带飞行控制系统飞机颤振试飞的结构动响应研究

对带飞行控制系统飞机在颤振飞行试验中的结构动力响应分析进行了研究,建立了采用FES(flight excitation system)系统激励和小火箭激励两种方式的动力学分析模型,在此基础上构建了软件分析平台并对某型带飞行控制系统飞机进行了应用,为该飞机颤振试飞激励方式和参数选取提供了参考依据。最后提出了气动伺服弹性和结构动响应研究下一步的发展方向。     

Modal parameter identification in atmospheric turbulence excitation flutter test based on Hilbert-Huang transform

In flutter tests, particularly in wind tunnel experiments, the aircraft model is generally excited by atmospheric turbulence, which increases the difficulty in precisely identifying the modal parameters. To estimate the modal parameters under turbulence excitation for flutter boundary prediction, a technique was developed and evaluated depending on the Hilbert-Huang transform in this paper. The results of simulated flutter cases show that the developed technique can identify modal frequencies more precisely than the modal damping ratio, while the estimation of the modal damping ratio is quite good. Finally, in a wind tunnel flutter test, good flutter boundaries were predicted in advance by using the modal parameters identified from the turbulence response at low airspeeds.

     

连续变速颤振试验的实时颤振边界预测系统

实时颤振边界预测系统主要用于完成飞机颤振试验过程中对颤振临界速度的预测。该系统基于非平稳信号处理理论设计开发,融合了多种结构阻尼与稳定性分析方法。本文概述了系统的主要结构与工作原理,并应用数值仿真和实际工程试验验证考核了系统的有效性。该系统操作简便、结果可靠、界面友好,可以满足连续变速颤振试验的工程要求。     

ON-LINE MODAL MONITORING OF AIRCRAFT STRUCTURES UNDER UNKNOWN EXCITATION

In this paper, we present the application of recently proposed subspace-based damage detection and isolation algorithms in on-line structural monitoring of an airplane structure under unknown excitation. The first step of the approach is a subspace-based modal analysis of the safe structure, using output-only measurements. The monitoring step consists in the computation of a χ²-variable, which reflects possible deviations of newly collected output-only data w.r.t. the reference (safe) modal behaviour. No re-identification of the possibly damaged structure is required. An on-line version of the detection algorithm is proposed. Monitoring certain critical modes can also be achieved through sensitivity tests. Experimental results for the proposed monitoring algorithms are reported, in the case of the Paris MS760 airplane, on which mass as well as stiffness changes are introduced. Moreover, the results of the output-only subspace-based modal analysis are compared with the modal appropriation method.     

Smoothing of power spectral densities by successive autocorrelation: An application to flight flutter tests

A simple modal parameters mxtraction method (natural frequencies and damping ratios) from response power spectral densities (PSD) due to random excitations is presented. Firstly, the noisy PSD are smoothed using the ‘successive autocorrelation method’. The inverse of the resulting smoothed displacement-PSD is then fitted in the frequency domain using a hysteretically damped sdof receptance model.The validity and efficiency of the method is shown using a small plate. The method is then applied to the delicate flight flutter testing problem.     

An approach to vibration analysis using wavelets in an application of aircraft health monitoring

This paper explores an application of vibration detection in aircraft. Fatigue and breakdown of aircraft structure are common. Thus, efforts are made to constantly improve the monitoring and diagnostic systems for aircraft. These improvements have led to various approaches to fault monitoring in aircraft. In this work, the characteristic features of vibration signals are extracted from noise using the Haar, Daubechies, and Morlet wavelets. Then, detection of the vibration signal is achieved using the signal's scalogram information. Based on initial results, the wavelet-based algorithm is optimised through threshold experimentation. Additionally, the algorithm is verified using the simulation of a sinusoidal waveform and real flight data from the F-15B/836 research airplane.     

