Nonlinear coupled dynamic model and response characteristics for drilling riser with new soft hang-off system

Riser safety in hang-off modes is a critical concern in marine operations. A new soft hang-off system equipped with a complex hang-off joint system and nonlinear hydraulic compensation system is proposed to improve safety. However, a coupled dynamic model that integrates the proposed system with the riser system for dynamic response analysis has not yet been established. Therefore, a nonlinear dynamic model of the riser system is developed, incorporating coupled axial and lateral vibrations. A new soft hang-off system nonlinear model is presented considering nonlinear factors such as piston friction, centralizer friction, throttle value loss force, and hydraulic pipeline friction. Finally, a comprehensive analysis solver is proposed by the finite element method, Newmark β integration, Newton-Raphson iteration, and trial algorithms. The analysis results demonstrate that the hydraulic compensation system combined with the hang-off joint significantly improves the riser system's dynamic response. Damping forces within the hydraulic compensation system are increased by nonlinear factors, thereby enhancing riser effective tension. Larger throttle openings and hydraulic pipeline diameters reduce both the maximum amplitude and peak effective tension in risers, while the maximum amplitude and peak bending moment at the hang-off joint decrease with larger throttle openings but increase with larger pipeline diameters. • A nonlinear coupled dynamic model for the riser system and a new soft hang-off system is established. • The dynamic model of the riser system accounts for both axial and lateral coupled vibrations. • Nonlinear factors, such as piston friction, centralizer friction, throttle value loss force, and hydraulic pipeline friction, are incorporated into the nonlinear model of the new soft hang-off system. • A comprehensive analysis method is proposed by Newmark β integration method, Newton-Raphson iteration method, and trial algorithm.