Global-local Knowledge Coupling Approach to Support Airframe Structural Design

Abstract

The outsourcing that has taken place in the aircraft industry over the last few decades has created a globalized supply chain from and to a limited number of original equipment manufacturers (OEMs). This has led to multi-level design due to the shift from airframe subsystem design to suppliers. Increasingly OEMs focus on requirement allocation and definition of airframe subsystems and verification at a global level, whereas suppliers focus on the realization and improvement of airframe subsystems at the local level. Relying on a supply chain for innovative designs and builds can cause OEMs to have insufficient bottom-up knowledge about subsystem design, in particular, the innovative local designs, e.g. composites and new production methods, however, in the overall aircraft conceptual design phase, the analysis and evaluation of different subsystem designs, by OEM internally, rely heavily on assumptions and estimations which are usually based on statistical/empirical data. Although global designs can be quickly analyzed using assumptions and estimates, this risks costly design changes if the assumptions and estimations are proven incorrect in the later overall aircraft design phases. Suppliers who have detail-level knowledge should be involved early in the overall aircraft conceptual design phase, creating various local designs, and conducting more accurate analyses and evaluations of these designs. Early local design studies can help suppliers help OEMs to reduce the risk of design changes related to incorrect assumptions and estimations, and convince OEMs of the benefits of new material and new production methods. The objective of this research was to develop a design approach which can support suppliers to perform local design fast from which critical results, i.e. cost and weight, can be generated during the overall aircraft conceptual design phase. A fast airframe subsystem design is highly beneficial for suppliers wishing to increase their competiveness, providing fast response and being flexible in the overall aircraft conceptual design phase. It is also beneficial for OEMs to reduce the risk of design changes due to incorrect assumptions and estimations. Several issues in the current design process that hamper a fast study of airframe subsystems were identified in this research, some of which have to be addressed from the supplier’s side. 1) The dependency of suppliers on the OEMs to get coherent, consistent and timely design information, e.g. geometry and load cases, needed to start local design. This dependency causes suppliers wait until all the required information is available from the OEMs in the overall aircraft preliminary design phase. Therefore, the suppliers cannot proactively participate in the overall aircraft conceptual design, in which the airframe subsystem design relies heavily on assumptions and estimations. 2) The manual processes used by suppliers to update computer aided design (CAD) and analysis models to follow design changes at the global and local level. In the overall aircraft conceptual design phase, both the global and local design are not fixed yet and tend to change. Manually model updating at local design level takes significant engineering efforts, and hence slows down the supplier’s response to the changes in the global design. 3) There is a lack of multidisciplinary design optimization (MDO) capability and capacity at a local design level due to this lack of MDO knowledge and a lack of tools to build parametric product and process models. Therefore, in the short conceptual design phase, suppliers often just deliver a (few) feasible design solution(s) instead of a family of Pareto design solutions. To address these issues, and hence to increase supplier competitiveness, a global-local knowledge coupling approach is proposed, which comprises two modules at the global and local design level. The module at global design level is the cross-over, which is used as a substitute for global design and provides the inputs required for starting a local design. The cross-over is used to make the global and local designs concurrent in the early aircraft design phase. The module at the local design level is a set of parametric product and process models of airframe subsystems used to automate repetitive design actions at local design level, such that the analysis and evaluation of subsystem designs can be quickly performed. Knowledge based engineering (KBE) is adopted to implement the two modules for two main purposes: 1) parameterization of product models that allows automatic model (re)generation; 2) automation of pre-processing to prepare inputs for disciplinary analysis tools. Multidisciplinary design optimization is used as the technical implementation mean of the proposed approach to automate the process of finding an optimal design for a complex airframe subsystem. Three demonstration systems are developed, each of them formed as a design framework, called the Airframe Design and Engineering Engine (ADEE), which is a specialized Design and Engineering Engine (DEE). The design and engineering engine (Tooren, 2003) is a MDO system aimed at supporting and accelerating the design process of complex products, through the automation of non-creative and repetitive design activities. The verification design systems are the fuselage ADEE, the fuselage panel ADEE and the movable ADEE. One of the main contributions of this research is to identify the issues in the airframe design process which involves OEM and suppliers, and how these issues can be solved for quickly performing local design in the aircraft conceptual design phase. Another contribution lies in the development of the global-local knowledge coupling approach and its demonstration systems for the new design approach, which provide tools and methods to address these issues. Each verification tool is an ADEE, which is supported by KBE to perform global design and local design in an automatic fashion, such that cross-over can quickly generate the required inputs for local design and the local design module can quickly generate and analyse various subsystem design variants. The fuselage ADEE is used to address issue 1 by increasing design independence for panel suppliers The fuselage ADEE is implemented as a cross-over, in which finite element analysis (FEA) based weight estimation is developed to capture the effects of material and structural layout on fuselage weight. The global knowledge is captured in the cross-over, including the knowledge of how to generate fuselage outer mould line (OML) and knowledge of how to perform disciplinary analysis such as load calculation and structural analysis using FEA. The ADEE is validated using data from fuselages of conventional aircraft such as the ATR 42, Fokker 100, Boeing 737-200, Airbus A320-200 and Airbus A300B2. The fuselage ADEE is also used to estimate fuselage weight of a joint wing aircraft. The fuselage panel ADEE is used to address issue 2 by automating repetitive model (re)generation for local design The fuselage panel ADEE is the local design module of the global-local knowledge coupling, which comprises a parametric panel product model and disciplinary analysis models, i.e. structural analysis, cost estimation and weight evaluation models. The fuselage ADEE is a cross-over which provides inputs for the fuselage panel ADEE. A KBE-enabled parametric panel product model is implemented in the fuselage panel ADEE to model various configurations of fuselage panels flexibly, which are composed of skin with multiple layers and back-up structural members, such as frames and stringers. These structural members are modeled based on the OML generated by the fuselage ADEE. The structural analysis uses global-local FEA in which a global FE model is obtained from the cross-over to predict the overall fuselage behavior, whereas a refined FE panel model is built for investigating panel behavior. The local panel process knowledge is captured in the panel ADEE so as to automate the panel modeling, structural analysis, parametric bottom-up cost estimation and weight evaluation. Using the accelerated local panel design process, the local panel design can quickly respond to the change of global design, while the model consistency between global and local levels can be guaranteed. The movable ADEE is used to address issue 3 by automating repetitive design actions in the MDO process The movable ADEE is developed to perform cost/weight multi-objective optimization of movable structures, e.g. rudders and elevators, including large topology variations of the structural configuration. The KBE-enabled modelling module of this ADEE is able to model very different product configurations and variants and extract all data required to feed the weight and cost estimation modules, in a fully automated fashion. The weight estimation method uses FEA to calculate the internal stresses of the structural elements and an analytical composite plate sizing method to determine their minimum required thicknesses. The manufacturing cost estimation module was developed on the basis of a cost model available in the literature. The capability of the framework is successfully demonstrated by designing and optimizing the composite structure of a business jet rudder. The study case indicates that this ADEE is able to find the Pareto optimal set for minimum structural weight and manufacturing cost quickly. The demonstration systems developed demonstrate that the global-local knowledge coupling approach can support suppliers wishing to perform fast airframe subsystem design in the overall aircraft conceptual design phase.