Assessment of Tropical Cyclone Wind and Wave Hazards and Their Effect on the Reliability of Wind Turbines
Abstract
Tropical cyclone (TC) induces strong winds, heavy rainfalls, and storm surge. They cause fatalities and property damages, especially in the coastal regions that are prone to TC hazards. The TC wind or wave assessments were reported in the literature. The assessment provides the required hazard characterizations for assessing the reliability and risk of structures such as onshore and offshore wind turbines (WTs). The present study considered sites near the coastline of mainland China. It is focused on 1) the assessment of using different historical best-track datasets on the development of stochastic TC track models and on the estimated TC wind hazard, 2) the establishment of a procedure to assess the joint TC wind and wave hazards, to assess their correlation, and the joint probabilistic model, 3) the development of a database-driven simulation-based (DDSB) framework to estimate the reliability of offshore WTs, and 4) the calibration of the design TC wind and wave loads and companion load factors for designing monopile onshore and offshore monopole WTs for selected target reliability indices, and recommend site-dependent and information-sensitive design TC wind and wave loads for such WTs.
For the analysis, both the historical best-track datasets from China Meteorological Administration (CMA) and from Joint Typhoon Warning Center (JTWC) are considered for developing the physical-based beta-advection model. The impact of using one or the other track database on the TC wind hazard is quantified. Based on the stochastic TC track model, available TC wind and wave field models, the joint TC wind and wave hazard is assessed. The quantified TC hazard indicates that the correlation of the extreme (annual or event-based) TC wind speed and wave height should not be neglected. It is proposed that the joint TC wind and wave hazards to assess the reliability of offshore WTs can be carried out according to a database-driven simulation-based procedure. This allows the combined use of synthetic tracks database, the prepared wind and wave fields database, and the structural response database of WTs subjected to combined wind and wave actions. The application of this procedure is shown for a semi-submersible WT. Moreover, the procedure is used to carry out reliability-based calibration of design TC wind and wave loads by considering monopile WTs that are placed on the onshore or offshore locations that are near the coastline of mainland China. Simple to use empirical equations are developed to evaluate the required return periods for evaluating the design TC wind and wave loads. These equations depend on the coefficient of variation of the annual maximum TC wind speed and significant wave height and the selected target reliability index. Also, maps of the required return periods, ranging from 50 to 500 years for two considered tolerable failure probability levels, are given for calculating the design wind load and wave load. The calibration analysis results also indicate that the companion load factor of 0.9 is to be considered for the wave load if the TC wind load is taken as the principal load and the wave force is dominated by the drag force component. This companion load factor becomes 0.85 if the TC wave load is dominated by the inertial force component. Also, the companion load factor of 0.85 for the wind load should be considered if the wave load acts as the principal load.