Forthcoming articles


International Journal of System of Systems Engineering


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International Journal of System of Systems Engineering (12 papers in press)


Regular Issues


  • An LMI approach to design robust H_infinity controller for 2-D systems with delays   Order a copy of this article
    by Khalid Badie, Zakaria Chalh, Alfidi Mohammed 
    Abstract: This paper focuses on $H_{infty}$ controller design for two-dimensional (2-D) discrete state delay systems described by the second Fornasini-Marchesini local state space (FM LSS) model with polytopic uncertainties. The objective is to design a robust state feedback controller such that the corresponding closed-loop system achieves robust asymptotic stability and guarantees a prescribed $H_{infty}$ performance index for all admissible uncertainties. Based on parameter-dependent Lyapunov functions and Finsler's lemma, a new sufficient condition for $H_{infty}$ performance analysis of 2-D discrete systems with delays is developed. Then a stabilizing state feedback controller is designed. A simulation example is exploited to show the effectiveness of the proposed approach.
    Keywords: 2-D state-delayed systems; State feedback; $H_{infty}$ performance; polytopic uncertainties.

  • Hypergraph Restructuration for the Supervision of System of Systems   Order a copy of this article
    by Hamza Cherif Bouchaour, Hafid Haffaf 
    Abstract: This article focuses on the ability of System of Systems (SoS) to cope with failures of one of its constituents. The aim is to avoid the collapse of the whole system. To find a new state of the operation, we introduce a hypergraphic model-based supervision framework dedicated to SoS. It involves two main steps named the modelling and the reconfiguration. Our main objective is to reduce computational complexity of the supervision procedure. For the modelling part, given the high density of connections of the hypergraph representing SoS, we propose to decompose this model by means of the hypergraph tree-based acyclicity property. The latter yields a resolution of the problem in linear time. For the reconfiguration part, we introduce a new subgraph isomorphism procedure enhanced by a filtering function. The lens is to deal with the hypergraphs constraints of complexity induced by such method. Finally, constraint programming method, and according to solver approaches, some models are implemented.
    Keywords: SoS; hypergraph; constraint satisfaction; acyclicity; subgraph isomorphism; computational complexity.

  • Multi-objective multi-customer project network: Visualizing interdependencies and influences   Order a copy of this article
    by Frank Stumpe, Polinpapilinho Katina 
    Abstract: Project management methods involve elements planning, organizing and managing the effort to accomplish successful projects. Such activities produce specific outputs. However, there is a lack of model visually describing project level interdependencies and influences in portfolios. The aim of this paper was to extend previous research (Stumpe and Katina, 2017) by developing a visualization approach for dependencies in a multi-objective multi-customer project. Using a network analysis tool, NodeXL different nodes and project node-node dependencies are developed based a case study. The rules for developing a network are the basis for the model. After model construction, which involves key performance indicators as well as internal and external disturbances, a case study involving over 1000 projects is analyzed. We found that soft and hard links in the project can be explained using meme theory. Finally, the research concludes with research implications as well as potential research directions.
    Keywords: complex system governance; hard-linked dependency; key performance indicators; multi-objective project; NodeXL; project network; project portfolio; system modelling.

  • A System of Systems Architecture for the Internet of Things exploiting Autonomous Components   Order a copy of this article
    by Basil Nikolopoulos, Alexandros Dimopoulos, Mara Nikolaidou, George Dimitrakopoulos, Dimosthenis Anagnostopoulos 
    Abstract: As the Internet of Things (IoT) becomes more popular, supporting systems and their components become more complex and largely heterogeneous. This paper discusses on a System of Systems (SoS) architecture for IoT systems composed by autonomous components. The proposed architecture focuses on a middleware transforming sensor services to REST services, for the development of mixed-criticality applications. The middleware consisting of autonomous aggregation software running on commodity multi-core devices, such as Raspberry Pi. Self-management policies applied are discussed in the paper. The analysis of a smart building system, developed as a use case, provides solid evidence that such an architecture is realistic and can lead to highly competitive systems.
    Keywords: IoT; SoS; Edge Devices; Aggregation Software; Autonomous components; self-management policies.

