Keywords: karoo array telescope, numerical design optimisation, structural optimisation, size optimisation, shape optimisation, topology optimisation, finite element model.

The present paper provides an overview of the application of structural optimisation to a real-life design problem. Within structural optimisation, the optimisation problem is most often formulated to minimize the mass of a structure. Although mass minimization is an important application, other applications include: (1) concept generation, (2) concept evaluation, (3) structure failure prevention and (4) data matching. These applications are discussed in the paper, while an illustration of mass minimization and concept evaluation are given by means of the engineering problem.

A prototype design of the KAT (Karoo Array Telescope) which is a predecessor of the SKA (Square Kilometer Array), is used to illustrate different optimisation applications. A full scale prototype of the design was built, but found to be too expensive. A detailed finite element model of the final design was considered as a testbed for reducing costs using structural optimisation techniques. The goal of the present study is to find the lightest structure that will satisfy all the design requirements.

Numerical design optimisation provides a powerful tool that aids the designer in the design process. It is especially helpful, in the design of complex systems where it is often difficult to understand the interaction between variables within the system, especially when the number of variables becomes large.

Size- and shape optimisation are applied to three components of the KAT, using a detailed finite element analysis, while considering wind, temperature and gravity loads. The constraints used during the design cycle are stress, displacement, frequency and dish surface accuracy. The coupling of a structural optimisation code with an external analysis program to include non-structural responses, in this case dish surface accuracy, will also be illustrated.

In conclusion, it is shown that if a finite element model is readily available, it is generally possible to apply structural optimisation to improve the existing design. In the present work a real-life engineering problem was considered. This problem passed through the design process and a full scale prototype was built. Even for this finalized design, the application of structural optimisation resulted in a reduction of 1834 kg of steel, a weight saving of 25.2 % for the the components that were optimized. Looking only at the material cost of a single antenna will result in a large cost saving without even considering manufacturing, transport and labour costs. If it is considered that a large amount of these antennas will be manufactured, then a small cost saving for one antenna will result in a large cost saving for the whole project.

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