Optimization and Multi-Model Approaches for Maximizing Ship Decarbonization

Aligned with the International Maritime Organization's (IMO) aim to lower greenhouse gas emissions, the use of Wind-Assisted Ship Propulsion (WASP) in maritime transport is gaining increased attention. The study and optimization of WASP remain challenging due to complex physics and the high number of parameters involved. This includes interactions between aerodynamics, hydrodynamics, and structural dynamics, which require advanced multi-physics modeling. Additionally, numerous factors must be optimized, from design and control parameters to route selection, all within the variable maritime environment. Addressing these challenges demands multi-model approaches and multi-criteria optimization methods to maximize energy efficiency effectively. In this context, the laboratories of Ecole Navale, IFREMER, ENSM, and ENSTA Bretagne are collaborating on several research projects, with a selection of two thematic studies presented here.

The first study is carried out as part of the SHIVA and SAWASP projects, jointly led by Ecole Navale, IFREMER and ENSTA Bretagne. The goal of these projects is to optimize the hydrodynamic performance of innovative, fully electric, Vertical-Axis Propellers (VAPs) and their optimal use in conjunction with a wind-assisted ships. To achieve this, the SHIVA project implements a multi-criteria optimization of the propeller blade-pitching laws, utilizing multi-fidelity numerical and experimental surrogate models. These optimizations enable the determination of a set of optimal pitch laws for different operating points of the propeller. In the SAWASP project, a 6-meter wind-assisted ship equipped with VAPs is developed to study the optimal aerodynamic-hydrodynamic coupling. In particular, the energy gains from using VAPs as the main propulsion system, generating a lateral anti-drift force, are studied. The use of Reinforcement Learning (RL) methods to maintain optimal ship operation performance at sea, as an uncertain environment, is also part of this project.

The second study is conducted within the framework of the SOMOS project, jointly managed by ENSM and ENSTA Bretagne. The project's goal is to create and validate a set of numerical tools, that allow for rapid and precise assessment of the energy efficiency of wind-assisted ships. For the purposes of this study, a modular and comprehensive ship motion solver is formulated as an optimal control optimization problem, to evaluate, compare, and optimize energy performance. Such an approach is very complex to implement and, depending on the fidelity-level used, may require very high modeling costs. This is why most research efforts focus on specific aspects of the broader problem, often overlooking the coupling of maritime routing, ship motion analysis, and the optimization of control parameters along the planned sea route. The present work provides an innovative approach for the calculation of optimized trajectories for wind-assisted ship, by both considering the ship's maneuvering capabilities and the optimization of ship control and/or design parameters. In contrast to conventional routing methods, the proposed approach achieves high computational efficiency and relies on direct multiple shooting methods to determine optimal ship control parameters (RPM, rudder angle, etc.) and design variables (rotor Flettner or sail positioning, rudder area, etc.) along the sea route, satisfying the constraints of complying with the ship's equations of motion.