Simple Method to Introduce Artificial Damping in Oscillating Surge Wave Energy Converters under Regular Waves Considering Viscous Effects

Abstract

The Morison equation is extensively employed to consider viscous effects in hydrodynamic investigations of diverse wave energy converters using the boundary element method (BEM). Nonetheless, linearizing the nonlinear drag component in frequency-domain analysis and determining the appropriate drag coefficients present a challenge. This paper proposes a simple method using the completely linear form of the artificial damping torque equation to consider the energy dissipation due to viscosity in the frequency-domain BEM analysis of bottom-hinged oscillating surge wave energy converters (OSWECs) under regular waves. Similar to the drag coefficient, a constant artificial damping ratio demonstrates applicability across various wave periods for a given OSWEC, with its most pronounced effects observed near the natural periods. Through scanning different values, the fittest artificial damping ratio is determined by minimizing the deviation between the BEM responses and the experimental or high-fidelity computational fluid dynamics data. In contrast to the widely varying drag coefficients, the fittest artificial damping ratios for three OSWECs with different dimensions fall within a narrow range. Hence, a recommended artificial damping ratio is proposed for the rapid approximate estimation of responses, particularly in the absence of validation data during the initial design phase.