基于激光点阵的TIG焊熔池自由表面三维形貌测量方法

测量弧焊熔池自由表面三维形貌对研究电弧与熔池耦合作用机理,控制焊缝成形及全熔透等有着重要意义。针对现有的三维测量方法难以应用于强弧光、熔池表面镜面反射情况,提出一种点阵激光测量熔池自由表面三维形貌的新方法。通过分析建立熔池自由表面反射成像激光点与投射激光点之间的映射模型,提出基于投射激光点更新的熔池自由表面三维恢复算法。重建连续钨级惰性气体保护焊(Tungsten inert gas arc welding,TIG)熔池自由表面三维形貌,提取其宽度和高度尺寸,并与实际测量结果进行对比。结果表明,点阵激光测量法不仅有效避免弧光干扰实现了熔池自由表面的动态测量,而且重建的熔池自由表面三维形貌几何尺寸变化与实测结果吻合较好,宽度和高度误差分别为1.73%,2.32%,为更好地研究TIG焊熔池自由表面行为演化规律提供一种新方法。     

高精度平面检测技术及在发动机制造中的应用

高精度平面检测技术主要应用于测量平面的平面度、表面波纹度。利用激光反射后的干涉波携带有被测表面高度信息,将干涉图像进行转换生成3D高度图来表示被测零件的表面状态。本文主要介绍高精密平面检测技术在发动机制造过程中的应用。     

非球面补偿板三维面形检测方法的研究

本文对准直激光束检测非球面方法进行了研究。它不用接触被检件表面,同时也无须处理干涉条纹。测量时只要保证激光细束保持一致的入射方向扫描被检表面,用CCD光电探测器检出面形的斜率变化,而后在扫描范围内积分便能获得面形高度。本文以测量光学系统中用于波面补偿目的的旋转对称镜面为例对测量系统进行分析。该系统不仅可以进行一维测量,通过转台旋转亦可进行二维测量,通过面形重构获得三维的被测体面形。给出了三维面形重构方法,并编制数据处理软件,可以把测量数据处理成高度曲线或三维面形。     

非球面补偿板三维面形检测方法的研究

本文对准直激光束检测非球面方法进行了研究。它不用接触被检件表面,同时也无须处理干涉条纹。测量时只要保证激光细束保持一致的入射方向扫描被检表面,用CCD光电探测器检出面形的斜率变化,而后在扫描范围内积分便能获得面形高度。本文以测量光学系统中用于波面补偿目的的旋转对称镜面为例对测量系统进行分析。该系统不仅可以进行一维测量,通过转台旋转亦可进行二维测量,通过面形重构获得三维的被测体面形。给出了三维面形重构方法,并编制数据处理软件,可以把测量数据处理成高度曲线或三维面形。     

电驱动微流体粒子图像测试系统

为了研究微米量级管道机械特性对小雷诺数流体运动传质机理的影响,建立了电驱动微流体粒子图像测试系统,系统包括倒置荧光显微镜、致冷图像传感器、微流体驱动高压电源及微流场位移矢量识别算法.通过实验测试及理论分析给出了系统的关键技术参数;通过测量示踪粒子表面电荷特性,以消除粒子电泳运动对电驱动流体PIV方法产生的测量偏差;测量了水力直径为30μm微管道中电渗流场,测量结果与理论分析的塞状流型一致;分析了布朗运动、粒子电泳运动以及相关算法误差,对粒子图像测速方法不确定度的影响.     

光栅衍射法测量材料平面度和平行度

一、材料表面形状的测量方法材料表面形状轮廓的测定是光学干涉计量的一个基本应用。对于不同的料材和生产加工过程中的不同要求,测量方法也各不相同,基本上可以分成两大类,一类是利用传统的干涉仪;另一类是近期发展起来的,以全息技术为基础的全息干涉度量技术。我们要测量材料表面的形状,基本思想就是用一个已知形状的标准波面去和被测材料表面形状(形变后的波面)进行比较,从而获得材料表面形状的信息。如果被测表面是平面,那么标准波面通常选用平面波。两个波面的比较是通过干涉来进行的,得到的等厚干涉条纹就是物体表面和一组等间距的平面波相截得到的     

