Scour Effects on the Structural Integrity of Offshore Wind Turbine Monopiles

Abstract

Large diameter monopiles are widely used for the installation of offshore wind turbines in relatively shallow water depth applications. Monopiles are considered as a cost and time-efficient foundation solution, taking advantage of the experience gained from the Oil&Gas industry. Due to their relatively large diameter, monopiles are susceptible to scour effects that threaten their structural integrity and necessitate the application of high-cost mitigation measures. The mitigation measures are also associated with heavy environmental impact at the local subsea environment, as well as increased CO2 emissions for their application. The present work examines the effect of scour on the structural integrity of monopiles using integrated simulation models that combine advanced finite element analysis (FEA) and computational fluid dynamics (CFD) techniques. A typical monopile geometry and North Sea representative metocean data are used in a case study. In this example analysis emphasis is given on the structural integrity deterioration resulting from the scour development over time. Advanced techniques are employed to simulate the soil-pile interaction. Furthermore, fluid-structure interaction effects due to the water flow around the monopile are examined using CFD techniques. Finally, fatigue life predictions of sensitive areas are conducted based on the “S-N methodology” and are enhanced by employing crack-growth analyses based on linear elastic fracture mechanics principles.