VIV Strakes

Cylindrical structures, such as free-standing riser pipes or flowlines in free spans, interact with a uniform fluid such as seawater and shed Karman vortex sheets. If the vortex shedding frequency is close to the cylinder’s natural frequency, the structure will start to oscillate, or vibrate.

The VIV oscillations of submerged pipes are known to increase drag and may lead to structural fatigue. One proven means of suppressing this vibration is the use of strakes, which modify the flow along the pipe, tripping the production of Karman vortices so that they act less coherently.

Lankhorst VIV Strakes
Lankhorst VIV Strakes are typically recognized for their perpendicular intermittent vanes, wound around the pipe in a triple helix. The pitch of these helices is equal to 16 times the pipe OD, however alternative pitches are possible. The standard Lankhorst vane height will deliver a suppression efficiency that is well beyond the generally required 90% compared to bare pipe. The drag increase is relatively low.

VIV suppression solutions optimized for installation
Lankhorst VIV suppression strakes have been designed with ease and speed of installation as a key design feature in order to minimize the expense of offshore installation time. By using the tri-shell concept, strakes are light and installation speed is optimized. Tri-shells also have a high packing density, so that the number of supply barge movements offshore and needed deck space can be kept to a minimum.

In case of installation with heavy loads, such as by roller boxes on a J-lay tower or an S-lay stinger, Lankhorst can provide VIV suppression solutions with materials that have proven to withstand the loads. Further load and impact testing can be done in-house by the Lankhorst stinger roller test rig or the impact tower.

Brochure VIV Strakes