In this study, the underwater behavior of a model drill pipe rotating in uniform flow was investigated through experimental and numerical analyses. The hydrodynamic force acting on the rotating equipment of the model drill pipe was measured, and its coefficient was derived. The displacement of the model drill pipe was also observed and measured. The numerical estimation of the model's displacement was implemented by applying computational fluid dynamics and absolute nodal coordinate formulation.
In recent years, offshore drilling has become increasingly important for the exploration of new resources (e.g., seafloor minerals and methane hydrate) and scientific research, such as the elucidation of the mechanism of earthquake occurrence. There are two types of offshore drilling: riser drilling (in which riser pipes are connected to the seafloor and hull of the vessel, and drill pipes pass through the riser pipes) and riser-less drilling (in which drill pipes are lowered directly into the sea). Riser-less drilling is used for large-depth and shallow-depth drilling to overcome the operating depth limit of the riser, whereas riser-less drilling is used for riser drilling until a blowout preventer and riser pipe are installed. For riser drilling, detailed measurements have been conducted and reported for the 2000[m] length of actual riser assembly in terms of riser pipe vibration caused by drilling (Blevins et al. 2017). On the other hand, the interest of experiments and numerical sumulation for riser-less drilling is the drill pipe failure and fatigue failure of the drill pipe due to impact forces and cyclic loading acting on the drill pipe.(for example, Zaho et al.,2018)
In riser-less drilling, the drill pipe is directly exposed to the external environment, and the drill pipe behavior becomes more complex. In deep drilling, the drill pipe behavior becomes more complicated as the drill pipe becomes longer, and the natural period of the drill pipe approaches the predominant period of the ship motion. Although drill pipe dynamics do not cause major problems in conventional drilling, they affect the drilling operation. For example, the fluctuating axial stress in the drill pipe caused by ship motion may be up to 10 times greater than that in rigid body hypothesis due to the influence of drill pipe dynamics. Vortex excitation in tidal currents is complicated by drill pipe rotation; its characteristics differ from those of vortex excitation in a fixed pipe (Inoue et al., 2013). Furthermore, the drill pipe rotation in tidal current generates a lift force called the Magnus effect, which deforms the pipe. These dynamics may have contributed to the damage and rupture of drill pipes as well as to the disruption of drilling operations (Inoue et al., 2017a).
