两相流测量的三光束偏振型LDV装置

两相流的测量是许多工业装置中遇到的一个十分重要的课题,本文引入了一种新的测量装置。它采用三光束偏振型光路消除了边缘效应,输出信号由计算机软件处理,采用双阁值法方便、有效地对两相流的速度进行测量。适当改进后,本装置能同时对两相流的粒子尺度及粒子速度进行测量。     

离心力对干涉测量光路的影响及其修正

本文分析了旋转载体上离心力造成的干涉测量光路中空气介质压强的不均匀变化，给出了与光路介质折射率相应的分布规律，分析了由此引起的干涉测量系统动态测量的示值偏差，据此分析计算的结果可用于测量结果的精密修正。本文的讨论结果为精密离心机及类似的运动载体上的动态干涉测量系统的分析设计提供了依据。     

测量脉冲大电流的双光路光学电流传感器技术

提出了双光路光学电流传感器检测方法及其数据处理方法，即激光输出功率保持不变时，可采用双光路结构和反正切函数处理方法求出待测脉冲大电流。采用双光路光学电流传感器和罗果夫斯基线圈对比测量了充电电压为18 kV、电容为31.8 F的电炮的短路电流，两种测试方法的实验结果取得了较好的一致性,证明了双光路光学电流传感器的有效性。     

基于电子散斑干涉法的高弹性连轴器挠性杆位移分析

本文重点讨论了应用电子散斑干涉法测量弹性元件的挠曲线的方法.将电子散斑测量离面位移的光路引入到高弹性连轴器挠性杆的横向弯曲变形测量中.新的离面位移测量光路并结合相移技术是其特点.首先采用类似于麦克尔逊式光路的方式将物光和参考光垂直分布,使得离面位移的结果是直接并且是纯粹的获得;其次,固体泵浦激光的相干长度很长,从而在设计光路时带来了便利,光路可以很紧凑而不考虑物光与参考光的光程差;最后,在参考光路中引入精密的PZT相移器,从而实现了位相技术,使得测量的结果能数字化输出.电子散斑干涉方法在光学非破坏性检测领域得到了广泛的应用,采用电子散斑干涉技术可以测量物体的变形、位移、振型等.该方法具有实时显示、全场非接触测量、精度和灵敏度高、采用位相技术可以方便的实现测量结果的数字化等优点.本文采用电子散斑干涉结合相移技术,得到了的数字化结果,再和有限元模拟计算进行了比较,证明了方法的正确性.     

压剪炮的激光测速系统的研究

压剪炮试验是获取材料超高应变率下本构关系的最常用手段,其中普遍采用的测试方法是利用激光干涉技术同时测量靶板背面一点的纵向和横向速度。但传统的横向位移干涉仪抵抗靶板撞击过程中的运动而引起的光路偏移能力很有限,因而压剪试验成功率很低。本文讨论了撞击过程中靶板运动对横向位移干涉仪试验信号的影响,为提高横向位移干涉仪特别是非理想撞靶情况下的测量能力,对几种不同干涉光路进行详细分析。通过改进传统横向位移干涉光路,研制了一种新干涉光路,并通过试验证明:相对于传统光路,新光路更简单并更可靠。     

高灵敏云纹干涉法测量应变场

云纹干涉法是一种新的实验力学方法,具有高灵敏度,测量范围广,条纹对比度好等优点.通过在光路中添加一楔块或晶体玻璃,可以实时的观察云纹条纹,一次曝光就可得到全场的应变.     

一种新型MOEMS陀螺的提出及理论分析

提出一种新型的光路结构，构成利用空间光路的干涉式MOEMS陀螺。介绍了此种陀螺的基本原理，并从提高基本探测极限的角度，对此种空间光路的各种参数进行了理论分析，提出了设计思路和方法。指出了此种陀螺的特点及其应用领域。     

大型结构变形及形貌摄像测量技术研究进展

船体、机翼、工程建筑等大型结构的变形与形貌的精确测量是实验力学的基本任务之一.摄像测量具有测量精度高、范围大、非接触、可动态测量等优点,是结构形貌与运动测量的重要手段.本文介绍了作者及其所在科研团队近年来利用摄像测量技术在大型结构变形、形貌测量等方面的研究成果和典型应用范例,主要包括:提出折线光路像机链摄像测量方法与技...     

单光束楔形镜云纹干涉法

本文利用单光束楔形镜云纹干涉法代替传统的双光束云纹干涉法进行位移场和应变场的测量.单光束云纹干涉法具有光路简单,不受环境干扰等特点.本文将云纹干涉法的波前理论与近代光学信息技术有机地结合起来,对单光束干涉系统进行了分析,得到了记录的光强和再现的位移应变公式.利用该系统,得到了三点弯矩形梁的全场位移条纹图和应变条纹图.     

