Methods for Refinement of Structural Finite Element Models: Summary of the GARTEUR AG14 Collaborative Programme

Abstract

The finite element model is the main tool used by helicopter manufacturers for the analysis of helicopter structures and in particular for the prediction of vibration. High fidelity models that can accurately represent the structural dynamics are the key to producing effective low vibration designs. Helicopters with ‘jet’ smooth comfort are demanded by discriminating customers who also require ownership of vehicles with high reliability, low maintenance and reduced through life costs. The finite element model is an important tool in the assessment of aircraft modifications after the initial design and production when adverse vibration levels may become apparent. At this stage a structure is available and measured dynamic data from a shake test may be used to validate and improve the initial finite element model. The model derived from test data is not, by itself, comprehensive enough to allow the study and manipulation of the structural dynam-ics but its role in conjunction with the finite element model is a vital step towards improving the helicopter structural design. The main purpose of this GARTEUR collaboration was to explore methods and procedures for improving finite element models through the use of dynamic testing. For the foreseeable future it is expected that shake tests combined with finite element models will be the major tool for improving the dynamic characteristics of the helicopter structural design. It is there-fore of great importance to all participants that the procedure of validating and updating heli-copter finite element models is robust, rigorous and effective in delivering the best match based on realistic engineering adjustments to the finite element model. The industry need for finite element models, the variety of update procedures and their advan-tages are discussed in this paper together with some requirements for dynamic testing. The results of a systematic study on the model updating of a Lynx Mk7 airframe are presented and conclusions drawn. Recommendations are made with regard to performing subsequent dy-namic tests, model updating and for future collaborative study.