Free spans or suspended spans normally occur in subsea pipelines due to the irregularity of seabed and/or the scouring action of sea water. A problem of significance to the free spans of subsea pipeline is that currents or waves flowing across pipelines can shed vortices and induce vibration which may cause fatigue damage to the pipelines. Natural frequencies of free spans are required when solving vibration amplitude and cyclic stresses in the free span. The natural frequency is usually calculated with simplified equations, where factors such as boundary conditions and axial forces are not accurately taken into account. In this study, the influence of boundary conditions, mass of hydrocarbon products, axial force, and multiple spans on the natural frequencies of pipeline are investigated and corresponding suggestions are provided for frequency calculation.

中文翻译：

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自由跨海底管道固有频率的预测

由于海床的不规则性和/或海水的冲刷作用，通常在海底管道中会发生自由跨度或悬浮跨度。对于海底管道的自由跨度而言，一个重要的问题是流过管道的电流或波会掉出涡流并引起振动，这可能会对管道造成疲劳损伤。解决自由跨度中的振动幅度和循环应力时，需要自由跨度的固有频率。通常使用简化的方程式来计算固有频率，其中未精确考虑边界条件和轴向力等因素。在这项研究中，边界条件，烃产品质量，轴向力，