A multi-strategy pigeon-inspired optimization approach to active disturbance rejection control parameters tuning for vertical take-off and landing fixed-wing UAV

In this paper, Active Disturbance Rejection Control(ADRC) is utilized in the pitch control of a vertical take-off and landing fixed-wing Unmanned Aerial Vehicle(UAV) to address the problem of height fluctuation during the transition from hover to level flight. Considering the difficulty of parameter tuning of ADRC as well as the requirement of accuracy and rapidity of the controller, a Multi-Strategy Pigeon-Inspired Optimization(MSPIO) algorithm is employed. Particle Swarm Optimization(PSO), Gen...     

航天器非平稳振动环境TVAR时频分析(英文)

Predicting the time-varying auto-spectral density of a spacecraft in high-altitude orbits requires an accurate model for the non-stationary random vibration signals with densely spaced modal frequency. The traditional time-varying algorithm limits prediction accuracy, thus affecting a number of operational decisions. To solve this problem, a time-varying auto regressive （TVAR） model based on the process neural network （PNN） and the empirical mode decomposition （EMD） is proposed. The time-varying system is tracked on-line by establishing a time-varying parameter model, and then the relevant parameter spectrum is obtained. Firstly, the EMD method is utilized to decompose the signal into several intrinsic mode functions （IMFs）. Then for each IMF, the PNN is established and the time-varying auto-spectral density is obtained. Finally, the time-frequency distribution of the signals can be reconstructed by linear superposition. The simulation and the analytical results from an example demonstrate that this approach possesses simplicity, effectiveness, and feasibility, as well as higher frequency resolution.     

Multi Objective Robust Active Vibration Control for Flexure Jointed Struts of Stewart Platforms via H∞ and μ Synthesis

Active vibration control is needed for future space telescopes, space laser communication and other precision sensitive payloads which require ultra-quiet environments. A Stewart platform based hybrid isolator with 6 hybrid struts is the effective system for active/passive vibration isolation over 5-250 Hz band. Using an identification transfer matrix of the Stewart platform, the coupling analysis of six channels is provided. A dynamics model is derived, and the rigid mode is removed to keep the signal of pointing control. Multi objective robust H∞ and μ synthesis strategies, based on singular values and structured singular values respectively, are presented, which simultaneously satisfy the low frequency pointing and high frequency disturbance rejection requirements and take account of the model uncertainty, parametric uncertainty and sensor noise. Then, by performing robust stability test, it is shown that the two controllers are robust to the uncertainties, the robust stability margin of H, controller is less than that of μ controller, but the order of μ controller is higher than that of H, controller, so the balanced controller reduction is provided. Additionally, the μ controller is compared with a PI controller. The time domain simulation of the μ controller indicates that the two robust control strategies are effective for keeping the pointing command and isolating the harmonic and stochastic disturbances.     

冲压发动机助推段压强振荡现象数值分析

为了揭示串连式冲压发动机飞行助推段进气道和补然室内压强振荡产生的机理,针对冲压发动机的助推段开展了进气道和补燃室内流动的大涡模拟,获得了进气道和补然室内压强振荡的频率和振幅,并和飞行实验数据进行了对比。结果表明,在助推段串连式冲压发动机进气道和补燃室内发生的压强振荡现象属于典型的整体模式不稳定现象;助推飞行马赫数、飞行高度的变化对整体模式不稳定现象压强振荡的频率和振幅影响不大。     

月球重力转弯软着陆的模糊变结构控制

针对月球软着陆的最终段,提出了以重力转弯方式进行软着陆的模糊变结构制导律.首先设计了次优滑动面,然后引入模糊控制器,使滑动变量逐渐收敛到0,实现安全着陆.考虑了发动机推力偏差、着陆器初始质量估计偏差、月球引力加速度偏差、初始条件干扰、敏感器测量误差及姿态跟踪误差.并用Monte Carlo技术验证了所设计的模糊变结构制导律具有很强的鲁棒性,能够克服各种随机偏差及干扰的影响.因此,所设计的软着陆制导律是可行的,并且只须以斜向距离和斜向速度作为输入,工程实现简单.      

