The trend towards fully autonomous navigation or reduced manning concepts, coupled with increased integration and interdependence of onboard systems due to the shift towards sustainable fuels and ever-increasing electrification and automation, has stressed the significance of ship systems’ reliability. These developments reinforce the demand for a clear assessment of the robustness of main and auxiliary systems in early-stage ship design. Network theory offers a promising approach to address this demand. However, current graph measures do not align with industry-specific requirements for improving system robustness. This study aims to augment robustness evaluation components, such as modularity (independent subsys-tems), redundancy and reconfigurability, with additional considerations specific to Dynamic Positioning (DP) applications in the maritime industry. The enhanced robustness evaluation components are translated into graph measures. By employing these graph measures, different systems can be compared with respect to robustness, enabling informed decision-making in the trade-offs typical to early stages of the design pro-cess (e.g., cost versus redundancy). The proposed methodology combines the principles of network theory and industry-specific DP requirements to provide a comprehensive framework for evaluating the robustness of ship systems. System reliability can be assessed by integrating the identified robustness components and incorporating them into the graph measures. The early findings of this study show the potential to improve ship design processes by providing a systematic and quantifiable approach to enhance robustness.@en

Reduced crewing concepts require a higher level of control and integration of platform systems. A clear reliability assessment of these systems in early design stages reduces the need for alternations in later design stages but remains challenging to perform. This paper addresses the design of reliable and integrated onboard systems such as cooling water, power distribution, and control systems. Current approaches to making platform systems more reliable, such as redundancy, modularity (independent subsystems) and reconfigurability, are analysed from a network theory perspective. Current graph measures do not align with experience-based requirements for improving system robustness. Our method combines the principles of network theory and experience-and rule-based system requirements to provide a comprehensive framework for a reliability comparison of integrated multilayer platform systems (distributing more than one type of flow). The robustness requirements are translated into network metrics to facilitate a quantitative trade-off typical to the early stages of the design process. The case study offers a preliminary view of the system topology of a notional naval vessel, consisting of power distribution, cooling water distribution and control systems. The network metrics facilitate an assessment of the system’s reliability compared to alternative system topologies with differentiating numbers of nodes, edges and density. This study finds varying dependencies of the robustness metrics on the network properties, shining new light on whether and how one should compare distribution system robustness.

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Spark-ignition (SI) engines emerge as a viable solution for specific marine applications, offering low-noise operation and emissions mitigation, as well as great potential to utilize high-octane number alternative fuels, such as methanol, ammonia, and hydrogen. However, heavy-duty (HD) SI engines still face challenges such as knocking and combustion instability. Particularly for lean combustion conditions, these engines exhibit the most pronounced cyclic combustion variations. This paper investigates the combustion stability of a 500 kW marine lean-burn natural-gas (NG) engine, a promising candidate for reducing emissions in marine applications. We focus on analyzing in-cylinder pressure measurements to quantify combustion characteristics, emphasizing cycle-to-cycle combustion variation, and exploring the influence of operating parameters like spark timing (ST) and air excess ratio (λ). Our findings demonstrate a clear trade-off between NO_x and COV_IMEP emissions through variations in the λ and ST. We identified a transition zone characterized by an increasing number of late-burning cycles at higher λ, before partial burning cycles began at further dilution. Following this, we established a new threshold of 6% for COV_IMEP to determine unstable combustion. Notably, increasing dilution from a λ of 1.12 to 1.61 decreased NO_x emissions from 17.83 g/kWh to 0.16 g/kWh, well below IMO Tier III standards, while COV_IMEP increased from 1.72% to 13.42%. These insights highlight the potential for advancing SI technology for marine applications and the need for further research to optimize both combustion and emissions in such engines.

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In response to the leading narrative of increasing sustainability in the yachting sector, a research collaboration is started between the Delft University of Technology and Dykstra Naval Architects (DNA) to examine the potential use of hydro generation on board large sailing yachts. By harvesting energy from the water flow when a yacht is sailing, diesel generator use can be limited, reducing overall emissions. However, it is a challenge to quickly identify the impact of a chosen hydro generation system on the overall design during the early stages of yacht design. A design method, with a primary focus on the propeller, is therefore developed to quantify this impact. This allows the designer to explore various hydro generation systems in an early design stage. This paper describes the developed method and presents results from a case study to provide insight into the applicability of the method.@en

