Wake Shielding Model Effect on Riser Dynamic Response

Abstract

The paper provides a method to estimate the clearance between two flexible risers in tandem arrangement by taking into account the wake interference when subjected to a combined current plus waves flow. The wake interference of a pair of risers due to current is studied by combining the results from global riser analysis software Riflex and Blevin’s wake model [1]. The deflection shapes of a pair of tandem risers with steep-wave configuration, with and without wake interference, are presented and discussed. The effect of the wake interference on dynamic response of a pair of 2D cylinders due to a current plus waves flow is investigated by assuming that the Blevins’ wake model, originally established for cylinders in steady flow, to be valid for current plus waves as well as current-dominant flow conditions. A simplified clearance assessment is also proposed by which a static wake interference effect is considered during the dynamic analysis, and comparisons are made between the two methods.