FBG 传感技术在飞机机翼动态形变监测中的应用

机翼是飞机的关键部件之一,在飞行过程中对机翼形变进行在线监测,有助于提升飞机的安全性能及任务执行能力。 为此,本文提出一种基于光纤布拉格光栅传感技术的机翼动态形变测量系统;理论分析了 FBG 波长变化量与机翼表面曲率变 化的关系,利用 FBG 温度传感器实现应变补偿,利用三次样条插值实现离散曲率的连续化,采用基于连续曲率的形变重构算法 实现机翼形变测量;在 CA42 飞机的 4 个翼面上布置了 36 个 FBG 应变传感器,4 个 FBG 温度传感器,通过地面静力试验得到了 机翼的形变测量误差为 2. 5% ;最后,针对机翼动态形变测量系统开展了飞行试验,试验过程完整地记录下了机翼表面的应变、 温度及形变信息。 试验结果表明,由机翼形变产生的翼梢位移量正比于机翼法向过载,系数分别为 86. 33 mm/ g(左机翼)及 80. 04 mm/ g(右机翼),翼梢最大位移量 250 mm,发生在法向过载为 2. 25 g 的时刻。 此外,飞机机动半径越小,机翼形变量越 大。 机翼动态形变测量系统体现了良好的工程适应性。     

Dynamic instability characteristics of laminated composite plates subjected to partial follower edge load with damping

The study of vibration and dynamic instability behaviour of laminated composite plates subjected to partially distributed non-conservative follower forces is presented by using the finite element technique. The first-order shear deformation theory is used to model the plate, considering the effects of shear deformation and rotary inertia. The modal transformation technique is employed to the resulting equilibrium equation for subsequent analysis. Structural damping is introduced into the system in terms of equivalent viscous damping to study the significance of damping on stability characteristics. The effects of load width, boundary condition, aspect ratio, ply orientation, direction control of the load and damping parameters are considered for the stability behaviour of the plates. The results show that under follower loading, the system is susceptible to instability due to flutter alone or due to both flutter and divergence, depending on system parameters.     

民用飞机燃油系统负加速度试飞技术与结果分析

负加速度试飞是民用飞机适航取证试验的重要组成部分,民机负加速度试飞在国内尚属首次,具有对机组操纵技术要求高、风险难度大的特点。本文结合已经完成的燃油系统负加速度试飞,对负加速度时飞机的飞行状态,动作要领进行了总结。另外,对负加速度飞行时动力装置的燃油系统的工作情况进行了分析。     

AUTONOMOUS STRUCTURAL HEALTH MONITORING—PART I: MODAL PARAMETER ESTIMATION AND TRACKING

A growing interest for techniques and systems allowing the early detection and monitoring of damage based on vibration analysis is clearly present in different research and application areas, such as civil constructions, mechanical systems, and aircraft and aerospace industry. However, an important element for the applicability of modal-based damage assessment techniques in practice is the automation of the identification and tracking procedure.In this contribution it is shown that, by using a frequency-domain maximum likelihood estimator, features such as high accuracy and confidence bounds for the estimated parameters and robustness for high measurement noise levels create the possibility to automate the modal identification process. For the validation of the model, criteria based on a statistical approach were developed in addition to the well-known criteria such as modal phase colinearity and mode complexity, while the final mode selection is done by means of a fuzzy clustering algorithm. At the same time, an accurate mode-tracking algorithm is presented. It is shown that the problem of coinciding poles, due to shifting or crossing modes under changing structural dynamics, can hamper the mode tracking and a robust solution is proposed. The possibilities and limitations of the automated approach are investigated and tested for a slat track of an Airbus A320 commercial airplane, providing a preliminary study for future monitoring practices during life cycle tests on slat tracks.     

Tracy-Widom distribution based fault detection approach: application to aircraft sensor/actuator fault detection

The fault detection approach based on the Tracy-Widom distribution is presented and applied to the aircraft flight control system. An operative method of testing the innovation covariance of the Kalman filter is proposed. The maximal eigenvalue of the random Wishart matrix is used as the monitoring statistic, and the testing problem is reduced to determine the asymptotics for the largest eigenvalue of the Wishart matrix. As a result, an algorithm for testing the innovation covariance based on the Tracy-Widom distribution is proposed. In the simulations, the longitudinal and lateral dynamics of the F-16 aircraft model is considered, and detection of sensor and control surface faults in the flight control system which affect the innovation covariance, are examined.     

