Internal laminar flow effect on the nonlinear dynamic response of marine risers under uniform ocean current

Abstract

ABSTRACT Under the actual marine environment, slender risers suffer from external ocean current and internal flowing fluid. When the viscosity of internal fluid is included, the riser’s nonlinear dynamic response is worthy of extra concern. This paper adopts a force-decomposition model to simulate VIV hydrodynamic forces, the embroil force, relative inertia force and Coriolis force induced by internal flow are included in the motion equation of marine riser. The internal fluid viscosity in essence affects the relative inertia force and Coriolis force, and its effect has to be considered. The comparable ideal flow with Ui = Ui, max/2 brings the dynamic response closer to the laminar flow case than that with Ui = Ui, max, while Ui = Ui, max/2 underestimates the fatigue damage with internal laminar flow. Generally, the internal laminar flow effect on structural cumulative fatigue damage is more significant than that on dynamic response.