This presentation synthesizes a wide variety of wave measurement and modeling studies, suggesting that depth-limited wave breaking (also known as “surf breaking,” as distinguished from “white-capping” in third-generation wave models) can occur when the maximum wave height to water depth ratio is as low as 0.34 to 0.39. This is less than half the 0.78 ratio at which wave breaking is specified in Annex B of the IEC 61400-3 offshore wind standard. Dissipative spilling breakers, typical of white-capping, generate wave loads quite similar to those of non-breaking waves. Plunging breakers, typical of surf breaking, generate impulsive impact loads as the near-vertical face of the breaking wave slams against any surface-piercing structure. Analysis of measured wave data at the UK Blyth offshore wind project indicates that monopile bending moments at the seabed are 3 to 4 times greater for breaking waves than non-breaking waves of the same height and wavelength. Accurately estimating the probability of depth-limited wave breaking will be critical to understanding the contribution of these high-loading events to the fatigue-history of Mid-Atlantic offshore wind substructures, particularly for monopile foundations. Sea states subject to depth-limited breaking should be suspected whenever the significant wave height is greater than or equal to one-third the local water depth, and this may have design implications for many US East Coast offshore wind projects now under development.
George Hagerman is a Senior Project Scientist at Old Dominion University’s Center for Coastal Physical Oceanography in Norfolk, Virginia. Previously, he was a Senior Research Associate at the Virginia Tech Advanced Research Institute in Hampton, Virginia, where he served as a member of the front-end engineering design team for an offshore wind technology advancement project led by Dominion Energy, where he helped prepare work scopes and reviewed work products for the metocean design basis. Now named the Coastal Virginia Offshore Wind pilot project, these two demonstration turbines were erected offshore in June 2020 and are now operational.
With over 40 years’ experience researching marine renewable energy systems, including offshore wind power, wave power, tidal stream power, and ocean thermal energy conversion (OTEC), he has served on the Virginia Intergovernmental Offshore Renewable Energy Task Force since it was established by the Minerals Management Service (now BOEM) in 2009.