【作者】 刘燕；

【导师】 于起峰；

【作者基本信息】 西北工业大学 ， 固体力学， 2020， 博士

【摘要】 飞行器在飞行过程中机翼往往要承受巨大的气动载荷,导致机翼产生过大的变形,最终影响飞行器的性能、安全及寿命。因此飞行器机翼结构在运行过程中的变形监测是飞行器能否安全稳定运行的关键指标。传统的应变片和加速度计等接触式测量技术以及非接触式激光测量技术存在测量点数少、精度低、实时性差、测量系统布置繁琐、对飞行器本身的设计干扰大等缺点,已经无法满足高亚音速下的特殊测量需求。基于摄像测量技术可以实现对被测物体非接触、高精度、高效、实时、稳定地三维变形测量,且受环境影响小,能很好地克服传统的测量方法应用于机翼变形测量中的不足,对于飞行器飞行安全的实时监测具有重要的意义,是目前机翼变形测量研究的主要方向。因此,本文对基于摄像测量技术的机翼变形测量方法进行研究,主要的研究内容和研究成果如下:(1)针对机翼变形摄像测量中的气动光学效应问题,通过风洞实验手段对飞机机翼上游和下游尾迹区非均匀流场产生的气动光学效应进行了测量和研究。建立了气动光学效应对于机翼变形摄像测量的影响评估方法,提出了机翼变形摄像测量中气动光学效应的评价指标——虚变形,包括虚位移和虚应变。在飞行速度为Ma=0.3、0.5和0.7,飞行攻角范围为α=-7.02°～12.18°的条件下,采用数字图像相关法对OA309翼型的上游流场和下游尾迹区的气动光学效应进行了定量评估,并分析了气动光学效应对测量的影响。实验结果证实了气动光学效应是摄像测量的一个重要的误差源;气动光学效应产生的虚变形场中分布着一些旋涡和带状结构;摄像机的成像光束穿过翼型上游区产生的气动光学畸变要比穿过翼型尾迹区低50%;飞行器的飞行速度和攻角对虚变形的影响很大,气动光学效应产生的虚变形(?)随马赫数的平方呈线性增长,(?)与攻角α的正割函数“1/cosα”线性相关。(2)对机翼表面非均匀流场产生的气动光学效应及其引起的机翼变形摄像测量误差,建立了基于CFD数值模拟的仿真评估方法,揭示了气动光学效应对于机翼变形摄像测量的影响机理。给出了机翼变形摄像测量中气动光学效应仿真分析的基本思路,提出了基于CFD仿真分析和基于三角网格的折射率场参数插值的光线追迹方法。通过仿真和实物实验,对所提出的光线追迹算法精度进行了评估。基于OA309翼型,通过光线追迹仿真计算,研究了马赫数、攻角、摄像机到机翼的距离以及摄像机观测机翼的视角等参数对气动光学效应引起的虚位移的影响。(3)相比于实验室环境下利用摄像测量技术进行的机翼变形测量,风洞试验和飞行试验会面临过曝光、曝光不足、对比度差、背景太暗、摄像机因运动而引起图像模糊等不理想的拍摄环境。提出了同心环形编码标志点(Concentric circular coded target,以下简称为CCCT)设计及定位识别方法。提出了一种选取编码标志点合适尺寸的方法以提高测量精度。为了解决大倾角测量引起的编码标志点透视成像变形较大的问题,利用编码区域背景的四个顶点进行局部图像透视校正以提高CCCT的识别率。从拍摄角度、光照恶劣、模糊、复杂背景和夜间场景这些方面,对所提出的CCCT编码标志点及相应的定位识别性能进行了实验验证,结果表明本文的CCCT设计方案以及相应的定位和识别方法,能够有效地保证定位的精度和解码的准确性,鲁棒性强,稳定性好,可满足测量的需求。(4)飞行或风洞试验中摄像机安装结构的弹性变形或气流的脉动和冲击等因素会引起双目摄像机之间以及摄像机与机翼之间发生相对运动,进而会给机翼变形摄像测量结果带来测量误差。提出了基于摄像机实时位姿估计的摄像机运动误差消除方法,并对位姿估计算法进行性能评价,结果表明RPn P+LHM算法在12种典型的摄像机位姿估计算法中综合性能最优,因此在针对机翼变形摄像测量中摄像机运动误差的消除方法中,选择RPn P+LHM算法进行摄像机位姿实时估计。最后通过实验,给出了摄像机运动误差消除前后变形的测量值与真值的对比,证明了所提出的摄像机本身运动误差消除方法的有效性和可行性,具有重要的工程应用前景。基于前面所研究的理论和技术,本文搭建了机翼变形摄像测量系统,并通过机翼变形摄像测量实验对测量技术与系统的可行性、准确性和可靠性进行验证。实验结果表明,所研发的机翼变形测量系统(采用两台Basler工业摄像机,分辨率为1280×1024,最高帧频为200fps,配置KOWA8.5mm定焦镜头),在大约6m×5m的视场中测量展长为3.49m的机翼变形时,获得的位移结果相对于激光位移传感器的偏差低于0.8mm。本文的测量系统设备简单、操作容易,所提出的CCCT标志点设计方案、尺寸选取以及制作方法便于工程应用,CCCT标志点定位识别、三维重建以及变形计算等数据处理过程完全由计算机完成,实现了测量的自动化,测量结果稳定可靠且能直观显示。另外,在不增加硬件成本的前提下,利用本文提出的摄像机运动误差消除方法对摄像测量结果进行修正后,位移测量误差在1.5mm左右,相比校正前的误差下降了50%,摄像机运动状态的位移测量精度几乎可以达到静止状态的精度;方法简单方便,稳定性好,有效提高了摄像机运动过程中测量的精度。因此,可用于大型飞机飞行过程中机翼的变形测量。更多还原

【Abstract】 While the aircraft is in flight,the wings often have to bear huge aerodynamic loads,causing excessive deformation of the wings,and ultimately affecting the performance,safety and life of the aircraft.Therefore,the actual wing deformations need to be measured quantitatively and accurately to prove the safety of the aircraft.Traditional methods like strain gauges and accelerometers as well as non-contact laser displacement sensors are difficult to use because of problems with their complicated equipment installation,the data transmission,providing their data only at the location where they have been installed,low accuracy,poor real-time performance.Furthermore,such sensors often yield to strong modifications of the aircraft structure.To address these limitations,the researchers have been actively exploring new technologies that can advance the current state-of-the-practice in deformation measurement of the aircraft structure.Due to the advances in cameras and computer vision algorithms,the videometrics are used increasingly and mainly for wing deformation measurement because of their advantages of only