In this paper a Concept Exploration Tool (CET) for naval ship power plants is presented. The ideas behind the CET are introduced as well as the inner workings of the tool. Objective functions for different relevant design criteria (energy efficiency, emissions, signatures, etc.) are shortly discussed, after which the results for a Frigate case study will be shown. Interesting solutions that are outside the well-known zone of conventional configurations, that may lead to new insights and innovative designs, are amongst the results of the CET; demonstrating the advantages of Design Space Exploration. The main development of this CET compared to earlier versions is however in the computational effectiveness of the tool, which is amongst others made possible by so-called Intermediate Design Algorithms (IDeAs). The major improvement in computational time provides additional room for further development of the objective functions used.@en

Reliability and survivability play a key role in the ship operation and ship design process of navy ships, but increasingly also of complex commercial vessels. These requirements prove relevant for different elements within the ship design scope, including the distribution system design of data, energy and fluid (water, fuel, oil, etc.). In early-stage ship design, distribution system robustness estimation is crucial in performing a substantiated trade-off between system availability and system investment costs. Van Mieghem et al. have developed a framework for computing topological network robustness; a generally applicable robustness approach using a graph representation as network system model. This framework has been applied on on-land power grids and more abstract networks such as the internet. However, due to the general nature of the framework, the applicability of the framework to on-board distribution systems is not self-evident. In this study, the required assumptions and adjustments to applyt his mathematical approach to on-board distribution systems are described. Moreover, the usefulness of this method for system robustness estimation in early-stage ship design is considered and demonstrated. In conclusion, an improved robustness estimation of distribution systems makes for an overall more reliable ship; a property to be pursued for increasingly complex ships.@en

Current EEDI (Energy Efficiency Design Index) regulations striving to reduce the installed engine power on new ships for a low EEDI may lead to underpowered ships having insufficient power when operating in adverse sea conditions. In this paper, the operational safety of a low-powered ocean-going cargo ship operating in adverse sea conditions has been investigated using an integrated ship propulsion, manoeuvring and sea state model. The ship propulsion and manoeuvring performance, especially the dynamic engine behaviour, when the ship is sailing in heavy weather and turning into head sea, have been studied. According to the results, the dynamic engine behaviour should be considered when assessing the ship operational safety, as the static engine operating envelope is inadequate for the safety assessment. The impact of PTO/PTI (power-take-off/in) operation and changing propeller pitch on the ship thrust availability in adverse sea conditions have also been investigated. To protect the engine from mechanical and thermal overloading, compressor surge and over-speeding during dynamic ship operations and/or in high sea states, the engine and propeller should be carefully controlled. The paper shows that if in (heavy) adverse weather the propeller pitch can be reduced or if the shaft generator can work as a motor (PTI), more thrust can be developed which can significantly improve the operational safety of the ship.

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Several news items and short movies have appeared online recently, announcing that the AmmoniaDrive Consortium was awarded a prestigious NWO Perspectief grant. But what is the AmmoniaDrive research project? How does it contribute to combatting shipping-induced climate change? Who are in the consortium and why? And finally, what research activities will take place?@en

Analysis of ship propulsion system performance is often performed using detailed hydrodynamic models to assess load changes, which are subsequently compared to static engine limits, or by detailed engine models that are rarely integrated with sufficiently detailed propulsion models for load change estimation. To investigate the dynamic engine (overloading) behaviour and ship propulsion performance under various heavy operating conditions, a Mean Value First Principle Parametric (MVFPP) engine model is integrated into a ship propulsion system model in this paper. An upgraded thermodynamic-based MVFPP model for two-stroke marine diesel engines is presented, in particular a newly developed MVFPP gas exchange model. Based on the integrated propulsion system model of a benchmark ocean-going chemical tanker, the engine dynamic behaviour during ship acceleration, deceleration and crash stop has been investigated. Results show that, during dynamic processes, the engine could be thermally overloaded even if the engine power trajectory is inside the static engine operating envelope. The paper contributes to finding proper indicators for thermal overloading of modern two-stroke marine diesel engines. It is demonstrated that when matching the engine with the propeller and designing the ship propulsion control system, not only the static engine operating envelope, but also the dynamic engine behaviour should be considered.

