复杂动态场景下目标检测与分割算法

在动态场景等复杂条件下,往往难以对序列图像目标进行准确的检测与分割。根据序列图像中目标在复杂条件下的成像特点,提出了一种基于融合尺度不变特征变换(SIFT)流特征显著模型的动态场景目标检测与分割算法。通过对SIFT流算法表示运动特征信息的优势进行分析,并结合图像国际照明协会(CIE)Lab颜色空间的颜色和亮度特征信息,建立四维特征向量空间。利用改进的多尺度中心-环绕对比方法生成各特征通道的显著图并进行线性融合,建立序列图像的动态场景目标显著模型。最后利用均值漂移聚类算法和形态学处理实现对检测目标的精确分割。实验结果表明,相比传统检测与分割算法,该算法在动态背景与航拍等复杂场景下能够分割出更为完整的目标区域,具有良好的鲁棒性和高分割精度。      

Research of multi-path routing based on network coding in space information networks

A multi-path routing algorithm based on network coding is proposed for combating long propagation delay and high bit error rate of space information networks. On the basis of traditional multi-path routing, the algorithm uses a random linear network coding strategy to code data pack- ets. Code number is determined by the next hop link status and the number of current received packets sent by the upstream node together. The algorithm improves retransmission and cache mechanisms through using redundancy caused by network coding. Meanwhile, the algorithm also adopts the flow distribution strategy based on time delay to balance network load. Simulation results show that the proposed routing algorithm can effectively improve packet delivery rate, reduce packet delay, and enhance network performance.     

Effect of assisted transverse magnetic field on distortion behavior of thin-walled components in WEDM process

Machining performance of thin-walled components made by aeronautical difficult-toprocess materials is a significant issue in the aviation manufacturing industry. Although wire electric discharge machining-low speed(WEDM-LS) is one of typical non-contact machining processes without macro cutting force, which does well in removing hardness and brittleness materials via pulsed discharge at high temperature, but few researchers have studied the thermal distortion behavior leading to a considerable g...     

密切曲面锥导乘波体的设计与理论分析

将密切锥导乘波体技术应用于一般曲面锥流场,以期获得升阻比、容积率更高的密切曲面锥导乘波体。首先,设定不同乘波体后缘激波型线,在两种代表性曲面锥流场内,生成了四种乘波体构型,利用数值方法验证乘波体设计方法可行性;然后构造了三类典型单一控制变量的曲面锥流场,对比分析了对应密切曲面锥导乘波体性能变化规律。研究表明：（1）密切曲面锥导乘波体流面压力分布、后缘激波型线与理论设计吻合,关键位置压力与理论值相对偏差约1%,说明利用密切技术在曲面锥流场中“截取”乘波体的方法是可行的。（2）曲面锥流场控制参数不同,可获得升阻系数、容积率、压缩量增加,升阻比降低的乘波体,也可获得升阻比、容积率增加,升阻系数降低的乘波体。     

纳米SiC增强碳纤维层合板摩擦磨损性能

为了探寻一种简便的制备纳米SiC增强碳纤维层合板的方法,本文将纳米SiC颗粒均匀分散在无水乙醇中,制备成不同质量分数的SiC试剂,然后均匀喷涂在碳纤维预浸料表面,固化成型。对不同试件进行摩擦磨损实验,得到不同含量的纳米SiC颗粒对碳纤维层合板摩擦因数、磨损量的影响规律,并且对磨损形貌和复合材料的硬度进行分析。实验结果表明：在碳纤维预浸料表面喷涂纳米SiC颗粒能够有效改善碳纤维层合板的摩擦磨损性能;当纳米SiC浓度为1%时,层合板的摩擦因数、磨损量、磨痕的宽度及深度较于不含纳米SiC的层合板分别降低52%,63%,32.3%,54.8%,摩擦磨损性能最好。     

Fatigue life prediction model of 2.5D woven composites at various temperatures

As one of the new structural layout in the family of woven composites, 2.5D Woven Composites(2.5D-WC) have recently attracted an increasing interest owing to its excellent properties, i.e. high specific strength and fatigue resistance, in the aerospace and automobile industry. Indepth understanding of the fatigue behavior of this material at un-ambient temperatures is critical for the engineering applications, especially in aero-engine field. Here, fatigue behavior of 2.5D-WC at different temperatures was numerically investigated based on the unit cell approach. Firstly, the unit cell model of 2.5D-WC was established using ANSYS software. Subsequently, the temperature-dependent fatigue life prediction model was built up. Finally, the fatigue lives alongside the damage evolution processes of 2.5D-WC at ambient temperature(20 ℃) and unambient temperature(180 ℃) were analyzed. The results show that numerical results are in good agreement with the relevant experimental results at 20 and 180 ℃. Fatigue behavior of 2.5D-WC is also sensitive to temperature, which is partially attributed to the mechanical properties of resin and the change of inclination angle of warp yarns. We hope that the proposed fatigue life prediction model and the findings could further promote the engineering application of 2.5D-WC, especially in aero-engine field.     

