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The Supercritical Carbon Dioxide Brayton Cycle (sCO2-BC) is a highly efficient and eco-friendly alternative for marine propulsion. The adoption of sCO2-BC aligns with the industry's focus on sustainability and can help meet emission regulations. In this context, the current study introduces a cascade system that harnesses the exhaust gases from a marine Gas Turbine Propulsion System to serve as a heat source for a bottoming Supercritical Carbon Dioxide Brayton Cycle (sCO2-BC), which facilitates an onboard heat recovery system. The investigation primarily focuses on the recompression cycle layouts of the sCO2-BC. To assess the performance of the bottoming cycle layouts and the overall cascade system, various parameters of the recompression sCO2-BC are analyzed. These parameters include the mass flow rate of CO2 in the bottoming cycle and the effectiveness of both the low-temperature recuperator (LTR) and the high-temperature recuperator (HTR). For conducting the cycle simulations, two codes are built and integrated; this first code models the thermodynamic cycle, while the second code models the recuperators. The research shows that incorporating the sCO2 Brayton Cycle as a bottoming cycle has the potential to greatly improve the efficiency of the entire system, increasing it from 54% to 59%. Therefore, it provides a useful framework for advancing energy-efficient gas turbine systems and future research. [ABSTRACT FROM AUTHOR]

Using the efficient, space-saving, and flexible supercritical carbon dioxide (sCO2) Brayton cycle is a promising approach for improving the performance of nuclear-powered ships. The purpose of this paper is to design and compare sCO2 cycle power systems suitable for nuclear-powered ships. Considering the characteristics of nuclear-powered ships, this paper uses different indicators to comprehensively evaluate the efficiency, cost, volume, and partial load performance of several nuclear-powered sCO2 cycles. Four load-following strategies are also designed and compared. The results show that the partial cooling cycle is most suitable for nuclear-powered ships because it offers both high thermal efficiency and low volume and cost, and can maintain relatively high thermal efficiency at partial loads. Additionally, the new load-following strategy that adjusts the turbine speed can keep the compressor away from the surge line, making the cycle more flexible and efficient compared to traditional inventory and turbine bypass strategies. [ABSTRACT FROM AUTHOR]

Abstract This paper proposes a dependent optimisation (DO) method for the dual‐contra‐rotating motor to improve the full‐cycle efficiency and increase the space utilizstion rate of the autonomous underwater vehicle (AUV). Particularly, using the DO not only improves the efficiency of the machine at low speed and high speed, but also reduces its total weight by 6.2%, which is beneficial to the heavy‐buoyancy matching and range improvement of the AUV. Moreover, the dependent optimized machine can leave about 5.5 L more space for other AUV systems. Firstly, the geometric constraints and the load characteristics of the dual‐contra‐rotating motor are presented. Based on the analytical model of the electromagnetic field and electromagnetic performance, this paper compares two analytical optimization methods for the machine. One is the independent optimization, that is, the geometric association between the dual‐contra‐rotating motors and the AUV is not considered in the optimization process. The other is DO, which considers the geometric association in the optimization process. After verifying the electromagnetic performance and temperature field with the FEA method, the dual‐contra‐rotating motor prototype was developed. Finally, the consistency of the optimization results and the prototype is verified through experiments.

The interaction between ship propulsion machinery, propellers and the highly dynamic environment which is the sea is a complex yet highly relevant subject. During a storm, for example, waves and ship motions may cause the propeller to draw air, or ventilate, resulting in rapid changes in propeller thrust and load torque. These fluctuations propagate through the propulsion system, potentially causing excessive loads on propulsion machinery, while also reducing the ship's manoeuvrability. A profound understanding of these complex interactions still lacks. One result of this knowledge gap is the limited acceptance of new technologies for ship propulsion, especially those technologies known to have limited transient capabilities. In this paper, hardware in the loop (HIL) is proposed as a solution to this knowledge gap. Paying specific attention to propeller ventilation, HIL is used to identify new aspects of interaction between engine and propeller, thus demonstrating the added value of HIL for ventilation studies. [ABSTRACT FROM AUTHOR]

This paper proposes a dependent optimisation (DO) method for the dual‐contra‐rotating motor to improve the full‐cycle efficiency and increase the space utilizstion rate of the autonomous underwater vehicle (AUV). Particularly, using the DO not only improves the efficiency of the machine at low speed and high speed, but also reduces its total weight by 6.2%, which is beneficial to the heavy‐buoyancy matching and range improvement of the AUV. Moreover, the dependent optimized machine can leave about 5.5 L more space for other AUV systems. Firstly, the geometric constraints and the load characteristics of the dual‐contra‐rotating motor are presented. Based on the analytical model of the electromagnetic field and electromagnetic performance, this paper compares two analytical optimization methods for the machine. One is the independent optimization, that is, the geometric association between the dual‐contra‐rotating motors and the AUV is not considered in the optimization process. The other is DO, which considers the geometric association in the optimization process. After verifying the electromagnetic performance and temperature field with the FEA method, the dual‐contra‐rotating motor prototype was developed. Finally, the consistency of the optimization results and the prototype is verified through experiments. [ABSTRACT FROM AUTHOR]

