Role of wing morphing in thrust generation

In this paper, we investigate the role of morphing on flight dynamics of two birds by simulating the flow over rigid and morphing wings that have the characteristics of two different birds, namely the Giant Petrel and Dove Prion. The simulation of a flapping rigid wing shows that the root of the wing should be placed at a specific angle of attack in order to generate enough lift to balance the weight of the bird. However, in this case the generated thrust is either very small, or even negative, depending on the wing shape. Further, results show that morphing of the wing enables a significant increase in the thrust and propulsive efficiency. This indicates that the birds actually utilize some sort of active wing twisting and bending to produce enough thrust. This study should facilitate better guidance for the design of flapping air vehicles.

Quantitative analysis of the morphing wing mechanism of raptors:Morphing kinematics of Falco peregrinus wing

Raptors are getting more attention from researchers because of their excellent flight abilities.And the excellent wing morphing ability is critical for raptors to achieve high maneuvering flight,which can be a good bionic inspiration for unmanned aerial vehicles(UAV)design.However,morphing wing motions of Falco peregrinus with multi postures cannot be consulted since such a motion database was nonexistent.This study aimed to provide data reference for future research in wing morphing kinetics.We used the computed tomography(CT)approach to obtain nine critical postures of the Falco peregrinus wing skeleton,followed with motion analysis of each joint and bone.Based on the obtained motion database,a six-bar kinematic model was proposed to regenerate wing motions with a high fidelity.

Piezoelectric energy harvesting from morphing wing motions for micro air vehicles

Wing flapping and morphing can be very beneficial to managing the weight of micro air vehicles through coupling the aerodynamic forces with stability and control. In this letter, harvesting energy from the wing morphing is studied to power cameras, sensors, or communication devices of micro air vehicles and to aid in the management of their power. The aerodynamic loads on flapping wings are simulated using a three-dimensional unsteady vortex lattice method. Active wing shape morphing is considered to enhance the performance of the flapping motion. A gradient-based optimization algorithm is used to pinpoint the optimal kinematics maximizing the propellent efficiency. To benefit from the wing deformation, we place piezoelectric layers near the wing roots. Gauss law is used to estimate the electrical harvested power. We demonstrate that enough power can be generated to operate a camera. Numerical analysis shows the feasibility of exploiting wing morphing to harvest energy and improving the design and performance of micro air vehicles.

Hierarchical Honeycomb-Structured Electret/Triboelectric Nanogenerator for Biomechanical and Morphing Wing Energy Harvesting

Flexible,compact,lightweight and sustainable power sources are indispensable for modern wearable and personal electronics and small-unmanned aerial vehicles(UAVs).Hierarchical honeycomb has the unique merits of compact mesostructures,excellent energy absorption properties and considerable weight to strength ratios.Herein,a honeycomb-inspired triboelectric nanogenerator(h-TENG)is proposed for biomechanical and UAV morphing wing energy harvesting based on contact triboelectrification wavy surface of cellular honeycomb structure.The wavy surface comprises a multilayered thin film structure(combining polyethylene terephthalate,silver nanowires and fluorinated ethylene propylene)fabricated through high-temperature thermoplastic molding and wafer-level bonding process.With superior synchronization of large amounts of energy generation units with honeycomb cells,the manufactured h-TENG prototype produces the maximum instantaneous open-circuit voltage,short-circuit current and output power of 1207 V,68.5μA and 12.4 mW,respectively,corresponding to a remarkable peak power density of 0.275 mW cm^(−3)(or 2.48 mW g^(−1))under hand pressing excitations.Attributed to the excellent elastic property of self-rebounding honeycomb structure,the flexible and transparent h-TENG can be easily pressed,bent and integrated into shoes for real-time insole plantar pressure mapping.The lightweight and compact h-TENG is further installed into a morphing wing of small UAVs for efficiently converting the flapping energy of ailerons into electricity for the first time.This research demonstrates this new conceptualizing single h-TENG device’s versatility and viability for broad-range real-world application scenarios.

