Conceptual Design and Analysis of a Submerged Wave Energy Device in Shallow Water

Abstract

Preliminary conceptual design of a submerged wave energy converter (WEC) device in shallow water is presented. The WEC consists of a fully submerged, horizontal, flat plate that is restricted to vertical oscillations due to surface waves. Thin rails are used to guide the vertical oscillations and restrict the motion in all other directions. The vertical oscillation of the plate is converted to electricity by use of a direct drive power take-off (PTO) device located on the seafloor. The PTO is a linear generator consisting of a translator, directly linked to the plate by a solid shaft, and a stator. The plate oscillation is controlled by use of a spring, and by the damping effect of the PTO. The oscillations of the horizontal plate is determined by coupling the fluid governing equations with the equation of vertical motion of the horizontal plate that consists of sum of all vertically acting forces on the plate, including the vertical wave-induced force, the frictional force due to the guide rails, the spring force, and the damping force due to the PTO. The fluid flow is governed by use of the Level I Green-Naghdi equations. We also used the Navier-Stokes equations coupled with the volume of fluid method, solved through OpenFOAM. Comparison and discussion of the results from the two theoretical approaches are provided. The wave energy device has a very simple configuration, and the energy output is independent of the direction of incoming waves. Moreover, the entire device is fully submerged at all times and hence it is protected from the impact of breaking waves on the surface. It is concluded that the proposed wave energy device can be a reliable solution for wave energy harvesting in shallow to intermediate water, while minimizing the common challenges seen in many WEC devices.