FSI Study of internal Multiphase Flow in Subsea Piping Components
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Multi-phase petroleum wells usually produce different configurations of oil and gas with addition of water and sand particles depending on the reservoir characteristics. This four-phase flow introduces many challenges in understanding and analyzing its unpredicted and unsteady behavior, and it sometimes induces significant amplitude vibrations due to oscillating forces, in particular on bends of well jumpers. It is currently an interest to investigate the effect of the oil-gas-water mixture on the structure of pipelines since a significant response would lead to potential fatigue damage, specifically when oil brings dense sand particles or slug flow develops in the flowline. Oil sands reservoirs might develop chunks or slugs acting as severe dynamic loads such that the pipe starts vibrating at a large magnitude and it collapses. In this thesis, understanding this Flow Induced Vibration (FIV) phenomenon is important to identify the flow and geometry variables predicting the structural response, and therefore a screening methodology is proposed to examine the potential damage of the amplitude vibrations. FIV is also considered a lock-in mechanism in which it is important to avoid that the slug or fluid frequency falls within ±20% of the natural frequencies. The frequency spectra of the pressure and volume fraction were obtained as a screening technique to identify if the energy of the fluid excites one of the modes of the structure. This work consists of numerical simulations using a fluid solver (STAR-CCM+) and a stress solver within STAR-CCM+. Computational Fluid Dynamics (CFD) simulations describe the flow patterns developed in the horizontal and vertical sections of the jumper for oil-gas flow, oil-gas-water flow, and oil-gas-water with sand particles. On the structural side, modal analysis was performed using Finite Element Method (FEM) to determine the modes of the structure with its respective natural frequencies. A Fluid Structure Interaction (FSI) methodology was also proposed to study in more detail the response of the system in terms of stresses and displacements if the FIV methodology fails to satisfy the design criteria.