Floating offshore structures often exhibit low-frequency oscillatory motions in the horizontal plane, with amplitudes in the same order as their characteristic dimensions and larger than the corresponding wave-frequency responses, making the traditional formulations in an inertial coordinate system inconsistent and less applicable. To address this issue, we explore an alternative formulation completely based on a non-inertial body-fixed coordinate system. Unlike the traditional seakeeping models, this formulation consistently allows for large-amplitude horizontal motions. A numerical model based on a higher-order boundary element is applied to solve the resulting boundary-value problems in the time domain. A new set of explicit time-integration methods, which do not necessitate the use of upwind schemes for spatial derivatives, are designed to deal with the convective-type free-surface conditions. To suppress the weak saw-tooth instabilities on the free surface in time marching, we also present novel low-pass filters based on optimized weighted-least-squares, which are in principle applicable for both structured and unstructured meshes. For ship seakeeping and added resistance analyses, we show that the present computational model does not need to use soft-springs for surge and sway, in contrast to the traditional models. For a spar floating offshore wind turbine (FOWT), the importance of consistently taking into account the effects of large horizontal motions is demonstrated considering the bi-chromatic incident waves. The present model is also referred to as a complete 2nd order wave-load model, as all the 2nd order wave loads, including the sum-frequency and difference-frequency components, are solved simultaneously.

中文翻译：

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具有大水平运动的浮动结构的完整且一致的二阶流体动力学模型

浮式海上结构物在水平面经常表现出低频振荡运动，其振幅与其特征尺寸相同，且大于相应的波频响应，使得惯性坐标系中的传统公式不一致且不太适用。为了解决这个问题，我们探索了一种完全基于非惯性体固定坐标系的替代公式。与传统的耐波模型不同，这种公式始终允许大幅度的水平运动。应用基于高阶边界元的数值模型来解决时域中产生的边界值问题。一组新的显式时间积分方法，不需要对空间导数使用逆风方案，设计用于处理对流型自由表面条件。为了在时间推进中抑制自由表面上的弱锯齿不稳定性，我们还提出了基于优化加权最小二乘法的新型低通滤波器，原则上适用于结构化和非结构化网格。对于船舶耐波性和附加阻力分析，我们表明，与传统模型相比，当前的计算模型不需要使用软弹簧来进行喘振和摇摆。对于翼梁浮动海上风力涡轮机 (FOWT)，考虑到双色入射波，证明了始终考虑大水平运动影响的重要性。本模型也称为完整的二阶波浪载荷模型，因为所有二阶波浪载荷，