Nonlinear hydrodynamic modeling of an offshore stationary multi-oscillating water column platform

Abstract

The hydrodynamics of an offshore stationary platform consisting of four cylindrical Oscillating Water Column (OWC) Wave Energy Converters (WECs) are considered in this paper. Based on the potential flow theory, a second-order Higher-Order Boundary Element Method (HOBEM) model is developed to simulate the wave interaction with the multi-OWC platform in time domain. Laboratory tests of a carefully instrumented scale model are also conducted, and the results from the two methods are compared for the validation. It is found that the linear model overestimates the relative capture width of the OWC device by approximately 10% around the resonant frequency. Subsequently, the hydrodynamic properties of the multi-OWC platform are investigated systematically in terms of the air pressure and free surface oscillations in the chamber, as well as the relative capture width. The isolated cylindrical OWC device is also considered for the comparison. The effects of the incident wave direction, the column and row spacing between the OWC devices are explored. The surface elevation distribution inside and around the OWC device is discussed. The occurrence of the maximum free surface elevation inside the chambers is found to lag behind the crest of the incident wave. The optimum angle of wave incidence in terms of energy capture is β = 0, i.e. multi-OWC platform aligned with the incoming waves. A strategic design of the column and row spacing can lead to a significant improvement for capturing wave energy.