Experimental investigation of the effect of rotation rate and current speed on the dynamic response of riserless rotating drill string

Abstract

Dynamic responses of rotating riserless drill string were investigated by varying rotation rate and current speed. Rotation rate ranged from 20 to 180 r/min, current speed ranged from 0.1 to 0.8 m/s, corresponding to Reynolds number of 1600–12,800 and rotation Reynolds number of 134–1206. Results show that the vibration energy of the rotating drill string is concentrated in rotation frequency, and its frequency doublings are stable in time series; equilibrium deflections are consistent in cross-flow (CF) and in-line (IL) directions and trajectory shows an oval-shape in still water. IL dominant frequency of rotating drilling string coupling VIV decreases, while CF dominant frequency and overall section dominant frequency increase with rotation rate. Vibration frequency transitions from high to low and its bandwidth increases in high shear-rate flow. Equilibrium deflection and vibration amplitude are higher than those of non-rotating drill string when Re ≤ 2400 due to the strong coupling of rotation and current. Rotation reduces mode participation, vibration envelopes are deflected to one side with both traveling and standing waves coexisting. Vibration amplitude reaches a maximum due to multiple resonances. Therefore, rotation rate near natural frequency should be avoided, and the rotation interference effect at low reduced velocity should not be overlooked.