Numerical study on the performance of a floating circular cross section U-tube type wave energy extractor unit in the ocean environment

A wave energy converter (WEC) unit based on a floating U-tube liquid column has been investigated in this paper. The whole system resembles to a tuned liquid column damper supported by two buoys. It is having six rigid body degrees of freedom (DOFs) like any floating object, and additionally the movement of the water column is assumed to be coupled with surge, heave, and pitch of the floating U-tube. A coupled analysis approach has been adopted to solve the problem. The mathematical model of the motion of the liquid column has been obtained through Lagrangian mechanics. Simpler problems related to the liquid column dampers with smaller number of DOFs studied for the vibration suppression of buildings, bridges, etc., whose solutions are well established in the literature, have been used to validate the mathematical model. The power take off system has been modelled as a linear damper to reduce the complexity in the current work. The preliminary dimensions of the current unit have been chosen after a few random trials focussing to generate around 50 kW power from regular waves of around 1–2 m height. Thereafter the sensitivity of the generated power with respect to the basic structural parameters defining the geometry has been studied. The survival performance during an extreme event has also been investigated. The presented results prove the technical feasibility of deploying such a unit for generating the chosen range of renewable power from the ocean waves.