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。     

应用层次分析法的航天器健康评估方法

采用层次分析法,实现各故障模式对航天器系统、分系统、单机设备影响权重的量化和分析,并提出航天器健康评估体系分级构建思想;结合航天器遥测数据特性对故障预测技术和健康评估方法进行了研究,设计了新陈代谢GM(1,1)等动态预测模型,给出了故障模式预测仿真结果。研究结果可为航天器在轨任务规划、故障处理维护等提供借鉴。     

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.     

Mechanical behaviour of adhesively single lap joint under buckling conditions

Adhesive Single Lap Joints have been subjected to tensile and bending investigations by many researchers. However, the joint is also likely to experience buckling loading in some aerospace applications. The aim of this work is to investigate the joint behaviour under quasi-static buckling conditions. For this purpose, the joints with three different adherend thicknesses and 25 mm overlap length were tested using two different types of adherends and an adhesive film. They were modelled using a non-linear Finite Element Method via the ABAQUS Explicit package programme. Load to failure and stress distributions in the joints were predicted and compared with the experimental results, which were found in a good agreement. The adhesive layer in the joint was assumed to experience shear stresses under the buckling mode, similar to that in tensile loading, yet, the stress concentrations at the ends of the overlap, the main cause of the failure, resulted in different effects on the joint performance; for the buckling mode the critical stresses were in compression but for the tensile case in peeling. Unlike the latter, the former was found to prevent failure of the layer depending on the adherend thickness, causing different failure mechanisms. There were two different failure modes of the joints; a complete failure in the adhesive layer and large plastic deformation of adherends which could be a good source for crashworthiness situations. Mechanical properties of the adherends were found to play important roles on the joint performance.     

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.     

超声速翼型气动优化设计

首先分析了几何外形和相对厚度对超声速翼型气动特性的影响。基于遗传算法(GA)和气动力快速工程算法,对于相对厚度为3.5%的多边形翼型进行优化设计,多边形翼型的优化外形趋于四边形,最大厚度点后移到翼型弦线的60%左右,随着迎角或者马赫数增大下翼面会变薄,上翼面变厚,最大厚度点相应稍有后移。对于相对厚度为4%的双圆弧翼型,采用两步优化设计方法,第1步优化结合基于B样条的类别形状函数变换(CST)参数化方法与小波分解方法,实现几何外形的局部控制与光顺处理,并且采用本征正交分解(POD)代理模型降低优化过程中流场计算的工作量;第2步优化采用基于Navier-Stokes方程的最速下降法(SDA),修正第1步优化中代理模型和小波光顺引入的误差;优化设计得到的翼型近似为四边形,其相对厚度最大点后移到翼型弦线的60%~65%处,升阻比可以提高7%。     

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.