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In offshore facilities, the most widely spread way to transport fluids in relatively short distances is through submarine pipelines. These structures are subject to internal and external forces. Nowadays, most of the proposed models to study submarine pipelines subjected to vortex induced vibrations feature a circular cylinder, submitted to a cross-flow, and are able to display oscillations in just the transverse direction to the fluid flow velocity. In this paper three different models that consider a two-dimensional fluid flow around a pipeline were studied via ANSYS CFX®, for Reynolds numbers between 100 and 700, with the purpose of determining the limitations of the 1-DOF models based on the Strouhal number and lift and drag coefficients and account its influence in fatigue lifespan. These models consisted of a static cylinder — i.e. no oscillations —, a cylinder with 1-DOF — i.e. cross-flow oscillations — and a cylinder with 2-DOF — i.e. cross-flow and inline oscillations —. It was found that, although fluid flow Reynolds numbers were very small as to make the submarine pipeline models fall within the finite-life region, a 1-DOF model is accurate enough to predict fatigue lifespan, since it presents respect to the 2-DOF model little deviation in the chosen comparison parameters.

Pigging procedures are common maintenance operations used to perform cleaning, draining and pipeline inspection in order to improve flow efficiency and operation cost. Despite these procedures are commonly used, questions still remain regarding the flow and the PIG motion features due to the complex interaction among pig, wall and flow, and the changes in internal fluid pressure and local fluid density. Currently, the PIG dynamic predictions are based on experimental data from short scale laboratory experiments and numerical models founded on physical simplification. So far, the transient of PIG motion calculated by methods that combine CFD and fluid-structure interaction in a 3D model and the influence of the physic and numerical features over the pig dynamics has not been analyzed yet. To provide a better understanding of pigging runs, this paper proposes a CFD methodology to obtain a 3D transient simulation of PIG motion. A moving control volume attached to the PIG let to solve the governing equation in a stationary mesh. This methodology is used to obtain the transient simulation of a PIG launched in a straight water pipeline for different PIG mass, launching time and turbulence models in order to study its influence over the PIG dynamics. The numerical results show a linear relation between the mass and the pressure drop in the transient state, but with no influence over the final stationary state. Also, an asymptotic relation between the transient pressure drop and the launching time was observed with no influence over the PIG terminal velocity. Besides, it is exposed the influence of the turbulence models (κ-ε, SST and BSL Reynolds Stress) in the results of pig motion; appreciable difference between the drop pressure of Omega-Based Stress Models (SST and BSL) and κ-ε turbulent model at steady state is shown, and, finally, a comparison of the velocity profiles at the interstice for each model was developed, this one shows an inaccuracy of the κ-ε model to describe the velocity profile in the walls proximities.

Flow in microchannels is an important area of research in engineering because its importance in areas such as micro-machinery. In addition, hydrophobic materials have become increasingly attractive for use in fabrication of microfluidic devices. However, even when in macroscopic flows the non-slip boundary condition on solid wall has been well accepted, a number of recent studies have found evidences of slip velocities for liquid flow on hydrophobic surface. In this study, numerical simulations of two-phase flow of micro-droplet in a continuous base fluid in a 2D microchannel were performed using a commercial software package. Both slip and non-slip flows were considered. Continuous phase slip over wall channels was considered modeling all range of possible Knudsen numbers. Three drops of different sizes were modeled. Results were expressed in term of pressure drop and Reynolds numbers. Droplet interface deformation and velocity fields inside both droplets and continuous phase were determined. Results show that for Knudsen numbers between 0.01 and 0.1, Reynolds number increases in a proportion in the order of 20%. In addition pressure drop notably increase when large drops are considered.