  • A study of an adaptive approach for systems-of-systems integration   Order a copy of this article
    by Ilyas Ed-daoui, Mhamed Itmi, Abdelkhalak El Hami, Nabil Hmina, Tomader Mazri 
    Abstract: Systems-of-systems are a growing composition of complex, autonomous and heterogeneous systems that collaborate in order to achieve complex and evolving targets that exceed the sum of the parts. In fact, the biggest challenge in such environment lays in the preservation of the viability of the system-of-systems and its evolvement while handling component systems' dynamic integrations. This also represents a pressing issue in systems-of-systems engineering. In this paper, we present a collection of definitions dedicated to sire the system-of-systems' concept, their characteristics and typology. Next, we detail the challenges facing the integration process in systems-of-systems. Then, we present our proposition to manage this issue. It is based on an adaptive integration approach to systems-of-systems typology. Two case studies are provided in order to experiment our theory. We evaluate the performance of the approach in both cases. Results are cross-compared.
    Keywords: interoperability; systems-of-systems architecture; simulation; performance evaluation; systems-of-systems integration.
    DOI: 10.1504/IJSSE.2019.10019208
  • Scoring the risk matrix   Order a copy of this article
    by Paul R. Garvey 
    Abstract: In systems engineering, the risk matrix is a popular protocol for binning risks into a collection of probability and consequence cells. In its traditional form, the risk matrix produces a ranking of cells according to their position in an ordered list. From this, management can distinguish whether a set of risks collected in one risk matrix cell has a higher priority than a set of risks collected in another cell. However, if decisions require measuring the relative differences between pairs of cells across their rank positions, then it is necessary to map them from their ordinal scale to an interval scale. This paper introduces methods from representational measurement theory to transform a rank ordered list of risk matrix cells into an interval measurement scale. The transformation produces a scored risk matrix. This allows relative differences among cells to be meaningfully compared, which broadens its use in management decisions. A scored risk matrix provides greater insights into the urgency of risks grouped within cells than is possible in a traditional risk matrix, while remaining within its ease and popularity of use.
    Keywords: systems engineering; engineering management; risk management; risk matrix; risk.
    DOI: 10.1504/IJSSE.2019.10019210
  • Spark!: an integrated resource planning and dispatch tool for power grid modelling   Order a copy of this article
    by Ange Lionel Toba, Mamadou Seck 
    Abstract: The power grid infrastructure faces multiple challenges due to, not only the growing demands, but also the widespread deployment of renewable generation. The increasing level of renewable penetration in the energy mix requires to re-think the way the grid works, operates, and also how it is structured. This makes energy planning more critical as it will necessarily have to account for the effects of intermittence and variability of these sources, and the dynamic behaviour of the overall system. Power grid models can play an important role in performing that task. What is needed, is a new, faster computational model that can simulate large-scale grid operations, while capturing generating units' constraints, system flexibility and architecture. We present Spark!, a grid simulation model, for large scale future power grids over long term horizons. The model developed in Python, and built on a DEVS (Discrete Event System Specification) platform, captures the intermittent and stochastic nature of renewable energy resources and their associated forecast error, the thermal constraints of conventional generation resources, geographical and climate information, the transmission network, with a flexible time resolution.
    Keywords: renewable energy; grid modelling; grid balancing; discrete-event simulation; power grid; electrical systems; data-driven modelling; emissions; grid reliability; DEVS; resource planning; systems engineering.
    DOI: 10.1504/IJSSE.2019.10019214
  • Minimum variance control strategy for closed loop linear time invariant system   Order a copy of this article
    by Jian-hong Wang 
    Abstract: To design one feedback controller in a closed loop linear time invariant system, the idea of minimum variance control is used to realise this goal. Two explicit forms corresponding to the closed loop system are considered, i.e., its general form and rational transfer function form respectively. Firstly one closed form solution of the minimum variance controller is derived in the general form of the closed loop linear time invariant system, and an optimisation algorithm is proposed to obtain controller in practice. Secondly in the rational transfer function form of the closed loop linear time invariant system, the minimum variance controller is determined, while guaranteeing the modified variances of output and input as small as possible.
    Keywords: minimum variance control; modified cost; closed form solution; alternating direction method of multipliers.
    DOI: 10.1504/IJSSE.2019.10019220
  • The need for simple educational case-studies to show the benefit of soft operations research to real-world problems   Order a copy of this article
    by Andrew Collins, John Shull, Ying Thaviphoke 
    Abstract: Soft operations research (OR) methods have the potential to provide deep qualitative insights into the complex problems that face our world. However, the propagation of soft OR has, at best, stagnated in recent years and it has been rejected from mainstream academic hard (quantitative) OR. In this paper, it is proposed that there is a need for simple educational example that actually shows the benefit of soft OR. The paper suggests that these examples should be real-world case studies that do not include convoluted graphics or verbose prose descriptions. An example case study has been included in this paper. This case study investigates the impact of beer price changes to two virtually identical restaurant-bars in the Hampton Roads region of the USA. The case study shows that a simple quantitative analysis results in erroneous conclusions which could be avoided by conducting a simple qualitative analysis.
    Keywords: qualitative methods; soft operations research; problem structuring methods; restaurant revenue management; educational case studies.
    DOI: 10.1504/IJSSE.2019.10019225

