Multispan classification methods and interaction mechanism of submarine pipelines undergoing vortex-induced vibration

Abstract

Due to the complicated conditions of the seabed, pipelines may have multiple free spans adjacent to each other, forming a multispan pipeline. Because a submarine pipeline is a continuous structure, the vortex-induced vibration (VIV) of free spans can produce interactive effects. However, little attention has been focused on methods for classifying multispan interactions and on the interaction mechanism. This paper therefore investigates the interaction mechanism of multispan pipelines from static and dynamic perspectives, and two multispan classification methods based on modal frequencies and energy transfer are proposed. For static analysis, the natural frequencies of multispan pipelines under different conditions are calculated, and the changes in frequency are used to characterize the influences of different spans. For dynamic analysis, a multispan vibration prediction approach considering the fluid-structure-sediment interaction is constructed, and the dynamic characteristics of the pipeline undergoing VIV are analysed. The mutual influence between spans is judged by the energy transfer between different pipe sections. In addition, a series of experimental tests on a multispan pipeline with sediment coupling is carried out to verify the proposed multispan classification methods for submarine pipelines.