Numerical analysis of extreme water slamming damage and residual strength of ring-stiffened columns of a semi-submersible floating offshore wind turbine

Foundation platforms of floating offshore wind turbines (FOWTs) must withstand harsh weather conditions, during which wave slamming is an important loading condition. Slamming is a complex dynamic problem involving fluid–structure interactions (FSI) but is often simplified as simple pressure loads neglecting the coupling effects during design. This paper examines the local structural response of a column of a FOWT floater during slamming, offering deeper understanding of impact dynamics and a measure of accuracy for design methods. An initial benchmark study on numerical techniques of modeling FSI during water impact of a thin plate was conducted adopting three approaches, i.e. arbitrary Lagrangian–Eulerian (ALE), smoothed particle hydrodynamics (SPH) and incompressible computational fluid dynamics (ICFD). Subsequently, water impact on a ring stiffened cylindrical column of a FOWT floater was investigated using ALE simulations in a range of idealized impact conditions. The structural responses and impact pressures were analyzed, focusing on structural damage evolution. Simplified design methods for predictions of slamming damage were compared with the coupled FSI simulations, using four methods for generating design pressures. Finally, the residual bending strength of the damaged column was determined as an assessment of the consequences of slamming regarding structural integrity. This paper provides insights into accuracy levels of different numerical techniques for FSI modeling and contributes to efficient design of offshore structures subjected to severe wave slamming.