An improved coupled model for axial dynamic analysis of deepwater drilling risers under a soft hang-off mode

Soft hang-off is an emergency operation for drilling risers to survive under harsh environments. Buckling of the suspended riser and overstroke of the tensioner piston rod would probably occur. Conventional analysis methods usually ignored the dynamic interaction of the riser and tension fluctuation. This paper is devoted to developing an improved coupled model for the axial dynamic analysis of the riser under soft hang-off mode. In the developed model, the mathematical model of the tensioner was established considering gas state variations, internal friction and pressure loss, the mechanical model of the riser considering axial hydrodynamic load was developed, and the two models were coupled through the kinematic variables. A case study is carried out to analyse the axial dynamic characteristics of the riser under soft hang-off mode, and the comparison showed that the conventional tensioner models will underestimate the axial dynamic response of the riser in soft hang-off mode.