包覆层性能对输气管道纵向模态导波传播特性的影响

对带黏弹性包覆层管道中纵向模态的传播特性进行了理论分析，对纵向模态尤其是L（0，2)模态的频散和衰减特性进行了研究。建立了沥青包覆层管道的三维有限元模型，研究了激励频率、包覆层密度以及包覆层纵波衰减系数对导波传播的影响，并在带沥青包覆层钢管中进行激励和接收 L（0，2)模态的实验。结果表明，在低频范围下，随着激励频率和包覆层密度的增大，L（0，2)模态受沥青包覆层的影响也增加，其能量衰减也逐渐增大；对于带沥青包覆层的管道，其衰减频散曲线可用作模态选取的理论指导，采用低频纵向模态超声导波对带低密度包覆层管道检测时效果较好。

Influences of Coating Performance on Longitudinal Modal Propagation Characteristics of Gas Pipelines

The propagation characteristics of the longitudinal modes in the viscoelastic coatings were analyzed theoretically，and the dispersion and attenuation characteristics of the longitudinal mode，especially the L（0，2) mode，were studied.A three-dimensional finite element model of the asphalt coating pipes was established.The influences of the excitation frequency，the coating density and the attenuation coefficient of the coating wave on the guided wave propagation was studied，and the excitation and reception of the asphalt clad steel pipe toward L（0，2) modal experiments were carried out.The results show that in the low frequency ranges，as the excitation frequency and the coating density increase，the L（0，2) mode is also affected by the asphalt coatings，and the energy attenuation is gradually increased.The attenuation curves may be used as the theoretical guidance for the modal selection of the pipelines with asphalt coatings.The low frequency longitudinal mode ultrasonic guided waves are better for the detection of the pipelines with low density coatings.