Comparison Between Coupled and Uncoupled Dynamic Analysis of Floating Offshore WTG Support Structure

Abstract

Abstract This study presents a comparative analysis of hydrodynamics for floating offshore structures, with a focus on the coupled and uncoupled analysis methods for a floating offshore Wind Turbine Generator (WTG) support structures. The primary objective is to assess the impact of these two parallel methods on key parameters such as fairlead tension and platform responses. The hydrodynamic analysis performed for this study employs two distinct software platforms, OpenFAST by NREL (National Renewable Energy Laboratory) and MOSES by Bentley, and highlights the effects of using coupled and uncoupled methods for response characteristics of the mooring lines. The authors conducted a similar study on the fixed offshore WTG support structure. This study established a benchmark methodology for the industry to calibrate uncoupled analysis to facilitate the exchange of information between turbine manufacturers and substructure designers within the restrictions of intellectual property rights. The study proposes checks and balances to verify intermediate outputs at various stages of design development. (Gupta, et al. 2023).In this study, VolturnUS-S reference floating offshore wind turbine semisubmersible designed by University of Maine along with International Energy Agency (IEA)-15- 240-RWT 15 megawatt (MW) reference wind turbine is used for the analysis. For the coupled analysis, an integrated global model of the floating hull structure with a WTG is modeled in OpenFAST and the coupled effect is captured by combining the hydrodynamic and aerodynamic responses. For the uncoupled analysis, response is generated by combining the hydrodynamic forces calculated in MOSES with aerodynamic forces using the AeroDyn module from OpenFAST. Results from both analyses are compared and presented in the paper.The coupled analysis provides a comprehensive representation of the system's behavior, capturing intricacies of the coupled behavior of the integrated model. In contrast, the uncoupled analysis simplifies the system but may potentially overlook vital coupling effects. The study contributes to a deeper understanding of the coupled and uncoupled analysis methods and their implications while providing valuable insights to engineers for the design process with respect to the varying effects of these methods on dynamic behavior of the integrated system.