共查询到18条相似文献,搜索用时 686 毫秒
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提出了一种测量汽轮机叶片动态扭转变形的新方法──激光截线法.利用He—Ne激光截线长的变化对叶片扭转恢复角进行动态测量,其精度可达到和高于激光超高速摄影测量法 相似文献
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黄桂平 《航空精密制造技术》2009,45(4)
几何量大尺寸测量主要指"几米至几百米范围内物体的空间位置、尺寸、形状、运动轨迹等的测量"[1].目前可以实现大尺寸三维坐标测量的方法和系统按照所使用的主要传感器可以分为经纬仪测量系统、激光跟踪测量系统、激光扫描测量系统、关节式坐标测量机和数字近景摄影测量系统等[2]. 相似文献
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PIV技术在复杂二相流场中的应用 总被引:2,自引:0,他引:2
光学元器件随飞行器在大气中飞行时,其工作性能越来越多地受到大气悬浮汇聚微粒的影响。大气微粒在复杂流场中呈现何种运动汇聚效应,对于合理准确评估机载光学元器件的工作效能具有十分重要的工程意义,而复杂气动流场中微粒分布状态的预估一直是飞行器外界环境研究中的一个难点。气动问题的复杂性、大气中微粒的多样性一直是制约各种试验手段展开、数值模型建立的主要因素。利用先进的激光粒子图像技术,在风洞中对舵面旋涡主导的复杂流场中的微粒速度及分布特性进行了实验研究。在测量舵面翼梢脱落旋涡特性的基础上,通过激光片光扫描流场全域,同时高帧频CCD相机同步曝光,利用PIV 拍摄到的流场中涡流截面内微粒分布的瞬态图像。结合图像后处理技术,对原始粒子图像进行互相关、二值化处理,通过对图像区域内的灰度值计算,统计相对流场截面内的粒子浓度系数,得到在复杂旋涡结构流场内瞬态粒子的分布特性规律。研究结果表明,利用大气中微粒在激光片光下的米氏散射原理,可以有效地拍摄到复杂流场结构下粒子光学散射及分布的特性图像,解决了传统环境测试设备无法对复杂条件下流场内粒子分布进行实时测量的缺陷;在旋涡为主导的流场中,大气中的微粒由向心力牵引,在涡核周围达到平衡运动状态,微粒环绕涡核形成一条环状带,这一区域中的粒子浓度系数要远大于自由流场中的微粒,涡核中心粒子呈“空洞”状态。 相似文献
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激光清洗微电子器件制造中最令人头痛的是有机物和微粒污染。对于亚微米尺度的半导体器件来说,其失效缺陷是微粒污染造成的。加工中,灰尘直径只及器件最小几何尺寸的1/3至1/10就能造成器件失效。传统的超声清洗和强声清洗对微米级及更小尺寸的微粒越来越无能为力了。目前正在研究开发以下几种激光清面:①微粒或表面吸收激光能量后,热扩散产生的力使微粒离开表面;②激光能量被微粒周围和下面的转移介质(例如,少量的水)吸收,导致介质爆炸性汽化,把微粒推离材料表面;③激光能量被基体材料吸收,然后把吸附的转移介质加热,产生爆炸性汽化。初步试验表明,这些激光辅助去除微粒(LAPR)的方法是有效的,使半导体器件生产成品率的提高有了光明的前景。上述清洗方法同样适用于要求特别严格的光学器件表面。 相似文献
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一、前言二十余年来,我国靶场光电跟踪测量设备——以光电经纬仪为主要代表,已经发展到第四代。今天的光电经纬仪,除了具备摄影这一基本测量记录手段外,通常还具有电视跟踪测量、红外跟踪测量、激光跟踪测量及激光测距等技术。测角、测距精度,自动跟踪性能及仪器自动化程度日趋提高完善,并广泛采用微机来提高整机及各分系统的性能,与国外近年来发展的同类产品相比,性能相差无几。与此同时,由于抗电子干扰的需要,我国也开始发展光电火控系统,光电制导系统。尽 相似文献
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《Aerospace Science and Technology》2007,11(1):33-38
Two different approaches are used in this work to reduce the burning times of aluminium particles with the ultimate goal to improve the performances of solid propellants. One method is to coat the micro-sized particles by nickel, and the second is to decrease the particle sizes to nano-metric scales.A thin coating of Ni on the surface of Al particles can prevent their agglomeration and at the same time facilitates their ignition, thus increasing the efficiency of aluminized propellants. In this work, ignition and burning of single Ni-coated Al particles are investigated using an electrodynamic levitation setup and laser heating of the particles. The levitation experiments are used to measure the particle ignition delay time and burning time at different Ni contents in the particles.Decreasing the size of Al particles increases their specific surface, and hence decreases the burning time of the same mass of particles. In this investigation, a cloud of Al nano-particles formed in a combustion tube is ignited by an electric spark. The cloud experiments are used to measure comparative flame front propagation velocities for different Al particle sizes with and without organic coating.The results and their analysis show that both methods reduce the Al burning time. Ni coating reduces significantly the ignition time of micro-sized Al particles and hence the total burning time compared to non-coated particles. Nano-sized particle clouds burn faster than micro-sized Al particle clouds. 相似文献
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提出了一种基于低密度粒子图像的微流体粒子图像全场测速技术。经过背景噪声去除、阈值过滤、图像增强等图像预处理过程,获得了高质量的低密度荧光示踪粒子图像。对100对图像进行图像叠加处理,得到了满足互相关算法求解二维速度场的高密度叠加粒子图像。针对宽度为250μm,深60μm的长直微通道开展了覆盖全场不同流体层平面的二维速度测量,并利用多个流体平面的二维速度场实现了微通道内全场速度的构建。研究结果表明:由于图像叠加法去除了像径大但灰度低的背景粒子图像,采用互相关分析能够准确获得分层二维速度场,所构建的全场速度场正确反映了长直微通道内流流场特征。 相似文献
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Martin Walt 《Space Science Reviews》1971,12(4):446-485
Small fluctuations in magnetospheric electric and magnetic fields lead to random changes in the radial positions of trapped
