周期光照下液晶弹性体简支梁的振动响应研究

液晶弹性体(LCE)因其具有快速的光热响应和可逆变形等特性,在能量转换、软机器人和非接触控制等领域具有广泛的应用前景。本文利用液晶弹性体在外部光刺激下可与机械变形耦合的特性,建立了LCE简支梁的动态模型,研究了其在周期光照下的弯曲振动现象。首先建立了LCE简支梁的光驱动控制方程,然后通过振型叠加法获得方程的半解析解,再用Matlab软件编程计算其变化规律。计算结果表明,周期光照可以使LCE简支梁发生周期性振动,梁跨中的振动幅值可以通过阻尼因子、热弛豫时间、光照强度、光照周期和光照时间率来调节,振动平衡位置可以通过光强与热弛豫时间来调节,振动反应时间可以通过热弛豫时间与阻尼来调节。本文结果对光驱动运动的控制和光机能量转换系统的设计具有一定的指导意义。     

A new technique for the determination of stress-optical constants using the shadow spot method

A new technique has been developed to determine both the transmitted and the reflected stress-optical constants. The reflected optical constant is associated with the light reflected from the rear face of a transparent material. The stress-optical constant related to the light reflected from the front surface is not considered in this paper since it is equal to Poisson's ratio divided by Young's modulus. In this new method, a monochromatic light beam emitted from a He–Ne laser impinges on the area surrounding a circular hole under load in a plate. A digital image-analysis system, EYE-COM III, is used to determine the points of the highest light intensity of the caustic that results from the light transmitted or reflected from the rear face of the plate. The effect of the hole size in optically isotropic materials is investigated.Paper was presented at the 1988 SEM Spring Conference on Experimental Mechanics held in Portland, OR on June 5–10.     

New technique for high-speed microjet breakup analysis

In this paper we introduce a new technique for visualizing the breakup of thin high-speed liquid jets. Focused light of a He–Ne laser is coupled into a water jet, which behaves as a cylindrical waveguide until the point where the amplitude of surface waves is large enough to scatter out the light from the jet. Observing the jet from a direction perpendicular to its axis, the light that appears indicates the location of breakup. Real-time examination and also statistical analysis of the jet disruption is possible with this method. A ray tracing method was developed to demonstrate the light scattering process.     

一种描述非偏振光的矩阵方法及其应用

本文根据完全消偏振光的性质,提出了一种描述完全消偏振光的矩阵方法,并从理论上证明了这种列矩阵也可用来表示完全非偏振光,从而能够应用统一的Jones矩阵方法来处理包括非偏振光在内的全息光弹性问题。     

A matrix method for describing unpolarized light and its applications

A matrix method for describing fully depolarized light is proposed. According to the properties of fully depolarized light it is proved theoretically that this column matrix (Jones vector) can be used to describe unpolarized light as well. Thus, it enables the problems of holographic photoelasticity, including holographic photoelasticity of unpolarized light, to be simply treated by using a unified matrix calculus (Jones calculus).     

Threshold excitation of photoabsorption convection

The article considers questions of the stability of the equilibrium states of a liquid which absorbs light. Threshold values are found for the intensity of the light in the problem of the stability of the equilibrium of a liquid in a square cavity with three thermally insulated walls. A steady-state integro-interpolation scheme is presented for the numerical calculation of problems of photoabsorption convection. The propagation of light waves in absorbing media is accompanied by the dissipation of radiant energy. In heavy liquids, absorption heating of a substance in the field of a wave may be the reason for the appearance of convection [1–3]. It is important to study the conditions for the appearance and the special characteristics of this type of convection, and its inverse effect on the structure of the light field. The first problem is important when the light beams are regarded only as a source of convection [4], and the second in questions of the directed propagation of light [5] and of self-focusing phenomena [2, 3, 6–10]. For high-energy heat fluxes and a liquid with a strong temperature dependence of its dielectric permeability, the convective self-stress will be very considerable; in this case, both problems are mutually interconnected. The excitation of convection by the absorption of light, without taking account of the inverse effect on the structure of the light beam, was studied numerically in [1, 4]. Equations for photoabsorption convection, taking account of convective self-stress in the Boussinesq approximation and of the geometry of the optics, were formulated in [11]. Several economical finite-difference schemes for solving problems of photoabsorption convection problems in rectangular cavities are discussed in [12]. The present article is devoted to an investigation of the threshold intensities of light for the excitation of photoabsorption convection. The existence of critical intensities of light, above which the mechanically equilibrium states of the liquids absorbing the light become unstable, was demonstrated in [1, 4].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 128–135, September–October, 1971.The authors thank A. V. Lykov for his continuing interest and aid, and G. I. Petrov and V. I. Polezhaev for their useful evaluation of the work.     

