March 6 - 8, 2017 | Berlin
LEADING ENGINEERING SIMULATION CONFERENCE
Offshore drilling is commonly performed with a top-tensioned drilling riser system. Operational uptime of the system is estimated through a global riser analysis, with input of hydrodynamic coefficients assumed by treating riser joints as circular cylinders. This is not accurate because the system consists mainly of buoyant riser joints with complex cross-sections. Buoyant joints have a generally circular shape but also have MUX recesses and stacking flats forming its outer profile. These surface features change its flow behaviour and hydrodynamic performance. This work aims to define more accurate hydrodynamic coefficients for the buoyant joint.
A two-dimensional approach is selected as it achieves sufficient result accuracy and accommodates quick global analysis turnaround requirements. Model validation is based on flow past a cylinder for Reynolds number of up to 1,000,000 in transient conditions. Following this, the detailed buoyant joint cross-sectional representations are created. The average drag force is determined by subjecting the components to various flow attack angles across the 360 degrees range. From the averaged drag forces, Re-dependent hydrodynamic coefficients are calculated and variations in vortex shedding behaviour observed.
Validation results show good agreement with literature in terms of hydrodynamic coefficients, separation point location and Strouhal number. Variation of the buoyant joint outer profile and flow attack angle show variation in the drag and lift forces as well as the vortex shedding behaviour. More accurate hydrodynamic coefficients were produced for the various components which will result in more representative riser loads in the connected global riser analysis. The benefit is potentially increasing drilling operations uptime, and accurately calculating fatigue life. Ultimately, this enables drilling operators and their stakeholders to make better-informed decisions on their offshore operations.
Keywords: Cylinder drag, vortex-induced vibration, offshore drilling riser