Evaluation of the influence of multiphase fluid parameters on the natural frequencies of above-ground field pipelines

The most common method for constructing field pipelines on permafrost  is above-ground installation on supports. The span between these supports must be determined  to avoid resonance frequencies caused by vortex excitation from wind loads. While many studies have aimed to determine natural frequencies, the impact of multiphase fluids has not been thoroughly explored.

The purpose of the study is to determine how the parameters of multiphase fluids influence the natural frequencies of oscillations in above-ground field pipelines.

As a leading method, we use solution of the differential equation of the mathematical model of transverse deformations of a rod under the influence of longitudinal forces.

The study found that changes in natural frequencies resulting from changes in the parameters of the transported multiphase fluid remain within a manageable range. This assessment considers the fluid solely as an additional mass, both under no pressure conditions and at the maximum allowable pressure for which the pipeline was designed. Additionally, changes in water cut and gas factor affect the density of the overall flow, which, in turn, alters the mass of the transported fluid. This change in mass has a greater influence on natural frequencies than internal pressure.

It is demonstrated that, when determining the placement of supports for above-ground field pipelines, it is essential to use the natural frequencies that account for the additional mass, considering both no-pressure and maximum-allowable-pressure conditions.

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