布里渊光纤陀螺增大动态范围新方案

针对布里渊光纤陀螺动态范围较小的问题,在比较了以往各种方案动态范围的基础上,提出了一种基于光强补偿的布里渊光纤陀螺动态范围增大方案.该方案使用大功率窄带激光器做泵浦源,在光路中引入光衰减器以及分光比不对称的耦合器,并通过反馈回路对两路光光强进行实时调节,从而可以消除泵浦游走效应对布里渊光纤陀螺动态范围的影响.通过分析和...     

应用梯度折射率透镜的光纤加速度计系统中的光功率耦合分析

研究了在光功率分布为高斯分布的情况下，光纤加速度计系统中光功率耦合的数学模型，并着重分析了几种情况下位移与光功率耦合之间的关系。通过对理论曲线的分析找出良好的线性区间，为该类加速度计的研制提供了科学依据。     

Throughput and coupling in optical fibers

Optical throughput, namely the product of area times subtending solid, is a useful concept in calculations of light coupling to optical fibers. It is invariant through an optical system, thus providing a simple and elegant way to derive the maximum coupling efficiency between a light source and a fiber, regardless of intervening optics. Because throughput is proportional to the number of modes supported by an optical structure, it also yields the distribution of modal power within a fiber.In this paper, we illustrate applications of throughput by calculating light coupling into fibers and mode distribution within.     

采用电子散斑干涉法对车灯配光镜内部缺陷问题的研究

在汽车车灯配光镜的生产过程中，由于用热压工艺而产生的热应力无法完全释放，积聚在其内部，产生不可见的细微缺陷。这些缺陷在一定的外界条件下扩展、生长，导致表面开裂、破碎，造成产品的报废。目前通常采用的有损检测方法虽然能够检测出缺陷的存在，但也破坏了车灯。为此，本文用采用电子散斑干涉法(ESPI)对车灯配光镜表面由于热应力而造成的变形以及细微裂纹缺陷的无损检测进行了实验研究，量化得到了配光镜表面在热载荷作用下的连续热变形分布。实验表明，用ESPI在热载荷的方式下可以成功地测量出配光镜缺陷的存在，并通过进一步研究，对同一型号但在残余应力分布上存在微小差异的两个车灯，我们给出了判别它们的定量标准。     

Experimental investigation of helicity in turbulent swirling jet using dual-plane dye laser PIV technique

This paper reports a new method of generating two light sheets using a dye laser system and the use of this dual-plane dye laser system to analyse average helicity and energy dissipation in a turbulent swirling flow. The dual-plane PIV system that was used in this study consisted of three cameras and a single frequency Nd:YAG laser, which was used to generate two parallel light sheet planes with differing wavelengths(colour). The method of generating two different light sheet wavelengths using a single laser source is an innovative and new technique. Stereoscopic PIV measurements were obtained in one plane with the use of two CCD cameras, and standard PIV measurements were obtained in the other plane with the use of one CCD camera. The light scattered by the particles on two different light sheets were separated using appropriate optical filters. The measurements obtained were used to estimate the components of the velocity gradient tensor. The tensor components were then used to determine the average vorticity components and helicity quantities of the fluid that was investigated. To determine the average turbulent kinetic energy dissipation, the continuity equation was used to infer the out-of-plane gradient of the out-of-plane velocity. From the analysis of the results, it was found that regions with high helicity were correlated with regions of high turbulent kinetic energy dissipation.     

Dynamic-stress concentration using photoelasticity and a laser light source

Since experimental techniques using dynamic photoelasticity are, in general, limited by suitably intense monochromatic light sources, it was of primary importance to describe a ruby-laser system which would completely remove this particular aspect of the problem. Modulation of the system, in this case by a Kerr cell, provides the necessary control of the light output such that a complete series of results can be obtained by putting together the results of many individual tests recorded on a conventional still camera. In this case, the dynamic-stress-concentration factor in a strut with a symmetrically located circular discontinuity was determined to establish definitely the potential of the system.     

