Nonlinear Three-Dimensional Dynamic Analysis of Marine Risers

Marine risers are modeled as thin-walled, slender, extensible or inextensible, tubular beams subject to nonlinear three-dimensional hydrodynamic loads of interactive nature, torsion and distributed couples, inertia forces and varying axial tension. A finite element, time-incremental algorithm is developed which utilizes equilibrium and kinematic constraints to reduce the required computational time. Iterations are used within each increment to assure convergence of deformation, stiffness matrices and external loads. The algorithm is implemented numerically and the developed computer code is used in several numerical applications to show that a structurally linear model may not be accurate enough and may occasionally be nonconservative in predicting the dynamic riser response.