扑翼飞行的气动建模与仿真分析

用计算流体力学的数值仿真方法对微扑翼飞行的非定常空气动力学问题进行了建模与仿真研究。在对昆虫扑翼飞行运动的仿生模拟基础上,建立了简化的扑翼运动二维翼型的运动学与空气动力学模型。利用任意拉格朗日欧拉（ALE）有限元方法求解出N-S方程的数值解,将流场仿真结果与实验进行了对比,并分析了扑翼运动产生的前缘漩涡对升力的作用。文中的建模、分析方法和结论对微扑翼飞行器的分析设计和应用提供了一定的理论依据。     

Nonlinear prediction of subsonic aerodynamic loads on wings and bodies at high angles of attack

This paper predicts numerically the nonlinear aerodynamic loads on wings and bodies at high angles of attack in subsonic flow separating along certain known lines. It is assumed that the separation vortices are symmetric and unbursting. The wing mean surfaces and body surfaces are simulated by bound vortex lattices, and the separation vortex surfaces by free vortex lines. The vortex system satisfies boundary conditions on wing and body surfaces, separation conditions, and the condition that free vortex lines are tangent to local velocity. The velocity induced by a vortex is computed by the Biot-Savart law with Göthert transformation for subsonic small perturbation flows. The vortex strengths and the free vortex locations are solved by relaxation method. Then the aerodynamic loads on wings and bodies are computed. They agree well with experimental tests.     

Dissection of a Flexible Wing's Performance for Insect-Inspired Flapping-Wing Micro Air Vehicles

We present a computational study on the aerodynamic performance of flexible wings aiming to facilitate the design of insect-inspired flapping-wing micro air vehicles (FMAVs). First, we propose using a two-dimensional mechanical model for a flapping wing to help understand the mechanism underlying its unsteady deformation when exposed to aerodynamic and inertia forces. This is followed by comparative analyses of both flexible wings and fixed wings in flight. In particular, a 'swaying propulsion' mechanism is proposed to mimic the flapping of the winged insects, and a new concept of 'initial torsion angle' is introduced to provide an equivalent means to account for the asymmetry of the torsional stiffness of the thorax muscle during upstroke and downstroke flapping. Subsequently, the aerodynamic forces and power requirements for a bumblebee's wings under various flight conditions are systematically examined. Our results indicate that flexibility of the wings largely contributes to the high lifts and that gliding forces play a significant role in improving flight performance, suggesting that optimal design of the structure and flapping motions of wings could achieve improved efficiency in FMAVs. These studies promote a brand new design concept for future insect-inspired FMAVs.     

A Visualization System for Analysis of Micro Aerial Vehicle Scaled Flapping Wings

This paper presents a visualization system for analysis of micro aerial vehicle (MAV) scaled flapping wings. By synchronizing to the wing under test, multiple devices can be triggered at precise phases in the flapping cycle with a high degree of accuracy and repeatability. The system can control devices such as strobe lights, lasers and cameras to capture wing motion and flow visualization data at the point of interest. The system was developed, then implemented and tested under ideal and real-world conditions to evaluate several aspects of performance. The effectiveness of the system was then demonstrated in a flow visualization experiment, where it was used to capture images of the average airflow around a flapping wing at several wing phases. Performance measurements showed the high accuracy of the system, while flow visualization results demonstrated significant improvements in the quality and accuracy of images when the system was used for analysis of a flapping wing. These results indicate the potential of the developed system to considerably improve visualization analysis of MAV scaled flapping wings.     

仿生扑翼“0”形轨迹机构的设计及气动力特性

针对仿生扑翼飞行器的驱动结构进行设计,提出了一种空间摇杆式的驱动机构与机翼扭转机构,实现机翼扑动过程中的"0"形空间运动轨迹.针对机翼的空间"0"字形运动,建立仿生飞行器气动分析模型,采用动网格与非定常数值计算方法,对机翼拍动过程中不同相位下的升阻特性进行分析,并通过空气动力效率与流场对比分析,得到不同参数条件下的气动效率,为仿生扑翼飞行器的设计及扑动模式的选择提供参考.通过气动力测量实验、台架姿态标定和外场飞行测试,验证了结构设计的合理性.     

一款模拟昆虫飞行方式的微小型扑翼机

设计了一款模拟昆虫飞行方式的微小型扑翼机,仿照蜻蜓的两翼,直升机式尾翼,以STC15F2K60S2为主控芯片,应用主流无线模块来完成实现遥控仿生扑翼机的设计与制作,经过实际测试能够满足飞行要求.     

