Session: 16-10-01 Marine Hydrodynamics and Subsea Technology

Submission Number: 182312

Full-Scale CFD Investigation and Net Power Savings Methodology for AIs on Tankers 

The maritime industry, driven by stringent regulations like the Energy Efficiency Existing Ship Index (EEXI) proposed by IMO, is focused on achieving decarbonization goals. The Air Lubrication System (ALS), specifically the Air Layer Drag Reduction (ALDR) method, is a key technology for reducing ship resistance and fuel consumption. As a viable solution for existing hulls (without requiring major retrofit), this study details a comprehensive numerical investigation primarily focused on two distinct tanker classes (Suezmax and Aframax) and proposes a robust methodology to determine the net power savings accurately. Full-scale Computational Fluid Dynamics (CFD) were performed, utilizing VOF to modeling the air injection on the bottom and to capture the complex multiphase flow dynamics. Additionally, an extensive discussion regarding the prism layer and the dimensionless wall distance (y+) was included, given their critical relevance to accurately modeling the near-wall viscous flow and the air-water mixture. This precise modeling is essential to properly capture the physical phenomenon and accurately compute the shear force reduction on the hull. A detailed matrix of ten operational conditions was analyzed for each ship, comprising five speeds and two loading scenarios (fully loaded and ballast). A comprehensive verification process was conducted to assess the numerical uncertainty, ensuring the confidence interval of the computed results aligns with the target gain magnitude of the ALS technology. Furthermore, The computational model was rigorously validated against extrapolated experimental data obtained from model basin tests for the naked hull, demonstrating minimal discrepancies (below 3%). This high level of adherence confirms the computational approach's reliability. The ALS computations were also validated by comparing the frictional resistance reduction measured via virtual sensors distributed across the hull with experimental data obtained from a similar scheme found in the literature, providing a strong foundation for the forces computed. The ALS proved highly effective in reducing total resistance, particularly in the ballast condition (up to 32% gross saving at 10 knots) and showing notable gains in the loaded condition (up to 18.5%). This reduction stems primarily from the attenuation of frictional resistance, with a secondary beneficial effect on viscous pressure resistance (form resistance). While the net power savings were significant in the ballast condition (ranging from 2 to 5%), the loaded condition showed predominantly negative net savings due to high compressor power demand. The methodology developed in this research to calculate these net gains represents a contribution to address the current literature gap.

Presenting Author: Maria Eduarda Chame Numerical Offshore tank - University of Sao Paulo

Presenting Author Biography: Maria Chame earned her Master's degree in Naval Engineering in 2019, subsequently completing her Doctoral degree in 2024, both from the University of São Paulo. During her Master's, she studied \gls{viv} and CFD Verification and Validation (\gls{vv}) of hydrodynamic problems in collaboration with the Maritime Institute of Netherlands (MARIN) and the University of Tokyo. During the PhD, she participated in an exchange program with the Norwegian University of Science and Technology (NTNU). Her research relies on computational fluid dynamics using the open-source code OpenFOAM, new energy devices, and ship maneuverability. Recently, she was nominated as a member of the ITTC Wind Propulsion Committee (2024-2027).

Authors:

Maria Eduarda Chame Numerical Offshore tank - University of Sao Paulo
Ferdinando Ribeiro Freire Numerical Offshore tank - University of Sao Paulo
Claudio Mueller Prado Sampaio Numerical Offshore tank - University of Sao Paulo
Eduardo Aoun Tannuri Numerical Offshore tank - University of Sao Paulo