一种仿蜜蜂类昆虫扑翼悬停控制的仿真估算研究

基于准稳态气动力模型,推导了仿蜜蜂类昆虫扑翼气动力和力矩估算公式,建立了扑翼运动函数.将仿蜜蜂类昆虫扑翼视为空间运动刚体,在其动力学方程基础上,采用分层控制策略研究悬停控制问题.外层为位置控制,X和Y位置应用PD控制算法,Z位置应用切换控制方法;内层姿态控制采用切换控制方法,并选择了一套机翼运动参数用于切换控制.最后进行了仿蜜蜂类昆虫扑翼悬停控制仿真试验,试验结果表明所设计的控制策略是有效的,一旦昆虫扑翼受到干扰偏离平衡位置后,通过自动调节能够回到平衡位置附近.      

Proposal for a multiple-asteroid-flyby mission with sample return

Asteroid exploration provides a new approach to study the formation of the solar system and the planetary evolution. Choosing a suitable target and designing of feasible profile for asteroid mission are challenging due to constraints such as scientific value and technical feasibility. This paper investigates a feasible mission scenario among the potential candidates of multiple flybys and sample return missions. First, a group of potential candidates are selected by considering the physical properties and accessibility of asteroids, for the sample return missions. Second, the feasible mission scenarios for multiple flybys and sample return missions to various spectral-type asteroids are investigated. We present the optimized design of preliminary interplanetary transfer trajectory for two kinds of missions. One is the single sample return mission to asteroids with various spectral types. The other is the multiple flybys and sample return mission to several asteroids. In order to find the optimal profiles, the planetary swing-by technique and Differential Evolution algorithm are used.     

食蚜蝇悬停飞行时的气动特性

用数值求解N-S(Navier-Stokes)方程的方法得到了食蚜蝇在拍动平面倾斜悬停飞行时的气动力和气动力矩,利用得到的气动力矩和已知的翅膀的惯性矩求得食蚜蝇悬停时的能耗,并将得到的气动力和能耗与正常悬停时的进行比较.主要结果为:维持食蚜蝇体重所需的举力主要由下拍产生,该举力是由翅膀的升力和阻力共同贡献的,这两点均与水平拍动的情形不同;飞行的比功率为31.71 W·kg^-1,与正常悬停时接近,这表明此种悬停方式有便于进行机动飞行的优点,但不带来额外的能耗.     

倾转三旋翼飞行器地面效应风洞试验

倾转旋翼飞行器在近地悬停或低速前飞时有明显的地面效应,对飞行器的气动载荷有强烈影响。针对倾转三旋翼(TTR)飞行器的地面效应问题,采用0.5 的缩比模型,在低速回流式开口风洞中设计了可移动地面平台,模拟TTR飞行器悬停和低速前飞时的离地高度,利用杆式天平测量机体所受载荷大小并使用粒子图像测速(PIV)技术捕捉机体下方的动态流场。试验结果表明:当TTR飞行器悬停离地高度在1.25倍旋翼直径以下时,地面效应影响显著,机体受到的最大上载荷约为旋翼总推力的4%,并观测到明显的涡旋喷泉流现象;在低速前飞状态,受旋翼尾流和前向来流影响,相对于悬停状态机体所受上载荷明显减小,喷泉流中心后移。试验结果对TTR无人飞行器动力系统选择,控制増稳系统设计以及借助地面效应优势提高承载能力具有一定参考价值。     

非圆轨道卫星实现共面悬停的方法

通过矢量控制,使任务卫星始终在目标卫星的轨道平面内飞行,同时保证"任务卫星-目标卫星-地心"的夹角和两颗卫星间的相对距离保持不变,从而实现共面悬停飞行。重点进行了任务卫星悬停飞行的动力学理论分析,推导了悬停飞行过程中任务卫星相对于目标卫星的径向和切向加速度需求,给出了开环控制方案,对不同悬停任务的能量需求进行了对比分析,最后对悬停飞行过程进行了动力学仿真。     

