The revelation of propagating ultrasonic guided waves through simulation when they encountered defects in a pipe

In Hong Kong, there are many gas and water pipelines buried under buildings and roads. A rupture of the water or gas pipeline may cause serious interruption to traffic and even human casualties. Therefore, a single-point based and easy-to-install pipeline inspection system is essential to Hong Kong daily living and crucial to public safety. One of the effective and convenient inspection methods for underground pipeline inspection is the ultrasonic-based guided waves. The success in pipe inspection relies on the emission of proper mode of guided waves to a particular type of pipe. To derive the necessary parameters in helping the selection of optimal mode of waves, one can use simulation or real experiments. The cost and difficulty in conducting live experiments on roads are too high, especially in a dense living area like Hong Kong. Hence, simulation is preferred to minimize the frequency and number of experiments necessary to be conducted. A finite element method (FEM) tool, called ANSYS, was selected to build the required dynamical models. However, several obstacles must be solved prior to the development of 3D models for pipes suffering from various defects. These obstacles include the complexity in simulating high frequency guided waves when they are propagating inside a pipeline, the requirements of huge memory space and intensive computational resources. In this paper, we present detailed descriptions on solving these obstacles. The methods to determine the optimal element size and time step are also reported so that the best trade-off can be achieved in terms of efficiency and computational intensity. To verify the accuracy in simulations, selected experiments were conducted for verification purpose. The results show good agreement between the results of simulations and experiments.