VIV suppression: changing the current in subsea operations

摘要

Suppression devices like helical strokes and fairings can help prevent substantial fatigue damage of risers and tendons. The upsurge of deepwater E&P activities during the last 20 years has caused operators to think smarter and prioritize complex matters to minimize financial, health, environmental and safety risks while simultaneously improving project economics and insuring asset integrity. One important issue that impacts the outcome of all of these goals is vortex-induced vibration (VIV). While VIV was a well-known occurrence before this time, its importance has grown due to an increased probability of encountering large ocean currents and the difficulty associated with predicting and suppressing VIV in deepwater. When a current flows past a cylindrical object such as a riser, tendon, jumper or horizontal pipeline span, it creates VIV. The friction against the cylinder's surface causes boundary layers to form on each side of the cylinder. The retardation of the flow due to the friction ultimately causes the boundary layers to separate from the tubular and form vortices. The vortices shed from the cylinder in an alternating pattern, thereby imposing alternating (oscillating) forces on the cylinder. For a long deepwater tubular, the frequency of this vortex shedding will be sufficiently close to one or more of the natural frequencies associated with bending, thereby causing VIV.