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.