3D solid fin model construction from 2D shapes using non-uniform rational B-spline surfaces

Abstract

A computer aided design (CAD) tool has been specifically developed for rapid and easy design of solid models for surfboard and sailboard fins. This tool simplifies the lofting of advanced fin cross-sectional foils, in this instance based upon the family of standard airfoil series set by the National Advisory Committee for Aeronautics (NACA), whilst retaining a basic parametric description at each cross-section. This paper describes the way in which non-uniform rational B-spline (NURBS) surfaces are created from 2D profile splines, and are then used to generate 3D geometrical surfaces of the fins, which can be imported directly into commercial software packages for finite element stress analysis (FEA) and computational fluid dynamics (CFD). Pressure distributions, lift and drag forces are determined from a CFD flow analysis for various fins designed with this tool, and the results suggest that the incorporation of advanced foils into surfboard fins could indeed lead to increased performance over fins foiled using current standard techniques.