Enhanced Hydrodynamic Modeling of Offshore Wind Turbines using Morison's Equation with Frequency-Dependent Coefficients

Abstract

This paper presents a novel approach for implementing frequency-dependent hydrodynamic coefficients in Morison's equation, which is widely used in hydrodynamics modeling. Accurate hydrodynamic predictions using Morison's equation necessitate the incorporation of frequency-dependent drag coefficients due to their variation with wave frequency. To address this, the proposed method segments the frequency domain into different regions, such as low-frequency (resonance) and high-frequency (wave) regions. Instead of using a constant drag coefficient across the entire spectrum, different drag coefficients are assigned to these regions. To implement this, a fifth-order low-pass Butterworth velocity filter is applied for the resonance zone, while a first-order high-pass Butterworth velocity filter is applied for the wave-dominated zone. The approach is validated using the INO WINDMOOR 12MW semisubmersible offshore wind turbine, comparing the simulation results against the experimental data. By incorporating frequency-dependent drag coefficients, the model shows improved agreement with experimental surge motion data across both frequency regions, demonstrating the effectiveness of the proposed method.