Analysis and Flexible Structural Modeling for Oscillating Wing Utilizing Aeroelasticity

Making use of modal characteristics of the natural vibration of flexible structure to design the oscillating wing aircraft is proposed. A series of equations concerning the oscillating wing of flexible structures are derived. The kinetic equation for aerodynamic force coupled with elastic movement is set up, and relevant formulae are derived. The unsteady aerodynamic one in that formulae is revised. The design principle, design process and range of application of such oscillating wing analytical method are elaborated. A flexible structural oscillating wing model is set up, and relevant time response analysis and frequency response analysis are conducted. The analytical results indicate that adopting the new-type driving way for the oscillating wing will not have flutter problems and will be able to produce propulsive force. Furthermore, it will consume much less power than the fixed wing for generating the same lift.

Computational aerodynamics of low Reynolds number plunging,pitching and flexible wings for MAV applications

Micro air vehicles （MAV＇s） have the potential to revolutionize our sensing and information gathering capabilities in environmental monitoring and homeland security areas. Due to the MAV＇s＇ small size, flight regime, and modes of operation, significant scientific advancement will be needed to create this revolutionary capability. Aerodynamics, structural dynamics, and flight dynamics of natural flyers intersects with some of the richest problems in MAV＇s, inclu- ding massively unsteady three-dimensional separation, transition in boundary layers and shear layers, vortical flows and bluff body flows, unsteady flight environment, aeroelasticity, and nonlinear and adaptive control are just a few examples. A challenge is that the scaling of both fluid dynamics and structural dynamics between smaller natural flyer and practical flying hardware/lab experiment （larger dimension） is fundamentally difficult. In this paper, we offer an overview of the challenges and issues, along with sample results illustrating some of the efforts made from a computational modeling angle.

A simulation-based study on longitudinal gust response of flexible flapping wings

Winged animals such as insects are capable of flying and surviving in an unsteady and unpredictable aerial environment.They generate and control aerodynamic forces by flapping their flexible wings.While the dynamic shape changes of their flapping wings are known to enhance the efficiency of their flight,they can also affect the stability of a flapping wing flyer under unpredictable disturbances by responding to the sudden changes of aerodynamic forces on the wing.In order to test the hypothesis,the gust response of flexible flapping wings is investigated numerically with a specific focus on the passive maintenance of aerodynamic forces by the wing flexibility.The computational model is based on a dynamic flight simulator that can incorporate the realistic morphology,the kinematics,the structural dynamics,the aerodynamics and the fluid-structure interactions of a hovering hawkmoth.The longitudinal gusts are imposed against the tethered model of a hovering hawkmoth with flexible flapping wings.It is found that the aerodynamic forces on the flapping wings are affected by the gust,because of the increase or decrease in relative wingtip velocity or kinematic angle of attack.The passive shape change of flexible wings can,however,reduce the changes in the magnitude and direction of aerodynamic forces by the gusts from various directions,except for the downward gust.Such adaptive response of the flexible structure to stabilise the attitude can be classified into the mechanical feedback,which works passively with minimal delay,and is of great importance to the design of bio-inspired flapping wings for micro-air vehicles.

In-flight deformation measurement for high-aspect-ratio wing based on 3D speckle correlation

In order to get an effective solution of the in-flight wing deformation measurement for high-wing aircrafts with high-aspect-ratio,a method based on three-dimensional(3D)speckle correlation technique is proposed.Firstly,an in-flight wing deformation measurement system with two sets of conjugate cameras is designed based on structural characteristics and test requirements of high-wing aircrafts with large-aspect-ratio.Secondly,the in-flight wing deformation measurement method based on 3D speckle correlation technique is introduced including three aspects:measuring system and wing datum calibration,speckle image matching and 3D reconstruction,and wing deformation analysis.Fi-nally,ground simulation test of dynamic deformation measurement of a scaled model wing and flight test of dynamic deformation measurement of a large transport wing are carried out.The test results show that the measuring accuracy of single point coordinate in ground simulation test is better than 0.1 mm/m,in the airborne vibration environment,the static single-point positioning accuracy is bet-ter than 5 mm,and the in-flight wing deformation measurement data is well received by the flight test engineers.This method can satisfy the requirements of stability,reliability,high precision,non-con-tact and full-field measurement for dynamic deformation measurement of aircraft wing with high-as-pect-ratio.

