Design and optimisation of an Ariane LOX line cover: Use of IDL in B2000

In June 2000 a two-year joint programme by Fokker Space (FS), Centre of Lightweight Structures (CLC), and the National Aerospace Laboratory NLR was started to develop, manufacture, and qualify a demonstrator fairing. The programme is funded by the Netherlands Agency for Aerospace Programmes (NIVR) within the framework of the national NRT programme. Within the joint programme NLR contributed to the preliminary design and was responsible for the design optimisation. The design optimisation was performed with the B2000 code. In the preliminary design phase the loads on, and the requirements for, the Liquid Oxygen (LOX) fairing were investigated. Different options were considered for materials, manufacturing processes and design concepts. Trade-offs supported by preliminary analyses showed that a CFRP stiffened skin concept in combination with Vacuum Assisted Resin Transfer Moulding (VARTM) technology was the most promising concept in terms of cost reduction, weight reduction and possibilities to use the same concept for other fairings as well. For the design optimisation, first the LOX fairing was discretised into a FEM analysis model. This has been done manually using the Input Description Language (IDL) of the B2000 code. Using this scripting language it is possible to build the model in substructures. Also loads, boundary conditions and materials were translated into B2000 FEM-format. Next, a FEM optimisation model was made. The optimisation model describes which design parameters may vary, which conditions should be met, and how the search for better designs is controlled. The description was done manually using the Optimisation Model Input Description Language (OMIDL) of the B2000 code. The same kind of structuring has been used as for the analysis model. Several initial designs, each with a different number of stiffeners, have been analysed and optimised, resulting in a range of optimised designs, from which one design has been selected and analysed in detail. This design is the result of analyses and optimisations with estimated material properties. B-basis allowables will become available from a test programme, which will be completed in the beginning of 2001. The B-basis allowables will be used in a new set of optimisations and analyses, resulting in a final design. This design, which will be further detailed and analysed (e.g. connections), will result in the issue of production drawings of a mould and a full scale fairing demonstrator in the year 2001. Paper presented at the 3rd B2000 Workshop, University of Twente, 27-28 November 2000.