具有复合材料柔性梁的无轴承旋翼气动弹性稳定性

建立了一种悬停状态下无轴承复合材料旋翼气动弹性稳定性分析的新模型。修正了Bauchau的大变形梁理论建立了无轴承复合材料旋翼桨叶的非线性应变-位移关系,根据复合材料的特点推导了桨叶的本构关系并构造了一个新的24自由度梁单元,桨叶视为多路传力系统,应用Hamilton原理建立了桨叶运动的有限元方程,分析了悬停状态下具有复合材料柔性梁无轴承旋翼气动弹性的稳定性。数值计算结果表明：（1）采用本文模型的无轴承旋翼气动弹性稳定性的计算结果与试验数据的吻合程度比传统的中等变形梁理论更好。（2）具有负变距-摆振耦合的复合材料柔性梁结构提高无轴承旋翼气动弹性的稳定性,正变距-摆振耦合的结构降低旋翼气动弹性的稳定性;负的铺层角比相同大小正的铺层角旋翼的气动弹性稳定性更好;铺层厚度减少有利于增加旋翼气动弹性的稳定性。     

悬停状态带磁流变减摆器直升机的动稳定性分析

建立了适用于直升机悬停状态动稳定性的磁流变减摆器模型,悬停状态下动力入流模型采用动量理论模型,与直升机旋翼/机体耦合动力学方程组联立,采用Simulink时域仿真的方法计算得到磁流变减摆器对悬停状态下直升机动稳定的影响,对比了不同电压下磁流变减摆器对桨叶挥舞摆振运动的影响.结果表明:对于磁流变减摆器,施加不同电压可得到不同的阻尼力,该性质可以抑制直升机悬停状态动不稳定性.     

利用桨叶后缘小翼运动的旋翼桨毂振动载荷优化控制

利用桨叶后缘小翼运动是控制旋翼桨毂振动载荷的一种有效方法。采用非定常气动力和弹性力耦合的气弹分析方法,对附加了桨叶后缘小翼的直升机旋翼系统的振动载荷进行了研究。采用弹性桨叶和后缘刚性小翼的结构动力学模型、翼型剖面气动力采用Leishman-Beddoes二维非定常动态失速模型、后缘小翼剖面气动力采用Hariharan-Leishman非定常气动力模型,建立了带后缘小翼的旋翼桨毂振动载荷分析模型。采用伽辽金和数值积分相结合的方法,求解旋翼系统在前飞状态下的气弹响应。分析了后缘小翼各运动参数对桨毂振动载荷的影响。针对桨毂4阶振动载荷,采用改进的主动控制方法,优化了小翼的运动,使桨毂振动载荷得到显著降低。     

大前进比变转速旋翼气弹动力学建模与载荷特性分析

针对大前进比变转速旋翼气弹动力学问题开展分析研究.基于Hamilton原理以及中等变形梁理论建立旋翼动力学方程,并针对大反流区气动力计算方法和大前进旋翼气弹配平计算方法进行修正,集成考虑大前进比的旋翼气弹计算模型.在旋翼动力学模型的验证基础上,开展大前进比下变转速旋翼气弹动力学计算分析.通过计算桨叶剖面气动和结构载荷表...     

低振动旋翼桨尖代理优化设计

为探索直升机低振动旋翼的工程设计方法,将代理优化与旋翼气弹耦合分析相结合,开展了旋翼桨尖几何外形设计,推导了非平直桨叶气弹动力学方程,训练了旋翼功率、模态阻尼以及振动载荷预测的Kriging代理模型.以气动性能与气弹稳定性为约束,以桨毂振动载荷最小化为目标,采用自适应加点准则设计了优化流程.以某旋翼为例,计算了其气动性...     

采用光纤传感测量的直升机旋翼桨叶分布载荷识别

针对直升机旋翼载荷识别的传统技术具有测量信/噪比低、不易分布式识别等缺点,基于光纤传感测量技术,建立了一种新的旋翼桨叶分布载荷识别方法.首先建立了基于分布测量应变和模态分析的旋翼桨叶分布载荷识别理论,然后进行了悬停状态下模型旋翼桨叶的光纤传感测量,最后应用建立的识别理论,识别出了模型旋翼桨叶沿径向分布的载荷.     

直升机旋翼桨叶鸟撞动态响应计算

基于旋翼综合气弹分析程序,求解出直升机旋翼桨叶在飞行过程中的稳态响应。以此作为鸟体撞击桨叶的初始状态,采用非线性流-固耦合算法,建立了直升机旋翼桨叶鸟撞动力学方程,利用直接数值积分方法求解桨叶的动态响应。并讨论了鸟体速度、质量、撞击位置、桨叶根部约束和离心力等参数对桨叶动态响应的影响,从而为直升机桨叶抗鸟撞设计提供一些理论依据。     