This paper presents thermodynamic (energy and exergy) analysis and comparison of two diff erent marine propulsion steam turbines based on their operating parameters from exploitation. The fi rst turbine did not possess steam reheating and had only two cylinders (high-pressure and low-pressure cylinders), while the second turbine possesses steam reheating and has one additional cylinder (intermediate-pressure cylinder). In the literature at the moment, there cannot be found a direct and exact comparison of these two marine steam turbines and their cylinders based on real exploitation conditions. Along with energy and exergy analyses, the research it is investigated the sensitivity of exergy parameters to the ambient temperature change for both turbines and each cylinder. It is also presented the infl uence of the steam reheating process on the energy and exergy effi ciency of the entire power plant. For both observed turbines and their cylinders it is valid that relative losses and effi ciencies (both energy and exergy) are reverse proportional. The operation of an intermediate pressure cylinder from a steam turbine with reheating is the closest to optimal. Due to the diff erent origins of losses considered in energy and exergy analyses, each analysis detects diff erent turbine cylinders as the most problematic ones. The steam reheating process decreases losses and increases effi ciencies (both energy of each turbine cylinder and the whole turbine. The whole turbine with reheating has an energy effi ciency equal to 81.46% and an exergy effi ciency equal to 86.48%, while the whole turbine without reheating has energy and exergy effi ciencies equal to 76.47% and 80.94%, respectively. Exergy parameters of a steam turbine without reheating as well as its cylinders are much more infl uenced by the ambient temperature change in comparison to the steam turbine with reheating and its cylinders. The steam reheating process will increase the effi ciency of the whole power plant in real exploitation conditions between 10% and 12%. [ABSTRACT FROM AUTHOR]

According to the International Maritime Organization (IMO)'s Greenhouse Gas (GHG) strategy whose aim is to reduce the shipping industry's total carbon emissions by 50% by the year 2050, it is desirable to increase ships energy efficiency to reduce GHG emissions and fuel costs. To do so, a short-term measure is to develop innovative engine control strategies in waves that will reduce ship's GHG emissions. In this study, a mathematical model is developed to assess two engine control strategies: the standard constant rotational speed mode and an innovative constant fuel rack approach. The coupled model is made of a mean value engine, propeller curves and a ship behavior simulator. Emphasis is placed on the presentation of the engine model and references are given for further details on the ship simulator. After verifying the coupling between the engine model and the ship simulator, the fuel consumption is compared, for the two strategies, at the same average speed and for three head regular waves. This paper presents the basics of a further long time research project and shows that coupling ship simulators with engine simulators leads to promising simulation tools for a ship's GHG emissions reduction. Results from a first application case show that the constant fuel rack approach reduces fuel consumption (up to 1.6%). [ABSTRACT FROM AUTHOR]

The scientific aim of this paper is to analyse the topicality of the turbocharger explosions and to attempt to answer the question of whether some technical characteristics of the engine can be perceived as directly connected with the risk of the turbocharger explosion. Moreover, our objective was also to calculate the turbocharger explosion probability. This article presents the results of a quantitative and qualitative analysis of 42 explosions of marine main engine turbochargers occurring between 1977 and 2022. The number of explosions was analysed, and the average and instantaneous frequencies of turbocharger explosions each year were determined. An analysis was performed of the number of explosions with respect to the age and type of ship on which the accident occurred. An analysis of the contribution of different types of main engine to the studied population of explosions was also carried out. Criteria such as the number of strokes, engine speed, type of crank-piston mechanism, cylinder arrangement, engine power per cylinder, and number of cylinders were considered. An analysis was carried out of the disasters that had occurred, considering the contribution of the various engine manufacturers. An integrated distribution of the number of turbocharger explosions by year was presented, considering the engine speed, the maximum continuous rating of the engine, and the engine design. The analysis did not indicate a significant correlation between the type of ship and the number of explosions that occurred. More than half of the analysed population of explosions (median) occurred on vessels no older than 15 years. It is highly likely that engine type does not directly affect the number of turbocharger explosions and the risk of explosions. On the other hand, it is not possible to exclude the influence of the individual characteristics of an engine built to a particular manufacturer's design on the magnitude of the risk of a turbocharger exploding during engine operation. Considering the number of ships worldwide, the probability of an explosion in a given year on a given ship is not less than 1.61 × 10−7. [ABSTRACT FROM AUTHOR]

Abstract Ship motions affect the propulsion system, which causes fluctuations in the power system. Mutually, the power system variations impact the ship velocity by generating speed changes in the propeller. Therefore, interconnecting the ship hydrodynamic and power system has paramount importance in designing and analysing an all‐electric ship (AES). The lack of an integrated model that can be evaluated in various operating conditions, such as manoeuvring, is evident. This paper explores the required perceptions for the power system and hydrodynamic analysis of an AES. Then, an integrated theoretical model comprising both the ship motion and power system is proposed. In addition to providing an accurate model for the ship in varying situations, this study demonstrates that the ship speed estimation during a ship route change differs from when the interconnections are overlooked. In the light of this determination, a straightforward enhancement for the ship speed control system is proposed. The effects of this modification on the ship power system are explored using the proposed model. The developed model is examined in different scenarios, and its advantages are discussed. It is shown that this model is suitable for employing in the model‐based design of AESs.

Climate protection goals and the transformation of the mobility sector are pushing the shipping industry to develop new propulsion systems emitting fewer or no greenhouse gases. One promising approach to eliminate greenhouse gas emissions from ships is a hybrid propulsion system powered by fuel cells and batteries. A high-temperature solid oxide fuel cell (SOFC) can supply heat and the electrical power demand in combination with a battery. Due to the low dynamic performance of the SOFC when faced with sudden load changes, a battery is responsible for providing the power for the dynamic load components. To ensure the resource-efficient operation of the propulsion components, intelligent energy management methods are required for power distribution control. Implementing a machine-learning-based energy management method based on twin-delayed deep deterministic policy gradient (TD3) improves the overall system efficiency, lifetime, and fuel economy compared to conventional energy management methods. To verify the technical feasibility of the propulsion system including its controls, the system is tested in a hardware-in-the-loop (HIL) environment. By implementing the TD3-based algorithm within the energy management used on the test bench, hydrogen consumption was reduced by approximately 10% and the remaining battery capacity after five years was 6% higher in comparison to conventional energy management methods. [Display omitted] • Hybrid electric propulsion system for a marine application. • Development of machine-learning-based energy management algorithms. • Validation measurements with propulsion components. • Assessment of the economic performance for a large cruise ship application. [ABSTRACT FROM AUTHOR]