基于漏斗试样的C250钢高温扭转低周疲劳行为

C250钢的扭转疲劳破坏是其主要失效形式之一。为了获得航空材料C250钢的扭转疲劳特性,并消除等直圆棒试样在扭转试验中产生的弊端,依据漏斗试样完成了C250钢在3种高温(150、200、350℃)环境下的扭转低周疲劳试验,获得了在扭转低周疲劳下的扭矩-名义扭转角曲线。基于试验结果,利用FAT方法分析得到了C250钢在3种高温环境下的材料循环本构关系,利用该循环本构关系对漏斗试样进行三维扭转有限元分析,获得漏斗根部剪切应力与扭矩之间的转换公式及漏斗根部剪切应变与名义扭转角之间的转换公式。基于以上试验与分析方法,得到了材料的剪切应变幅-倍循环次数曲线、剪切应力幅-循环分数曲线以及剪切应力-剪切应变的稳定滞回线,发现材料呈现出循环软化特性,并基于Manson-Coffin模型对材料寿命进行了分析。     

3-D有限元转子系统动力减缩的部件模态综合方法及应用

为了对3-D有限元转子模型进行动力学减缩,提出基于部件模态综合的旋转子结构方法.该方法利用实模态振型矩阵减缩子结构自由度,不同转速下的减缩陀螺矩阵由转速系数乘以单位转速的减缩陀螺矩阵得到.与复模态减缩相比,避免了重复求解变换矩阵的缺点,减缩精度优于基于Guyan减缩的旋转子结构法.利用该方法减缩了某航空发动机转子模型87%的自由度数.经比较,由Campbell图所得临界转速的最大误差为0.04%,稳态不平衡响应计算结果与原模型也几乎完全相同,使用的内存和计算时间均不到原模型的20%,验证结果证明该方法可行.      

旋转状态下方形通道内部流场特性热线实验

为了解决旋转条件下热线技术应用问题并且在此基础上精确测量旋转方形通道内部流场特性,搭建了用于旋转通道流场测试实验平台,采用了两种连线方式对热线进行了标定实验,获得了热线测量旋转通道内部平均速度的相对误差为±6%,对雷诺数和旋转数范围分别是5000~10000和0~0.222的旋转通道流场进行了测量,结果表明:旋转导致速度型整体向后缘面（Y/D=-0.5）偏转,X/D和旋转数越大,速度型偏转越明显;旋转数为0.222时,后缘面附近边界层速度型出现了一个拐点,可能与由哥氏力不稳定性引起的二次流有关.      

机翼对螺旋桨发动机旋转颤振的影响研究

为了研究机翼对螺旋桨发动机旋转颤振的影响规律,揭示其影响机理,通过片条理论计算螺旋桨气动载荷,在MSC.NASTRAN软件平台上进行二次开发,对不同结构参数的吊舱-螺旋桨系统和机翼-吊舱-螺旋桨系统进行了旋转颤振分析。研究表明,机翼结构的弹性会大幅降低发动机俯仰模态频率,而小幅降低发动机偏航模态频率,从而改变两模态频率之差,影响模态耦合的程度,进而改变旋转颤振速度。另外,当发动机的运动与机翼翼面的运动耦合紧密时,机翼翼面的气动载荷能够显著提高发动机的旋转颤振速度。     

利用受限张力的拖曳变轨欠驱动姿态稳定策略

在空间绳系拖曳变轨中,目标和平台形成一种哑铃型绳系系统,且仅依靠有限的平台推力和系绳张力来抑制系绳的摆动。针对此类输入受限的欠驱动控制问题,提出了一种利用受限张力的姿态稳定策略。首先,推导了组合体姿态动力学模型。然后通过数值求解姿态平衡方程得出理论面内姿态指令,再采用高斯伪谱法对其优化获得实际指令。最后,基于分层滑模理论设计欠驱动张力控制律,并嵌入抗饱和模块以缓解张力饱和。仿真表明空间平台能在正向有限的张力控制下,平滑地收放系绳使面内角和绳长跟踪实际姿态指令。此外,所提策略对目标体摆动和传感器误差也具有良好的鲁棒性。