小波时-频变换的高强钢丝弹性波传播模态分析

超声导波是近年来桥梁拉索无损检测研究的重要方法之一。针对弹性波在高强钢丝介质中传播的多模态频散问题,采用单点时域波形的小波时频变换进行混叠信号的模态识别分离。通过数值求解Pochhammer频率超越方程,计算得到0~1.5 MHz范围内纵向导波模态理论频散曲线;采用有限元模拟半波正弦脉冲激励导波在钢丝中传播过程,由小波时-频变换得到导波模态分布,并进行了不同腐蚀程度钢丝实验对比分析。结果表明,经小波时-频变换得到的第1、2、3阶纵向导波模态与理论值对应吻合,单点时域波形的小波时-频变换结果能够有效识别高强钢丝中的导波模态;钢丝在无腐蚀状态下,一阶纵向导波模态能量占比达57.74%,随腐蚀程度增加,能量更为集中到一阶纵波模态,二阶模态能量逐渐减小。

Modal analysis of elastic wave propagating in highstrength steel wires based on wavelet time-frequency analysis

Ultrasonic guide wave is one of effective methods in studying nondestructive testing in bridge cables. In view of the multi-modal dispersion characteristics of elastic wave in high strength steel wires, this paper adopts the wavelet time-frequency transform method to identify and separate multi-modal signals, which is from one point vibration.Frequency dispersion curves of longitudinal modes in the range of 0-1.5MHz were obtained by solving Pochhammer frequency equation with numerical method. Then, finite element method was used to simulate the guide wave propagating in steel wire which is excited by a half sine pulse, and the guide wave modal is acquired by wavelet time-frequency analysis, and the experiment comparison analysis is carried out finally. The results show that wavelet time-frequency transform method can accurately recognize the first, second and third order longitudinal modals in the frequency range of 0-1.5MHz;The wavelet time-frequency transform of time-histories data measured in the end section is in good agreement with the theoretical result, and the energy of separated first order longitudinal mode accounting for 92%.