Effect of wing morphing on stability and energy harvesting in albatross dynamic soaring

Dynamic soaring,which harvests energy from the wind,can enhance Unmanned Aerial Vehicles'(UAVs')range and endurance.However,energy harvesting efficiency issues hinder UAV applications,which can be addressed by wing morphing.Therefore,this study investigates the influence of albatross wing morphing during dynamic soaring.By constructing a parametric model,the shape of the albatross wing can be modeled and achieve morphing based on joints.From the video data,this paper summarizes the typical wing morphing patterns of the albatross and notices that changes primarily occur during the leeward descent phase.This paper first analyzes the aerodynamic performance of different wing morphing patterns and finds that the drag coefficient can be reduced by 7.75%with a suitable morphing pattern.This paper also explores the drag coefficient reduction mechanism and finds that downwash airflow decreases by 30.32%after wingtip anhedral.Interestingly,the lift-to-drag ratio shows minimal variation under different morphing patterns,within 2%.From the stability perspective,this study finds that the neutral point position changes after morphing.The maximum longitudinal static margin change is 4.9%,enhancing longitudinal stability by increasing the restorative moment arm.The lateral neutral point is 4.87%closer to the center of gravity,decreasing the roll and yaw moments.It can be observed that wingtip anhedral significantly increases the stability of the albatross.Moreover,a flight simulation is carried out to study the morphing influence on trajectory and energy harvesting.The results show that maximum energy gained is improved by 47.99%,and endurance is increased by 13.05%.The results also indicate that the effects of wing morphing are global rather than limited to the phase of morphing occurrence.Finally,based on the results,this paper proposes wing morphing regularity about the wingtip for UAVs.Wingtip bends downward can significantly increase the UAVs'stability and reduce drag,but the overall trajectory needs to be reconsidered after introducing wing morphing.

Smooth free-cycle dynamic soaring in unspecified shear wind via quadratic programming

Harvesting wind energy is promising for extending long-endurance flights,which can be greatly facilitated by a flight technique called dynamic soaring.The presented study is concerned with generating model-based trajectories with smooth control histories for dynamic soaring maneuvers exploiting wind gradients.The desired smoothness is achieved by introducing a trigonometric series parameterization for the controls,which are formulated with respect to the normalized time.Specifically,the periodicity of the trigonometric functions is leveraged to facilitate the connection of cycles and streamline the problem formulation.Without relying on a specified wind profile,a freefinal-time quadratic programming-based control strategy is developed for the online correction of the flight trajectory,which requires only the instant wind information.Offline and online numerical studies show the trade-off to achieve the smoothness and demonstrate the effectiveness of the proposed method in a varying wind field.