FUSDESOPT

Numerical Simulation and Design Optimization of a Lower Fuselage Structure with Advanced Integral Stiffening

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 Obiettivo del progetto (Objective)

'This proposal is for the structural analysis and design optimization of the lower fuselage of an aircraft. The objective of the structural optimization is minimum weight and the design constraints fall into two categories; firstly the capability to withstand structural loads with sufficient margins, and secondly constraints relating to the manufacturing methods. The structure to be optimized is a thin-walled metallic structure with stiffening elements (stringers and frames) using three options for the manufacturing technology: 1. Riveted stiffeners (conventional technology), 2. Laser welded integral stiffeners, 3. Load-adapted stiffeners with welded integral knots. The first two options are reference designs to be analyzed and compared with a new proposal based on the third manufacturing technology. Additionally, two types of aluminium alloy will be considered for the weldable options. The work shall be carried out by experienced aerospace engineers at AOES Group BV, a Dutch SME with many years specialist experience in the structural design, analysis and verification of aircraft and spacecraft structures, including FEM-simulation of large components for aircraft fuselage structures. AOES will use design optimization and topology optimization tools in NASTRAN for identifying the preliminary layout and sizing then standard stress and buckling analysis approaches for the accurate simulation of the load-bearing characteristics and detailed mass calculation. For seamless transmission of data and dissemination of results, data can be received or transmitted as engineering drawings, neutral CAD files or CATIA files. AOES also intends to use the resources of its Medialab department to provide attractive 2-D and 3-D rendering of the results of the work performed.'

Descrizione progetto (Article)

Reducing the weight of aircraft can provide important reductions in fuel consumption and associated emissions. EU-funded scientists initiated the project (FUSDESOPT) to evaluate relevant manufacturing methods and structural loads associated with the lower fuselage of an aircraft.

Scientists compared laser beam welding technologies with conventional riveting for thin-walled metallic structures with stiffening elements (stringers) to determine the potential mass savings. They implemented conventional hand calculations first and then analysed the utility, accuracy and computational load of various 2D and 3D finite element method models.

Researchers compared the failure modes of welded stringer configurations predicted by 2D pull-tests with the 3D analyses of panel compression. Panel compression is used to test the dominant static load of aircraft fuselage components. Differences in predicted local failure modes demonstrated that the strength of 3D compression panels cannot be interpolated from 2D pull-test specimens. However, the 2D analyses are valuable for assessing the relative strength of materials and of joints in general. Resistance to structural deformation in pull-test loading suggests good resistance to stringer rotation.

Partners compared a 3D shell model with a 3D solid model to optimise the trade-off between computational load and accuracy. Shell finite elements modelled global behaviours in large regions well in a relatively short time of only a few hours. However, they could not capture the local failures of weld seams with required accuracy.

FUSDESOPT highlighted the advantages and disadvantages of various models of light-weight, stringer-reinforced fuselage components in evaluating laser beam welding versus conventional riveting. Further optimisation of codes to balance accuracy with computational load will facilitate faster development of better designs. Lighter fuselage weight leading to decreased fuel consumption and emissions will benefit the environment. It will also enhance the global competitive position of the EU aircraft industry that is facing an increasingly green consumer profile.