Propulsion Performance of Spanwise Flexible Wing Using Unsteady Panel Method

In this paper, the propulsion performance of a spanwise flexible oscillating wing, which is broadly similar to the undulation of a fin fluke, is investigated. The geometry of the fluke underwent three prescribed harmonic oscillating motions simultaneously while surging with constant velocity. The effect of deflection phase angle, flexibility parameter, and wing tip deflection amplitude on thrust coefficient and swimming efficiency was studied. A low-order unsteady panel method coupled with a time stepping algorithm for free wake alignment is implemented in a computer program to estimate the propulsion efficiency of lifting bodies. A novel approach is introduced to evaluate the singular integrals of line vortices by using an adaptive mollifier function. This method is an efficient way to accelerate computational speed by reducing the order of problem from R^3 to body boundaries. Results present the significant effect of phase angle on the propulsion characteristics of oscillating fluke.

Gust response of an elasto-flexible morphing wing using fluid–structure interaction simulations

Small and micro unmanned aircraft are the focus of scientific interest due to their wide range of applications.They often operate in a highly unstable flight environment where the application of new morphing wing technologies offers the opportunity to improve flight characteristics.The investigated concept comprises port and starboard adjustable wings,and an adaptive elastoflexible membrane serves as the lifting surface.The focus is on the benefits of the deforming membrane during the impact of a one-minus-cosine type gust.At a low Reynolds number of Re=264000,the morphing wing model is investigated numerically by unsteady fluid-structure interaction simulations.First,the numerical results are validated by experimental data from force and moment,flow field,and deformation measurements.Second,with the rigid wing as the baseline,the flexible case is investigated,focusing on the advantages of the elastic membrane.For all configurations studied,the maximum amplitude of the lift coefficient under gust load shows good agreement between the experimental and numerical results.During the decay of the gust,they differ more the higher the aspect ratio of the wing.When considering the flow field,the main differences are due to the separation behavior on the upper side of the wing.The flow reattaches earlier in the experiments than in the simulations,which explains the higher lift values observed in the former.Only at one intermediate configuration does the lift amplitude of the rigid configuration exceeds that of the flexible by about 12%,with the elastic membrane resulting in a smaller and more uniform peak load,which is also evident in the wing loading and hence in the root bending moment.

An efficient stiffness analysis model based on shear deformation theory for flexible skin shear variable-sweep wing

Fixed-wing aircraft cannot maintain optimal aerodynamic performance at different flight speeds.As a type of morphing aircraft,the shear variable-sweep wing(SVSW)can dramatically improve its aerodynamic performance by altering its shape to adapt to various flight conditions.In order to achieve smooth continuous shear deformation,SVSW’s skin adopts a flexible composite skin design instead of traditional aluminum alloy materials.However,this also brings about the non-linear difficulty in stiffness modeling and calculation.In this research,a new SVSW design and efficient stiffness modeling method are proposed.Based on shear deformation theory,the flexible composite skin is equivalently modeled as diagonally arranged nonlinear springs,simulating the elastic force interaction between the skin and the mechanism.By shear loading tests of flexible composite skin,the accuracy of this flexible composite skin modeling method is verified.The SVSW stiffness model was established,and its accuracy was verified through static loading tests.The effects of root connection,sweep angles,and flexible composite skin on the SVSW stiffness are analyzed.Finally,considering three typical flight conditions of SVSW:low-speed flow(Ma=0.3,Re=5.8210^(6)),transonic flow(Ma=0.9,Re=3.4410^(6)),and supersonic flow(Ma=3,Re=7.5110^(6)),the stiffness characteristics of SVSW under flight conditions were evaluated.The calculated results guide the application of SVSW.

