This paper examines the potential benefit of the spaced arrangement of buoyancy modules to reduce the vortex induced vibration of deepwater drilling risers. Buoyancy modules are most often continuously applied to a riser to manage the top tension in the riser but they can also be spaced apart so that segments of bare riser are exposed. Field experience suggests this “staggering” of the buoyancy modules tends to suppress vortex induced vibration (VIV). However, the effects of staggered buoyancy are not well understood. In this paper we use CFD simulations to find the flow characteristics of various combinations of buoyancy modules and bare sections which include choke and kill lines. The effect of varying the percentage of buoyancy coverage is estimated based on the forced and free vibration characteristics of individual sections and combinations of the sections. Some direct reduction in VIV was observed but the benefits seem small.

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