可压缩流动的高分辨率低耗散混合格式研究(英文)

针对可压缩流场的计算,提出了一种混合型激波捕捉格式来获得对于光滑区域和流场间断都具有高精度的解。该混合方法采用有限体积形式的五阶WENO格式来计算流场的光滑区域,而采用MUSCL格式来捕捉流场中的间断。该混合格式结合WENO格式的低耗散特性和MUSCL格式的高分辨率特性。两种格式之间通过一个间断感受因子进行切换。文中选择了三种典型的间断感受因子进行对比研究。WENO格式和MUSCL格式均为激波捕捉格式,因此混合开关中的常数的选择范围相对较宽。选取了若干典型算例对于混合格式的性能进行了研究,并对不同格式的计算精度和效率进行了对比。数值结果表明,与WENO和MUSCL相比,本文提出的混合方法在较广的范围内均表现出良好的特性。     

多变量气动伺服弹性系统的鲁棒稳定性研究

根据现代控制理论,对多输入-多输出气动伺服弹性系统的鲁棒稳定性进行研究.分别采用小增益原理和最小奇异值理论两种方法,对涉及飞行器互相耦合的横滚和偏航回路的控制系统进行分析,得出了气动伺服弹性系统抵抗建模误差、保持鲁棒稳定的范围.这两种方法都分别给出了稳定性判据,根据判据可以确定其鲁棒稳定性(或稳定裕度).作为系统扰动的表达形式,文中还对系统不确定性矩阵进行了描述.算例是在某ACT战斗机的计算模型上完成的,两种方法的计算结果取得了一致.      

An archival study of extended X-ray emission from classical and recurrent novae

I discuss morphology and spectrum of the first resolved and detected classical nova shell in the X-rays – the remnant of GK Persei (1901). The existence of such a nebulosity brings about the possibility of other nova remnants emitting X-rays. I calculate that the X-ray luminosity should be about 10²⁶–10³³ ergs s⁻¹ on the onset of cooling for nova remnants. I have done an archival search on 250 classical and recurrent nova candidates using Chandra, XMM-Newton, ROSAT and ASCA databases. There is no significant extended emission detected which places an upper limit of F_x < × 10⁻¹² erg s⁻¹ cm⁻² (unabsorbed). Only exceptions are GK Per, RR Pic and DQ Her (all observed by Chandra ACIS-S and GK Per also by ROSAT HRI) where the latter two show marginal extended emission in the X-rays associated with emission knots (DQ Her) or an equatorial ring (RR Pic).     

Polarization studies of magnetic cataclysmic variables

I discuss methods and results in the use of photo-polarimetry and spectro-polarimetry in the studies of magnetic cataclysmic variables. In particular I show how polarimetry can be used to derive the geometry of the accretion region on the surface of the white dwarf, the accreting geometry of the system as a whole and how polarimetry aides in the interpretation of X-ray/optical photometry and spectroscopy. I finish by describing the high speed spectro-polarimetric capabilities of SALT (Southern African Large Telescope) due for completion in 2005.     

Observations and theory of cataclysmic variables: On progress and problems in understanding dwarf novae and nova-like stars

After brief historical and theoretical introductions to the field, observed properties of dwarf novae and non-magnetic nova-like stars are reviewed. Photometric observations splitted into events on time-scales of months to years (outburst light curves), hours (orbital light curves) and minutes and below (flickering and oscillations), respectively, and spectroscopic observations are presented. The emphasis is on one hand on the features common to many objects in an attempt to gain some impression on what could be considered typical features. On the other hand observations are highlighted that spectacularly deviate from these common trends as they may give some hint as to what the possible range of variability is. Whenever possible, the implications for the physical properties and possible models of the systems are pointed out. Furthermore, for each section the current status of the conceptual understanding and attempts to model this are briefly reviewed and, finally, confronted with the observations.     

解不可压N—S方程的PCIMG法

本文提出了一种解不可压N-S方程的预测、修正、迭代、多重网格法。这种算法程序简单,结果精确及收敛快速。     

The variability of eta Car: A tool for the LBV phenomenon

We discuss the historical light curve of the most peculiar superluminous star Car, and the spectroscopic variations during the last 100 y. After the nova-like spectral evolution following the 1889 light maximum, the star underwent many shell episodes which were characterized by a large fading of the higher ionization emission lines. We describe the most recent 1992 event when the Hei and [Nii] emission lines nearly faded out, and a broad P Cygni absorption appeared in the Hi and Hei lines. A recurrence time of about 5 years is suggested from the times of the spectroscopic episodes and the IR light curve. The results are discussed in the light of possible models.     

利用厄密特多项式的配置和非线性规划进行小推力最优变轨

提出了一种计算在反平方场中采用小推力变轨的最优轨道的直接方法,这种方法采用了近段发展起来的使用分段的多项式来代替状态和控制变量的直接优化方法,然后最优控制问题就转化成可以用数值方法解决的非线性规划问题。     

反射面型天线结构多工况离散变量优化设计

根据反射面型天线结构受载和工作状态的复杂性，以及总有一些变量只能按离散变量处理，建立了符合工程结构的反射面型天线结构多工况离散变量优化设计数学模型，编制了一套具有一定通用性及工程实用价值的优化设计软件，并用其对八米反射面型天线进行了优化计算，取得了比较满意的效果。     

一种非线性最优导弹制导律

以质点飞行器的非线性运动方程为基础，研究了导弹拦截目标问题。运用线化变换理论和线性二次型微分对策理论，导出了导弹和目标的最优控制策略，对导弹最优策略进行了综合分析，给出了一种可以实时实现的最优制导律。并以某型中远程地－空导弹的气动数据和数学模型为基础，进行了全弹道拦截数字仿真，仿真结果表明：该制导律在减少终端脱靶量方面比空间比例导引的效果好。