Session: 06-11-01 Ocean Engineering Technology

Submission Number: 156285

A Method for Computing the Equilibrium Heading of Turret-Moored Platforms With Validation Using Real Data 

Turret-moored vessels are characterized by allowing free rotation around the turret, independently of it being mounted internally or externally, according to the exposed environmental conditions. Such weathervane behavior significantly reduces the general motion experienced on the platform and even the impact of greenwater on the deck, as the heading follows the prevailing environment; generally leading to an increase in operational weather window for offloading, better crew comfort and production plant uptime. Nonetheless, although the effect of the incoming environmental condition on the platform heading is well-known, the exact equilibrium heading angle is not so simple to calculate.

For large FPSOs/FSOs/FSRUs/FLNGs using turret mooring systems, incorrect assumptions about the platform heading can lead to significant maneuvering time and fuel costs, or, in worst-case scenarios, loss of an entire offloading or transfer operation. A method to predict the equilibrium heading—days in advance based on weather forecasts—could enhance logistical efficiency for Platform Supply Vessels (PSVs) and helicopter operations for cargo and personnel transfers. This study presents a novel approach to compute the equilibrium heading for a turret-moored vessel based on specific environmental inputs.

The environmental factors considered include wind, current, and wave actions, which are typical for deepwater locations where turret mooring is employed. Hydrodynamic coefficients for wind and current forces are obtained through wind tunnel or towing tests or via Computational Fluid Dynamics (CFD) simulations, while wave effects are estimated using wave basin tests or numerical methods like the panel method. With these hydrodynamic parameters defined, environmental inputs can be converted into forces and moments on the vessel, allowing the equilibrium heading and corresponding motion to be computed.

To validate this approach, real data from a Brazilian turret-moored platform was used, highlighting key comparisons between the predicted and observed heading angle. Dynamic simulations further illustrate specific cases, demonstrating the method’s strengths and limitations. These findings provide a basis for improved operational planning and safety in turret-moored platforms operating in variable environmental conditions.

Presenting Author: Asdrubal Do Nascimento Queiroz Filho University of São Paulo / Numerical Offshore Tank Laboratory (TPN-USP)

Presenting Author Biography: Undergraduated in Electrical Engineering, yet has always admired fishing boats since childhood, which lead to pursuing his dreams to work in Naval and Ocean Engineering afterwards. Impressed with Amyr Klink's nautical achievements, along with the inspiring words of the renowned British Admiral Horatio Nelson: "I cannot command winds and weather"; nowadays works in developing and improving a maritime simulator with applications such as Dynamic Positioning control algorithms. After being exposed to the fictional Science in the Marvel movies, specially the Iron Man franchise (which my daughters are huge fans), started to explore Machine Learning techniques applied to Offshore problems.