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141.
142.
The GFZ real-time GNSS precise positioning service system and its adaption for COMPASS 总被引:1,自引:0,他引:1
Xingxing Li Maorong Ge Hongping Zhang Thomas Nischan Jens Wickert 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Motivated by the IGS real-time Pilot Project, GFZ has been developing its own real-time precise positioning service for various applications. An operational system at GFZ is now broadcasting real-time orbits, clocks, global ionospheric model, uncalibrated phase delays and regional atmospheric corrections for standard PPP, PPP with ambiguity fixing, single-frequency PPP and regional augmented PPP. To avoid developing various algorithms for different applications, we proposed a uniform algorithm and implemented it into our real-time software. In the new processing scheme, we employed un-differenced raw observations with atmospheric delays as parameters, which are properly constrained by real-time derived global ionospheric model or regional atmospheric corrections and by the empirical characteristics of the atmospheric delay variation in time and space. The positioning performance in terms of convergence time and ambiguity fixing depends mainly on the quality of the received atmospheric information and the spatial and temporal constraints. The un-differenced raw observation model can not only integrate PPP and NRTK into a seamless positioning service, but also syncretize these two techniques into a unique model and algorithm. Furthermore, it is suitable for both dual-frequency and sing-frequency receivers. Based on the real-time data streams from IGS, EUREF and SAPOS reference networks, we can provide services of global precise point positioning (PPP) with 5–10 cm accuracy, PPP with ambiguity-fixing of 2–5 cm accuracy, PPP using single-frequency receiver with accuracy of better than 50 cm and PPP with regional augmentation for instantaneous ambiguity resolution of 1–3 cm accuracy. We adapted the system for current COMPASS to provide PPP service. COMPASS observations from a regional network of nine stations are used for precise orbit determination and clock estimation in simulated real-time mode, the orbit and clock products are applied for real-time precise point positioning. The simulated real-time PPP service confirms that real-time positioning services of accuracy at dm-level and even cm-level is achievable with COMPASS only. 相似文献
143.
针对现代飞行器设计等工程优化问题中面临的约束高耗时难题,在标准追峰采样(MPS)方法的基础上,提出了一种基于过滤器的MPS-DCP设计空间智能探索方法(FMPS-DCP),训练径向基函数网络预示高耗时目标函数与约束条件响应,利用KS方程聚合高耗时约束并根据过滤器思想筛选优质简单样本点,定制了一套新增样本点选择策略引导优化过程快速向全局可行最优解收敛,从而提高了求解高耗时约束优化问题的效率。采用一组标准约束测试算例验证FMPS-DCP方法的性能,并与CiMPS、Extended ConstrLMSRBF、ARSM-ISES和KRG-CDE智能探索方法进行对比。结果表明,FMPS-DCP在优化效率与鲁棒性方面具有显著的性能优势。最后,通过全电推进卫星平台多学科设计优化案例,验证了FMPS-DCP的工程实用性。 相似文献
144.
145.
根据飞机作动系统的工作原理,针对液压源能量有限的现状,提出作动系统的功率约束条件。同时考虑操纵面的物理约束,提出了功率受限的操纵面控制分配问题,并给出相应的解决方案。功率受限的操纵面控制分配方法将控制律设计与操纵面任务分配分割为两个模块独立运行,以动态逆控制律为基础,建立控制指令和操纵面间的动态映射关系,考虑操纵面的物理约束并以功率最小作为优化指标,将控制分配问题转化为一个二次规划问题,通过数值求解实现控制系统功率受限下的控制分配。仿真结果表明,考虑功率约束的控制分配方法,可以在系统满足一定稳定性及飞行品质要求的前提下,分配和管理多个冗余操纵面达到指令要求,同时实现系统消耗总功率最小,保证了作动系统的稳定性与安全性。 相似文献
146.
In the current practice of multi-axis machining of freeform surfaces, the interface surface between the roughing and finishing process is simply an offset surface of the nominal surface. While there have already been attempts at minimizing the machining time by considering the kinematic capacities of the machine tool and/or the physical constraints such as the cutting force, they all target independently at either the finishing or the roughing process alone and are based on the simple premise of an offset interface surface. Conceivably, since the total machining time should count that of both roughing and finishing process and both of them crucially depend on the interface surface, it is natural to ask if, under the same kinematic capacities and the same physical constraints, there is a nontrivial interface surface whose corresponding total machining time will be the minimum among all the possible (infinite) choices of interface surfaces, and this is the motivation behind the work of this paper. Specifically, with respect to the specific type of iso-planar milling for both roughing and finishing, we present a practical algorithm for determining such an optimal interface surface for an arbitrary freeform surface. While the algorithm is proposed for iso-planar milling, it can be easily adapted to other types of milling strategy such as contour milling. Both computer simulation and physical cutting experiments of the proposed method have convincingly demonstrated its advantages over the traditional simple offset method. 相似文献
147.
