Abstract The vortex-induced motions (VIM) of offshore floaters occur when the frequency of the vortex shedding is close to the natural frequency, and this phenomenon can severely affect the fatigue life of risers and moorings. During the design and operation stage of the semi-submersible (SS), VIM behavior has emerged as an important issue in offshore engineering. The shape of the columns, circular or square, and the wake interference, characterize the VIM of the SS. Numerical studies using the validated Detached Eddy Simulation (DES) method are carried out for parametric analysis of the VIM performance of various SS models consisting of different column shapes: with four rounded square columns, four circular columns and the mixed square-circular columns. The results show that the most significant transverse responses at 0 ∘ current incidence are observed for the SS with four circular columns and the one with two circular upstream columns. At a diamond configuration (i.e., 45 ∘ and 135 ∘ ), the SS models with a square upstream column all present the most pronounced VIM. The analysis shows that the vortex shedding characteristics of each column at different current incidence govern the VIM of the SS models. The square and circular columns both do large positive work on the transverse motions, and thus improve the VIM response at a certain current incidence. Therefore, the design of SS with square, circular and multi-shape columns can not mitigate the VIM behaviors efficiently. Designing a SS model with irregular polygon-shaped columns or twisted columns to avoid the strong vortex shedding may work.

中文翻译：

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柱形和构型对半潜器涡激运动的影响

摘要 当涡旋脱落频率接近固有频率时，海上漂浮物会发生涡激运动（VIM），这种现象会严重影响立管和系泊设备的疲劳寿命。在半潜式 (SS) 的设计和运行阶段，VIM 行为已成为海洋工程中的一个重要问题。圆柱的形状（圆形或方形）以及尾流干扰是 SS 的 VIM 的特征。使用经过验证的分离涡流模拟 (DES) 方法进行数值研究，对由不同柱形组成的各种 SS 模型的 VIM 性能进行参数分析：具有四个圆形方柱、四个圆形柱和混合方圆柱。结果表明，对于具有四个圆形柱的 SS 和具有两个圆形上游柱的 SS，在 0 ∘ 电流入射时观察到最显着的横向响应。在菱形配置下（即 45 ∘ 和 135 ∘ ），具有方形上游柱的 SS 模型都呈现出最明显的 VIM。分析表明，不同电流入射下每列的涡旋脱落特性决定了 SS 模型的 VIM。方柱和圆柱都在横向运动上做大量的正功，从而改善了在一定电流入射下的 VIM 响应。因此，具有方形、圆形和多形柱的 SS 设计不能有效地减轻 VIM 行为。设计具有不规则多边形柱或扭曲柱的 SS 模型以避免强烈的涡旋脱落可能会奏效。