某支线飞机超临界机翼设计研究

文章在翼身组合体构形下,采用面向机翼的精细修形设计方法针对某支线飞机进行了超临界机翼设计.由于支线飞机机翼面积较小,在满足气动性能的前提下,能否满足结构设计的要求就成为本次修形设计所考虑的主要因素.设计实践表明,在合理的设计思想指导下,当初始外形与设计目标相差较大时,采用渐近修形设计技术仍然可以得到比较满意的结果.     

基于轴变形的脚楦匹配方法*

提出并实现了通过脚楦匹配方法来仿真人脚穿上鞋子的状态,能够直观、便利地检查和分析鞋类产品的舒适度。该方法包括三个步骤：首先,保持鞋楦的位置不动,调整脚型的位置,使其与鞋楦严格对齐;其次,基于轴线变形算法,对脚型进行略微变形,使其与鞋楦姿势匹配;最后,根据匹配结果生成脚楦多个截面的分析图,指导对鞋楦舒适度的分析和楦体修改。实验结果表明,该方法能够有效地检查鞋楦的舒适度,可应用到个性化定制业务。     

观测几何对目标探测性能影响的仿真分析

在光电武器作战探测目标性能问题的研究中,不同大气/气溶胶模式、不同观测几何条件下的光电武器作战效能差异显著.针对上述问题,通过分析大气传输和观测几何对视在对比度的影响,建立了视在对比度传递模型,结合TIP准则提出了观测几何对目标探测性能的影响模型.利用Modtran软件离线计算的基础数据,提出了探测性能模型快速仿真计算方法,实现了典型地区、全天时、不同观测几何和观测距离条件下的成像系统探测性能的快速仿真计算.采用快速仿真计算方法,选取典型参数,计算并分析了不同大气/气溶胶模式、观测几何等因素对视在对比度、探测概率和探测距离等指标的影响.结果表明:观测几何对目标探测性能影响显著,50％探测概率条件下,顺光探测距离是逆光探测距离的1.38 ～1.7倍;不同大气/气溶胶模式条件下,观测几何对探测距离影响差异明显,海洋性气溶胶模式下影响较大,乡村型气溶胶模式下影响较小.文中提出了观测几何对目标探测性能的影响模型和快速仿真计算方法,为光电武器系统任务规划和作战效能评估提供了理论和技术支持.     

多视图动量对比学习算法

比较同一图像不同增强的相似性是对比学习取得显著成果的关键。传统对比学习方法使用了图像的两个不同视图,为了学习到图像更多的信息以提高分类准确率,在MoCo(momentum contrast for unsupervised visual representation learning)的基础上,提出了一种多视图动量对比学习算法。每次迭代中,对于图像的多个数据增强分别使用一个查询编码器和多个动量编码器进行特征提取,使得本次迭代可以使用更多的数据增强和负样本。使用优化的噪声对比估计(InfoNCE)来计算损失,使得查询编码器能得到更有益于下游任务的特征表示。对查询编码器使用梯度回传更新网络,对各动量编码器使用改进的动量更新公式以提高模型的泛化能力。实验结果表明,使用多视图动量对比学习可以有效提高模型的分类准确率。     

基于图嵌入的自适应多视降维方法

随着监控摄像头的普及和数据采集技术的快速发展,多视数据呈现出规模大、维度高和多源异构的特点,使得数据存储空间大、传输慢、算法复杂度高,造成“有数据、难利用”的困境。到目前为止,国内外在多视降维方面的研究还比较少。针对这一问题,本文提出一种基于图嵌入的自适应多视降维方法。该方法在考虑视角内降维后数据重构原始高维数据的基础上,提出自适应学习相似矩阵来探索不同视角之间降维后数据的关联关系,学习各视数据的正交投影矩阵实现多视降维任务。本文在多个数据集上对降维后的多视数据进行了聚类/识别实验验证,实验结果表明基于图嵌入的自适应多视降维方法优于其他降维方法。     

