空气动力二阶核函数辨识方法

采用截断三阶Volterra级数模型来研究空气动力二阶核函数的辨识问题,选取一簇正交化的切比雪夫多项式对二阶核函数进行参数化处理,并将非参数辨识问题转化成参数辨识问题。相比于其他方法,本文模型能有效降低对激励信号幅值的敏感程度,保证辨识出的核函数具有较好的保真度;只针对三阶Volterra降阶模型中的一阶、二阶核函数进行辨识,即可提升原系统一阶、二阶核函数的辨识精度,却不会显著增加辨识过程的工作量;参数化辨识方法属于整体性辨识,根据已有的部分数据对(输入、输出数据)就能完成系统辨识,且能达到较好的辨识精度,从而有效地减少了执行计算流体力学(CFD)代码程序的总次数,节约了大量的时间成本。算例表明,与目前流行的非参数化方法相比,本文提出的切比雪夫函数辨识方法,精度上达到预期要求,辨识过程消耗的CFD总时间量至少可降低一个数量级。     

教学新摸式在专项课教学中的运用

本文主要阐明了新的教学模式在专项课教学中的运用,并对新模式的结构及运用作了分析。通过讨论讲述了新模式的优势,并提出运用新模式的具体要求。     

三阶段法与活动周期图

对二种离散系统仿真建模方法，三阶段法和活动周期图进行系统的介绍，分析与讨论，指出它们的特点，应用情况及最新发展，三阶段法是分析研究仿真问题的一种世界观，具体反映在仿真软件及模型的程序结构，活动周期图往往与三阶段法一道使用，用于描述系统内实体的逻辑流程，这两种方法的特点使它们成为欧洲，尤其是英国最重要的离散系统仿真建模方法。     

基于Lyapunov方法的空间飞行器大角度姿态机动控制

本文研究空间飞行器大角度资态机动的控制问题，为了克服大角度机动时使用欧拉角可能产生的奇异问题，文中使用四元参形式的微分方程来描述飞行器的运动，飞行器的动力学方程具有不确定性和非线性。本文应用Lyapunov方法设计在大角度姿态机动控制器，这个控制器具有按指数规律变化的增益，它大大减小了对初始力矩的要求，最后，本文给出一个例子来说明所导出的控制器的优点。     

卫星远距离伴飞的变结构控制

主要研究卫星远距离稳态伴飞的控制问题。首先,根据线性相对运动方程(C-W方程)设计了能实现稳态伴飞的变结构控制律,并证明了其在有干扰情况下的有效性。然后,推导了适用于远距离相对运动的非线性方程解析解,并在此基础上对伴飞控制律进行了改进,以实现远距离的稳态伴飞。通过仿真,比较了上述控制律的效果,证明了基于非线性相对运动的变结构控制能有效地实现远距离稳态伴飞。     

Bayesian approach to retrieval of vertical ozone profile from radiometry data

A technique for retrieving vertical distributions (profiles) of atmospheric gas constituents from data of passive remote sensing of the atmosphere is proposed. The goal of the technique based on the statistical (Bayesian) approach to solution of inverse problems is construction of probability distribution for a sought quantity throughout the interval of the studied heights. It is assumed that initial data contain measurement noise, and a priori information about properties of the profile is used. It is proposed to approximate the sought profile by a function in the form of an artificial neural network. This approximation allows optimal inclusion of a priori information into retrieval procedure, thus ensuring the most effective regularization of the problem. Efficiency of the proposed technique is demonstrated on an example of retrieval of vertical ozone profile from data of ground-based sounding of the atmosphere in the millimeter wavelength range. Results of profile retrieval from model data and from spectra of radiation temperature of the atmosphere measured in the Apatity (67° N, 33° E) in the winter of 2002–2003 are presented.     

燃气源控制气流热效应数值模拟研究

为了解迷宫形导热套环与流体之间的热交换对控制气流温度及压力的影响,采用整体求解法求解控制气流与多层套环之间的耦合传热问题。为确保计算结果在物理上的真实性,采用“假密度法”求解以温度T为求解变量的能量方程。计算得到了控制气流参量随时间的变化情况以及迷宫形多层导热套环的温度在不同时间点的分布情况,结果表明流场的三维复杂结构使得每个小孔射流与各层套环的传热情况都不同,流体与固体区域之间的换热量随时间变化,其中内套环和中套环对流体的吸热量随时间的增长而急速下降,从而导致控制气体的温度和压力都随时间而逐渐增大。计算所得的控制气流温度和压力与试验测量值的变化趋势相同,验证了计算方法的有效性。     

民用飞机复合材料C型框分析方法研究

以层压板理论为基础,提出一种复合材料C型框结构的工程分析方法,并通过试验给出了C型框结构设计许用值。通过工程分析结果与试验结果的对比,说明此工程分析方法可用于指导C型框结构设计。     

Prediction of horizontal gas–solid flows under different gravitational fields

In this paper the performance of horizontal pneumatic conveying under different gravity environments is evaluated. An Euler–Lagrange approach validated versus ground experiments is employed to predict the relevant particle variables such as particle mass flux, mean conveying and fluctuating velocities in terrestrial, lunar and micro-gravity conditions. Gravity reduced computations predict a reduction in the global particle–wall collision frequency. Also, in the case of low wall roughness and small particle mass loading, reduction of gravity acceleration implies an increase of particle–wall collision frequency with the upper wall of the channel affecting greatly the particle mass flux profile. In the case of high wall roughness and/or high particle-to-fluid mass loading (i.e., around 1.0) particle conveying characteristics are similar in the three gravity conditions evaluated. This is due to the fact that both, wall roughness and inter-particle collisions reduce gravitational settling. However, the influence of gravity on the additional pressure loss along the channel due to the conveying of the particles is much reduced.     

Precise coseismic displacements from the GPS variometric approach using different precise products: Application to the 2008 MW 7.9 Wenchuan earthquake

The Global Positioning System (GPS) variometric approach has emerged as an attractive alternative to traditional well-developed positioning techniques including relative positioning and precise point positioning. Previous studies have demonstrated the capability of the variometric approach to retrieve coseismic displacements at centimeter-level precision, in a real-time manner using only readily available broadcast ephemeris. This study presents the first results comparing the performance of the variometric approach by using a variety of precise satellite orbit and clock products. Totally six kinds of products are included in our evaluation, namely the broadcast, IGS (International GNSS Service) ultra-rapid (predicted), ultra-rapid (observed), rapid, final (30-s clock) and CODE (Center for Orbit Determination in Europe) final (5-s clock) products. Static and dynamic experiments are conducted using 1-Hz GPS data covering a relatively large area in China during the 2008 Wenchuan M_W 7.9 earthquake. After removing the linear trend, the displacements using broadcast, ultra-rapid (predicted), ultra-rapid (observed) and rapid products reach nearly equivalent precisions at centimeter level. By using final and CODE final products, the precision of displacements can be significantly improved from 1.9–2.0 cm to 0.4–0.7 cm horizontally, and from 6.0–6.2 cm to 1.0–1.7 cm vertically for the dynamic experiments. The displacements using the CODE final products achieve the best precision, improved by more than 40% compared to those using the IGS final products. With the availability of IGS high-rate real-time precise products, this approach is promising to capture coseismic displacements more precisely in real time, which is crucial for earthquake and tsunami early warning.