Modeling Approach of Hydropneumatic Tensioner for Top-Tensioned Riser

A three-dimensional (3D) finite element analysis (FEA) model of top-tensioned riser (TTR) with hydropneumatic tensioner is proposed in this work. First, the tension calculation equation of the hydropneumatic system is derived, and the kinematic relationship of the platform–tensioner–riser system is established. Second, a 3D FEA model is established based on the FEA code ABAQUS, considering the actual riser string configuration and the Christmas tree. At last, four kinds of tensioner models, i.e., a constant vertical tension model, a conventional simplified model, a linear spring–damper model, and a nonlinear spring–damper model, are compared and analyzed in this study. Results show that the constant vertical tension model is not recommended as it cannot reflect the actual tension in the tensioner and the response of the TTR. The conventional simplified model indeed overestimates the tension of tensioner and may lead to inaccurate estimation results of the TTR response. The linear model is applicable when the environmental condition is relatively mild, but it is strongly recommended to use the nonlinear model especially in harsher environmental conditions.