2219铝合金热变形行为对精密旋压成形的影响

采用Gleeble-3500热力模拟试验机对2219铝合金进行物理模拟。通过应力-应变曲线和金相组织观察研究了2219铝合金的高温塑性流变行为及其对合金旋压变形的影响。结果显示:2219铝合金在高温塑性变形过程中的流变应力主要受变形温度和应变速率的影响,变形量对其影响不明显;随着变形温度的提高或应变速率的降低,应力-应变曲线中的峰值应力和稳态流变应力均呈现下降的趋势。另外,采用"Gleeble"物理模拟+工艺试验的研制路线有助于实现2219铝合金大型结构件旋压成形的"控形",基于热模拟结果设计特征旋压温度(300～350℃)、进给比(0.6～1.5 mm/r)、变形量(30%)对2219铝板进行旋压变形,可获得内、外表面质量均良好的大型铝合金壳体,其壁厚差0.2 mm,且壳体内型面与理论型面样板单边间隙0.1 mm。     

Application of shear-sensitive liquid crystal coating to visualization of transition and reattachment in compressor cascade

The present paper aims at introducing Shear-Sensitive Liquid Crystal Coating (SSLCC) technology into compressor cascade measurement for the first time and serves as a basis for better understanding of the influence from the boundary layers. Optical path layout, which is the most significant difficulty in internal flow field measurement, will be solved in this paper by self-designed image acquisition device. Massive experiments with different Mach number and incidence are conducted at a continuous subsonic cascade wind tunnel to capture the boundary layer phenomenon. Image processing methods, such as Three-Dimensional (3-D) reconstruction and Hue conversion, are used to improve the accuracy for transition position detection. The analysis of the color-images indicates that complex flow phenomena including transition, flow separation, and reattachment are captured successfully, and the effect of Mach number and incidence on the boundary layer flow is also discussed. The results show that: the Mach number has a significant effect on transition position; the incidence has little effect on transition position, but it has a great impact on the transition distance and leading-edge separation; influenced by the end-walls, the reattachment occurs in advance under positive angle of attack conditions.     

Fatigue behavior of direct laser deposited Ti-6.5Al-2Zr-1Mo-1V titanium alloy and its life distribution model

The present work aims to investigate the fatigue behavior of Direct Laser Deposition (DLD) Ti-6.5Al-2Zr-1Mo-1V titanium alloy under constant amplitude stress. 22 pieces of DLD Ti-6.5Al-2Zr-1Mo-1V titanium alloy standard cylinder specimens were tested under a stress level of 800?MPa with a stress ratio of 0.06. Fatigue fractography and fatigue life data were obtained. Through the fracture surface analysis, the specimens were divided into two categories in accordance with the location of crack initiation and defect types. Comparison of fatigue life and behavior between two specimen types was given, which was followed by a discussion about the impact of defect type, size and position on the fatigue life of the specimen. The fatigue test results also show a large variation of fatigue life. To illustrate the statistical characteristics of the fatigue life, probabilistic analysis was performed, and a novel bimodal lognormal model was established. The model has a good fit with the experimental data and can reduce the scatter of the fatigue life significantly.     

基于自由胀形的弯曲管材变形行为

随着制造业轻量化的发展趋势,复杂弯曲异形充液成形管件的应用日益广泛。为了更好地研究弯曲异形复杂管件在充液成形过程中的变形规律,进行可靠的工艺设计。本文通过结合薄膜理论和塑性变形理论对弯曲管件在自由胀形状态下的应力应变进行了理论解析,并通过有限元(FE)分析对理论计算模型进行了验证。FE分析结果与理论模型基本吻合。同时分析了管材在绕弯过程的硬化行为,并探索了在不同的弯曲硬化状态下弯曲管材在自由胀形过程下的破裂位置的规律,并且用实验进行了验证,实验结果与FE分析结果吻合。