Bio-inspired energy-harvesting mechanisms and patterns of dynamic soaring
Bio-inspired energy-harvesting mechanisms and patterns of dynamic soaring
复制标题
仿生能量收集机制和动态翱翔模式
DOI：
10.1088/1748-3190/aa547c
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发表时间：
2017-02-01
影响因子：
3.4
通讯作者：
Gao, Xian-Zhong
中科院分区：
文献类型：
--
作者：
Liu, Duo-Neng;Hou, Zhong-Xi;Gao, Xian-Zhong
信天翁可以利用动态翱翔技术，从风场中提取能量，实现无襟翼的大范围运动，激发了人们对小型无人机轻松飞行的兴趣。然而，在之前的研究中使用不同的参考系时，从风到飞行器（信天翁或无人机）的能量转移的能量收集机制仍然是不确定的且存在争议。本文引入经典的顺风爬升、顺风转向、顺风俯冲和逆风转向的四阶段瑞利循环，利用信天翁的运动方程和动态翱翔的模拟轨迹进行能量增益分析。分析和数值结果表明，空气相对系中的能量增益主要来源于爬升和俯冲时较低处的大风梯度，而惯性系中的能量增益则来自于较高高度爬升、俯冲和顺风转弯时倾斜于风速方向的升力矢量。这两种能量增益机制在能量来源和参考系方面并不等同，但在能量中性动力飙升循环方面必须同时满足。对于每个参考系，能量损失阶段对于连接能量增益阶段是必要的。基于动态翱翔的这四个基本阶段和信天翁的飞行轨迹，示意性地描绘了不同的动态翱翔模式并计算相应的最佳轨迹。最佳动态翱翔轨迹分为“O”形和“8”形两种闭合模式，以及“O”形、“a”形、“C”形和“S”形四种飞行模式。分析和讨论了这些模式之间的相关性。通过列出和总结过去几十年研究中显示的动态飙升轨迹，证实了不同模式分类的完整性。
Albatrosses can make use of the dynamic soaring technique extracting energy from the wind field to achieve large-scale movement without a flap, which stimulates interest in effortless flight with small unmanned aerial vehicles (UAVs). However, mechanisms of energy harvesting in terms of the energy transfer from the wind to the flyer (albatross or UAV) are still indeterminate and controversial when using different reference frames in previous studies. In this paper, the classical four-phase Rayleigh cycle, includes sequentially upwind climb, downwind turn, downwind dive and upwind turn, is introduced in analyses of energy gain with the albatross's equation of motions and the simulated trajectory in dynamic soaring. Analytical and numerical results indicate that the energy gain in the air-relative frame mostly originates from large wind gradients at lower part of the climb and dive, while the energy gain in the inertial frame comes from the lift vector inclined to the wind speed direction during the climb, dive and downwind turn at higher altitude. These two energy-gain mechanisms are not equivalent in terms of energy sources and reference frames but have to be simultaneously satisfied in terms of the energy-neutral dynamic soaring cycle. For each reference frame, energy-loss phases are necessary to connect energy-gain ones. Based on these four essential phases in dynamic soaring and the albatrosses' flight trajectory, different dynamic soaring patterns are schematically depicted and corresponding optimal trajectories are computed. The optimal dynamic soaring trajectories are classified into two closed patterns including 'O' shape and '8' shape, and four travelling patterns including 'O' shape, 'a' shape, 'C' shape and 'S' shape. The correlation among these patterns are analysed and discussed. The completeness of the classification for different patterns is confirmed by listing and summarising dynamic soaring trajectories shown in studies over the past decades.