Tensile Deformation Properties of Corrugated Style Fiber Reinforced Composite Skin for a Morphing Wing

A type of skin structure which is made by a Circular Arc Corrugated Style Fiber Reinforced Composite （CACSFRC） is proposed to meet the requirements of the large and continuous deformation and high load capacity of a morphing wing skin. A mechanical model is developed to predict the tensile deformation properties and equiva- lent elastic modulus of the composite skin. Corrugated and plane skin samples are manufactured and tested. The theoretical analysis and tension tests show that CCSFRC skin has markedly much more tensile deforming capability than plane skin in the range of elasticity. The quantity of tensile deformation is in direct proportion to the number of ripples, and in inverse proportion to the cubic of ratio thickness, while the equivalent elastic modulus is in direct proportion to the cubic of ratio thickness approximately. Experiments prove that the predicted theoretical models are reliable and effective.

Constrained cooperative control design for distributed morphing wing systems

An efficient design method is proposed for the cooperative control problem of morphing wing systems with distributed structures and bounded control inputs. The multi-agent model of the distributed morphing wing system is established. The cooperative controllers with saturation constraints are presented. By introducing the concepts in consensus algorithms, the cooperative information links in the controllers are described by graphs, and the corresponding Laplacian matrix is defined. The design conditions of the cooperative controllers are proposed, in the form of linear matrix inequalities. For the case of undirected information links, the controller design conditions are simplified as algebraic inequalities, which highly reduce the computation cost. The designed controllers are implemented on a distributed morphing wing platform, and experiments are carried out. Simulation and experiment results show that the controllers can make all the actuating units in the morphing wing system cooperatively achieve the desired positions, which demonstrates the effectiveness of the proposed theory.

Modeling and Experiment of a Morphing Wing Integrated with a Trailing Edge Control Actuation System

Morphing wing has attracted many research attention and effort in aircraft technology development because of its advantage in lift to draft ratio and flight performance.Morphing wing technology combines the lift and control surfaces into a seamless wing and integrates the primary structure together with the internal control system.It makes use of the wing aeroelastic deformation induced by the control surface to gain direct force control through desirable redistribution of aerodynamic forces.However some unknown mechanical parameters of the control system and complexity of the integrated structure become a main challenge for dynamic modeling of morphing wing.To solve the problem,a method of test data based modal sensitivity analysis is presented to improve the morphing wing FE model by evaluating the unknown parameters and identifying the modeling boundary conditions.An innovative seamless morphing wing with the structure integrated with a flexible trailing edge control system is presented for the investigation.An experimental model of actuation system driven by a servo motor for the morphing wing is designed and established.By performing a vibration test and the proposed modal sensitivity analysis,the unknown torsional stiffness of the servo motor and the boundary condition of the actuation mechanism model is identified and evaluated.Comparing with the test data,the average error of the first four modal frequency of the improved FE model is reduced significantly to less than 4%.To further investigate the morphing wing modeling,a wing box and then a whole morphing wing model including the skin and integrated with the trailing edge actuation system are established and tested.By using the proposed method,the FE model is improved by relaxing the constraint between the skin and actuation mechanism.The results show that the average error of the first three modal frequency of the improved FE model is reduced to less than 6%.The research results demonstrate that the presented seamless morphing wing integrated with a flexible trailing edge control surface can improve aerodynamic characteristics.By using the test data based modal sensitivity analysis method,the unknown parameter and boundary condition of the actuation model can be determined to improve the FE model.The problem in dynamic modeling of high accuracy for a morphing wing can be solved in an effective manner.

Trajectory Optimization Design for Morphing Wing Missile

This paper presents a new particle swarm optimization( PSO) algorithm to optimize the trajectory of morphing-wing missile so as to achieve the enlargement of the maximum range. Equations of motion for the twodimensional dynamics are derived by treating the missile as an ideal controllable mass point. An investigation of aerodynamic characteristics of morphing-wing missile with varying geometries is performed. After deducing the optimizing trajectory model for maximizing range,a type of discrete method is put forward for taking optimization control problem into nonlinear dynamic programming problem. The optimal trajectory is solved by using PSO algorithm and penalty function method. The simulation results suggest that morphing-wing missile has the larger range than the fixed-shape missile when launched at supersonic speed,while morphing-wing missile has no obvious range increment than the fixed-shape missile at subsonic speed.

