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The objective of this paper is to study different analysis methodologies for the design of floating production systems. The main issues are the use of uncoupled and coupled analysis methods, and the integration in the analysis and design of the mooring system and the risers. This paper is a companion to another paper also presented in the OMAE2002 Conference [1] The present paper begins describing a “basic” classic, uncoupled methodology, and proceeds with comments on some refinements in the representation of the behavior of the lines in the motion analysis of the vessel. Comments regarding the introduction of some level of integration between mooring line and riser behavior are also presented. These issues are illustrated with studies applying some of the considered design methodologies to the P-18 semi-submersible platform in Campos basin. The companion paper [1] proceeds describing a fully coupled methodology, and some hybrid methodologies that combine coupled and uncoupled analysis tools, and illustrates their application to a DICAS system for deepwater applications in Campos basin.

SUMMARYThis 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.

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In recent years, the design procedures of risers and mooring system for floating production systems (FPS) have had more feedback. In this way mooring and risers designers can identify, even in an early stage, the constraints imposed by one system over the other. This work presents an evaluation of the crossing of the information obtained from the analyses of risers and mooring system. Different riser and mooring analysis procedures are applied to a typical FPS for deep water applications. First, failure zones of the riser system are identified, so a safe operating limit zone can be defined. Then, the excursions of the platform are calculated taking into account the global response of the coupled system (hull, mooring lines and risers). Finally, the results are crossed in order to verify if the excursions of the platform are within the safe operating area. The evaluation presented here shows the important of correctly defining the safe operational zones and how the crossing of information can be conservative or not within the design process of mooring lines and risers.