To promote fuel-efficient and safe marine propulsion, hybrid power and propulsion systems are proven to be a promising alternative to conventional mechanical propulsions. This paper proposes an optimization framework for the power management of hybrid propulsion systems based on a novel combinator surface approach, which enables the most fuel-efficient operation with safety considerations against overloading and propeller cavitation. Four ship operational modes including mechanical propulsion, Power Take-in (PTI), Power Take-off (PTO), and Boost mode are comprehensively considered. The developed optimal power management presents significant efficiency advantages, reliability, and flexibility compared to the conventional method such as the combinator curve. It also enables comparisons of propulsion efficiency, cavitation, and overloading risks among different operational modes. Moreover, the proposed controller facilitates the intuitive design of acceleration paths by a trade-off between fuel efficiency and acceleration time. For validation and benchmarking, a real operation case study is performed on a line-fishing vessel equipped with a controllable-pitch propeller (CPP). The results show that the PTO mode is not always beneficial compared to mechanical propulsion, and the gear ratio selection plays an important role in determining propulsion fuel efficiency and operation safety. Also, the acceleration path that reduces the acceleration time results in increased fuel consumption. • A new combinator surface optimization method for efficient hybrid ship propulsion. • The new method reduces risks of cavitation and overloading for ship operations. • Comprehensive comparison of pros and cons for different modes and gear ratios. • Intuitive guideline for mode selection based on operating conditions. [ABSTRACT FROM AUTHOR]

Ship motions affect the propulsion system, which causes fluctuations in the power system. Mutually, the power system variations impact the ship velocity by generating speed changes in the propeller. Therefore, interconnecting the ship hydrodynamic and power system has paramount importance in designing and analysing an all‐electric ship (AES). The lack of an integrated model that can be evaluated in various operating conditions, such as manoeuvring, is evident. This paper explores the required perceptions for the power system and hydrodynamic analysis of an AES. Then, an integrated theoretical model comprising both the ship motion and power system is proposed. In addition to providing an accurate model for the ship in varying situations, this study demonstrates that the ship speed estimation during a ship route change differs from when the interconnections are overlooked. In the light of this determination, a straightforward enhancement for the ship speed control system is proposed. The effects of this modification on the ship power system are explored using the proposed model. The developed model is examined in different scenarios, and its advantages are discussed. It is shown that this model is suitable for employing in the model‐based design of AESs. [ABSTRACT FROM AUTHOR]

The importance of mathematical and numerical simulation in marine engineering is growing together with the complexity of the designed systems. In general, simulation a makes it possible to improve the engineering design, reducing working time and costs of production as well. In this respect, the implementation of a simulation model for cycloidal propellers is presented. Cycloidal thrusters are being increasingly used in marine applications. Their best performance concerns low-speed applications, due to their ability to steer thrust in any direction. The proposed simulator is able to assess the performance of cycloidal propellers in terms of the generated thrust and torque, without resorting to consuming and demanding computational tools, such as CFD methods. This feature makes the presented model particularly suitable for the simulation in the time domain of the maneuverability of surface units, equipped with cycloidal propellers. In this regard, after embodying the implemented model in an already existing simulation platform for maneuverability, we show the most significant outputs concerning some simulated maneuvers, performed at cruise speed. [ABSTRACT FROM AUTHOR]

The scientific aim of this paper is to analyse the topicality of the turbocharger explosions and to attempt to answer the question of whether some technical characteristics of the engine can be perceived as directly connected with the risk of the turbocharger explosion. Moreover, our objective was also to calculate the turbocharger explosion probability. This article presents the results of a quantitative and qualitative analysis of 42 explosions of marine main engine turbochargers occurring between 1977 and 2022. The number of explosions was analysed, and the average and instantaneous frequencies of turbocharger explosions each year were determined. An analysis was performed of the number of explosions with respect to the age and type of ship on which the accident occurred. An analysis of the contribution of different types of main engine to the studied population of explosions was also carried out. Criteria such as the number of strokes, engine speed, type of crank-piston mechanism, cylinder arrangement, engine power per cylinder, and number of cylinders were considered. An analysis was carried out of the disasters that had occurred, considering the contribution of the various engine manufacturers. An integrated distribution of the number of turbocharger explosions by year was presented, considering the engine speed, the maximum continuous rating of the engine, and the engine design. The analysis did not indicate a significant correlation between the type of ship and the number of explosions that occurred. More than half of the analysed population of explosions (median) occurred on vessels no older than 15 years. It is highly likely that engine type does not directly affect the number of turbocharger explosions and the risk of explosions. On the other hand, it is not possible to exclude the influence of the individual characteristics of an engine built to a particular manufacturer’s design on the magnitude of the risk of a turbocharger exploding during engine operation. Considering the number of ships worldwide, the probability of an explosion in a given year on a given ship is not less than 1.61 × 10−7.

