불규칙 내부유동에 의한 Riser VIV단기 피로 평가

Abstract

In delivering the fluids from seabed to the available topside structure any offshore development, the integral parts of such system are the pipelines on the seabed and the risers. Since the offshore development is moving towards deep water, the floating production systems are required. As the production system has been changed from fixed to floater, the connection system between seabeds to topside such as the riser should be accommodated in conjunction with the floater’s movement. Therefore, the variable riser systems have been developed to satisfy system integrity and economical advantage. As a result, the deep water development, with floating production systems, is complex and taken into account many design parameters. The riser system, in connection with the floating production system, should verify strength and fatigue capacity according to various sources such as riser installation, vortex induced vibration (VIV) of riser and floater motion. The variables that affect the design sources of riser systems are environment, soil interaction and internal fluid characteristics. Although many design variables have been defined and developed for riser design over the decades, design challenges of riser system, which are soil interaction, the effect of variety internal flow condition representatively, still remain. Therefore, many research have been developed in regards to those items. The objective of this research was to verify the effect of the non-uniform flow to riser VIV analysis. Non-uniform flow condition is expected in every production riser during the production of hydrocarbons in deep water. Previously, the non-uniform flow was proven to be ineffective to the dynamics of a riser in shallow water. However, in deep water depth, the non-uniform flow could affect the riser’s characteristic in dynamic and VIV performance. Therefore, production riser design for both steel catenary riser (SCR) and wave lazy riser (LWR) as the considered and represented riser types, was investigated in various partial content locations and coverage for VIV fatigue damage in the study. This study showed that the partial content location is effective on the riser response at the critical location such the hog bend area for lazy wave riser, but neglected for steel catenary riser. In the present riser design, the un-uniform internal flow was not considered for production riser design. However, since the non-uniform flow could obviously affect riser VIV fatigue performance as proven in this study, thus this study would like to be the initial point to apply the non-uniform flow in the riser analysis in stimulating further research.