空间站微重力环境研究与分析

太空中的微重力环境对基础科学研究和新技术开发具有重要意义,为了满足未来我国空间站开展微重力科学实验的需求,需要对空间站上的微重力水平进行分析和评估,指导高微重力要求实验载荷的布局和微重力实验期间的飞行任务规划。空间站上的微重力水平用加速度值度量,通常可以分为准稳态加速度、瞬态加速度和振动加速度。针对此问题调研总结了国际空间站的微重力研究情况,并以400 km轨道高度上100吨级"T"字型积木式空间站作为算例,估算其准稳态加速度大小及分布,并初步分析瞬态加速度水平的量级。结果表明,空间站准稳态加速度水平在1μgn量级,主要贡献来自重力梯度效应;瞬态加速度可达103μgn量级。文章对将来我国空间站微重力应用支持的设计工作有一定的借鉴意义。     

长时间小过载条件下发动机流场特征及绝热层烧蚀分析

以揭示固体火箭发动机在飞行条件下绝热层的异常烧蚀特性为目的,针对小过载、长作用时间条件下大长径比流道的发动机开展了三维两相流场的数值模拟研究,详细分析了发动机内流道内不同区域的颗粒聚集特征,并结合发动机失效部位处绝热层的烧蚀形貌进行了失效模式分析,针对性地提出了改进措施.研究结果表明:(1)不同过载条件下发动机内颗粒聚集和分布状态受过载大小和发动机流道结构共同作用且影响规律复杂,所引起的绝热层异常烧蚀模式和机理不同,特别是小过载长作用时间条件下的异常烧蚀需要引起设计者重视.(2)颗粒聚集在绝热层表面的换热或冲蚀都将引起绝热层局部烧蚀加剧,形成的“凹坑或凹槽”烧蚀形貌会造成颗粒的二次聚集效应,进而加剧烧蚀过程.(3)通过增加发动机旋转动作和局部绝热层加厚,可以提高发动机的飞行安全性.     

基于预测模型迭代优化的改进比例导引律

为了提高对加速度时变机动目标的制导精度,将预测决策理论与传统比例导引(PN)相结合,提出了一种通过泰勒级数预测模型迭代控制加速度修正项的改进比例导引律。首先,以预设的低阶泰勒级数预测模型预测特定时间的位移,并计算位移预测值与测量值的差值;然后,通过迭代方法逐阶增加泰勒级数预测模型阶数,直至满足精度要求;最后,计算泰勒级数预测模型的二阶导数,修正比例导引律的加速度指令。仿真结果表明,传统PN和APN的脱靶量分别约为195 m和95 m,提出的改进比例导引律的脱靶量约为8.3 m,极大地提高了制导精度。     

正弦力校准中质量块加速度分布影响的理论修正研究

通过理论分析得到质量块加速度分布影响的理论修正公式,并利用有限元法验证了理论公式,同时对实际应用中理论公式的修正偏差作出估计,为动态力校准的不确定度分析提供了可靠依据。     

Heating heavy ions in the polar corona by collisionless shocks: A one-dimensional simulation

Recently a new model for explaining the observations of preferential heating of heavy ions in the polar solar corona was proposed ( and ). In that model the ion energization mechanism is the ion reflection off supercritical quasi-perpendicular collisionless shocks in the corona and the subsequent acceleration by the motional electric field E = −V × B/c. The mechanism of heavy ion reflection is based on ion gyration in the magnetic overshoot of the shock. The acceleration due to the motional electric field is perpendicular to the magnetic field, giving rise to large temperature anisotropy with T_⊥ ? T_∥, in agreement with SoHO observations. Such a model is tested here by means of a one dimensional test particle simulation where ions are launched toward electric and magnetic profiles representing the shock transition. We study the dynamics of O⁵⁺, as representative of coronal heavy ions for Alfvénic Mach numbers of 2–4, as appropriate to solar corona. It is found that O⁵⁺ ions are easily reflected and gain more than mass proportional energy with respect to protons.     