requiring simple equipment,ability to obtain non-contact measurements,wide range of usability,providing high-precision and robust results.Therefore,this paper investigated the major problems of in-flight wing deformation measurement based on videometrics and focused on developing reliable and easy-to-use measurement systems.The main contents and achievements are listed as follows:(1)To address the problem of aero-optical effects in optically measuring the wing deformation,the deformation error produced by the upstream and downstream non-uniform flow field of the aircraft wing were measured and studied by wind tunnel experiments.A method for evaluating the influence of aero-optical effects on the wing deformation measurement by videometrics,and two types of errors are identified: virtual displacement and virtual strain,which are proposed as the evaluation parameters.The digital image correlation technique is used on background dot patterns to quantitatively characterize the virtual deformation caused by imaging through the upstream and downstream region over the Mach number range from 0.3 to 0.7 and the angle of attack varied from-7.02° to 12.18°.The experimental results show that aero-optical effect is an important source of measurement error.The virtual deformation field exhibits some eddy and ribbon-like structures which is believed to be imposed by the coherent structures in the subsonic mixing layer.The beam propagation of the camera through the upstream region rather than the downstream region behind the wing might cause the virtual strain to fall by approximately 50%.The virtual strain varies linearly with the square of Mach number and reciprocal of the cosine of the angle of attack.(2)A numerical evaluation method based on CFD is established for evaluating the aero-optical effects caused by non-uniform flow field over the wing surface and the wing deformation measurement error.The influence mechanism of the aero-optical effect on the wing deformation measurement by videometrics is revealed.The basic process for evaluating the aero-optical effect in optically wing deformation measurement is given.Based on CFD simulation analysis,a ray tracing method in combination with triangular mesh interpolation is proposed.Also,three sets of simulation and real experiments are conducted to verify the effectiveness of the proposed ray tracing method.Based on the OA309 airfoil,the effects of the key parameters such as Mach number,angle of attack,and the placement of the camera on wing deformation measurement by videometrics are investigated through ray tracing simulation calculations.(3)Compared to laboratory applications of measuring wing deformation by optical methods,wind-tunnel and in-flight tests are facing with major challenges such as overexposure,underexposure,very dark background,image blur caused by camera motion and so on.To address these problems,an improved concentric circular coded target(CCCT)based on Schneider’s design is presented.Correspondingly,the positioning and recognition algorithms of CCCT are proposed to ensure high-precision results of optical wing deformation measurement even in extreme conditions.A novel and simple method on size selection of circular targets is proposed for high-precision measurement.To solve the problem of a serious image deformation