The hydrodynamic analysis of flapping foil inspired by the thunniform fish propulsion is carried out numerically. The hydrodynamic performances of 2D and 3D rigid oscillating foils are analysed for a range of Strouhal numbers (St). The performance parameters such as thrust coefficient, power coefficient and hydrodynamic efficiency are obtained in both open water and behind ship conditions, where the wake effect of the ship influences the hydrodynamic performance parameters of the foil. Thrust and efficiency variations with Strouhal number are estimated and it is found that the efficiency reaches maximum at St = 0.3. [ABSTRACT FROM AUTHOR]

A nuclear submarine has significant performance advantages over the conventional dieselelectric submarine. Its powerful nuclear propulsion can be operated independently of air and does not require refueling throughout the 25-year life span. Recent progresses of medium voltage direct current (MVDC) techniques applied in industry push the energy-saving and extremely long-time operation to a new stage with a feasible solution of smaller scale nuclear reactor embedded inside the vessel. Thus, there is a need to investigate the new MVDC-based nuclear submarine power distribution system and its real-time hardware-in-the-loop (HIL) emulation to test the control systems, device stresses, etc. This paper proposes a comprehensive MVDC-based nuclear submarine power distribution system emulated in real-time on a multi-FPGA hardware platform with system-level transients (validated by Matlab/Simulink) at 20 μs time-step and device-level transients (validated by SaberRD) at 400 ns time-step.

Three methods were explored to estimate the efficiency for the conversion of mechanical power to electrical power using synchronous generators in ships at low power factors. Generally, the generator efficiency data is provided by manufacturers as shop trial data and is measured by operating generators under power factor of 0.8 and 1.0. However, the efficiency of synchronous generators is not measured under low power factor of less than 0.8. In practice, onboard generators occasionally operate at low power factor and it is desirable to clarify their characteristics for power system designers of large vessels. By substituting the shop trial data into the proposed efficiency estimation formulas, the generator efficiency at low power factor was extrapolated. To evaluate the validity of these methods, the fuel consumption characteristics of diesel engines as prime movers was focused. The estimation of the generator efficiency was indirectly validated using a statistical analysis of long-term observational data of the generator in operation. As a result, the efficiency estimation method based on a power loss mechanism gave the most reliable result among the three estimation methods. The root mean squared error of the calculated specific fuel consumption was 3.5 g/kWh, which is approximately 1.66 % error rate.

This paper presents the characteristics of ferry shipping with particular emphasis on large RoPax vessels operating in the Baltic Sea. A critical review of main propulsion system used on large RoPax ferries has been done. Optimal propeller parameters and required brake power have been estimated on the basis of total resistance of bare hull and appendages approximated according to Holtrop-Mennen method. Main engines and generating sets have been selected for minimized fuel consumption approximated with quadratic regression. Operational parameters and costs of analysed large RoPax main propulsion systems have been compared. [ABSTRACT FROM AUTHOR]

In the path towards the decarbonization of the maritime sector, Low Temperature Polymer Electrolyte Membrane Fuel Cells (LT-PEMFC) fed by hydrogen are gaining attention as they could guarantee zero local emissions propulsion. In this study, a process simulation model is implemented to analyze the influence of peak shaving in a hybrid LT-PEMFC/lithium-ion battery power plant for the propulsion of a small size RoRo car and passenger ferry in different operative conditions. Results show that battery peak shaving could allow a reduction of FC installed power of up to 72%. As for compressed H 2 storage, the results show that for sailing time in the range of 5–10 min, Type I cylinders at 250 bar are a viable option. For longer routes, Type III cylinders at 350 bar or Type IV cylinders at 700 bar should be considered in order to avoid excessive reduction in the pay-load. • Overview of marine fuel cells projects. • H 2 and PEM fuel cells considered for the propulsion of a small RoRo ferry. • Different operative profiles analyzed. • Energy efficiency improved by 10% compared to diesel oil. • Zero local emissions. [ABSTRACT FROM AUTHOR]

The importance of mathematical and numerical simulation in marine engineering is growing together with the complexity of the designed systems. In general, simulation a makes it possible to improve the engineering design, reducing working time and costs of production as well. In this respect, the implementation of a simulation model for cycloidal propellers is presented. Cycloidal thrusters are being increasingly used in marine applications. Their best performance concerns low-speed applications, due to their ability to steer thrust in any direction. The proposed simulator is able to assess the performance of cycloidal propellers in terms of the generated thrust and torque, without resorting to consuming and demanding computational tools, such as CFD methods. This feature makes the presented model particularly suitable for the simulation in the time domain of the maneuverability of surface units, equipped with cycloidal propellers. In this regard, after embodying the implemented model in an already existing simulation platform for maneuverability, we show the most significant outputs concerning some simulated maneuvers, performed at cruise speed.

This study presents the electromagnetic, thermal and mechanical analysis of a 750 kW, 1200 rpm, 690 V surface permanent magnet motor aimed at marine propulsion (azimuth thruster). Based on a preliminary machine design, key electromagnetic design aspects including magnet demagnetisation and magnet loss reduction by tangential and axial segmentation are assessed. Then, three different cooling solutions are evaluated via computational fluid dynamics simulations combining the use of a water‐jacket surrounding the stator, wafters attached to the rotor structure and the addition of an inner fan. Subsequently, the dynamic design analysis method is applied in order to check the machine's response to shock loadings due to underwater explosions. Finally, a machine prototype is successfully manufactured and tested, showing the proper fulfilment of the design requirements. [ABSTRACT FROM AUTHOR]

The propulsion system of a medium‐voltage dc (MVDC) ship is subject to large thrust/torque variations due to interactions of the ship and the propeller with sea waves. These variations induce steep power fluctuations on the MVDC bus, adversely impacting the stability, efficiency and power quality. Hybrid energy storage system (HESS) is a promising solution for mitigating these power fluctuations. Dictating the energy that the HESS components must deliver/absorb, the energy management strategy (EMS) impacts the size/capacity of the energy storage system (ESS). Based on this consideration, sizing and EMS of a battery/supercapacitor (SC) HESS are jointly optimised by using a deep reinforcement learning‐based method. The proposed method splits the power between the HESS components such that while the operational constraints are satisfied, energy storage size and losses are minimised. Its features are adaptability to varying sea states, real‐time implementation feasibility, while obviating the requirement for knowledge of the ship propulsion power profile. The efficacy of the joint sizing/EMS on reducing the ESS size is validated by comparing the sizes when battery‐only, SC‐only and HESS are employed in the MVDC shipboard power system. Real‐time implementation feasibility and adaptability to various ship propulsion power profiles is confirmed through real‐time simulations. [ABSTRACT FROM AUTHOR]

