Implicit domain decomposition methods for coupled analysis of offshore platforms

Abstract

This work presents the implementation of optimized numerical tools for the coupled analysis of floating platforms for offshore oil exploitation. The focus is on time-domain, nonlinear dynamic analysis, considering the coupling between the hydrodynamic behaviour of the hull and the structural behaviour of the mooring lines and risers modelled by finite elements (FEs). Some aspects of the formulation and solution of the large-amplitude equations of motion of the hull of the platform are presented, including a brief description of the hydrodynamic models and calculation of the environmental forces. The main aspects of the formulation for the spatial and time discretization of the structural model for the lines are also discussed. Since coupled analyses may require excessive computational costs, the objective of this work is to present the implementation and application of domain decomposition methods, adapted and specialized for the problem at hand, in order to optimize the efficiency of the computational tool. Two groups of domain decomposition methods are considered: the first is a subcycling technique that takes into account the natural partition that exists between the hull and the lines; the second considers the internal decomposition of the mesh of FEs to represent the mooring lines and risers. The methods are devised having in mind their implementation in computers with parallel architecture. Results of a numerical application are presented in order to assess the performance of the methods.