Laser Doppler Velocimeter Development

A new two-channel laser Doppler velocimeter developed for the Ames High Reynolds Channel No. II is described. Design features required for the satisfactory operation of the optical system in the channel environment are discussed. Fiber optics are used to transmit the megahertz Doppler signal to the photodetectors located outside the channel pressure vessel, and provision is made to isolate the optical system from pressure and thermal strain effects. Computer-controlled scanning mirrors are used to psoition the laser beams in the channel flow. Techniques used to seed the flow with 0.5-?-diam polystyrene spheres avoiding deposition on the test-section windows and porous boundary-layer removal panels are described. Preliminary results are presented with a discussion of several of the factors affecting accuracy.     

Design issues for MIL-STD-1773 optical fiber avionics data buses

In this paper, several design issues on highly reliable MIL-STD-1773 (or 1553B) optical fiber avionics data buses are investigated. Two optical modulation techniques are proposed for avionics data buses, and they can be used to efficiently solve the problems associated with the fast identification of correct operation states for optical transmitters while maintaining less complexity of transceivers. The implementation of the proposed techniques is discussed. We also deal with the selection of optical devices and fibers to improve the reliability and power budget of optical fiber avionics data buses. Furthermore, some future improvements on avionics data bus systems are pointed out     

Mechanical wear debris feature,detection, and diagnosis: A review

Mechanical debris is an important product of friction wear, which is also a crucial approach to know the running status of a machine. Many studies have been conducted on mechanical debris in related fields such as tribology, instrument, and diagnosis. This paper presents a comprehensive review of these studies, which summarizes wear mechanisms (e.g., abrasive wear, fatigue wear, and adhesive wear) and debris features (e.g., concentration (number), size, morphology, and composition), analyzes detection methods principles (e.g., offline: spectrograph and ferrograph, and online: optical method, inductive method, resistive-capacitive method, and acoustic method), reviews developments of online inductive methods, and investigates the progress of debris-based diagnosis. Finally, several notable problems are discussed for further studies.     

Error Performance of M-ary DPPM Communication System

Error performance in optical communication, where the information is transmitted by means of the differential pulse-position modulated optical carrier, is discussed. Additive independent background radiation and thermal noise are taken into account. Both threshold type and maximum value type of decision schemes are also considered. The effects of several parameters, such as the number of time slots, the duty ratio, the extinction ratio, the count dimension, the signal-to-background radiation power ratio, and the signal-to-thermal noise power ratio are discussed in detail. The detection characteristic of this system are made clear by comparison with a pulse-position modulation system.     

复合材料力学中的光学方法

 本文较为广泛地探讨了光学方法在复合材料力学中的应用。根据几种近代光学方法的各自特点与长处,较全面地、成功地分别应用到复合材料构件的位移、应变和应力测量上。结果表明,光学方法是复合材料力学研究中的一种十分有效的手段,它为许多迄今难以解决的问题提供了可靠而准确的求解方法。     

An Optical Technique for Simultaneous Beamforming and Cross-Correlation

This paper presents a method of greatly simplifying the processing of received signals from antenna arrays through the use of a coherent optical system for signal processing. It is shown that a coherent optical system is ideally suited for carrying out beamforming operations. Several other advantages of coherent optics for this application are also discussed. A major result is a technique for forming several unambiguous beams simultaneously by correlating the signals from two linear arrays. The coherent optics technique permits this operation to be carried out with extreme simplicity.     