Aeroelastic Analysis and Optimization of High-aspect-ratio Composite Forward-swept Wings

In order to analyze the effects of forward-swept angle and skin ply-orientation on the static and dynamic aeroelastic characteristics, the aeroelastic modeling and calculation for high-aspect-ratio composite wings with different forward-swept angles and skin ply-orientation are performed. This paper presents the results of a design study aiming to optimize wings with typical forward-swept angles and skin ply-orientation in an aeroelastic way by using the genetic/sensitivity-based hybrid algorithm. Under the conditions of satiated multiple constraints including strength, displacements, divergence speeds and flutter speeds, the studies are carried out in a bid to minimize the structural weight of a wing with the lay-up thicknesses of wing components as design variabies. In addition, the effects of the power of spanwise variation function of lay-up thicknesses of skins and iugs on the optimized weights are also analyzed.

Structural Modeling and Aeroelastic Analysis of High-Aspect-Ratio Composite Wings

A unified structural model for high-aspect-ratio composite wing with arbitrary cross-section is developed. Two types of lay-ups of the composite wing, namely, circumferentially uniform stiffness （CUS） configuration and circumferentially asymmetric stiffness （CAS） configuration, are investigated. The present structural modeling method is validated through ANSYS FEM software for the case of a composite box beam. Then, the case of a single-cell composite wing with NACA0012 airfoil shape is considered. To investigate the aeroelastic problem of high-aspect-ratio composite wings, the linear ONERA aerodynamic model is used to model the unsteady aerodynamic loads under the case of small angle of attack. Finally, flutter speeds of the high-aspect-ratio wing with various composite ply angles are determined by using U-g method.

Stall Flutter Analysis of High-Aspect-Ratio Composite Wing

The stall flutter characters of high-aspect-ratio composite wing are investigated, and the effects of structure geometric nonlinearity and stiffness couple created by composite anisotropy on them also are discussed. Firstly, the high-aspect-ratio wing is modeled as a composite thin-walled closed section Euler beam whose displacement and rotation both could be of finite value, and the nonlinear dynamic equations is build up on it with all the effects of geometric nonlinearity, aerodynamic nonlinearity and anisotropy of material being considered. Then vibration equations are deduced through perturbing the dynamic equations at wing＇s equilibrium position, and coupled with unsteady stall aerodynamic model and ONERA model, to obtain the nonlinear stall flutter analysis equations of wing. Finally, the flutter stabilities with various wind speeds are determined by the harmonic balance method. With several exampies, the validity of the stall flutter model is proved, and the significant effects of geometric nonlinearity on the stall flutter various characters as wall as the effects of ply angle on the stall flutter speed and frequency also are discussed.

Stiffness Distribution and Aeroelastic Performance Optimization of High-Aspect-Ratio Wings

The relationship between stiffness distribution and aeroelastic performance for a beam-frame model and a3-D model is investigated based on aeroelastic optimization of global stiffness design for high-aspect-ratio wings.The sensitivity information of wing spanwise stiffness distribution with respect to the twist angle at wing tip,the vertical displacement at wing tip,and the flutter speed are obtained using a sensitivity method for both models.Then the relationship between stiffness distribution and aeroelastic performance is summarized to guide the design procedure.By using the genetic/sensitivity-based hybrid algorithm,an optimal solution satisfying the strength,aeroelastic and manufacturing constraints is obtained.It is found that the summarized guidance is well consistent with the optimal solution,thus providing a valuable design advice with efficiency.The study also shows that the aeroelastic-optimization-based global stiffness design procedure can obtain the optimal solution under multiple constraints with high efficiency and precision,thereby having a strong application value in engineering.

柔翼结构飞行器智能控制系统关键技术与途径

柔翼结构飞行器具有轻质、空间集成、重复使用、有较大的阻力面积和升力系数等优点,可实现巡航飞行、低速驻空、再入返回、气动减速、定点归航、着陆缓冲等功能,是当前的研究热点。智能控制系统是柔翼结构飞行器飞航与回收着陆系统的核心技术之一,结合智能技术在控制系统中的应用研究与工程实践,对柔翼结构飞行器智能控制系统及其技术特征进行了分析;介绍了刚-柔组合体一体化控制与仿真、环境感知与健康状态在线评估、航迹规划与跟踪飞行控制、集群飞行控制、着陆与缓冲智能控制、智能硬件容错与重构等关键技术。对柔翼结构飞行器智能控制系统的未来发展进行了思考,提出了飞行环境的智能及柔性感知、气动参数的在线识别、多任务模式自主执行及控制系统的演进学习等发展建议,通过对智能控制技术持续不断地研究与实践,为柔翼结构飞行器系统的研制提供强有力的支撑。