Interactive separating streak surfaces

Streak surfaces are among the most important features to support 3D unsteady flow exploration, but they are also among the computationally most demanding. Furthermore, to enable a feature driven analysis of the flow, one is mainly interested in streak surfaces that show separation profiles and thus detect unstable manifolds in the flow. The computation of such separation surfaces requires to place seeding structures at the separation locations and to let the structures move correspondingly to these locations in the unsteady flow. Since only little knowledge exists about the time evolution of separating streak surfaces, at this time, an automated exploration of 3D unsteady flows using such surfaces is not feasible. Therefore, in this paper we present an interactive approach for the visual analysis of separating streak surfaces. Our method draws upon recent work on the extraction of Lagrangian coherent structures (LCS) and the real-time visualization of streak surfaces on the GPU. We propose an interactive technique for computing ridges in the finite time Lyapunov exponent (FTLE) field at each time step, and we use these ridges as seeding structures to track streak surfaces in the time-varying flow. By showing separation surfaces in combination with particle trajectories, and by letting the user interactively change seeding parameters such as particle density and position, visually guided exploration of separation profiles in 3D is provided. To the best of our knowledge, this is the first time that the reconstruction and display of semantic separable surfaces in 3D unsteady flows can be performed interactively, giving rise to new possibilities for gaining insight into complex flow phenomena.     

面向扑翼飞行控制的建模与奇异摄动分析

针对扑翼飞行中的周期性和时标不一现象,以及扑翼飞行实际控制中的问题,本文基于奇异摄动理论,提出了一种针对扑翼周期系统的稳定性分析方法.具体而言,首先建立了扑翼飞行器的多刚体模型,为后文对翅翼动力学的奇异摄动分析铺平道路;其次,对多刚体模型进行简化,抽象出扑翼飞行动力学的核心问题,并针对实际控制中的问题,提出了利用奇异摄...     

Flapping flight for biomimetic robotic insects: part I-system modeling

This paper presents the mathematical modeling of flapping flight inch-size micro aerial vehicles (MAVs), namely micromechanical flying insects (MFIs). The target robotic insects are electromechanical devices propelled by a pair of independent flapping wings to achieve sustained autonomous flight, thereby mimicking real insects. In this paper, we describe the system dynamic models which include several elements that are substantially different from those present in fixed or rotary wing MAVs. These models include the wing-thorax dynamics, the flapping flight aerodynamics at a low Reynolds number regime, the body dynamics, and the biomimetic sensory system consisting of ocelli, halteres, magnetic compass, and optical flow sensors. The mathematical models are developed based on biological principles, analytical models, and experimental data. They are presented in the Virtual Insect Flight Simulator (VIFS) and are integrated together to give a realistic simulation for MFI and insect flight. VIFS is a software tool intended for modeling flapping flight mechanisms and for testing and evaluating the performance of different flight control algorithms.     

Study on the structural optimization of a flapping wing micro air vehicle

The development of flapping wing micro air vehicles (MAVs) has yielded remarkable progress over the last decades. Achieving high component stiffness is often in conflict with low weight requirement, which is highly desirable for longer flight time and higher payload. Moreover, vibration originated predominantly from the wings, gears and frames excitations, may compromise the flapping wing MAV’s stability and fatigue life. In order to improve the vehicle’s efficiency and performance, optimization of these various parameters is necessary. In this work, we present the structural optimization of a flapping wing micro air vehicle. We focus particularly on the gearbox optimization using Simulia Tosca Structure in Abaqus, which is a robust tool for designing lightweight, rigid and durable components. Various numerical experiments have been conducted towards optimizing the components’ topology, aimed at increasing the stiffness and reducing weight. The finding and results provide a better understanding of the optimal design topology for a spur gear among other structural components used in MAVs.     

仿鸟类扑翼飞行器研究进展

仿生扑翼飞行器有着优异的气动性能和灵活的飞行能力,在军民领域均有广泛的应用前景,学者们在原理样机研制、扑翼气动机理、驱动机构、飞行控制等多领域取得了一系列重要进展.本文从总体设计方法、驱动机构设计与优化、气动机理等方面综述了仿鸟类扑翼飞行器技术的发展历程与研究进展.首先,从扑翼总体设计方法入手,总结了仿鸟类扑翼飞行器仿生构型,归纳了总体设计参数估算方法;其次,综述了多种构型曲柄连杆机构在扑翼驱动中的应用与优缺点;接着总结了扑翼气动机理研究的实验方法与数值计算方法,分析了不同扑翼气动算法针对不同应用场景在计算成本和准确度方面的优劣情况;最后,对仿鸟类扑翼飞行器系统设计研究现状进行总结,针对原理样机研制过程提出展望.     

三铰扑翼建模及数值计算

为研究鸟类翅膀展向变形对扑翼气动特性的影响,基于对鸟类翅膀变形的观察,分别用动静法和拉格朗日方程建立三铰扑翼的数学模型,并利用数值计算研究该模型.结果表明：使用NACA0004作为截面的三铰扑翼在对称扑动时能够产生净升力;随着中翼弹性系数比的增大,周期平均升力因数增大,但周期平均阻力因数不存在单调性;三铰扑翼比双铰翼的周期平均升力因数明显小;随着外翼弹性系数比的增大,周期平均升力因数和周期平均阻力因数也不存在单调特性.     

Towards efficient flight: insights on proper morphing-wing modulation in a bat-like robot

In this article, we address the question of how the flight efficiency of Micro Aerial Vehicles with variable wing geometry can be inspired by the biomechanics of bats. We use a bat-like drone with highly articulated wings using shape memory alloys (SMA) as artificial muscle-like actuators. The possibility of actively changing the wing shape by controlling the SMA actuators, let us study the effects of different wing modulation patterns on lift generation, drag reduction, and the energy cost of a wingbeat cycle. To this purpose, we present an energy-model for estimating the energy cost required by the wings during a wingbeat cycle, using experimental aerodynamic and inertial force data as inputs to the energy-model. Results allowed us determining that faster contraction of the wings during the upstroke, and slower extension during the downstroke enables to reduce the energy cost of flapping in our prototype.     

