Fatigue due to vortex induced cross-flow oscillations in free spanning pipelines supported on elastic soil bed

Abstract

An analytical solution is presented for fatigue response due to crossflow vibration of free spanning submarine pipelines supported on semi-infinite elastic soil bed at the ends. The formulation includes the second order bending effect of axial force present in the pipeline. Free vibration response parameters are obtained by solving the governing differential equations and satisfying the appropriate boundary conditions for both symmetric and anti-symmetric modes.These parameters are used for assessing the fatigue damage due to crossflow vortex induced vibration under wave and current action as per new draft guidelines of DNV. Results are presented illustrating the effect of axial force and soil stiffness on the fatigue life of a free span under a combined wave and current loading scenario. The maximum permissible spans obtained from the full fatigue analysis are compared with those obtained from onset of cross-flow vibration criteria.