Hydrodynamic Interaction of Ice Sheet and a Floating Platform

Abstract

Arctic is the one of the final frontiers in the field of oil and gas exploration. It is also a potential source of the vast amount of renewable energy using wind turbines and wave energy converters. Floating platforms hold certain advantages over fixed platforms for such harsh environment, as they allow disconnection and reconnection in the event of large icebergs or vast multi-year ice floes. They are also commercially attractive as they allow redeployment in other regions during the Arctic off-peak periods. However, such platforms will still need to encounter and withstand first-year level ice of varying sizes and from different directions. Such large ice floes will interfere with the hydrodynamic response of the floater. The hydrodynamic analysis of an isolated floater without accounting for the effect of the level ice is incomplete and may result in a un-conservative prediction of the floater’s response. The lack of any simple methodology to account for the effect of level ice on the hydrodynamic behavior of the floater is the motivation behind this study. This study aims to identify the most relevant parameters affecting the multi-body hydrodynamic behavior of level ice and a single floater. A standard semi-submersible represents the floater, and a range of geometric variations of the level ice simulates the varying nature of the ice environment encountered by the floaters in the Arctic. This study validates the hydrodynamic analysis procedure against model test on an ice floe and wave interaction. The calibration of the model test provides the damping coefficient required for the frequency domain, multi-body hydrodynamic model. This investigation varies the ice orientation and distance from the floater for a detailed parametric study employing the calibrated model. Current research finds that the presence of a comparably sized level ice floe near the floater significantly influences the hydrodynamic Response Amplitude Operator (RAO) of the floater. It can diminish the RAOs in some degree of freedom while enhancing the RAOs in other degree of freedoms. This study identifies the wave direction, ice floe distance, ice floe orientation as the most important parameters. Sway and pitch motion of the floater experienced the most enhancements due to the presence of level ice floe along the incoming wave direction. Additionally, this study proposes some initial upper bound values to account for the effect of level ice floes on the RAOs generated from a single body hydrodynamic analysis.