Session: 02-06-02 Reliability of Mooring and Riser Systems 2

Paper Number: 79098

79098 - A Monte Carlo Approach for Fatigue Analysis of Mooring Lines Subjected to Simultaneous Environmental Actions 

Fatigue damage of mooring lines components is one of the main issues in the design and life extension monitoring of deepwater floating production units mooring systems.  Floating units operating at several ocean regions, as in the Brazilian southeast coast and Africa west coast, are almost permanently subjected to wind-sea waves and remote waves (swell), besides wind and maritime current actions.  Fatigue assessment of mooring systems operating under these environmental conditions shall consider an extensive number of simultaneous environmental action load cases or rely on some simplification of the load cases.  In the first case, the fatigue assessment may require a large amount of computer resources and time, making it unfeasible, for example, in the early phases of the mooring system design, where normally the analysis of several configurations is necessary. In the second case, some important aspects of the actual behavior of the environmental actions may not be considered in the fatigue analyses.

This paper presents a new engineering approach for the fatigue assessment of mooring systems based on a Monte Carlo Simulation resampling using a set of simultaneous environmental conditions available in a database, sampled every 3 hours for several years. Studies show that damage estimates considering just a few resampled cases, say 5 to 10% of the cases in the database, compare very well to estimates considering the entire database.  A second approach, also presented in the paper, is based on the Monte Carlo Simulation sampling of environmental conditions from a joint distribution fitted to the environmental parameters database. Finally, the paper also presents how to estimate confidence intervals of the fatigue damage estimates.    

Presenting Author: Paulo Videiro Federal University of Rio de Janeiro

Authors:

Pedro Seabra PETROBRAS S.A.
Mauro Oliveira PETROBRAS S.A.
Marina Simão Federal University of Rio de Janeiro
Paulo Videiro Federal University of Rio de Janeiro
Luis Sagrilo Federal University of Rio de Janeiro