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The current literature on solid oxide fuel cell and internal combustion engine (SOFC-ICE) integration is focused on the application of advanced combustion technologies operating as bottoming cycles to generate a small load share. This integration approach can pose challenges for ships such as restricted dynamic capabilities and large space and weight requirements. Furthermore, the potential of SOFC-ICE integration for marine power generation has not been explored. Consequently, the current work proposes a novel approach of SOFC-ICE integration for maritime applications, which allows for high-efficiency power generation while the SOFC anode-off gas (AOG) is blended with natural gas (NG) and combusted in a marine spark-ignited (SI) engine for combined power generation. The objective of this paper is to investigate the potential of the proposed SOFC-ICE integration approach with respect to system efficiency, emissions, load sharing, space and weight considerations and load response. In this work, a verified zero-dimensional (0-D) SOFC model, engine experiments and a validated AOG-NG mean value engine model is used. The study found that the SOFC-ICE integration, with a 67–33 power split at 750 kWe power output, yielded the highest efficiency improvement of 8.3% over a conventional marine natural gas engine. Simulation results showed that promising improvements in efficiency of 5.2%, UHC and NOx reductions of about 30% and CO₂ reductions of about 12% can be achieved from a 33–67 SOFC-ICE power split with comparatively much smaller increments in size and weight of 1.7 times. Furthermore, the study concluded that in the proposed SOFC-ICE system for maritime applications, a power split that favours the ICE would significantly improve the dynamic capabilities of the combined system and that the possible sudden and large load changes can be met by the ICE.

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Hybrid propulsion and using liquefied natural gas (LNG) as the alternative fuel have been applied on automobiles and some small ships, but research investigating the fuel consumption and emissions over the total voyage of ocean-going cargo ships with a hybrid propulsion and different fuels is limited. This paper tries to fill the knowledge gap by investigating the influence of the ship mission profile, propulsion modes and effects of different fuels on the fuel consumption and emissions of the ship over the whole voyage, including transit in open sea and manoeuvring in close-to-port areas. Results show that propulsion control and electric power generation modes have a notable influence on the ship's fuel consumption and emissions during the voyage. During close-to-port manoeuvres, propelling the ship in power-take-in (PTI) mode and generating the electric power by auxiliary engines rather than the main engine will reduce the local NOx and HC (hydrocarbons) emissions significantly. Sailing the ship on LNG will reduce the fuel consumption, CO₂ and NOx emissions notably while producing higher HC emissions than traditional fuels. The hybridisation of the ship propulsion and using LNG together with ship voyage optimisation, considering the ship mission, ship operations and sea conditions, will improve the ship's fuel consumption and emissions over the whole voyage significantly.

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The hybrid internal combustion engine-solid oxide fuel cell AmmoniaDrive concept is a single-fuel, high-efficiency, high-tech ship power/propulsion plant solution that will produce no pollutant emissions. It also strikes the right balance between different, relevant ship design considerations. Too good to be true?@en

Naval ships are designed to operate and survive in hostile environments. As such, vulnerability reduction is a major topic of interest during the design of a naval ship. For modern naval ships the vulnerability is largely determined by the design and layout of distributed systems. The vulnerability of these systems needs to be assessed early on, as design decisions made in this stage are decisive for the vulnerability of the final ship. Various early stage methods for assessing vulnerability exist, but a clear structure on when to use what types of methods, how these methods relate to each other, and how these methods provide relevant answers, is still lacking. To address this gap, this paper introduces a framework for early stage design of distributed systems, in the context of vulnerability reduction. This framework supports in choosing the right vulnerability method at the right design stage. The framework considers an operationally oriented systems perspective on vulnerability, and a physically oriented ship perspective. In addition to that, early stage design is subdivided in concept exploration and concept definition, which have different purposes and contributions in the design process. The framework provides examples of methods that can be used to investigate vulnerability for the various perspectives and design stages. These examples consider methods that have been developed by joint Delft University of Technology (TU Delft) and the Netherlands Defence Materiel Organisation (DMO) research efforts, as well as other methods. Opportunities and challenges for integrating these methods between themselves and in the design process in general are discussed.@en

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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The increasing economic cost and environmental impact of maritime transportation necessitate the reduction of fossil fuel consumption of ocean-going cargo ships. Although fundamental ship propulsion system theory is well-known and is at a mature stage of development, there is still an enormous variety in the assessment methodology of (environmental) transport performance of ships. Furthermore, calibration of ship propulsion system model parameters with testbed, towing tank and full-scale measurement data is rare, as these measurements are both difficult and expensive. Finally, the effects of different power management strategies on the ultimate energy conversion effectiveness of typical cargo ships have rarely been investigated systematically. In this paper these three issues are discussed, addressed and solved for a representative benchmark chemical tanker. This ship was chosen to investigate the so-called energy conversion effectiveness under various propulsion control and electric power generation modes, as ample real ship data is available. The transport performance assessment of the ship's power plant is generalised for hybrid arrangements with either Power-Take-Off or Power-Take-In. The results show that an optimal combination of propulsion control, power management and voyage planning will further reduce the global fuel consumption and CO₂ emissions produced by the shipping industry.