基于“指节”驱动刚柔耦合式变弯度机翼后缘结构的设计方法

利用刚性机构驱动的变形翼,蒙皮易出现不光滑变形的现象,而用柔顺机构设计的变形翼,虽蒙皮曲线光滑,飞机的稳定性和机动性增强,但难以满足变形与承载双重优化。为此,基于“指节”驱动式仿生刚柔耦合的设计思想,本文设计了一种瓦特I型六杆驱动的变弯度机翼后缘三“指节”刚性机构,并建立了可承受气动载荷和光滑变形的柔顺机构拓扑优化方法。先设计了一种由单电机驱动的瓦特I型六杆操控机构,再改进了“指节”式驱动下变形翼后缘的变密度拓扑优化方法,后求解并给出了一种具有三“指节”式杆驱动特点的变弯度后缘柔顺驱动机构,最后对优化模型进行了刚柔体动力学、空气动力学以及流固耦合仿真,并搭建了试验平台和样机模型,对柔性变形翼的可行性及其设计方法有效性进行论证,结果表明该机翼可以光滑、连续地大变形,同时又具有较强的承载能力。

Fluid-structure interaction simulation for multi-body flexible morphing structures

The multi-body flexible morphing airfoil can improve the aerodynamic characteristics based on different flight missions continuously.Recently researches have focused on the unsteady aerodynamic characteristics of flexible wings under passive actuation.However,the unsteady aerodynamic characteristics with the fluid-structure interaction effects in the multi-body active actuation process of morphing airfoil deserve further investigation.In this paper,a fluid-structure coupled simulation method for multi-body flexible morphing airfoil with active actuation subsystem was investigated,and the aerodynamic characteristics during deformation were compared with different skin flexibility,flow field environment,actuation mode and actuation time.The numerical results show that for the steady aerodynamic,the skin flexibility can improve the stability efficiency.In the unsteady process,the change trend of the transient lift coefficient and pitching moment are consistent with those of the active drive characteristics,while the instantaneous lift-drag ratio coefficient is greatly affected by the driving mode and can be improved by increasing the driving duration.

带有非均质刚柔耦合翼的无人机边界控制

随着无人机技术的快速发展及工程应用需求的不断增长,具有隐蔽性好、快速灵活及经济性能好等许多优点的扑翼无人机在国民经济生活中发挥着越来越重要的作用.然而,受无人机使用环境限制及自身快速机动运行的特点,扑翼无人机的机翼通常存在连续高频振动,这些不理想的振动会影响系统的稳定性及无人机使用寿命.因此,本文研究带有刚柔耦合翼的扑翼无人机的振动抑制及姿态控制问题.首先,考虑外部干扰对扑翼无人机系统的影响,运用哈密顿原理,将由均质刚性连杆链接非均质柔性连杆组成的扑翼系统建模为无穷维分布参数系统.随后,基于反步法,设计两个边界控制律来镇定系统.运用鲁棒控制策略,构建辅助输入信号及干扰自适应律来抵消外部干扰的影响.通过在无人机本体及刚柔耦合翼的链接处布置传感器及执行器来抵消柔性翼的振动并调节刚性翼及柔性翼的姿态至期望角位置.其后,运用李雅普诺夫稳定性理论严格证明了闭环系统的一致有界稳定性.最后,开展数值仿真实验来证明所设计控制方案的可行性及控制效果.

不同折叠角下含间隙折叠机翼极限环振荡分析

折叠机翼作为变体飞行器的重要变体机构之一,其气动弹性响应规律研究为变体飞行器稳定性及操纵性的提升奠定基础。本文提出基于干风洞的含间隙折叠机翼地面颤振虚拟试验模型建模方法,其中折叠机翼翼面子结构采用Craig-Bampton方法建立其刚柔耦合降阶模型,子结构连接采用线性/非线性弹簧连接,气动力采用偶极子格网法获得并转化为激振器集中力,由于地面颤振试验中气动力建模需基于统一的模态振型,针对含间隙折叠机翼采用虚拟质量法获得统一坐标下的虚拟模态振型。仿真结果表明,基于Craig-Bampton方法建立的线性折叠机翼地面颤振虚拟试验模型预测颤振速度与商用软件相比误差低于2%。当模型中采用非线性弹簧连接时,折叠机翼在低于和高于线性颤振速度下均会形成极限环振荡,仿真表明由于间隙非线性的影响,极限环的临界速度比线性颤振降低。研究发现折叠角0°下间隙大小对极限环幅值具有显著影响,而折叠角30°下间隙大小则对极限环幅值几乎不产生影响。

