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Abstract: Air-lift artificial upwelling was simulated through a simplified computational fluid dynamics (CFD) model of two-phase flow in an upward pipe. This model is based on the momentum transfer between the two phases. An algebraic turbulence model was employed to enclose the equations. The volumetric flow rates of the liquid and the gas phases, the void fraction distribution, and the pressure and velocity profiles along the axial coordinate were calculated in the stationary state. Numerical tests were conducted to verify the model. The good agreement obtained between the computational results and the field test measurements with cross-shaped air injectors demonstrates the capability of this model for dispersed bubbly flow conditions. Comparisons with the analytical theory were also made. The results indicated that the proposed engineering-oriented model is efficient for the optimization of the system. [Copyright &y& Elsevier]

Hydrodynamic motion of rigid body in narrow space is a common phenomenon in nature and ocean engineering application. In this paper, a new simulation model based on Fluent is proposed to solve this kind of fluid-structure interaction problem in which added-mass effect is strong. In this new model, hydrodynamic force is decomposed, and a new six-degree-of-freedom rigid-body motion equation is formed with added mass force being added to both sides of the motion equation used by 6DOF solver in Fluent. First of all, numerical results of free-floating rigid body in open domain by 6DOF solver and experimental data of free-falling sphere in still water are presented for the validation of this new simulation model. Then, the scope of this model is studied. It is found that 6DOF solver in Fluent cannot solve the hydrodynamic motion of rigid body if added-mass effect is strong, while this new model is apt for this kind of problem and has good convergent characteristics. Finally, hydrodynamic behavior of rigid body in a changing domain is simulated by the new model. Acceleration and spatial displacement curves are obtained, and details of flow at some key moments are presented and analyzed. • A new simulation model improves Fluent in solving hydrodynamic behavior of rigid body with strong added-mass effect. • The scope of the new simulation model is introduced by comparative analyses with 6DOF solver in Fluent. • Added mass of rigid body in the changing domain is estimated. • The hydrodynamic motion of rigid body in the changing domain is analyzed. [ABSTRACT FROM AUTHOR]

The subsea tree acts as an important role in underwater production system. During its installation procedure, hydrodynamic loads significantly affect its dynamic performance. Hence, the drag coefficient of the subsea tree is addressed in detail in the paper by experiment and numerical simulation. Numerical simulation was carried out with finite difference method to get the drag force and drag coefficient. A new experimental method was proposed to conduct an array of model experiments for drag coefficient of subsea tree. The numerical results in drag coefficient were slightly different with experimental results, that was to say, the accuracy and reliability of the experimental data were proved. The drag coefficient is 0.432 in x-direction, 0.479 in y-direction and 0.446 in z-direction, which provide the accurate fundamental hydrodynamic data for underwater production system installation. • Hydrodynamic coefficient plays an important role in hydrodynamic and motion response. • Towing test in the tank can obtain the hydrodynamic data of subsea equipment. • Drag force has a gradual rise with the increase of flow velocity. • Drag coefficient is slightly differ with different flow velocity. [ABSTRACT FROM AUTHOR]