Measurement, identification and modelling of damping in pneumatic tyres

This paper deals with a research approach specifically designed for the measurement, identification and modelling of damping in pneumatic tyres. As a less rigorous and more global approach of characterizing the engineering property of tyre damping, experimental modal analysis and methodologies based on both real and complex modes are introduced. In the context of the real modal analysis, the flexible ring tyre model is also investigated. A standard testing procedure is employed for the collection of vibration data in pneumatic tyres, and the linearity and reciprocity of the tyre structure and the orthogonality of its modes is proven at the initial stage of investigation. After demonstrating the disadvantages of the proportional damping assumption in describing the tyre vibration, the first-order complex modal interpretation with general viscous damping assumption is implemented and discussed, including an appropriate normalization of the complex modes. As a further extension to the analysis, the second-order Rayleigh's small-damping approximation is introduced into the complex modes framework, in order to obtain an accurate global estimation of the damping distribution.As a natural evolvement of the applied damping models in this paper, from the simplest single-valued proportional damping in flexible ring tyre model, proportional viscous damping in real modal interpretation, up to the generally distributed viscous damping in second-order approximation of the complex modal interpretation, the finally identified damping matrices, both in modal and physical coordinates, present a reasonable explanation of damping effect in pneumatic tyres. Agreement between the theory and experimentally identified results also proves the suitability of this approach for damping identification in complex structures.     

壁板结构热屈曲后模态特性试验

高速飞行器在服役期间面临着严酷的气动加热效应,热载荷会引起材料性能变化,会在结构内部产生热应力、热变形及热屈曲,从而改变结构的有效刚度,影响其动力学特性。针对铝合金壁板结构开展热屈曲后模态特性的试验,采用石英灯辐射加热方法模拟气动加热,利用热应变与温度的关系,获得了壁板结构热屈曲临近温度,进而选取屈曲前、屈曲后一系列温度状态开展热模态试验。试验结果表明,模态频率随加热温度的增加先降低,在临近屈曲温度附近达到最低值,热屈曲后随着温度增加又逐渐增加。由于不同阶模态对热载荷的敏感程度不一样,第3阶和第4阶模态在加热过程中发生交换,而模态阻尼随着加热温度的增加呈现增加的趋势。     

民用液压舵机动刚度研究浅析

液压伺服舵机广泛应用于民机电传飞行控制系统,舵机的众多特性引起了设计者的重视。动刚度作为液压舵机的一项重要性能指标,对飞机飞行安全有重大意义,其设计必须满足飞机操纵面颤振抑制要求。介绍了液压舵机动刚度的定义、动刚度特性研究的重要性、操纵面防颤振抑制设计原则以及舵机防颤振抑制设计方法。建立了液压舵机系统数学模型,提出了舵机动刚度特性的分析和测试验证方法。随着电液伺服技术和民用舵机设计的发展,舵机动刚度特性的研究将引起更多工程设计人员的重视。     

EXTRACTION OF RITZ VECTORS FROM VIBRATION TEST DATA

Modal parameters obtained from modal testing (such as modal vectors, natural frequencies, and damping ratios) have been used extensively in system identification, finite element model updating, and structural health monitoring. As an alternative to modal vectors, load-dependent Ritz vectors have been shown useful in various areas of structural dynamics such as model reduction and damage detection. The applications of Ritz vectors, however, have been mainly limited in analytical and numerical analyses because of the difficulty to identify them from vibration tests. This paper presents a procedure to extract load-dependent Ritz vectors using a complete flexibility matrix constructed from measured vibration test data. The proposed method cannot only construct the Ritz vectors corresponding to the actual load pattern employed in vibration tests, but also generate Ritz vectors from arbitrary load patterns. Experimental data obtained from the vibration test of a grid-type bridge structure are employed to validate and illustrate the proposed extraction procedure.     

