The interaction of the wake between pairs of long flexible cylindrical structures is of major consequence in the design of offshore oil and gas production facilities. Modern designs of these facilities often utilize arrays of flexible pipes (risers) extending from the mean water line to the mud-line and then to the subsea reservoir. As ocean currents interact with these structures, wakes are formed at the upstream structure and propagate to the downstream structure (a perturbed flow-field) resulting in a modified force on the downstream structure. This effect, known as the shielding effect, needs to be properly accounted for during the design of offshore facilities. Conservative yet realistic estimates of the effect of separation between the structures under a variety of ocean currents are sought. It is common industry practice to evaluate the clearance between a pair of long flexible cylindrical structures using a finite element based tool. Hydrodynamic loads are based on experiments on a pair of short rigid cylinders. Recent advances in Computational Fluid Dynamics (CFD) technology have made it cheaper and quicker to perform simulations of these conditions without compromising the underlying physics. This alternative is preferred to more expensive and time consuming physical prototype experiments. This paper presents the results of high resolution, time accurate CFD simulations used to understand and quantify the wake interaction between a straked cylinder and a cylinder mounted with the AIMS Dual Fin Splitter (ADFS). No prior experimental data were available for the riser configurations and conditions that were investigated. The simulations were performed using prototypic current velocities and geometries. This paper will describe the CFD technology used in detail. The paper will cover the model setup, the extent of and discretization of the model, the choice of time-step, the boundary conditions, and a discussion on the results from the simulation.

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