Analysis of the Motion of Deep-Water Drill Strings—Part 2: Forced Rolling Motion

An equation of motion for a drill string, considering elastic, dynamic, and drag forces, was derived in a previous paper and was applied to two types of beam behavior: A beam having constant axial tension and a perfectly flexible cable. A drill string was then considered as consisting of short beam sections at the top and bottom, joined by a perfectly flexible cable. The lateral deflection of the drill string was obtained by joining the beam and cable solutions subject to boundary conditions at each junction. In this paper, the drill string is considered built-in at the ocean floor and to be experiencing a harmonic change of slope at the ocean surface imposed by roll (or pitch) of the ship, the ship remaining stationary vertically above the point of entry at the ocean floor. Examples are discussed and results are compared with experimentally measured values. The combined effects of roll and displacement are obtained by superposition of the two solutions.