85th European Study Group with Industry

16th–20th April 2012, University of East Anglia, Norwich

Efficient Geometrical Description of Perturbations to Designed Shape

A problem brought to the 85th European Study Group with Industry by Airbus Operations Ltd.

Problem Description

Manufactured artefacts such as major aircraft components (wings, fuselage, tailplane) are defined at the concept and design stages using a variety of methods, namely Computer Aided Design (CAD), NACA aerofoil definitions or purely analytical descriptions (polynomials, splines, etc.). These descriptions are used in a variety of ways for aerodynamic or structural analysis using computational (numerical) and analytical methods, as well as for physical testing.

At the end of the design, development and testing phases the final manufactured artefact can only be verified if it is measured. This measurement data is always a set of discrete points commonly described as a point cloud of data (x, y, z coordinates) describing the surface or surfaces of the component under consideration. The accuracy of these measurements is an essential part of the assessment of whether design intent has been achieved.

The types of component under consideration in this project are ones which are required to be made to a very high accuracy and precision so that extremely demanding performance requirements are met. Under these conditions there are well understood sources of error in the manufacture which will necessarily cause unwanted deviations from the intended design shape. It is these deviations that we wish to characterise and parameterise so that it becomes possible (and maybe even much simpler) to analyse them and determine their effect on component performance.

Study Group Report

Airbus wish to have efficient ways of describing perturbations of a manufactured aerofoil from its design shape. The typical kind of perturbations expected are waves, steps, and bumps, and automatic classification into the classes is desired. Various possible methods of analysis were proposed and studied in some detail, including projection onto suitable basis functions, wavelets, and radial basis functions. Other methods were studied in less detail, but with the aim of giving a digital signature of defects that could be used to classify them.