A comparison of full non‐linear and reduced order aerodynamic models in control law design using a two‐dimensional aerofoil model

The prediction of the flutter boundary of an aircraft is a necessary but time consuming process, particularly as for the most realistic results a time accurate simulation of the interaction between the non‐linear aerodynamic and structural forces is required. Extension of the flight envelope by the design of active control laws to suppress flutter further increases the demands on computational time, to presently unrealistic levels. Use of a reduced order model (ROM) derived from, and in place of, the full non‐linear aerodynamics greatly reduces the time required for calculation of aerodynamic forces. However, this is necessarily accompanied by some loss in accuracy, and hence the method must be verified by comparison with results obtained by the full aerodynamic model before it may be used with confidence. Such a comparison is presented here, using a two‐dimensional aerofoil and control surface combination as a test case. Active control of the deflectable surface is used to attempt to increase the flutter speed across the complete Mach range, feedback control being achieved by gains acting on heave and pitch proportional and differential signals, interpreted as a hinge moment demand. Full non‐linear and reduced order aerodynamic models are then used to obtain optimum control law gain for flutter suppression. The results demonstrate that the ROM accurately predicts the open loop flutter boundary, gives a good approximation to the increase in flutter speed that may be produced by gain optimization, and produces a similar response given the identical gain values in each system for a significantly reduced cost. Copyright © 2005 John Wiley & Sons, Ltd.     

鸭式布局机翼非线性气动力计算的一种简化方法

本文提出了一种计算鸭式布局机翼非线性气动力的简化方法，通过引入鸭翼的当量集中涡概念，使计算模型得到简化，大幅度地减少了计算量，加快了收敛速度，算例结果表明：本文方法计算结果与实验是吻合的。     

竞技运动服功能性研究进展

随着竞技体育的竞争日益激烈,运动服已成为影响竞技成绩的重要因素.本文从克服运动阻力、提高运动员表现水平、避免运动损伤、改善运动技术这4个方面对竞技体育运动服的研究进展进行综述.     

Nature of pressure waves induced by a high-speed train travelling through a tunnel

The pressure waves generated by a train entering and running through a tunnel are studied experimentally and numerically with the aim of gaining a solid understanding of the flow in the standard tunnel geometry and in the configuration with airshafts along the tunnel surface. Laboratory experiments were conducted in a scaled facility where train models travelled at a maximum velocity of about 150 km/h through a 6-m-long tunnel. The flow was simulated by a one-dimensional numerical code modified to include the effect of the separation bubble forming near the train head. The numerical simulations reproduced well the experimental results. We tested the influence of the train cross-sectional shape and length on the compression wave produced by the vehicle entering the confined area. The cross-sectional shape was not found to be influential as long as the blockage ratio, namely the ratio between the train and tunnel cross-sectional areas, is constant. The pressure waves are one-dimensional sufficiently downwind of the tunnel mouth, which validates the comparison between the experimental and computational results. It is further shown that the numerical code can satisfactorily reproduce the pressure variations for the case with airshaft apertures along the tunnel surface.     

Molecular dynamics-based unstructured grid generation method for aerodynamic applications

A new approach to triangular mesh generation based on the molecular dynamics method is proposed. Mesh nodes are considered as interacting particles. After the node placement by molecular dynamics simulation, well-shaped triangles or tetrahedra can be created after connecting the nodes by Delaunay triangulation or tetrahedrization. Some examples are considered in order to illustrate the method’s ability to generate a mesh for an aircraft with a complicated boundary. Mesh adaptation technology for molecular dynamics simulation is presented.     

横风下桥梁高度对高速列车交会性能的影响

为研究横风下桥梁高度对高速列车会车性能的影响,基于空气动力学和列车系统动力学,分析指数风分布下不同高度桥梁周围的流场,建立高速列车多体系统动力学模型,模拟横风下列车在不同高度桥梁上会车时的表面压力特性和气动载荷特性.将得到的气动力作为外加载荷作用于列车上,分析桥梁高度对高速列车会车安全性能的影响.结果表明:当列车在环境风下交会时,背风侧列车的气动力波动大于迎风侧列车的气动力波动;当监测点风速固定且桥梁高度小于15 m时,随着桥梁高度的增加,列车的气动载荷最大幅值和安全指标最大幅值均有所减小;当桥梁高度为15～30 m时,随着桥梁高度的增加,列车的气动性能和动力学性能基本保持不变.     

高速列车车内低频气动噪声预测

为研究气动载荷下高速列车的车内低频噪声,建立高速列车空气动力学模型,采用大涡模拟(Large Eddy Simulation,LES)法计算中间车的表面脉动压力.将脉动压力加载到高速列车的有限元模型上,通过瞬态分析得到车体的振动位移响应;将位移响应作为边界条件,采用边界元法(Boundary Element Method,BEM)分析车内噪声.结果表明：车窗振动位移最大,车顶和车底次之;中间车车厢的两端声压比中部大;在低频范围内,车厢内声压呈强弱交替分布,声场强弱界限较明显,且随着频率的增大,沿车体纵向和横向干涉条纹增多;车内低频气动噪声随速度二次方的增大而增加.     

带有气动参数不确定性的导弹自动驾驶仪设计

针对一类不确定导弹系统,考虑系统中存在气动参数不确定性,研究其自动驾驶仪的设计问题;由导弹俯仰面的力学模型及气动参数的多项式模型,考虑舵偏角为控制输入建立二阶导弹系统模型,基于自适应控制得到导弹自动驾驶仪的设计方法,使得闭环系统稳定且攻角快速跟踪指令信号;文章充分考虑系统模型攻角通道中存在舵偏项的影响且不需假设导弹攻角为小量,使得系统模型更具有一般性;仿真中马赫数分别取为2.5、1.8、3.0并考虑50%的参数摄动,结果表明文章设计的自动驾驶仪指令跟踪精度高,鲁棒性强。     

微型扑翼飞行器诱导角与几何攻角的研究

基于准稳态模型和动量理论,探讨了微型扑翼飞行器诱导角和最佳几何攻角的计算问题.针对高斯-牛顿法求解诱导角方程时存在的不收敛问题,使用能保证计算过程收敛的列文伯格-马夸尔特算法求解,得到实验样机的诱导角为15°.实验样机的实际升力为40 g,忽略诱导角后准稳态模型理论升力为46 g,而考虑诱导角的理论升力为37 g,验证了计算诱导角可以提高准稳态模型预测升力的准确性.基于实验样机翅膀被动扭转的实际,采用最小二乘法计算出实际最佳几何攻角为55°,能有效指导微型飞行器翅膀的设计,从而提高飞行器最大升力和飞行效率.