particles. The characteristics of this radial diffusion are described theoretically in terms of the statistical properties
of the field fluctuations, in particular the power spectra of the various spatial components. A large body of trapped particle
data demonstrates that diffusion with the predicted properties actually takes place. These data include the average radial
and energy distributions and the time variations in particle fluxes. This radial diffusion has a major influence on the structure
of the radiation belts; and since the net flow of particles is inward at most positions of the magnetosphere, the process
acts as a strong source of trapped particles. Further experiments are needed to establish the importance of this mechanism
relative to magnetic storm effects and to collective instabilities. 相似文献
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F. Arnold 《Space Science Reviews》2006,125(1-4):169-186
A physical mechanism which may have a potential to connect climate with cosmic rays (CR) involves aerosol particle formation
by CR generated atmospheric ions followed by new particle growth. Only grown particles can scatter sunlight efficiently and
can eventually act as cloud condensation nuclei (CCN) and thereby may influence climate. Moreover grown particles live longer
as they are less rapidly scavenged by pre-existing larger particles. The present paper discusses aerosol particle formation
and growth in the light of new measurements recently made by our MPIK Heidelberg group. Emphasis is placed upon the upper
troposphere where very low temperatures tend to facilitate new particle formation by nucleation. The new measurements include:
laboratory measurements of cluster ions, aircraft measurements of ambient atmospheric ions, and atmospheric measurements of
the powerful nucleating gas H2SO4 and its precursor SO2. The discussion also addresses model simulations of aerosol formation and growth. It is concluded that in the upper troposphere
new aerosol formation by CR generated ions is a frequent process with relatively large rates. However new particle formation
by homogeneous nucleation (HONU) which is not related to CR also seems to be efficient. The bottleneck in the formation of
upper troposphere aerosol particles with sizes sufficiently large to be climate relevant is not nucleation but growth of small
particles. Our recent upper troposphere SO2 measurements suggest that particle growth by gaseous sulphuric acid condensation is at least occasionally efficient. If so
CR mediated formation of CCN sized particles should at least occasionally be operative in the upper troposphere. 相似文献
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Frank Arnold 《Space Science Reviews》2008,137(1-4):225-239
This paper discusses atmospheric ions and their role in aerosol formation. Emphasis is placed upon the upper troposphere where very low temperatures tend to facilitate new particle formation by nucleation. New measurements addressed include: Laboratory measurements of cluster ions, aircraft measurements of ambient atmospheric ions, atmospheric measurements of the powerful nucleating gas H2SO4 and its gaseous precursor SO2. The paper also discusses model simulations of aerosol formation and growth. It is concluded that in the upper troposphere new aerosol formation via ions is a frequent process with relatively large rates. However new particle formation by homogeneous nucleation which does not involve ions also seems to be efficient. The bottleneck in the formation of upper troposphere aerosol particles with sizes sufficiently large to be climate relevant is mostly not nucleation but sufficient growth of new and still very small particles. Our recent upper troposphere SO2 measurements suggest that particle growth by gaseous sulphuric acid condensation can be efficient in certain circumstances. If so, cosmic ray mediated formation of CCN sized particles should at least occasionally be operative in the upper troposphere. 相似文献