柔版印刷套印误差检测技术研究

目的为了提高柔版印刷过程中套印误差的检测精度。方法分析了柔版印刷产生套印误差的主要原因,并提出了一种基于机器视觉的套印误差检测方法。首先进行工业相机的标定,获取原始的"十"字圆环标记图像,采用融合滤波算法对图像进行预处理,对预处理后图像进行数据分析时,提出一种二次分割算法进行图像色彩分离;再使用模板匹配算法进行模板匹配,获取偏差数据进行套印偏差分析。结果使用该算法在实验中对5组标记图像的轴向、纵向检测误差,均控制在0.03 mm以内,符合行业检测误差在0.2mm以内的检测标准。结论提出的基于视觉的套印误差检测方法具有识别准确率高、处理速度快的特点,能可靠稳定地运行,具有一定的可行性。     

光面式高压氢气泄漏快速可视化检测方法及数值仿真研究

针对高压氢泄漏扩散的检测问题,国内外学者利用实验和数值模拟等方法进行了相关研究,提出了一些检测方法,这些检测方法结果可靠,但是普遍存在反映速度慢的不足。本文提出了一种光面式高压氢气泄漏快速可视化检测方法,利用半导体激光器发射激光,通过柱面透镜组及反射镜后形成光面（laser sheet）照射储氢罐,利用安装在储氢罐上方特定位置的CCD相机拍照采集图像并传输至计算机,经数字图像处理后对高压氢气泄漏情况进行鉴别。基于该方法开展仿真实验,建立高压氢气射流的分层流动模型,实验结果与前人研究的实验公式吻合,证明了该方法的可行性;开展了泄漏口直径为1 mm 时3,5,7 MPa压强的仿真实验,以及压强为5 MPa时泄漏口直径为0.5,1,1.5 mm的仿真实验,获得了高压氢气泄漏口直径与特定高度、气射流边界层直径的解析关系,以及高压氢气压力与射流边界层直径的解析关系,为实现高压氢气泄漏快速准确检测提供了有力支撑。     

基于冰内孔隙率的冰中声速经验公式的研究

冰介质中的声速特性受温度、盐度、密度等因素影响,是一个随时间和空间变化的不稳定值。研究了冰介质中温度、盐度、密度三个物理量在垂直方向上的变化特性,引入孔隙率作为冰中声速特性的表征因子,利用孔隙率与温度、盐度、密度已有的函数关系,通过大量天然冰的实验数据,得到淡水冰中声速关于温度、盐度和密度的经验公式。进行了河冰声速测量的外场试验,验证了淡水冰中声速的经验公式的有效性,并利用该声速经验公式研究了淡水冰垂直方向上的声速剖面。文中所做的相关研究可为以后研究利用冰介质中的声速特性提供借鉴,为以后利用声学方法,在极地或我国北方高纬度地区进行冰层厚度监测,了解寒地冰层的更替、演化以及气候变迁等工作奠定研究基础。     

激光Raman分光计中杂散光的测试方法、技术及其最新进展（Ⅱ）──测试技术研究进展及其检测标准的几点考虑

重点就激光Ｒａｍａｎ分光计中杂散光测试的若干方案与主要技术进行了全面综述与评价,简单介绍了近十年来国内有关激光Ｒａｍａｎ分光计中杂散光测试与研究工作的发展概况、实验结果及其最新进展,并就建立有关“激光Ｒａｍａｎ分光计中杂散光检测标准”提出了几点考虑或建议。     

An Effective Steganalysis Algorithm for Histogram-Shifting Based Reversible Data Hiding

To measure the security for hot searched reversible data hiding (RDH) technique, especially for the common-used histogram-shifting based RDH (denoted as HS-RDH), several steganalysis schemes are designed to detect whether some secret data has been hidden in a normal-looking image. However, conventional steganalysis schemes focused on the previous RDH algorithms, i.e., some early spatial/pixel domain-based histogram-shifting (HS) schemes, which might cause great changes in statistical characteristics and thus be easy to be detected. For recent improved methods, such as some adaptive prediction error (PE) based embedding schemes, those conventional schemes might be invalid, since those adaptive embedding mechanism would effectively reduce the embedding trace and thus increase the difficulty of steganalysis. Therefore, a novel steganalysis method is proposed in this paper to detect recent adaptive RDH schemes and provide a more effective detection tool for RDH. The contributions of this paper could be summarized as follows. (1) By analyzing the characteristics for those adaptive HS-RDH, an effective “flat ground” based detection method is designed to fast identify whether the given image is used to hide secret data; (2) According to the empirical statistical model, double check mechanism is provided to improve the detection accuracy; (3) In addition, to further improve detection ability, some detailed information for secret data, i.e., its content and embedding location are further estimated. Compared with conventional steganalysis methods, experimental results indicate that our proposed algorithm could achieve a better detection accuracy and meanwhile acquire more detailed information on secret data.     

