Functional prototyping through advanced similitude techniques



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The advent of rapid prototyping (RP) technologies has led to significant improvements in many aspects of the mechanical design process. Among these enhancements is the ability to quickly evaluate the fit and form of a product. Limited material properties and part sizes available from common RP systems, however, have prevented rapid prototypes from being widely used in functional testing. Using rapid prototypes in place of traditional prototypes in functional evaluations of product performance has the potential to significantly reduce overall design costs and improve time to market. Similitude techniques are proposed as a means of correlating the behavior of rapid prototypes with the behavior of a product. The research presented in this dissertation expands our understanding of the capabilities and limitations of current similitude techniques. The similitude techniques that are evaluated include the traditional similitude method (TSM), which is also known as dimensional analysis, and the empirical similitude method (ESM). The concept of system distortion, which causes a model to exhibit a different behavior than the product it represents, is developed for both the TSM and the ESM. Errors in predicted product behavior that result from system distortions are illustrated through numerical and experimental examples. An advanced ESM technique that accounts for system distortions is also presented. The advanced technique utilizes additional models to capture changes in behavior that are caused by system distortions. The increased accuracy that is available from the advanced technique comes at the price of increased effort in model fabrication and testing. Guidelines for selecting the most appropriate similitude approach for a given set of circumstances are presented.