一种解决经验模态分解端点效应的边界延拓法

用于电子设备或系统辐射发射趋势预测的数据大多呈现非线性、样本量小的特点,这大大增加了预测建模的难度,而经验模态分解(EMD)可以将非线性、非平稳的数据分解成若干个呈现一定周期性的本征模态函数(IMF),并且EMD具有完备性和正交性,可通过分别对分解得到的IMF分量建模,从而完成对原始数据的建模。但EMD被端点效应问题所困扰,为了提高EMD的分解精度,针对分解过程中的端点效应问题,以及辐射发射趋势预测的时间序列数据样本量小的特点,利用建立灰色均值GM(1,1)预测模型所需数据量小的优点,提出了一种基于灰色均值GM(1,1)预测模型的边界延拓方法,在原始数据两端各拓展一个极大值和一个极小值,对原始数据进行边界延拓,从而抑制EMD的端点效应。仿真对比结果表明:该方法在分解层数和平均相对误差方面均优于未经延拓处理的EMD,且对数据样本量要求不高。     

绳系卫星的一种新型高阶滑模控制器设计

针对绳系卫星轨道转移控制问题,给出绳系卫星在轨机动模型并将面内运动处理为典型的欠驱动形式;为实现对面内摆角的跟踪控制,定义滑模面并建立积分链系统,设计一种新型高阶滑模系绳张力控制律,得到无抖振控制量,这种控制律在保证高精度跟踪的前提下,有效避免了控制抖振现象;关于滑模面的高阶滑模运动建立后,在平衡点对闭环系统线性化,根据劳斯判据,闭环系统在平衡点是局部渐近稳定的。最后,通过仿真分析,验证了所提出控制算法的有效性。     

面向非沿迹成像的姿态跟踪扩展观测器滑模控制

针对地面兴趣点不沿星下点轨迹的动态非沿轨迹成像问题,设计一种结合扩展状态观测器的非奇异快速终端滑模控制器。首先根据非沿轨迹成像模型的需求推导卫星姿态参考轨迹。其次,根据由误差四元数描述的跟踪误差运动模型设计了非奇异快速终端滑模控制律。考虑到干扰抑制,引入了扩展状态观测器来观测系统的总扰动,从而降低滑模控制律中的切换增益,削弱系统抖振。然后再用模糊自适应系统对切换项进行在线逼近,柔化控制信号,进一步减振。最后,对具有干扰和参数不确定的姿态控制系统进行了数值仿真,结果表明该方法收敛速度快,控制精度高。     

一种DSMC方法的并行策略

为提高直接模拟蒙特卡罗（DSMC）仿真模拟的并行计算效率,基于消息传递接口（MPI）的并行环境,通过对比分析主从模式及对等模式两种程序设计模式下的并行效率,探讨了对等模式下非结构网格DSMC并行程序实现的关键技术及实施途径。提出了一种非结构网格下动态负载平衡DSMC仿真模拟的并行策略,设计了基于对等模式动态负载平衡的DSMC并行算法。最后以钝锥外形的高超声速绕流问题进行仿真模拟,验证本文并行算法的有效性,结果表明,本文设计的基于对等模式动态负载平衡的DSMC并行算法能够以高效的并行效率给出合理的结果。     

带中介轴承的双转子系统振动耦合作用评估

为了评估中介轴承对双转子系统的振动耦合作用,从临界转速位置振型变化、临界转速变化、模态振型与稳态不平衡响应的应变能分布变化、中介轴承受力变化等多角度,阐释双转子耦合振动的表现形式和关联关系,提出了相应的评价指标或评估方法,并以典型燃气涡轮发动机双转子系统为对象,进行了分析评估。结果表明,单转子的模态振型可能在双转子模态振型中表现为3种形式,一一对应出现、重复出现或耦合出现,对应的临界转速及应变能分布也会随之产生相应的变化;中介轴承受力在临界转速位置出现峰值,而应变能分布变化最大的转速位置与系统临界转速位置不一致,同时还受不平衡激励位置影响;各单元应变能占比变化量随转速变化曲线可详细分析特定不平衡激励下系统应变能分布变化情况。所提方法可为双转子-中介轴承系统的设计、故障诊断提供参考。     

航空机电作动器神经网络快速终端滑模控制

目前机电作动器由于具有干净、维护方便等优点,越来越受到航空业的青睐。航空机电作动器的特点是控制精度、稳定性和响应速度要求高,针对以上特点,提出了一种基于多层神经网络的快速终端滑模控制策略。为了提高航空作动器响应速度和跟踪精度,设计了快速终端滑模控制策略,不仅可以加快系统响应而且可以在无扰动情况下实现系统的有限时间稳定。针对系统参数不确定性和外部扰动,设计多层神经网络进行估计并通过前馈方法加以补偿。针对神经网络的重构误差,设计了非线性鲁棒项加以克服。利用李亚普洛夫稳定性定理证明了控制系统在有扰动情况下可以实现有界稳定。实验结果表明：所设计的控制器具有良好的参数自适应和抗干扰能力,同时具有更高的跟踪精度和更快的响应速度。     

