A multifidelity assessment of breaking and non-breaking wave-structure interactions on monopile offshore wind turbines

Wave-induced loads are critical to the design of offshore wind turbine substructures; however, significant uncertainties arise when comparing models of differing fidelity under breaking and non-breaking wave conditions. This study compares tools recommended in current standards including a low-fidelity Morison based method, a mid-fidelity OpenFAST model (developed by the U.S. National Renewable Energy Laboratory), and a high-fidelity coupled CFD-FEA framework. The comparison is conducted for conditions representative of a site offshore the U.S. East Coast, considering wave loading only and neglecting soil-structure interaction to isolate uncertainties associated with wave-induced loading. Historical data indicate that major hurricanes can occur along the eastern U.S. coastline. Consequently, some standards require a 500-year return period hurricane load for these areas. Such storms can generate large waves that shoal and break in water depths of around less than twenty-five meters, making breaking waves a credible and important design scenario for several sites currently under study or construction. The results of this study show that, for non-breaking waves, assuming the high-fidelity CFD solution as benchmark, OpenFAST tends to overpredict the total hydrodynamic force and overturning moment, by approximately five to fifteen percent, while errors in the Morison-based analytical approach can underestimate up to seventy percent. Under breaking-wave conditions, high-fidelity simulations indicate increases exceeding one hundred percent in wave-induced loads and structural stresses compared with the non-breaking scenario. Traditional analytical methods and mid-fidelity models cannot accurately capture these effects, a limitation that should be explicitly recognized and addressed in engineering standards and current professional practice.