Tethered space orientation via adaptive sliding mode

Here, we study the problem of a rotating tethered satellite system (TSS) orientation. The rotation TSS is used for propellantless delivery of the payload from low earth orbits to geostationary orbits or other transfer orbits. Driving the angular positions to correct desired orientation in rendezvous and tossing moments, in fact, is important operation in many real sceneries. We suggest the mathematical model describing the dynamics of TSS and catch mechanism/payload rendezvous with external disturbance terms. Here is shown that using sliding mode control (SMC), we are able to control successfully the position of TSS. The conventional and adaptive versions of SMC are considered. We show that SMC with the gain matrix adaptation based on the equivalent control method can significantly reduce the undesirable chattering effect provoking possible damages of TSS. Copyright © 2015 John Wiley & Sons, Ltd.     

Analysis of General Ideal Proportional Navigation Guidance Laws

In this work, the capture region of the general ideal proportional navigation guidance law is analyzed with the following constraints: (i) the target's input acceleration is subject to independent or magnitude saturation, and (ii) the missile's input acceleration is subject to magnitude saturation. In addition to the case of unbounded maneuverability of missile with or without knowing the target acceleration, the necessary and sufficient condition for a bounded maneuvering missile that captures a nonmaneuvering target is also derived. Furthermore, the conditions that result in zero impact velocity are discovered and discussed in some of the cases. The capture regions that cannot be obtained analytically are determined numerically by a powerful classifier, the least square support vector machines. To have the capture region ready for least square support vector machines, all the state variables are transformed into modified polar variables and non‐dimensionalized to reduce the number of independent variables. In order to make the implementation possible in real time, an approximation of the Gaussian radial basis function is adopted to obtain the corresponding nonlinear feature mapping function. Through numerous numerical experiments, the proposed technique is found to be adequate for storing the capture region in an onboard fire control computer.     

基于.NET技术动态导航菜单的设计与实现

通过树型菜单,用户可以对资源的结构、类型有直观的了解,但目前很多B/S系统的菜单还是通过代码生成的。为此,基于.NET技术,通过开源项目Peta Poco实现代码,设计并实现了动态导航菜单系统;介绍了数据库设计、算法思想。该技术避免了静态目录树下因数据源经常性改变而频繁修改程序代码的弊端,导航菜单通过数据库进行控制,提高了系统的安全性,使管理变得更加灵活、高效。     

基于北斗的高速摄像机时间同步器设计

为了满足民用飞机在飞行试验中高速摄像机对时间同步的需求,基于国产北斗卫星导航系统设计了具有精确输出IRIG-B(AC)码的时间同步器,用于机载高速摄像机的精确时间同步。以FPGA为核心,使用直接数字频率合成技术实现了IRIG-B(AC)码的产生。实验结果表明,该同步器时间同步精度满足要求,可以实现对高速摄像机进行时间同步的功能。     

中国水电工程技术创新实践与新挑战

近十余年来,中国的水电工程建设发展迅猛,建设了以三峡工程为代表的多座高坝大库,水电工程技术也取得了一系列重大突破。结合众多工程实践,阐述了我国水电工程在坝工技术、电站、通航建筑物等方面的创新成就。根据我国水电发展的现状,分析了我国水电工程建设面临的新挑战,并从工程安全、技术、环保、移民等方面提出了未来的水电科技创新方向。     

Designing multimodal tracks for mobile users in unfamiliar urban environments

While there have been many studies of navigation design guidelines for integrating maps in mobile devices, we argue that the research focus should turn more towards the design of multimodal navigation aids, which would reflect the impact of typical human wayfinding behaviour. Therefore, we suggest an interdisciplinary design approach, i.e. building on urban design practice that focuses on supporting the navigation of pedestrians in urban areas. The design implications are explored in this study with the subjects being pedestrians accomplishing wayfinding tasks in an unfamiliar, urban area. The main areas that this paper contributes to are: investigating the design implications of multimodal navigation aids; evaluating these in the context of mobile wayfinding tasks; and reflecting the results according to the user's wayfinding strategies and spatial anxiety. It is concluded that through designing multimodal tracks into mobile navigation applications we can help users to find their way in unfamiliar, urban environments.     

三峡水库航运流量补偿调度效益

三峡水库在枯水季节(简称“枯季”)为下游航运实施流量补偿调度是三峡工程主要设计任务之一。依据初步设计,三峡水库自2006年汛末进入初期运行期以来,开始承担大坝下游航运流量补偿任务,实际运行过程中,根据上游来水情况,充分利用水库调节库容实施航运流量补偿调度。本文对三峡水库蓄水发电以来枯季航运补偿运用进行了分析总结,提出了今后枯季水库运用中应注意的问题。     

资水梯级电站施工期闸孔通航方式工程实践

有通航要求的水利水电工程施工期通航问题,是施工导流设计和工程实施期间需要妥善解决的问题之一。以资水柘溪电站以下河段修建的修山水电站、东坪水电站和株溪口水电站工程为例,介绍了施工期利用工程既有的闸孔通航并取得较好技术经济效果的实际做法。工程实践表明,利用闸孔通航,技术上是可行的,并具有导流程序简单、施工期通航工程措施费用低、电站发电时间可提前等优点,经济效益显著。其工程经验可在类似工程中推广应用。     

地磁辅助惯性组合导航技术分析

从地磁导航的特点出发,指出了地磁／惯性组合导航在未来发展中的优势,并对实现该种组合导航需要的技术手段做了全面的分析,包括：信息融合策略、高精度地磁场模型的构建方式以及滤波算法的设计。同时,阐述了其中的改进方向,为进一步提高该种组合导航性能提供思路。     

Impoverishment of YOY‐fish assemblages by intense commercial navigation in a large Lowland river

Navigation‐induced physical forces have been suggested to modify the structure of riverine fish assemblages by impeding especially the recruitment of littoral bound species. To investigate the effect of vessel frequency on fish, we compared the composition and seasonal succession of young‐of‐the‐year (YOY) fish assemblages in three similarly degraded river reaches differing in average vessel passages (2, 6 and 41 per day). Fish were caught by electrofishing biweekly between May and September. Multivariate tests were used to analyse differences between YOY‐fish assemblages and hurdle regression models applied to determine abiotic factors predicting fish occurrence and abundance. Roach (Rutilus rutilus) and perch (Perca fluviatilis) densities were compared. Roach larvae remain in the littoral zone while perch larvae shift to the pelagic zone immediately after hatch. YOY‐fish assemblage structure substantially changed along the traffic intensity gradient. In the high traffic intensity reach, species number and total fish density were markedly reduced compared to the other reaches. Roach densities were lowest in the high traffic intensity reach whereas perch densities did not decline along the gradient. Hurdle regressions confirmed a stronger effect of commercial navigation traffic intensity on roach than on perch. The total zooplankton biomass was highest in the high traffic intensity reach. Our results provide empirical evidence that intensive commercial navigation impoverishes fish assemblages in width‐restricted waterways. They underlined that in particular those species that have their first nursery habitats in shoreline areas were more affected by intensive commercial navigation than species whose larvae live predominantly pelagic. The results indicate that the negative effect of intensive navigation on riverine fish results primarily from the navigation‐induced hydraulic disturbances along the banks. Therefore, mitigation of navigation‐induced hydraulic forces is required to prevent degradation of fish communities in waterways. Copyright © 2010 John Wiley & Sons, Ltd.