Parameterized design of abort trajectories with a lunar flyby for a crewed mission

This article proposes an analytical preliminary design method for abort trajectory with a lunar flyby and the trajectory ergodic representation based on parameterization, as well as their application in studying the abort trajectories’ characteristics. First, by introducing two parameters, the perilune altitude and the perilune transfer time, the preliminary solution is developed parametrically using pseudostate theory to connect two special Lambert processes. The fast convergence of the improved differential correction under the high-fidelity gravity field verifies the accuracy of the proposed preliminary design method. Next, the two parameters are regarded as a set of variables to define an abort trajectory. Based on this, an ergodic representation of the abort trajectory with a certain abort time is yielded using the proposed design method, which offers a global view of the feasible abort trajectories. In addition, the influences of some factors on the performance of these abort trajectories are investigated based on the proposed design method and ergodic representation. The simulation results show that the abort time and the transfer time of the nominal trajectory significantly affect the ergodic representation and characteristics of the abort trajectory.     

基于灰色模型的故障预报技术及其在空间推进系统上的应用

研究了灰色预测建模,把灰色理论、预测技术和诊断专家系统相结合建立了一个故障预报系统,使用该系统针对空间推进系统气路部分故障,实现了故障预测预报。     

气流速度振荡场中幂律液膜不稳定性分析

采用线性稳定性分析研究了处于气流速度振荡场中幂律液膜时间模式的不稳定性。振荡的气流速度导致动量方程为含有时间周期系数的希尔方程,采用Floquet理论进行求解。详细研究了不同振荡幅值和振荡频率下表观雷诺数、幂律指数及无量纲速度因子对各不稳定区间的影响。结果表明：振荡幅值的增加或振荡频率的减小会使液膜不稳定区域的个数增加,且Kelvin-Helmholtz（K-H）不稳定区域的最大增长率、主导波数和截止波数随振荡幅值和振荡频率的增加而增加;表观雷诺数、幂律指数和无量纲速度因子的增加增强了K-H不稳定区域内的不稳定性,使参数不稳定区域内的增长率先减小后增加;振荡幅值的变化不改变最大增长率发生转折时对应的流变参数,而当振荡频率较小时,幂律指数和无量纲速度因子的增加却使最大增长率单调增加。     

Basic belief assignment approximations using degree of non-redundancy for focal element

Dempster-Shafer evidence theory, also called the theory of belief function, is widely used for uncertainty modeling and reasoning. However, when the size and number of focal elements are large, the evidence combination will bring a high computational complexity. To address this issue, various methods have been proposed including the implementation of more efficient combination rules and the simplifications or approximations of Basic Belief Assignments (BBAs). In this paper, a novel principle for approximating a BBA into a simpler one is proposed, which is based on the degree of non-redundancy for focal elements. More non-redundant focal elements are kept in the approximation while more redundant focal elements in the original BBA are removed first. Three types of degree of non-redundancy are defined based on three different definitions of focal element distance, respectively. Two different implementations of this principle for BBA approximations are proposed including a batch and an iterative type. Examples, experiments, comparisons and related analyses are provided to validate proposed approximation approaches.     

Mode selection mechanism and magnetic diffusivity in a non-axisymmetric solar dynamo model

The generation of solar non-axisymmetric magnetic fields is studied based on a linear α²–Ω dynamo model in a rotating spherical frame. The model consists of a solar-like differential rotation, a magnetic diffusivity varied with depth, and three types of α-effects with different locations, i.e. the tachocline, the whole convective zone and the sub-surface. Some comparisons of the critical α-values of axisymmetric (m = 0) and longitude-dependent modes (m = 1,2,3) are presented to show the roles of the magnetic diffusivity in the problem of modes selection. With the changing of diffusivity intensity for the given solar differential rotation system, the dominant mode possibly changes likewise and the stronger the diffusivity is, the easier the non-axisymmetric modes are excited. The influence of the diffusivity and differential rotation on the configurations of the dominant modes are also presented.     

COMPUTATION OF COMPRESSIBLE FLOW PAST SLENDER WING－BODY USING FULL－POTENTIAL EQUATION

ＣＯＭＰＵＴＡＴＩＯＮＯＦＣＯＭＰＲＥＳＳＩＢＬＥＦＬＯＷＰＡＳＴＳＬＥＮＤＥＲＷＩＮＧ－ＢＯＤＹＵＳＩＮＧＦＵＬＬ－ＰＯＴＥＮＴＩＡＬＥＱＵＡＴＩＯＮＨｕａｎｇＭｉｎｇｋｅ（ＤｅｐａｒｔｍｅｎｔｏｆＡｅｒｏｄｙｎａｍｉｃｓ，ＮａｎｊｉｎｇＵｎｉｖｅ...     

无穷观问题的研究(Ⅱ)——从Hausdorff的直觉和Poincaré的名言到Brouwer剧场现象

本组系列论文 ( )～ ( )从数学和认识论的角度系统地研究了无穷观问题的历史发展和现状 ,确立了无穷观背景世界的三分法原则 ,指出了两种无穷观相互排斥的局限性 ,形成了统一两种无穷于同一框架中的基本观点 ,并建立了一个统一实无限与潜无限于同一框架中的公理集合论系统 APAS。     

牛顿流理论及其在谐振机翼上的应用

根据牛顿流理论,文中讨论了高马赫数、任意迎角、一般剖面在均匀来流中作沉浮和俯仰谐振的翼型和机翼。导得翼型和机翼表面的牛顿撞击压强和安定性导数公式。给出楔、平板三角翼、双抛物线剖面三角翼俯仰刚性导数(-C_(mθ)和阻尼导数(-C_(m))的数值例子。数值结果与现有的牛顿-布兹曼流理论、薄激波层理论、欧拉方程摄动理论的结果作了比较,算例表明本文的结果令人满意。     

SPECIAL HIGH-ORDER BENDING CRACK TIP FINITE ELEMENT FOR THE REISSNER PLATE

ＳＰＥＣＩＡＬＨＩＧＨ┐ＯＲＤＥＲＢＥＮＤＩＮＧＣＲＡＣＫＴＩＰＦＩＮＩＴＥＥＬＥＭＥＮＴＦＯＲＴＨＥＲＥＩＳＳＮＥＲＰＬＡＴＥＪｉａｎｇＣｈｉｐｉｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＦｌｉｇｈｔＶｅｈｉｃｌｅＤｅｓｉｇｎａｎｄＡｐｐｌｉｅｄＭｅｃｈａｎｉ...     

烧蚀外形计算的一种自动调节人工粘性项的差分格式

在再入端头烧蚀外形计算中,通过对物形参数的自动滤波处理,构造出了一种附加人工粘性项三层显式差分格式。这种格式在外形变化波动区达一阶精度,在外形变化平稳区达二阶精度。数值试验表明,这种格式在保障外形计算精度和增大时间步长、节省计算机时都是有效的。