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Steel Catenary Riser Design Based on Coupled Analysis Methodology

[+] Author Affiliations
Marcos V. Rodrigues, Rodrigo A. Bahiense, Celso V. Raposo

Det Norske Veritas, Rio de Janeiro, RJ, Brazil

Oddrun Steinkjer

Det Norske Veritas, Ho̸vik, Norway

Paper No. OMAE2008-57365, pp. 289-300; 12 pages
doi:10.1115/OMAE2008-57365
From:
  • ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering
  • Volume 3: Pipeline and Riser Technology; Ocean Space Utilization
  • Estoril, Portugal, June 15–20, 2008
  • Conference Sponsors: Ocean, Offshore and Arctic Engineering Division
  • ISBN: 978-0-7918-4820-3 | eISBN: 0-7918-3821-8
  • Copyright © 2008 by ASME

abstract

In a riser design, the traditionally assessment adopted by industry for attainment of platform motions applied to the top of riser consists in the use of de-coupled methodologies. These formulations consider the static environmental loads over the platform (current and wind) through a static offset and the dynamic environmental loads due to wave through imposition of top riser displacement calculated from cross spectral response of sea spectrum and vessel’s RAOs (Response Amplitude Operators). Nowadays due to shift of oil and gas exploitation to deeper waters more accurate methodologies, based on coupled analysis, have been introduced. The coupled analysis considers the interaction between the hydrodynamic behavior of the hull and the structural behavior of mooring lines and risers submitted to environmental loads. For deep waters the coupling effects of lines over platform motions are especially significant and a reduction of the amplification of platform motions if compared to the platform motions obtained from de-coupled analysis is observed. This paper presents a typical Steel Catenary Riser design, connected to a semi-submersible platform, where the motions applied to the top of riser are obtained from the “traditional” way (de-coupled) and from the coupled analysis. Numerical application is presented in order to assess the comparison of the two presented methods in terms of SCR analysis results and to confirm the reduction of platform motions due to coupling effects. The coupled model here studied is composed of approximately 80 lines connected to the platform which requires an excessive computational effort. In order to reduce the computational time some additional studies are performed considering the variation of line mesh discretization and time step size. The objective of this study is the adoption of an optimized model where the required accuracy is achieved and the computational time consuming is the minimum possible. The computational time consuming and platform motions are also presented. The conclusion of this work is that coupled analysis should be adopted by industry as usual practice of SCR design in deep waters, where more realistic and optimum results are presented, without an excessive computational effort.

Copyright © 2008 by ASME

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