Airborne digital holographic system for cloud particle measurements

An in-line holographic system for in situ detection of atmospheric cloud particles [Holographic Detector for Clouds (HOLODEC)] has been developed and flown on the National Center for Atmospheric Research C-130 research aircraft. Clear holograms are obtained in daylight conditions at typical aircraft speeds of 100 m s(-1). The instrument is fully digital and is interfaced to a control and data-acquisition system in the aircraft via optical fiber. It is operable at temperatures of less than -30 degrees C and at typical cloud humidities. Preliminary data from the experiment show its utility for studies of the three-dimensional spatial distribution of cloud particles and ice crystal shapes.     

Complexity Effective Frequency and Sidelink Synchronization Algorithm for LTE Device-to-Device Communication Systems

Device-to-device (D2D) communication is considered as a major challenge in the long term evolution (LTE) network wherein devices directly communicate with each other. One of the key challenges in D2D sidelink is reliable and reduced-complexity synchronization. To address this issue, a computationally efficient sequential detection scheme for integer carrier frequency offset and sidelink identity is proposed in the LTED2D system. To perform the frequency offset detection without retrieving the sidelink identity, the conjugate relation between two primary sidelink synchronization sequences is exploited, which facilitates the detection tasks of frequency offset and sidelink identity to be decoupled. It is demonstrated from simulation results that the inherent property of the sidelink synchronization sequences is effectively used for joint detection of frequency offset and sidelink identity with significantly reduced complexity, compared to existing estimation schemes.     

De-icing by slot injection

Summary We consider the removal of ice from a plate in a cold cross flow by injection of hot fluid through a slot in the plate. De-icing of this sort is required in a number of diverse industrial scenarios, and is particularly relevant to the aviation industry, where the presence of ice on aircraft wings is a major safety hazard. Thin aerofoil theory is used to determine the flow above the injected fluid layer, and this is coupled to flow and energy equations in the injected layer and the ice. The key non-dimensional parameters and ratios in the problem are identified. The result is a nonlinear singular integro-differential equation which is coupled to a convection/diffusion equation and a Stefan condition. Some special cases are discussed and some asymptotic limits are identified. The problem is then solved numerically, and results for a number of different cases are presented.     

Experimental investigation of the kinematics of post-impact ice fragments

Hail is more hazardous for aircraft engines compared to rain and snow, mainly, because of its solid nature and high water content. In extreme cases it can lead to engine flame out. In order to avoid such situations, aero engines should be designed to withstand hail ingestion. For this purpose we have studied the post-impact characteristics of ice, such as particle velocity and directions of travel. To achieve this goal, a large experimental program has been undertaken, in which spherical ice specimens were projected against a rigid plate. Three specimen diameters (6.2, 12.9 and 27.5 mm) and four impact angles (20, 45, 67.2 and 90°) were considered, as well as a wide range of impact velocities (60-200 m/s). From this experimental work, we can conclude that the ice fragments formed after impact do not bounce back and that the post-impact ice trajectory angle is lower than 2°. This is in line with observations found in the literature. On the other hand, the ice fragments are mainly organised in a circular cloud, when observed in the target plane. The center of this cloud has the same velocity as the initial ice ball tangential impact velocity. Furthermore, the cloud radius expands with a rate proportional to the ice ball normal impact velocity. Finally, each fragment inside the cloud has a relative velocity which varies linearly with its distance from the cloud center. These experimental observations should be very helpful in developing models and simulations of hail ingestion by aircraft engines.     

Anomaly detection of aircraft lead-acid battery

The lead-acid battery has been widely used in various fields. In civil aviation aircraft, it plays a vital role in the power system to maintain normal operation during the flight mission. Thus, an effective abnormal detection system for monitoring and diagnosing the status of aircraft lead-acid battery is essential to ensure its safety and reliability. This paper aims to effectively identify aircraft battery faulty using unsupervised anomaly detection techniques. It introduces state-of-the-art anomaly detection algorithms and evaluates their performance on a large real civil aviation battery data. The experimental results show that the latest isolation-based anomaly detectors, iForest and iNNE, have outstanding performance on this task and have promising applicability as efficient methods for guaranteeing the lead-acid battery quality and reliability in civil aviation aircraft.     

