基于飞行任务的飞行品质评估方法

提出一种基于飞行任务的飞行品质的评估方法.介绍了基于飞行任务的飞行品质评估方法的流程,以及常规迎角下机动动作的选取方法与大迎角下机动动作的选取方法,分析了标准评估机动任务库的选取方法.以实际飞行任务和战术要求为依据,建立了标准评估机动任务库,并明确了各机动动作与飞行品质分析的对应关系,飞行品质评估的环境组成.并基于大迎...     

ISTP science data systems and products

The International Solar-Terrestrial Physics (ISTP) program will provide simultaneous coordinated scientific measurements from most of the major areas of geospace including specific locations on the Earth's surface. This paper describes the comprehensive ISTP ground science data handling system which has been developed to promote optimal mission planning and efficient data processing, analysis and distribution. The essential components of this ground system are the ISTP Central Data Handling Facility (CDHF), the Information Processing Division's Data Distribution Facility (DDF), the ISTP/Global Geospace Science (GGS) Science Planning and Operations Facility (SPOF) and the NASA Data Archive and Distribution Service (NDADS).The ISTP CDHF is the one place in the program where measurements from this wide variety of geospace and ground-based instrumentation and theoretical studies are brought together. Subsequently, these data will be distributed, along with ancillary data, in a unified fashion to the ISTP Principal Investigator (PI) and Co-Investigator (CoI) teams for analysis on their local systems. The CDHF ingests the telemetry streams, orbit, attitude, and command history from the GEOTAIL, WIND, POLAR, SOHO, and IMP-8 Spacecraft; computes summary data sets, called Key Parameters (KPs), for each scientific instrument; ingests pre-computed KPs from other spacecraft and ground basel investigations; provides a computational platform for parameterized modeling; and provides a number of data services for the ISTP community of investigators. The DDF organizes the KPs, decommutated telemetry, and associated ancillary data into products for duistribution to the ISTP community on CD-ROMs. The SPOF is the component of the GGS program responsible for the development and coordination of ISTP science planning operations. The SPOF operates under the direction of the ISTP Project Scientist and is responsible for the development and coordination of the science plan for ISTP spacecraft. Instrument command requests for the WIND and POLAR investigations are submitted by the PIs to the SPOF where they are checked for science conflicts, forwarded to the GSFC Command Management Syntem/Payload Operations Control Center (CMS/POCC) for engineering conflict validation, and finally incorporated into the conflict-free science operations plan. Conflict resolution is accomplished through iteration between the PIs, SPOF and CMS and in consultation with the Project Scientist when necessary. The long term archival of ISTP KP and level-zero data will be undertaken by NASA's National Space Science Data Center using the NASA Data Archive and Distribution Service (NDADS). This on-line archive facility will provide rapid access to archived KPs and event data and includes security features to restrict access to the data during the time they are proprietary.     

Global and local geospace modeling in ISTP

The objective of the University of Maryland ISTP theory project is the development of the analytical and computational tools, which, combined with the data collected by the space and ground-based ISTP sensors, will lead to the construction of the first causal and predictive global geospace model. To attain this objective a research project composed of four complementary parts is conducted. First the global interaction of the solar wind-magnetosphe re system is studied using three-dimensional MHD simulations. Appropriate results of these simulations are made available to other ISTP investigators through the Central Data Handling Facility (CDHF) in a format suitable for comparison with the observations from the ISTP spacecrafts and ground instruments. Second, simulations of local processes are performed using a variety of non-MHD codes (hybrid, particle and multifluid) to study critical magnetospheric boundary layers, such as the magnetopause and the magnetotail. Third, a strong analytic effort using recently developed methods of nonlinear dynamics is conducted, to provide a complementary semi-empirical understanding of the nonlinear response of the magnetosphere and its parts to the solar wind input. The fourth part will be conducted during and following the data retrieval and its objective is to utilize the data base in conjunction with the above models to produce the next generation of global and local magnetospheric models. Special emphasis is paid to the development of advanced visualization packages that allow for interactive real time comparison of the experimental and computational data. Examples of the computational tools and of the ongoing investigations are presented.     

Mission-oriented cooperative 3D path planning for modular solar-powered aircraft with energy optimization

Modular Solar-Powered Aircraft(M-SPA) is a kind of High-Altitude Long-Endurance(HALE) aircraft which exploits the mission advantage of swarm UAV and the HALE advantage of large aspect-ratio SPA. M-SPA’s separated mode and combined mode give it the potential to maximize the mission efficiency with limited solar energy. In this paper, firstly, oriented by the mission of maximizing the cruise area, the overall design of the M-SPA is modeled, including the energy model, the aerodynamic model and the...     