翅尖轨迹对食蚜蝇悬停时气动特性的影响

食蚜蝇悬停飞行时的抬升角相对较小,在上下拍起始和结束时刻要比拍动中部的大,这样就使得翅尖的拍动轨迹呈现出浅“U”形。为了分析该翅尖轨迹是否会对其气动特性产生影响,利用计算流体力学的方法分别计算了4只食蚜蝇在考虑抬升角和忽略抬升角2种情形下的气动力,分析对比了2种情形下的不同时刻绕翅膀的瞬时流线,并计算比较了2种情形下气动功率系数与平均举力系数的比值。研究结果表明:抬升角的存在会使其维持体重所需的举力增加10%左右;举力增大的同时能耗却比忽略抬升角情形下要低3%左右。      

桨叶翼型弯度对摆线桨悬停状态的气动性能影响

以悬停状态下的摆线桨为研究对象,利用数值模拟方法,分别研究了桨叶相对弯度X和最大弯度位置Y对摆线桨气动性能的影响。结果表明:与桨叶为对称翼型的摆线桨相比,当桨叶具有一定弯度且最大弯度位置适中时,摆线桨气动性能得到很大的提升。当桨叶相对弯度X为4%C(C为翼型弦长)、最大弯度位置Y距离前缘40%C~50%C时,摆线桨升力和气动功耗比较低,悬停效率最高,整体气动性能更好。      

Asteroid interception and disruption for terminal planetary defense

Modern techniques for planetary defense from comets and asteroids involve the deflection of the bolide via kinetic, gravitational, ablative, or radiative means. While potentially effective, none of these methods are capable of operating in a terminal interdiction mode wherethe threat is discovered with little time prior to impact. We present a practical and effective method for planetary defense which enables extremely short interdiction time scales, but can also operate within longer time scales and can be effective for extremely large threats. Called PI (“Pulverize It”), the method makes use of an array of hypervelocity penetrators which uses the kinetic energy of the asteroid or comet to disrupt it. In the terminal interdiction mode, the fragments of maximum $～10$ m diameter disperse laterally as they continue towards the Earth, and then enter the Earth’s atmosphere where they burn up as a series of airburst events which spatially and temporally de-correlate the energy of the original parent bolide for any arbitrary observer on the ground in the form of acoustical shockwaves and optical pulses. We show that terminal interdiction modes ranging from 2 minutes prior to impact for 20-meter class bolides (such as the Chelyabinsk asteroid), 1 day prior to impact for 100 m-class asteroids, 10 days prior to impact for Apophis-class asteroids ($～370$ m), and even 60 days prior to impact for 1 km-class threats are all possible, though longer warning times are always preferred. Using only technologies readily available today, the PI method allows for a cost-effective and practical roadmap towards robust planetary defense capability.     

The effect of a rocky terrain for CubeSat landing on asteroid surfaces

The paper describes a general modelling procedure to build a simulation tool to investigate contact motion of a CubeSat on an asteroid surface. We investigate landing performance and landing success for the case of elastic rocky terrain and flat surfaces. As a case study, we focus on the disposal of ESA’s Hera Milani CubeSat by landing on the moon of Didymos binary asteroid system. The simulation environment includes the modelling of real shape and 6-DOF motion of the lander, the shape-based gravity models of Didymos and Dimorphos and rocks on surface, that are generated as physical obstacles. Trends and estimates on the performance of the landing phase and the most relevant effects on the outcome of the soil interaction process, are inferred. The statistical results on settling time, dispersion area and motion characteristics, such as number of bounces, show and quantify the effect of rocks on a successful passive and permanent landing.     

Simulation and analysis of asteroid force closure anchoring performance based on discrete element method

Asteroid exploration is significant for studying the origin of the solar system, establishing planetary defenses, and alleviating the resource crisis of the Earth. Asteroid anchoring is the basis of in-situ exploration and resource development and utilization. Therefore, the performance of asteroid force-closure anchoring is investigated using the discrete element method. The micro parameters of the simulated materials are calibrated with angle of repose and uniaxial compression experiments, based on which the regional modeling method is adopted to establish the anchoring discrete element model. Asteroid anchoring experiments are conducted on a self-developed microgravity simulation platform to verify the accuracy of the simulation model. The asteroid anchoring simulations are performed to investigate the influence of external force on the anchoring performance. The analysis of anchoring force varying with time and the interaction between the anchor and regolith particles reveals the influence mechanism of external force direction on the anchoring performance. The external force direction affects the critical anchoring force by influencing the failure of the force-closure structure. The comprehensive analysis of simulation results clarifies the variation of the critical anchoring force with the external forces. Finally, a stable anchoring region is established, beneficial for asteroid anchoring device design.