发光光弹性涂层荧光信号强度的影响因素

为提高发光光弹性涂层方法中涂层的荧光信号强度,以液态E-44型环氧树脂为光弹性材料、罗丹明B为荧光染料,制作了新、旧两种不同结构的发光光弹性涂层.通过对新、旧两种结构发光光弹性涂层受465nm光波激发时荧光发射光谱的比较,说明新的发光光弹性涂层结构比原有发光光弹性涂层在提高测量信号强度方面的优势,测量结果还表明:发光光弹性涂层测量信号的强度提高还与合理选择涂层中荧光染料浓度、荧光信号发射波长有直接关系.     

用于冲击波和爆轰物理实验中的声光开关

针对冲击波和爆轰物理实验中对光开关的使用要求,提出了一种基于布拉格衍射效应的行波式声光开关,得到了声光开关的开关波形、消光比、抗激光损伤特性及能量利用率等。结果表明,与传统的普克尔电光开关相比,声光开关有效地消除了开关光信号顶部的振铃现象,消光比达到5000∶1,同时减小了开关体积、提高了开关工作稳定性。声光晶体抗激光损伤阈值大于2.26 kW/cm2,开关能量利用率达70％。开关触发固有延迟和上升沿时间分别为900和440 ns,满足测试系统对开关同步性的要求。另外开关光信号宽度可由触发信号任意调节,能满足不同测试情况的需要。     

小比距离密闭空腔爆炸爆后气体温度和压力测量技术研究

为实现空腔爆炸温度、压力变化趋势的准确测量，基于铠装K型热电偶和压力变送器，建立密闭空腔爆后气体温度、压力测量系统。设计密封隔热防护装置，将传感器的敏感端与信号调理模块分别安装在两个密封腔内，有效提高了传感器在大当量爆炸冲击条件下的存活率。在0.86 m/kg1/3比距离密闭空腔大当量爆炸条件下，对传感器及防护装置的性能进行考核验证，爆后测量采集到了有效的气体温度及压力变化历程，且传感器状态能够最终恢复至正常状态。测试结果表明，使用密封隔热安装的K型热电偶和压力变送器可以满足小比距离密闭空腔爆后气体静态温度、压力测量需求。     

黑火药烟雾浓度对激光透过率影响的实验研究

利用烟箱法测量532、1550nm激光在不同黑火药烟雾浓度下的透过率,结合朗伯-比尔定律,得到黑火药烟雾浓度对532、1550nm激光透过率影响的定量关系。实验表明,532nm和1550nm激光的透过率随着黑火药烟雾浓度的增加而指数衰减,1550nm激光的透过率明显高于532nm激光的透过率。     

光力学多波长法的研究

1.引言识别条纹级数的问题是全息光弹性、全息干涉位移测量和散斑干涉技术等光力学方法中一个共同的重要问题.在五十多年以前,Coker和Filon对光弹性的权威贡献中广泛地使用了白光.十几年以后Frocht曾描述过作为决定分数级条纹的“彩色匹配”的概念.在普通光弹性中白光用作识别等差线零级条纹和辨别最大及最小条纹级次,以及识别脊部以便确定条纹的增减.由于白光光源是连续光谱,条纹可以由任何的“补充色”定义.在偏振仪暗场情况下条纹的色序近似是浅黄、黄、红、兰、绿.一定数值的程差对应着一定的颜色,受力模型上程差为零的点对所有不同波长的光消光,零级条纹的颜色永为黑色.但当程差继续增加时,到一定数值将出现消光重叠现象,因此     

高速流动激光器的稳定振荡条件、模式结构与输出功率特性

1.高速流动激光器的稳定振荡条件与GDL输出功率表达式 假定介质沿x方向流动(图1),两块平面反射镜M_1,M_2也沿x方向放置,光轴平行于z轴而垂直于流动方向。激励区位于坐标原点上游。当气体到达光腔的上游边界x=0时,在气体中产生了     

