Study of typhoon impacts on the foundation design of offshore wind turbines in Taiwan

摘要

Taiwan is hit by an annual average of three to four typhoons with different intensities and routes. To consider theimpacts of typhoon events on offshore substructure design, the historical metocean data for storm event-basedfrequency analysis are generally applied. However, whether a supertyphoon passes directly over an offshore windfarm has a great influence on the results of frequency analysis. Therefore, the American Bureau of Shipping hasrecently increased the return period of hydrodynamic loads from 50 to 100 years to address the higher variation in theseverity of extreme storms in typhoon-prone offshore regions. In this paper, to assess the impacts of the increase inthe return period (from 50 to 100 years) on the design of offshore substructures, case studies of different types ofsubstructures (i.e. monopile, three-leg jacket and four-leg jacket) with different water depths were conducted for theoffshore wind farms off the coast of Changhua County in central Taiwan. The quantitative differences in foundationdesign are presented by way of a comparison of substructure weights, overturning moments and pile lengths. Thepreliminary results of the case studies show that the monopile design is more obviously dominated by earthquakesthan by typhoons and the jacket-type foundation is more significantly dominated by typhoons.