The cross-section and the structural twist angle of a typical wind turbine blade vary along its span. This complicates its realistic modeling in nonlinear dynamic analysis of wind turbines when seismic performance estimates are sought. As a result, the lumped mass approach is most commonly used to model the rotor-nacelle-assembly (RNA). The RNA is eccentric to the tower top, and the blades tend to induce rotary inertia on the tower. The exclusion of this rotary inertia and the rotor eccentricity can impact the structural response of the wind turbines as the RNA contributes significantly to the total mass of the system. Moreover, the blades are long, slender structural components that can vibrate and deform independently under seismic excitation. The lumped mass approach intrinsically considers the rigid-body inertia for the RNA, which inevitably acts as a part of the tower top. This can affect the seismic vulnerability estimation of the offshore wind turbines (OWT) at a degree that has not yet been properly quantified. To explore this issue, the present study discusses the effects of the three key RNA parameters, i.e., (i) rotary inertia of the blades, (ii) rotor eccentricity, and (iii) blades’ flexibility, on the seismic failure and fragility of OWT under shallow crustal earthquakes. Results show that the rotary inertia affects the higher modes, which in turn influence the height of the tower failure zones. It is also shown that different levels of RNA modeling refinement affect the predicted failure probabilities, particularly under pulse-like ground motions, while the same estimates are overestimated if the conventional rigid body lumped mass rotary inertia is used. Even worse, they can be underestimated (thus less safe) when the rotary inertia is completely ignored, compared with the refined modeling of flexible turbine blades. These results are revealing as they highlight that seismic hazard can indeed pose a significant design issue for OWTs in some regions.

典型的风力涡轮机叶片的横截面和结构扭转角沿其跨度变化。当寻求抗震性能评估时，这会使其在风力涡轮机非线性动态分析中的逼真的建模变得复杂。因此，集总质量方法最常用于对转子-机舱组件（RNA）进行建模。RNA偏心于塔架顶部，叶片倾向于在塔架上引起旋转惯性。排除这种旋转惯性和转子偏心率会影响风力涡轮机的结构响应，因为RNA对系统的总质量有很大贡献。此外，叶片是细长的结构部件，可以在地震激励下独立振动和变形。集总质量方法本质上考虑了RNA的刚体惯性，不可避免地充当塔顶的一部分。这可能会以尚未正确量化的程度影响离岸风力涡轮机（OWT）的地震易损性评估。为了探讨这个问题，本研究讨论了三个关键RNA参数的影响，即（i）叶片的旋转惯性，（ii）转子偏心率和（iii）叶片的柔性对地震破坏和脆性的影响。在浅层地壳地震下的OWT。结果表明，旋转惯性会影响较高的模态，进而会影响塔架故障区域的高度。还显示出不同水平的RNA建模改进会影响预测的故障概率，尤其是在脉冲状地面运动下，而如果使用常规的刚体集总质量转动惯量，则相同的估算值会被高估。更糟糕的是，与改进的柔性涡轮叶片模型相比，当完全忽略旋转惯性时，它们可能会被低估（因此安全性较低）。这些结果表明，地震危险确实会给某些地区的小水船带来重大设计问题。