Aerial shaking performance of wet Anna's hummingbirds

External wetting poses problems of immediate heat loss and long-term pathogen growth for vertebrates. Beyond these risks, the locomotor ability of smaller animals, and particularly of fliers, may be impaired by water adhering to the body. Here, we report on the remarkable ability of hummingbirds to perform rapid shakes in order to expel water from their plumage even while in flight. Kinematic performance of aerial versus non-aerial shakes (i.e. those performed while perching) was compared. Oscillation frequencies of the head, body and tail were lower in aerial shakes. Tangential speeds and accelerations of the trunk and tail were roughly similar in aerial and non-aerial shakes, but values for head motions in air were twice as high when compared with shakes while perching. Azimuthal angular amplitudes for both aerial and non-aerial shakes reached values greater than 180° for the head, greater than 45° for the body trunk and slightly greater than 90° for the tail and wings. Using a feather on an oscillating disc to mimic shaking motions, we found that bending increased average speeds by up to 36 per cent and accelerations of the feather tip up to fourfold relative to a hypothetical rigid feather. Feather flexibility may help to enhance shedding of water and reduce body oscillations during shaking.     

桨叶附着涡环量分布的迭代算法

结合升力线理论和叶素理论给出了一种桨叶附着涡环量分布的迭代算法,并用此算法计算了悬停状态下模型旋翼桨叶的附着涡环量分布,计算结果与实验数据吻合较好,且收敛较快,证明了该方法的有效性。     

空间相对悬停轨道闭环控制方法研究

空间相对悬停轨道在空间操作中具有重要的作用。提出了一种相对圆轨道目标星任意位置的悬停闭环控制方法,并基于李雅普诺夫方法设计了反馈系数,解决了由于Hill方程线性化误差导致开环控制难以保持悬停效果的问题。实验结果表明,在服务星上增施加少量的额外燃料,可以实现服务星相对目标星长时间、高精度、稳定的悬停,并通过数值仿真验证了该方法的有效性。     

The Aurora Project

The new opportunities for simulation and representation that computer modelling affords designers has been well charted. Jason Kelly Johnson and Nataly Gattegno of Future Cities Lab, however, are combining these new potentials with dynamic mapping and modelling methods derived from modern cartography. The most familiar of these tools is Google Earth, which provides a unique new bird's-eye view of the earth's surface. Other geographical softwares also combine to enable the manipulation of real-time, open-source, user-generated data as never before. Copyright © 2010 John Wiley & Sons, Ltd.     

基于金字塔光流法的无人机室内定点悬停设计

针对GPS定位系统建筑物内信号弱,小型无人机很难在室内实现定点悬停.本文提出了一种利用计算机视觉融合惯性导航的组合控制方案.在光流估计上,采用金字塔LK光流算法,提高特征点跟踪精度.在速度融合上,采用卡尔曼+互补混合融合方案,提高飞行速度的准确性.在飞行控制上,采用高度、姿态串级闭环控制方案,光流作为姿态估计的补偿值,...     

悬停回转试飞方法在直升机超短波天线方向图测试中的应用

借鉴飞机天线方向图地面自由空间测试场测试方法,利用直升机空中悬停特性进行天线方向图测试,以达到节省试飞架次的目的.分析了如何进行直升机悬停位置的选择以及直升机到测试点的距离和垂直高度的计算,总结了直升机超短波天线方向图测试中的定点悬停试飞驾驶技术.该试验方法在飞行试验中得到了验证,与传统试飞方法进行对比,工作效率提高2倍.     

旋翼模型悬停状态桨尖涡特性

直升机旋翼桨尖涡特性研究是直升机旋翼气动特性研究的关键要素,为提高对旋翼悬停状态桨尖涡特性的认识以及准确掌握其流动机理,利用Bo-105旋翼模型在Φ5 m立式风洞开口试验段进行了桨尖马赫数相似情况下的悬停试验,并采用TR-PIV流场测量系统对旋翼悬停状态下不同总距时的流场进行了精细化测量,得到了该副旋翼32帧/圈的详细流场图像,并运用更为合理的涡核中心判定、涡核流动数据提取以及涡核模型拟合方法对试验结果进行了精细化处理与分析,进一步揭示了旋翼模型悬停状态下桨尖涡的演化发展过程.研究表明:高速PIV设备能准确捕捉旋翼悬停状态下的流场运动特征,有助于旋翼流场的精细化研究;采用涡量加权平均的方法来计算涡核中心位置可以消除涡核中心平移速度的影响,进而更加准确地定位涡核中心;采用环量分析的方法可以更加可靠地确定涡核尺寸和最大诱导速度,且分析结果显示随涡龄角的增加,涡核半径缓慢增大、涡核最大诱导速度缓慢减小;在桨尖涡发展演化过程中,不同发展阶段具有不同的涡核模型n参数.     

室内无人机定点悬控系统

针对室内环境下无人机传统定位方法失效的问题,设计了一种基于图像处理的室内定位方法,上位机通过外部相机采集定位空间的斜投影图像,经颜色空间处理与分析后确定无人机机体质心投影点位置;结合机载高度传感器获得的竖直位置信息,成功解算出无人机水平坐标,克服了传统定位方法存在的位置漂移和精度低问题.利用上述方法结合机载惯性测量单元...