昆虫飞行的空气动力学

昆虫是最早出现、数量最多和体积最小的飞行者. 它们能悬停、跃升、急停、快速加速和转弯, 飞行技巧十分高超. 由于尺寸小, 因而翅膀的相对速度很小, 从而进行上述飞行所需的升力系数很大. 但昆虫翅膀的雷诺数又很低. 它们是如何在低雷诺数下产生高升力的, 是流体力学和生物学工作者都十分关心的问题. 近年来这一领域有了许多研究进展. 该文对这些进展进行综述, 并对今后工作提一些建议. 因2005 年前的工作已在几篇综述文章有了详细介绍, 该文主要介绍2005 年以来的工作. 首先简述昆虫翅的拍动运动及昆虫绕流的基本方程和相似参数; 然后对2005 年之前的工作做一简要回顾. 之后介绍2005 年后的进展, 依次为: 运动学观测; 前缘涡; 翅膀柔性变形及皱褶的影响; 拍动翅的尾涡结构; 翼/身、左右翅气动干扰及地面效应; 微小昆虫; 蝴蝶与蜻蜓; 机动飞行. 最后为对今后工作的建议.      

卫星编队飞行动力学与控制研究

简要介绍了卫星编队飞行的动力学与控制研究的最新进展，对今后研究工作的重点提出了建议．     

地球轨道航天器编队飞行动力学与控制研究综述

航天器编队飞行被定义为跟踪或维持航天器之间的期望相对间隔、期望指向和相对位置。本文概括介绍了近年来地球轨道飞行编队的动力学和控制方面研究的发展状况,包括传统推进系统和新型无推进剂编队系统的动力学建模方法和控制器设计技术等。在传统推进编队系统中,航天器由使用化学燃料或等离子体的推进器提供推力,可以实现高精度地相对姿态/位置保持或重构,控制简单,灵活性高,但是需要消耗较多的能源。相比之下,在新型无推进剂编队系统中,航天器通过新的推力方式,如大气阻力作用,非接触内力,地磁洛伦兹力,动量交换等,将大大延长编队任务的寿命,并有效地避免羽流污染,但会带来新的控制问题。本文总结了这些领域中动力学与控制方面的研究方法及取得的成果,并提出了相关领域值得深入研究的问题和后续发展的方向。     

平流层飞艇动力学与控制研究进展

本文简要介绍了飞艇的发展沿革和研究现状. 通过同传统的航空器、航天器、潜艇和低空飞艇进行比较, 阐述了平流层飞艇的飞行原理. 从基本运动模型和复杂受力情况的角度, 系统地讨论了飞艇动力学研究进展, 包括空气动力学研究、静力分析、热力学分析、柔性体动力学及流固耦合研究. 然后综述了飞艇控制方法研究进展, 包括小扰动线性化控制、输入输出反馈线性化控制、基于Lyapunov 非线性稳定性的控制及其他控制方法. 最后展望了在平流层飞艇动力学与控制领域需要从6 个方面加强研究.      

地球轨道航天器编队飞行动力学与控制研究综述1)

航天器编队飞行被定义为跟踪或维持航天器之间的期望相对间隔、期望指向和相对位置。本文概括介绍了近年来地球轨道飞行编队的动力学和控制方面研究的发展状况,包括传统推进系统和新型无推进剂编队系统的动力学建模方法和控制器设计技术等。在传统推进编队系统中,航天器由使用化学燃料或等离子体的推进器提供推力,可以实现高精度地相对姿态/位置保持或重构,控制简单,灵活性高,但是需要消耗较多的能源。相比之下,在新型无推进剂编队系统中,航天器通过新的推力方式,如大气阻力作用,非接触内力,地磁洛伦兹力,动量交换等,将大大延长编队任务的寿命,并有效地避免羽流污染,但会带来新的控制问题。本文总结了这些领域中动力学与控制方面的研究方法及取得的成果,并提出了相关领域值得深入研究的问题和后续发展的方向。     

空气动力学研讨课建设的探索与实践

为了丰富基础课堂教学资源、满足本科生通识教育的需求,北京航空航天大学近期推出建设名师研讨课、新生研讨课、专业研讨课等,毫无疑问这些对学校本科教学的深化改革具有重要的促进作用.针对我校国家级精品课程空气动力学教学改革的实践,总结了在建设空气动力学名师研讨课过程中的构思和经验,以供参考.空气动力学是一门理论与实际紧密结合的基础课程,在研讨课建设中,提出以空气动力学典型问题为引导,通过启发、实验、讨论、分析等多种形式,引导学生积极主动思考,从鸟的飞行原理、实验现象和结果中获取灵感、凝练科学问题,对激发学习兴趣、提高创新实践能力等具有明显效果.     