Estimation of access failure probability in D2D underlaid cellular networks

Device-to-Device (D2D) communication can reduce the mobile devices' energy consumption and increase the spectral efficiency in D2D underlaid cellular networks. However, D2D users will interfere with co-channel cellular users, which can lead to cellular communication access failures. There are two reasons for cellular communication access failures: (1)D2D interference and (2)insufficient spectrum resources. To address the absence of research on the performance of cellular services' access in D2D underlaid cellular networks, this paper defines the new services' access failure probability and handoff services' access failure probability to evaluate the effect of both D2D interference and limited resources on cellular communication access. Based on the stochastic geometry and stochastic process, a random network model is presented to estimate the access failure probabilities, which can provide guidelines for network design to ensure cellular services' access. The accuracy of the estimated access failure probability is validated through extensive simulations.     

三维裂隙网络管单元模型确定岩体渗透张量

根据现场测量所获得的裂隙产状统计参数,利用Monte-Carlo法模拟生成相应的裂隙网络。采用管单元模型,将三维裂隙渗流网络简化为空间一维渗流网络,以工程实际校正的渗透张量作为目标,采用改进的遗传算法进行拟合,得到等效管单元直径与隙宽比值为12.337 1。据此,可得到给定产状岩体的等效渗透张量。同时,利用裂隙几何参数张量法计算渗透张量,通过比较可见裂隙网络模型更加符合实际。     

Evaluation of form data using computational geometric techniques—Part I: Circularity error

The present work deals with evaluation of form error from the measured profiles obtained using a form tester, namely roundness/cylindricity measuring instrument. In Part I, details of circularity evaluation are presented. Due to eccentricity in component setting and radius-suppression inherent in the measurement, circularity error has to be evaluated with reference to a limacon. A computational geometry-based algorithm is proposed for establishing minimum circumscribed, maximum inscribed and minimum zone limacons. A new type of control hull for directly constructing equi-angular diagrams and a new procedure for updating are introduced. Validation has been done with bench-mark data set and corresponding results available in the literature. Being geometry-based algorithm, it is simple to follow and each iteration can be visualized and interpreted geometrically. On comparison with simplex search method, the proposed algorithm is found to be computationally efficient in terms of accuracy and time taken. The proposed methods can be easily implemented in computer-aided roundness measuring instruments. Extension of this work for evaluation of cylindricity error has been dealt in Part II.     

Surface finish generated in hard turning of quenched alloy steel parts using conventional and wiper ceramic inserts

Significant progress has already been achieved in green manufacturing including dry and hard, often high-speed, machining technologies. For instance, the demand for higher productivity has resulted in the wider application of ceramic and PCBN tools with special multi-radii (wiper) geometry. This paper reports some important characteristics of the surface roughness produced in the turning of a hardened low-chromium alloy steel using mixed alumina–titanium carbon (TiC) ceramic cutting tools equipped with both conventional and wiper inserts. The characteristic geometrical features of surfaces obtained in both these turning operations have been assessed by means of representative two-dimensional (2D) surface roughness parameters, and some 3D visualizations, which allowed more complete characterization of the surface topography and prediction of its service properties. Results show that keeping equivalent feed rates, i.e. 0.1 mm/rev for conventional and 0.2 mm/rev for wiper tools, the surfaces obtained have similar 3D height roughness parameters, and comparable values of skew and kurtosis. At defined cutting parameters, surfaces produced by wiper tools contain blunt peaks with distinctly smaller slopes resulting in better bearing properties. Only marginal changes of Ra parameter were recorded during 15 min machining trials.     

虚拟数控车床加工技术的研究

论文提出了数控车床仿真系统的总体方案，深入研究了虚拟制造的关键技术及具体实现方法。在OpenGL与VC＋＋的平台上，基于NC代码直接驱动仿真加工过程的虚拟现实技术，利用3ds Max对静态物体进行几何建模，利用重画技术和粒子系统方法对动态物体进行行为建模和物理建模，然后将几何建模、行为建模和物理建模结合起来模拟整个数控加工过程。