含弯头管道超声导波检测

来源期刊:中南大学学报(自然科学版)2020年第10期

论文作者:朱龙翔 赵时 王悦民 张海兵 段刚

文章页码:2844 - 2855

关键词:导波;含弯头管道;频散曲线;弯头反射;缺陷检测

Key words:guided wave; pipeline with elbow; dispersion curves; elbow reflection; defect detection

摘    要:使用半解析有限元法对弯管中导波传播特性进行研究,计算导波频散曲线和各模态导波的振动特征,并分析两者之间的关系;在ANSYS软件中对L(0,1)模态导波检测含弯头管道进行数值模拟,并使用L(0,1)模态导波对U型管道进行检测实验。研究结果表明:弯管与直管中导波频散曲线的差异与两者中导波振动特征的差异密切相关。在低频条件下,弯管中L(0,1)和T(0,1)模态导波存在截止频率,频散曲线与直管中的差异较大,此时弯管与直管中L(0,1)和T(0,1)模态导波的振动变形差异也较大;随着频率的增加,L(0,1)和T(0,1)模态导波在弯管和直管中振动变形趋于相似,弯管和直管中两者频散曲线也趋于相近。在某些频率范围内,L(0,1)和T(0,1)模态导波与某些弯曲模态导波振动特征类似,此时,在频散曲线中存在“模态耦合”现象;由于弯管不具有轴对称性,弯曲模态导波2个分支的振动特征不再等效,两者的相速度及群速度不再相同,导致频散曲线中存在“模态分支”现象;数值模拟中在截止频率区域和模态耦合区域都出现了较明显的弯头反射信号,弯头反射现象与直管、弯管中频散曲线的差异有关,差异越大,弯头反射越明显;在实际检测中,通过选择合适的频率可以避免弯头反射现象的干扰,有效地对含弯头管道进行检测,且L(0,1)模态导波对于弯头拱腹、拱背处的缺陷具有不同的检测灵敏度。

Abstract: The propagation characteristics of guided waves in pipeline with elbow were studied using semi-analytical finite element method. The dispersion curves and vibration characteristics of guided waves were calculated, and the relationship of them was analyzed. Detecting pipelines with elbow using L(0, 1) mode guided waves was numerically simulated in ANSYS software, and L(0, 1) mode guided waves were used to detect the U-shaped pipeline in experiment. The results show that the dispersion curves differences between elbow and straight pipes are closely related to the vibration characteristics differences. At low frequencies, there are cutoff frequencies for L(0, 1) and T(0, 1) mode guided waves in elbow pipes, and the dispersion curves are significantly different from those in straight pipes. Similarly, the differences between the vibration deformations in elbow and straight pipes are also large. As the frequency increases, the vibration deformations tend to be similar in elbow and straight pipes, and the dispersion curves of both sides tend to be the same. In some frequency ranges, the vibration characteristics of L(0, 1) and T(0, 1) mode are similar to some flexural modes, along with "mode coupling" phenomenon in dispersion curves. As the elbow pipe loses axial symmetry, the vibration characteristics of the two branches of flexural mode guided waves are no longer equivalent, so the phase velocity and group velocity of the two are no longer the same, resulting in "mode branch" phenomenon in dispersion curves. Obvious elbow reflection signals appear in both the cut-off frequency region and the "mode coupling" region in numerical simulation. The elbow reflection phenomenon is related to the difference in the dispersion curves of the straight and elbow pipes. The larger the difference is, the more obvious the elbow reflection is. The pipeline with elbow can be detected effectively in experiment by selecting appropriate frequency as the interference of elbow reflection is avoided, and L(0, 1) mode guided waves have different detection sensitivities for the defects in the intrados and extrados of elbow pipe.

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