一种机器人砂带磨削的路径规划方法(英文)

机器人砂带磨削系统具有弹性接触和宽行加工两个显著优点,被广泛应用在具有复杂工件的终加工领域,提高表面质量和加工效率。有关在曲率约束下的磨削路径规划研究较为少见。由于工件与接触轮之间存在复杂的弹性接触,因此,机器人磨削路径可以利用接触运动学的一般方法来求解。机器人砂带磨削过程且需要满足一般的砂带磨削工艺要求,其中最重要的是保证接触轮与工件的局部几何特征贴合。在曲率较小的局部,相邻刀位点的弧长加大,以保证加工效率。相反地,在曲率较大的局部,相邻刀位点的弧长较小,以保证加工精度。利用一系列平面与目标曲面相截,得到相应的截平面的轮廓曲线。对于任意一条轮廓线,优化相邻刀位点之间的弧长,在曲率较大的局部增加一个中间刀位点。本文提出了一种包含弧长优化和主曲率匹配的磨削路径生产方法,通过离线仿真验证了有效性,并利用该方法提高了曲面的磨削质量。该路径规划方法为生成光顺且精确的机器人曲面磨削路径提供了理论依据。     

离心式喷嘴液膜破碎过程实验

为了研究离心式喷嘴出口液膜破碎以及雾化锥角变化规律,对直径2.5~6 mm之间6个不同直径、不同几何特性参数的离心式喷嘴运用高速阴影设备进行实验,喷注压降从0.1~3 MPa,每次实验间隔0.2 MPa。通过实验,得到液膜破碎长度、液膜锥角随喷注压降、喷孔直径以及几何特性参数的变化规律。随着喷注压降的增加,液膜破碎长度减小,液膜锥角增大,该种类型喷嘴破碎长度在40 mm左右,液膜锥角不大于60°;随着几何特性参数A值增加,同一喷注压降下的液膜破碎长度增大,液膜锥角增加;将液膜锥角实验结果与Abromvich,Lefebvre等理论公式进行了比较,在常用的喷嘴特性参数范围内,液膜锥角的变化趋势与理论公式相吻合,但实验值远小于公式计算值。     

等离子体天线的原理及特性

根据等离子体柱天线的系统构成,分析了等离子体柱天线的基本工作原理,讨论了表面波在等离子体柱天线中的传播特性、等离子体柱内的电子分布,以及天线的长度、噪声与辐射特性。分析表明：表面波能激发和维持等离子体柱,等离子体柱可构成等离子体天线,且具易隐身、可控性等优点。     

Debris area distribution of spacecraft under hypervelocity impact

Cross-sectional area is an important parameter for spacecraft breakup debris as it is the directly measured data in space observation. It is significant for observing and analysing the spacecraft breakup event to accurately modelling the area distribution of the breakup debris. In this paper, experimental study has been performed on debris area distribution characteristics of spacecraft under hypervelocity impact. The tests are carried out at the ballistic ranges of CARDC. Aluminium projectiles are launched to normally impact the simulated spacecrafts at about 3.0 km/s. The simulated spacecrafts are made up of aluminium plates, filled with some simulated electronics boxes, each of which was installed with a circuit board. “Soft-catch” devices are used to recover the breakup fragments. The test results show that: 1) the relationship between the cross-sectional area and the characteristic length of debris, which can be obtained in the logarithmic coordinates by linear fitting, represents the debris shape characteristic in a certain extent; 2) the area-to-mass ratios of fragments show normal distributions in the logarithmic coordinates; 3) debris made of different materials can be distinguished by different peaks on the distribution curves; 4) the area-to-mass ratio distributions can be expressed by a linear superimposition of several normal functions which represent the main materials of the spacecraft.     

