Detection of a straight groove in a metal plate by acoustic scattering in water with applications to marine current turbines

• The present study is the first step for the monitoring of a marine current turbine.
• To simplify this study, the blade of a marine current turbine is a plane plate.
• The acoustic scattering from the plane plate is studied in low frequency.
• The echoes related to the propagation of guided waves in the plate are identified.
• These echoes allow us to characterize a defect in the plate.

The developed method is based on acoustic underwater scattering measurements and can be applied to characterize a defect in a blade of a marine current turbine. To simplify the study, the blade is replaced by a rectangular plate immersed in water having a groove opening out. The measurements are made on horizontal plane perpendicular to the long axis of the stainless steel plate. The frequency range of signal is between 50 and 400 kHz. The transducer is remote from the plate. The measurements are recorded on 360° with a 1° step. The experimental trajectories of the scattering signals are compared to the trajectories calculated from the group velocities of Lamb waves A and S0. Spectra give also an information on groove position. The present study is the first step toward remote monitoring of blades on a marine current turbine.