摘要:
航天器密封结构在轨长期运行期间会受到空间碎片撞击,使密封结构出现不同程度的损伤。如果这些损伤不能被及时检测出来并采取相应措施,可能会带来灾难性的后果。对碎片撞击进行监测可以为航天员采用正确修复方案提供依据。本文利用基于超声导波的结构健康监测技术感知空间碎片对航天器密封结构的撞击。首先,在 Abaqus 有限元仿真软件中,用不同速度的钢球冲击模拟真实的冲击形式。具体分析了超声导波在该壁板结构中的传播特性。用小波变换的方法进行信号处理,据此提取了合适的冲击监测所需的信号频率。其次,设计了一种基于信号互相关分析的冲击成像算法确定撞击位置。比较了不同压电传感器网络定位准确度以及监测效率,选择了一种可靠的组网形式进行监测。最后针对航天器壁板,在实验室环境中验证了该算法的有效性。实验结果表明,该监测系统具有良好的准确性与可靠性。
Abstract:
During long-term work,the spacecraft seal structure suffers impacts from the space debris.If the damage can not be detected immediately,disastrous consequences will happen. Therefore the detection of the impacts caused by space debris is essential and meaningful.This work focuses on an ultrasonic guided wave structural health monitoring (SHM)system developed for the spacecraft seal structure inspection.In part one of the study,the Finite Element Modeling of the reinforced panel is created using the finite element software ABAQUS.Then the simula-tion of the impact made by a small iron ball is presented,and the velocity of the ball increases from 500m/s to 10000m/s.Besides,the elastic wave propagation in the panel is also discussed, and the elastic wave propagation characteristics in the stiffened panel are analyzed.The wavelet transform method is used to find out the appropriate analysis frequency of the elastic waves.The conclusion is that the signal components in 50kHz is the optimal selection to detect and locate the iron ball impact.In part two,permanently mounted ultrasonic piezoelectric (PZT)disc sensors arranged as a spatially distributed array is considered for in situ impact monitoring.The impact location and imaging algorithm is based upon the cross correlation between waveforms received by two different transducers.The cross correlation waveforms,which capture the arrival time difference between two pairs,are similarly distributed and summed to form the final image via a hyperbolic relationship.In order to find out the optimal solution among the sensor number,the accuracy of the impact location and the time-consuming,several different arrangements of the sensors are presented.A comparison based on location accuracy in central region,border area and computing time-consuming is made to find out the optimal sensor arrangement in the reinforced panel.In part three,the effects of the algorithm and the sensor arrangement are tested in a labo-ratory environment.Hammer percussion is used as a substitute for the iron ball impact in these tests.As many as 20 repeated hammer shocks are made for each selected point in the stiffened panel.The results verify the accuracy and stability of the algorithm for impact detection and lo-calization in the complex spacecraft structure.
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