Design with uncertain qualitative variables under imperfect knowledge

To support early design and design under risk, it is necessary to have methodologies to process the various forms of uncertainties. Three independent dimensions of uncertainty are identified in the paper as certainty of analysis (epistemic uncertainty), random variability (stochastic variability and design indecision) and type of variable. The type of variable is further categorized into six scales that are broadly grouped into quantitative and qualitative. Common engineering modelling tools used for design do not operate well on combinations of random variables, qualitative variables and imperfect knowledge. The hypothesis of this paper is that a modelling system could be developed to accommodate the multiple types of uncertainty that can exist during engineering design. This is worth doing as accommodating design uncertainty is an important part of risk management in engineering. The paper then proceeds to describe the way in which the design for system integrity (DSI) methodology meets these objectives. DSI may be used to create models with uncertain variables (including textual and non-ordered), given subjective and imperfect knowledge (including uncertain opinion). Consequently, DSI supports risk management in engineering design.