Experimental studies of forward and backward whirls of drill-string

In this work we investigate forward and backward whirls of a drill-string using a novel experimental drilling rig (Wiercigroch, 2010) capable of reproducing major types of drill string vibration, including stick-slip, bit-bounce and whirling. We focus our attention on whirling motion of the Bottom Hole Assembly (BHA) with a particular attention to the co-existence of forward and backward whirls. We present experimental results, showing for the first time co-existing whirling solutions and characterizing the parameter space in which different whirls can be observed. Those results are then used to calibrate a simple mathematical model, which can be used for further studies of whirling phenomena. (C) 2017 Elsevier Ltd. All rights reserved.