With increasingly stringent emission regulations, marine natural gas engines need to improve their performance. Various proven advantages of hydrogen-natural gas (H-NG) blends make them a promising enhanced fuel solution. Although modelling of H-NG combustion has been investigated before, mostly using CFD models, the literature on the modelling capabilities of Seiliger-based and Wiebe-based zero-dimensional (0-D) models is limited for H-NG combustion. Especially for the application of marine lean-burn spark-ignited (SI) engines. Therefore, the aim of this paper is to compare the capabilities of Seiliger-based and double Wiebe function-based 0-D models to capture H-NG combustion in a marine SI engine for different H-NG fuel blends, engine leaning (lean-burn operation) and engine loads. In this work, measurements on a turbocharged, SI marine natural gas engine were used to develop a heat release rate model, which was subsequently used as a basis for the Seiliger and double Wiebe function-based H-NG combustion characterization models. Results from the two combustion modelling approaches were compared for different H-NG fuel blends, engine leaning (lean-burn operation) and engine loads. The modelling results were also compared against engine measurements for different experimental conditions. This paper shows that the Seiliger modelling approach can be used to define different physical phenomenon in H-NG combustion, while accurately capturing the effects of hydrogen addition and engine leaning on the H-NG combustion process at varying engine loads. This research also found that the variations in late burn phase present in lean-burn NG and H-NG combustion can be captured using the double-Wiebe modelling approach, however, clear trends of the Wiebe combustion parameters for varying fuel blends and engine loads could not be identified to accurately capture the H-NG combustion process. Furthermore, Wiebe-based modelling approach produced larger errors in the estimations of work output and combustion heat for all test conditions.

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Direct internal reforming enables optimal heat integration and reduced complexity in solid oxide fuel cell (SOFC)systems, but thermal stresses induced by the increased temperature gradients may inflict damage to the stack. Therefore, the development of adequate control strategies requires models that can accurately predict the temperature profiles in the stack. A 1D dynamic modelling platform is developed in this study, and used to simulate SOFCs in both single cell and stack configurations. The single cell model is used to validate power law and Hougen-Watson reforming kinetics derived from experiments in previous work. The stack model, based on the same type of cells, accounts for heat transfer in the inactive area and to the environment, and is validated with data reported by the manufacturer. The reforming kinetics are then implemented in the stack model to simulate operation with direct internal reforming. Although there are differences between the temperature profiles predicted by the two kinetic models, both are more realistic than assuming chemical equilibrium. The results highlight the need to identify rate limiting steps for the reforming and hydrogen oxidation reactions on anodes of functional SOFC assemblies. The modelling approach can be used to study off-design conditions, transient operation and system integration, as well as to develop adequate energy management and control strategies.

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With the growing demand of large-scale heavy lift vessels in the deep-sea offshore construction works, high performance of Dynamic positioning (DP) systems is becoming ever crucial. However, current DP systems on board of heavy lift vessels do not consider model uncertainty (typically arising from mooring forces). In this paper, an observer-based robust controller is designed that can tackle model uncertainty in hydrodynamic damping and mooring forces, environmental disturbances as well as can filter out the high-frequency vessel movement. Closed-loop system stability is analytically established in terms of uniformly ultimately boundedness. In addition, several key performance indicators are provided for tuning the performance of the controller. The effectiveness of the proposed control framework is studied in simulation with a crane-vessel system.@en

Offshore heavy lift vessels are designed for transporting, installing and removing offshore facilities. Previous studies have shown that the time-varying forces acting on the main crane may result in an unstable Dynamic Positioning (DP) control system, which adversely affects the safety of the heavy lifting operation. Solutions based on force feedforward control thus has been proposed, i.e., the low-frequency horizontal component of the crane force is forwarded to the DP controller or observer. Accurate estimation of the horizontal component of the crane force is essential for the feedforward solution, but it is extremely difficult to obtain it from a measurement due to its time-varying nature and the non-linear system dynamics stemming from the ship-environment interaction. Therefore, in this work, we focus on the estimation of the low-frequency crane force in the horizontal direction during loading and offloading stages of a heavy lift operation in various environmental conditions. To achieve this goal, a novel time-varying mooring stiffness term is introduced, which is included in the nonlinear passive observer of the vessel and used in a joint parameter-state estimator to estimate the horizontal crane force and vessel states. Afterward, simulations are performed to test the estimator in various environmental and loading conditions. The results indicate that an accurate estimation of the low-frequency horizontal component of the crane force can be achieved by measuring the position of the ship and the tension in the wires even in the presence of large parameter uncertainty.@en