TIG焊熔池表面流动行为的研究

针对钨极惰性气体保护(Tungsten inert gas,TIG)焊熔池表面流动行为,在确定TIG焊熔池表面可采用粒子示踪的方法来进行其表面流动行为示踪的基础上,在以激光为试验背光光源,通过激光在TIG焊熔池表面镜面反射后,使得熔池及示踪粒子清晰成像于成像屏上。在此基础上,开展对304不锈钢和Q235普通碳钢的熔池表面流动行为的试验研究,对所获得这两种材料的TIG焊熔池试验数据进行处理与对比分析,探究熔池表面流动规律。研究结果表明:在TIG焊过程中,其焊接熔池存在两种运动模式,在304不锈钢焊接过程中熔池表面的液态金属由边缘向熔池中心流动;在Q235碳钢焊接过程中熔池表面的液态金属不定向、不规则地由熔池中心向熔池边缘流动,并测量304不锈钢TIG焊过程中熔池表面的液态金属流动速率为12 mm/s左右,Q235碳钢的熔池表面的流动速率为15 mm/s左右。     

目标激光反射率测试方法研究

反射率的测量可分为两种方法绝对测量法(直接测量法)和相对测量法(比较测量法).当被测反射功率与入射功率相比时,则为绝对测量;先测出被测目标的反射功率和已知反射率的标准反射板的反射功率,再用其比乘以已知的标准反射板的反射率,就可以得到被测目标的反射率,这种测量的方法称为相对测量.本文论述了一种采用相对测量反射率测试方法,用于激光反射率的测量,并对测量进行了分析.     

高精度三维物体轮廓测量系统

西安交通大学精密工程研究所研制成功的高精度三维物体轮廓测量系统 ,不久前通过了由陕西省科技厅组织并主持的科技成果鉴定。高精度三维物体轮廓测量系统是以三角测量原理为基础 ,通过出射点、投影点和成像点三者之间的几何成像关系来确定被测物体轮廓各点的高度信息。具体方法是将一线结构光源 (光刀 )投射到被测物体表面 ,由两个对称分布的 CCD摄像机从不同角度获取光刀图像 ,通过图像处理和数据处理的方法得到整个被测表面各点的三维坐标 ,最终将此数据信息形成标准的 CAD/CMA数据文件 ,为产品的进一步设计、开发及数控加工成快速成…     

相干计量技术评述

综述了相干计量技术在测长、光学波面误差检测、表面粗糙度测量中的应用,目前的状况及未来的发展趋势。     

Exploiting the orbital motion of water particles for energy extraction from waves

In wave motion, the water particles are known to follow orbital paths. This orbital motion was used to drive five-bladed Savonius rotors. Experiments were performed on an array of four rotors placed in a two-dimensional (2-D) wave channel. The flow around the rotors was documented using particle image velocimetry measurements. The submergence of the rotors and the distance between them were varied, and the rotational speeds of the rotors (N_n) were recorded at different wave frequencies. It was found that rotational speeds increased with an increase in the wave frequency, as it amplified the wave height that increased the kinetic energy of the particles in their orbital motion. The rotational speeds decreased when the distance between the rotors increased. High rotational speeds are recorded when the array of the rotors is placed close to the water surface at the smallest centre-to-centre distance between the rotors.     

一种毫米波天线反射面板精密成形的数值模拟

天线反射面板的成形方法对面板精度有着重要的影响。根据具有大面积、主动反射面的毫米波天线对面板的成形要求,提出了一种基于高精度模具、蒙皮开缝、真空负压和胶粘背筋的成形方法。建立了该成形过程的有限元模型,并利用接触算法实现了该过程的数值仿真。研究发现蒙皮开缝后能有效降低蒙皮内的应力水平。面板回弹引起背筋的不均匀变形是面板成形误差产生的主因。分析了面板形面曲率、蒙皮开缝长度和背筋高度等面板结构参数对面板成形精度的影响规律,为合理设计该工艺过程和提高面板的成形质量提供了重要依据。     