Particle acceleration and gamma rays in solar flares: Recent observations and new modeling

Experiments on SMM, GAMMA, Yohkoh, GRANAT, Compton GRO, INTEGRAL, RHESSI and CORONAS-F satellites over the past three decades have provided copious data for fundamental research relating to particle acceleration, transport and energetics of flares and to the ambient abundance of the solar corona, chromosphere and photosphere. We summarize main results of solar gamma-astronomy (including some results of several joint Russian–Chinese projects) and try to appraise critically a real contribution of those results into modern understanding of solar flares, particle acceleration at the Sun and some properties of the solar atmosphere. Recent findings based on the RHESSI, INTEGRAL and CORONAS-F measurements (source locations, spectrum peculiarities, ³He abundance etc.) are especially discussed. Some unusual features of extreme solar events (e.g., 28 October 2003 and 20 January 2005) have been found in gamma-ray production and generation of relativistic particles (solar cosmic rays, or SCR). A number of different plausible assumptions are considered concerning the details of underlying physical processes during large flares: (1) existence of a steeper distribution of surrounding medium density as compared to a standard astrophysical model (HSRA) for the solar atmosphere; (2) enhanced content of the ³He isotope; (3) formation of magnetic trap with specific properties; (4) prevailing non-uniform (e.g., fan-like) velocity (angular) distributions of secondary neutrons, etc. It is emphasized that real progress in this field may be achieved only by combination of gamma-ray data in different energy ranges with multi-wave and energetic particle observations during the same event. We especially note several promising lines for the further studies: (1) resonant acceleration of the ³He ions in the corona; (2) timing of the flare evolution by gamma-ray fluxes in energy range above 90 MeV; (3) separation of gamma-ray fluxes from different sources at/near the Sun (e.g., different acceleration sources/episodes during the same flare, contribution of energetic particles accelerated by the CME-driven shocks etc.); (4) asymmetric magnetic geometry and new magnetic topology models of the near-limb flares; (5) modeling of self-consistent time scenario of the event.     

降低亚轨道飞行器再入法向过载峰值的攻角设计方法

针对亚轨道飞行器再入中的大过载问题,提出一种通过保持法向过载动态平衡以大幅降低法向过载峰值的攻角设计方法。该方法基于再入飞行中过载演化特性,通过自主分段、预测反馈及迭代修正对再入攻角进行设计,使攻角变化率与法向过载的期望平衡值相适应,并可经过重复计算及收敛实现法向过载峰值最小化。仿真计算的结果表明,该方法能够大幅降低亚轨道飞行器再入中的法向过载,且按照该方法设计所获攻角策略可有效用于亚轨道飞行器再入任务规划、再入轨迹和制导律设计。
     

助推-滑翔导弹射程管理技术研究

针对助推-滑翔导弹全程弹道设计问题,提出了基于能量管理的射程管理技术,采用助推段能量管理机动和滑翔段阻力加速度能量管理方法,研究并提出了具体的射程管理方案,分析了不同射程管理方案对射程的影响及其射程区间,验证了通过能量管理实现射程管理的可行性,确定了助推-滑翔导弹射程的可覆盖范围,并给出了一组特定射程下的飞行参数。研究结果表明,通过能量管理技术可实现大范围的射程调节,最小射程可到最大射程的49.3%,采用该射程管理技术可实现助推-滑翔导弹弹道快速、灵活设计,为其发射参数的装订提供了一种新的途径。     

超声速磁流体加速实验及一维模型分析

为了获得负载系数、电导率等参数变化对超声速磁流体加速效果的影响规律,利用激波风洞,采用氩气与碳酸钾作为工质,电容提供电能的方式,在磁感应强度为0.5T的条件下,进行了不同电容充电电压下的超声速磁流体加速实验研究,并对一维定常理想分段法拉第型磁流体加速模型进行了分析.通过实验获得了不同电容充电电压下#10电极间的电压、电流、负载系数、电导率及#20电极开路电压等数据,在300, 400V电容充电电压下,气流速度分别增加11.4%和24.0%,在500V电容充电电压下气流速度减小11.1%.实验及模型分析得出不同的负载系数会使超声速磁流体处于加速或减速的不同状态,而电导率会影响注入总能量的大小,使磁流体流动的速度梯度大小发生改变.      

光滑粒子流体动力学的一种并行数值计算方案

在三维超高速碰撞数值计算方面,针对三维光滑粒子动力学（SPH）方法计算量大和耗时长的缺点,文章提出了一种简单直接、易于编程实现的SPH并行计算方案,并简述了该方案的基本思想、任务划分、变量存储、信息传递以及主要计算步骤。最后利用自编并行程序计算了两个超高速碰撞实例,结果表明:针对几百万个粒子,在运算速度为每秒5万亿次的“银河”计算机上申请23个核并行计算,每步约需要8 s,加速比约为10,并行效率约为50%,计算时间显著减少。