大型漂浮式风电装备耦合动力学研究: 历史、进展与挑战

风电是可再生能源的主力军, 在优化能源结构、缓解气候变化方面发挥着重要作用. 经过数十年的发展, 风电装备逐渐向大型化和离岸化方向发展, 并由此形成“由陆向海, 由浅入深, 由固定式向漂浮式”的演变之路. 在水深大于50米的深远海域, 采用漂浮式支撑基础搭载大型或超大型风电机组是兼顾技术可行度和成本优势的理想选择. 如今, 大型漂浮式风机已成为下一代深远海风能大规模开发的主力装备, 是深化海洋风能开发的先导战略性高端装备, 是风电领域的研究热点和技术高地. 本文围绕大型漂浮式风电装备耦合动力学问题, 综述了国内外浮式风电技术的发展历程和研究现状, 结合作者团队多年的研究与实践经验, 介绍了浮式风机耦合动力学及其优化控制中的基础问题与研究现状, 总结了现阶段浮式风机耦合动力学研究中的困难与挑战, 为浮式风电研究人员提供参考.      

编队飞行星座相对运动的运动学描述与编队构型设计

分别以纬度幅角和平近点角、平纬度幅角及偏近点角为变量,推导了几种简单的编队飞行星座相对运动的运动学模型,这些模型和动力学模型(Hill方程)相一致,但更便于应用。并在此基础上,给出了当编队构型为空间圆形和星下点圆形时进行编队构型设计的一种运动学方法,该方法直接给出了星座中各星的轨道根数的计算方法,实例证明该方法简单实用。     

飞行和游动的生物力学与仿生技术--香山科学会议第214次学术讨论会介绍

在隆重纪念香山科学会议举办十周年之际,香山科学会议第214次学术讨论会于2003年10月21日-23日在北京香山饭店举行.本次讨论会的主题是“飞行和游动的生物力学与仿生技术”.出席讨论会的代表42人,包括来自高等院校和中国科学院、航天科技集团等有关研究所的专家、学者,以及有关部门的科技管理专家.讨论会的执行主席为童秉纲院士和崔尔杰院士. 20世纪末,各种先进微型制造技术、微机电系统、微电子和一体化技术有了迅速发展.在此基础上,人们提出了微     

仿生扑翼飞行机器人翅型的研制与实验研究

模仿昆虫和小鸟飞行的扑翼飞行机器人将举升、悬停和推进功能集于一个扑翼系统,与固定翼和旋翼完全不同,因此研究只能从生物仿生开始。生物飞行的极端复杂性使得进行完整和精确的扑翼飞行分析非常复杂,因此本文在仿生学进展基础上,通过一些合适的假设和简化,建立了仿生翅运动学和空气动力学模型,并以此为基础研制了多种翅型。研制了气动力测量实验平台,对各种翅型进行了实验研究。实验结果表明,研制的翅型都能产生一定的升力,其中柔性翅具有较好的运动性能和气动性能,并且拍动频率和拍动幅度对升力有较大影响。     

Perfect Plasticity Theory: State of the Art and Development Trends

The state of the art and development trends of model conceptions in perfect plasticity theory are overviewed. The paper does not consider limit equilibrium theorems, theory of optimum design and adaptability, flow problems in metal forming, dynamic behavior of rigid–plastic and elastic–plastic bodies, etc     

Dynamic flight stability of a bumblebee in forward flight

The longitudinal dynamic flight stability of a bumblebee in forward flight is studied. The method of computational fluid dynamics is used to compute the aerodynamic derivatives and the techniques of eigenvalue and eigenvector analysis are employed for solving the equations of motion. The primary findings are as the following. The forward flight of the bumblebee is not dynamically stable due to the existence of one （or two） unstable or approximately neutrally stable natural modes of motion. At hovering to medium flight speed [flight speed Ue = （0-3.5）m s^-1; advance ratio J = 0-0.44], the flight is weakly unstable or approximately neutrally stable; at high speed （Ue = 4.5 m s^-1; J = 0.57）, the flight becomes strongly unstable （initial disturbance double its value in only 3.5 wingbeats）.     

Dynamic flight stability of a model dronefly in vertical flight

The dynamic flight stability of a model dronefly in hovering and upward flight is studied.The method of computational fluid dynamics is used to compute the stability derivatives and the techniques of eigenvalue and eigenvector used to solve the equations of motion.The major finding is as following.Hovering flight of the model dronefly is unstable because of the existence of an unstable longitudinal and an unstable lateral natural mode of motion.Upward flight of the insect is also unstable,and the instability increases as the upward flight speed increases.Inertial force generated by the upward flight velocity coupled with the disturbance in pitching angular velocity is responsible for the enhancement of the instability.     

Elastic Energies in Circular Inhomogeneities: Imperfect Versus Perfect Interfaces

The change in the total potential energy in a stressed elastic plane system, consisting of an unbounded matrix containing a cylindrical inhomogeneity of circular cross-section, is studied, when an imperfect bonding is formed across the interface. The imperfect bonding is simulated by linearly elastic springs distributed over the interface. Two loading cases are examined: an equilibrium system of fixed uniform tractions acting in the remote boundary of the matrix, and a phase transformation in the inhomogeneity prescribed by stress free uniform eigenstrains distributed in the inhomogeneity region. For both loadings, the fully elastic fields in explicit forms are derived involving the spring compliances and three new two-phase parameters depending on the elastic properties of the two materials. The elastic energies stored in the whole system and in its constituents are determined in simple and compact forms. It is shown that, in both loading cases, the total potential energy of the system is reduced. It is found that, in nanoscale, the ratio of the elastic energy stored in interface to the elastic energy stored in inhomogeneity increases rapidly for small values of the circular radius and tends to zero for large values. Also, this ratio increases as the matrix becomes softer compared to the inhomogeneity.     

