## 5 Conclusions and Future Work  
In the present study, the authors conducted wave propagation and defect detection modelling using COMSOL to investigate the potential of using GWT as a novel NDT technique for the inspection of steel sheet piles. Due to its non-dispersive nature, the present study preferred \(\mathcal{SH0}\) for signal excitation. The LSA principle was used to design shear transducer arrays having high \(\mathcal{SH0}\) mode purity and directionality. A 12 \(\times\) 2 configuration and a 7 \(\times\) 2 configuration shear transducer array were modelled for the inspection of the web and flange of a U-shaped steel sheet pile, respectively. Initially, a wave propagation comparison study was conducted between the web of a 7.5 m U-pile and a plate having the same length and cross-sectional area as the web of the pile. Results demonstrated the back wall reflection signal from the web of the U-pile to be 11.5% higher than the reflection signal from the plate. Another wave propagation comparison study was conducted between the web and flange of a 7.5 m U-pile. Results concluded that the excitation signal on the flange at 5.65 m and 7.12 m was respectively 35% and 46% less than the excitation signal on the web at the same distance. To evaluate defect detection capability, models of five defect scenarios, 50 mm hole, 100 mm hole, 150 mm hole, 200 mm hole and 100 mm slot, were considered at two locations, 5.65 m and 7.12 m, on both the web and flange of a U-pile model. Defect detection numerical models were validated by comparing the theoretical and numerical \(\mathcal{SOA}\). Defect reflection was measured to demonstrate the ability to use UGW for defect detection in the U-piles.  
These numerical models allowed the current authors to carry out their investigations without conducting countless time-consuming and expensive empirical experiments. The next stage for this research is to build only the respective shear transducer arrays modelled for pile inspection and conduct experiments in order to validate the numerical modelling results. Further research will also be completed on transducer characterization to develop novel transducer arrays with higher \(\mathcal{SH0}\) mode purity and directionality.  
[PERSON]. ([PERSON]) was the lead author and main contributor to this paper. He conducted the numerical investigation and literature review and wrote the original draft of the manuscript. [PERSON]. ([PERSON]) contributed to data analysis and visualization for the manuscript and to reviewing and editing the original manuscript. [PERSON] contributed by research supervision, project management and coordination of research activity. [PERSON] created the LSA model and shear transducer array design, and also contributed to reviewing the original manuscript. [PERSON] contributed to supervision along with the review and editing of the manuscript. [PERSON]-[PERSON] contributed to supervision and project administration along with the review and editing of the manuscript. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Innovate UK, grant number 104362.  
Not applicable.  
The authors would like to express gratitude to Innovate UK, Transmission Dynamics Ltd. and TWI Ltd. for all their efforts and contributions to the project and this work.  
The authors declare no conflict of interest.