Coordinated attitude control for flexible spacecraft formation with actuator configuration misalignment

This paper investigates the coordinated attitude control problem for flexible spacecraft formation with the consideration of actuator configuration misalignment. First, an integral-type sliding mode adaptive control law is designed to compensate the effects of flexible mode, environmental disturbance and actuator installation deviation. The basic idea of the Integral-type Sliding Mode Control (ISMC) is to design a proper sliding manifold so that the sliding mode starts from the initial time instant, and thus the robustness of the system can be guaranteed from the beginning of the process and the reaching phase is eliminated. Then, considering the nominal system of spacecraft formation based on directed topology, an attitude cooperative control strategy is developed for the nominal system with or without communication delay. The proposed control law can guarantee that for each spacecraft in the spacecraft formation, the desired attitude objective can be achieved and the attitude synchronization can be maintained with other spacecraft in the formation. Finally, simulation results are given to show the effectiveness of the proposed control algorithm.     

Scaling effects on combustion modes in a single-side expansion kerosene-fueled scramjet combustor

The combustion modes in two different scramjet combustors with the mass flow rates of 1.8 kg/s and 3.6 kg/s are experimentally investigated to explore the scaling effects on supersonic combustion with a Mach number 2.0 inflow. It is found that the scramjet combustor with a larger scale can broaden the flame rich blowout limit. As the Equivalence Ratio (ER) increases, the combustion in the small-scale combustor maintains in the cavity-stabilized mode, and the flamebase moves downstream along the cavity shear layer; however, the combustion in the large-scale combustor gradually transfers from the cavity-stabilized mode to the jet-wake-stabilized mode. The differences in the cavity residence time, the ignition delay time and the Damkohler number caused by different scales of the scramjet combustor are likely to account for the scaling effects on the combustion modes.     

模型预混燃烧室线性稳定性分析

针对钝体火焰稳定器结构的模型预混燃烧室进行了线性稳定性分析.利用COMSOL Multiphysics软件求解了三维Helmoholtz方程,方程的源项为耦合指数-延迟时间模型.对模型预混燃烧室进行非定常计算得到了化学反应速率的周期性变化,确定了非定常热释放发生在火焰的尖端.由压力和温度信号的相位差得到了当量比为0.72,0.8,0.88,0.97四个工况的延迟时间,分别为0.6,0.3,0.9,0.6ms.线性稳定性分析得到了模型预混燃烧室系统纵向模态频率的实部和虚部,当虚部为负数时表示线性不稳定.结果显示:系统的前5阶纵向模态中,2~4阶是线性不稳定的.其中3阶纵向模态的虚部绝对值最大,它的物理意义是对小扰动的增长率最大.因此在有扰动时,3阶纵向模态最有可能线性失稳,产生燃烧不稳定性现象.      

Optimal spacecraft formation establishment and reconfiguration propelled by the geomagnetic Lorentz force

The Lorentz force acting on an electrostatically charged spacecraft as it moves through the planetary magnetic field could be utilized as propellantless electromagnetic propulsion for orbital maneuvering, such as spacecraft formation establishment and formation reconfiguration. By assuming that the Earth’s magnetic field could be modeled as a tilted dipole located at the center of Earth that corotates with Earth, a dynamical model that describes the relative orbital motion of Lorentz spacecraft is developed. Based on the proposed dynamical model, the energy-optimal open-loop trajectories of control inputs, namely, the required specific charges of Lorentz spacecraft, for Lorentz-propelled spacecraft formation establishment or reconfiguration problems with both fixed and free final conditions constraints are derived via Gauss pseudospectral method. The effect of the magnetic dipole tilt angle on the optimal control inputs and the relative transfer trajectories for formation establishment or reconfiguration is also investigated by comparisons with the results derived from a nontilted dipole model. Furthermore, a closed-loop integral sliding mode controller is designed to guarantee the trajectory tracking in the presence of external disturbances and modeling errors. The stability of the closed-loop system is proved by a Lyapunov-based approach. Numerical simulations are presented to verify the validity of the proposed open-loop control methods and demonstrate the performance of the closed-loop controller. Also, the results indicate the dipole tilt angle should be considered when designing control strategies for Lorentz-propelled spacecraft formation establishment or reconfiguration.