Abstract

The objective of the present thesis is to quantify designer's mental stress during the conceptual design process, in which designers usually describe the design problem and design solutions using natural language, combined with sketches. In the process of solving a design problem, the design problem itself will evolve according to the design solutions generated at each step of the design. The design problem together with its solutions at each step is called a design state. Quantifying the designer's mental stress would assist in understanding the designer's creative and innovative design process, through which a design methodology can be optimized. In the present thesis, a cognitive experiment is used to study the quantification of the designer's mental stress. Subjects were invited to design a new litter-disposal system in a passenger compartment located in the trains of NS (Dutch Railways). In quantifying the designer's mental stress, the recorded design protocol data is firstly segmented into design states, each of which is then encoded into a Recursive Object Model diagram through linguistic analysis. The number of objects and relationships included in an ROM diagram is then used to quantify the designer's mental stress. The validation through the cognitive experiment shows that ROM is an effective encoding scheme. The analysis presented in this research shows that the designer's mental stress changes in a dynamic, nonlinear, and spiral manner along with the time.