Optimising the propeller hull interaction of a parametric aft ship using optimisation algorithms

Abstract

The ongoing pursuit of efficiency in the shipping industry is driven by both economic and environmental objectives. While historically focused on reducing fuel consumption to enhance market competitiveness, recent regulations such as the International Maritime Organisation’s Energy Efficiency Design Index (EEDI) and Energy Efficiency Existing Index (EEXI) have emphasized the need to minimize harmful emissions. To achieve these goals, Simulation-Based Design (SBD) and Computational Fluid Dynamics (CFD) have become essential tools for optimizing ship design. This research aims to develop and implement an optimization strategy to minimize the propeller power required for a vessel to maintain a constant speed by refining the aftbody shape while accounting for propeller-hull interaction effects.

The study addresses a critical gap in current methodologies, where many existing optimization strategies neglect propeller effects and studies including propeller effects use too computationally intensive methods to be used in an optimisation strategy. The research explores strategies to reduce computational load, ensuring a balance between accuracy and efficiency. Key questions include determining the optimal geometrical parameters for aftbody design, refining CFD procedures to be computationally light yet accurate, incorporating propeller effects efficiently, and identifying the most effective optimization algorithm.

The research findings reveal that by varying specific geometrical parameters, such as the aft arc angle and transom angle, an approximately 10\% reduction in required propeller power can be achieved. The study also evaluates different strategies for reducing computational load, including a grid refinement study and the exclusion of free surface effects, while noting the trade-offs in accuracy. The use of the virtual disk method to model propeller effects is identified as the most practical approach given computational constraints. Among the optimization algorithms tested, the NSGA-III algorithm is found to be the most effective, offering significant improvements with fewer computational resources compared to alternatives.

Overall, the research demonstrates that the proposed optimization setup can lead to a significant reduction in propeller power, contributing to the development of more efficient ship designs. However, further research is needed to refine the exclusion and estimation of free surface effects to ensure broader applicability across different vessel designs.