Abstract
This paper presents a new method for the identification of geometric design parameters of ISO 484 class propeller blades from scanned point cloud data. The method can be used for tolerance inspection and in-line measurement of manufactured blades, and for wear assessment and reverse engineering of propellers in service. The geometry of the propeller blades is specified by a set of blade sections stacked radially on concentric cylindrical surfaces. For each of these sections, the chord line and mean camber line is determined, and geometric design parameters such as the pitch, skew, chord length, camber, and thickness distributions are identified. The proposed method is a complete procedure for identifying the design parameters of marine propeller blades from point cloud data, and includes a novel method for the precise identification of the mean camber line based on Voronoi diagrams and Delaunay triangulation. The paper includes validation of the proposed method in experiments where reverse engineering is applied to a propeller blade of the KVLCC2 propeller, and in 3D scanning of a large, high-skew thruster blade where the results were compared to CMM measurements.
Highlights
The surface profile of a propeller blade has a vital impact on the efficiency of the propeller
The approach based on Voronoi diagrams and Delaunay triangulation forms a fork in the mean camber line at the section edges if the radius of the Delaunay triangle circumcircles is less than the edge radius, or if the trailing edge has sharp corners
We demonstrate our procedure by identifying the design parameters of two marine propeller blades: a propulsion blade made from synthetically generated data, and a high-skew thruster blade of which we have
Summary
The surface profile of a propeller blade has a vital impact on the efficiency of the propeller. Airfoils are found in fans, compressors, and turbines, which makes it relevant to consider studies on optical blade inspection for other sectors These studies include extraction of the sectional foil curves [10], reconstruction of mean camber line [11], leading edge and trailing edge localization [12], shape matching [13], and position and orientation error evaluations. Patrikalakis and Bardis [14] presented a set of algorithms for the extraction of gross geometrical features of marine propeller blades represented in terms of B-spline surfaces Their approach for camber line calculation requires an involved integration of a system of differential equations along with a complicated error evaluation scheme. Yeo and Choong [6] characterized the design parameters for a small outboard marine propeller Their method is based on interpolating a CAD model of the scanned data, which is a complicated step that is prone to errors and involves several manual steps.
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