Experimental investigations of the functional morphology of dragonfly wings

Nowadays, the importance of identifying the flight mechanisms of the dragonfly, as an inspiration for designing flapping wing vehicles, is well known. An experimental approach to understanding the complexities of insect wings as organs of flight could provide significant outcomes for design purposes. In this paper, a comprehensive investigation is carried out on the morphological and microstructural features of dragonfly wings. Scanning electron microscopy （SEM） and tensile testing are used to experimentally verify the functional roles of different parts of the wings. A number of SEM images of the elements of the wings, such as the nodus, leading edge, trailing edge, and vein sections, which play dominant roles in strengthening the whole structure, are presented. The results from the tensile tests indicate that the nodus might be the critical region of the wing that is subjected to high tensile stresses. Considering the patterns of the longitudinal corrugations of the wings obtained in this paper, it can be supposed that they increase the load-bearing capacity, giving the wings an ability to tolerate dynamic loading conditions. In addition, it is suggested that the longitudinal veins, along with the leading and trailing edges, are structural mechanisms that further improve fatigue resistance by providing higher fracture toughness, preventing crack propagation, and allowing the wings to sustain a significant amount of damage without loss of strength.     

从竹蜻蜓到直升机旋翼系统

通过对蜻蜓目昆虫的古文献记载、蜻蜓的飞行特点以及葛洪在《抱朴子》中有关"飞车"记载的分析,指出现有文献中关于"竹蜻蜓"起源说法的不当之处.在分析竹蜻蜓的直升飞行状态和倾斜飞行的进动特性的基础上,阐述了直升机旋翼系统与竹蜻蜓的不同之处.指出直升机旋翼系统的拉力产生原理虽近似于竹蜻蜓,但现今已发展成为一个非常复杂的系统,科技含量远高于竹蜻蜓.古代的发明是由生活经验促成,与现代许多发明之原理相近,但是没有及时形成知识体系,仅停留在个案层面,不易推而广之;需要把经验逻辑化、体系化,才便于指导工程实践,形成良性循环.     

蜻蜓眼睛光栅

介绍了蜻蜓眼睛光栅的制作过程.通过对蜻蜒眼睛光栅的衍射图样进行分析、测量和计算,从而推出蜻蜒眼睛光栅的结构和光栅常量,推测结果与电镜下拍到的结果基本一致.用3片互成60°的普通一维光栅做成二维三重光栅,通过实验和计算机编程2种方法得到的衍射图样与蜻蜒眼睛光栅的衍射图样非常吻合.     

Aerodynamic interaction between forewing and hindwing of a hovering dragonfly

The phase change between the forewing and hindwing is a distinct feature that sets dragonfly apart from other insects.In this paper,we investigated the aerodynamic effects of varying forewing-hindwing phase di ff erence with a60 inclined stroke plane during hovering flight.Force measurements on a pair of mechanical wing models showed that in-phase flight enhanced the forewing lift by 17%and the hindwing lift was reduced at most phase differences.The total lift of both wings was also reduced at most phase di ff erences and only increased at a phase range around in-phase.The results may explain the commonly observed behavior of the dragonfly where 0 is employed in acceleration.We further investigated the wing-wing interaction mechanism using the digital particle image velocimetry（PIV）system,and found that the forewing generated a downwash flow which is responsible for the lift reduction on the hindwing.On the other hand,an upwash flow resulted from the leading edge vortex of the hindwing helps to enhance lift on the forewing.The results suggest that the dragonflies alter the phase di ff erences to control timing of the occurrence of flow interactions to achieve certain aerodynamic effects.     

昆虫飞行的高升力机理

对近年来关于昆虫产生非定常高升力的研究进行了综述和归 纳.这方面的工作对生物学研究和微型飞行器等微型机械的仿生设计 有重要意义.研究表明：果蝇等昆虫翅膀的拍动运动可产生很大的非 定常升力，其平均值是定常值的2~3倍，足够平衡昆虫的重量，并有 较大的富余用于机动飞行；产生高升力有三个因素:一是拍动开始阶 段翅的快速加速运动，二是拍动中的不失速机制，三是拍动结束阶 段翅的快速上仰运动.人们从能耗的角度考察了这些非定常高升力机 制的正确性和可行性.当作悬停飞行的果蝇用以上机制产生平衡其重 量的升力时，其比功率(支持单位身体质量所需的功率)约为29W/kg, 生化/机械效率约为17%. 这些值与人们基于对昆虫肌肉力学特性的研 究所预估的值接近.果蝇前飞时，其比功率随速度变化的曲线是一J形 曲线，而不是象飞机或鸟的那样是一U形曲线；这与人们基于昆虫新 陈代谢率的测量数据所推断的结果一致.对于蜻蜒等(功能上)有前、 后两对翅膀的昆虫，有以下初步结果：翅的下拍主要产生升力，上挥 主要产生推力；下拍时的平均升力系数可达2~3,十分大，上挥时的平 均推力系数可达1~2, 也很大，它们主要由非定常效应产生；前、后 翅的相互干扰并未起增大升力和推力的作用，反而有一定的不利作用.     

蜻蜒飞行姿态的实时模拟测量

作为昆虫自由飞行姿态实时测量的预研课题,本文利用投影栅线法对真实蜻蜓翅膀在以适当频率摆动的机械驱动下模拟真实飞行时的三维形状变化进行了实时测量.由于在图像采集,预处理,位相提取,抑噪声去包络等环节采取了一系列措施,克服了由于蜻蜓翅膀透明度高,表面微观起伏变化剧烈所导致的栅线条纹图的平均灰度、对比度和信噪比都很低而给数据处理带来的困难.并最终得到了满意的结果.