Stochastic stability theory for systems containing intervalmatrices

Known conditions for the stability of stochastic, linear time-varying (LTV) dynamical systems based on Liapunov theory are applied to LTV dynamical systems containing interval matrices; both discrete and continuous time processes are considered. These conditions are sufficient for stability with probability 1 (wp1) and, in the case of discrete time, also necessary for stability in m.s. They lead to a simple, noniterative technique that involves the computation of eigenvalues of matrices whose elements often consist of first- and/or second-order moments. The results are useful in areas such as robust design, feedback control, perturbation analysis, and fault tolerant systems     

OS-CFAR theory for multiple targets and nonuniform clutter

The performance of a cell averaging constant false-alarm rate (CA-CFAR) detector degrades rapidly in nonideal conditions caused by multiple targets and nonuniform clutter. The ordered-statistic CFAR (OS-CFAR) is an alternative to the CA-CFAR. The OS-CFAR trades a small loss in detection performance relative to the CA-CFAR in ideal conditions for much less performance degradation in nonideal conditions. A formula is given for the detection probability of the OS-CFAR when there are multiple Swerling I targets in the CFAR window, and a formula is given for the probability of false alarm in nonuniform Raleigh clutter     

面向精准工程湍流模型的理论研究

长期以来,工程湍流模型建立在量纲分析和经验修正的基础上,绝对预测能力不足而且模型参数的意义不明确。关于湍流边界层的理论研究一直平行地在两条路线上前行,或是经验性地构造有关平均速度或动能的分布,或是利用数值模拟等技术对于湍流脉动结构进行精细刻画。二者之间的分割导致对湍流边界层物理图像的不完整,从而限制了对一系列相似性关系的揭示。新近发展的结构系综理论,立足于探索由于固壁对于流场的雷诺应力各个分量所表现的拉伸对称性约束,完成了一个对于平均速度和动能剖面的统一描述,从而形成了一个构建工程湍流模型的新思路:一方面,理论指导如何开展湍流DNS(Direct Numerical Simulation)和LES(Large Eddy Simulation)的大数据分析,提炼对定量描述复杂流动有物理意义的多层结构参数;另一方面,指导开发物理图像清晰、定量描述精确的新型湍流(代数)模型。结构系综理论揭示了壁湍流所共有的普适多层结构,完整地刻画了边界层湍流的雷诺数、马赫数相似性,有望推动理论空气动力学研究进入一个定量化、精确化的新阶段。     

高鲁棒性的螺旋桨片条理论非线性修正方法

针对螺旋桨极端状态分析计算的问题,对片条理论（BEMT）方法进行了一定的改进。虽然片条理论在常规工况下能够比较准确地计算拉力和功率,但在考虑严重非线性的部分工况下,如很低或很高前进比状态,传统片条理论存在一定的局限性,无法可靠地计算拉力、功率、环量分布及诱导速度。鉴于此,分析了传统片条理论方程解的不唯一性和诱导速度的奇异性,然后结合涡流理论提出了一种环量迭代修正方法,解决了传统片条理论在极端工况下的计算困难。另一方面,为了兼顾多种叶素非线性效应,应用人工神经网络对叶素的大迎角特性、低雷诺数特性及跨声速特性进行特征提取,并为片条理论提供高效的叶素非线性气动特性预测。通过与计算及试验结果对比,验证了修正片条理论方法针对本文计算模型能够在很低/很高前进比下进行准确计算。在本文算例中,拉力和功率的相对误差在常规工作段可以保持在5%以内,在很低和很高前进比下仍可以保持在10%以内。     

基于相似理论的航空发动机转速自适应PID控制

根据航空发动机在相似坐标系中特性不变的特点，提出一种基于相似理论的航空发动机转速自适应PID控制。该方案采用衰减曲线法进行换算PID参数整定，获得自适应调节律。仿真结果表明控制器具有良好的动静态性能，自适应性和鲁俸性。所得参数变化规律对数控系统全包线内PID控制器的参数选择具有一定的指导意义。     

Wave propagation analysis for a second strain gradient rod theory

In this work, an enriched model describing the longitudinal wave propagation is established based on Mindlin’s Second Strain Gradient(SSG) theory, which can describe the heterogeneity caused by the micro-structure interactions in the frame of continuum mechanics. The governing equation and associated boundary conditions are derived based on Hamilton’s principle, then the dispersion relation of non-classical longitudinal wave together with the extra-waves appearing exclusively in SSG theory model...     

