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  • 1.
    Kaufmann, Markus
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Cost Optimization of Aircraft Structures2009Doctoral 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.

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  • 2.
    Kaufmann, Markus
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Cost/Weight Optimization of Aircraft Structures2008Licentiate 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.

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  • 3.
    Kaufmann, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Czumanski, Thomas
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Manufacturing process adaptation for integrated cost/weight optimisation of aircraft structures2009In: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 38, no 2, p. 162-166(5)Article in journal (Refereed)
    Abstract [en]

    A methodology is developed that enables cost-efficient design of composite aircraft structures. In earlier work, a cost/weight optimisation framework was presented. This framework is here enhanced by a module that minimises the manufacturing cost in each iteration by adaptation of manufacturing parameters. The proposed framework is modular and applicable to a variety of parts and geometries. Commercially available software is used in all steps of theoptimisation. The framework extension is added to an existing cost/weight optimisation implementation and tested on an airliner centre wing box rear spar. Three optimisation runs are performed, and a low cost, an intermediate and a low weight design solution are found. The difference between the two extreme solutions is 4.4% in manufacturing cost and 9.7% in weight. Based on these optimisation trials, the effect of the introduced parameter adaptation module is analysed.

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  • 4.
    Kaufmann, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Czumanski, Thomas
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Manufacturing Process Adaptation for the Cost/Weight Optimization of Aircraft Structures2008Conference paper (Other academic)
    Abstract [en]

    Composite materials can be used in primary structures of an aircraft if a cost-efficient design is applied. In earlier work, a cost/weight optimization framework has been presented. This is now enhanced by a module that minimizes the manufacturing cost in each iteration by the adaptation of manufacturing parameters. The framework itself is modular and applicable to arbitrary parts and geometries; therefore, commercially available software modules are used. The framework extension is added to an existing cost/weight optimization implementation and tested on an airliner center wing box rear spar. Three opti-mization runs are performed, and a low-cost, an intermediate and a low-weight design solution are found. The difference between the two antagonistic solutions is 4.4% in manufacturing cost and 9.7% in weight. Based on these optimization trials, the effect of the parameter adaptation module is analyzed.

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    fulltext
  • 5.
    Kaufmann, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Mattei, Christophe
    Cost optimization of composite aircraft structures including variable laminate qualities2008In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 68, no 13, p. 2748-2754Article in journal (Refereed)
    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 in which cost, weight and the desired laminate quality are taken into account. This paper proposes an optimization framework for composite aircraft structures that minimizes the direct operating cost on a part level. In addition to previous models, a non-destructive testing model is implemented that calculates design allowables of a laminate based on ultrasonic scan parameters. In a case study, the effect of the laminate quality on the direct operating cost is discussed. It is investigated how the permissible flaw size and therefore the scan pitch of a composite laminate can influence the optimal solution in terms of cost and weight; thus, the manufacturing cost, the non-destructive testing cost and the weight of a component can be balanced by optimizing the laminate quality in an early design phase.

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    fulltext
  • 6.
    Kaufmann, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Wennhage, Per
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Integrated cost/weight optimization of aircraft structures2010In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 41, no 2, p. 325-334Article in journal (Refereed)
    Abstract [en]

    A methodology for a combined cost/weight optimization of aircraft components is proposed. The objective function is formed by a simplified form of direct operating cost, i.e. by a weighted sum of the manufacturing costs and the component weight. Hence, the structural engineer can perform the evaluation of a design solution based on economical values rather than pure cost or weight targets.The parameter that governs the balance between manufacturing cost and weight is called weight penalty and incorporates the effect of fuel burn, environmental impact or contractual penalties due to overweight. Unlike previous work, the analytical cost model and structural models are replaced by commercially available software packages that allow a more realistic model of the manufacturing costs; further, arbitrary constraints for the structural analysis can be implemented. By means of parametric studies it is shown that the design solution strongly depends on the magnitude of the weight penalty.