基于分形的航天故障诊断

本文提出了一种基于分形的航天器的故障检测新方法。由于故障发生时系统表现异常,这此异常可导致测量信号发形维数的变化,根据这些变化可进行故障检测。基于分形的故障检测方法可以实现实时的检测系统的状态,包括系统的动态量以及静态量参数。该方法还能将测量信号的分析处理和故障的定位很好地结合起来。     

Evaluation of bergy bit populations on the Grand Banks

Shuttle tankers and hydrocarbon production platforms operating on the Grand Banks of Newfoundland must be designed for some level of ice loading. In some cases, high ice loads can result from relatively small icebergs, bergy bits, or growlers. This is particularly true when wave-induced ice motions are significant (in high sea states) or when vessel speeds are high (e.g., a transiting tanker).Safe and economic operations can be achieved by designing structures that are strong enough to withstand ice loads, planning for and managing ice to reduce the risk of collisions, or a combination of the two. In all cases, accurate information on the number of small ice masses is important. Unfortunately, reliable information on small ice mass populations is not available. The extensive, detailed aerial surveys that would be required to build up meaningful statistics on bergy bit populations would be prohibitively expensive, and other methods of estimating bergy bit populations are required for the development of a reliable database.The approach used in this study was a reanalysis of International Ice Patrol (IIP) operational iceberg observations. Although the IIP does not detect and report all bergy bits and growlers, their database contains critical information on the location of small ice masses in relation to the aircraft track, and the prevailing visibility and sea-state conditions. By resampling only those ice masses observed when detection conditions were favourable, and within a prescribed distance from the aircraft, more accurate bergy bit statistics have been determined.A convenient measure of the number of bergy bits and growlers is the ‘small ice mass to parent iceberg’ (SIMPI) ratio. This relates the number of small glacial ice masses to the number of parent icebergs from which most small ice masses are calved. The average SIMPI ratio for the study region was 0.59. Some interesting phenomena revealed in the study include the apparent geographical variation in the small ice mass to parent iceberg ratio, with increasing values to the north and west. The ratio also varied seasonally. Of the months in which sufficiently large numbers of icebergs were observed to produce meaningful statistics, the SIMPI ratio was lowest in March (0.25) and highest in May (0.81).     

Early warning and prediction of flight parameter abnormalities for improved system safety assessment

It is widely accepted that human error is a major contributing factor in aircraft accidents. The early detection of a subsystem abnormality that is developing during flight is potentially important, because the extra time before an alert range is reached may improve the crew's situation awareness. The flight crew may thus consider and try more options for dealing with the failure situation. Robust numerical algorithms and techniques are proposed for rapid recognition of faulty situations, which have the potential for such early detection. The warning system includes a model-based multi-step ahead predictor, which provides predictive information on some flight critical parameters. A key feature of the proposed techniques is that it takes advantage of the on-board information redundancy, computer technology and graphics displays, uses the already available measurements and hence requires only input–output processing for implementation in on-board computers. This is an important aspect when considering the testability and certificability of the software implementation. The system is tested on a simulated typical landing approach scenario of a civil aircraft using the RCAM¹ benchmark.     

三峡工程第一套砼加冰预冷系统的设计和使用

阐述了三峡工程第一套砼加冰预冷系统的工作原理、构造以及主要技术参数的确定,并对使用情况作了分析;着重对IS120—60冰库、气力输送片冰装置、输冰螺旋机和称冰装置作了探讨;对照实际使用的经验和尚存的一些问题,提出了切合实际的技术措施,以促使砼加冰预冷技术进一步完善.     

线性啁啾相位掩模的设计

啁啾相位掩模法是啁啾光纤光栅的一种非常重要的制作方法。本文研究讨论了用全息干涉方法制作线性啁啾位相掩模的设计方法,提出用两球面波干涉产生条纹密度随空间距离线性变化的干涉条纹记录啁啾位相光栅,按设定光栅端点空频和端点空频差两种优化设计方法设计了长度100mm、啁啾量1nm/mm的线性啁啾光栅,理论和实验结果给出两种设计方案的非线性系数分别为2.5%和1.6%,理论设计和实验结果相符。     

Eddy Current Probability of Detection for Mid-Bore and Corner Cracks in Bolt Holes of Service Material

Fatigue cracks are prone to develop around fasteners found in multilayer aluminum structures on aging aircraft. Probability of detection (POD) studies using eddy current techniques within the bolt holes contribute to risk assessments used in evaluating the serviceability of these aircraft. Signal response to corner and mid-bore cracks by eddy current testing using standard split-D differential probes has been examined for in-service material from the horizontal stabilizer of a Hercules aircraft. Results are compared to data obtained from laboratory samples with drilled holes. Based on a logistic regression analysis, the results show no significant difference for a_90/95 (90% of the cracks of size a will be detected 95% of the time) for mid-bore crack length of 0.60 mm in this study compared to 0.62 mm in earlier work on drilled holes. However, there was a substantial loss of sensitivity for corner cracks. In this study on in-service material, the a_90/95 for corner cracks was 0.82 mm compared to 0.31 mm obtained from drilled holes. Decrease in sensitivity was attributed to damage at the hole’s corners of the in-service material, including rounding, folded metal, and burrs. Hole damage also significantly increased the risk of a false call.     

