Local shape optimisation of a firtree root using NURBS

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Description/Abstract

This paper describes a general shape
optimisation method for a structural optimisation
problem using a combined feature-based and B-spline
based free form geometry modelling approach. The
geometry is defined by a number of features for the
global shape and by Non-Uniform Rational B-splines
(NURBS), via the use of control points for the local
shape. The coordinates of the control points along
with other dimensions are chosen as design variables.
A knot insertion/removal process is introduced to
increase flexibility and to obtain a compact definition
of the final optimised shape. Here the geometry is
modelled using an intelligent CAD system (ICAD),
which enables complete automation of the design-toanalysis
process. Stresses are obtained from finite
element analysis. A two-stage hybrid strategy is used
to solve the formulated optimisation problem. Its
application to the design of a turbine disc firtree root
is demonstrated. This new approach is compared to a
more traditional optimisation analysis using a
geometry model based on straight-lines and circulararcs.
Improvements in the objective function and
flexibility in geometry definition are achieved
compared to designs obtained using the traditional
approach.