A non-invasive airborne wave monitor

This work presents a new acoustical method for remote measurement of the surface characteristics of the dynamic air–water interface in turbulent free-surface flows. The technique uses the reflection of a monochromatic ultrasonic wave by the dynamically rough air–water interface to measure the water surface position. It is found that with careful selection of the acoustical components and their configuration, the phase of the reflected signal responds to the local fluctuations in the fluid interface at the point of specular acoustic reflection. In order for the method to be applicable, three criteria must be satisfied: (1) the dominant wavelength of the surface under investigation must be greater than the first Fresnel zone corresponding to the wavelength and component geometry of the acoustical system; (2) the mean magnitude of the instantaneous local surface gradient must not exceed 0.025; and (3) the root-mean-square wave height must be greater than 1% of the acoustic wavelength. Under these conditions the mean error of the system is within 5% (and usually within 1%) of the acoustic wavelength, and is generally within 10% of the wave amplitude for turbulence generated waves, and 3% of the amplitude for gravity waves. This error may be reduced by optimising the acoustic wavelength for the surface of interest. For turbulent depth limited flows, the surface waves fall well within the criteria, and the absolute errors are independent of wave height, so for larger wave heights, the relative error can be considerably lower. The technique provides a robust system for monitoring the dynamics of free surface flows, which is non-invasive, low cost, and low power. The method has been tested on laboratory flows but should be applicable to remote sensing of free surface properties on a local scale in field environments where invasive techniques are difficult to implement such as might be found in coastal, river and wastewater environments.     

Some features of echo signals of longitudinal waves from flat-bottom reflectors in the far-field zone of a normal transceiver

Features of reflection of longitudinal elastic waves from flat rectangular, elliptic, and segmental reflectors (flaws) placed in the far-field zone of a normal transceiver are investigated for continuous (quasi-monochromatic) and pulsed transmission-reception modes. It is shown that, as the dimensions of the reflector increase, the echo-signal amplitude oscillates and approaches a value determined by the limiting shape of this type of reflector. It has been established that, for the reflector models considered, the character of an echo signal is determined by the value of the generalized parameter depending on the distance to the reflectors, their characteristic dimensions, and the wave number of the acoustic wave.     

The measurement of discharge using a commercial digital video camera in irrigation canals

This paper presents measurements of the discharge by image techniques on the surface velocity field and water stage in irrigation canals. The velocity and stage gauge are obtained from a commercial digital video camera. The time series of the surface velocity and stage were collected simultaneously. Particle image velocimetry (PIV) was used to determine the surface velocities in the irrigation canal. PIV proceeds by using bubbles floating on the water surface as tracer particles, and making a cross-correlation analysis between two continuous images. The whole surface velocity distribution in the irrigation canals can be obtained. The water stage of the canal is obtained from the digital video camera images by making use of image segments to separate the stage gauge and the background. The discharge is computed by using the surface velocities and water stage via open channel velocity distribution theory. Comparing the discharge measured using image techniques with Parshall flume data shows that the differences are less then 5%. The results suggest that the image measurement techniques developed can be used in applications to estimate the discharge in irrigation canals effectively.     

双摄像机双光源视线追踪系统标定方法研究

针对现有平面镜反射标定方法的不足,提出了一种基于多摄像机全局标定的视线追踪系统标定方法.通过在屏幕对面放置一对标定摄像机与系统摄像机构成多摄像机系统,标定摄像机直接拍摄标定目标,测量系统摄像机、光源和屏幕之间的空间位置关系.通过多摄像机全局标定确定系统摄像机和标定摄像机的坐标转换关系.通过坐标转换最终标定出系统摄像机坐标系中摄像机、光源、屏幕的空间位置关系.该方法解决了屏幕和光源不在系统摄像机视野范围内的问题,减小了图像误差.系统标定结果验证了该方法的有效性,同时为其他同类系统标定提供了一种解决问题的思路.     

On the calculation of characteristics of echo signals of transverse and longitudinal waves from reflectors with flat surfaces

On the basis of an earlier developed model on scattering of transverse waves at a crack in the form of a strip, exact and approximate (estimated) scattering indicatrices for transverse and longitudinal elastic waves are studied, taking into account the influence of their transformation at the flat free surface of a reflector into other wave types on the change in the echo-signal amplitude. The limits of applicability of the estimated indicatrices for mirror and back reflections are numerically studied. The exact results for longitudinal waves are compared to those obtained by the Kirchhoff method.     

Numerical simulation of bubble resonance in an acoustic field

The resonant motion of a compressible bubble in an acoustic field is numerically investigated by using a level-set method, which is extended to examine compressible two-phase flows of air and weakly compressible liquid water. Computations are performed for bubble motion on a solid surface that is exposed to a periodic pressure wave. Numerical results show that the resonant bubble motion is significantly magnified by the surrounding compressible liquid when a specific height is reached. The effects of liquid height, contact angle, and bubble size on the oscillation amplitudes of bubble radius and pressure are quantified.     

波高传感器的数学模型

通过对波高传感器的实验测试和研究,建立了波高传感器的输出电压与水深及水温的数学模型。这个数学模型,适宜于波浪高度的数据采集,可以提高波高传感器的测试精度。