CPT磁力仪暗态耦合磁场测量技术

相干粒子数俘获(CPT)磁力仪是通过精确追踪光与原子相互作用下获得的透射信号来计算磁场强度的。针对由于透射信号的方向性衰减特性而造成的系统测量盲区的问题,提出了一种暗态耦合测量方案,通过使用特定频率的调制光场来实现多个暗态的同时激发和耦合测量,基于原子密度矩阵法建立了原子五能级系统模型并进行数值仿真研究,分析了该方案的控制条件和特点。实验结果证明,使用暗态耦合测量技术获得的透射信号幅值可以达到相同条件下单暗态测量时信号幅值的两倍左右,能够有效消除测量盲区,提高透射信号的信噪比,从而进一步提高CPT磁力仪的测量灵敏度。     

钻孔爆破过程中顺倾边坡软弱夹层的运动力学模型

针对顺倾边坡爆破时爆轰气体冲刷、压密软弱夹层而形成爆腔从而影响边坡稳定的问题,应用爆轰流体动力学和气液两相流理论,分析了在钻孔爆破过程中软弱夹层在爆轰气体作用下的压密和推移机理,建立了爆破过程中软弱夹层的运动力学模型,导出了爆腔在爆轰气体作用下的运动速度、最终半径和扩腔时间同装药参数和软弱夹层力学参数的定量关系。将该运动力学模型应用于两个典型实例的爆腔计算中,计算值与实测值的相对误差仅为4%左右,软弱夹层的运动速度随距炮孔中心距离的关系曲线也与试验曲线变化规律一致。     

激光多普勒测速技术讲座(三)——多普勒信号的分析处理

一、多普勒信号的产生、变换和频谱 现以双光束差动模式光路为例,说明多普勒信号的产生及变换过程。在两根光束的相交部位——测量体中,根据条纹模型的解释,存在明暗相间的干涉条纹。所用激光束是高斯光     

激光散射,透射消光方法应用于测量同质核化率的实验研究

应用激光散射方法和透射消光方法，对戊醇在２５０Ｋ、１．０ｂａｒ状态附近同质核化凝结过程中微滴浓度和尺度进行了测算，并根据脉冲成核时间长短确定了戊醇同质核化率大小。实验结果表明：戊醇在携带气体—氦气中，在２５０Ｋ、１．０ｂａｒ附近的同质核化率范围为１．６０３×１０１５～６．６４５×１０１５ｍ－３ｓ－１，相应的饱和比范围为１３．０４～２０．７６。     

Simulation on spread of fire smoke in the elevator shaft for a high-rise building

Spread of fire smoke in the elevator shaft of a high-rise building is influenced by many driving facts. We simulate smoke spreading in the elevator shaft, stair room, and pre-chamber with and without different supplied pressurized air. The simulation shows that smoke moves very fast in the elevator shaft. When a 12 floor high-rise building is in fire, smoke can fill up the elevator shaft in less than 1.5 min after a fire started, temperature in the elevator shaft can be higher than 187°C in 5 min, and the concentration of CO can also reach a high level. The elevator shaft has a very low visibility in less than about 100 s.     

载人航天器火灾安全研究进展

理论上和实际上, 载人航天器都有发生火灾的可能, 载人航天器的火灾安全问题是微重力燃烧研究的重要内容. 氧气浓度和气流速度对给定固体材料的可燃性具有显著影响,在固体表面的逆向和同向传播火焰中, 都存在由氧气浓度和气流速度决定的可燃极限, 即气流速度较高时的吹熄和气流速度较低时的冷熄. 极限氧气浓度和极限气流速度两个极限参数, 是衡量材料可燃性的关键指标. 在微重力条件下, 当低速气流存在时, 固体材料发生有焰燃烧和闷烧的可能性都大大增强. 因此, 剔除材料中的潜在燃料是航天器防火的主要措施.但是, 在航天器使用的材料中, 仅有很少一部分是阻燃的, 为了保证火灾安全, 还必须采取火灾检测和灭火措施. 当前美国和俄罗斯采取的火灾安全方案, 既有相似性, 也有各自的特点. 在载人航天器的火灾安全问题中, 尚有很多问题和方案有待研究或检验. 考虑到我国的实际情况, 作者认为, 通过实验对照和数值模拟的方法, 开展材料在微重力条件下的燃烧特性的常重力模拟, 对于我国载人航天器的火灾安全具有现实意义.      

