ROM for localization of multiple defects with ultrasonic guided waves
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Due to their short wave length, high frequency Lamb waves interact with small flaws allowing for early detection of these defects. However, scattered Lamb waves form complicated patterns, impeding the interpretation of measurements. Therefore, monitoring with Lamb waves benefits from model assisted approaches, where a numerical or analytical model is compared to the sensor responses. As the simulation of high frequency waves requires a fine discretisation in space and time, such models are numerically expensive and reduced order models (ROMs) are needed for model assisted approaches. We propose a ROM, which exploits the concept of ray tracing. Thereby, each ray is described through a frequency response function (FRF) or transmissibility function. These functions are efficiently learned in the offline phase, with the information from only two full order models. The high speedup of the presented ROM allows for a large number of evaluations in an inverse setting. To localize flaws, a multi step particle swarm optimisation (PSO) is used, where in each step the location of one flaw is determined. The method will be demonstrated with a virtual example of an aluminum plate with notch like flaws.