On Design Evaluation Based on Functional Modeling

During early stages of the design process, functional descriptions are often used to describe the design object behavior. Based on the knowledge of such functional descriptions of the design object (i.e. the design parameters contained in these functional relationships), the Pi-theorem is used to derive the associated dimensionless groups. These dimensionless groups are shown to fullll the necessary conditions commonly expected of evaluation parameters. Based on the validity of the consequently established evaluation hypothesis that \any minimal description in the sense of the Pi-theorem is an evaluation", these automatically generated dimensionless groups then serve as evaluation parameters for the purpose of design object evaluation. The properties of this evaluation method, such as minimality, completeness, hierarchical decomposition, consistency, causality and sensitivity analysis of the design variables, are derived and discussed. A brief example of the conceptual design of a gas turbine shows the feasibility of the suggested approach. This design evaluation method should in principle be common to the reasoning process of the engineer since it relies on the traditional engineering technique of dimensional analysis.