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,...     

小型多旋翼飞行器悬停效率分析

多旋翼的不同配置方式直接影响着小型飞行器整机悬停效率。为了得到不同气动参数下多旋翼系统的悬停效率,通过搭建试验平台测量了多旋翼系统在不同的旋翼位置、桨叶数量、旋翼臂形状尺寸、共轴间距、非共轴旋翼重叠区域时的推力和功耗,分析了不同旋翼配置方式下整机悬停效率随桨盘载荷的变化规律。试验结果表明：旋翼桨叶数为2且在旋翼下置时多旋翼飞行器的悬停效率最高;旋翼臂尺寸比形状对悬停效率的影响更大;不同间距比的共轴旋翼在桨盘载荷较高时可以接近无干扰单旋翼的效率,且在间距比为30.4%时具有较高的悬停效率;通过合理配置非共轴重叠区域的竖直间距比和水平间距比可以有效降低能量损失,且在较小竖直间距比时将水平间距比保持在10％~15％的范围可以大幅度提高悬停效率。     

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.     

四旋翼飞行器悬停建模及控制

四旋翼飞行器是近几年发展起来的具有低功耗、高机动性的一种无人机,具有较高的军用及民用价值.四旋翼飞行器悬停的控制模型可近似为一个线性定常欠驱强耦合系统.通过建模得出的状态空间表达式的状态矩阵A的特征值存在正实部,是一个不稳定系统.由于系统的不稳定利用二次型最优控制对系统进行镇定,同时得到悬停状态下某一虚拟能量指标达到最小值时的二次型最优控制.利用Matlab对系统进行分析及二次型最优控制相关参数的优化.     

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.     

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.     

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.     

基于单目视觉的微型空中机器人自主悬停控制

针对微型空中机器人在室内环境下无法借助外部定位系统实现自主悬停的问题,提出一种基于单目视觉的自主悬停控制方法.采用一种四成分特征点描述符和一个多级筛选器进行特征点跟踪.根据单目视觉运动学估计机器人水平位置;根据低雷诺数下的空气阻力估计机器人飞行速度;结合位置和速度信息对机器人进行悬停控制.实验结果验证了该方法的有效性.     

Flight force production by flapping insect wings in inclined stroke plane kinematics

The unsteady flow structure and the time-varying aerodynamic forces acting on a 2D dragonfly model wing are studied by numerically solving the Navier-Stokes equations. The incompressible Navier-Stokes equations are discretized and solved on a non-body confirming Cartesian grid; the concept of immersed boundary method is made use of to impose the no-slip boundary condition on the surface of the wing. The objective of the present study is to investigate the influence of the following kinematic parameters on the flight performance of inclined stroke plane hovering: Reynolds number (Re), stroke amplitude, wing rotational timing and rotational duration. While the effects of the above mentioned parameters on the stroke averaged force coefficients are the same in both horizontal and inclined stroke plane motions, the spatiotemporal dynamics of vorticity which produce the effects are entirely different. Our results also indicate that the drag mechanism proposed for tiny insects does not seem to augment the vertical force generation in inclined stroke plane motion.