This thesis investigates the nature of systems problems and the need for an open viewpoint to explain a system by viewing it as part of a larger whole and explaining its role in terms of that larger whole. The problem this research investigates is wicked and hence is unique in each instance. Therefore, an empirical proof would only hold for that particular instantiation of the problem, not the problem as a whole. After exposing some of the limitations of traditional systems engineering to this type of problem it is clear that a new approach is needed. The approach taken in the thesis is model driven and it is the architecture of this approach that is the stable artefact rather than the artefacts of a particular solution. The approach developed in this research has been demonstrated to be practicable. Specifically, this research has developed and demonstrated a novel approach for a decision support system that can be used to analyse a system of systems as part of a larger whole from both open and closed viewpoints in order to support the decision of which systems to use to conduct a particular military mission. Such planning decisions are wicked due to the uncertain and unique nature of military missions. Critical rationalism was used to validate the model driven approach and to falsify a parametric approach representative of traditional systems engineering through historical case studies. The main issue found with the parametric approach was the entanglement of functionality with the individual systems selected to implement the system of systems. The advantage of the model driven approach is that it separates functionality from implementation and uses model transformation for systems specification. Thus, although wicked problems do not have an exhaustively describable set of potential solutions this thesis has shown that they are not unapproachable.

This investigation considers the composition, status, principles and defence acquisition setting of systems engineering. From these some opportunities for enhancement of its practice are considered. It opens with a re-assessment of the disciplinary essence of systems engineering. Systems engineering is considered as an amalgam of three components – systems reasoning, engineering and management – that form a coherent and distinctive discipline. It is advanced that a fresh balance of system-related factors, characterised in this text as systems reasoning, is the distinguishing essence of systems engineering. It conveys a rationale for present-day practice and provides a basis for advancements. Consideration is given to the construction of a systems engineering framework, built from a re-interpretation of engineering and management science constructs. A triptych of viewpoints of systems engineering, comprising connected representations of business process, organisational capability and individual competence, is proposed and outlined. These three essential views define a paradigm of systems engineering able to structure present-day engineering complexities and risks, and permit project and enterprise control of business achievement and risk exposure. An analysis of the UK MOD acquisition setting for systems engineering, and an Integrated Project Team Leader survey of prevailing system engineering attitudes, experiences, expectations and concerns, set the scene for practice advancements. The first of these is based on a rigorous view of what capability means and how this impacts IPT technical contributions and responsibilities. The effectiveness of the current MOD acquisition cycle is then considered. An alternative, that might better serve the changing nature of investment constraints and effective capability delivery, is presented. Approaches to systems engineering planning are then analysed and a conclusion drawn regarding a planning instrument for IPTs that balances prescription, guidance and didacticism. An assessment of how requirements assist and hinder working with customers and suppliers dissects the intent and content of requirements, including their contrasting technical and commercial purposes. System descriptions, their relationship and their concordance are then considered in a detailed look inside the technical processes, and this includes the principles and methods employed to design architecture. The resolution of current conflicts and confusions over architecture is seen to lie in observance of disciplined systems engineering principles. Finally the systems engineering views of humans inside and outside the system boundary are explored, and the investigation closes with a consideration of the degree to which systems engineering may reasonably address social influences.

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Hybrid models are those containing continuous and discontinuous behaviour. In constructing dynamic systems models, it is frequently desirable to abstract rapidly changing, highly nonlinear behaviour to a discontinuity. Bond graphs lend themselves to systems modelling by being multi-disciplinary and reflecting the physics of the system. One advantage is that they can produce a mathematical model in a form that simulates quickly and efficiently. Hybrid bond graphs are a logical development which could further improve speed and efficiency. A range of hybrid bond graph forms have been proposed which are suitable for either simulation or further analysis, but not both. None have reached common usage. A Hybrid bond graph method is proposed here which is suitable for simulation as well as providing engineering insight through analysis. This new method features a distinction between structural and parametric switching. The controlled junction is used for the former, and gives rise to dynamic causality. A controlled element is developed for the latter. Dynamic causality is unconstrained so as to aid insight, and a new notation is proposed. The junction structure matrix for the hybrid bond graph features Boolean terms to reflect the controlled junctions in the graph structure. This hybrid JSM is used to generate a mixed-Boolean state equation. When storage elements are in dynamic causality, the resulting system equation is implicit. The focus of this thesis is the exploitation of the model. The implicit form enables application of matrix-rank criteria from control theory, and control properties can be seen in the structure and causal assignment. An impulsive mode may occur when storage elements are in dynamic causality, but otherwise there are no energy losses associated with commutation because this method dictates the way discontinuities are abstracted. The main contribution is therefore a Hybrid Bond Graph which reflects the physics of commutating systems and offers engineering insight through the choice of controlled elements and dynamic causality. It generates a unique, implicit, mixed-Boolean system equation, describing all modes of operation. This form is suitable for both simulation and analysis.