Response of nonlinear offshore spar platform under wave and current

Abstract

Several advanced floating structures have been proposed and developed with varying cost effectiveness and productiveness in deep water exploration. Among them, Spar platforms have been accepted as an efficient platform for the exploration. Many research works have been conducted on floating structure but a few on Spar platform. Nonlinear dynamic analysis of a 3D model of floating Spar platform structure is a resourceful tool to predict the responses, where the main body of the Spar hull and mooring lines are considered as an integrated coupled system. To define accurately the interaction between the Spar and mooring lines, coupled dynamic analysis was found to be appropriate for studying responses in the deep sea. Numerical simulation and motion analyses were carried out with the ABAQUS/AQUA. The responses of Spar platform were extracted and evaluated in time histories along with Response Amplitude Operator (RAO). The behaviours of coupled Spar platform have been investigated under real sea environments for increasing water depth to ultra-deep together with the load variability employing sea current for surge, heave, pitch and mooring tension responses. Motions show the consistency in the behaviour of Spar platform responses. Surge response indicates the static offset of the platform due to the static current force under wave plus current. The current force compresses oscillations and reduce heave and pitch magnitude. For larger water depth the platform responses reduce significantly due to the increased damping of mooring line.