Optimization of system of Oscillating Water Columns to mitigate pitch response of FPSO platforms submitted to head waves

Abstract

This work presents a novel method for reducing the pitch response of FPSO (Floating, Production, Storage and Offloading) platforms submitted to head waves. The method is based on installing a couple of moonpools, modeled as opened Oscillating Water Columns (OWC), on the vessel. According to detailed literature review, the effects of the vortex shedding can be represented through a nonlinear damping factor, which is proportional to the relative motion between the vessel and the water column within the moonpool.Optimization solvers are adopted to design the moonpools, using potential theory to calculate the vessel response with an iterative procedure to properly account for the nonlinear viscous damping factor related to the vortex shedding.The use of metaheuristic optimization method is discussed, with the choice of Particle Swarm Optimization. Different mono-objective functions are explored by weighing the minimization of the peak response and the area underneath the response curve. The importance of imposing restrictions on the modified vessels to avoid increasing heave motion is presented, using the penalty function also by weighing the peak response and the area. Results show the effectiveness of the procedures proposed in the study and indicate the possibility of expanding to implement it in other applications.