基于金字塔光流法的无人机室内定点悬停设计

针对GPS定位系统建筑物内信号弱,小型无人机很难在室内实现定点悬停.本文提出了一种利用计算机视觉融合惯性导航的组合控制方案.在光流估计上,采用金字塔LK光流算法,提高特征点跟踪精度.在速度融合上,采用卡尔曼+互补混合融合方案,提高飞行速度的准确性.在飞行控制上,采用高度、姿态串级闭环控制方案,光流作为姿态估计的补偿值,...     

A passerine spreads its tail to facilitate a rapid recovery of its body posture during hovering

We demonstrate experimentally that a passerine exploits tail spreading to intercept the downward flow induced by its wings to facilitate the recovery of its posture. The periodic spreading of its tail by the White-eye bird exhibits a phase correlation with both wingstroke motion and body oscillation during hovering flight. During a downstroke, a White-eye''s body undergoes a remarkable pitch-down motion, with the tail undergoing an upward swing. This pitch-down motion becomes appropriately suppressed at the end of the downstroke; the bird''s body posture then recovers gradually to its original status. Employing digital particle-image velocimetry, we show that the strong downward flow induced by downstroking the wings serves as an external jet flow impinging upon the tail, providing a depressing force on the tail to counteract the pitch-down motion of the bird''s body. Spreading of the tail enhances a rapid recovery of the body posture because increased forces are experienced. The maximum force experienced by a spread tail is approximately 2.6 times that of a non-spread tail.     

椭圆形悬挂轨道控制策略研究

为了实现椭圆形悬挂轨道,文中以航天器相对运动动力学模型为基础,对椭圆形悬挂轨道的控制策略进行了分析研究.根据悬挂轨道的定义,通过理论分析和推导,得到了悬挂星在椭圆悬挂轨道上运行时所需要的控制加速度,并对其进行了数值仿真.仿真结果表明:控制加速度曲线平滑,易于实现和控制,且仿真结果与泛开普勒轨道所需的控制加速度一致,椭圆形悬挂轨道实现方法正确可行.     

近水面悬停远航程AUV受波浪的影响

远航程自主水下航行器(简称:AUV)在水下航行一定的距离后需要上浮到近水面悬停进行GPS导航定位,而在近水面AUV受波浪的影响不能忽略,因此有必要研究AUV在近水面悬停时受波浪的影响。在建立AUV六自由度运动数学模型的基础上,基于二元规则波的波浪理论建立了AUV所受波浪力的计算模型,并仿真计算了AUV在近水面悬停时受海洋波浪力的影响。结果表明AUV在2级和4级海况下都可以稳定地完成在近水面悬停作业的任务。     

半转翼悬停和前进飞行升力估算方法

在分析半转翼运动模型和翼面气流特点的基础上,建立了悬停和前进两种飞行状态下的半转翼升力计算模型。根据半转翼的运动特性,推导出适合半转翼运动的升力计算解析表达式。结合半转翼样机参数,应用导出的理论公式和基于CFD软件的数值仿真模型,分别计算不同飞行条件下半转翼的升力,获得半转翼悬停和前进两种飞行状态下升力变化规律。理论计算与数值仿真所得升力曲线的对比验证了升力估算解析法的有效性和可行性。研究结果可为半转翼飞行器的参数设计与升力预估提供理论指导。     

Hovering performance of Anna's hummingbirds (Calypte anna) in ground effect

Aerodynamic performance and energetic savings for flight in ground effect are theoretically maximized during hovering, but have never been directly measured for flying animals. We evaluated flight kinematics, metabolic rates and induced flow velocities for Anna''s hummingbirds hovering at heights (relative to wing length R = 5.5 cm) of 0.7R, 0.9R, 1.1R, 1.7R, 2.2R and 8R above a solid surface. Flight at heights less than or equal to 1.1R resulted in significant reductions in the body angle, tail angle, anatomical stroke plane angle, wake-induced velocity, and mechanical and metabolic power expenditures when compared with flight at the control height of 8R. By contrast, stroke plane angle relative to horizontal, wingbeat amplitude and wingbeat frequency were unexpectedly independent of height from ground. Qualitative smoke visualizations suggest that each wing generates a vortex ring during both down- and upstroke. These rings expand upon reaching the ground and present a complex turbulent interaction below the bird''s body. Nonetheless, hovering near surfaces results in substantial energetic benefits for hummingbirds, and by inference for all volant taxa that either feed at flowers or otherwise fly close to plant or other surfaces.     

