Methodology for creating nonaxisymmetric WECs to screen mooring designs using a Morison Equation approach

Abstract

This paper outlines a methodology to derive the rigid body motions from Morison Equation forces for a floating Backward Bent Duct Buoy (BBDB). This Wave Energy Converter (WEC) is a particular style of Oscillating Water Column (OWC). The methodology details how to decompose the BBDB into a series of ‘hydrodynamic bodies’ to account for inertial and viscous effects, ‘structural bodies’ to account for structural mass and inertia, and freely flooding bodies to account for the time dependent variation of entrained water mass in the OWC of the device. Separating these effects allows for independent treatment of the phenomena being modeled and for an easily adaptable WEC model. Because effects of the PTO can be eliminated when considering extreme conditions, OrcaFlex, a validated mooring time domain solver, is applied to this problem. Thus coupled analysis between the proposed mooring system design and the BBDB dynamic response allows for mooring system component specification. Due to the dependence of Morison Equation force magnitudes on empirically derived drag coefficients, the paper concludes with a study quantifying the effect of drag coefficient magnitude on survival mooring loads.