含不同桨尖的无轴承旋翼直升机气动机械稳定性

直升机旋翼桨尖形状可以有效提高旋翼气动性能,但可能会降低旋翼气弹稳定性。这方面的研究包括不同桨尖形状的旋翼气动性能、孤立旋翼气弹稳定性、无铰式旋翼直升机气动机械稳定性。不同桨尖形状的无轴承旋翼直升机的气动机械稳定性研究还未见到报道。研究了含不同桨尖无轴承旋翼直升机的气动机械稳定性,基于哈密顿原理和中等变形梁理论,并通过桨尖形状引起的非线性位移协调条件,建立了含不同桨尖形状的无轴承旋翼/机体耦合系统的气动机械动力学模型。计算的ITR无轴承旋翼直升机地面共振和空中共振的稳定性与实验结果一致,证明了建立的气动机械动力学模型的准确性。计算了桨尖前掠、后掠、上反、下反、尖削和形状组合对无轴承旋翼直升机地面共振和空中共振稳定性的影响,计算结果表明,桨尖形状能有效改变无轴承旋翼直升机的气动机械稳定性。     

大型水平轴风力机叶片二自由度气弹稳定性分析

本文根据Kallesøe大型水平轴风力机叶片模型下的动力学方程对无阻尼系统进行有限差分离散后,运用Greenberg气动理论施加分布气动力,得到不对称刚度和一般粘性阻尼的二自由度气弹方程。通过建立系统的线性定常状态空间方程,利用极点实部最大值对叶片的气弹稳定性进行了解析,得到了风速、转速、弹性模量、桨距角、空气密度和叶片密度的稳定性曲线,最后用系统的阶跃时间响应进行了验证。     

前飞状态下直升机旋翼系统气弹响应及稳定性分析

将铰接式直升机桨叶挥舞、摆振及变矩铰的刚性转角作为广义坐标,采用中等变形梁理论,结合有限元法,在旋转坐标系下,根据Ham ilton 原理推导出桨叶前飞状态下的非线性周期时变动力学方程。使用拟线性化方法及New m ark 数值积分技术求解桨叶的气弹响应。对稳态解进行摄动,应用Floquet理论分析桨叶的气弹稳定性。     

Aeroelastic analysis of bearingless rotors with a composite flexbeam

An aeroelastic analysis of bearingless rotors is investigated using large deflection beam theory in hover and forward flight. The bearingless configuration consists of a single flexbeam with a wrap-around torque tube and pitch links located at the leading edge and trailing edge of the torque tube. The outboard main blade, flexbeam, and torque tube are all assumed as an elastic beam undergoing arbitrary large displacements and rotations, that are discretized into beam finite elements. In the bearingless rotors, a flexbeam has various sections made of laminate. The sectional elastic constants of a composite flexbeam, including the warping deformations, are determined from a refined cross-sectional finite element method. Numerical results of the static deflections and the aeroelastic modal damping are presented for various configurations of a composite flexbeam and are compared with previously published experimental results and theoretical values obtained from a modal analysis using a moderate deflection-type beam theory.     

振荡压气机叶栅叶片表面非定常响应以及气弹稳定性分析

发展并验证了一种适用于叶轮机内部非定常跨音流动诱导的叶片气弹问题的高效、准确的数值模拟方法。采用有限体积的多块结构化网格形式,多重网格方法加速收敛,隐式的双时间步时间推进,Spalart-Allmaras（S-A）湍流模型求解非定常雷诺平均Navier-Stokes方程。通过气动弹性标准算例10,叶片在高亚音和跨音流动下做弯曲振动,分析了流动状态、折合频率以及叶片间相位角对叶片表面非定常气动力响应以及叶栅气弹稳定性的影响。分析结果表明激波在此跨音振荡压气机叶栅中起失稳作用,叶片间相位角对气弹稳定性的影响在高折合频率下被加强。     

Active aeroelastic flutter analysis and vibration control of supersonic composite laminated plate

The active aeroelastic flutter analysis and vibration control at the flutter bounds of the supersonic composite laminated plates with the piezoelectric patches are studied. The piezoelectric patches are bonded on the top and bottom surfaces of the composite laminated plate to act as the sensor and actuator so that the active aeroelastic flutter suppression and vibration control for the supersonic laminated plate can be conducted. The unsteady aerodynamic pressure in supersonic flow is computed by using the supersonic piston theory. Hamilton’s principle with the assumed mode method is used to develop the governing equation of the structural system. The controller is designed by the velocity feedback and proportional feedback control algorithm, and the active damping and stiffness are obtained. The solutions for the complex eigenvalue problem are obtained by using the generalized eigenvalue methodology. The natural frequencies and damping ratios are also gotten. The aeroelastic flutter bounds of the supersonic composite laminated plate are calculated to investigate the characteristics of the aeroelastic flutter. The impulse responses of the structural system are calculated by using the Houbolt numerical algorithm to study the active aeroelastic vibration control. The influences of ply angle of the laminated plate and the control method on the characteristic of flutter and active vibration control are analyzed. From the numerical results it is observed that the aeroelastic flutter characteristics of the supersonic composite laminated plate can be improved and that the aeroelastic vibration response amplitudes can be reduced, especially at the flutter points, by the proportional feedback or the velocity feedback control algorithm using the piezoelectric actuator/sensor pairs. The effectiveness of the flutter control by the two control algorithms is also compared. The results of this study are of great significance to the flutter analysis and aeroelastic design of the aircraft.     

