Dynamic recoil response of tensioner and riser coupled in an emergency disconnection scenario.

As the tension force provider for the riser system, the hydro-pneumatic tensioner system plays an essential role in riser recoil. However, Existing riser recoil analyses rarely adopt hydro-pneumatic tensioner, and main nonlinear characteristics of the tensioner, including internal friction, pressure loss of hydraulic oil flowing, and stroke limit, are almost ignored. In this paper, a recoil model that couples the nonlinear hydro-pneumatic tensioner and riser system is proposed to explore the recoil response under the action of these characteristics. A non-Newtonian mud discharge model in the concentric annular channel is developed and incorporated into the coupled model. Effects of the nonlinear characteristics of the tensioner on recoil behaviors are analyzed. Results show that internal friction and pressure loss increase the peak-to-peak value of the top tension, inhibit the recoil displacement in the recoil early stage, and advance the phase of recoil behaviors. The piston rod reaching the stroke limit will produce impact loads on the riser system, intensify the riser oscillation and result in dynamic compression of the riser. Some factors affecting the riser recoil involving the heave phase point, opening of the anti-recoil control valve, and mud density are identified on the basis of the proposed model. • A recoil dynamic model of coupling the nonlinear hydro-pneumatic tensioner and the riser is proposed. • A non-Newtonian mud discharge model in the concentric annulus is developed and incorporated into the riser-tensioner model. • Effects of some nonlinear characteristics of the hydro-pneumatic on riser recoil are identified. • Key factors affecting the riser recoil are identified on the basis of the proposed model. [ABSTRACT FROM AUTHOR]