Shivaprasad S, Pandala Abhishek, Krishnamurthy C V, Balasubramaniam Krishnan
Centre for Non-Destructive Evaluation, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, 600036, India.
Department of Physics, Indian Institute of Technology Madras, Chennai, 600036, India.
J Acoust Soc Am. 2018 Dec;144(6):3313. doi: 10.1121/1.5082298.
Ultrasonic studies based on the first arrived signals are of utmost importance when dealing with heterogeneous material especially to seismology, biomedical imaging, as well as for nondestructive evaluation and structural health monitoring applications. Numerical modelling of elastic waves through polycrystalline features has been primarily held back by huge computational requirements. This article discusses the development of a robust and efficient numerical scheme based on finite-difference-time-domain (FDTD) by introducing wave-localized approach to simulate elastic waves in polycrystalline media. The numerical scheme adopts a rotated staggered grid in velocity-stress configuration. The numerical efficiency is improved by adopting parallel computing using efficient graphical processors and by introducing wave-localized computations. It is demonstrated that the proposed tool, especially with the introduction of wave-localized approach, is computationally faster and can handle large-scale grains in comparison with the commercial finite element software, especially when dealing with first arrived signals. This article reports an optimal ratio of FDTD grids per grain to minimize the staircasing effects at the polycrystalline boundaries and was found to be valid over a range of grain sizes. The article also addresses the orientation averaging requirements achieving statistically significant first arrived signal and suggests optimal averaging trials for various grain size models. The developed two-dimensional model shows good agreement with the prediction across the Rayleigh and Stochastic scattering regimes for the chosen model material (Inconel 600) having a cubic symmetry.
基于初至信号的超声研究在处理非均质材料时至关重要，尤其对于地震学、生物医学成像以及无损评估和结构健康监测应用而言。通过多晶特征对弹性波进行数值建模主要受到巨大计算需求的限制。本文通过引入波局部化方法来模拟多晶介质中的弹性波，讨论了基于时域有限差分（FDTD）的一种稳健且高效的数值方案的开发。该数值方案在速度 - 应力配置中采用旋转交错网格。通过使用高效图形处理器进行并行计算以及引入波局部化计算提高了数值效率。结果表明，与商业有限元软件相比，所提出的工具，特别是引入波局部化方法后，计算速度更快，并且能够处理大尺寸晶粒，尤其是在处理初至信号时。本文报道了每个晶粒的FDTD网格的最佳比例，以最小化多晶边界处的阶梯效应，并且发现在一系列晶粒尺寸范围内都是有效的。本文还讨论了实现具有统计显著性的初至信号所需的取向平均要求，并针对各种晶粒尺寸模型提出了最佳平均试验方法。所开发的二维模型与所选具有立方对称性的模型材料（因科镍合金600）在瑞利和随机散射区域的预测结果显示出良好的一致性。
