卫星故障诊断的最优奇偶向量法

 提供一种卫星故障诊断方法以提高 GPS导航的完整性。该方法利用最优奇偶向量来检测和诊断卫星故障以提高卫星故障诊断的准确性。仿真结果显示,在故障幅值较小的情况下最优奇偶向量方法相比广义似然比方法可以提高故障的正确检测率和正确诊断率。该方法还可以缩短检测斜坡型故障的时间,从而提高了系统的可靠性。     

Online scheduling of distributed Earth observation satellite system under rigid communication constraints

This paper focused on online scheduling of distributed Earth observation satellite system in a dynamic environment. The objective was to maximize the total profit of the overall system by efficiently coordinating the different satellites with stochastic arrival of urgent tasks, subject to rigid communication and observation time window constraints. We formulated this problem as a single-task, single-robot, time-extended assignment problem with intra-schedule dependency using the multi-robot task assignment taxonomy and formulated the sub-problem after releasing urgent tasks in a mixed-integer linear programming model. We first described the online scheduling algorithm for a single satellite, then we proposed the modified consensus-based bundle algorithm (m-CBBA) and modified asynchronous consensus-based bundle algorithm (m-ACBBA) with synchronous and asynchronous communication, respectively. Compared with initial versions of CBBA and ACBBA, the modified versions added the communication loop prediction phases to efficiently utilize scarce communication opportunities and reduce the communication requirements. Additionally, we introduce two contract net protocol (CNP)-based algorithms for comparison, respectively SingleItem-CNP-based (SI-CNP) algorithm and Batch-CNP-based (BA-CNP) algorithm. Computational experiments indicated that both the total profit and percentage of scheduled urgent tasks achieved by the m-ACBBA and m-CBBA algorithms were much higher than those achieved by both SI-CNP and BA-CNP. Additionally, the number of communications needed by either m-ACBBA or m-CBBA algorithm was lower than that by SI-CNP. When the communication cost in the system is high, the m-CBBA algorithm is preferred because it balances the profit and the required number of communications. When the communication cost is low, the m-ACBBA algorithm is preferred because it achieves high total profit and high percentage of scheduled urgent tasks.     

基于非连续算子广义变分不等式强解的存在性

在算子不连续的情况下,利用FKKM定理和Weierstrass定理及标量化方法得到了广义向量变分不等式的强解存在性定理.     

球形粒子在流体中的跟随性

本文从Maxey和Riley的粒子运动基本方程出发,得到了球形固体粒子在相对流动雷诺数很小情形下的分析解。讨论了粒子跟随性对外力、初始条件和流场性质的依赖关系;对均匀湍流场,分析了不同密度比和扰动频率对跟随性的影响     

Solar modulation model with reentrant particles

We developed a one dimensional model of particle transport in the heliosphere. As opposite to widely used models, we apply a method where a quasi-particle is traced back in time. The model gives us the possibility to work on the possible existence of reentrant particles in the heliosphere that can be hardly solved by the traditional forward tracking method. Particles escape from the heliosphere and may reenter back. We estimate how these particles affect the modulation process in the heliosphere. Presented here are the results for different values of particles mean free path in the interstellar space and for different interstellar magnetic field values.     

Self-similar stochastic processes in solar wind turbulence

Solar wind data is used to estimate the autocorrelation function for the stochastic process x(τ) = y(t + τ) − y(t), considered as a function of τ, where y(t) is any one of the quantities B²(t), n_p(t)V²(t), or n_p(t). This process has stationary increments and a variance that increases like a power law τ^2γ where γ is the scaling exponent. For the kinetic energy density and the proton density the scaling exponent is close to the Kolmogorov value γ = 1/3, for the magnetic energy density it is slightly larger. In all three cases, it is shown that the autocorrelation function estimated from the data agrees with the theoretical autocorrelation function for a self-similar stochastic process with stationary increments and finite variance. This is far from proof, but it suggests that these stochastic processes may be self-similar for time scales in the small scale inertial range of the turbulence, that is, from approximately 10 to 10³ s.     