On the estimate of the FRFs from operational data

In this paper, the effects of different mass loadings required for the estimation of the frequency response functions, FRFs, from data gained by the emerging technique of operational modal testing, is proposed. This technique allows the evaluation of the natural frequencies, mode shapes and damping ratios from operational data achieved from a first session of tests, then the scaling factors are derived from a further experimental investigation. The approach is based on the sensitivity of the eigenproperties to structural modifications, such as the mass and stiffness distribution. It is shown that the generalized modal parameters could be derived by the measurements of the natural frequency shifts due to a controlled mass variation in the structure, assuming negligible changes in the mode shapes. Such generalized modal parameters are finally used to estimate the FRFs. This mode shape scaling technique, together with the investigation of the effects of the mass positioning on the uncertainties in the estimates of the scaling factors will be experimentally investigated on simple aerospace structures.     

磁流变减振车刀模态仿真与实验研究

针对车削加工过程中出现的刀具与工件之间的颤振,设计并研制了一种基于磁流变液挤压工作模式的减振车刀。为研究不同励磁电流下减振车刀的动态特性变化,通过类固体定义的方式在软件中定义磁流变液的参数,利用有限元仿真软件ANSYS Workbench对减振车刀进行了模态仿真分析;通过设计的瞬态激振实验方案对减振车刀进行了模态测试实验。仿真与实验得出减振车刀的前4阶模态值。结果表明,随着励磁电流的增大,各阶模态值均增大,对应的刚度值也增大。     

System identification and stability evaluation of an unmanned aerial vehicle from automated flight tests

This paper presents a consequence of the systematic approach to identify the aerodynamic parameters of an unmanned aerial vehicle (UAV) equipped with the automatic flight control system. A 3-2-1-1 excitation is applied for the longitudinal mode while a multi-step input is applied for lateral/directional excitation. Optimal time step for excitation is sought to provide the broad input bandwidth. A fully automated programmed flight test method provides highquality flight data for system identification using the flight control computer with longitudinal and lateral/directional autopilots, which enable the separation of each motion during the flight test. The accuracy of the longitudinal system identification is improved by an additional use of the closed-loop flight test data. A constrained optimization scheme is applied to estimate the aerodynamic coefficients that best describe the time response of the vehicle. An appropriate weighting function is introduced to balance the flight modes. As a result, concurrent system models are obtained for a wide envelope of both longitudinal and lateral/directional flight maneuvers while maintaining the physical meanings of each parameter.     

RP-3和RP-5煤油对飞机动力装置和燃油系统试飞的影响

RP-3号航空煤油是军用飞机和民航客机最为常用的燃料,但是舰载飞机通常使用RP-5号航空煤油,RP-5号煤油突出特点是密度大、闪点高。此外,两种燃油在成分、黏度、饱和蒸气压、比热容、导电率等方面有诸多差异。这些差异会对飞机重心、燃油系统通气增压、供油流动损失、燃烧热值等造成影响,分析这些影响对飞机试飞具有重要的价值。     

一种小型无人直升机姿态陀螺减振平台设计及试飞验证

介绍了起飞重量为120 kg的小型无人直升机总体结构布局,简述了该飞机自动驾驶系统的工作原理,提出了要采用自动驾驶的核心感应器——姿态陀螺。对飞机进行空中振动环境测试,得到飞机悬停、前飞状态下局部部位幅频特性,为陀螺的减振平台提供设计依据。本文着重论述了减振平台设计方法,重点在平台的关键部件减振器研制;通过理论分析和实验研究,研制出了一个内腔为硅油、外部为橡胶囊,重量轻、阻尼大、结构新颖减振器。飞机经过大量飞行实验,验证了研制的陀螺减振平台性能良好,解决了陀螺共振翻倒,输出假信号难题,为无人直升机进行自驾飞行提供保证。本文为相关的陀螺减振平台提供工程设计依据。