Steel Catenary Riser Design Based on Coupled Analysis Methodology

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.

Steel Catenary Riser Design Based on Prescribed Motions From Coupled Analysis Methodology

“…Those results are important to explain the difference between the offset obtained for the analyses performed in DEEPC and MIMOSA submitted to the extreme loading cases presented in [3]. Figures 7 and 8 show the comparative results for the vertical motions of the SCR top obtained from coupled and decoupled analyses when that riser was submitted to the same environmental loads.…”

“…It could be observed that the system considering all lines in DEEPC presents horizontal stiffness significantly higher than the one obtained from MIMOSA with mooring lines only, which resulted in smaller static offsets as shown in Figures 5 and 6. Other studies considering the same offshore floating system submitted to the extreme environmental loads are presented in [3]. • System Restoring Comparison: Important conclusions are also obtained with the comparison between the system restoring comparison of coupled model (DEEPC), considering all lines (riser + mooring) connected and the platform model without any lines connected.…”

“…Those comparisons presented here are the basis for the comparison of SCR Ultimate Limit State considering coupled and de-coupled models presented in [3].…”

Static and thermo-mechanical coupled analysis of turing tools based on ANSYS

“…In the equation (1) [6], A as the thermal conductivity of materials(w/m.k), q as heat flux(w/m 2 ) , T x -T 2 as the temperature difference between solid surfaces( °C ), q as physical distance between two surfaces (m), as the temperature gradient between surfaces.By the formula (1) , obtained: q = h(T l -T 2 )ld ■> known as A = 20.93 (tool material) [7], T X = 350 °C , T 2 = 20 °C , d = 0.03m > heat flux can be calculated as, q = 0.23w / mm 1 .…”