As global concerns about climate change and environmental impacts continue to grow, there is a strong demand for cleaner, greener, and more efficient propulsion solutions in the maritime industry. By leveraging nuclear energy, which offers low carbon emissions and high efficiency, naval vessels can significantly reduce their environmental footprints and contribute to global efforts to combat climate change. Additionally, the ability to produce electricity and freshwater simultaneously addresses the critical need for self-sufficiency during long missions, particularly in remote or resource-constrained areas where access to freshwater may be limited. This study explores a novel approach to address water and energy supply challenges in naval applications through a nuclear-driven supercritical carbon dioxide (sCO2) power cycle–Reverse Osmosis (RO) cogeneration system. The aim is to assess the feasibility and benefits of this system for meeting water and electricity demands in maritime operations and enhancing the sustainability, efficiency, and self-sufficiency of naval vessels with nuclear energy and advanced technologies. A parametric study has been performed to understand the effects of important parameters such as the maximum and minimum cycle temperature and pressure, seawater inlet conditions, pressure vessel design, and membrane properties on the system performance. Moreover, an optimization study has been performed to determine the best possible combination of these parameters to achieve the highest system efficiency. For the determined optimal set of parameter values, it is possible to have an sCO2 power cycle with a cycle efficiency of 40.5 %, an electrical power output of 121.6 MW and an RO system with an efficiency of 29.4 %, a recovery ratio of 29.3 %, a specific fuel consumption (SEC) of 2.29 kW·h/m3, and a freshwater production rate of 1531.6 m3/d by utilizing 145.9 kW electrical power. The positive outcomes of this study indicate that the system has the potential to be a viable and effective solution for addressing water and energy supply challenges in naval operations. • This study pioneered a nuclear-driven sCO2-RO cogeneration system for naval use, reshaping maritime energy solutions. • An innovative mathematical model for seawater RO advances understanding of desalination processes. • Comprehensive studies have optimized system efficiency and freshwater production in naval operations. • Key insights provide information on the optimal power cycle considerations, and membrane enhancements. • Study offers promising sustainable solutions for naval energy and water challenges that appeal to industry and academia. [ABSTRACT FROM AUTHOR]

This study develops system-level models of ammonia-fuelled powertrains that reflect the characteristics of four oceangoing vessels to evaluate the efficacy of ammonia as an alternative fuel in the marine environment. Relying on thermodynamics, heat transfer, and chemical engineering, the models adequately capture the behaviour of internal combustion engines, gas turbines, fuel processing equipment, and exhaust aftertreatment components. The performance of each vessel is evaluated by comparing its maximum range and cargo capacity to a conventional vessel. Results indicate that per unit output power, ammonia-fuelled internal combustion engines are more efficient, require less catalytic material, and have lower auxiliary power requirements than ammonia gas turbines. Most merchant vessels are strong candidates for ammonia fuelling if the operators can overcome capacity losses between 4% and 9%, assuming that the updated vessels retain the same range as a conventional vessel. The study also establishes that naval vessels are less likely to adopt ammonia powertrains without significant redesigns. Ammonia as an alternative fuel in the marine sector is a compelling option if the detailed component design continues to show that the concept is practically feasible. The present data and models can help in such feasibility studies for a range of vessels and propulsion technologies.

This study addresses the problem of Dynamic Travelling Salesman Problem for a multi-agent system using a fleet of sailboats. A genetic algorithm (GA) is proposed, which attributes to each agent a varying number of targets to be collected. GA allows obtaining a suboptimal solution in the shortest time possible. Moreover, this study adapts it to the specific problem involving a fleet of sailboats, which is a challenging task with comparison to autonomous underwater vehicles or motorised vehicles in terms of the propulsion. Therein motors can be flexibly controlled while sailboat movements are constrained by available wind direction and speed. Thus the method takes into account wind conditions at various locations of the sailboat. Simulation results demonstrate the effectiveness of the proposed approach.

[Objectives]In view of the lack of complete definition, confusion about denotation of basic concepts of waterjet and pumpjet and confusion of product appellations both at home and abroad at present,[Methods]the common and special characteristics of the two propulsors were refined out and their differences distinguished based on the analysis of their working principle and concrete structures,the definitions of waterjet propulsion and pumpjet propulsion were proposed and their common characteristics, special characteristics and differences were pointed out.[Results]The waterjet and pumpjet are all pump-type propulsors,all of which rely on the matching design of rotors and stators on the flow field inside a duct to produce an axial jet. The first design index of waterjet is high efficiency and the rapidity shall be ensured primarily,whose design result is a waterjet. The first design index of pumpjet is low noise (the acoustic stealth)shall be ensured primarily,whose design result is a pumpjet.[Conclusions]This definition not only includes and distinguishes all existing waterjets and pumpjets,but also points out the problems of some foreign pump-type propulsor's nomenclature and classification. This definition helps the public understand and distinguish between waterjet propulsion and pumpjet propulsion.

Thrust generation is a crucial aspect of fish locomotion that depends on a variety of morphological and kinematic parameters. In this work, the kinematics of caudal fin motion of a robotic fish are optimised experimentally. The robotic fish actuates its caudal fin with flapping and rotation motion, and also measures the fin hydrodynamic force and torque. Total nine designs of the caudal fins are investigated, with three different shapes (or inclination angles) and three stiffness. The optimisation is based on a policy search (PS) algorithm, which is used to maximise the thrust-generation efficiency of the caudal fins. The authors first parametrise fin spanwise-rotation as a sinusoidal function using rotation amplitude and phase delay and test whether it is beneficial to thrust-generation efficiency. The result shows that the rotation does not contribute to the efficiency, as the efficiency is maximised at zero amplitude. Next, the authors optimise flapping amplitude and trajectory profile without fin rotation. Results show that smaller flapping amplitude results in higher efficiency and linear flapping trajectories are preferred over sinusoidal ones. Fins that have the highest flexibility are more efficient in thrust generation although they generate less thrust, while an inclination angle of 30° yields the most efficient fin shape.

