Vortex-induced vibration (VIV) is produced by the flow of ocean currents past long slender tubulars such as production risers, steel catenary risers, drilling risers, tendons, pipelines, jumpers, and cables. The friction of the cylinder 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.
The separated boundary layers, commonly called “shear layers” roll up into vortices because the flow near the cylinder is flowing much slower than the flow at the outer edge of the boundary layers and shear layers and the shear layers are near a lower pressure region in the wake of the tubular. The vortices grow and interact with the shear layer on the opposite side of the wake which is then associated with a shedding of a vortex on one side of the cylinder. When this vortex sheds the now growing vortex on the opposite side of the cylinder grows quickly until it interacts with the opposite shear layer and the process is repeated. This cycle is known as vortex shedding.
Vortex shedding produces oscillating forces on the tubular surface primarily due to the low pressure in the growing vortex while it is attached to the tubular surface. The resulting oscillating forces from the vortex shedding can cause the tubular to experience an oscillatory motion. This motion is generally known as VIV, though VIV is usually most pronounced when the motion frequency can excite a structural natural frequency of the tubular.
Tubulars experiencing VIV can eventually fail due to fatigue. To prevent substantial fatigue damage, it is often prudent 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 helical strakes and fairings.