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。

折叠翼飞行器气动弹性变体飞行仿真平台

折叠翼飞行器的变体过程伴随质量分布、刚度分布及气动载荷分布的大幅动态变化,是一个高度复杂的动力学过程。为实现该过程各种动力学问题的有效分析,基于共享内存技术开发了一套高性能的耦合计算程序,并在此基础上整合了Adams多体动力学计算软件、非定常气动力计算程序及飞行控制技术,搭建了折叠翼的气动弹性变体飞行仿真平台。基于该平台,对折叠翼进行了气动弹性分析和飞行变体过程仿真,验证了平台强大的计算和分析能力。

鱼骨柔性翼等效结构建模及其气动弹性特性分析

鱼骨柔性翼(Fish bone active camber,FishBAC)是一种依靠结构变形实现机翼弯度变化的结构形式,相较于传统的离散式控制面和增升装置,可以在实现机翼弯度变化的同时保持气动表面的连续与光滑。然而,其依靠结构弹性变形实现机翼变弯度的基本特征可能引发潜在气动弹性问题。针对柔性翼潜在的气动弹性问题,本文从结构特性和气动弹性特性两方面进行了研究。在结构特性方面,基于欧拉梁理论和逐段刚化法建立等效结构模型,经有限元验证发现简化模型在计算非均质梁结构保持精度的同时提高了计算效率。在气动弹性特性分析方面,基于等效刚柔耦合翼型模型和非定常气动理论完成了气动弹性特性分析。结果表明,FishBAC建模时需考虑结构柔性,忽略结构柔性会对气动弹性特性的预测存在一定偏差。在驱动力矩低于1.5 N·m时,本文简化的等效结构模型可较好地预测考虑静气动弹性特性的机翼结构形变。使用本文提出的翼型模型考虑结构存在刚柔耦合特性,并预测柔性段所发生的弯度颤振,简化模型与MSC Nastran相比在颤振速度预测上保持了一致性。

可变厚度机翼气动特性优化方法

为了使飞行器在不同飞行状态下均保持良好气动特性,提出了一种可变厚度机翼气动特性优化方法.首先,以NACA0012为设计翼型,采用CST方法将翼型参数化,利用Isight集成XFoil对目标翼型优化,得到优化后翼型参数并进行气动特性分析;其次,基于优化结果,利用Fluent对翼型气动特性进行分析,得到翼型变截面厚度变化前后表面压力分布情况.结果表明,对于NACA0012翼型,在飞行马赫数为0.3、迎角为10°时,变形优化后可以使升阻比提高13.06%.

高超声速变体飞行器关键技术研究综述

高超声速变体飞行器有潜力通过变形提升飞行器在宽速域、大空域飞行全包线下的适用性,在未来的民用与军事领域都具有极大的战略意义。本文主要对高超声速变体飞行器的研究进展进行综述,阐述了国内外高超声速和变体飞行器项目的研究进展和现状,并且对现有的高超声速变体飞行器的主要变形方式进行了分类与介绍。同时,总结了高超声速变体飞行器在变构型机构设计方法与理论、高功重比与快速响应的驱动设计、可承载大变形蒙皮、承载/热防护一体化结构设计等方面的技术难点,提出了高超声速变体飞行器的后续研究发展方向,以期对后续高超声速变体飞行器的相关研究提供一定的参考。

基于多峰分布的大尺度变形翼机构时变可靠性分析

针对机构可靠性的工程问题,提出了一种基于多峰分布的时变可靠性分析方法(iTRPD),并应用于大尺度变形翼机构的可靠性分析。首先,将变形翼结构模型离散为几个瞬时功能函数,并将其转换为独立正态变量。然后,计算出不同时刻的瞬间可靠度与各向量间的自相关系数矩阵,得到对应的概率密度函数。最后,根据协方差特性与各向量间的相关性,利用1次高维高斯积分将独立标准正态空间的时变可靠度简化为大尺度变形翼机构整体的时变可靠度。结果表明:iTRPD在分析大尺度变形翼时变可靠性时,与蒙特卡洛仿真法(MCS)的相对误差仅为-2.842%,比常规方法TRPD好;对功能函数调用次数为415,远小于MCS的1×10^(9)次;对高维高斯积分的调用,常规时变可靠性方法为35次,iTRPD仅为1次。可见,iTRPD对涉及多模态分布的时变可靠性分析具有较高的计算精度和计算效率。

