The rapid advancement of wind turbine technology has enabled the deployment of increasingly powerful wind turbine generators (WTGs). This study focuses on a Siemens Gamesa Renewable Energy (SGRE) WTG with a rotor diameter of 236 m and a hub height of 154 m, installed in a wind farm in the seismically active Taiwan Strait. Seismic ground motions can impose significant loads on WTGs, particularly during the idling state, where the absence of aerodynamic damping can lead to amplified structural responses and potentially challenge project feasibility.

Current deterministic seismic load calculation methods do not account for the probability of such combined scenarios and lack a clear connection with the safety philosophy, where seismic design is associated with a target annual probability of failure that balances the consequences of failure against the cost of the necessary safety measures. Without accounting for these considerations in the simulation, the resulting loads may become either overly conservative or insufficient. This study applies a probabilistic approach to seismic load calculation to address these limitations and provide a clearer understanding of the results

The probabilistic approach models dependencies among four key environmental variables: wind speed, wind direction, wind shear exponent, and ocean wave direction, using a Non-Parametric Bayesian Network (NPBN). In the NPBN, dependencies are captured via a rank correlation matrix describing both conditional and unconditional monotonic relationships. Given wind speed (defining turbine operating conditions), conditional sampling of the remaining variables is performed through Monte Carlo simulation (MCS), preserving these dependencies. Independent variables such as azimuth angle, seismic wave direction, and seismic seeds are also sampled using MCS.

Seismic loads are computed for four seismic return periods (100, 475, 1300, and 4500 years) using SGRE’s aeroelastic simulation tool, BHawC, under both deterministic and probabilistic approaches. The annual probability of failure associated with deterministic seismic load limits is evaluated and compared with optimal load limits derived through iterative optimization to meet the target recommended by the IEC standard and supported by literature. Results show that deterministic approach results in a seismic load limit on the blade that can be up to 26 % higher than what is required, whereas for the tower component, it can be approximately 8 % lower than the optimal level.

The probabilistic framework not only improves the computational efficiency of seismic load simulations by requiring significantly fewer simulation groups but also produces more realistic, site-specific load distributions. Moreover, it enables the seismic load limits to be defined based on a target probability of failure, allowing the wind turbine designs to optimally balance the consequences of failure against economic benefits, such as the material costs of safety measures. This approach is particularly valuable to SGRE, contractor, and client, as even a small percentage reduction in load limit can lead to substantial cost savings for the entire project.