Special Issue on: Soft Operations Research Methods for Complex Systems

  • Categorizing and clustering knowledge in Fuzzy Cognitive Maps   Order a copy of this article
    by Alexander Metzger, Steven Gray, Ellen Douglas, Paul Kirshen, Nardia Haigh 
    Abstract: The literature on managing environmental hazards in complex human-natural systems increasingly acknowledges the importance of integrating diverse stakeholder mental models into decision-making. Participatory Fuzzy Cognitive Mapping (FCM) provides an effective tool in this process, as it allows representation of mental models as complex causal networks that aid in the study of knowledge and understandings. While most participatory FCM research has studied mental model variation using graph theory and other structural metrics, our goal is to demonstrate a generalizable approach for analyzing perspectives and content. We use a novel method of knowledge categorization to identify variation among stakeholder mental models and explore its implications for social learning and collaboration. In our case study of flood managers in Boston, Massachusetts, our findings include identification of knowledge gaps, differing priorities among individuals and across jurisdictional scales and opportunities for learning and collaboration.
    Keywords: soft systems; fuzzy cognitive mapping; mental models; social-ecological systems; participatory modeling; environmental hazards; flooding; adaptive management; social learning; collaboration; knowledge clustering; knowledge categorization.

  • Systemic Analysis of a Drug Trafficking Mess   Order a copy of this article
    by Nick Sapiano, Patrick Hester 
    Abstract: The United States, in an effort to combat drug trafficking at the federal level, faces an unenviable task. Trying to address this situation involves considerations of drug production, importation, and consumption. The Think-Act-Observe (TAO) approach (Hester & Adams, 2017) provides a multi-methodology for systemically addressing these, and other, complex, interconnected problems. The three stages (Think, Act, Observe) draw on a theoretical foundation of systemic thinking and provide a practical, iterative approach for increasing understanding of the mess under consideration, executing an intervention framework, and analyzing that implementation. This paper presents a practical demonstration of the TAO approach by describing the application of the Think stage and its six constituent perspectives as they pertain to international drug trafficking. After an articulation of the constituent problems of the mess (drug production, importation, and consumption) and their collective stakeholders, the problems are individually subjected to systemic analysis through the perspectives of who, what, why, where, how, and when to build an expanding Fuzzy Cognitive Map; further, the production problem analysis is reported in detail as a case study. These problem-level analyses are then integrated to form a meta-perspective of the drug trafficking mess, which is then utilized in the Act stage to analyze the systemic impact of simulated potential interventions. Recommendations for future action are provided in support of the Observation stage. Armed with these recommendations, problems owners can move forward in an effort to resolve all identified problems in a manner satisfactory to all affected parties.
    Keywords: Systemic thinking; systems analysis; drug trafficking; systems theory; wicked problems; mess.

  • Using rich pictures outside of soft systems methodology: a case study analysis   Order a copy of this article
    by Tessa Berg, Simon Bell, Steve Morse 
    Abstract: The aim of this paper is twofold. Firstly we will highlight how a problem structuring tool, namely the Rich Picture, is being used across many disciplines outside of the soft system methodology which has historically been its home. Secondly, we highlight the controversial presence of non-conforming Rich Picture research and an apparent reluctance to publish from the systems community. In this paper we provide examples of rich picture research used independent from methodology and focus on one case study that uses a novel method of content analysis to appreciate the significance of the stories within their pictures. We demonstrate the theoretical justification and efficacy of an innovation in the assessment of the Rich Picture and its use as a tool to discern issues of importance across mixed groups. We discuss the responses to this work and the implications for innovation within soft OR research. We propose that the Rich Picture should not be seen as sacrosanct just because it derives from a well-established and much respected methodology. We argue that the Rich Picture can be a flexible space where any practitioner can negotiate shared understanding without methodological constraint.
    Keywords: rich picture; soft systems methodology; SSM; innovation; problem structuring.