Motion analysis of the riser on the drilling rig using flexible multibody dynamics

Abstract

Dynamic analysis is broadly used in offshore and ship building industry for determining dynamic loads of a block lifting and a subsea equipment installation operation, and a coupled analysis of the offshore drilling rig and a riser. If the bodies in simulated system regard as rigid bodies, the results of the simulation result cannot reflect the behavior due to the deformation of the bodies. This leads that we cannot simulate the system that has large deformation bodies which affect to the behavior of the system such as coupled analysis of a platform and a riser. Therefore, deformation of the bodies have to be considered in dynamic analysis. From this reason, this study investigated Absolute Nodal Coordinate Formulation which is one way of the flexible multibody dynamics that takes account of the deformation of the bodies in the multibody system. The developed flexible multibody dynamics code is verified with analytic soluation and the commercial code, and applied to the motion analysis of a drilling rig and a riser. For the modeling of a drilling rig with a riser, a semi-submersible platform, telescopic joints that connects the platform and ther riser, a lower flex joint that connects the riser and the BOP(Blow Out Preventer) are modeled as rigid body, and the riser is modeled as ANCF(Absolute Nodal Coordinate Formulation) beam. The wire-line riser tensioner which pull the riser to maintain tension of riser to prevent buckling, and keep the vertical position of the riser is modeled as pneumatic spring. Each body is interconnected by some types of joints such as fixed joint, cylindrical joint, and ball joint. The hydrostatic and hydrodynamic force on the platform, current force on the riser, gravity on the all bodies are considered as external forces. Finally, the coupled motion analysis of a drilling rig and a riser has performed by using flexible multibody dynamics.