Abstract Deep-draft semi-submersible platforms may present significant second-order resonant motions in severe sea states. Evaluating the slow-drift motions of such floating systems is important from the initial stages of their designs considering not only the offset requirement and mooring line load but also the air-gap responses beneath the lower deck. Theories and corresponding applications for these second-order resonant motions have been investigated for decades, but the problem has not been solved completely considering the requirements of a model that is sufficiently accurate and expedient. In this study, high-quality numerical simulations and model tests were conducted. Numerical calculations were carried out with the applications of full quadratic transfer function (QTF) matrices by means of commercial boundary element method (BEM) code. Comparisons show perfect agreement between the wave-frequency components obtained from both the model tests and the numerical calculations. Furthermore, the results also indicate that the second-order resonant motions can be to some extent estimated numerically by the second-order potential theory and that deviations can still be observed compared with those motions obtained by the model tests.

中文翻译：

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极端不规则波浪激励下深吃水半潜器的二阶共振运动

摘要 深吃水半潜式平台在恶劣的海况下可能会出现明显的二阶共振运动。评估此类浮动系统的缓慢漂移运动从其设计的初始阶段开始就很重要，不仅要考虑偏移要求和系泊线载荷，还要考虑下甲板下方的气隙响应。这些二阶共振运动的理论和相应应用已经研究了几十年，但考虑到模型足够准确和方便的要求，这个问题还没有完全解决。在这项研究中，进行了高质量的数值模拟和模型试验。数值计算是通过商业边界元法 (BEM) 代码应用全二次传递函数 (QTF) 矩阵进行的。比较表明从模型测试和数值计算中获得的波频分量之间完全一致。此外，结果还表明，二阶共振运动可以在一定程度上通过二阶势理论进行数值估计，并且与模型试验获得的那些运动相比仍然可以观察到偏差。