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Underwater exhaust systems are employed on board ships to allow zero direct emissions to the atmosphere with the possibility of drag reduction via exhaust gas lubrication. However, underwater expulsion of exhaust gases imparts high and dynamic back pressure, which can fluctuate in amplitude and time period as a ship operates in varying sea-states depending on its geographical location and weather conditions. Therefore, this research aims to experimentally investigate the performance of a marine diesel engine against varying amplitudes and time periods of dynamic back pressure at different sea-states due to underwater exhaust systems. In this study, a turbocharged, marine diesel engine was tested at different loads along the propeller curve against dynamic back pressure waves produced by controlling an electronic butterfly valve placed in the exhaust line after the turbine outlet. Engine performance was investigated against single and multiple back pressure waves of varying amplitudes and wave periods based on real sea-state conditions and wave data. We found that the adverse effects of dynamic back pressure on engine performance were less severe than those found against static back pressure. Governor control and turbocharger dynamics play an important role in keeping the fuel penalty and thermal loading low against dynamic back pressure. Therefore, a marine engine may be able to handle much higher levels of dynamic back pressures when operating with underwater exhaust systems in higher sea-states.

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This paper demonstrates the usefulness of an automatic topology generator that uses genetic algorithm techniques to generate many alternative system designs and in doing so enables design space exploration for on-board energy distribution systems. This will provide better insight in the relation between design requirements (e.g. budget), system design solutions and important perfor-mance characteristics like ship survivability in early design stages. The basic idea is to apply proven techniques as used for ship configuration (i.e. hull and layout design) to the design of “ship service systems”. The case study will consist of multiple, interconnected systems on board an Ocean-going Patrol Vessel that distribute electric power, chilled water and mechanical (propulsion) power.@en

Several studies address early design of land-based and automotive energy distribution systems using network theory. Energy distribution systems on board of high-risk maritime craft are however rarely investigated in this way. In this article a method for automatically generating network topologies for vital energy distribution systems on board of ships is presented. The method combines fundamentals of network theory with marine engineering heuristics to introduce a generic yet realistic framework for node and edge differentiation. The framework is combined with a genetic algorithm to enable Automatic Topology Generation for design space exploration. The developed ATG tool enables trade-off analysis by visualising a Pareto front of optimal design solutions with respect to the opposing design objectives of system robustness and the “claim” of the systems on the ship (i.e. weight and space requirements, costs and operability). A novel robustness metric for vital on-board energy distribution systems is presented that enables the assessment of system reconfigurability. A critical review of this metric is provided in the article as well, as robustness as a design objective is particularly hard to capture. The method can be used by system designers as a decision support tool in early-stage ship/on-board system design.@en

A naval submarine sails in different operational modes: surfaced, at periscope depth or submerged. It needs an appropriate power plant to do so. The impact of the selected power plant on the overall submarine design is significant. Selecting the right components of the power plant in an early stage is therefore key to a successful design. Current early-stage design methods are based on known design solutions like diesel-electric or fuel-cell driven power plants and have difficulty coping with novel solutions like a combination of diesel-electric and fuel cells or permanent magnet propulsion motors. An earlier developed mean value first principle power plant model is extended in this research with a PEM Fuel Cell model as Air Independent Power (AIP) system and a Permanent Magnet Synchronous Machine model as propulsion motor. The overall power plant model covers energy generation, storage and distribution to the main power demands “propulsion” and “auxiliary”. The model enables optimization of a submarine power plant to balance the required space, mass and operational performances based on a pre-set operational profile. A total of eight configurations (mix of Lead acid or Li-Ion battery, Fuel Cell AIP, compound or permanent magnet motor) were assessed against ten operational profiles. The result is insight into optimized design concepts considering volume, mass and efficiency (ultimately operational cost) given operational needs that extend beyond current submarine capabilities.@en