Methods for determining unimpeded aircraft taxiing time and evaluating airport taxiing performance

The objective of this study is to improve the methods of determining unimpeded (nom-inal) taxiing time, which is the reference time used for estimating taxiing delay, a widely accepted performance indicator of airport surface movement. After reviewing existing methods used widely by different air navigation service providers (ANSP), new methods relying on computer software and statistical tools, and econometrics regression models are proposed. Regression models are highly recommended because they require less detailed data and can serve the needs of general per-formance analysis of airport surface operations. The proposed econometrics model outperforms existing ones by introducing more explanatory variables, especially taking aircraft passing and over-passing into the considering of queue length calculation and including runway configuration, ground delay program, and weather factors. The length of the aircraft queue in the taxiway system and the interaction between queues are major contributors to long taxi-out times. The proposed method provides a consistent and more accurate method of calculating taxiing delay and it can be used for ATM-related performance analysis and international comparison.     

在线实时工件测长系统开发

在线实时工件测长系统是将数字图像处理技术与在线图像检测技术应用于工业生产现场的一个典型实例，系统中采用光学摄像机采集工件图像信息，应用图像增强、边缘检测、图像识别等数字图像处理技术对所采集到的图像信息进行处理识别，实现了在远距离条件下以非接触方式对生产线上的工件进行实时长度测量，并实现了对测量结果的显示、记录及传送。大量实验表明，在线实时工件测长系统能够准确地进行在线工件全天候测长，保证了检测的客观性和真实性。此外，系统还具有耐高温耐污染的特点，适合于工业现场的环境。     

中美波音机型成本比较分析

在国内航空运输业中,飞机拥有费、维修费和燃油费大约占航空公司总成本的57.2%。中国航空公司若想实施低成本的经营战略,就必须竭尽全力降低这三大费用。对于中国民航具有典型代表意义的B767-300,B747-400和B737-300机型与美国骨干航的对比分析,说明当飞机日利用率以及机队规模数量等增加时,费用的单位成本就会降低。     

燃烧室长度对固体燃料超燃冲压发动机燃烧室性能的影响

基于国外研究者完成的固体燃料超燃冲压发动机的实验数据,通过分别改变燃烧室等直段长度和扩张段长度,对不同总长的燃烧室工作过程进行数值模拟.采用基于压力的2阶迎风差分数值方法,物理模型为轴对称结构,燃烧模型采用有限速率/涡耗散模型(finite-rate/eddy-dissipation),湍流模型采用SST(shear stress transport) k-ω模型.聚甲基丙烯酸甲酯(PMMA)燃料进口边界由用户自定义函数的方式给定,分别分析了不同长度,即不同等直段长度或扩张段长度下超燃冲压发动机燃烧室内流场特性及其性能变化.结果表明:随着等直段长度的增大,燃烧室出口处燃烧效率逐渐减小,从72.74%降低至66.81%,而燃烧室内总压损失逐渐减小,燃烧室推力逐渐增大,可由85.83N增加至108.55N;改变扩张段长度,发现扩长段长度变化对燃烧室流场结构的影响较小,随着扩张段长度的增大,燃烧室出口燃烧效率和燃烧室推力都略微减小.在燃烧室长度的设计范围内,增大等直段的长度要比增大扩张段长度对提升燃烧室各项性能有帮助.      

煤体变形局部化的梯度塑性理论研究

摘 要 本文采用白光数字散斑相关方法对煤在单轴压缩下变形破坏进行研究，定量的测出了煤的变形局部化带宽度。并通过应变梯度塑性理论，在屈服函数中引入应变梯度二阶项。采用Drucker－Prager准则解析得出了煤试件的变形局部化带宽度公式并根据试验确定煤的材料内部长度。     

LEO卫星网络的切换策略及性能分析

采用Dijkstra算法,分析了低轨(LEO)卫星网络的距离最短、时延最小、跳数最小、持续时间最长等典型路由切换策略,并比较了性能。在综合考虑切换性能和时延等指标的基础上,提出了一种持续时间最长和时延最小组合,以及完全路由重构与部分路由重构结合的混合切换策略。各切换策略性能比较的结果表明,该混合切换策略的性能较优。