This thesis presents a case study which is based on our experience and lessons learnt from modelling a control system using the state-of-the-art modelling language for systems engineering, Systems Modelling Language (SysML). The goals of this thesis are to (1) capture the structure and behaviour of a control system using SysML, (2) handling the development of safety requirements, (3) support generation of safety cases, a structured collection of arguments for system safety, by creating traceability links between requirements and model elements, (4) assess SysML capabilities in modelling control systems and supporting generation of safety cases.
This case study is part of the “ModelME!” project which is conducted at Simula Research Laboratory with industry partners. The aim of the “ModelME!” project is to devise better software engineering practices for Integrated Software-Dependent Systems in the Maritime & Energy sectors.
Based on the experiences of this and other simultaneous projects in the “ModelME!” project, a methodology for modelling control systems to support safety certification has been proposed. We use this methodology to present the SysML model, developed in this case study. The methodology takes a systematic approach and guides us through the process of designing a control system, from the first steps of capturing requirements, system functionality and environmental assumptions through the development of structural and behavioural diagrams and last, but not least the modelling of safety design, developing the requirements to avoid ambiguity and tracing model structures to the requirements.
In this thesis we create a comprehensive set of models to capture our case study from requirement, structure and behaviour points of view and present these models following the methodology mentioned above. We create traceability links between the requirements and design model elements/slices with the goal of assisting safety engineers in the generation of safety cases. Then we discuss the capabilities of SysML and our chosen tool regarding the creation of models for control systems and supporting safety case generation. Further we summarize lessons learned, potential improvements and directions for future work.