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  • 7.
    Kaufmann, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Wennhage, Per
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Integrated cost/weight optimization of composite skin/stringer elements2007In: Proceedings of the 16th International Conference on Composite Materials, Springer, 2007, p. 325-334Conference 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.

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  • 8.
    Kaufmann, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Cost/weight optimization of composite prepreg structures for best draping strategy2010In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 41, no 4, p. 464-472Article in journal (Refereed)
    Abstract [en]

    The application of hand-laid carbon fiber prepreg is very expensive from a labor perspective. Therefore the manufacturing cost should be included in the design process. In this work, we propose a novel optimization framework which contains a draping simulation in combination with a detailed cost estimation package and the calculation of the structural performance based on FE. We suggest applying the methodology in two steps. First, a draping knowledge database is generated in which combinations of seed points and reference angles are evaluated in terms of fiber angle deviation, scrap, ultrasonic cuts and material shear. Second, a cost/weight optimization framework picks the best sets of plies during the subsequent optimization. The methodology is tested by means of a curved C-spar which is designed using plain weave and unidirectional prepreg. Different objectives in the generation of the draping database lead to different design solutions.

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  • 9.
    Kaufmann, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Material Selection for a Curved C-Spar Based on Cost Optimization2011In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 48, no 3, p. 797-804Article in journal (Refereed)
    Abstract [en]

    A case study for the cost optimization of aircraft structures based on the operating cost as an objective function is presented. The proposed optimization framework contains modules for estimation of the weight, manufacturing cost, nondestructive inspection cost, and structural performance; the latter is enhanced by a kinematic draping model that allows the fiber angles to be simulated more realistically. The case study includes five material systems: aircraft-grade aluminum, two types of resin-transfer molded noncrimp fabric reinforcements, and two types of M21/T800 prepreg. The results are compared in relation to each other, and it is shown that (depending on the estimated fuel burn share of the component) a different material system is favorable when optimizing for low-operating cost.

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  • 10.
    Zenkert, Dan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Kaufmann, Markus
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Optimisation of Composite Stuctures: Design for Cost2011In: International Conference for Composites 21st Century: Current and Future Trends / [ed] B. Dattaguru, et al, 2011Conference paper (Other academic)
    Abstract [en]

    Components made in composite material can lower the weight of structures significantly. The higher production and material cost, however, require the application of novel design strategies which allow for the cost-efficient production of these components. A methodology for a combined cost/weight optimization of composite components is presented herein. The objective function is formed by a simplified form of direct operating cost, i.e. by a weighted sum of the manufacturing cost and the component weight. The parameter that governs the balance between manufacturing cost and weight is called weight penalty and incorporates the effect of fuel burn, environmental impact or contractual penalties due to overweight. In addition, a non-destructive testing model is implemented that calculates design allowables of a laminate based on ultrasonic scan parameters. In a case study, the effect of the laminate quality on the direct operating cost is discussed. It is investigated how the permissible flaw size and therefore the scan pitch of a composite laminate can influence the optimal solution in terms of cost and weight; thus, the manufacturing cost, the non-destructive testing cost and the weight of a component can be balanced by optimizing the laminate quality in an early design phase. The optimization framework also contains a draping simulation in combination with a detailed cost estimation package and the calculation of the structural performance based on FE. First, a draping knowledge database is generated in which combinations of seed points and reference angles are evaluated in terms of fibre angle deviation, scrap, ultrasonic cuts and material shear. Second, the cost/weight optimization framework picks the best sets of plies during the subsequent optimization. By means of parametric studies it is shown that the design solution strongly depends on the magnitude of the weight penalty. It is also shown that the non-destructive testing affects the cost and choice of design concept and the permissible flaw size should be altered in order to save both weight and cost. Finally, the methodology is tested by means of a curved C-spar which is designed using plain weave and unidirectional prepreg. Different objectives in the generation of the draping database lead to different design solutions.

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    fulltext
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