Condition Based Maintenance on diesel engines can help to reduce maintenance load and better plan maintenance activities in order to support ships with reduced or no crew. Diesel engine performance models are required to predict engine performance parameters in order to identify emerging failures early on and to establish trends in performance reduction. In this paper, a novel approach is proposed to accurately predict engine temperatures during operational dynamic manoeuvring. In this hybrid modelling approach, the authors combine the mechanistic knowledge from physical diesel engine models with the statistic knowledge from engine measurements on a sound engine. This simulation study, using data collected from a Holland class patrol vessel, demonstrates that existing models cannot accurately predict measured temperatures during dynamic manoeuvring, and that the hybrid modelling approach outperforms a purely data driven approach by reducing the prediction error during a typical day of operation from 10% to 2%.

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Energy storage has the potential to reduce the fuel consumption of ships by loading the engine(s) more efficiently. The exact effect of on-board energy storage depends on the ship functions, the configuration of the on-board power system and the energy management strategy. Previous research in this area consists of detailed modelling, design, and comparisons of specific on-board power systems for explicitly defined operational profiles. The necessary inputs for these studies are rarely known initially however, since the effect of energy storage on the fuel consumption is not necessarily always positive, it is essential to know the limitations of fuel savings obtained by an on-board energy storage early in the design stage. To that effect, the paper proposes a set of algebraic formulas for the equivalent specific fuel consumption of on-board power systems equipped with electrical energy storage, which give a quick estimation of the maximum fuel savings obtainable. Depending on the specific fuel consumption of the prime mover, the loading point of the system and the use scenario of the battery, relative efficiency improvements can vary between −48% and 57%. A set of design guidelines is also proposed based on the obtained results.

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A novel ship propulsion concept employs natural gas to reduce ship emissions and improve overall ship propulsion efficiency. This concept proposes a serial integration of Solid Oxide Fuel Cell (SOFC) and a natural gas engine, while anode-off gas (gas at the fuel cell exhaust) is used in the natural gas engine. This study focusses on SOFC-gas engine integration by experimentally analyzing the effects of adding hydrogen, which is the main combustible component of the fuel cell anode-off gas, in marine natural gas engines. The overall challenge is to employ the anode-off gas to improve the performance of marine natural gas engines. To study the effects of anode-off gas combustion in natural gas engines, experiments with hydrogen addition in a marine natural gas engine of 500 kW rated power were performed. Natural gas was replaced with 10 % and 20 % of hydrogen, by volume, without any penalties in terms of output power. We found that the high combustion rate of hydrogen improved combustion stability, which allowed for better air-excess ratio control. Thus allowing leaning to higher air-excess ratios and extending the, otherwise, limited operating window. Hydrogen addition also improved brake thermal efficiency by 1.2 %, while keeping NOx emissions below the maritime emission regulations. The improvement in engine efficiency with a larger operating window may help improve the load-taking capabilities of marine natural gas engines.@en

Solid oxide fuel cell (SOFC) technology offers a clean and efficient way to generate electricity from natural gas. Since various integration options with thermal cycles have been proposed to achieve even higher electrical efficiencies, it is interesting to see how these compare. In addition, the influence of the SOFC operating parameters on thermal cycles is not yet adequately addressed. In this study, a stand-alone SOFC system is thermodynamically analysed and compared to configurations combined with a gas turbine or steam turbine, as well as a novel SOFC-reciprocating engine combined cycle system. The results are mapped in contour plots for the entire SOFC operating envelope, revealing the influence of fuel utilisation, cell voltage, average stack temperature and gas turbine pressure ratio on different combined cycles. An exergy analysis is included to quantify notable losses in the systems and identify potential further improvements. The pressurised SOFC-gas turbine combined cycle achieves the highest electrical efficiencies for stack operation at moderate cell voltages and high temperatures, while the steam turbine combined cycle is more efficient at high cell voltages and low stack temperatures. The SOFC-reciprocating engine combined cycle shows similar behaviour to the steam turbine combined cycle, but achieves slightly lower efficiencies.

