悬跨海底电缆涡激振动特性及疲劳损伤分析

悬跨海底电缆作为细长柔性结构，在静力平衡状态下具有一定的垂度，在水流作用下的涡激振动特性与海底管线和海洋立管等结构也有很大的不同，其振动模态受垂跨比影响很大。通过物理模型试验开展了不同垂跨比下悬跨海缆的涡激振动和疲劳损伤特性研究。试验模型按照水弹性相似准则设计，试验中测量了不同流速下海缆模型产生涡激振动时的应变历时数据，采用模态分析法获得了模型涡激振动时的振动模态和振幅。分析了不同流速下海缆模型的振动模态、应变和疲劳损伤的变化和分布特征。试验结果表明：垂跨比显著影响了海缆的涡激振动模态和应变幅值大小。在本试验流速范围内，对一定长度的悬跨海缆模型，当垂跨比较大时，随着流速的增大，模型涡激振动的主响应振动依次出现反对称1阶和对称1阶模态；当垂跨比较小时，模型涡激振动的主响应模态依次出现反对称1阶和对称2阶模态。当涡激振动主响应模态为反对称1阶时，疲劳损伤最大值达到0. 1~0.7。

Analysis of vortex-induced vibrations and fatigue damage of a free spanning submarine power cable

Free spanning submarine power cables exhibit more complex vortex-induced dynamics than the submarine pipelines and top-tensioned risers, because their modal properties are significantly affected by the ratio of sag to span. The characteristics of vortex-induced vibrations and fatigue damage of a submarine power cable with different ratios of sag to span are studied by laboratory experiments. The scaled laboratory model is designed based on the gravity similarity and elastic similarity. The strain signal caused by the vortex-induced vibrations of the model are measured. The modal analysis technique is used to determine the response modes and amplitudes. The response modes and space variations of strain and fatigue damage over the whole cable versus different current velocity are discussed. The results show that the VIV features and the maximum strain amplitudes of the submarine power cable are significantly affected by the ratio of sag to span. In this test, for a certain length of the cable model, with the increase of velocity, when the ratio of sag to span is relatively large, the dominate mode appears in the order of first antisymmetric and first symmetric mode; when the ratio of sag to span is relatively small, the dominate mode appears in the order of first antisymmetric and second symmetric mode. When the dominate response mode is first antisymmetric mode, the maximum fatigue damage reaches 0. 1~0. 7.