Modelling the propagation of underwater acoustic emissions for condition monitoring of marine renewable energy

Abstract

Marine Renewable Energy (MRE) has progressed towards commercialisation over the recent years but significant barriers still exist. This includes the currently high cost of energy, leaving MRE uncompetitive with respect to other more established renewable energy technologies. A significant proportion of this cost comes from Operation and Maintenance (O&M) activities. O&M activity can be reduced through the use of condition-based maintenance scheduling. In offshore environments, the submerged location of most devices enables the use of underwater Acoustic Emission (AE), a new condition -monitoring technique. It combines acoustics (used for environmental monitoring of MRE influence on noise levels) with AE condition monitoring as used in air. This paper assesses the practicality of such an approach in complex ocean environments through detailed sound propagation modelling using the propagation model Bellhop in the Matlab toolbox AcTUP. Results show that acoustic propagation is very sensitive to variations in the shallow water environments considered. When concerning sensor placement, multiple-path interferences mean that the location of the measuring sensor(s) needs to be carefully considered, but might not cover all environmental variations over the several months necessary for accurate long-term monitoring. Associated to the shallow depths, these environmental variations also mean that some frequencies cannot be back-propagated easily, generally limiting access to the monitoring of Received Levels. The results presented here are the first steps toward optimizing AE sensor positions and AE measuring strategies for arrays of devices.