风扇进口噪声预测模型的改进

针对Heidmann模型对风扇进口低频噪声(1k Hz)预测结果偏低的情况,通过引入风扇叶尖弦长雷诺数和相关几何参数改进了Heidmann模型中风扇进口宽频噪声的频谱修正函数,确定了其中频谱修正系数为0.085。对比改进模型和Heidmann模型的风扇进口噪声预测结果发现:在亚声速工况下,改进的模型很好地改善了风扇进口低频噪声的预测结果,改进幅值可以达到约45d B;而在超声速工况下,由于风扇进口产生的组合单音噪声成为风扇进口噪声的主要组成部分,除了在小于100Hz的频域内,改进的模型与Heidmann模型的预测结果差别不大。     

高速颤振模型设计中颤振主要模态的判断

颤振模型设计时难以实现完全的动力学相似,需要对颤振主要模态进行合理选择。采用数值分析方法,对颤振模型设计时主要模态的选取问题进行研究。通过各阶模态振型下气动刚度系数的比较、指定运动形式下广义非定常气动力的计算和不同模态截断下颤振结果的收敛特性分析,研究了颤振分析时不同模态运动之间的相互影响,对模态运动引起的气动力和颤振特性变化进行评估。以高超翼面模型为研究对象的数值算例结果表明,几种分析方法所判断的颤振主要模态基本一致。其中基于振型的广义气动刚度系数参数,避免了非定常气动力的计算,可作为颤振模型设计或颤振分析时主要模态选取的快速判断方法。     

大型客机低速构型高雷诺数风洞腹撑支架干扰数值模拟

风洞到飞行相关性修正是获取现代大型客机低速气动特性的重要手段，通常采用增压提高风洞试验雷诺数，而支架干扰修正是该修正体系的一个关键环节。采用数值模拟研究了增压风洞腹撑的支架干扰，并分析了腹撑对飞机各部件的干扰及其对风洞流场的影响。通过数值模拟与风洞试验对比，表明升力系数相差0.006，阻力系数最大相差0.001 2，俯仰力矩系数最大相差0.01，验证了CFD数值模拟方法的可靠性。CFD计算结果表明：腹撑使得全机升力增加、阻力减小，俯仰力矩增加；腹撑对升力影响的主要部件是机翼，腹撑使得风洞中心以上动压增加，提升上翼面流速，从而增加了机翼的升力；与传统认识不同的是腹撑对阻力影响为负，且主要影响部件为缝翼，原因为缝翼下偏使得法矢分量向前从而减小了阻力；腹撑对俯仰力矩影响的主要部件是机身及平尾。研究结果揭示了腹撑对飞机气动特性影响的量级、主要影响部件及其流场变化，可为支架干扰数据修正及支架优化设计提供参考。所得结论可更好用于支架干扰试验的开展及风洞到飞行数据的修正，具有一定的工程实用性。     

重型燃气轮机高雷诺数CDA叶型转捩特性数值计算

为研究重型燃气轮机的压气机叶片在高雷诺数工况下的气动性能,基于Gamma-Theta转捩模型的雷诺时均方程对某可 控扩散叶型进行了数值计算。通过对比不控制马赫数与控制马赫数,分析高雷诺数对可控扩散叶型气动性能及转捩特性的影响。 结果表明：在不控制马赫数条件下,在零攻角时,雷诺数从7×10 5 增大为9×10 5 ,总压损失增加了约391.95%;在高雷诺数工况下随 着雷诺数的增大,叶片流动损失不断增大,叶片可用攻角范围减小,同时在叶片吸力面出现激波,干扰转捩的产生。在控制马赫数 条件下,当Ma=0.6时,在零攻角工况下,雷诺数从8.2×10 5 增大为1×10 7 ,总压损失减小了约38.98%,吸力面转捩起始点从4.78%弦 长处前移至1.11%弦长处;在高雷诺数工况下,叶片流动损失随着雷诺数的增大不断减小,吸力面转捩位置前移。