基于空间光调制器获得空心光束的数值模拟和实验研究

光镊技术中,会聚的空心光束形成的能量光阱可用来捕获吸光性颗粒或操纵吸光性颗粒沿光轴方向运动。采用Gerchberg-Saxton(GS)算法计算所需相位,并将相位载入相位型空间光调制器来获得空心光束。为了提高会聚的空心光束能量,对空间光调制器相位屏进行预处理,叠加数字闪耀光栅位相,实现了将四个一级衍射谱闪耀至零级干涉极大位置,空心光束能量提高到原来的4.7倍。为了消除空间光调制器二维光栅结构所形成的零级谱亮斑以及高级谱的影响,在相位屏上加入球面波相位,使得空心光束衍射谱平面与零级谱平面的空间位置分离,并采用带通滤波器将空间光调制器的零级谱亮斑和高级谱滤掉。采用高度会聚透镜将所得空心光束会聚为微米尺寸,可应用于捕获吸光性颗粒。另外,利用离散傅立叶变换的平移原理实现空心光束实时平移,该方法可应用于实时操纵吸光性颗粒移动。     

井下巷道围岩变形的散斑分析法

通过对散斑计量法原理分析、数学描述及观测实例的论述，证明激光散斑法是研究煤矿地下结构物相似模型变形状态的一种新的无损检测技术，若采用白光作为光源，该项技术可用于二维变形场的实地测试。     

Measurements of admixture concentration fluctuations in a turbulent shear flow using an averaged Talbot image

The present study is concerned with adopting of a Talbot effect-based technique for analyzing flows with random phase inhomogeneities. It is shown that this method is a powerful tool for diagnostics of turbulent flows. The potential of the technique is illustrated by measuring mean and fluctuating values of admixture concentration of two-dimensional turbulent helium jet issuing into the ambient air. Averaged air and helium concentrations throughout the flow field are determined using local light refraction measurements with a high spatial resolution from a long-exposed Talbot image of the jet. The analysis of light intensity distributions in light spots of a Talbot-image shows that the jet turbulence is inhomogeneous and anisotropic. Quantitative information on rms fluctuations of concentration gradients throughout the flow field is obtained from local photometric measurements at the Talbot light spots.     

Sub-picosecond ballistic imaging of a liquid jet

A diesel jet visualisation based on an ultra-short light pulse and a time-resolved detection is proposed. An optical gate, consisting of a beta barium borate crystal, allows to separate ballistic, refractive and scattered light. An imaging pulse passes through the studied medium, while a gating pulse is used to open the gate. With this configuration, a spatial resolution of 10 μm and a temporal resolution of 270 fs are obtained. The gate duration is compatible with the typical dimensions of a liquid jet generated by a commercial automotive fuel injector. Preliminary results show that spatio-temporal diagrams of transmitted light through a spray may be acquired, showing clearly the separation between ballistic, refracted and scattered light.     

On the location of flame edge in Shadowgraph pictures of spherical flames: a theoretical and experimental study

In this paper, a theoretical model based on geometrical optics has been developed to analyze the light intensity pattern of Shadowgraph pictures of spherical flames. The theoretical results have been compared with experimental measurement of light intensity profiles across the flame front using commercially available image processing software. These results are in good agreement. The theory predicts that the sudden change of light intensity from dark to bright does not coincide with the flame edge unless the flame thickness is negligible. Experimental results agree very well with the theoretical predictions.     

反射焦散线实验中斜入射光对应力强度因子测试精度的影响

本文用空间解析几何方法,推导了在一般非平行斜入射光条件下,裂纹体表面所形成的反射焦散线和初始曲线的方程.分析了倾斜入射光造成的焦散线畸变,给出了这种畸变造成的裂端应力强度因子测量误差的解析表达式.     

On longitudinal impact IV

Summary A survey is given of common pile-driving formulae, and special attention is paid to the so-called dynamic formulae whose characteristic features are compiled in a table and a diagram. The well-known situation that these formulae are fairly reliable for drop-hammers (heavy rams) but quite unreliable for double-acting compressed air hammers (light rams) is analyzed and illustrated by means of an example from the literature. An alternative method of computing the dynamic resistance of the ground by means of the measured set and the data of the hammer is presented, and evidence is given that it can be expected to apply equally well to light rams as to heavy ones. It is based on the graphodynamical method of treating longitudinal impact according to the complete pulse solution of the one-dimensional wave equation which was presented and developed in the previous articles of this series. One important parameter of this computing method is the elastic property of the ground. Suggestions are given for the experimental determination of this parameter. Contrary to common opinion this theory leads to the conclusion that high efficiency may well be obtained with light rams (compressed air hammers). In order to give best results, ram, capblock, helmet etc. should be constructed according to the demands of the pulse theory, and if this is done, a reduction of pile stresses can sometimes be obtained. Examples show that the assumptions of current dynamic formulae are better valid for heavy rams (short piles) than for light rams (long piles). Suggestions are given for further theoretical and experimental development of the new method.