直升机金属结构的全范围安全S-N曲线确定方法

本文介绍了直升机结构安全S-N曲线的确定方法.在常用的三参数S-N曲线公式Stromeyer方程的基础上,根据直升机载荷的特点,介绍了一种适合直升机疲劳评定的全范围S-N曲线公式,并提供一套根据中值S-N曲线获得安全S-N曲线的方法.     

A rendezvous navigation algorithm for orbit determination, based on visual measurements by space vehicle crew members

At present, various radio navigation systems are employed during the automated approach of a transport vehicle to a space station. Experience has shown that emergency situations can occur in which it is necessary to revert to manual override of the automatic approach.Such situations have indeed occurred during flight operations of the space station Mir. The crews of the transport vehicles and the Mir used manual steering more than 30 times for successful docking, and four times for approach to the station.Successful manual steering demands absolute understanding of the relative orbit parameters. The decisive task of the crew is to determine these relative parameters. This is possible using visual observations from either the transport vehicle or the station using simple and reliable instruments. This article explains the algorithm for determining the relative orbits from visual crew observations, based on similarities of relative orbit families.     

On prediction of re-entry time of an upper stage from GTO

The evolution of objects in geostationary transfer orbit (GTO) is determined by a complex interplay of atmospheric drag and luni-solar gravity. These orbits are highly eccentric (eccentricity >0.7) and have large variations in velocity and perturbations during a revolution. The periodic changes in the perigee altitudes of these orbits are mainly due to the gravitational perturbations of the Sun and the Moon. The re-entry time of the objects in such orbits is sensitive to the initial conditions. The aim of this paper is to study the re-entry time of the cryogenic stage of the Indian geo-synchronous launch vehicle, GSLV-F04/CS, which has been decaying since 2 September 2007 from initial orbit with eccentricity equal to 0.706. Two parameters, initial eccentricity and ballistic coefficient, are chosen for optimal estimation. It is known that the errors are more in eccentricity for the observations based on two line elements (TLEs). These two parameters are computed with response surface method using a genetic algorithm for the selected eight different zones, based on rough linear variation of the mean apogee altitude during 200 days orbit evolution. The study shows that the GSLV-F04/CS will re-enter between 5 December 2010 and 7 January 2011. The methodology is also applied to study the re-entry of six decayed objects (cryogenic stages of GSLV and Molniya satellites). Good agreement is noticed between the actual and the predicted re-entry times. The absolute percentage error in re-entry prediction time for all the six objects is found to be less than 7%. The present methodology is being adopted at Vikram Sarabhai Space Centre (VSSC) to predict the re-entry time of GSLV-F04/CS.     

Finite Element Modelling of Failure of a Multi-Material Target due to High Velocity Space Debris Impacts

Lagrangian finite element methods have been used extensively in the past to study the non-linear transient behaviour of materials, ranging from crash tests of cars to simulating bird strikes on planes. However, as this type of space discretisation does not allow for motion of the material through the mesh when modelling extremely large deformations, the mesh becomes highly distorted. This paper describes some limitations and applicability of this type of analysis for high velocity impacts. A method for dealing with this problem by the erosion of elements is proposed, where the main driver is the definition of element failure strains. Results were compared with empirical perforation results and were found to be in good agreement. The results were then used to simulate high velocity impacts upon a multi-layered aluminium target in order to predict a ballistic limit curve. LS-DYNA3D was used as the FE solver for all simulations. Meshes were generated using Truegrid.     

Effect of Multi-wall System Composition on Survivability for Spacecraft Impacted by Orbital Debris

Long-duration spacecraft in low earth orbit such as the International Space Station (ISS) are highly susceptible to high-speed impacts by pieces of debris from past earth-orbiting missions. Among the hazards that accompany the penetration of a pressurized manned spacecraft are critical crack propagation in the module wall, crew hypoxia, and uncontrolled thrust due to air rushing out of the module wall hole. A Monte Carlo simulation tool was used to determine the effect of spacecraft wall construction on the survivability of ISS modules and crew following an orbital debris penetration. The simulation results indicate that enhanced shield wall designs (i.e., multi-wall systems with heavier inner bumpers) always lead to higher overall survivability of the station and crew due to an overwhelming decrease in likelihood of module penetration. The results of the simulations also indicate that changes in crew operations, equipment locations, and operation procedures can significantly reduce the likelihood of crew or station loss following an orbital debris penetration.     

贩毒吸毒的微分方程模型及定性分析

贩毒吸毒是人类丑恶行为表现出的社会丑恶现象，在人类正常的生活环境中时有发生。特别近年来有的国家或地区呈现流行的趋势，各国对此都十分关注。建立三个描述贩毒吸毒社会丑恶现象的微分方程模型。借助于微分方程定性论的基本理论，分析微分方程模型基本理论，分析贩毒吸毒流行的趋势，流行的结局，得到基本符合实际的效果。     

确定高速碰撞试验中碎片特性的测试技术

文章介绍了高速碰撞试验中碎片特性的几种测试技术,软捕获技术、照相技术、间接测量技术,及其适用情况。     

空间碎片数据形式及轨道演化算法

根据建立空间碎片工程模型的需要,定义了一种描述单个空间碎片运行位置及其物理特性的数据形式。基于空间碎片运动规律给出了一种用于计算单个空间碎片运行时＂平均位置＂的演化算法。计算的演化结果与STK软件计算的标称轨道比较表明：该演化算法正确。     

地球静止轨道卫星撞击解体的数值模拟

分析了地球静止轨道（GE0）环内的物体现状,引入美国家航空航天局（NASA）的标准解体模型,给出了卫星撞击解体算法,编写了数值仿真软件,仿真研究了GEO卫星撞击解体形成碎片的特征及其轨道分布。结果表明：撞击会产生大量碎片,对空间环境造成长期的严重危害。研究结果对分析卫星撞击解体特性、保护空间环境有一定的参考价值。     

基于三阶解析解的小行星平衡点附近halo轨道确定方法研究

尽管周期解的存在性已经被证明,但要在给定的动力学系统中寻找到满足一定精度要求的周期解依然是一件极富挑战性的工作.提出如下方法确定小行星平衡点附近精确的周期轨道(halo轨道).首先扩展运动方程:将小行星平衡点附近轨道运动方程的右端项在平衡点处展成三阶幂级数.从而将非线性运动学方程扩展为拟线性微分方程.然后求近似解析解:应用Lindstedt-Poincaré方法求解扩展后的运动方程组,将周期解和其运动频率展开成三阶幂级数,并将二者代人扩展后的拟线性微分方程中.这样就可以得到三个不同阶的线性运动方程,逐次求解三个微分方程并消除解中的永年项即可得到hal.轨道的三阶解析解.最后微分校正:将周期轨道在三阶解析解附近线性化,得到状态转移矩阵,并使用状态转移矩阵和轨道终端状态的偏差修正轨道初值,从而得到满足精度要求的精确引力场中的halo轨道.