Optimal seeding for long pathlength multi-component laser Doppler anemometers

There are optimal combinations of size and number density of seed particles which can maximize the processed data rate of laser Doppler anemometers (LDAs). When optical pathlengths are long, as in large scale water facilities, the choice and density of seeding particles determines the balance between the scattered-light intensity at a measuring volume and its extinction along the rest of the optical path, and so its intensity at a photodetector. These considerations must generally be coupled with knowledge of particle arrival statistics, detector performance, processor characteristics and signal conditioning to optimize data rate. However, in multicomponent LDAs, coincidence requirements in data arrival times enforce a close approximation to a Poisson distribution in the processed data rate as a function of the number density of seed particles. This result leads to simple models for optimal number densities for seeding as a function of optical pathlength and related parameters.     

Density-sensitive whole-field flow measurement by optical speckle photography

An optical whole-field, line-of-sight method is surveyed that allows the measurement of the refractive deflection angles of light transmitted through a flow with density changes. The method uses the principles of speckle photography. In comparison to classical optical methods such as interferometry, a much higher number of data values can be obtained from one record without the need of interpolating between experimental data. This high signal density is particularly advantageous for analyzing turbulent flows with density fluctuations. Such an analysis is, so far, restricted to the existence of axisymmetric turbulence. A number of applications to this type of turbulent flow are reported, and proposals are made for future developments that will allow this speckle technique to be applied to the study of turbulent shear flow.     

Optical measurement of velocity and drag coefficient of droplets accelerated by shock waves

The drag coefficient of micron-sized droplets accelerated by a shock wave has been investigated. The motion of the droplets was studied by an optical measurement system, and an inertial relaxation in the mist flow is discussed in detail. An expansion-shock tube was employed in the present experiment, in which water droplets were produced by a homogeneous condensation when humid nitrogen gas expanded adiabatically in the test section. The local mean diameter and local number density of the droplet cloud were 1.0 m and on the order of 10¹² particles/m³, respectively, as estimated using a light scattering measurement in a preliminary experiment. The droplet cloud accelerated behind a shock wave was observed using a direct shadowgraph method with a spatial filter. Since the intensity of transmitted light through the mist flow is a function of the radius and number density of droplets, we can obtain the locally averaged number density distribution under an adequate approximation. The transmitted light intensity was related to the velocity distribution of droplets under the adequate assumption. So, the acceleration of droplets was estimated from the velocity ratio between the droplets and gas flow. Then, the drag coefficient was calculated for the particle Reynolds number. The experimental result was also compared to a numerical prediction.     

Global modelling of heat release during initiation and propagation of detonation and deflagration waves in methane-air-particle systems

In the present paper the direct initiation of a self supporting detonation and propagation of a low-speed combustion in methane-air-coal particles mixtures are solved. For particles, a heterogeneous regime of combustion is used, for methane one overall chemical reaction is taken into account: CH + 2O = CO + 2HO. The heat release rate is assumed to be defined as a delay time based on the well-known thermal theory of Frank-Kamenetsky (1967). The proposed model allows one to investigate the influence inert particles or coal dust on the explosion limits of methane-air mixtures. It is shown that the addition of a limited quantity of particles leads to detonation stability. In low speed combustion problems this method allows one to get a good correlation between theoretical and experimental velocities of steady flame propagation in carbon-hydrogen gaseous mixtures. Coal dust influence on gasdynamics of a methane-air mixture combustion is investigated in an unsteady problem by using of the global modelling. It is shown that limited coal dust concentration increases the flame wave intensity in lean methane-air mixtures in contrast to inert particles. In stoichiometric gas mixtures, sand and coal dusts decrease a flame velocity. Far from the ignition point flame, the velocity is largely defined by the dust mass concentration and not by the size of particles. Received 5 July 1997 / Accepted 13 July 1998     

