Simulation model of a ship’s energy performance and transportation costs

Doktorsavhandling, 2020

Society faces a major challenge to reduce greenhouse gas emissions to limit the effects and propagation of climate change. As the main contributor to global trade, the shipping industry adds significantly to global greenhouse gas emissions and must actively work towards reducing, or eliminating, emissions in a short period.  This thesis contributes by developing a generic model for quick and accurate prediction of the fuel consumption of existing ships or newbuilds in operational conditions. The aim is to be able to predict the potential of fuel-saving measures, e.g., design features, retrofitting, alternative propulsion, and operational improvements, and evaluate the impact of such measures both, logistically and technically.

A novel energy systems model called “ShipCLEAN” was developed, which provides the opportunity to predict the propulsion power, fuel consumption, and daily costs and income of ships in realistic operational conditions, i.e., a wide variety of drafts, speeds, and environmental conditions. ShipCLEAN is a unique coupling of a generic power prediction model and a marine transport economics model. Aside from a calm-water power prediction based on empirical and standard series methods, the power prediction model includes simulating alternative propulsion methods (i.e., wind-assisted propulsion), respects all environmental loads acting on a ship at sea (e.g., wind, waves, current), is valid for multiple operational conditions (i.e., speed and draft of the ship), and balances the forces and moments in four degrees of freedom. Validation studies using five example ships (a container ship, a tanker, a cruise ferry, and two RoRo ships) show good agreement of the predicted propulsion power with both model tests in the design condition and full-scale measurements in variable operational conditions. A detailed uncertainty analysis provides an overview of how to further increase the prediction accuracy.

Special focus of the study is put on evaluating measures to decrease the emissions of ships through operational optimization, i.e., speed optimization, alternative propulsion concepts, and new design of zero-emission concepts. ShipCLEAN includes novel methods to evaluate the aerodynamic interaction effects of Flettner rotors on a ship (in between the rotors and between the rotors and the ship), to control the rpm of each rotor in an array on a ship and to evaluate the hydrodynamic forces acting on a ship sailing at a drift angle.

Results from application studies show that fuel savings of around 3% are achievable by optimizing the speed profile of a ship in operation. Wind-assisted propulsion shows the potential to save up to 30% of fuel if applied to a tanker on a Pacific Ocean trade. It is concluded that flexible power prediction models requiring limited input data help to identify and quantify potential fuel savings and to identify motivators for ship owners and operators to apply fuel-saving measures. Further, it is concluded that four degrees of freedom analysis and methods to respect aero- and hydrodynamic interaction effects are crucial to accurately predict the performance of wind-assisted propulsion.