Ice Load Assessment for Jack-Up Units

摘要

Strengthened and efficient jack-up drilling units are considered viable for operations in shallow ice-infested waters with mild ice conditions because of their mobility which allows them to leave the site for a sheltered area when ice conditions warrant it. However, current recognized design standards and codes do not specifically address jack-ups in ice. One of the key ice-jack-up interaction scenarios is an ice floe impact on the legs. While this is addressed in some of the codes in general terms, no specific requirements are given regarding the effects of the structural deformation and dynamic effects (compliance of the structure). In this study, ISO 19906 was used as the primary standard to assess the ice loads. A spring-mass system was developed to model the interaction between the ice and jack-up during the impact event. The jack-up legs are modelled considering local and global stiffness. The effect of the ice crushing against the jack-up structure is modelled as a nonlinear spring. The ice floe collision event and the dynamic behaviour of the Jack-Up are solved using numerical solution in time domain. The effect of floe size, strength of ice and the ice drift speed on the ice loads are evaluated, and the effects of the stiffness of the jack-up legs on the ice impact load are compared with a rigid structure and with the level ice case.