The Hydrodynamic Impact Numerical Analysis Of Small Diameter Subsea Pipelines To The Mainsubsea Pipelines

In recent years, oil and gas exploitation move to the deep-sea, it requires marine structures unit such as offshore platforms, risers more security. In offshore oil and gas projects, it often uses multiple-pipelines of different diameters in pipelines pave due to technical considerations and economical requirements. Now, study in flow behaviors and VIV of multiple-pipelines with different diameters is not much, the paper use finite element method to study flow past two tandem cylinders of different diameters.A numerical large eddy simulation method combined with the characteristic-based operator-splitting finite element method is proposed in paper. The backward-facing step flow and the flow past a single cylinder at different Reynolds number are adopted to validate the model. The results agree well with the existing numerical results and experimental data, which prove that the model in paper is reasonable. Other more, the flow past two cylinders in tandem arrangement is studied with Re=1000. It is obtained that the critical distance is 2.25D?2.5D, agree well with others.To study the hydrodynamic influence on main pipelines that cause by mall diameter subsea pipeline, the flow past two tandem cylinders of different diameters in different spacing is simulated. The diameter ratio is0.2,0.4,0.6,0.8 and the spacing ratio is 1.75, 1.8, 1.9, 2.0, 2.1, 2.2, 2.25, 2.5.The wake structure of the fluid and force conditions of the pipelines indicate that the critical spacing range at 1.8D to 1.9D when the diameter ratio is 0.2, and the critical spacing range at 2.1D to 2.2D when the diameter ratio is 0.4, 06, 0.8. The lift and drag coefficients of the two pipeline reduce firstly and then increase, the increase in the critical spacingrange.We also analyze the reason of the increasing of the lift and drag of the cylinders. Which provide rational on the layout optimization of the piggybacking propagation subsea pipeline.