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This article presents a case study determining the optimal preventive maintenance policy for a light rail rolling stock system in terms of reliability, availability, and maintenance costs. The maintenance policy defines one of the three predefined preventive maintenance actions at fixed time-based intervals for each of the subsystems of the braking system. Based on work, maintenance, and failure data, we model the reliability degradation of the system and its subsystems under the current maintenance policy by a Weibull distribution. We then analytically determine the relation between reliability, availability, and maintenance costs. We validate the model against recorded reliability and availability and get further insights by a dedicated sensitivity analysis. The model is then used in a sequential optimization framework determining preventive
maintenance intervals to improve on the key performance indicators. We show the potential of data-driven modelling to determine optimal maintenance policy: same system availability and reliability can be achieved with 30% maintenance cost reduction, by prolonging the intervals and re-grouping maintenance actions.@en

After-treatment technologies are adopted in automobiles and ships to meet strict emission regulations, which increase exhaust back pressure. Furthermore, underwater exhaust systems are employed on board ships to save space, and reduce noise and pollution on working decks. However, water at exhaust outlet creates a flow resistance for the exhaust gases, which adds to the back pressure. High back pressure reduces the operating limits of an engine, increases fuel consumption, and can lead to exhaust smoke. While the effects of back pressure were recognized earlier, there is a lack of experimentally validated research on the performance limits of a turbocharged, marine diesel engine against high back pressure for the entire operating window. The focus of this research is to provide a comprehensive understanding of back pressure effects on marine diesel engine performance, and to identify limits of acceptable back pressure along with methods to tackle high back pressure. In this work, a pulse turbocharged, medium speed, diesel engine was tested at different loads and engine speeds; against different values of static back pressure. Additionally, mean value model simulations could be validated and were used to compare the performance of a pulse and constant pressure turbocharged engine against high back pressures of 1 meter water-column (mWC), and for two different values of valve overlap. Using the validated simulation model, the conceptual basis for the engine smoke limit as well as for thermal overloading is investigated. A methodology applying the conceptual basis to define boundaries of acceptable back pressures has been presented in this paper. A combination of pulse turbocharger systems and small valve overlap showed to significantly improve back pressure handling capabilities of engines.

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In this paper we focus on integration of batteries with ship power systems for three application cases. Presented application cases include two platform supply vessels, one equipped with diesel engines and other with dual fuel engines, and a heavy lift crane vessel. Besides reducing the number of running engines and maintaining original dynamic positioning capabilities, we also demonstrate novel possibilities of battery usage, such as harvesting of waste energy, and implementation of dual fuel engines for dynamic positioning. In all application cases, results indicate significant fuel savings and reduction of running hours due to spinning reserve function of batteries.@en

This paper presents a methodology for evaluating different on-board power systems in the concept design phase. From an energy efficiency perspective, the potential advantages of a modern on-board power system are dependent on two major considerations: The design ratio between propulsion and auxiliary loads and the operational profile. These factors vary significantly for different ships and they can be roughly estimated very early in the design process, when only the main ship functions are known. An energy efficiency calculation method is proposed that has only these factors as input and is therefore applicable in the early stages of ship design.

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The applicability of different selection methods for power systems on board ships is highly dependent on the number of options possible. With the introduction of new technologies in the maritime sector, this number is increasing. However, its exact value, or even its order of magnitude is still unknown. This article shows the complexity of modern on-board power system by quantifying the number of possible system configurations currently available. A constraint satisfaction algorithm generates different configurations and the results are supported by combinatorics principles. The set of constraints used led to a significant reduction in the design space, and the influence of each of the constraints is investigated independently. Traditional mechanical propulsion is present in less than 1% of the generated configurations, whereas electric and hybrid propulsion are dominant. In particular, the impact of energy storage on the size of the design space is made evident. The order of magnitude of the total number of configurations obtained supports the use of modern selection methods instead of ones based on expert intuition and past experience. The presented work offers a tool to determine and restrict the size of the design space. It can therefore be integrated into existing selection methods and is a starting point for the development of new ones.@en

