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Integrated cost/weight optimization of composite skin/stringer elements
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.ORCID iD: 0000-0002-9744-4550
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.ORCID iD: 0000-0003-0198-6660
2007 (English)In: Proceedings of the 16th International Conference on Composite Materials, Springer, 2007, 325-334 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, a methodology for a combined cost/weight optimization of composite elements is proposed. The methodology is similar to the work of Curran et al. [1], where the objective function is formed by manufacturing costs and a so-called weight penalty. This weight penalty could include the effect of fuel burn, environmental impact or con-tractual penalties due to overweight, and depends on the view of the "optimizer". In our approach, the analytical cost model is replaced by a commercial software package that allows a more realistic model of the manufacturing costs. In the spotlight is a parameter study, in which the weight penalty is varied from zero to infinity, literally varying from pure cost to pure weight opti-mization. This is done for three material configura-tions: a metal/metal, a composite/metal and a com-posite/composite skin/stringer panel. It is shown that the design solution depends on the magnitude of the weight penalty and that - depending on this magni-tude - another material configuration has to be re-garded as the optimum.

Place, publisher, year, edition, pages
Springer, 2007. 325-334 p.
Keyword [en]
Cost/Weight Optimization, Weight Penalty, Direct Operating Cost, Composite Structures
National Category
Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-8015Scopus ID: 2-s2.0-79960055319ISBN: 978-493113605-2 (print)OAI: oai:DiVA.org:kth-8015DiVA: diva2:13222
Conference
16th International Conference on Composite Materials, ICCM-16 - "A Giant Step Towards Environmental Awareness: From Green Composites to Aerospace", Kyoto, Japan, 8 July 2007 through 13 July 2007
Note

QC 20101112

Available from: 2008-04-22 Created: 2008-04-22 Last updated: 2015-07-09Bibliographically approved
In thesis
1. Cost/Weight Optimization of Aircraft Structures
Open this publication in new window or tab >>Cost/Weight Optimization of Aircraft Structures
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Composite structures can lower the weight of an airliner significantly. The increased production cost, however, requires the application of cost-effective design strategies. Hence, a comparative value is required which is used for the evaluation of a design solution in terms of cost and weight. The direct operating cost (DOC) can be used as this comparative value; it captures all costs that arise when the aircraft is flown. In this work, a cost/weight optimization framework for composite structures is proposed. It takes into account manufacturing cost, non-destructive testing cost and the lifetime fuel consumption based on the weight of the aircraft, thus using a simplified version of the DOC as the objective function.

First, the different phases in the design of an aircraft are explained. It is then focused on the advantages and drawbacks of composite structures, the design constraints and allowables, and non-destructive inspection. Further, the topics of multiobjective optimization and the combined optimization of cost and weight are addressed. Manufacturing cost can be estimated by means of different techniques; here, feature-based cost estimations and parametric cost estimations proved to be most suitable for the proposed framework. Finally, a short summary of the appended papers is given.

The first paper contains a parametric study in which a skin/stringer panel is optimized for a series of cost/weight ratios (weight penalties) and material configurations. The weight penalty, defined as the specific lifetime fuel burn, is dependent on the fuel consumption of the aircraft, the fuel price and the viewpoint of the optimizer. It is concluded that the ideal choice of the design solution is neither low-cost nor low-weight but rather a combination thereof.

The second paper proposes the inclusion of non-destructive testing cost in the design process of the component, and the adjustment of the design strength of each laminate according to the inspection parameters. Hence, the scan pitch of the ultrasonic testing is regarded as a variable, representing an index for the (guaranteed) laminate quality. It is shown that the direct operating cost can be lowered when the quality level of the laminate is assigned and adjusted in an early design stage.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. ix, 45 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2008-08
Keyword
Cost/Weight Optimization, Weight Penalty, Direct Operating Cost, Composite Structures, Non-destructive testing, Finite element analysis (FEA)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-4645 (URN)978-91-7178-888-7 (ISBN)
Presentation
2008-04-30, D3, KTH, Lindstedtsvägen 5, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20101112Available from: 2008-04-22 Created: 2008-04-22 Last updated: 2010-11-12Bibliographically approved
2. Cost Optimization of Aircraft Structures
Open this publication in new window or tab >>Cost Optimization of Aircraft Structures
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Composite structures can lower the weight of an airliner significantly. Due to the higher process complexity and the high material cost, however, the low weight often comes with a significant increase in production cost. The application of cost-effective design strategies is one mean to meet this challenge.

In this thesis, a simplified form of direct operating cost is suggested as a comparative value that in combination with multidisciplinary optimization enables the evaluation of a design solution in terms of cost and weight. The proposed cost optimization framework takes into account the manufacturing cost, the non-destructive testing cost and the lifetime fuel consumption based on the weight of the aircraft, thus using a simplified version of the direct operating cost as the objective function. The manufacturing cost can be estimated by means of different techniques. For the proposed optimization framework, feature-based parametric cost models prove to be most suitable.

Paper A contains a parametric study in which a skin/stringer panel is optimized for a series of cost/weight ratios (weight penalties) and material configurations. The weight penalty (defined as the specific lifetime fuel burn) is dependent on the fuel consumption of the aircraft, the fuel price and the viewpoint of the optimizer. It is concluded that the ideal choice of the design solution is neither low-cost nor low-weight but rather a combination thereof.

Paper B proposes the inclusion of non-destructive testing cost in the design process of composite components, and the adjustment of the design strength of each laminate according to inspection parameters. Hence, the scan pitch of the ultrasonic testing is regarded as a variable, representing an index for the guaranteed material quality. It is shown that the cost for non-destructive testing can be lowered if the quality level of the laminate is assigned and adjusted in an early design stage.

In Paper C and Paper D the parameters of the manufacturing processes are upgraded during the cost optimization of the component. In Paper C, the framework is extended by the cost-efficient adaptation of parameters in order to reflect the situation when machining an aluminum component. For different weight penalties, the spar thickness and stringer geometry of the provided case study vary. In addition, another cutter is chosen with regard to the modified shape of the stringer. In Paper D, the methodology is extended to the draping of composite fabrics, thus optimizing not only the stacking layup, but also the draping strategy itself. As in the previous cases, the design alters for different settings of the weight penalty. In particular, one can see a distinct change in fiber layup between the minimum weight and the minimum cost solution.

Paper E summarizes the work proposed in Papers A-D and provides a case study on a C-spar component. Five material systems are used for this case study and compared in terms of cost and weight. The case study shows the impact of the weight penalty, the material cost and the labor rate on the choice of the material system. For low weight penalties, for example, the aluminum spar is the most cost-effective solution. For high weight penalties, the RTM system is favorable. The paper also discusses shortcomings with the presented methodology and thereby opens up for future method developments.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. xii, 53 p.
Series
Trita-AVE, ISSN 1651-7660 ; 83
Keyword
aircraft structures, optimization, cost estimation, manufacturing cost, direct operating cost, multiobjective optimization, multidisciplinary optimization, composites, airframe design
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-11482 (URN)978-91-7415-500-6 (ISBN)
Public defence
2009-12-11, D2, Lindstedtsvägen 5, KTH, 10044 Stockholm, 10:15 (English)
Opponent
Supervisors
Projects
European Framework Program 6, project ALCAS, AIP4-CT-2003-516092Nationella flygtekniska forskningsprogrammet (NFFP) 4, project kostnadseffektiv kompositstruktur (KEKS)
Note
QC 20100723Available from: 2009-11-19 Created: 2009-11-16 Last updated: 2012-01-27

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Zenkert, DanWennhage, Per

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