Internal flow effect of a flexible riser system for a floating offshore wind turbine with on-board carbon dioxide capture

This paper designs a flexible riser for transporting carbon dioxide (CO2) off a floating offshore wind turbine (FOWT)-powered CO2 capture platform, and analyzes the internal flow-induced effects caused by the CO2 on the flexible riser. Internal effects on flexible risers due to the pressurized and internal dynamic flow are a well-studied problem in offshore oil and gas (O&G) applications, which typically requires the use of tools capable of representing their pressurized contents and flows. However, because the flow rates and pressure conditions expected from individual FOWT-CO2 capture platforms are much lower than those used in O&G installations, we studied the importance of internal flow effects on riser dynamics. To determine their relevance, we designed and modelled the flexible riser in OrcaFlex™ with different design pressure and flow conditions under normal and extreme environmental events. The results indicate that the riser's effective tension and curvature are not significantly affected by internal flow effects, but differences were observed in the von Mises stress arising from the shear stress, which is a purely hydrostatic term. As such, as long as the shear term is properly accounted for, these results enable future work to utilize simplified models for the flexible riser system, similar to models for dynamic power cables employed in FOWT farms. This simplification allows us to design and analyze the whole FOWT-CO2 system alternatively with lower fidelity and open-source offshore wind turbine simulation tools, like OpenFAST, without overlooking relevant riser-dynamics phenomena. •Analysis of the effect of internal flow on a flexible riser for offshore carbon dioxide sequestration.•Insignificant impacts on the effective tension and curvature, but not on the shear stress.•Results suggest that models that ignore internal flow effects could be utilized provided the shear stress is accounted for.•A similar analysis is performed transporting hydrogen instead – an important e-fuel in the green transition.•Same conclusions can be drawn for both the carbon dioxide and hydrogen cases.