使用单彩色相机的单相机三维数字图像相关方法

介绍了一种基于单个彩色相机的新型全靶面、单相机三维数字图像相关(3D-DIC)方法。借助于设计巧妙的颜色分光光路,被测物体表面图像可以通过两条不同的光路达到相机靶面,采集的标定靶和实验件表面的彩色图像可以分离得到蓝色和红色子图像。通过使用3D-DIC分析标定靶和实验件表面分离后的蓝色和红色子图像,可以获得物体表面的三维形貌和变形。形貌测量、面内和离面平移、以及静动态三维变形实验验证了该单彩色相机3D-DIC方法的有效性和测量精准度。由于可避免双相机同步,且能实现无分辨率损失的全靶面三维形貌和变形测量,本文方法在需要实现瞬态位移和变形测量的爆炸、冲击、振动等领域中具有广阔重要的应用前景。     

A Novel Contactless Flow Rate Measurement Device for Weakly Conducting Fluids Based on Lorentz Force Velocimetry

This paper presents an improved experimental setup for the contactless flow rate measurement in a weakly electrically conducting fluid on the base of Lorentz force velocimetry (LFV) and discusses the measurement results. The new setup embodies major improvements over the setup reported in Wegfraß et al. (Appl Phys Lett 100:194103, 2012). This measurement setup consists of a newly designed fluid channel with well defined flow profiles – a plug profile at the inlet and quasi parabolic profile at the outlet of the test section. Another improvement is the force measurement system which is based on electromagnetic force compensation (EMC). Furthermore an optimized Halbach array is used as a magnet system. The results of our measurements confirm the feasibility of LFV in a model fluid (salt water) with conductivities less than 10 Sm^???1 and demonstrate that the optimized magnet system increases the measurement signal. The used force measurement system had to be particularly calibrated for this purpose, so that in combination with the new magnet system design a three times higher signal resolution for the fluid velocity under laboratory conditions was achieved.     

The surface hot wire as a means of measuring mean and fluctuating wall shear stress

 The paper describes some applications of a wall shear stress sensor technique which is based on hot-wire anemometry. The “surface hot wire” is a flush-mounted thermal resistive wire with a tiny slot underneath. The arrangement of this sensor guarantees an improved signal-to-noise ratio compared to a common surface hot film. The setup and the application of single sensors and of surface hot-wire arrays are shown. Some results are presented that were acquired in several experiments in the field of laminar-turbulent transition. Received: 26 May 2000/Accepted: 7 February 2001     

Multi-Axial Deformation Setup for Microscopic Testing of Sheet Metal to Fracture

While the industrial interest in sheet metal with improved specific-properties led to the design of new alloys with complex microstructures, predicting their safe forming limits and understanding their microstructural deformation mechanisms remain as significant challenges largely due to the inadequacy of the existing experimental tools. The investigation of the strain-path dependent failure mechanisms requires miniaturized testing equipment, which can be placed in a scanning electron microscope for in situ experiments. So far, such tests could only be carried out for a single strain path (uniaxial tension). In this work, in order to fill this gap, a miniaturized Marciniak test setup is designed, built and tested. With this setup real-time, multi-axial tests of industrial sheet metal can be carried out to the point of fracture within a scanning electron microscope. Proof-of-principle experiments demonstrate that a realm of information can be obtained, crucial for the understanding of the mechanical behavior of new alloys.     

Remote displacement analysis using multimode fiber-optic bundles

An improved method for holographically recording displacement through fiber optics is presented. The object is illuminated by focusing the exit end of a multimode fiber bundle on the test surface. The real image of the object is transmitted through a second coherent bundle to a photographic plate where it is recorded using a reference wave front. The resulting image-plane hologram is reconstructed in white light. Experimental results agree well with theory and demonstrate the potential of measuring displacement on surfaces far removed from the basic holographic setup; or, in remote areas of a structure where optical access is limited.     

