In both of scientific and industrial drilling, it is not desirable to any have accompanying vibrations, large fluctuations, or other unexpected dynamics disturbing a steady and stable drilling process. One of the origins of such disturbances can be the flexibility of the drill pile; drill pipe is easily deformed by external perturbations because it is very long and slender. To specify the stable range of parameters of drill pipe, we theoretically and numerically analyzed a Cosserat-type mathematical model of drill pile. The values of the parameters of this model were set to appropriate values representing actual riserless drilling situations adopted in the operations of the scientific deep-sea drilling vessel Chikyu owned by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). We concluded that the buckling of pipe should be treated as a possible accident, but buckling does not happen in the normal operations of the Chikyu.

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