仿生折叠翼扑动过程气动特性分析

以甲虫后翅为仿生对象,基于四板机构理论设计了一种仿甲虫四板折叠翼,并对其气动特性进行研究。建立了仿甲虫四板折叠翼动力学仿真模型,采用双向流固耦合数值模拟方法,分析了扑动幅值、拍动频率与前飞速度对柔性折叠翼的升阻力系数和空气流场的影响,并对柔性折叠翼扑动过程进行了流场研究。研究表明,柔性折叠翼能提高飞行器的升力特性和推力特性,其扑动幅值为80°,频率为50Hz时,折叠翼的气动特性最为显著。本研究工作为优化折叠翼的设计及控制奠定了基础。

空间长方形绳网展开动力学及多参数特性分析

空间绳网系统是一种针对空间碎片的柔性捕获系统,针对带有太阳翼的空间目标,提出一种用于捕获目标主体的长方形绳网。为分析其展开效果,建立有限元模型,通过对比地面试验结果来验证有限元模型的可靠性。建立长方形绳网的评价指标,并通过各项评价指标对比不同牵拉模式、牵引绳分布圆直径及牵引体发射角度下的绳网展开特性。结果表明:仿真结果与试验结果吻合,有限元模型可靠;在八点牵拉、十点牵拉和十二点牵拉3种模式下,十点牵拉所能达到的展开效果最好;牵引绳分布圆直径增大,所能达到的最大展开面积和保形距离减小,展开距离增大;牵引体的发射角度增大,长方形绳网的最大展开面积和保形距离增大,展开距离减小。

基于电磁力的机翼非接触式加载试验平台特性研究

目的研究分析基于电磁力的非接触式翼面加载的可行性与适用特点。方法利用多匝铜线绕制的驱动线圈,通入大电流产生强磁场,柔性线圈贴附于机翼表面,柔性线圈中的电流与强磁场相互作用产生较大的电磁力,实现对翼面的稳定加载。建立电磁力加载仿真计算模型,基于该模型分析不同线圈结构时电磁力特性,并设计力学加载平台,开展试验测试。结果对比了柔性线圈和薄铁片2种电磁力加载方式的不同,柔性线圈产生的电磁力比薄铁片小,但具有更好的线性度和可控性。上下布置2个驱动线圈能产生更大电磁力,但需要使2个驱动线圈电流方向相反,电流方向相反时产生的电磁力比方向相同时增强了16倍。减小驱动线圈间距,使柔性线圈靠近驱动线圈,也能显著提高电磁力。开展了力学加载平台试验,柔性线圈产生的电磁力达到57 N,并可持续加载320 s。结论通过试验验证了提出的基于电磁场非接触式翼面加载的可行性,柔性线圈易贴附于机翼表面,可为复合材料、复杂翼形的力学加载测试提供一定参考。

纤维增强复合材料柔性封堵结构分析与验证

变弯度机翼展向翼端面封堵结构对于提升可变体机翼的变形精度、防止气流分离重要作用。本文针对刚柔耦合变弯度前缘结构,提出了以纤维增强复合材料为壳体,填充弹性基柔性材料的柔性封堵结构设计方案,建立了有限元模型在结构载荷作用下对其力学性能、封堵性能进行分析,制备所设计的柔性封堵结构并对其进行了试验验证。结果表明:(1)柔性封堵结构仿真模拟结果符合实际变形情况,最大应力为412.96 MPa,最大应变为4.15%;沿机翼弦向方向的位移从固定端向前缘逐渐变大,最大位移为6.28 mm;(2)所制备的柔性封堵结构在进行初次压缩试验后,其载荷值随位移的变化近似线性变化,满足变弯度机翼前缘的变形需求。