Parametric Design of Three-Dimensional Hydrodynamic Shapes

Naval Research Laboratory, Washington, DC

A method of parametric design of bodies having arbitrary three- dimensional shapes has been invented. The method is intended mainly for use in the design, analysis, and manufacture of propeller and propulsor blades, submarine sails, ship hulls, rudders, control vanes, sonar domes, and other bodies for which hydrodynamic or aerodynamic properties are important considerations.

A Parametric Design System converts an initial design of a three dimensional shape from a standard CAD form into a parametric form in which geometric features are more easily correlated with performance. In an iterative design process, the design is modified in the parametric form and converted back into the standard form for further analysis.

The method can be implemented by means of a system of computer hardware and/or software. In a typical application of the method (see figure), the parametric design system is used in conjunction with a computer-aided design (CAD) system and a computational fluid dynamics (CFD) system in an iterative design-and-analysis process. An initial design in a standard CAD form is generated by or with the help of the CAD system. A feature extractor in the parametric design system converts the design into parametric forms in which geometric features are more easily correlated with streamlines and with hydrodynamic or aerodynamic performance. For example, in the case of a propeller blade, the feature extractor converts the initial standard-form CAD specification of the three-dimensional blade shape into several parametric forms that notably include two-dimensional spanwise and chord-wise thickness distributions and chord-wise camber distributions.

The output of the feature extractor is fed to a geometry modifier, which modifies the parametric representations of the design in response to a database representing the relationships among performance and design parameters. The modified parametric representations of design are fed to a design generator, which processes them into a new design of the three-dimensional shape. A design analyzer, which can include or utilize a CFD system, effects a performance analysis of the new design and contributes the results of the analysis to the performance/ parameter database. Depending on the results, the design can be used either to generate a final CAD file or else further modified and analyzed.

This work was done by James L. Dick of the Naval Undersea Warfare Center for the Naval Research Laboratory.