Operational rules and control strategies of the chemically recuperated gas turbine (CRGT) in the marine propulsion are investigated in this paper. The Minimization of Gibbs free energy method is used to calculate the diesel-steam reforming reaction which products synthetic hydrogen rich fuels, and a universal model of the chemical regenerator which is easily applied to different application environments is created. The hydrogen production and hydrogen molar fraction are investigated to verify that the CRGT improve the combustion performances under low working conditions. Off-design calculations are performed to derive proper operational rules, and transient calculations are performed to investigate the best control strategies for the systems. The modelling approach of the chemical regenerator can be generally used in the chemically recuperated gas turbine. The elaborate operational rules can greatly improve the thermal efficiencies under every working condition. The system using synchronous control strategies have better regulation speed and operation stability than that using asynchronous control strategies. • The hydrogen rich synthetic fuels improve the thermal efficiencies. • The elaborate operational rules are propitious to the novel gas turbine cycle. • Good synchronous control strategies can be derived through the proposed models. • The recovery capacity depends on temperature, steam-to-fuel ratio, and pressure. [ABSTRACT FROM AUTHOR]

In this study, the effect of the channel dimensions on the performance of a marine MHD thruster is investigated using a fully three-dimensional numerical model. In this model, all electric, magnetic and fluid flow fields are considered in three dimensions. In addition, a simple analytical model is developed for comparison purpose and an optimisation method is proposed for the channel design to achieve the maximum efficiency and power density. The results show that at a specific output power and flow rate, the channel dimensions can be optimised to achieve the maximum efficiency or output power density, but not both. [ABSTRACT FROM AUTHOR]

• A deterministic method to assess the effect of biofouling on the performance of a ship by on-board vessel monitoring. • A review of existing methodologies is given. • The principal features of performance monitoring are examined from data acquisition to long-term performance analysis. • The proposed system was implemented and installed on the R/V ' The Princess Royal '. • Full-scale performance monitoring results using the proposed approach are presented and commented. This paper provides a description of the deterministic ship performance monitoring system developed and installed on Newcastle University's Research Vessel, The Princess Royal , for the estimation of the effect of hull and propeller fouling on the vessel's performance. The study revolves around the principle of data normalisation, both in its theoretical and practical aspects. A procedure for correcting weather and operational disturbances is introduced that takes into account plausible resources limitations. According to the needs emphasised by the normalisation process, the required onboard measurement system is described as it was implemented on the research vessel. A robust method to prepare the raw data for the analysis and suitable for all ship types and sizes is then proposed. A performance analysis method is finally defined using four different indicators of the vessel hydrodynamic performance. On-board measurements are presented and analysed according to the proposed methodology. Results show an increase in resistance of over 20% with extensive shell fouling and prove the effectiveness of the used method. [ABSTRACT FROM AUTHOR]

Abstract If international agreements regarding the need to significantly reduce greenhouse gas emissions are to be met then there is a high probability that the shipping industry will have to dramatically reduce its greenhouse gas emissions. For emission reductions from ships greater than around 40% then alternatives to fossil fuels - such as nuclear energy - will very likely be required. A Small Modular Pressurised Water Reactor design has been developed specifically to meet the requirements of a large container ship with a power requirement of 110 MWe. Container ships have a number of requirements - including a small crew size and reduced outages associated with refuelling - that result in a greater focus on design simplifications, including the elimination of the chemical reactivity control system during power operation and a long core life. We have developed a novel, soluble-boron free, low power density core that does not require refuelling for 15 years. The neutronic and fuel performance behaviour of this system has been studied with conventional UO 2 fuel. The size of the pressure vessel has been limited to 3.5 m in diameter. Furthermore, to ensure the survivability of the cladding material, the coolant outlet temperature has been reduced to 285 °C from 320 °C as in conventional GWe-class PWRs, with a resulting reduction in thermal efficiency to 25%. The UO 2 core design was able to satisfactorily meet the majority of requirements placed upon the system assuming that fuel rod burnups can be limited to 100 GWd/tHM. The core developed here represents the first workable design of a commercial marine reactor using conventional fuel, which makes realistic the idea of using nuclear reactors for shipping. [ABSTRACT FROM AUTHOR]

A magnetohydrodynamic (MHD) thruster is a type of electric motor which does not have mechanical moving parts and directly converts electrical energy into mechanical energy. In this paper, a multiphysics numerical simulation has been performed to investigate the phenomena occurred in the channel of marine MHD thrusters. In this simulation, all electric, magnetic, and fluid flow fields have been considered 3-D. For this purpose, a marine MHD thruster model with saddle-shaped coils is selected, and its dimensions are determined. Then, this thruster is simulated numerically, and its electromagnetic and fluid flow parameters are studied. In this simulation, the effects of seawater electrolysis and end loss are taken into account. An experimental setup is established to validate the results obtained from the numerical simulation. The results reveal that the nonuniformities of the electric and magnetic fields along the channel have a great impact on the performance of the thruster. Unlike the results obtained in the previous studies, it is shown that the velocity near the electrodes is higher than that near the sidewalls arisen from the higher electromagnetic force close to the electrodes. [ABSTRACT FROM AUTHOR]

