Li J, Rose R L
Matec Instrument Companies Inc, Northboro, Massachusetts 01532, USA.
J Acoust Soc Am. 2001 Feb;109(2):457-64. doi: 10.1121/1.1315290.
Excitation and propagation of non-axisymmetric guided waves in a hollow cylinder is studied by using the normal mode expansion method (NME). Different sources such as angle beam, tube end excitation with normal beam, and comb transducer possibilities are discussed based on the derivations of the NME method. Numerical calculations are focused on the case of angle beam partial loading. Based on the NME method, the amplitude coefficients for all of the harmonic modes are obtained. Due to the difference of phase velocities for different modes, the superimposed total field varies with propagating distances and hence makes particle displacement distribution patterns (angular profile) change with distance. This varying non-axisymmetric angular profile of guided waves represents a nonuniform energy distribution around the hollow cylinder and thus has an impact on the inspection ability of guided waves. The angular profiles of an angle beam source are predicted by theory and then verified by experiments. The predicted angular profiles also provide information for determining the transducer location to find defects in a certain position on the hollow cylinder.
采用简正模式展开法（NME）研究了空心圆柱中轴对称导波的激发与传播。基于NME方法的推导，讨论了不同的源，如斜探头、垂直于管端的法向波束激励以及梳状换能器的可能性。数值计算聚焦于斜探头局部加载的情况。基于NME方法，获得了所有谐波模式的振幅系数。由于不同模式的相速度不同，叠加后的总场随传播距离而变化，从而使粒子位移分布模式（角分布）随距离而变化。这种变化的非轴对称导波角分布代表了空心圆柱周围能量分布不均匀，因此对导波的检测能力有影响。通过理论预测并经实验验证了斜探头源的角分布。预测的角分布还为确定换能器位置提供了信息，以便在空心圆柱的特定位置发现缺陷。
