Whirling dynamics of a drill-string with fluid-structure interaction

Fluid-structure interaction models for drill-string vibrations are often of reduced order. However, both the structure and the surrounding fluid are non-linear, which can lead to complex coupled dynamic. In this paper, a coupled fluid-structure model is developed, where the flow is reduced to multiple cross-sections and solved with the lattice-Boltzmann method, while the finite element method is employed to discretize a region of the drill-string. In sequence, the whirling dynamics and the fluid forces are analysed for different configurations. The process is repeated disregarding the fluid-interaction with the aim of evaluating the fluid forces. The fluid forces estimated through the solution of the Navier-Stokes equation shows that the fluid acts in both dissipation and excitation of the vibrations. The dissipation is seen when high frequency dynamics is expected, whereas the lower frequencies are excited.