The surge in interest surrounding autonomous vehicles has prompted extensive research in the maritime sector, specifically in the development of Maritime Autonomous Surface Ships (MASS). A crucial aspect of MASS functionality is the ability to navigate predefined sea routes, accounting for obstacles, water depth, and the ship's maneuverability.
The imperative nature of adhering to these routes becomes apparent in adverse weather conditions, where any deviation poses risks of collisions, contact, or grounding incidents. To address this, autonomous ships need robust mechanisms to resist deviations effectively.
Current methods for assessing the path-following performance of autonomous ships rely on simplified mathematical models, which fall short in capturing the intricate interactions between the ship's components. This limitation leads to inaccurate estimations of path-following capabilities.
In response to environmental concerns and the International Maritime Organization's call for reduced greenhouse gas emissions, the Marine Environment Protection Committee has issued guidelines to determine the minimum propulsion power necessary for maintaining ship maneuverability in adverse weather.
A multinational team, led by Assistant Professor Daejeong Kim from the National Korea Maritime & Ocean University, recently conducted a study on the path-following performance of MASS. Using a free-running Computational Fluid Dynamics (CFD) model combined with the Line-of-Sight (LOS) guidance system, the team focused on low speeds under adverse weather conditions.
"We employed a CFD model based on a fully nonlinear unsteady Reynolds-Averaged Navier-Stokes solver that can incorporate viscous and turbulent effects and the free surface resolution critical to path-following problems, enabling a better prediction of path-following performance," explains Dr. Kim.
The study, published in Ocean Engineering, utilized the CFD-based analysis of the popular KRISO container ship model with the autonomous LOS guidance system. Disturbances from bow, beam, and quartering sea waves were modeled as adverse weather conditions, with three different speeds studied to assess the impact on path-following performance.
Simulations unveiled oscillatory deviations in all cases. Notably, propulsion power mitigated deviations in bow and beam waves, but its effect was negligible in quartering waves. Heave and pitch responses were influenced by incident wave direction, with consistent roll amplitudes below 1.5 degrees in all cases. However, the study couldn't conclusively determine the effectiveness of increased speed on path-following performance.
Dr. Kim emphasizes, "The proposed CFD-based model can enhance the safety of autonomous marine navigation and provide low-cost alternatives to experiments or full-scale sea trials."
In conclusion, this study lays the groundwork for analyzing the path-following performance of MASS in adverse conditions at low speeds, contributing to the advancement of safer autonomous marine navigation.
