Film thickness measurement with an ultrasonic transducer

A technique for measuring condensate film thickness using an ultrasonic transducer is described. In the experiment, the condensate film thickness with R-113 and FC-72 (a fluorinert compound developed by the 3M Company) condensing on the horizontal lower surface of a rectangular duct was measured at several locations. From the measured values a power law relation between the condensate film thickness and the axial distance from the leading edge of the condensing surface was derived by regression analysis. Assuming a linear temperature profile in the condensate film, local and average heat transfer coefficients were computed from the condensate film thickness. The average heat transfer coefficients were compared with the values obtained by measuring the heat transfer rate to the coolant. The two values were within ±12% of each other. As yet there is no satisfactory analytical model to predict the local heat transfer coefficient even in the annular condensation regime. One of the main difficulties in modeling the condensation is the lack of a suitable model to predict the interfacial shear stress. With the measurement of the film thickness it is possible to determine the interfacial shear stress. It is hoped that the shear stresses so determined will lead to the development of a satisfactory model for interfacial shear stress with condensation.     

用PVDF实时测量激光诱导的冲击波压力

本文用自己研制的ＰＶＤＦ（ｐｏｌｙｖｅｎｙｌｉｄｅｎｆｌｕｏｒｉｄｅ）压电传感器测量了０．２ｍｍ厚铝和２．０８ｍｍ厚Ｔ３００／环氧复合材料中激光诱导的冲击波压力，首次获得了这些材料中激光冲击波压力的时间演化波形。实验在中国科大强激光实验室的ＹＡＧ脉冲激光器上进行，激光波长１．０６μｍ，脉宽３３ｎｓ，靶面平均功率密度为１０９Ｗ／ｃｍ２量级。从所得数据估计了表面入射压力，其值与已有结果符合良好。实验结果证实，ＰＶＤＦ压电传感器频响高，量程宽，多次使用重复性好，可有效应用于激光冲击波压力的实时测量     

旋转IMU在光纤捷联航姿系统中的应用

惯性测量单元输出信号的精度直接影响捷联惯性导航系统的精度,为了提高捷联系统的精度,以舰船光纤捷联惯性航姿系统为应用对象,采用了双轴旋转机构连续匀速旋转IMU的系统方法,把惯性测量单元输出信号中的漂移误差调制成正弦信号,通过捷联算法中的积分运算可以有效地消除陀螺和加速度计中的漂移误差,从而有效地提高捷联惯性航姿系统的精度,并进行了系统仿真实验。仿真结果表明:经过旋转以后的IMU输出信号误差较传统非旋转方法可以减小一个数量级。基于双轴旋转IMU的系统方法可以有效地减小IMU输出信号漂移误差和提高捷联惯性航姿系统的精度。     

A new interferometric method for vibration measurement by electronic holography

Electronic holography is a well-established technique used in real-time, non-contact, whole-field displacement measurements. When using the real-time, time-averaged method for vibration measurments, the quantitative interpretation of dense fringe patterns is difficult because of speckle noise. Even when speckle-reducing procedures are used, such as multiple-frame averaging or rotation of the illumination beam, the remaining speckles and decreasing visibility of higher-order Bessel fringes are serious limitations. The primary objective of this paper is to present a new realtime, interferometric method for mechanical vibration measurements and the associated quantitative interpretation. The fringe pattern obtained by this method is quasi-binary and half as dense as in the time-averaged method. The method greatly improves the overall visibility (contrast, resolution) of vibration fringe patterns without any sacrifice in the real-time capabilities. Quantitative fringe interpretation is straightforward and based on binary fringe tracking. It allows quantitative measurements in situations where the time-averaged fringe processing fails.     

Full-field speckle pattern image correlation with B-Spline deformation function

A full-field speckle pattern image correlation method is presented that will determine directly the complete, two-dimensional deformation field during the image correlation process on digital images obtained using computer vision systems. In this work, a B-Spline function is used to represent the object deformation field throughout the entire image area. This is an improvement over subset-based image correlation methods by implicitly maintaining position and derivative continuity constraints among subsets up to a specified order. The control point variables within the B-Spline deformation function are optimized iteratively with the Levenberg-Marquardt method to achieve minimum disparity between the predicted and actual deformed images. Results have shown that the proposed method is computationally efficient, accurate and robust. The general framework of this method can be applied ton-dimensional image correlation systems that solve for multi-dimension vector fields.     

白光数字散斑图像频域自动识别技术——用于逐点分析的数字相移法

提出了一种应用于白光数字散斑图像频域位移测量技术的数字相移方法,利用计算机本身的能力,无需增加任何设备,通过计算机生成的四幅图像进行相移计算,得到逐点分析的条纹的未去包裹图像,从该图像确定位移的方向和大小,实现了白光数字散斑图像的全自动化处理。白光数字散斑方法设备简单,对环境的要求低,无需防振和相干光源,引入本文提出的数字相移技术,由于充分利用了计算机数字图像处理的功能,在未增加任何设备的情况下实现了全自动位移测量,是一种适合工业现场测量的有发展前途的位移测试的技术。     

Viskositätsmessung mit dem longitudinal schwingenden Band

A method for the detection of small masses with the aid of a longitudinally vibrating band is described and further applications, e.g. for viscosity and humidity measurement are discussed. The complex Young's modulus of the band can also be determined.

     

单镜头三维粒子成像测速

本文提出了一种用单镜头进行三维流场测量的方法，建立了包括摄录系统、数字图象处理及识别系统及流动装置的３Ｄ－ＳＣＰＩＶ系统。完成了现有条件下的原理性定量测量实验。     

微推进器推力测试技术

对近年来微推进器(Microthruster)的推力测试技术和手段进行了较全面的综述，并对几种典型进行单脉冲冲量、平均推力等参数测量的推力测试系统和手段进行描述，分析各自的特点．文中对微推力测试过程中的细节进行了初步探讨、为未来微推进器推力测试和研究提供有益参考．     

The estimate and measurement of longitudinal wave intensity

Quasi-longitudinal waves are one type of structural waves, which are important at high frequencies. This paper studies the estimate theory and measurement technique of quasi-longitudinal waves, analyzes the bias error due to the effect of bending waves. In a two-dimensional quasi-longitudinal wave field, the intensity vector is the sum of the effective intensity vector and the intensity variation vector. Its axial component is proportional to two imaginary parts of cross spectral densities and in the measurement, it is measured by a pair of two-transducer arrays. In a onedimensional quasi-longitudinal wave field, the intensity variation is zero, the intensity is proportional to only one imaginary part of a cross spectral density and it can be measured using a two-transducer array. If bending and quasi-longitudinal waves coexist and the contribution from bending waves cannot be eliminated or reduced to a certain extent, the measured quasi-longitudinal wave intensity will contain a large error. The results measured on the three-beam structure show that quasi-longitudinal wave intensity can be accurately measured using the intensity technique when bending waves are negligible in comparison with quasi-longitudinal waves. The project supported by the National Natural Science Foundation of China