Abstract Free hanging is vulnerable to dynamic motion at the top end inducing axial compression at the touchdown point. Numerical approaches in consideration with multiple degrees of freedom and nonlinear drag force have been succeeded at evaluating dynamic characteristics of free-hanging slender structures accurately. On the other hand, analytical investigations into the mechanism determining dynamic tension and how design parameters affect dynamic tension based on sufficient reasoning are yet to be fully developed. In this paper, we aim for establishing a linear lumped mass model that gives sufficient explanations of the basic mechanism determining dynamic tension of free-hanging slender structure. The established model analytically describes how the key parameters, namely the ratio of the coefficient of the virtual mass to the coefficient of the weight in water, the maximum acceleration at the top end, and the static top angle, contribute to the dynamic tension behavior. In addition, we verify the results of the linear analytical model by OrcaFlex calculations in the time domain. We illustrate the contribution of nonlinear force on dynamic tension by introducing the ratio of the nonlinear force to the gravity force.

中文翻译：

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自由悬挂细长结构动态最小张力关键因素的简化集中质量模型解析研究

摘要 自由悬挂容易受到顶端动态运动的影响，从而在接地点引起轴向压缩。考虑多自由度和非线性拖曳力的数值方法已经成功地准确评估了自由悬挂细长结构的动态特性。另一方面，基于充分推理对决定动态张力的机制以及设计参数如何影响动态张力的分析研究尚未得到充分发展。在本文中，我们的目标是建立一个线性集中质量模型，该模型充分解释了确定自由悬挂细长结构动态张力的基本机制。建立的模型分析地描述了关键参数如何，即虚拟质量系数与水中重量系数之比、顶端最大加速度和静态顶角，对动态张力行为有贡献。此外，我们通过时域中的 OrcaFlex 计算验证了线性分析模型的结果。我们通过引入非线性力与重力的比值来说明非线性力对动态张力的贡献。