Effect of Strakes on Fatigure Damage due to Cross Flow VIV

摘要

Helical strakes are known to reduce and even eliminate the oscillation amplitude of vortex-induced vibrations (VIV). This reduction will increase the fatigue life. The optimum length and position of the helical strakes for a given riser will vary with the current profile. The purpose of the present paper is to describe how data from VIV experiments with suppressing devices like fairings and strakes can be used in an empirical model for prediction of VIV. Suppression devices are accounted for by introdusing user-defined data for hydrodynamic coefficients, i.e. lift and damping coefficients, in an existing computer program for VIV analysis. The effect of strakes on fatigue damage due to cross flow VIV is illustrated for a vertical riser exposed to sheared and uniform current. Comparison of measured and calculated fatigue life is performed for a model riser equipped with helical strakes. A systematic study of length of a section with strakes for a set of current profiles is done and the results are also presented.