Optical flow based guidance system design for semi-strapdown image homing guided missiles

This paper focuses mainly on semi-strapdown image homing guided (SSIHG) system design based on optical flow for a six-degree-of-freedom (6-DOF) axial-symmetric skid-to-turn mis-sile. Three optical flow algorithms suitable for large displacements are introduced and compared. The influence of different displacements on computational accuracy of the three algorithms is ana-lyzed statistically. The total optical flow of the SSIHG missile is obtained using the Scale Invariant Feature Transform (SIFT) algorithm, which is the best among the three for large displacements. After removing the rotational optical flow caused by rotation of the gimbal and missile body from the total optical flow, the remaining translational optical flow is smoothed via Kalman filtering. The circular navigation guidance (CNG) law with impact angle constraint is then obtained utilizing the smoothed translational optical flow and position of the target image. Simulations are carried out under both disturbed and undisturbed conditions, and results indicate the proposed guidance strat-egy for SSIHG missiles can result in a precise target hit with a desired impact angle without the need for the time-to-go parameter.     

超声速光学头罩流场的PIV研究

在马赫数Ma-3．8超声速风洞中,采用PIV（Particle Image Velocimetry,粒子图像测速）技术测量了超声速光学头罩流场的速度分布。PIV技术应用于超声速流场时,对系统的硬件配备、示踪粒子的跟随性以及PIV算法的精度有很高的要求。本文PIV系统选用高精度的同步控制器和高能量激光器;以纳米级粒径的粒子作为示踪粒子,通过斜激波响应实验分析了其在超声速流场中的跟随性;并采用多种高精度速度场算法对粒子图像进行处理。实验结果表明,示踪粒子在超声速流场中有很好的跟随性,采用的高精度速度场算法能够很好地反映超声速光学头罩流场的速度分布。     

Military avionics optical fiber data buses with active-couplerconfigurations

Military avionics optical fiber data buses of high reliability are discussed. Because Light Emitting Diodes (LED's) have better temperature performance and require less complex driver circuits than laser diodes, the former is normally chosen as an optical source in the severe aircraft environment at present. In this case, optical power budget becomes a critical factor which can significantly limit the number of terminals in a data bus. To effectively solve this problem while maintaining a high reliability, we present several configurations of all-active couplers and hybrid passive/active couplers for avionics optical fiber data buses using PIN photodiodes and LED's. The system design is also described, which incorporates a modulation scheme called partial trilevel Manchester II bi-phase coding     

图像序列中机动目标三维运动和结构的计算

综合视觉运动分析中的2类处理方法,选取图像中的角点作为特征点,在理论上证明了图像序列的光流场可以近似地用角点的位移场代替。利用已有文献中的建模思想,详细推导出递归计算机动目标三维运动和结构的非线性计算模型,采用广义卡尔曼滤波(EKF)递归地计算图像序列中机动目标的三维运动和结构。合成图像序列和真实图像序列实验结果表明该算法能取得较好的效果。     

激光空间流动显示及其应用

本文介绍激光空间流动显示技术及其在复杂流动中的应用。着重介绍了作者在激光诱导荧光流动显示(LIF)技术的研究和应用。较系统地讨论了若干原理和技术问题,并提供了一些实际应用的典型的流态照片。     

A long-range laser velocimeter

A long-range laser velocimeter (LV) developed for remote operation from within the flow fields of large wind tunnels is described. Emphasis is placed on improvements in optical hardware as well as additions to data acquisition and processing techniques. The method used for data reduction of photon resolved signals is outlined in detail, and measurement accuracy is discussed. To study the performance of the LV and verify the measurement accuracy, laboratory measurements were made in the flow field of a 10-cm-diameter, 30-m/s axisymmetric jet. The measured velocity and turbulence intensity surveys are compared with measurements made with a hot-wire anemometer. Additionally, the LV was used during the flow calibration of the 80-ft×120-ft wind tunnel to measure the test-section boundary layer thickness at the maximum wind tunnel speed of 51.5 m/s. The requirements and techniques used to seed the flow are discussed, and boundary-layer surveys of mean velocity and turbulence intensity of the streamwise component and the component normal to the surface are presented. The streamwise component of mean velocity is compared with data obtained with a total pressure rake     