A modal aeroelastic finite element analysis method for advanced turbomachinery stages

This paper presents a formulation suitable for the flutter analysis of rotating bladed assemblies. The blades are modelled using the finite element method. The aeroelastic displacements, expressed in terms of travelling wave co-ordinates, are written as a linear combination of a number of undamped modes leading to a complex eigenvalues eigenvectors problem. The associated unsteady aerodynamic model is either two or three dimensional, leading for both cases to a consistent and flexible aeroelastic analysis method. Three numerical applications are presented which illustrate the theory and emphasize the possible effects of blade cross-section (chord) deformation on aeroelastic damping.     

基于CFD/CSD耦合的颤振与动载荷分析方法

采用CFD/CSD耦合方法,建立了气动弹性仿真系统。基于系统辨识的方法,使用Volterra级数建立了降阶模型(ROM),实现了颤振边界的快速求解,分别使用CFD/CSD全耦合方法与ROM完成了AGARD 445.6标模的颤振分析,计算结果与实验相符较好。使用ROM完成了带边条平直翼的颤振分析。使用CFD/CSD耦合方法计算了此机翼在飞行动压下的气弹响应,结果表明即使在颤振边界内,仍然有可能出现极限环振荡（LCO）。对此,分析了其气弹响应中的动载情况。结果表明基于CFD/CSD耦合的方法可以真实地仿真气弹响应过程,准确地分析气弹响应中的动态载荷情况     

Uncertainties in blade flutter damage prediction under random gust

In the design of highly flexible engineering structures such as rotors of wind turbines, aeroelastic stability is an important issue. A bending-torsion oscillation problem of a model blade section with structural nonlinearity has been considered in the present study. The system is subjected to a horizontal random gust modeled as a stationary process. Uncertainty quantification in highlighting the relative importance of different sources of uncertainty on aeroelastic stability, and consequently the fatigue and failure is an important step of aeroelastic design, which is addressed here. The effect of different sources of uncertainty on the fatigue damage estimate of the structure is highlighted here. Specifically, the effect of the structural parameter, the choice of aeroelastic model (modeling error) and also the stress selection criterion for the damage estimate on the fatigue damage estimate is reported in this work. The structural parameter randomness is modeled through polynomial chaos expansion in analyzing its effect on the damage estimate. The unsteady inviscid flow-field in the aeroelastic model is resolved analytically and also using a higher fidelity vortex lattice algorithm and the relative effect on damage is seen. Finally, the effect of fatigue damage criterion selection is also observed. The damage calculation is done for torsion only, bending only and for multiaxial cases. Multiaxial stresses are converted to an ‘equivalent’ one using a signed von Mises criterion. A linear damage accumulation rule has been used to estimate the risk for fatigue damage.     

Fluid–structure interaction of FRP wind turbine blades under aerodynamic effect

Structural analysis of FRP wind turbine blades must take into account phenomena associated with aerodynamics as well as fluid–structure coupling, because aerodynamic loading causes blades to bend mostly in the flapwise direction, and simultaneously causes foil sections to rotate to create new fluid fields around the foils. This study developed an analytical process for calculating fluid–structure interaction, while considering the effects of aerodynamic pressure and finite element analysis in the design of wind turbine blades. In addition, we calculated turbine power efficiency to evaluate the results of fluid–structure interaction displaying approximately power capacity loss of 17% at a wind speed of 25 m/s, and proposed three feasible improvements to enhance the performance of wind turbines. The presented study provided a comprehensible means by which to interpret changes in the aeroelastic response of blades, and was helpful to modify the original wind turbine model.     

Structural health monitoring based on sensitivity vector fields and attractor morphing

The dynamic responses of a thermo-shielding panel forced by unsteady aerodynamic loads and a classical Duffing oscillator are investigated to detect structural damage. A nonlinear aeroelastic model is obtained for the panel by using third-order piston theory to model the unsteady supersonic flow, which interacts with the panel. To identify damage, we analyse the morphology (deformation and movement) of the attractor of the dynamics of the aeroelastic system and the Duffing oscillator. Damages of various locations, extents and levels are shown to be revealed by the attractor-based analysis. For the panel, the type of damage considered is a local reduction in the bending stiffness. For the Duffing oscillator, variations in the linear and nonlinear stiffnesses and damping are considered as damage. Present studies of such problems are based on linear theories. In contrast, the presented approach using nonlinear dynamics has the potential of enhancing accuracy and sensitivity of detection.     

船用长方体形空气弹簧隔振器刚度特性

长方体形空气弹簧因其结构特点可以通过改变特性参数和工况获得理想的垂向和横向刚度比,从而可以更好地满足工程应用的要求。综合考虑橡胶-帘布复合材料的材料非线性、大变形过程中的几何非线性以及基座刚性板与胶囊柔性体之间的接触非线性,建立长方体形空气弹簧的有限元模型,分别计算并绘制在不同的初始工作气压、气体容积、帘线层数以及帘线角度下空气弹簧的垂向与横向刚度特性曲线,并研究这些因素对其刚度特性的影响。最后,通过试验证明有限元分析结果的可靠性。