Development of floating offshore wind turbine analysis tool using OpenFAST and OpenFOAM coupled solver

Abstract

The growing demand for floating offshore wind turbines (FOWTs) in deep water has driven the need for accurate prediction tools capable of capturing their complex dynamic responses under combined environmental conditions. While mid-fidelity aero-hydro-servo-elastic simulation programs such as OpenFAST, Bladed, QBlade, and Orcaflex provide computationally efficient predictions of FOWT performance and loads, they rely on potential flow theory with Morison's equation for hydrodynamics, which may not adequately capture highly nonlinear phenomena including viscous damping, flow separation, wave breaking, and complex wave-structure interactions. High-fidelity Computational Fluid Dynamics (CFD) analysis offers enhanced capability by directly solving the Navier-Stokes equations, however full CFD simulation of entire FOWT including turbine system demands significant computational resources. In this framework, this study presents the development and validation of an integrated OpenFOAM-OpenFAST-MoorDyn coupled solver for comprehensive FOWT analysis. This framework is built upon OpenFOAM for high-fidelity hydrodynamics analysis and motion calculation, OpenFAST for aerodynamic loads and servo-control, and MoorDyn for mooring line dynamics. This coupling strategy enables load and position scaling between solvers, with turbine aerodynamics and mooring analysis performed at full scale and then appropriately scaled for the hydrodynamic solver operating at model scale to respect Reynolds and Froude similarity. Validation is performed using the 15MW Penta-semi floating platform under both regular and irregular wave conditions. Comparison of the coupled solver against OpenFAST predictions demonstrates that the coupled solver successfully captures platform motions, showing consistent trends for both regular and irregular waves. Future developments will incorporate structural flexibility to model tower elastic effects and conduct validation against real-time hybrid experimental data, further extending the solver's applicability to comprehensive FOWT design and analysis.