基于ILMI的直升机悬停控制律设计

提出了一种新的直升机悬停控制律设计方法。在建立了直升机数学模型后,通过迭代线性矩阵不等式方法(ILM I)求解基于线性二次型的直升机悬停控制律,使得直升机能达到满意的悬停性能指标,并且明显降低了控制器的保守性。仿真结果表明,使用该方法设计的控制器同时满足动态性能指标和稳态性能指标,与使用标准线性二次型方法设计的控制器相比,其性能指标在横侧向提高了12.3%,纵向提高了13.7%。     

应用太阳帆悬停探测哑铃形小行星

研究了太阳帆航天器在哑铃形小行星引力场内的悬停探测可行性问题。哑铃形小行星代表了一类细长形的小行星,文中首先建立哑铃形小行星的简化动力学模型。针对可变反射面积的太阳帆,给出其在小行星引力场内的悬停动力学方程,并仿真求解了哑铃形小行星附近的太阳帆可行悬停探测区域。     

蜻蜓翼三维流动结构的演变

为了与蜻蜓前后翼流动干扰的流动结构作比较,首先研究了悬停飞行状态下单个蜻蜓翼周围的三维流动结构,利用一套机电拍动翼运动模拟机构模拟了一个蜻蜓翼的拍动,使用数字体视粒子图像测速技术(DSPIV,Digital Stereo Particle Image Velocimetry)和多切面锁相技术分别测量了两个下拍拍动相位时刻(t=0.25T,0.375T)和两个上拍拍动相位时刻(t=0.75T,0.875T)蜻蜓翼周围的瞬时空间三维流场,运用局部涡识别准则中的λci准则来识别和显示了流场中的三维涡结构,还展示了蜻蜓翼各个展向测量截面中的|ωz|等值线、蜻蜓翼前缘涡的涡核线相对于蜻蜓翼上翼面的空间位置以及前缘涡在各个展向测量截面中的截面环量等.实验结果揭示了蜻蜓翼周围的三维流动结构在蜻蜓翼拍动时的演变历程.     

悬停状态下无轴承尾浆气弹稳定性分析

新型发愤浆型式无轴承尾浆的气弹稳定性分析非常复杂，而目前国内在这方面的研究还是空白。本文试图建立一套有工程实用意义的无轴承尾浆气弹稳定性分析方法和相应的分析程序，并进行参数影响分析和计算。在前期研究工作的基础上，本文推导出正交各向异性复合材料梁的应变能变分表达式，并将其用于推导旋翼／机身耦合系统的运动方程。再通过对系统的稳态周期解进行摄动，得到相应的线化周期时变动力学方程，用Floquet理论判断系统的稳定性。最后，分析计算了悬停状态下某无人直升机无轴承尾桨的气弹稳定性，表明其孤立桨叶及尾桨／传动轴／尾梁的耦合系统是稳定的；并进行了参数分析，得到一些有意义的结论。     

悬停状态旋翼流场显示的试验研究

介绍了悬停状态旋翼流场显示的试验方法及相应的试验装置，阐述了用干冰汽化时产生的烟雾作为流场显示介质的优越性。指出显示介质的选用应综合考虑介质对流场显示效果的影响、介质对设备和操作人员的危害及试验的经济性和可行性等因素。并对烟雾喷嘴与旋翼相对位置对流场真实性的影响进行了研究，着重研究了浆尖涡喷嘴的不同径向位置位置对流场边界的影响及确保流场真实边界应采取的措施。最后，用试验的方法定性分析了浆叶片数、浆尖速度及浆叶安装角对悬停状态旋翼流场几何开状的影响。试验结果表明，本文研究方法与国外同类试验相比，在达到同样的流场显示效果的情况下，具有试验费用低、操作简便和对人、设备无危害的优点。     