A laser extinction based sensor for simultaneous droplet size and vapor measurement

Multiphase flows involving liquid droplets in association with gas flow occur in many industrial and scientific applications. Recent work has demonstrated the feasibility of using optical techniques based on laser extinction to simultaneously measure vapor concentration and temperature and droplet size and loading. This work introduces the theoretical background for the optimal design of such laser extinction techniques, termed WMLE (wavelength-multiplexed laser extinction). This paper focuses on the development of WMLE and presents a systematic methodology to guide the selection of suitable wavelengths and optimize the performance of WMLE for specific applications. WMLE utilizing wavelengths from 0.5 to 10 μm is illustrated for droplet size and vapor concentration measurements in an example of water spray, and is found to enable unique and sensitive Sauter mean diameter measurement in the range of ～1–15 μm along with accurate vapor detection. A vapor detection strategy based on differential absorption is developed to extend accurate measurement to a significantly wider range of droplet loading and vapor concentration as compared to strategies based on direct fixed-wavelength absorption. Expected performance of the sensor is modeled for an evaporating spray. This work is expected to lay the groundwork for implementing optical sensors based on WMLE in a variety of research and industrial applications involving multi-phase flows.     

圆盘离心沉降法测定固体粉末的粒度分布

本文报道用圆盘离心沉降法对几种粉末样品的粒径大小及粒度分布测定的结果,并且讨论了颗粒形状、消光系数和粉末分散状态等因素的影响。试验结果表明,在给定的条件下,利用LKY-1型微粒测定仪对粉末粒度测定的重复性好,尤其适用于测定微细粉末的粒度分布;当石墨或MoS_2粉末样品的浓度为0.5％时,选用4％鞣酸作分散剂的效果最好。作者认为,固然光密度与微粒的消光系数有关,但对于黑灰色的粉末样品而言,因其产生的光学效应非常微弱,故可近似地把消光系数视为常数而忽略它的影响。     

A new application of differential interferometry for stress analysis

In the past, differential interferometry has found interesting applications in gas dynamics. The gradients of density could be measured in gas flows. Now, a first trial is made to extend this method to the experimental treatment of stress problems. A Wollaston prism with polarizing elements is used in the optical arrangement. This prism combines two beams of light which have penetrated the model at locally separated points. A field of interference fringes can be produced behind the Wollaston prism. The deflections of the different conjugated light beams, which are caused by the deformed elements of the model, lead to a shifting of the interference fringes. A Stress Differential-interferometer Law is derived theoretically in order to interpret the optical data According to this theory, the optical effect caused by the deflection in this arrangement is proportional to the gradient of the sum of principal stresses. A calibration test is performed by using a circular disk, this method is applied to a circular ring for measuring the stress gradients. Under special conditions, interference fringes could be produced which represent the loci of equal stress gradient. Plexiglas plane models are loaded diametrically by single loads. The experimental results verify the statements of the developed theory.     

一种爆炸二极管机理研究及熄爆通道尺寸对其性能的影响

依据爆炸逻辑元件的工作原理设计了一种爆炸二极管。实验研究了元件内部结构,确定了关键参数为熄爆通道的长度、隔爆序列。隔爆序列内采用激发装置、一次PETN装药、两次PETN装药不同密度分层装药序列。在A、B端连接导爆索,改变熄爆通道尺寸, 确定分层装药参数,进行传爆可靠性、隔爆安全性实验。结果表明:爆轰信号由A端正向输入时,可以顺利通过10~35 mm的熄爆通道并且可靠引爆B端导爆索,满足可靠性功能;爆轰信号由B端反向输入,在熄爆通道长度为15~35 mm时,爆轰信号在通过隔爆序列、熄爆通道时被可靠阻断无法引爆A端导爆索,满足隔爆安全性功能。最终元件选取长度为15~35 mm的熄爆通道, 确定不同密度分层装药参数作为设计标准。应用于爆破网络设计中,使爆轰波信号在网络中单向传播,增加了网络的安全性。