Accurate finite element modelling of guided wave scattering from irregular defects

Modelling the scattering of guided waves by defects in three dimensions (3D) can be challenging. The most popular way to achieve this is the finite element (FE) method, at the cost of high computational load, which generally leads to a compromise between the accuracy of the results and the computational time, even when the geometry of the scatterer is simple. In this paper, we describe a procedure aimed at calculating the scattering matrix of an irregular defect in the most efficient way. The use of a frequency domain hybrid model which combines the flexibility of FE modelling and the efficiency of an integral representation of the acoustic fields allows very accurate results to be obtained with low computational load. The modelling procedure that we propose includes optimization of the size of the absorbing region and that of the mesh elements, minimization of number of incident directions, and the study of a spatial filter to smooth the geometry of the defect prior to meshing. Finally, the scattering matrix of a representative example of an irregular corrosion patch is calculated using the optimized procedure. Energy balance criteria are implemented to check the accuracy of the results.