Erratum to: Analysis on the nonlinear response of cracked rotor in hover flight

Nonlinear Dynamics -     

Explosion of a body in flight

Little attention has been paid up to now in the theory of explosions to such an important and interesting problem as the explosion of a body in flight. A formulation of the problem presented by such an explosion in connection with the problem of simulating the explosion of a meteorite body flying at cosmic velocity is given in [1]. In this case the kinetic energy of the translational motion may be comparable to or even in excess of the internal energy of the explosive transformation, which will lead to a significant distortion of the flow pattern compared with the usual explosion process. An analysis of the effect of the initial velocity of particles on the course of an explosion in idealized formulations in the framework of one-dimensional flows with plane, cylindrical, and spherical waves was first made in [2–4]. The asymptotic flow properties were found in these papers. It is shown that if the internal energy E_o and the kinetic energy K_o are separated (the specification of the latter for a fixed mass is equivalent to specification of the initial momentum), some intermediate self-similar regimes corresponding to a short pulse [2] or to flows with a sink [3, 4] are observed, these becoming the solution for a strong explosion at long times [1]. The time of transition from one qualitative regime to another depends on the ratio K_o/E_o. In the present paper the next step in the investigation of the question is taken. An axisymmetric, basically realistic flow model is studied.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 126–129, September–October, 1984.     

Stability and integrity of mechanical joints in flight vehicles: Local and global energy density

A methodology is presented for analyzing the inlfuence of mechanical joint failure on the global instability of flight vehicles. Considered are the ways with which loading, geometry and material of the vehicle can affect the structure instability and/or integrity. The peaks and valleys of the volume energy density function are assumed to coincide with failure by fracture and/or yielding while the distance between their local and global stationary values govern the structure instability. A single length parameter l can thus be applied to provide a measure of stability. The simultaneous occurrence of high energy density and large l at the same location should be avoided as it may have undesirable consequences.A flight vehicle consisting of four cylindrical shell-like structures connected by three tongue-and-groove joints is analyzed. The time-dependent load can be axisymmetric or non-axisymmetric. A semi-analytical finite element program is developed and used to solve for the transient stress and strain distribution from which contours of the volume energy density in the structure are obtained as a function of time. The magnitudes and locations of their local and global stationary values are then calculated and discussed in connection with potential failure by fracture. Stability behavior does not alter appreciably for axisymmetric flight. Considerable fluctuations in the energy density and the dynamic stability length parameter are found when non-axisymmetric loads are considered.     

漫话中国古代的飞行

在美国莱特兄弟发明飞机百年之际,又有中国``神舟'五号太空飞行,人们自然想到飞行史前阶段人类曾经有过的飞行尝试. 本文叙述古代中国人的有关飞行思想与滑翔飞行的情况,并将原始文献展示读者,以供参读.     

Unlocking the secrets of supernovae through their light curves,spectra & polarization

Utilizing the radiative transfer code cmfgen, we have undertaken time-dependent radiative transfer calculations that compute the light curve and spectra for Type Ia, Ib, Ic, and II supernovae (SNe) through the photospheric and nebular phases. The non-LTE calculations allow for a multitude of atomic processes (bound–bound, bound–free, free–free, collisional, charge exchange, and Penning ionization) and for non-thermal excitation and ionization from non-thermal electrons created by the degradation in energy of high-energy (～1 MeV) gamma-rays. The proper inclusion of all these processes requires a vast amount of atomic data. Not all the atomic data is available, and the quality of the available atomic data varies considerably. We have confirmed the results of Utrobin and Chugai (2005) that time dependent terms must be included in the statistical equilibrium equations in order to model the Hα evolution of SN 1987A, shown that time dependent terms influence other spectral features, and shown that these conclusions also apply to the modeling of Type II SNe in general. The inclusion of non-thermal processes has allowed us to model Hα and He i emission in Type II SNe into the nebular phase, and to model the He i emission in Type Ib and Ic SNe. Our calculations show that the He deficiency in Ic SNe is unlikely to be real – instead, the absence of He i on SNe Ic spectra is more likely related to inefficient excitation of He iions. Simply by varying the amount of mixing we are able to create spectra of Type Ib and Ic SNe using the SAME progenitor model. Based on a new grid of SNe Ib/c models, we confirm previous findings that the typically fast-rising narrow-peak fast-declining SNe Ib/c light curves imply ejecta masses $\mathrm{?}5{\text{M}}_{\odot }$, favoring intermediate-mass massive stars in interacting binaries. We are successfully applying cmfgen to model Type Ia SNe, and are currently exploring the role of mixing and non-thermal processes in these SNe. We highlight the differences between the various classes of SNe.