A Markov-based vulnerability assessment of distributed ship systems in the early design stage

Naval ships are designed to operate in hostile environments. As such, vulnerability reduction is an important aspect that needs to be assessed during the design. With the increased interest in electrification and automation on board naval ships, the vulnerability of distributed systems has become a major topic of interest. However, assessing this is not trivial, especially in early stage design, where the level of detail is limited, but consequences of design decisions are large. As such, a new method for assessing the vulnerability of distributed systems in early stage design has been developed. This method not only evaluates the vulnerability of a pre-defined ship concept, but also provides direction for finding other, potentially better concept. This is done from the perspective of operational capabilities. The method helps ship designers and naval staff in setting vulnerability requirements, developing new concepts, and identifying trade-offs in operational capabilities. The method uses a discrete Markov chain and the eigenvalues of the associated transition matrix. A test case considering vulnerability of a notional Ocean-going Patrol Vessel (OPV) with two different powering concepts illustrates the method. Furthermore, the new method is discussed in terms of design knowledge, including a comparison with other early stage vulnerability reduction methods. In addition to that, an improvement of an existing early stage design procedure for distributed ship systems is made, which shows how the various methods, including the new method, are envisioned to be applied in practice.Ship Design, Production and Operation

The influence of the bow shape of inland ships on the resistance

Due to financial and environmental considerations there is a need to reduce the fuel consumption in the inland shipping sector. This can be realised by improving the hull design. This research focusses on the bow shape of inland ships. The bow shape with the lowest resistance is not by definition the best bow shape, since other factors such as load capacity play a role as well. Therefore it is researched what the influence of the bow shape is on the resistance. The designer could use this knowledge for finding an adequate trade-off between the resistance and the load capacity. The main research question is: What is the influence of bow shape parameters on the resistance of an inland ship? The research is limited to the ship type Groot Rijnschip, bulbous bows are not included and a reference stern shape is selected that remains unchanged during the research. First is has been investigated which parameters describe the bow. Eight parameters are defined: the bow length, the ship volume, the waterline entrance angle, the rake, the waterplane coefficient, the slope of the sectional area curve at two points in the bow and the ratio between to waterplane areas in the bow. A set of 133 ships with different bow shapes is generated, in which these parameters are varied in a random way. Subsequently it has been determined which parameters are relevant for sailing in restricted water. The sailing speed and water depth are selected for this. The wave making resistance is expected to be the resistance component that is influenced most by the bow shape. Therefore the wave making resistance is calculated with the potential code RAPID for all 133 bows at eight combinations of Froude numbers and water depths. The values for the wave making resistance that are returned by RAPID are suitable for comparing the different bow shapes, but not for predicting the absolute value of the resistance. Since the calculations are carried out at low Froude numbers, the results are subjected to relative large numerical uncertainties. Linear regression models are fitted to the results to evaluate which bow shape parameters have the largest influence on the wave making resistance. These parameters turn out to be the bow length, the ship volume and the two points that describe the slope of the sectional area curve. The way in which the parameters influence the wave making resistance is described in the models, which answers the main research questions. However, there are several restrictions to the models: they are not able to predict the absolute value of the wave making resistance and the coefficients in the models are strongly influenced by outliers in the data obtained from RAPID. The original assumption that the viscous resistance does not change significantly has been checked with several viscous double body calculations in PARNASSOS. The results support the assumption. For practical applications, the ratio between the wave making resistance and the ship volume should be as low as possible. This results in bows shapes with a steep increase of volume at the front part of the bow and a smooth transition between the bow and the parallel midship. For further research it is recommended to obtain a better estimate of the absolute value of the resistance. In this way it can be quantified what the influence of the bow shape on the wave making resistance means for the total ship resistance. If this more reliable data is obtained, it can be combined with data from the stern shape. In this way a detailed, adequate resistance prediction method for inland ships can be generated.Mechanical, Maritime and Materials EngineeringMarine and Transport Technolog

A Markov-based vulnerability assessment for the design of on-board distributed systems in the concept phase