Heavy lift crane vessels play an important role in offshore installations. Previous studies have shown that position control systems for these vessels can cause unstable positioning behavior during offshore construction assignments under specific conditions, e.g., change of environmental loads. Some control methods, such as crane force feedforward to the controller or the estimator, have been developed to improve the stability of the position control systems. However, these methods depend on the accurate estimation of the crane force and fast reaction of thrusters, which are difficult to obtain under working conditions. To make the positioning system stable, and compensate the controller for the changing crane stiffness and the systems onboard, two methods will be provided. One is to increase the flexibility of the system, while the other one is to increase the robustness. Two control methods, adaptive PID and H-infinity, are adopted and the results are compared. During simulations, the two controllers can dispose of crane modeling error and time delay of thrusters. Adaptive PID has a smaller variance under higher wind and wave load, while H-infinity controller has a larger clearance with the platform.

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Gearboxes are a necessary part of almost any propulsion train and their percentual losses are usually assumed to be small and constant. However, in low-load and part-load conditions, gearbox losses may be significant. With the current trend of slow steaming, the performance of gearboxes is once again in focus. In order to estimate the performance of maritime gearboxes, an evaluation of losses was done using a thermal network. The analysis was done for a standard double-input single-output maritime gearbox and over the entire range of torque and revolutions per minute. Results indicate that the transmission losses are not negligible in low-load condition; in fact they may as high as 10% of delivered power. Further results show that the maximum temperature in the teeth contact can reach 70 °C but this might be an overestimate. Finally, using the investigated thermal network models, a simplified model of transmission losses is proposed together with the fit coefficients for the torque and revolutions per minute.@en

Progressing limits on pollutant emissions oblige ship owners to reduce the environmental impact of their operations. Fuel cells may provide a suitable solution, since they are fuel efficient while they emit few hazardous compounds. Various choices can be made with regard to the type of fuel cell system and logistic fuel, and it is unclear which have the best prospects for maritime application. An overview of fuel cell types and fuel processing equipment is presented, and maritime fuel cell application is reviewed with regard to efficiency, gravimetric and volumetric density, dynamic behaviour, environmental impact, safety and economics. It is shown that low temperature fuel cells using liquefied hydrogen provide a compact solution for ships with a refuelling interval up to a tens of hours, but may result in total system sizes up to five times larger than high temperature fuel cells and more energy dense fuels for vessels with longer mission requirements. The expanding infrastructure of liquefied natural gas and development state of natural gas-fuelled fuel cell systems can facilitate the introduction of gaseous fuels and fuel cells on ships. Fuel cell combined cycles, hybridisation with auxiliary electricity storage systems and redundancy improvements are identified as topics for further study.

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When simulating a ship propulsion system, it is often required to evaluate various characteristics of a ship propulsion system and the selected modelling approach changes according to the goal of the simulation. For example, data-based models are sufficient for simulations of steady state conditions while first principle models are more suitable for transient conditions. Additionally, it is often necessary to compare different propulsion configurations. For component models, this might require different modelling approaches to describe various performances and/or different sets of parameters used to describe different propulsion configurations. Even though there are various databases of ship component models, none of them allows the user to change the modelling approach or pre-set values of parameters used to describe the component models. In order to allow the changing of the modelling approach together with the parameters of the component models, a novel two-part modelling approach is proposed in this paper. The proposed approach separates the component model into two parts: process and parametric part. By adjusting the process part of the component model, the modelling approach can easily be changed. And by adjusting the parametric part of the component model, it is possible to adjust the component¿s characteristics and accommodate different configurations. In this investigation, a mean value first principle diesel engine model has been selected as a case study to demonstrate the flexibility of the proposed approach. As shown in the paper, the proposed approach allows the user to combine the benefits of a first principle model with the accuracy of the data based models. Additionally, the functional mock-up interface (FMI) standard has been used in the investigation to show that the proposed approach can be used in different software environments.@en