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.     

基于线驱转向的仿蝴蝶扑翼飞行机器人系统设计与控制

作为一种新型飞行机器人, 仿蝴蝶扑翼飞行机器人模仿自然界蝴蝶的生物结构和飞行方式, 能够有效地融 入并适应复杂环境, 在军民融合领域具有广阔的应用前景. 目前针对仿蝴蝶扑翼飞行机器人的研究大多停留在对生 物蝴蝶飞行机理的研究, 鲜有能够实现自由可控飞行的机器人系统. 本文设计了一款基于线驱转向的仿蝴蝶扑翼飞 行机器人, 名为USTButterfly-S, 其翼展50 cm, 重50 g, 可实现长达5分钟的自由可控飞行. 首先结合生物蝴蝶翅膀的 扑动特征, 设计了双曲柄双摇杆对称扑翼驱动机构. 然后模仿凤蝶的翅翼形状, 设计了仿蝴蝶翼型. 对翅膀的几何学 分析表明, USTButterfly-S的翅膀与凤蝶具有较好的形态相似性. 接着针对仿蝴蝶扑翼飞行机器人的转向控制问题, 首次采用线驱动机构拉动翅膀调节翅翼面积, 进而实现了USTButterfly-S的无尾航向控制. 最后集成自主设计的飞 控系统, USTButterfly-S能够实现室内盘旋飞行并进行实时航拍. 在实际飞行实验中, USTButterfly-S展现出类似生 物蝴蝶的飞行特征.     

A predictor-corrector technique for visualizing unsteady flow

Presents a method for visualizing unsteady flow by displaying its vortices. The vortices are identified by using a vorticity-predictor pressure-corrector scheme that follows vortex cores. The cross-sections of a vortex at each point along the core can be represented by a Fourier series. A vortex can be faithfully reconstructed from the series as a simple quadrilateral mesh, or its reconstruction can be enhanced to indicate helical motion. The mesh can reduce the representation of the flow features by a factor of 1000 or more compared with the volumetric dataset. With this amount of reduction, it is possible to implement an interactive system on a graphics workstation to permit a viewer to examine, in 3D, the evolution of the vortical structures in a complex, unsteady flow     

Passive torque regulation in an underactuated flapping wing robotic insect

Recent developments in millimeter-scale fabrication processes have led to rapid progress towards creating airborne flapping wing robots based on Dipteran (two winged) insects. Previous work to regulate forces and torques generated by flapping wings has focused on controlling wing trajectory. An alternative approach uses underactuated mechanisms with tuned dynamics to passively regulate these forces and torques. The resulting ??mechanically intelligent?? devices execute wing trajectory corrections to realize desired body forces and torques without the intervention of an active controller. This article describes an insect-scale flapping wing mechanism consisting of a single piezoelectric actuator, an underactuated transmission, and passively rotating wings. Wing stroke velocities are passively modulated to eliminate net airframe roll torque. A theoretical model predicts lift generating wing trajectories and quantifies the passive reduction in roll torque. An experimental structure provides an at-scale demonstration of passive torque regulation.     

Modeling and Trajectory Tracking Control for Flapping-Wing Micro Aerial Vehicles

This paper studies the trajectory tracking problem of flapping-wing micro aerial vehicles(FWMAVs)in the longitudinal plane.First of all,the kinematics and dynamics of the FWMAV are established,wherein the aerodynamic force and torque generated by flapping wings and the tail wing are explicitly formulated with respect to the flapping frequency of the wings and the degree of tail wing inclination.To achieve autonomous tracking,an adaptive control scheme is proposed under the hierarchical framework.Specifically,a bounded position controller with hyperbolic tangent functions is designed to produce the desired aerodynamic force,and a pitch command is extracted from the designed position controller.Next,an adaptive attitude controller is designed to track the extracted pitch command,where a radial basis function neural network is introduced to approximate the unknown aerodynamic perturbation torque.Finally,the flapping frequency of the wings and the degree of tail wing inclination are calculated from the designed position and attitude controllers,respectively.In terms of Lyapunov's direct method,it is shown that the tracking errors are bounded and ultimately converge to a small neighborhood around the origin.Simulations are carried out to verify the effectiveness of the proposed control scheme.     

A numerical analysis of two-dimensional flow past a rectangular prism by a discrete vortex model

A discrete vortex model is developed to analyse the two-dimensional fully separated unsteady flow past a rectangular prism. The effects of viscous diffusion of vortices and the loss in vorticity after the stationary prism with a thickness ratio ranging from 0.5 to 2.0. The formation of Karman vortices, the vortex shedding frequency, and the fluid forces acting on the body are favourably compared with the experimental results by various research workers. The method of analysis is also shown to be applicable to the flow past a prism that is in forced vibration.