A fully coupled nonlinear dynamic model for drilling riser system

Dynamic model and analysis method of a complex system for the drilling platform/tensioner/riser/wellhead/conductor/casing is among the most significant challenges in offshore oil and gas engineering. Scholars have proposed numerous simplified mechanical models, based on the principle of equivalence, to analyze the mechanical characteristics of the complex system. However, achieving a comprehensive understanding remains challenging. Therefore, the features of axial-lateral coupling and large displacement vibration for risers, nonlinearity for the tensioner at the top boundary, and the multi-layered structural for the subsea wellhead system at the bottom boundary are considered. A fully coupled nonlinear dynamic model of the complex system is established based on energy method and Hamilton’s principle. A comprehensive analysis method for the fully coupled nonlinear dynamic model is developed by combining the finite element, Galerkin, Newton–Raphson iteration, and Newmark β methods. Impacts of model simplifications on dynamic responses of the complex system have been studied. Simulation results show that the platform’s motion in all directions increases the dynamic responses of the complex system, which cannot be ignored. Furthermore, the influence of risers on the dynamics of the subsea wellhead system is overestimated when the subsea wellhead system is neglected. The coupling effect between the axial and lateral vibrations of the complex system intensifies with the deformation of the risers.