Wave-attenuation efficiency of a floating distensible tube at different Keulegan–Carpenter numbers

Abstract A water-filled floating rubber tube is tested in a wave flume under regular waves of different steepness. The wave excited pressure bulges in the tube induce periodic oscillations of a forward-bent water column at its stern, which in turn activate a pneumatic power take-off system. The purpose of the experiment is to better understand how the tube’s working modes contribute to the wave energy absorption and to quantify the power extracted from the incident waves. By applying Bernoulli’s equation for incompressible airflow, the water column free-surface displacement measurements deliver the pneumatic chamber pressure and the volume flow through the power take-off. Video captions help to reveal the interactions of the tube with the incident waves and further relate them to the system’s efficiency. Additionally, an energy balance enables the assessment of the internal friction and flow separation losses, at different Reynolds and Keulegan–Carpenter numbers. The hydrodynamic and overall efficiencies of the system are ultimately provided.