The Study On Vibration Analysis Of Free Span Considering Pipe-soil Coupling And Internal Waves In Deep Ocean

There is a growing tendency that the exploration of the offshore oil and gas stepsto the deep ocean. The deep water pipeline project gains more and more popularity.Due to the irregular seabed terrain, the current scouring and the uneven soil, thereoften occurs free span. Free span is the most dangerous part of the pipeline system.This paper sums up the causes and types of the span in deep water.The boundary condition plays a very important role in the analysis of free span.In this article, the ABAQUS finite element calculation software is used to simulate thepipe-soil interaction which considers the initial ground stress. This is done to get thevertical and transverse resistance-displacement curves and the sensitivity analysis ismade to the soil cohesive force, Young’s modulus, soil density, seabed terrain and soilfriction coefficient. Then the resistance-displacement curves are added to the inp asthe free span’s boundary condition.The free span encounters current load mainly in the deep water, when the currentgoes though the pipeline at a certain velocity, vortex-induced vibration will occur. Thepaper selects two examples to proceed span’s modal analysis and vortex-inducedvibration analysis, these two examples are the horizontal span pipeline and theclimbing span pipeline. In addition, for the climbing span, the vortex-inducedvibration analysis also considers two current flow field: stratified flow and theopposite situation.Ocean internal wave is a fluctuation phenomenon, which is common in densitystratificational ocean. In this paper, the nature of ocean wave, its typical three-layermodel, and some degrade model are studied, as well as analytical solution of theocean wave field. Furthermore, three typical internal wave flow fields are given in thepaper which considering high frequency and low frequency, and the Morison formulais used to load the internal wave flow field.This paper put forward a set of suspended span analysis method, whichconsidering the stratified fluid, oceanic internal waves and pipe-soil interaction in thedeep ocean. It has some guiding significance to the actual project.