Sliding mode control based guidance law with impact angle constraint

The terminal guidance problem for an unpowered lifting reentry vehicle against a sta- tionary target is considered. In addition to attacking the target with high accuracy, the vehicle is also expected to achieve a desired impact angle. In this paper, a sliding mode control （SMC）-based guidance law is developed to satisfy the terminal angle constraint. Firstly, a specific sliding mode function is designed, and the terminal requirements can be achieved by enforcing both the sliding mode function and its derivative to zero at the end of the flight. Then, a backstepping approach is used to ensure the finite-time reaching phase of the sliding mode and the analytic expression of the control effort can be obtained. The trajectories generated by this method only depend on the initial and terminal conditions of the terminal phase and the instantaneous states of the vehicle. In order to test the performance of the proposed guidance law in practical application, numerical simulations are carried out by taking all the aerodynamic parameters into consideration. The effec- tiveness of the proposed guidance law is verified by the simulation results in various scenarios.     

燃烧室声学测量和仿真的误差影响因素分析

动态压力数据对于燃烧室声学特性及燃烧不稳定性的分析具有十分重要的意义,由于测点数量有限,实际工程分析中还需要借助声学仿真补充模态分布及频响曲线等多维信息。某些情况下,主次模态频率间隔较小、主模态幅值不太突出,声学测量和仿真之间的误差会严重影响对实际声模态类型的判断。通过燃气发生器缩尺件声学实验及仿真计算,具体分析了在燃烧室声学特性分析过程中的各种误差源,其中包括测量点位置、来流温度、喷注及测量缩进小腔等。研究表明:声学仿真能够准确得到实际的声学模态频率分布,平均温度引起的频率差异不可忽略,非波腹位置处测量的模态幅值需要考虑测点位置的影响,喷注缩进小腔能使特定模态幅值降低,而测量缩进小腔会导致某阶模态幅值的测量结果偏高。     

有线电视HFC网络与光纤链路设计

本文论述了双向传输有线电视ＨＦＣ网络结构并比较了其优缺点，文中还就工程应用的实例讨论了光纤链路的设计问题。     

国外航空公司对供应商的质量审核

叙述了沈阳飞机工业有限公司在签订并执行民机零部件转包生产合同中总结出来的国外航空公司对供应商质量管理的一般要求；介绍了国外航空公司的专家们对供应商质量保证系统进行质量审核的共同内容和要求，及沈阳飞机工业有限公司在通过国外航空公司质量审核后所取得的收获。     

三维可调的高精度顶尖尾座

Ｇ４８数控坐标磨机床是由计算机数控的连续轨迹坐标磨机床，这类机床的控制装置能同时对２个或２个以上的坐标轴进行连续控制，属于两轴半坐标数控机床。该机床有１个数控转台，可以使用数控转台加工轴类零件，但需要顶尖尾座配合。为此我们通过借鉴国内外高精度顶尖尾座...     

水族箱自动加氧系统的设计

传统的水族箱在进行加氧时具有机械性,需要多次的人工开停操作,已不适应现代的生活方式。本文介绍了一种由TH-2型水氧传感器,51单片机,模数转换器及其外围电路组成的水族箱自动加氧系统,实验证明该系统具有优良的性能和简捷的操作,节省了人工和电耗。     

基于AD7714的激光对中仪的设计与实现

为了提高机械轴对中的效率和准确度,研制了基于AD7714的激光对中仪系统,该系统通过一定的测量手段对设备的定轴和动轴的相对位置进行检测和调整,以保证其位于同一条直线上。系统通过自行研制的硬件对任意角度的激光点的位置信息进行测量,并通过LabVIEW的图形化界面和编程环境对数据进行采集和处理,最后给出垂直偏差和水平偏差。     

叉流管－管型换热器二维温度场的数值分析

建立并导出叉流管－管型换热器传热过程的二维数学模型及相应的差分格式。对比实验数据和性能计算结果，表明数值方法是有效可行的，据此编制的计算机程序已成功地用于组合发动机空气预冷换热器工作过程的预测。     

模拟中性大气边界层中污染物传输与扩散的动力相似讨论

文章从湍流雷诺数相等出发,推导出风洞中模拟中性大气边界层动力相似准则一充分发展的湍流中,运动相似的流动动力也相似。文章还讨论了模拟烟流抬升和扩散的相似准则,概述了国内外一些主要实验室应用的近似模拟技术。     

A solar type U burst in the decimetric range

This paper analyzes a Type U burst at 1.0 – 2.8 GHz which occurred between 12:36:26 – 12:36:32 UT on 1992 August 22, observed by Ond ejov Observatory, Czech Republic. This may be the first example of Type U bursts in the decimetric range, as far as we know. From analysis we came to the following conclusion: (1) The frequency drift rates of the ascending and descending branches are 1.25 and 0.225 GHz/s, respectively, and the velocities of the electron beam are 0.38 c and 0.26 c, respectively; (2) The burst decay of the ascending branch is larger than that of the descending branch; (3) The variations of the maximum frequencies of instantaneous spectra with time appear as from the highest (1.92 GHz) to the lowest (1.0 GHz), then toward higher frequency (1.53 GHz) (this is consistent with that predicted by plasma emission theory); (4) The bandwidths of the ascending branch are about twice that of the descending branch (this may be caused by the larger drift rates of the ascending branch); (5) The temperature of the coronal loop apex is 6.3 × 10⁶ K; (6) The magnetic field at the top of the loop is greater than 9.2 G; (7) This U burst emission is plasma radiation at the second harmonic.