Abstract This paper investigates the low frequency (LF) surge motion of a semi-submersible platform in storm sea states without current, where the influence of viscous drag forces on the LF surge motions is focused. Four hydrodynamic models including one potential flow panel model and three panel and Morison's hybrid models were established. LF surge motion was calculated in time domain using AQWA. Five sea conditions were considered, including two relatively small sea states, one moderate sea state and two storm sea states. Under each sea condition, four sets of drag coefficient in the Morison's model were used for calculation. By comparing mean offset, extreme offset and standard deviation of LF surge motion between different hydrodynamic models in different sea states, the influence of Morison's elements above still water level (SWL) or below SWL, drag coefficient and sea states were investigated. By comparing numerical results with model test results, it is concluded that the drag forces on Morison's elements below SWL is the major source of platform viscous damping forces, while the drag forces on Morison's elements above SWL is the major source of viscous drift forces, which provide an important contribution to the mean and extreme offset of the platform LF surge motion under storm sea conditions.

中文翻译：

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风暴海况下粘性拖曳力对半潜器低频浪涌运动影响的数值研究

摘要 本文研究了半潜式平台在无流风暴海状态下的低频（LF）浪涌运动，其中重点关注粘性阻力对LF浪涌运动的影响。建立了四种流体动力学模型，包括一种势流面板模型和三块面板以及 Morison 的混合模型。LF 浪涌运动是使用 AQWA 在时域中计算的。考虑了五种海况，包括两种相对较小的海况、一种中等海况和两种风暴海况。在每种海况下，采用 Morison 模型中的四组阻力系数进行计算。通过比较不同海况下不同水动力模型之间LF浪涌运动的平均偏移、极端偏移和标准偏差，Morison' 对高于静水位 (SWL) 或低于 SWL 的元素、阻力系数和海况进行了研究。将数值计算结果与模型试验结果进行比较，得出结论：SWL 下方 Morison 单元的阻力是平台粘性阻尼力的主要来源，SWL 以上 Morison 单元的阻力是粘性漂移力的主要来源。为风暴海条件下平台 LF 浪涌运动的平均和极端偏移提供重要贡献。