基于改进Cycle-GAN的光流无监督估计方法CSCD

卷积神经网络为光流的计算提供了一种新的方式,但作为一种数据驱动技术,用于训练网络的大规模光流真值在现实世界中不易获取。为了解决这个弊端,基于Cycle-GAN的循环对抗机制,提出了一种光流无监督估计方法。首先,引入双判别器机制在生成器生成的光流样本的底层和高层特征上进行鉴别,迫使生成器提高光流生成的精度。其次,引入Spynet作为教师网络,在生成器训练前期对其进行指导,防止网络陷入模式崩塌。最后,改进损失函数,提出了光流一致性损失和轮廓一致性损失函数,进一步提升光流估计精度。实验结果表明,与现有的先进算法相比,提出的方法达到与有监督算法相同的精度水平。     

一种基于光流拟和的航拍视频图像全局运动估算方法

在多分辨率光流估算的基础上,提出了一种基于光流拟和的方法用于对航拍视频图像中的全局运动进行估算。在利用光流对全局运动模型拟和时,针对光流估算的不确定性以及图像中独立目标运动的干扰,提出了一种光流分块拟和与评估的方法用于剔除光流场中不利于全局运动估算的干扰数据,从而有效提高了全局运动的估算精度。航拍视频图像配准与独立运动检测的仿真结果均验证了算法的有效性。     

Output Signal-to-Noise Ratio for Amplitude and Intensity Modulated Laser

General expressions are obtained for output SNR for both amplitude- and intensity-modulated lasers, where bandlimited Gaussian noise has been chosen as a modulating signal, and in the presence of background light. Two types of modulating signals are considered: the baseband and bandpass modulating signals. Detailed calculations are made for output SNR when an ideal narrowband optical filter is used. The dependence of output SNR on several parameters, such as the center frequency of the modulating signal, the effective average quantum rate, and input SNR, are discussed. In addition, the difference in performance between amplitude and intensity modulation is discussed. The detection characteristics of the homodyne system are also considered.     

Sco X-1

The physical properties of X-ray, optical and radio emissions from Sco X-1 are reviewed. Sco X-1 is a typical X-ray source which has an optically thick hot plasma. The observational spectra of X-ray and optical emissions are consistent with theoretical ones from the hot plasma, but the radio emission shows a non-thermal feature. The restrictive conditions for the model of Sco X-1 are discussed from the observational facts. In spite of numerous observational facts on Sco X-1 further detailed and elaborate studies are necessary to understand this object and general compact X-ray sources comprehensively.     

基于自适应纹理复杂度的仿生视觉导航方法研究

针对稠密光流在低纹理复杂度时精度较低的问题,提出了一种自适应纹理复杂度的稠密光流优化方法,以提升光流导航精度。根据三种不同大气条件下三种不同图像模糊程度的图像光流精度与纹理复杂度的统计图,推断稠密光流的精度与图像的纹理复杂度呈线性关系。通过建立图像纹理复杂度和稠密光流精度之间的直接联系,利用灰度共生矩阵的对比度参数评价图像纹理复杂度,采用最小二乘法拟合图像纹理复杂度和光流真值优化系数的函数关系,获得自适应纹理复杂度的稠密光流优化模型。基于该优化模型设计了仿真实验,实验结果表明,基于该模型可有效提升稠密光流在低纹理复杂度时的计算精度。     

Optical fiber data bus modulation techniques for military avionics

In this paper, we propose several modulation techniques for use in military avionics optical fiber data buses, namely, Extended Manchester II Bi-Phase Coding with Beginning-Stopping Flags, Partial Trilevel Manchester II Bi-Phase Coding, Four-ary Pulse Width Modulation, Two-ary Pulse Width Modulation with Amplitude-Distinguished Sync Field, Two-ary Message Pulse Width Modulation and Two-ary Sync Pulse Amplitude Modulation, respectively. Compared with an existing modulation scheme of MIL-STD-1773 avionics data buses, the proposed techniques can be effectively used to overcome the difficulty in recognizing the correct operation states of an active transmitter at the output of optical receivers. The feasibility of proposed modulation schemes are discussed, and their performance is also evaluated