突发事件下大规模空中交通流量管理的组合优化模型 总被引:2,自引:1,他引:1
为了解决危险天气和军航活动对管制运行的影响,使用动态网络流方法对突发事件下短期空中交通流量调度问题展开研究。首先,结合中国民航管制的特点,分析了突发事件对流量管理的影响。同时,根据航路航线网络及其高度层的特点,给出了网络和高度层的数学描述,并根据机型将航空器分成大、中和小3种交通流,介绍了使用多品种流描述3种机型的必要性;其次,根据网络拥挤程度随时间和流量变化的特点、危险天气随机变化的特点、空中等待和地面等待费用差异的特点构建了3个优化目标,考虑机场容量、扇区容量、航班连续性和扇区连续性约束建立了多目标优化模型;再次,针对军航活动时需要协调空域的特点,多品种流模型求解时间复杂度高,不能适应短期流量管理的缺陷,改进了逐步宽容约束法,设计了一种阶段式求解的近似算法;最后,以西南空管局管制的空域为例,利用实际流量数据,设计了3个场景进行仿真。结果表明,所提模型和算法能有效求解突发事件下的短期流量调度问题,算法效率比起传统算法在大流量下更具优势。 相似文献
148.
An integrated approach that considers the performance limitations of tracking control systems for air-breathing hypersonic vehicles is proposed. First, a set of ascent trajectories is obtained as candidates for tracking control through a trajectory design method that considers the available acceleration. Second, the basic theory of performance limitations, which is adopted to calculate the limits on control performance through the trajectory, is integrated. The open-loop dynamics of air-breathing hypersonic vehicles is responsible for these limits on the control system. Comprehensive specifications on stability, tracking accuracy, and robustness are derived, and the flight envelope with constraints and control specifications is identified. Simulation results suggest that trajectory design should consider restrictions on control performance to obtain reliable solutions. 相似文献
149.
大型客机气动设计综述 总被引:5,自引:2,他引:3
中国大型客机研制过程中追求三减,四性:减阻、减重、减排,安全性、经济性、舒适性、环保性。中国大型客机采用翼下常规布局形式,放宽静稳定技术,发动机选用CFM公司Leapx-1C发动机,这对气动设计技术在工程适用性上提出了极高的要求。大型客机是中国第1架完全自主知识产权民用飞机,本文综述了其设计过程中采用的先进气动优化设计方法、CFD分析和充分的风洞试验验证,说明了超临界机翼设计、高效增升装置设计、飞机/发动机一体化设计、尾翼设计、翼梢小翼设计和部件精细化减阻设计技术,能实现大型客机的减阻应用设计。研究表明,中国大型客机在气动设计水平和设计方法上取得了一系列的进展和突破,实现了设计具有较强竞争力的先进民用飞机的目标。 相似文献
150.
This paper proposes a backstepping technique and Multi-dimensional Taylor Polynomial Networks (MTPN) based adaptive attitude tracking control strategy for Near Space Vehicles (NSVs) subjected to input constraints and stochastic input noises. Firstly, considering the control input has stochastic noises, and the attitude motion dynamical model of the NSVs is actually modeled as the Multi-Input Multi-Output (MIMO) stochastic nonlinear system form. Furthermore, the MTPN is used to estimate the unknown system uncertainties, and an auxiliary system is designed to compensate the influence of the saturation control input. Then, by using backstepping method and the output of the auxiliary system, a MTPN-based robust adaptive attitude control approach is proposed for the NSVs with saturation input nonlinearity, stochastic input noises, and system uncertainties. Stochastic Lyapunov stability theory is utilized to analysis the stability in the sense of probability of the entire closed-loop system. Additionally, by selecting appropriate parameters, the tracking errors will converge to a small neighborhood with a tunable radius. Finally, the numerical simulation results of the NSVs attitude motion show the satisfactory flight control performance under the proposed tracking control strategy. 相似文献