IEEE Trans Ultrason Ferroelectr Freq Control. 2017 May;64(5):859-871. doi: 10.1109/TUFFC.2017.2683264. Epub 2017 Mar 15.
Ultrasonic guided wave tomography (GWT) methods for the detection of corrosion and erosion damage in straight pipe sections are now well advanced. However, successful application of GWT to pipe bends has not yet been demonstrated due to the computational burden associated with the complex forward model required to simulate guided wave propagation through the bend. In a previous paper [Brath et al., IEEE Trans. Ultrason., Ferroelectr., Freq. Control, vol. 61, pp. 815-829, 2014], we have shown that the speed of the forward model can be increased by replacing the 3-D pipe bend with a 2-D rectangular domain in which guided wave propagation is formulated based on an artificially inhomogeneous and elliptically anisotropic (INELAN) acoustic model. This paper provides further experimental validation of the INLEAN model by studying the traveltime shifts caused by the introduction of shallow defects on the elbow of a pipe bend. Comparison between experiments and simulations confirms that a defect can be modeled as a phase velocity perturbation to the INLEAN velocity field with accuracy that is within the experimental error of the measurements. In addition, it is found that the sensitivity of traveltime measurements to the presence of damage decreases as the damage position moves from the interior side of the bend (intrados) to the exterior one (extrados). This effect is due to the nonuniform ray coverage obtainable when transmitting the guided wave signals with one ring array of sources on one side of the elbow and receiving with a second array on the other side.
超声导波层析成像（GWT）方法已广泛应用于直管道腐蚀和侵蚀损伤的检测。然而，由于需要模拟导波在弯管中的传播，复杂的正问题计算量巨大，因此 GWT 在弯管中的应用尚未得到成功验证。在之前的一篇论文中[Brath 等人，IEEE 超声、铁电和频率控制汇刊，第 61 卷，第 815-829 页，2014]，我们已经表明，可以通过用 2-D 矩形域替代 3-D 弯管，来提高正问题的速度，在该矩形域中，基于人工非均匀各向异性（INELAN）声学模型来对导波传播进行建模。本文通过研究在弯管肘节上引入浅缺陷引起的传播时间偏移，进一步验证了 INLEAN 模型。实验与模拟结果的对比证实，可以将缺陷建模为 INLEAN 速度场的相速度扰动，其精度在测量的实验误差范围内。此外，还发现，随着损伤位置从弯管的内侧（内凸面）向外侧（外凸面）移动，传播时间测量对损伤存在的敏感性会降低。这种效应是由于在通过在弯管一侧的一个源环阵发送导波信号，并在另一侧的第二个环阵接收时，获得的射线覆盖不均匀所致。