The high quality of electrical power in high power and high reliability applications is a crucial necessity even under fault mode function. However, in these conditions, the quality of the torque is a key feature. To overcome this problem, the multiphase permanent magnet (PM) motors seems to be a very attractive choice. In order to highlight the robustness and reliability of this technology, this paper investigates the control of a five-phase PM motor under an open circuited phase fault conditions. Moreover, a High Order Sliding Mode (HOSM) controller combined to an optimal reference current generation is tested and compared to a PID controller under fault mode conditions. This original control strategy is proposed for faulted conditions. Compared to classical fault tolerant control, this strategy allows a better dynamic tracking of the non-sinusoidal reference currents and leads to a smooth torque with minimal losses even in severe fault conditions. To validate the proposed control strategy, simulation, and experimental results are presented and discussed. [ABSTRACT FROM AUTHOR]

The purpose and scope of this paper is to describe the complexity of the new generation marine propulsion technologies implemented in the shipping industry to promote green ships concept and change the view of sea transportation to a more ecological and environment-friendly. Harnessing wind, waves and solar power in shipping industry can help the ship’s owners reduce the operational costs. Reducing fuel consumption results in producing less emissions and provides a clean source of renewable energy. Green shipping technologies can also effectively increase the operating range of vessels and help drive sea transportation towards a greener future and contribute to the global reduction of harmful gas emissions from the world's shipping fleets.

The study aimed to verify whether it is possible to diagnose the coking of a marine diesel engine injector nozzle by performing a spectral analysis of the crankshaft’s torsional vibrations. The measurements were taken using laser heads, clocked at 16 MHz. The reasons for selecting this type of optical sensors are described as well. The tests were carried out under laboratory conditions, using a test stand with a Sulzer 3AL 25/3 engine, operating under a load created by a Domel GD8 500–50/3 electric generator. A unique method is presented in the paper, which enables the measuring and calculation of torsional vibrations of engine crankshafts. The method was developed at the Chair of Marine Power Plants at the Maritime University of Gdynia. It has been proven that the distribution of differences in the values of individual harmonic components depends on the location of a defective injector nozzle in the cylinder.

Failures of marine propulsion components or systems can lead to serious consequences for a vessel, cargo and the people onboard a ship. These consequences can be financial losses, delay in delivery time or a threat to safety of the people onboard. This is why it is necessary to learn about marine propulsion failures in order to prevent worst-case scenarios. This paper aims to provide a review of experimental, analytical and numerical methods used in the failure analysis of ship propulsion systems. In order to achieve that, the main causes and failure mechanisms are described and summarized. Commonly used experimental, numerical and analytical tools for failure analysis are given. Most indicative case studies of ship failures describe where the origin of failure lies in the ship propulsion failures (i.e., shaft lines, crankshaft, bearings, foundations). In order to learn from such failures, a holistic engineering approach is inevitable. This paper tries to give suggestions to improve existing design procedures with a goal of producing more reliable propulsion systems and taking care of operational conditions.

Recent and strict regulations in the maritime sector regarding exhaust gas emissions has led to an evolution of shipboard systems with a progressive increase of complexity, from the early utilization of electric propulsion to the realization of an integrated shipboard power system organized as a microgrid. Therefore, novel approaches, such as the model-based design, start to be experimented by industries to obtain multiphysics models able to study the impact of different designing solutions. In this context, this paper illustrates in detail the development of a multiphysics simulation framework, able to mimic the behaviour of a DC electric ship equipped with electric propulsion, rotating generators and battery energy storage systems. The simulation platform has been realized within the retrofitting project of a Ro-Ro Pax vessel, to size components and to validate control strategies before the system commissioning. It has been implemented on the Opal-RT simulator, as the core component of the future research infrastructure of the University of Genoa, which will include power converters, storage systems, and a ship bridge simulator. The proposed model includes the propulsion plant, characterized by propellers and ship dynamics, and the entire shipboard power system. Each component has been detailed together with its own regulators, such as the automatic voltage regulator of synchronous generators, the torque control of permanent magnet synchronous motors and the current control loop of power converters. The paper illustrates also details concerning the practical deployment of the proposed models within the real-time simulator, in order to share the computational effort among the available processor cores.

The aim of the present paper is to provide the state of the works in the field of hydrodynamics and computational simulations to analyze biomimetic marine propulsors. Over the last years, many researchers postulated that some fish movements are more efficient and maneuverable than traditional rotary propellers, and the most relevant marine propulsors which mimic fishes are shown in the present work. Taking into account the complexity and cost of some experimental setups, numerical models offer an efficient, cheap, and fast alternative tool to analyze biomimetic marine propulsors. Besides, numerical models provide information that cannot be obtained using experimental techniques. Since the literature about trends in computational simulations is still scarce, this paper also recalls the hydrodynamics of the swimming modes occurring in fish and summarizes the more relevant lines of investigation of computational models.

Abstract This study investigates the proper configuration of an electric propulsion system for a very large ethane carrier. The system consists of a dual-fuel diesel electric generator and a solid oxide fuel cell-gas turbine hybrid system to replace the mechanical propulsion system based on a marine diesel engine. When the ship navigates the open sea, the dual-fuel diesel electric generator and hybrid system run in parallel at a power rating of 16 MW. However, the hybrid system only operates during the berthing state for ship hoteling. The system efficiency, energy efficiency design index, and availability are considered to identify the optimal system configuration. When the dual-fuel diesel electric generator produces 10 MW, the hybrid system generates 6 MW. Because the electric propulsion system complies with international environmental regulations, it may be broadly acceptable for gas carriers in terms of eco-efficiency. The system achieves high availability by using fault tree analysis and minimal cut sets. Highlights • An electric propulsion system can replace mechanical propulsion machinery in a gas carrier. • An SOFC-gas turbine system solely generates electricity for ship hoteling service. • The marine generator-SOFC-gas turbine system satisfies the CO 2 regulation. • The availability of a hybrid system is high on maneuvering and berthing states. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

