Towards the Integration of Analysis and Design of Mooring Systems and Risers: Part II — Studies on a DICAS System

Abstract

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]. That paper describes a “basic” classic, uncoupled methodology, and 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 in the companion paper [1], and these issues are illustrated with studies applying some of the considered design methodologies to the P-18 semi-submersible platform in Campos basin. The present paper proceeds describing some hybrid methodologies that combine coupled and uncoupled analysis tools, and illustrates their application to a DICAS system for deepwater applications in Campos basin.

An integrated methodology for the design of mooring systems and risers

“…[10,11], even these refinements still involve several simplifications. They fail to completely represent the non-linear dynamic interaction between vessel and lines (including for instance the nonlinear behaviour of the damping of the lines that influence the LF motions of the vessel).…”

“…optimized time-domain methods including adaptive time-step variation [22e25], or frequency-domain methods [26e28]), the goal of obtaining a balance between accuracy and computational efficiency has also been sought by proposing "hybrid" analysis methodologies combining the use of coupled and uncoupled tools. Different procedures may be included into this classification [29,10,11,30,31]. In this work we will consider the "coupled motion analyses" [29,11,31] and the "semi-coupled analyses" [32] that will be described next.…”

Implicit domain decomposition methods for coupled analysis of offshore platforms

“…Recently, researchers have been acknowledging that the design of FPS should consider the fact that the moored system and the risers comprise a truly integrated system, that is, the overall behaviour of a floating system is dictated not only by the hydrodynamic behaviour of the hull, but also by its interaction with the hydrodynamic/structural behaviour of the lines [1][2][3][4][5][6][7][8][9][10]. Throughout the last decade, Petrobras (the Brazilian state oil company) have recognized this need of formulating and developing a computational system for the coupled numerical simulation of FPS.…”

“…For instance, Senra et al [1], Correa et al [2], Correa [12], and Senra [13] describe alternative design methodologies, in increasing order of complexity, considering different levels of integration between hull, mooring lines and risers.…”

Prescreening of Environmental Conditions for Prediction of Severe Operation Condition of Offshore Structures

“…Among these simplified analysis methods is the uncoupled analysis, e.g., Ormberg and Larsen(1998) showed that results from the uncoupled analysis have a reasonable degree of accuracy when considering current forces and low-frequency damping contributions from moorings and risers as additional loads on the platform. Correa et al (2002) proposed a numerical free decay test to estimate the equivalent inertia and damping coefficients used in the uncoupled method. The frequency-domain approach has also gained much attention as a practical method because of its computational efficiency.…”