A common method to avoid formation of vortices is to put some helical strakes around the pipeline in free span section [1]. Most data available in selecting strake geometry is from experiences of free spans in winds. For this category of problems Scruton and Walshe [2] concluded that 3-start strake with height range of 0.02D to 0.2D and a pitch of 15D could supress VIV effectively. They obtained that the optimum strake height is 0.118D. Followings are some OTC Papers regarding using strakes to avoid VIV:
- Performance Comparison of Helical Strakes for VIV Suppression of Risers and Tendons.
- Flow Induced Vibration of a Lon, Flexible, Straked Cylinder in Uniform and Linearly Sheared Currents.
References: [1]. Subrata. K., "The Theory and Practice of Hydrodynamics and Vibration,", World Scientific, 2002. [2]. Scruton, C. and Walshe, D. E. J., "A Means for Avoiding Wind-Excited Oscillations of Structures with Circular or Nearly Circular Cross Section," Natl Phy Lab (UK), Aero Report 335, 1957.
