Abstract:
Guided wave ultrasound (GWU) systems have been widely used for monitoring structures
such as rails, pipelines, and plates. In railway tracks, the monitoring process involves the complicated
propagation of waves over several hundred meters. The propagating waves are multi-modal and
interact with discontinuities differently, increasing complexity and leading to different response
signals. When the researcher wants to gain insight into the behavior of guided waves, predicting
response signals for different combinations of modes becomes necessary. However, the task can
become computationally costly when physics-based models are used. Digital twins can enable a
practitioner to deal systematically with the complexities of guided wave monitoring in practical or
user-specified settings. This paper investigates the use of a hybrid digital model of an operational
rail track to predict response signals for varying user-specified settings, specifically, the prediction
of response signals for various combinations of modes of propagation in the rail. The digital twin
hybrid model employs a physics-based model and a data-driven model. The physics-based model
simulates the wave propagation response using techniques developed from the traditional 3D finite
element method and the 2D semi-analytical finite element method (FEM). The physics-based model
is used to generate virtual experimental signals containing different combinations of modes of
propagation. These response signals are used to train the data-driven model based on a variational
auto-encoder (VAE). Given an input baseline signal containing only the most dominant mode excited
by a transducer, the VAE is trained to predict an inspection signal with increased complexity according
to the specified combination of modes. The results show that, once the VAE has been trained, it can
be used to predict inspection signals for different combinations of propagating modes, thus replacing
the physics-based model, which is computationally costly. In the future, the VAE architecture will be
adapted to predict response signals for varying environmental and operational conditions.
