REDWIN Foundation Models for Integrated Dynamic Analyses of Offshore Wind Turbines

Due to the complex nature of the loads on Offshore Wind Turbines (OWTs), accurate and optimized design of these structures require integrated simulation tools that can properly capture the various structural interactions governing the response. Considerable progress has been made in recent years on developing proper models for coupled aerodynamic and hydrodynamic loads together with advanced control systems for turbines. These efforts have resulted in a suite of aero-servo-hydro-elastic numerical simulation codes available to the industry. However, proper foundation models have been lagging behind in these tools despite availability of various advanced nonlinear models for foundations in general. This has led to uneconomical design of OWTs that have consistently failed to reproduce the measured natural frequencies and can negatively affect the design and structural performance of OWTs. This paper presents a library of recently developed foundation models based on the theory of plasticity together with their verification against large-scale field test data. These models are cast in the framework of macro-elements that represent the nonlinear response of the soil-foundation system due to arbitrary coupled loads at the seabed. The paper also presents results of the numerical simulations of the dynamic response of a monopile-based OWT in the North Sea using an aero-servo-hydro-elastic code and comparison with the data collected from one of the instrumented OWTs in the field. It is further presented how the characteristics of the measured dynamic response change with loading over a long period and the way the response characteristics relate to the basic features of the developed models.