Dynamic analysis of unbonded flexible pipe with bend stiffener constraint and bending hysteretic behavior

Nowadays the widespread application of unbonded flexible pipes in the offshore engineering requires more and more research on the global dynamic behavior. However, due to its complex internal structure, the relative slip between each layer may occur, which may result in the moment-curvature hysteretic behavior. Therefore, accurate knowledge of unbonded flexible pipe mechanical characteristics and global dynamic behavior is of major importance during the design phase and fatigue analysis. In this paper, the effects of bend stiffener constraint and bending hysteretic behavior are taken account of into the riser global model based on the rod theory. This development permits more realistic riser structural properties to be modeled in the dynamic simulation, and reports the detailed time history loading results. A finite element model by OrcaFlex is developed to demonstrate the validation of the proposed model. The static/dynamic responses of flexible riser in the top-end region and touchdown zone (TDZ) are well investigated. Besides, essential parametric analyses are presented and find that: bend stiffener can optimize both the curvature distribution and amplitude in the top-end region; the top angle mainly alters the curvature distribution; the impact of bending hysteretic behavior on the curvature is of great significance, especially for the TDZ.