Dipartimento di Ingegneria Meccanica e Aerospaziale, Sapienza Universitá di Roma, Rome, Italy.
IDMEC, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal.
PLoS One. 2020 Mar 3;15(3):e0229746. doi: 10.1371/journal.pone.0229746. eCollection 2020.
Dynamic soaring is a flight technique used by albatrosses and other birds to cover large distances without the expenditure of energy, which is extracted from the available wind conditions, as brightly perceived five centuries ago by Leonardo da Vinci. Closed dynamic soaring trajectories use spatial variations of wind speed to travel, in principle, indefinitely over a prescribed area. The application of the concept of closed dynamic soaring trajectories to aerial vehicles, such as UAVs, may provide a solution to improve the endurance in certain missions. The main limitation of dynamic soaring is its dependence on the wind characteristics. More than one century ago, Lord Rayleigh proposed a very simple model, based on the repeated crossing of a step wind profile, presently known as Rayleigh cycle, that provides a clear explanation of the physical phenomenon. The present paper studies the feasibility of closed, single-loop, energy-neutral trajectories for a broad set of wind and vehicle conditions. Through the use of trajectory optimization methods, it was possible to see how the shape of the wind profile, the initial flight conditions and the vehicle constraints influence the required wind strength to perform dynamic soaring trajectories and consequently their feasibility. It was possible to conclude that there are optimal values for the initial airspeed and initial height of the vehicle, that minimize the required wind strength. In addition, it was seen how the structural and aerodynamic constraints of the vehicle affect dynamic soaring at high and low airspeeds respectively. Finally, some new trajectories that can be performed in conditions of excess wind are proposed. The purpose is to maximize the time spent aloft and the path length while maintaining the concept of single-loop, energy-neutral trajectories, making them especially useful for aerial vehicles surveillance applications.
动力翱翔是信天翁和其他鸟类用于在不消耗能量的情况下覆盖长距离的飞行技术，这种技术从可用的风况中提取能量，这一点早在五百年前就被莱昂纳多·达·芬奇敏锐地察觉到了。闭式动力翱翔轨迹利用风速的空间变化来在规定的区域内无限期地行进，原则上。将闭式动力翱翔轨迹的概念应用于无人机等航空飞行器，可能为提高某些任务的续航能力提供解决方案。动力翱翔的主要限制是其对风特性的依赖。一个多世纪前，瑞利勋爵提出了一个非常简单的模型，基于对台阶风速剖面的反复穿越，即现在所知的瑞利循环，该模型对物理现象提供了清晰的解释。本文研究了在广泛的风和飞行器条件下实现闭式、单环、能量中性轨迹的可行性。通过使用轨迹优化方法，可以看出风速剖面的形状、初始飞行条件和飞行器约束如何影响执行动力翱翔轨迹所需的风速强度，从而影响其可行性。可以得出结论，对于初始空速和飞行器初始高度存在最优值，可以最小化所需的风速强度。此外，还分别研究了飞行器的结构和空气动力学约束对高低空速动力翱翔的影响。最后，提出了一些可以在过剩风速条件下执行的新轨迹。目的是在保持单环、能量中性轨迹概念的同时最大化在空中停留的时间和路径长度，使它们特别适用于无人机监视应用。
