M. Godjevac

Master thesis (2)

2 records found

Cooling system control of a fuel cell-powered inland container vessel

Master thesis (2024) - L.D. Vos (author) , Lindert van Biert (mentor) , M. Godjevac (mentor) , Peter de Vos (graduation committee member)

With fuel cells making their way into the maritime sector, cooling systems are becoming a more important aspect of ship design with regard to power saving. Because fuel cells generate heat at a lower temperature, they require a cooling system that is comparatively larger than that of conventional power trains. Ship cooling system research mainly focuses on the implementation of variable-speed pumps, with little research focusing on the control of cooling systems. For this reason, this research aims to examine the performance of different rule-based and optimisation-based control systems applied to the cooling system of a fuel cell-powered ship.

In this research, a cooling system based on the FPS Waal is modelled in Simulink using Simscape. The cooling system consists of two coolant pumps, two river water pumps, a three-way valve, and two heat exchangers that cool six fuel cell units.

Four rule-based control methods and three optimisation-based control methods were tested. Two rule-based control methods, standard rule and temperature difference, have a rule-set based on just temperature measurements. The other two, load-based flow and load-based pump, have an additional basic algorithm where the control system knows the current cooling system configuration. Two optimisation-based control methods, steady-state optimised and lookup, are based on steady-state operation, and current-state optimised is based on the current system state. The optimisation models used are Mixed Integer Quadratic Constrained Programs (MIQCP). The control methods are tested in three types of simulations. A constant heat load is used to compare temperature control, pump on/off cycles, and power consumption; a step load is used to compare temperature control, and scenario simulations are used to compare temperature control and power consumption.

Optimisation-based control methods perform better, with regard to temperature control, pump on/off cycles and cooling system power consumption, in constant load despite suffering from nonlinearities. With step load, the rule-based control methods have better temperature control because they have spare cooling capacity. In the scenario simulations, the optimisation-based control methods have significantly lower cooling system power consumption than rule-based control methods. Load-based flow has an average power consumption over the scenario simulations, which is 39.2% higher than the average power consumption of steady-state optimised. load-based pump, temperature difference, and standard rule perform significantly worse with 96.4%, 179.5%, and 197.0%, respectively. Current-state optimised only has a 0.85% higher average power consumption and lookup a 5.85% higher average power consumption.

While the overall performance of the optimisation-based control methods was superior, simplifications in the optimisation models resulted in steady-state errors in temperature control. Further research is required to implement optimisation-based control methods for cooling systems to reduce the errors from simplifications and take into account cooling system component degradation.

Analysis of risks related to maritime hydrogen-based propulsion solutions

Master thesis (2023) - G.W. Chen (author) , L. van Biert (mentor) , M. Godjevac (mentor)

The maritime sector is actively investigating new solutions for zero emissions in
response to climate change. One of the promising options is hydrogen-based propulsion, but there are currently no prescriptive rules or legislation to approve the design of such innovative, unproven technology. The International Maritime Organization (IMO) requires a quantitative risk assessment to demonstrate that the safety level of hydrogen-fueled vessels is equivalent to that of conventional-fueled vessels. To address this challenge, a risk-based design approach is needed, and the quantitative risk assessment process plays a crucial role in the early design stage.

This research contributes to the technical understanding and potential of zero-emission maritime hydrogen propulsion solutions, by designing a quantitative risk assessment system for analyzing and evaluating risks associated with this innovative technology. The developed risk-analysis system could be a useful tool for future development. While compressed hydrogen design has matured and undergone relevant risk studies, its low volumetric energy density limits its sailing distance. Liquid hydrogen provides a more energy-dense solution, enabling longer-distance sea-going missions, but its application in the maritime industry lacks related risk studies. Therefore, this study aims to design a quantitative risk assessment system for maritime liquid hydrogen propulsion that can analyze and evaluate risks adequately.

The methodology of this study includes a conceptual design of a liquid hydrogen-fueled vessel, followed by hazard identification and scenario selection. The Bayesian theory was used to assess the leak frequencies of components operating with liquid and gaseous hydrogen from published literature, with adjustments made for the harsh maritime environment and mechanical systems. Ignition probability models were proposed, and validated consequence models were used to simulate hazards. Risks are presented as individual and societal risks and compared to acceptance criteria to determine the acceptability of the design. Mitigation measures were proposed and examined. The study also compared the risks associated with liquid and compressed hydrogen configurations.

The conclusion of this study shows that the risks associated with maritime liquid hydrogen-based propulsion solutions can be acceptably managed with appropriate mitigation measures. Specifically, the results indicate that for the FPS Rijn vessel, the risks are acceptable for up to 20% of the operational time without any mitigation measures, as long as the liquid hydrogen system is located at least 45 meters away from crew rooms. However, with the implementation of mitigation measures, such as those proposed in this study, it is possible to operate the vessel 100% of the time with acceptable risks. Additionally, a comparison of liquid and compressed hydrogen designs demonstrate that liquid hydrogen designs have a similar risk level as compressed hydrogen designs but offer advantages in terms of space-saving and longer-distance characteristics, making them a promising candidate for maritime zero-emission propulsion solutions in the future.

Nonetheless, it is essential to validate the consequences and liquid hydrogen leak frequencies more rigorously, as limited information is currently available for this innovative technology. Overall, this research explores the risks of maritime hydrogen-fueled applications and challenges the perception of hydrogen as an impossible and dangerous substance.