Coverage length and density affect performance of fairings

When an ocean current flows past a cylindrical object such as a riser, tendon, jumper or horizontal pipeline span, it creates a phenomenon called vortex-induced vibration (VIV). 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 roll up into vortices and separate from the tubular—a process known as vortex shedding. Vortex shedding produces alternating forces on the cylinder, thereby creating VIV. Tubulars experiencing VIV can eventually fail due to fatigue. To prevent substantial fatigue damage, it is helpful to install VIV suppression devices over at least part of the tubular span (to reduce the vibration amplitude and/or frequency). VIV can usually be minimized with the careful selection and design of VIV suppression devices, such as fairings and helical strakes.

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