Comparison between Coupled and Uncoupled Dynamic Analysis of Offshore Wind Turbine Generators (WTG) Support Structures

Abstract

Abstract As offshore wind generation activities continue to expand in the United States, there is a growing need for more efficient, optimized, and reliable analysis of the foundation structures that support Wind Turbine Generators (WTGs). This paper aims to provide a comparison of coupled and uncoupled analysis methodologies for the design of offshore WTG foundation structures under complex dynamic loading from turbine operation and sea states. The focus is on an integrated turbine, turbine tower, and foundation model, which is essential for understanding the behavior of the entire system under various loading conditions. The goal of this paper is to provide insight into the strengths and limitations of two different analysis approaches, coupled and uncoupled, with the aim of helping engineers and designers make more informed decisions when it comes to the design and construction of offshore WTG foundation structures. In this research, an integrated substructure, turbine, and tower model was developed to support the offshore wind turbine. Both coupled and uncoupled dynamic analysis methods were applied to the analysis models. The dynamic turbine loads were calculated using wind turbine information from the National Renewable Energy Laboratory (NREL). Modal analyses were performed to determine the mode shapes and natural frequencies as well as dynamic time history analysis to determine hydrodynamic forces on the support structure. The forces and displacements at the interface joint were then compared to evaluate the difference in behavior between the uncoupled and coupled solutions. This study aims to fill a gap in the current literature by comparing coupled and uncoupled analysis methodologies specific to the integrated model of WTG foundation structure. The paper presents a side-by-side comparison of the coupled and uncoupled analysis using SACS analysis software by Bentley and the OpenFAST program by NREL. SACS is one of the most widely used software packages for the design and analysis of offshore structures in the United States. The findings from these case studies on monopile and jacket foundation types offer a deeper understanding of the distinctions and similarities between coupled and uncoupled analysis of the integrated structure model. This paper presents the conclusions from the study and summarize the key observations to assist engineers in creating simulation models and analyzing WTG foundation structures. These observations will aid in comprehending the complexities of the dynamic behavior of the WTG foundation structure under combined environmental and turbine loading.