统计能量分析预测飞机壁板隔声量及舱室内声场分布

飞机舱室内噪声的预测对改进飞机性能具有重要意义，并为实际飞机设计和噪声控制措施提供理论依据。文章建立了飞机壁板隔声的统计能量分析模型，研究了外部声场激励和振动激励通过飞机壁板的隔声量，预测了飞机舱室内的声场分布。在此基础上运用面向对象及可视化技术，开发出相应的专用软件，该软件界面友好，用户可根据需要选定结构参数，材料性能，更改外部激励，并对预测结果进行可视化处理。运用该软件对舱内噪声进行预测，可以缩短飞机设计周期，减小对已有结构进行噪声控制的困难，提高经济效益。文中通过对某型飞机的舱室内噪声进行预测，验证了统计能量法预测飞机壁板隔声量的可靠性和该软件的实用性。     

飞机多层金属板隐藏缺陷远场涡流探头设计及试验研究

由于飞机多层金属板结构厚度大、复杂等特性,现有检测方法无法发现原位内部缺陷,对于多层板金属缺陷的检测一直都是航空无损检测的难题。远场涡流检测技术因打破趋肤效应的限制,涡流能量可穿透较厚的被测试件,对金属板结构中隐藏缺陷的检测具有潜在优势。该文针对飞机多层金属板隐藏裂纹的原位检测,建立多层金属板构件隐藏裂纹平面远场涡流检测有限元仿真模型,研究不同角度、不同深度裂纹检测幅值、相位的变化规律。为验证该仿真模型的正确性,开展远场涡流检测多层金属板的试验。试验结果表明:设计开发的远场涡流探头可检测埋深13 mm的裂纹缺陷,当裂纹倾斜角度为0°时,检测灵敏度最高,当裂纹倾斜角度为90°时,检测灵敏度最低,与仿真结果保持一致,且能够对缺陷进行精准定位,可为飞机多层金属板构件隐藏裂纹的定量检测提供依据。     

Enhancing Probability of Detection and Analysis of Bolt Hole Eddy Current

Fatigue cracks are prone to develop around fasteners found in multi-layer aluminum structures on ageing aircraft such as the CC-130 Hercules and CP-140 Aurora (P-3 Orion). Probability of Detection (POD) studies using eddy current techniques within the bolt holes contribute to risk assessments used in evaluating the serviceability of these aircraft. Improving POD by optimizing the inspection system can reduce the required frequency of inspections, since assurance of detection of smaller crack sizes extends the interval for which growth of cracks to a critical size may occur. In this work signal analysis and POD of laboratory grown fatigue cracks in the corners of bolt holes of 7075-T6 aluminum is examined. A number of parameters that enhance crack detection are identified, including the use of intimate contact probes versus steel sheath (non-contact), higher frequencies and the use of C-Scan display. Results demonstrate better detectability at 1600 kHz, than at the normally used 400 kHz, and enhanced recognition and assurance of identification of peak crack signal for data recorded and displayed in a C-Scan format. Results are compared with a previous POD study, which used current field techniques for detection.     

Optimal fusion of multiple nonlinear sensor data

A framework for the detection of bandlimited signals by optimally fusing the multinonlinear sensor data is developed. Though most sensors used are assumed to be linear, none of them individually or in series gives the truly linear relationship, and errors are inevitable as a result of the assumption of linearity. A new approach, which takes the actual nonlinear characteristics of sensors into account, is advocated. Though the fusion of redundant information can reduce the overall uncertainty and, thus, serves to increase the accuracy of the process measurements, identifying the faulty readings and fusing only the reliable data are very difficult and challenging. An optimal multiple nonlinear sensor data fusion scheme in which multisensor data fusion is done by scheduling the sensor measurements is proposed. The main idea of the multisensor fusion schemes proposed in this paper is to pick only the reliable data for the fusion and disregard the rest. The proposed theoretical framework is supported by illustrative examples and simulation data.