Review and comparison of the modeling approaches and risk analysis methods for complex ship system.

Marine industry is leaning towards autonomous vessels with companies such as Rolls-Royce and Kongsberg leading the development. However, this rapid technological change invites greater risks and responsibilities for marine professionals. Ship systems are getting more complex with time as the interactions between components are increasing and software are getting embedded. As a result, the nature of risks in modern systems can be different than in the traditional systems, where the risks were mostly limited to human errors and component failures. However, for identifying risks in modern complex systems, it is first important to understand the structural composition of the system, and the component’s behavior, functions and interactions. Although, modern systems are quite different than traditional systems, traditional system-safety engineering techniques developed are still widely used. This thesis aims to review a modern modeling approach known as Systems Modeling Language (SysML) and a risk analysis method known as Systems-Theoretical Process Analysis (STPA); and compare them against widely used traditional methods known as the Tree structure method and Fault Tree Analysis (FTA). SysML, developed in 2006, is a graphical modeling language which presents structural composition, component functions, behavior, constraints and requirements of a system. SysML aims to support the analysis, specification, design, verification and validation of complex systems. STPA, developed in 2011, is a risk analysis method which aims to identify and mitigate risks in a complex system. Unlike traditional methods such as Fault Tree analysis (FTA), STPA focuses on risks due to the unsafe control actions and component interactions. Furthermore, STPA can be also used during the early phases of the system development process to generate safety constraints and requirements for a safer design of the system. This thesis also includes a workshop with Rolls-Royce where FTA, STPA, SysML and the Tr