Naval ships are designed to operate in a hostile environment. As such, vulnerability is an important aspect that needs to be assessed during the design. With the increased interest in electrification and automation on board naval ships, the vulnerability of distributed systems has become a major topic of interest. However, assessing this is not trivial, especially during the concept phase, where the level of detail is limited, but consequences of design decisions are large. Many existing vulnerability methods assess the vulnerability of pre-defined concepts, and focus on systems rather than capabilities. To address this, a new method for assessing the vulnerability of distributed systems in the concept phase has been developed. This method not only evaluates the vulnerability of a pre-defined concept, but also provides direction for finding other, potentially better solutions. This is done from a capabilities perspective. The method helps ship designers and naval staff in setting vulnerability requirements, developing new concepts, and identifying trade-offs in capabilities. The method uses a discrete Markov chain and the eigenvalues of the associated transition matrix. A test case considering vulnerability of a notional Ocean-going Patrol Vessel (OPV) with two different powering concepts illustrates the method.Accepted Author ManuscriptShip Design, Production and OperationsMarine and Transport Technolog

Towards a novel design perspective for system vulnerability using a Markov chain

In order to investigate to which extent naval ships can execute their operational scenario after damage, an early stage assessment of the vulnerability of distributed systems needs to be carried out. Such assessments are currently mostly done by evaluating the performance of predefined concepts. However, such an approach does not necessarily lead to the most desirable solution, since solutions outside the scope of the designer’s preconceived ideas or experience are inherently hard to investigate. This paper therefore proposes several steps towards an approach that enables a vulnerability assessment that is independent of predefined concepts. This is done by incorporating several additions to an existing system vulnerability approach developed by the authors, using a Markov chain. With this approach there is no longer a need for modelling individual hits or damage scenarios. Whereas the approach has previously been shown in concept, this paper introduces three improvements that contribute to the applicability of the approach: 1)it is scaled up in order to model a larger number of compartments and distributed systems, 2) the hit probabilities for different compartments can be adjusted, and 3) it is shown how the availability of main ship functions can be derived from the availability of individual connections. A test case that compares two powering concepts (conventional and full electric powering) of a notional Oceangoing Patrol Vessel (OPV) is provided to illustrate the principles behind the improvements. From the results the two main contributions of this paper can be obtained: 1)the possibility to assess the system vulnerability for different levels of required residual capacity at different impact levels, and 2) and the quantitative nature of the results, aiding ship designers and naval staff with understanding the consequences of various concepts on the system vulnerability.Ship Design, Production and Operation

Assessing complex failure scenarios of on-board distributed systems using a Markov chain

Vulnerability reduction is an important topic during the design of naval ships because they are designed to operate in hostile environments and because their on-board distributed systems are becoming increasingly complex. The vulnerability needs to be addressed in the early design stages already, in order to prevent expensive or time-consuming modifications in later, more detailed design stages. However, most existing methods for assessing the vulnerability are better suited for more detailed design stages. Furthermore, existing methods often rely on pre-defined damage scenarios, while damage–or system failure in general–may also occur in ways that were not expected beforehand. This paper proposes a method that addresses these gaps. This is done by incorporating several additions to an existing vulnerability method that has been developed by the authors, using a Markov chain. With this method, there is no longer a need for modelling individual hits or failure scenarios. The additions are illustrated by two test cases. In the first one, a notional Ocean-going Patrol Vessel is considered, and damage is related to physical locations in the ship. The second test case considers a chilled water distribution system in more detail, with failures modelled independent from the physical architecture. The quantitative nature of the results provide an indication of the generic, overall vulnerability of the distributed systems, which is meant to be used in the early design stages for identifying trade-offs and prioritising capabilities.Ship Design, Production and OperationsMarine and Transport Technolog

The Design Knowledge Management Square - a Framework for Early Stage Complex Ship Design

This paper presents and demonstrates a new design thinking framework for early stage complex ship design, called the Design Knowledge Management Square (DKMS) framework. The DKMS framework provides a structure that explicitly incorporates the collaborative nature of complex ship design, contrary to other models or frameworks that primarily focus on the technical integration of tools and methods to describe early stage complex ship design. The DKMS framework is applied to three case studies: 1) multi-disciplinary early stage design of complex ships, 2) the integration of concept design generation and analysis methods, and 3) the application of design rationale to support collaborative design decision-making. The case studies show that the DKMS framework provides added value by explicitly describing both the collaborative and technical nature of complex ship design. Thereby the framework helps to analyse, support, and understand complex ship design.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Ship Design, Production and Operation

A framework for vulnerability reduction in early stage design of naval ship systems

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.Accepted Author ManuscriptShip Design, Production and OperationsMarine and Transport Technolog