Abstract The response from steep and breaking waves for a monopile structure is investigated by analysis of experimental results and by application of numerical models for six irregular sea states. The experimental monopile was designed to reproduce the first and second natural frequencies of the NREL 5 MW reference monopile wind turbine. The measured response is reproduced in a finite element model using the Morison equation extended to full Lagrangian acceleration with second-order wave kinematics, and with fully non-linear kinematics and the axial divergence term. For the fully nonlinear wave kinematics, the additional point forces of Rainey and Kristiansen & Faltinsen (KF) are further added. In the latter model, the kinematics at the still water level are obtained by Taylor expansion of the kinematics from the free surface. The shear force at the sea bed and the structural accelerations are next compared between the force models and the experimental data. Among the findings are that the extreme force events are generally smallest for the second-order Morison approach, followed by the extended Morison model, and then the Rainey and KF model which produce similar results. While the total accelerations are found to generally match the measurements with fair accuracy, a modal decomposition shows that all models overpredict the response at the first eigenfrequency and underpredict it at the second eigenfrequency for extreme events. The latter is linked to the missing description of slamming loads in the modelling approach. The point force models of Rainey and KF are found to give quite similar results for the extreme events, the reasons for which are demonstrated by regular wave analysis.

中文翻译：

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有限水深单桩结构水动力荷载模型的临界评估

摘要 通过对试验结果的分析和应用六种不规则海况的数值模型，研究了单桩结构对陡波和破碎波的响应。实验单桩旨在再现 NREL 5 MW 参考单桩风力涡轮机的第一和第二自然频率。测量的响应在有限元模型中重现，使用 Morison 方程扩展到完全拉格朗日加速度，具有二阶波运动学，完全非线性运动学和轴向发散项。对于完全非线性的波浪运动学，进一步添加了 Rainey 和 Kristiansen & Faltinsen (KF) 的附加点力。在后一种模型中，静止水位的运动学是通过自由表面的运动学的泰勒展开获得的。接下来比较力模型和实验数据之间的海床剪切力和结构加速度。研究结果包括，二阶 Morison 方法的极端力事件通常最小，其次是扩展的 Morison 模型，然后是产生类似结果的 Rainey 和 KF 模型。虽然发现总加速度通常与测量结果相当准确，但模态分解表明，对于极端事件，所有模型都高估了第一个特征频率下的响应，而低估了第二个特征频率下的响应。后者与建模方法中缺失的砰击载荷描述有关。发现 Rainey 和 KF 的点力模型对极端事件给出了非常相似的结果，