Wake visualization of a heaving and pitching foil in a soap film

Many fish depend primarily on their tail beat for propulsion. Such a tail is commonly modeled as a two-dimensional flapping foil. Here we demonstrate a novel experimental setup of such a foil that heaves and pitches in a soap film. The vortical flow field generated by the foil correlates with thickness variations in the soap film, which appear as interference fringes when the film is illuminated with a monochromatic light source (we used a high-frequency SOX lamp). These interference fringes are subsequently captured with high-speed video (500 Hz) and this allows us to study the unsteady vortical field of a flapping foil. The main advantage of our approach is that the flow fields are time and space resolved and can be obtained time-efficiently. The foil is driven by a flapping mechanism that is optimized for studying both fish swimming and insect flight inside and outside the behavioral envelope. The mechanism generates sinusoidal heave and pitch kinematics, pre-described by the non-dimensional heave amplitude (0–6), the pitch amplitude (0°–90°), the phase difference between pitch and heave (0°–360°), and the dimensionless wavelength of the foil (3–18). We obtained this wide range of wavelengths for a foil 4 mm long by minimizing the soap film speed (0.25 m s⁻¹) and maximizing the flapping frequency range (4–25 Hz). The Reynolds number of the foil is of order 1,000 throughout this range. The resulting setup enables an effective assessment of vortex wake topology as a function of flapping kinematics. The efficiency of the method is further improved by carefully eliminating background noise in the visualization (e.g., reflections of the mechanism). This is done by placing mirrors at an angle behind the translucent film such that the camera views the much more distant and out-of-focus reflections of the black laboratory wall. The resulting high-quality flow visualizations require minimal image processing for flow interpretation. Finally, we demonstrate the effectiveness of our setup by visualizing the vortex dynamics of the flapping foil as a function of pitch amplitude by assessing the symmetry of the vortical wake.     

THE USE OF VACUUM PRESSURE IN STRUCTURAL TESTING

This paper presents an experimental setup for the method of simulating uniformly and varying distributed loads on structural members and roofing materials. The applications of this setup can be used for the study of beams, such as the lateral, torsional buckling behavior of cold-formed thin-walled structures. In addition, the method of measuring bending stiffness of composite materials in semimonocoque structures is illustrated. With a little modification to the setup, the study could possibly be extended to the investigation of elastic foundations and beam-column interaction.     

Investigation of the annular nozzle start in actual and virtual intermittent aerodynamic setups

The results of a numerical and experimental investigation of the starting of jet-engine annular nozzle blown with the air at room temperature and high-temperature combustion products of a stoichiometric acetylene-air mixture in an intermittent aerodynamic setup are presented. The regimes and the times of the attainment of quasi-steady stAte of the flow are studied in the virtual full-scale counterpart of the experimental setup. The special features of the starting stage and the quasi-steady flow are studied for entry channels of different shapes. The values of starting times, the pressures at different points of the flow duct, and the thrusts produced by the annular nozzle measured in the physical experiment and obtained in the virtual experimental setup are compared.     

Setup Instabilities in the Nearshore Hydrodynamics

The incoming wave field on a beach produces a setup on the mean water level elevation. In earlies studies, this setup had been hypothesized as an instability source in nearshore hydrodynamics capable of driving processes such as rip currents, horizontal eddies and rhythmic topography. An analytical study is presented in order to investigate if such a setup in isolation, that is, without longshore current and without wave-refraction, can cause the growth of infinitesimal disturbances capable of driving such processes. It is shown that the setup can not be considered as an instability source since the equation governing the disturbances is found to be a wave-type equation. However, the phase speed differs slightly from the classical value gD, and becomes anisotropic. This can be interpreted as an effect of the radiation stresses of short incoming waves on long wave propagation.     

集成光学角速度传感器及其关键器件的研制

本文介绍了清华大学研制的集成光学角速度传感器 ( IORS)系统方案及其关键器件 ,包括 :( 1 )窄线宽单模光纤 Bragg光栅外腔式二极管激光器 ( FBG- LD) ;( 2 )声体波的声光移频器 ( AOFS)及其直接数字合成 ( DDS)的控制电路 ;( 3)谐振型 IORS( R- IORS)的实验装置 ,采用光纤仿真的光波导 Sagnac敏感环 ( SSR) ;( 4 )干涉型 IORS( I- IORS)的实验装置 ,采用光纤仿真的再入式 SSR。采用上述 AOFS研制了一种全光纤延迟的自外差测量系统 ,用于测量上述 FBG- L D。初步的实验结果表明 ,所提出的上述 R- IORS和 I- IORS都可开发为新型光学陀螺的产品     

Performance analysis of the heterodyne schlieren system

The performance of the electronic heterodyne schlieren system is investigated. The sensitivity, spatial resolution, and dynamic range of the system are calculated. It is shown that these features are improved compared with the conventional intensity schlieren readout technique. Without changing the system setup, the sensitivity and accuracy of the system can be tripled by using the third harmonic of the heterodyne signal. In this case, the spatial resolution and the measurement range are reduced by a factor of three. The system is self-calibrated. For whole field measurements, the method is limited by the camera to milliseconds time scale. However, for selected points measurements fast variations, the order of tens of microseconds, can be measured. The system was evaluated experimentally by measuring the focal length of a weak lens and a multiscale phase plate.