集成弹流润滑理论及CFD方法的轴承热特性

为能准确预测传动系统内部角接触球轴承在喷油润滑方式下的热特性,通过建立轴承热弹流润滑(EHL)模型,获得球体与滚道微观接触界面间的载荷及摩擦因数,并采用局部生热法计算生热量;应用计算流体动力学(CFD)方法建立轴承油气两相热流耦合模型,研究湍流模型及流体域边界条件的设置,分析喷油速度、喷嘴位置及含气率对轴承内部传热性能的影响。结果表明:结合热弹流润滑理论及CFD方法可预测轴承在不同工况条件、润滑参数、几何参数下的最佳喷油速度、喷嘴位置及含气率;喷油速度为5 m/s时,轴承内部最高温度较其他喷油速度降低了4.40%;喷嘴位置在轴承下方时,轴承内部最高温度较其他位置降低了4.30%;含气率为15%时,轴承内部最高温度较其他含气率降低了1.57%。     

An algorithm for solving three-dimensional problem of elasticity theory for transversally isotropic medium

An algorithm for solving a boundary-value problem of deforming structures made of composite materials is considered. The polynomial solutions of the equation system for the linear theory of elasticity for the anisotropic medium in displacements are used in this algorithm.     

Solar wind theory

Some advances in the hydrodynamical large-scale theory, on the one hand, and in the kinetic theory, on the other hand, of the solar wind are reviewed. For brevity, we sketch the general frame, point out the problems and approaches and then illustrate by a few examples the ways in which progress has been achieved during the past four years.     

固体推进剂空穴损伤的理论与实验分析

在空穴累积损伤和微孔洞形核、长大和汇合损伤二种损伤模式分析的基础上，提出一个空实损伤细观力学模型，根据粘弹性对应原理和数学分析，求得空穴损伤演变的二个理论数学表达式。要用空穴损伤非接触诊断专利技术，进行老化药柱的空穴损伤实验研究，求得一种固体复合推进剂的空穴损伤演变的实验曲线和使用寿命。因为贮存失效临界点是实测的，对比实验分析表明：若药柱贮存时间超过贮存失效临界点，则药柱要出出裂纹，超过的时间越长则药柱中的裂纹就越大。     

Application of stress wave theory for pyroshock isolation at spacecraft-rocket interface

A large number of pyroshock devices are employed in spacecraft and rockets to realize stage separation and appendage deployment. Release of pyroshock devices induces high-level transient shock responses which tend to cause fatal damages in electronic equipment made of crystals and brittle materials. This paper aims to provide methods to isolate pyroshock and guarantee the safety of such equipment against high-frequency shocks. Firstly, stress wave transmission mechanism in stepped rods is investigated, upon which optimal area rate for shock isolation is achieved. Then, two spacecraft-rocket interface structures for pyroshock isolation, namely isolation hole and interim segment, are proposed. Both numerical simulations and experiments are carried out to validate the two shock isolation strategies. It is revealed that the interim segment structure shows better pyroshock isolation performance at the cost of increasing the weight of launching system whereas isolation hole is an optimal choice to reduce pyroshock response without causing weight increase.     

基于分岔理论的起落架撑杆式锁机构设计

提出了运用分岔理论研究锁机构性能问题的分析方法,以前起落架上下位一体式锁机构为对象,基于分岔理论,通过数值延拓,研究了收放作动筒和解锁作动筒对该机构稳定性能的影响,阐释了锁机构运动分岔图中分岔点与上锁、解锁行为的对应关系,并分别针对上、下位解锁过程按照不同解锁力共划分了5种锁机构解锁状态。论述了延拓解锁、上锁分岔点得到的轨迹曲线,并根据曲线临界尖点定义了临界解锁力和临界解锁角度2个状态变量,随后分析了弹簧刚度、原长和安装点位置对以上变量的影响趋势。基于影响分析结果,在锁机构上锁能力一定的前提下,改变参数,优化了下位临界解锁力。研究表明,分岔分析能够快速全面地把握锁机构动力学特性随不同参数的变化趋势,在分析锁机构性能、指导参数初步设计方面有一定优势。     

应用保护映射理论的高超声速飞行器自适应控制律设计

针对高超声速飞行器包线范围广、参数变化大的控制需求,应用保护映射理论提出一种高超声速飞行器的自适应控制律设计方法。首先建立整个飞行包线内的线性变参数(LPV)模型,在参数变化边界点设计一个初始的控制结构和参数,然后基于保护映射理论分析初始控制结构使闭环系统稳定的参数范围,通过迭代自动获取整个包线内满足性能指标的控制参数,进而通过多项式拟合设计出高超声速飞行器自适应控制律。所提出的方法能够根据初始控制结构自动寻找一系列满足性能要求的控制器参数,并确定这些控制参数满足闭环系统稳定的设计范围。仿真结果表明,所设计的自适应控制律能够确保高超声速飞行器大包线的设计要求,实现闭环系统的鲁棒稳定。