂的通用 Thiele模数 .计算结果还表明 ,分形维数只影响通用 Thiele模数的数值 ,但在相同的通用Thiele模数下 ,催化剂具有相同的效率因子 相似文献
14.
利用扫描探针显微镜考察了硅基材料的摩擦磨损性能,同时考虑了环境因素、循环扫描次数的影响;通过实验设计,得出了该材料表面的形貌,初步分析了其摩擦磨损性能。结果表明:压电陶瓷的滞后效应和非线性效应的影响比较显著;随着外界湿度的增加,湿度对材料表面黏附力和摩擦系数有较大的影响;外加载荷和扫描循环次数直接决定材料表面的耐磨性能。 相似文献
15.
The technique of real-time digital speckle pattern interferometry is proposed to study diffusion of surfactants in hydrogel.
The diffusion coefficient is simply and directly determined from the interferograms. An example of diffusion coefficient measurement
of surfactant in agarose gel demonstrates the usefulness of the method. The results obtained are compared with the theoretical
simulating values.
Project Supported by National Natural Science Foundation of China (No. 29904007), Zhejiang Provincial Natural Science Foundation
of China (No. 699031), and SRF for ROCS, SEM, China 相似文献
16.
世界各国新一代静止轨道气象卫星陆续发射升空,成像仪是主要载荷之一。通过对美国、日本、欧洲和中国等新一代静止气象卫星成像仪特性的研究分析,客观认识我国静止气象卫星水平的差距和不足,为我国风云四号02星成像仪特性优化提供参考。在波段设置方面,欧美日均为16个通道,我国的FY-4A为14个光谱通道;在时空分辨率方面,各国水平相当,略有差异,可见光波段分辨率为0.5~1km,红外波段2~4km,全圆盘观测10~15min;在观测模式方面,FY-4A的多通道扫描成像辐射计和MTG的灵活组合成像仪先进行一次全圆盘观测,再进行多次区域观测,不同扫描资料时间间隔不均等。GOES-R的先进基线成像仪和Himawari-8的先进葵花成像仪观测时间采用碎片化设计,即各种扫描模式交叉进行,不同扫描资料时间间隔均等,非常有利于预报员对天气进行系统分析。 相似文献
17.
ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｒａｔｅｏｆｄｉｆｆｕｓｉｏｎｏｆｓｕｒｆａｃｔａｎｔｓｉｎｇｅｌｓｉｓａｎｉｍｐｏｒｔａｎｔｐｒｏｐｅｒｔｙｂｏｔｈｆｏｒｔｈｅｃｈａｒａｃｔｅｒｉｚａ ｔｉｏｎｏｆｓｏｌｕｔｅ ｇｅｌｉｎｔｅｒａｃｔｉｏｎｓａｎｄｆｏｒｔｈｅｄｅｓｉｇｎｏｆｎｏｖｅｌａｐｐｌｉｃａｔｉｏｎｓｏｆｓｕｃｈｍａｔｅｒｉａｌｓ (Ｋｏｎｇｅｔａｌ.,1 997) .Ｃｏｎｖｅｎｔｉｏｎａｌｌｙ ,ｄｉｆｆｕｓｉｏｎｃｏｅｆｆｉ ｃｉｅｎｔｓｉｎｇｅｌｓａｒｅｍｅａｓｕｒｅｄｂｙｍｏｎｉｔｏｒｉｎｇｔ… 相似文献
18.
Derek C. Briggs 《Journal of Educational Measurement》2013,50(2):204-226
A vertical score scale is needed to measure growth across multiple tests in terms of absolute changes in magnitude. Since the warrant for subsequent growth interpretations depends upon the assumption that the scale has interval properties, the validation of a vertical scale would seem to require methods for distinguishing interval scales from ordinal scales. In taking up this issue, two different perspectives on educational measurement are contrasted: a metaphorical perspective and a classical perspective. Although the metaphorical perspective is more predominant, at present it provides no objective methods whereby the properties of a vertical scale can be validated. In contrast, when taking a classical perspective, the axioms of additive conjoint measurement can be used to test the hypothesis that the latent variable underlying a vertical scale is quantitative (supporting ratio or interval properties) rather than merely qualitative (supporting ordinal or nominal properties). The application of such an approach is illustrated with both a hypothetical example and by drawing upon recent research that has been conducted on the Lexile scale for reading comprehension. 相似文献