On the quasi-steady aerodynamics of normal hovering flight part I: the induced power factor

An analytical treatment to quantify the losses captured in the induced power factor, k, is provided for flapping wings in normal hover, including the effects of non-uniform downwash, tip losses and finite flapping amplitude. The method is based on a novel combination of actuator disc and lifting line blade theories that also takes into account the effect of advance ratio. The model has been evaluated against experimental results from the literature and qualitative agreement obtained for the effect of advance ratio on the lift coefficient of revolving wings. Comparison with quantitative experimental data for the circulation as a function of span for a fruitfly wing shows that the model is able to correctly predict the circulation shape of variation, including both the magnitude of the peak circulation and the rate of decay in circulation towards zero. An evaluation of the contributions to induced power factor in normal hover for eight insects is provided. It is also shown how Reynolds number can be accounted for in the induced power factor, and good agreement is obtained between predicted span efficiency as a function of Reynolds number and numerical results from the literature. Lastly, it is shown that for a flapping wing in hover k owing to the non-uniform downwash effect can be reduced to 1.02 using an arcsech chord distribution. For morphologically realistic wing shapes based on beta distributions, it is shown that a value of 1.07 can be achieved for a radius of first moment of wing area at 40% of wing length.     

新式桥型构想，解决城市拥堵

国内大中城市普遍存在交通拥堵现象,交通拥堵已成为城市发展进程中的绊脚石。本文通过分析交通拥堵现状及原因,我们提出了要解决道路拥堵,首当其冲的就是要解决信号灯问题。为此,设计了新式桥型,取缔信号灯,以实现车辆无阻运行。     

加工工艺对不同品种鸡翅品质特性和微观结构的影响

研究了不同加工工艺(腌制、焯水、卤制、杀菌)对不同鸡翅原料(蛋鸡、AA肉鸡、白羽肉鸡)的蒸煮损失、剪切力值和微观结构的影响。三种鸡翅原料的蒸煮损失随蒸煮时间的延长先增大而后保持不变。在不同处理条件下,蛋鸡鸡翅均比两种肉鸡鸡翅的剪切力值大,三种鸡翅结构因肌节的收缩而逐渐紧密。蛋鸡鸡翅肌纤维直径大于两种肉鸡鸡翅肌纤维直径,两种肉鸡鸡翅之间肌纤维直径无明显差别。卤制和杀菌之后的三种鸡翅肌纤维密度与原料相比均差异性显著(P<0.05)。     

变体飞行器的气动结构对控制系统的影响

为了研究变体飞行过程中不同的气动结构对控制系统产生的影响,利用多刚体动力学对飞行器各个通道进行建模,通过对变体过程气动参数的研究,探寻变体飞行器不同变形状态的升阻比变化规律,推导了飞行器实现最佳控制品质的控制律。设计了线性二次型控制器,并通过Simulink进行仿真验证,结果表明:计算条件下变体飞行器的最佳升阻比可以改变36%,收敛快速性可以提高128.61%; 通过变体,飞行器可以大幅度改变升阻特性,系统稳定性和收敛快速性都得到了很大提高。     

Transonic flow past thin wings

This paper is devoted to a discussion of steady inviscid transonic flow past thin wings, with subsonic free-stream Mach number M_∞ < 1, by the integral equation method. The integral equation formulation is developed for a thin unsymmetric wing at small incidence. A simple approximate analytical solution is presented for shock-free supercritical flow past a thin symmetric wing at zero incidence. The direct iteration scheme of Niyogi and Chakraborty is then extended to the three-dimensional zero incidence case, which may be used to obtain more accurate solutions for shockfree flows as well as for flows with shocks. The question of the existence and the uniqueness of a solution has been studied by means of the Banach contraction mapping principle in the spaceL ₂ (E₃), which establishes the condition of convergence of the direct iteration scheme. Simultaneously it provides us with an error estimate for the solution.     

Boundary control of flexible aircraft wings for vibration suppression

In this paper, we propose a boundary control strategy for vibration suppression of two flexible wings. As a basic approach, Hamilton's principle is used to ascertain the system dynamic model, which includes governing equations – four partial differential equations and boundary conditions – several ordinary differential equations. Considering the coupled bending and torsional deformations of flexible wings, boundary control force and torque act on the fuselage to regulate unexpected deformations of flexible wings. Then, we present the stability analysis of the closed-loop system through Lyapunov's direct method. Simulations are carried out by using finite difference method. The simulation experimental results illustrate the significant effect of the developed control strategies.     

空间多姿态下自动钻铆托架变形分析与调平方法

飞机壁板自动钻铆系统中托架具有自重大、跨距长、变形量大等特点,其变形误差随工作姿态的不同而改变,从而导致壁板钻铆超差。文章在对自动钻铆托架结构设计基础上,建立了托架横梁弯曲变形模型,根据钻铆点位与横梁变形曲线的空间关系构建了壁板钻铆点位变形量数学模型;针对传统调平补偿方法无法精确满足托架变形量动态变化的问题,采用迭代优化方法建立了托架多姿态变形补偿调平算法;并采用有限元仿真方法分析了托架处于各角度时钻铆点位的变形量及外法线向量;将理论算法数据与仿真数据进行了对比分析,验证了文中提出的托架变形分析与调平算法的正确性和有效性。     

基于偶极子的连续突风响应改进算法

文章阐述了基于亚音速偶极子网格法的连续突风响应改进算法.采用四次多项式来近似增量核函数分子,放宽了非定常气动力计算中对气动网格展弦比的限制.以弹性机翼结构为例,探讨了气动网格单元展弦比和网格数对连续突风响应计算结果的影响.对比经典算法、改进算法计算结果,表明改进算法可行有效.该算法减少了高频气动力计算中所需的展向网格数目,可以节约计算时间或存储空间并提高计算精度,对突风控制与减缓研究有一定的指导作用.     

A dynamic mesh strategy applied to the simulation of flapping wings

A robust and efficient dynamic grid strategy based on an overset grid coupled with mesh deformation technique is proposed for simulating unsteady flow of flapping wings undergoing large geometrical displacement. The dynamic grid method was implemented using a hierarchical unstructured overset grid locally coupled with a fast radial basis function (RBF)‐based mapping approach. The hierarchically organized overset grid allows transferring the grid resolution for multiple blocks and overlapping/embedding the meshes. The RBF‐based mapping approach is particularly highlighted in this paper in view of its considerable computational efficiency compared with conventional RBF evaluation. The performance of the proposed dynamic mesh strategy is demonstrated by three typical unsteady cases, including a rotating rectangular block in a fixed domain, a relative movement between self‐propelled fishes and the X‐wing type flapping‐wing micro air vehicle DelFly, which displays the clap‐and‐fling wing‐interaction phenomenon on both sides of the fuselage. Results show that the proposed method can be applied to the simulation of flapping wings with satisfactory efficiency and robustness. Copyright © 2016 John Wiley & Sons, Ltd.     

可伸缩机翼结构设计与振动实验研究

对一种可伸缩机翼实验装置进行结构设计、功能实现和振动实验进行研究利用三维建模软件优化设计了可伸缩机翼的作动机构,完成对可伸缩机翼结构的总体设计和各个子系统结构设计,基于可伸缩机翼实验装置进行了振动实验研究,详细分析了在不同的外伸速度和收缩速度情况下,可伸缩机翼的横向振动响应,得到有意义的实验结果,对工程应用具有一定的理...