高超声速变体飞行器宽速域气动特性研究

宽速域飞行是高超声速飞行器的重要设计目标和发展方向。然而,复杂的环境变化给固定外形飞行器在不同飞行条件下的气动布局设计带来了矛盾。高超声速变体飞行器可以通过呈现不同的构型来适应各种飞行条件并满足性能要求。本文通过数值模拟的方法来研究折叠翼高超声速飞行器的气动性能。研究重点是在不同飞行高度和马赫数下,探究不同机翼折叠状态对应气动布局的升阻比、纵向静稳定性和航向静稳定性。比较了不同机翼折叠角度(0°、45°、90°)对气动性能的影响。结果表明,在所研究的整个速度范围内(Ma=0~5),较小的机翼折叠角会导致较高的升力系数、阻力系数和升阻比。机翼折叠角为0°时,升阻比最高。在纵向稳定性方面,折叠角度较小的布局具有更好的纵向稳定性。随着马赫数的增加,不同折叠角度之间的纵向稳定性差异最初减小,然后增大。静态稳定裕度从1∶0.95∶0.84变为1∶0.98∶0.88,后变为1∶0.89∶0.79。此外,具有较大机翼折叠角的构型表现出更好的航向稳定性。所有3种机翼折叠布局状态在低速飞行阶段都是航向静稳定的。随着马赫数的增加,0°和45°折叠角逐渐变得航向静不稳定。

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.

变形翼无人机纵向动力学建模及飞行力学特性分析

文章建立了变形翼无人机(Morphing Wing UAV, MWUAV)的纵向动力学模型并在此基础上对其飞行力学特性进行了简要分析。首先,针对MWUAV的参数变化特点,建立纵向非线性参数变化(Nonlinear Parameter-Vayring, NPV)模型;其次,分析了参数变化对其静态特性的影响,包括升阻特性、转动惯量特性以及飞行包线的影响;最后,在建立模型和静态特性分析的基础上,在其飞行包线内选择典型分析点,进行了配平和线性化分析,得出了其配平量随参数变化的关系,并计算了其纵向长短周期模态特性。建模和分析结果可以为MWUAV的飞行状态设计以及控制器设计提供设计依据。

形状记忆合金力学性能及在变体结构中的应用研究

形状记忆合金(Shape Memory Alloys,SMA)由于其特有的形状记忆效应(Shape Memory Effect,SME)被大量研究和广泛应用。基于SMA的Müller-Achenbach-Seelecke模型进行了单根SMA丝的回复力数值计算验证,并设计了一种SMA丝驱动器应用于机翼变后掠角结构中,完成了机翼连续后掠偏转的原理、方案和具体的结构设计,并加工制备了后掠机翼模型;同时为了实现机翼后掠角变化的精确控制,采用PID控制方法设计了SMA温度与偏转角度双路信号反馈的闭环控制系统,完成了对机翼偏转的控制。实验结果表明,机翼可实现45°的偏转,偏转至设定角度后的平均稳态误差控制在±0.3°以内,实现了对偏转角度的精确控制。

跨域翼身融合变体飞行器结构/机构一体化设计

将变体设计与翼身融合飞行器结合,是提升其飞行性能、实现跨域飞行的有效途径。如何协调飞行器结构变形、力学承载和轻量化的关系至关重要。首先分析了翼身融合飞行器在典型变形状态下的气动特性,指出兼顾展向和弦向的机翼构型变化可有效扩展飞行包线、调整静稳定度,并给出典型飞行阶段中飞行器变形状态。其次为实现飞行器双向组合变形,提出了分布式异构连杆机构设计方案。再次为解决飞行器变形和承载之间的矛盾,根据各变形状态下气动载荷特点,提出了分布式变拓扑承载梁设计方案,实现兼顾轻量化的飞行器变形/承载一体化设计。最后在仿真分析的基础上,完成变形驱动方案样件加工,并对其变形能力进行试验验证。结果表明,跨域翼身融合变体飞行器可改变其形状以适应多种载荷条件,实现大空域、宽速域的敏捷飞行。

基于Bouc-Wen前馈及模糊PID反馈的三层MFC-PBP并联变形翼大位移控制

三层预压缩压电宏纤维复合材料双晶片(MFC-PBP)并联变形翼存在较强的迟滞非线性,严重影响变形控制精度。为了实现对其的精确变形控制,本文提出了以Bouc-Wen逆模型为前馈补偿,以模糊PID作为反馈控制器的三层MFC-PBP并联变形翼的大位移跟踪控制策略。首先,利用遗传算法对Bouc-Wen模型进行参数识别,构建前馈模型并对变形翼进行开环控制;其次,加入模糊PID反馈控制器,得到可以自适应改变PID参数的闭环控制。变形跟踪控制试验结果表明,BoucWen前馈控制的相对误差(RE)约为13.5%,将Bouc-Wen前馈模型与模糊PID结合后控制的相对误差在4%以内,提高了变形控制精度。