Numerical evaluation of the coupled/uncoupled effects of lower marine riser package and/or blowout preventer with a lower flex joint in a hang-off drilling riser

Abstract

Lower marine riser package and/or blowout preventer (LMRP/BOP) are key marine riser components. However, they are often oversimplified or ignored in traditional studies, which inevitably causes certain calculation deviations, especially when the risers are in hang-off modes. Considering the full size of LMRP/BOP and rotational stiffness of the lower flex joint (LFJ), a fully coupled multibody model compared with the traditional single lumped mass model, is developed using the self-made finite element method program. Different numerical methods and the results in the literature verify this model's accuracy. The coupled and decoupled effects of the LFJ and the LMRP/BOP in the two numerical models versus LMRP/BOP weight, LFJ rotational stiffness, pipe wall thickness, riser suspension length, and ship heave motion in different running stages are comprehensively studied. Significant differences in the inherent vibration and time-domain characteristics between the two models indicate the coupled effects of the large-diameter LMRP/BOP and the rotational stiffness of LFJ of a hang-off drilling riser during running and installation procedures should not be oversimplified but should be well equivalent and considered for accurate evaluations in ocean engineering.