The study of ship underwater radiated noise is nowadays a topic of great and largely recognized importance. This is due to the fact that in the last decades, the problem of the impact of anthropogenic noise on marine life has been addressed with higher emphasis, giving rise to different efforts aimed to the analysis of its effects on different organisms and, in parallel, to means for the reduction of shipping noise. In this context, attention is focused on the propeller noise, which, in cavitating conditions, may represent the most important noise source of the ship. The propeller noise has been studied for long time with different approaches. One of the most effective approaches is represented by model scale testing in cavitation tunnels or similar facilities. Despite having been adopted for several years, radiated noise experiments in model scale are usually affected by significant scale effects and technical issues. One of these aspects is represented by the correct modelling of the propeller inflow; different techniques are adopted, depending on the facility, in order to reproduce a certain target wake. One of the main problems is to define this target wake, which should in principle coincide with the ship wake; as it is well known, it is usually derived from model scale towing tank measurements, with the necessity for the prediction of the full-scale wake field. Starting from the outcomes of a previous work on the influence of different approaches for the prediction of the full-scale wake field for a single screw ship, in this work, attention is focused on the case of a fast twin screw vessel, analysing the different issues which may be connected to this hull form. [ABSTRACT FROM AUTHOR]

Conventional diesel‐electric propulsion systems in platform supply vessels (PSVs) use low‐voltage AC (LVAC) supply‐based architecture with multiple diesel‐generators feeding busbars at 690 V, 60 Hz. The busbars distribute power to thruster motor drives via multi‐pulse transformers and diode bridge rectifiers. Advancements in electrical power conversion and distribution technologies offer possibilities of AC or DC distribution at low/medium voltage (LV/MV) for reduced fuel consumption (FC), emissions, and equipment footprint. This study presents methodology to qualify propulsion system architecture for PSV application. Potential architectures, besides conventional one, are active front end (AFE) converter‐based LVAC (690 V), MVAC (3.3 kV), LVDC (1000 V), and MVDC (5000 V). Performances of these architectures are assessed quantitatively based on FC, emissions, weight, volume, efficiency, and reliability. FC is estimated based on brake‐specific FC data of diesel engine. NOx, SO2, and CO2 emissions are assessed based on their emission factors. The weight, volume, and efficiency are estimated based on parameters of individual components. Reliability is assessed based on component failure data using DIgSILENT Power Factory. The architectures are ranked based on performance parameters using a Pugh matrix. The most suitable architecture for the target PSV is LVDC, followed by MVDC, LVAC with AFE, MVAC, and conventional LVAC. [ABSTRACT FROM AUTHOR]

Growing concerns about anthropogenic climate change and its effects on the environment have encouraged significant recent developments towards decarbonizing the energy system. Developments in transportation technology, such as vehicle electrification, can result in significant CO 2 , particulate matter, and SO x reductions over the lifetime of a vehicle. The shipping industry alone accounted for 2.1% of global greenhouse gas emissions in 2012, however, due to energy requirements and weight restrictions, batteries and direct electrification cannot be used to mitigate emissions. Synthetic fuels, as an indirect electrification option, are a viable solution to achieve emission reduction goals. The purpose of this study is to determine the most cost effective combination of synthetic fuels and fuel cells or internal combustion engines to replace fossil oil as the main propulsion fuel in the shipping industry in 2030 and 2040. The fuels, namely RE-FT-Diesel, RE-LNG, RE-LH 2 and RE-MeOH, are analysed for both an internal combustion engine and a fuel cell. The scenarios were analysed by comparing the levelised cost of mobility (LCOM). The LCOM was composed of 5 different facets including the capex of the engines/fuel cells and the tanks, the opex of the engines/fuel cells, the cost of lost cargo space, fuel cost and the CO 2 cost. The final unit of comparison was €/1000DWT-km. It was determined that hydrogen fuel cells were the most likely to replace fossil internal combustion engines if the fuel cells follow their expected development. Significant gains in fuel cell average efficiency and decreases in production cost between today and 2030 and 2040 are factors contributing to the competitiveness. A CO 2 cost was set to 61 €/tCO 2 in 2030 and 75 €/tCO 2 in 2040. Most of the other technology combinations are close to competing with fossil diesel with a CO 2 price in 2040; however, hydrogen fuel cells are close to competing with fossil fuel without a CO 2 cost in 2040. [ABSTRACT FROM AUTHOR]

• The alignment of the drive motor and azimuth thruster L-drive varies with steering positions. • Steering system can cause shaft alignment variation exceeding alignment tolerances, leading to accelerated tooth wear. • A new alignment procedure aims to enhance system reliability by improving results evaluation and adjustments. • Reliable alignment analysis requires verification across multiple steering positions of the azimuth thruster steering system. • Proposed preventive actions through a specialized alignment procedure to prevent failures in marine propulsion systems. The propulsion system is one of the most important systems in a vessel. It is considered critical, since if it fails, directly compromises the operation and safety. A common fault on the azimuth propulsion L-drive system is the gear coupling failure, where on the last stage of damage the shaft can broke causing propulsion loss. The two main reasons of this problem are the shaft misalignment and lack of gear coupling teeth lubrication. Through a specific alignment measurement procedure, performed on three different vessels and 17 azimuth thruster L-drive, this study will prove that the shaft alignment between motor and thruster is affected by the steering rotation of the azimuth system. The alignment changes due to steering position sometimes can be greater than alignment tolerance values, generating gear coupling damages. Then a specific procedure is proposed to measure, evaluate, and correct the alignment to prevent gear coupling failures and improve the system reliability. [ABSTRACT FROM AUTHOR]