of the CCCT due to a large imaging angle,the perspective transformation of the CCCT local image is used to achieve the image deformation correction and then to improve the recognition accuracy rate.To verify the proposed CCCT design and corresponding algorithm,the real experiments are carried out with a digital camera to capture the images under extreme conditions such as overexposure,underexposure,large imaging angle,complex background.The results show that applying them can obtain better positioning and recognition results even in extreme conditions,and it is quite robust and reliable.(4)Slight movements of the cameras can often occur due to elasticity deformation of the camera support and the surrounding structure or pulse and shock of the air flow,which will introduce a deformation error to measurement results of videometrics.A method based on camera realtime pose estimation is proposed to correct the errors caused by camera movements,and the performance evaluation of pose estimation algorithms is performed.The results show that the RPn P + LHM algorithm has the best comprehensive performance among 12 typical algorithms.Excellent,so in the method of correcting the errors caused by camera movements,the RPn P +LHM algorithm is selected for real-time camera pose estimation.Finally,through experiments,the comparison between the true value and the measured value before and after correcting the camera movements is given,which proves the effectiveness and feasibility of the proposed correction method and has important engineering application prospect.According to the above theories and technologies,this paper develops a wing deformation measurement system based on videometrics,which has been applied in wing deformation measurement for large UAV in order to verify the feasibility,accuracy,and reliability.The results show that when the developed wing deformation measurement system using two Basler industrial cameras with a resolution of 1280 × 1024 and a KOWA fixed focus lens of 8.5mm is applied to measure the deformation of a wing with a span of 3.49 m in a field of view of about 6m × 5m,the deviation between the displacement obtained and the laser displacement sensor is less than 0.8mm;Furthermore,this system is simple in equipment and easy to operate;the proposed CCCT design scheme,size selection and manufacturing method are convenient for engineering applications;the CCCT positioning and recognition,3D reconstruction,and deformation calculation are completely performed by the computer,which realizes the automation of the measurement.The obtained results are stable and can be displayed intuitively.In addition,without increasing the cost of hardware,the proposed method based on the realtime pose estimation is used to correct the influence of camera movements.After correcting,the displacement measurement deviation is about 1.5mm compared with the laser displacement sensor,which is 50% lower than the error before correction.The measurement accuracy in the moving state of the cameras can almost reach the accuracy of the stationary state.This method is simple and convenient,with good stability,and effectively improves the measurement accuracy when camera movements occur.Therefore,it can be used to measure the deformation of the wing during the flight of a large aircraft.更多还原