Dynamics modeling of a three-legged sea floor drill rig hard-landing and analysis of influence of landing conditions on its responses

Abstract

Touchdown is a decisive step in the underwater deployment of the sea floor drill rig (SFDR), but the related research is still in its infancy. Therefore, a spatial seven degrees of freedom (DoF) dynamic model of the three-legged SFDR "Seabull Ⅱ" hard landing was established, and a simulation platform was built. In addition, the influence of landing conditions on the dynamic responses was understood through orthogonal simulations, which indicates that: (a) The maxima of outrigger axial-force-loads are mainly affected by the sediment elastic coefficient; the maximum of connecting strut lateral-force-load is mainly affected by the slope of the landing surface (SLS). (b) The acceleration-load is not a point that requires special attention for SFDR hard landing. (c) For control strategies, it is recommended to set the release height from seabed (RHFS) at 2–3 m, and to choose a smaller leg-opening-angle (LOA) based on the actual sea condition and seabed environment. (d) For the optimal design of the SFDR supporting system, it is advisable to increase the friction coefficient between the footpad and sediments by changing the structure and surface characteristics of the footpad, as well as to add a function of variable support area to the footpad.