Vortex wake,downwash distribution,aerodynamic performance and wingbeat kinematics in slow-flying pied flycatchers

Many small passerines regularly fly slowly when catching prey, flying in cluttered environments or landing on a perch or nest. While flying slowly, passerines generate most of the flight forces during the downstroke, and have a ‘feathered upstroke’ during which they make their wing inactive by retracting it close to the body and by spreading the primary wing feathers. How this flight mode relates aerodynamically to the cruising flight and so-called ‘normal hovering’ as used in hummingbirds is not yet known. Here, we present time-resolved fluid dynamics data in combination with wingbeat kinematics data for three pied flycatchers flying across a range of speeds from near hovering to their calculated minimum power speed. Flycatchers are adapted to low speed flight, which they habitually use when catching insects on the wing. From the wake dynamics data, we constructed average wingbeat wakes and determined the time-resolved flight forces, the time-resolved downwash distributions and the resulting lift-to-drag ratios, span efficiencies and flap efficiencies. During the downstroke, slow-flying flycatchers generate a single-vortex loop wake, which is much more similar to that generated by birds at cruising flight speeds than it is to the double loop vortex wake in hovering hummingbirds. This wake structure results in a relatively high downwash behind the body, which can be explained by the relatively active tail in flycatchers. As a result of this, slow-flying flycatchers have a span efficiency which is similar to that of the birds in cruising flight and which can be assumed to be higher than in hovering hummingbirds. During the upstroke, the wings of slowly flying flycatchers generated no significant forces, but the body–tail configuration added 23 per cent to weight support. This is strikingly similar to the 25 per cent weight support generated by the wing upstroke in hovering hummingbirds. Thus, for slow-flying passerines, the upstroke cannot be regarded as inactive, and the tail may be of importance for flight efficiency and possibly manoeuvrability.     

Analysis of 1/2 sub-harmonic resonance in a maneuvering rotor system

This paper focuses on the 1/2 sub-harmonic resonance of an aircraft’s rotor system under hovering flight that can be modeled as a maneuver load G in the equations of motion.The effect on the rotor system is analyzed by using theoretical methods.It is shown that the sub-harmonic resonance may occur due to maneuvering flight conditions.The larger the eccentricity E and the maneuver load G,the greater the sub-harmonic resonance.The effects of nonlinear stiffness,damping of the system,maneuver load,and eccentricity on the sub-harmonic resonance region in parameter planes are also investigated.Bifurcation diagrams of the analytical solutions are in good agreement with that of the numerical simulation solutions.These results will contribute to the understanding of the nonlinear dynamic behaviors of maneuvering rotor systems.     

涵道式无人机的悬停姿态控制与运动稳定性分析

进行了涵道式无人机的运动稳定性分析,指出无人机在悬停状态下受近地空间、气流颠簸和荷兰滚的影响,导致系统极易出现抖动甚至失控,而优化飞行器的结构参数对于提高飞行器运动稳定性具有重要意义.基于这种分析,从机械结构设计出发,通过Lyapunov指数方法建立飞行器结构参数与系统运动稳定性之间的量化关系,以此指导系统的机械结构设计及控制系统优化,为提高系统执行飞行任务的可靠性和稳定性奠定理论基础.该方法与Lyapunov直接法相比最大的优点是其可构建性,从而为分析其他机器人等非线性系统的运动稳定性提供了一种简单有效的工具.     

基于双目视觉的无人机悬停精度测量研究

为评测悬停状态无人机的稳定性,设计了一套基于双目立体视觉的无人机悬停状态评测系统。首先结合双目相机标定对视频图像校正,并利用提出的邻域灰度改进分级匹配策略,获取匹配特征点;然后根据重建原理计算求得视野中无人机三维坐标数据;最后利用悬停精度测量函数评测无人机的稳定程度。实验证明系统有效匹配目标的特征点,计算出目标三维坐标,同时根据其相对控制精度的浮动,对无人机悬停状态进行评测。