悬停状态下旋翼噪声声源反演的正则化方法

根据旋翼辐射的气动噪声求解气动声学反问题,给定合理的旋翼表面载荷并结合声类比方法得到观测点的信号,以此进行表面载荷反演。对建立的大型不适定性方程组采用奇异值分解结合正则化方法进行求解,为克服反演结果存在的数值振荡,采用多项式函数来表示未知量,并引入库塔条件作为先验信息。结果表明:理想条件下,该方法得到的旋翼表面的压力分布更接近输入值,尤其在载荷分布较大的叶尖区域,考虑干扰噪声影响后,该方法得到的展向截面吸力峰位置的最大相对误差从15%减小到4%。      

High precision dynamic model and control considering J2 perturbation for spacecraft hovering in low orbit

For spacecraft hovering in low orbit, a high precision spacecraft relative dynamics model without any simplification and considering J₂ perturbation is established in this paper. Using the derived model, open-loop control and closed-loop control are proposed respectively. Gauss's variation equations and the coordinate transformation method are combined to deal with the relative J₂ perturbation between the two spacecraft. The sliding mode controller is adopted as the closed-loop controller for spacecraft hovering. To improve the control accuracy, the relative J₂ perturbation is regarded as a known parameter term in the closed-loop controller. The external uncertainty perturbations except J₂ perturbation are estimated by numerical difference method, and the boundary layer method is used to weaken the impact of chattering on the sliding mode controller. The open-loop control of spacecraft hovering with the relative J₂ perturbation and without the relative J₂ perturbation are simulated and compared, and the results prove that the accuracy of open-loop control with relative J₂ perturbation has been significantly improved. Similarly, the simulation of the closed-loop control are presented to validate the effectiveness of the designed sliding mode controller, and the results demonstrate that the designed sliding mode controller including the derived relative J₂ perturbation can guarantee the high accuracy and robustness of spacecraft hovering in long-term mission.     

Finite-time asteroid hovering via multiple-overlapping-horizon multiple-model predictive control

This paper investigates the asteroid hovering problem using the Multiple-Overlapping-Horizon Multiple-Model Predictive Control method. The effectiveness of the predictive controllers in satisfying control constraints and minimizing the required control effort is making Model Predictive Control a desirable control method for asteroid exploration missions which consist of the asteroid hovering phase. However, the computational burden of Model Predictive Control is an obstacle to employing the asteroid’s complex gravitational field model. As an alternative option, the Multiple Horizon Multiple-Model Predictive Control method has been introduced previously, which could provide a solution with the less computational burden with respect to the nonlinear Model Predictive Control. It was shown that it is not necessary to deduce the exact dynamics model to predict the system’s behavior during a long period using this approach. However, the calculated control acceleration was not smooth enough because of the crisp borders of consecutive horizons, which may cause an image motion and degrades the geometric accuracy of high-resolution images in asteroid hovering missions. In this paper, the Multiple-Overlapping-Horizon Multiple-Model Predictive Control method is introduced instead to solve the problem of controlling acceleration fluctuations by overlapping consecutive horizons. Numerical simulation results are presented to validate the effectiveness of the proposed control method, and its advantage is demonstrated accordingly for the asteroid hovering problem in achieving the hovering position and velocity.     

直升机悬停纵向运动模态的耦合

针对直升机运动模态内状态量间的耦合,提出了一种定量分析方法.该方法基于解耦得到的运动模态,结合气动导数矩阵,定量描述运动模态内状态量间的耦合,通过耦合的瞬时特性和积分特性定量区分各耦合.以Lynx,Bo105和Puma直升机为例,分析了三者悬停纵向运动模态的耦合特性.分析表明,纵向线速度通过空速稳定性对俯仰角速度的耦合作用在不稳定的悬停纵向振荡模态中起重要作用.基于算例的定量分析,筛选主要耦合得到简化模型,因此得到的运动模态固有频率和阻尼比的偏差小于2%,优于文献中的简化模型,说明了通过定量分析得到简化模型的可行性.      

米-8型直升机侧风悬停反操纵原因与分析

本文以米-8型直升机侧风悬停试飞数据为依据,在涡原理论基础上,分析了反操纵现象,并做出侧风悬停方向舵曲线,供直升机驾驶员飞行时参考。