Occurrence Characteristics of Wave, Wind, and Seismic Loads for Offshore Wind Turbine Design

This study statistically analyzes the occurrence characteristics and joint tendencies of waves, wind, and seismic forces using long-term observational data from offshore wind farm candidate sites around Japan. The analysis revealed that wind speed follows a Weibull distribution, while seismic acceleration conforms to a log-normal distribution, each demonstrating distinct occurrence patterns. Wind waves show a strong correlation with wind speed, indicating their generation under localized wind conditions, whereas swells exhibit weaker correlations and are inferred to originate from distant sources such as typhoons or low-pressure systems. No significant correlation was found between wind and seismic forces, supporting the assumption that they occur independently. A joint occurrence analysis of the three external forces identified typical environmental conditions—including wave height, wind speed, and seismic acceleration—that are considered appropriate for offshore wind turbine design. These findings contribute to the development of more realistic and rational design criteria by reflecting actual environmental conditions, and may help avoid overly conservative assumptions. The study also underscores the importance of evaluating combined loading scenarios to improve structural safety and reliability.