抛物形吸气式脉冲爆震激光推力器性能预示的解析模型

考虑激光束、推力器构型以及大气环境三方面因素,建立了抛物形吸气式脉冲爆震 激 光推力器性能预示的解析计算模型。其中,将推力室内的流场发展过程分为吸收波和冲击波 衰减两个阶段,应用Sedov点爆炸理论,以等效锥形约束空间,引入单一的修正因子以反 映流场的不均匀性。计算表明,其结果同现有实验数据吻合。〖JP〗     

永磁同步电机定子系统模态振型研究

针对永磁同步电机振动及噪声的问题,从电机定子系统的结构模态入手,通过仿真分析不同铁心模型及不同机壳厚度对定子系统的影响,分析定子各参数对电机振动及噪声的影响。通过试验验证了仿真求解的可靠性,得到各参数对定子系统振型影响的一般规律。     

基于模态局部化效应的微机械加速度计研究进展

模态局部化效应是安德森局部化在结构动力学中的一种具体表现形式,其利用振动模态的能量局部集中效应实现了灵敏度的大幅度提高。因此,模态局部化效应近年来逐渐被用于研制高精度的谐振式传感器。介绍了模态局部化效应的基本原理及发展历程,及其在各类谐振式传感器中的应用及研究现状,包括质量传感器、电荷传感器、位移传感器以及刚度传感器。最后,着重介绍了模态局部化效应在惯性敏感器件加速度计中的应用及研究现状。     

An adaptive fast fixed-time guidance law with an impact angle constraint for intercepting maneuvering targets

Sliding mode guidance laws based on a conventional terminal sliding mode guarantees only finite-time convergence, which verifies that the settling time is required to be estimated by selecting appropriate initial launched conditions. However, rapid convergence to a desired impact angle within a uniform bounded finite time is important in most practical guidance applications. A uniformly finite-time/fixed-time convergent guidance law means that the convergence (settling) time is predefined independently on initial conditions, that is, a closed-loop convergence time can be estimated a priori by guidance parameters. In this paper, a novel adaptive fast fixed-time sliding mode guidance law to intercept maneuver targets at a desired impact angle from any initial heading angle, with no problems of singularity and chattering, is designed. The proposed guidance law achieves system stabilization within bounded settling time independent on initial conditions and achieves more rapid convergence than those of fixed-time stable control methods by accelerating the convergence rate when the system is close to the origin. The achieved acceleration-magnitude constraints are rigorously enforced, and the chattering-free property is guaranteed by adaptive switching gains. Extensive numerical simulations are presented to validate the efficiency and superiority of the proposed guidance law for different initial engagement geometries and impact angles.     

飞机电静液作动器滑模 PID控制器设计

在多电飞机应用环境中,由于电静液作动器（Electro Hydrostatic Actuator,以下简称EHA）系统本身的强非线性与承载交变动载荷的不确定性,简单PID控制无法达到理想控制效果。提出了滑模 PID复合控制,电机电流环和转速环构成控制系统内环,以PI控制器实现电机调速;作动筒位置环为外环,以滑模控制提升系统的快速性和鲁棒性。建立了EHA数学模型,并设计了滑模控制器结构。仿真结果表明,滑模 PID复合控制方法能有效地消除超调和减小跟随误差,实现对EHA位置的精确控制。     

发动机双发失效空滑策略研究

双发失效是飞机在发动机试飞中可能遇到的最大风险。通过提前规划双发失效后的垂直、水平路径,让飞行机组在遇到双发失效特情时能按照预先规划的路径飞行,遵循最有利的能量使用,减轻机组在特情时的负荷和避免做出不良决策,以期降低双发失效风险带来的影响。     

Fundamental (f) oscillations in a magnetically coupled solar interior-atmosphere system – An analytical approach

Solar fundamental (f) acoustic mode oscillations are investigated analytically in a magnetohydrodynamic (MHD) model. The model consists of three layers in planar geometry, representing the solar interior, the magnetic atmosphere, and a transitional layer sandwiched between them. Since we focus on the fundamental mode here, we assume the plasma is incompressible. A horizontal, canopy-like, magnetic field is introduced to the atmosphere, in which degenerated slow MHD waves can exist. The global (f-mode) oscillations can couple to local atmospheric Alfvén waves, resulting, e.g., in a frequency shift of the oscillations. The dispersion relation of the global oscillation mode is derived, and is solved analytically for the thin-transitional layer approximation and for the weak-field approximation. Analytical formulae are also provided for the frequency shifts due to the presence of a thin transitional layer and a weak atmospheric magnetic field. The analytical results generally indicate that, compared to the fundamental value ($\omega =\sqrt{\mathit{gk}}$), the mode frequency is reduced by the presence of an atmosphere by a few per cent. A thin transitional layer reduces the eigen-frequencies further by about an additional hundred microhertz. Finally, a weak atmospheric magnetic field can slightly, by a few percent, increase the frequency of the eigen-mode. Stronger magnetic fields, however, can increase the f-mode frequency by even up to ten per cent, which cannot be seen in observed data. The presence of a magnetic atmosphere in the three-layer model also introduces non-permitted propagation windows in the frequency spectrum; here, f-mode oscillations cannot exist with certain values of the harmonic degree. The eigen-frequencies can be sensitive to the background physical parameters, such as an atmospheric density scale-height or the rate of the plasma density drop at the photosphere. Such information, if ever observed with high-resolution instrumentation and inverted, could help to gain further insight into solar magnetic structures by means of solar magneto-seismology, and could provide further insight into the role of magnetism in solar oscillations.     

Kink mode m = 1 in magnetic tube with discontinuous magnetic field

In this paper, we study conditions of realization and stability of kink modes with azimuthal wave numbers $m=\pm 1$ in cylindrical plasma flex with twisted magnetic field and homogeneous current along its axis. We assume permanent axial magnetic field both inside and outside the flex, surrounded by currentless plasma. Azimuthal magnetic field decreases inversely proportional to the distance from the boundary beyond the flex. We derived dispersion equations for stable and unstable modes in approximation of “thin” plasma flex. The analysis of equations has been provided for the case of discontinuous axial magnetic field on flex’s boundary. Conditions of propagation of wave modes have been defined. It was shown, that unstable modes can be implemented in certain interval of longitudinal wavenumbers. Results can be applied for the interpretation of solar magnetic tubes behavior, using measurements, provided by spacecrafts.     

基于故障行为的惯导产品贮存寿命试验设计

以典型惯导产品加速度计贮存寿命评估为例,提出了一种基于故障行为模型的加速退化试验设计方法,解决了缺乏预试验数据情况下试验应力水平设计的问题。在通过对产品特性和主机理分析基础上,确定表征产品贮存寿命特征参数及试验应力,构建了考虑材料等分散性的加速度计故障行为模型,用以描述参数加速时变规律的特性。在试验应力最高水平确定的情况下,基于给定置信度和故障行为模型,以高应力水平下退化量的置信下限与低应力水平下退化量的置信上限不交叉为原则,采用基于仿真的加速退化试验设计方法,优化确定低应力和中间应力水平,从而设计给出试验剖面,并给出了加速退化试验方案优选流程,最终从备选方案集中确定加速度计试验最优方案。通过实际案例分析,验证了该方法的有效性。