Aeroelastic tailoring using lamination parameters

The aim of the present work is to passively reduce the induced drag of the rear wing of a Formula One car at high velocity through aeroelastic tailoring. The angle-of-attack of the rear wing is fixed and is determined by the required downforce needed to get around a turn. As a result, at higher velocity, the amount of downforce and related induced drag increases. The maximum speed on a straight part is thus reduced due to the increase in induced drag. A fibre reinforced composite torsion box with extension-shear coupled upper and lower skins is used leading to bending-torsion coupling. Three-dimensional static aeroelastic analysis is performed loosely coupling the Finite Element code Nastran and the Computational Fluid Dynamics panel code VSAERO using ModelCenter. A wing representative of Formula One rear wings is optimised for minimum induced drag using a response surface methodology. Results indicate that a substantial induced drag reduction is achievable while maintaining the desired downforce during low speed turns.     

Design of variable-stiffness conical shells for maximum fundamental eigenfrequency

Fiber-reinforced composite conical shells with given geometry and material properties are optimized for maximum fundamental frequency. The shells are assumed to be built using an advanced tow-placement machine, which allows in-plane steering of the fibers, resulting in a variable-stiffness structure. In this paper, different path definitions for variable-stiffness shells are provided and used to optimize conical shells for maximum fundamental frequency, while manufacturing constraints that apply for tow placement are taken into account in the process. The influence of manufacturing constraints on the performance is shown; and improvements of variable-stiffness conical shells over conventional, constant-stiffness shells are demonstrated.     

Supplier- and buyer-driven channels in a two-stage supply chain

In this paper we explore the impact of power structure on price, sensitivity of market price, and profits in a two-stage supply chain with a single-product, -supplier and -buyer. We develop and analyze the case where the supplier has dominant bargaining power and the case where the buyer has dominant bargaining power, and consider a pricing scheme for the buyer that involves both a multiplier and a constant mark up. We show that it is optimal for the buyer to set the mark-up to zero and use only a multiplier and that the market price and its sensitivity are higher when operational costs (namely distribution and inventory) exist. We also observe that the sensitivity of the market price increases nonlinearly as the wholesale price increases, and derive a lower bound for it. Through experimental analysis, we show that marginal impact of increasing shipment cost and carrying charge (interest rate) on prices and profits are decreasing in both cases.     

A displacement based optimization method for geometrically nonlinear frame structures

An extension of the displacement based optimization method to frames with geometrically nonlinear response is presented. This method, when applied to small-scale trusses with linear and nonlinear response, appeared to be efficient providing the same solutions as the classical optimization method. The efficiency of the method is due to the elimination of numerous finite element analyses that are required in using the traditional optimization approach. However, as opposed to trusses, frame problems have typically a larger number of degrees of freedom than cross sectional area design variables. This leads to difficulties in the implementation of the method compared to the truss implementation. A scheme that relaxes the nodal equilibrium equations is introduced, and the method is validated using test examples. The optimal designs obtained by using the displacement based optimization and the classical approaches are compared to validate the application to frame structures. The characteristics and limitations of the optimization in the displacement space for sizing problems, based on the current formulation, are discussed.     

Intratumoral differences in methotrexate levels within human osteosarcoma xenografts studied by microdialysis

A central tenet in oncology is the assumed relationship between drug concentration and cytotoxicity. Determinations of drug levels in tumor tissues are, however, generally not undertaken. Microdialysis is a method where continuous drug monitoring may be achieved by sampling of low molecular weight substances from the extracellular space. By employing this technique it is possible to observe variable drug levels within tissues, including tumors, over time. Herein, we present results from a nude rat model where subcutaneous human osteosarcoma xenografts were established prior to the administration of the antifolate methotrexate as an intravenous infusion. Significant differences in drug exposure within single tumors were evident. Generally, peak drug concentrations were lower and drug efflux slower from the center of the tumors as compared to the periphery. The use of microdialysis could be an important tool for optimizing current strategies in anticancer chemotherapy.     

Optimal design of imperfect,anisotropic, ring-stiffened cylinders under combined loads

Development of an algorithm to perform the optimal sizing of buckling resistant, imperfect, anisotropic ringstiffened cylinders subjected to axial compression, torsion, and internal pressure is presented. An axisymmetric, geometrically nonlinear prebuckling equilibrium configuration is assumed and both stress and stability constraints are considered. The enforcement of stability constraints is treated in a way that does not require any eigenvalue analysis. Case studies performed using a combination of penalty function and feasible direction optimization methods indicate that the presence of the axisymmetric initial imperfection in the cylinder wall can significantly affect the optimal designs. Weight savings associated with the addition of two rings to the unstiffened cylinder and/or the addition of internal pressure is substantial when torsion makes up a significant fraction of the combined load state.     

Tailoring for strength of composite steered-fibre panels with cutouts

A large number of composite parts include cutouts to accommodate windows, doors, and bolted joints. These regions are hot-spots in terms of design because they concentrate stresses, hence becoming critical in terms of the structural integrity of the part.A traditional approach to the problem of stress concentrations around cutouts is to locally increase the laminate thickness in order to improve the strength margins. Often this practice attracts more loads to the cutout besides increasing part weight. A more effective solution is to tailor the panel in-plane stiffness by means of fibre-steered laminates, and avoid the stress concentrations altogether.The present research demonstrates that it is possible to design and manufacture composite panels whose buckling and first-ply failure responses are insensitive to the existence of a central hole. Moreover, it is shown that the structural performance of these designs more than doubles that of straight-fibre configurations.     

Optimization of course locations in fiber-placed panels for general fiber angle distributions

Fiber-reinforced composites are usually designed using constant fiber orientation in each ply. In certain cases, however, a varying fiber angle might be favorable for structural performance. This possibility can be fully utilized using tow placement technology. Because of the fiber angle variation, tow-placed courses may overlap and ply thickness will build-up on the surface. This thickness buildup affects manufacturing time, structural response, and surface quality of the finished product.     

Genetic algorithms with local improvement for composite laminate design

This paper describes the application of a genetic algorithm to the stacking sequence optimization of a laminated composite plate for buckling load maximization. Two approaches for reducing the number of analyses required by the genetic algorithm are described. First, a binary tree is used to store designs, affording an efficient way to retrieve them and thereby avoid repeated analyses of designs that appeared in previous generations. Second, a local improvement scheme based on approximations in terms of lamination parameters is introduced. Two lamination parameters are sufficient to define the flexural stiffness and hence the buckling load of a balanced, symmetrically laminated plate. Results were obtained for rectangular graphite-epoxy plates under biaxial in-plane loading. The proposed improvements are shown to reduce significantly the number of analyses required for the genetic optimization.Presented at the ASME Winter Annual Meeting Structures and Controls Optimization, pp. 13–28. Printed with permission from ASME.     

Analyzing the solutions of DEA through information visualization and data mining techniques: SmartDEA framework

Data envelopment analysis (DEA) has proven to be a useful tool for assessing efficiency or productivity of organizations, which is of vital practical importance in managerial decision making. DEA provides a significant amount of information from which analysts and managers derive insights and guidelines to promote their existing performances. Regarding to this fact, effective and methodologic analysis and interpretation of DEA results are very critical. The main objective of this study is then to develop a general decision support system (DSS) framework to analyze the results of basic DEA models. The paper formally shows how the results of DEA models should be structured so that these solutions can be examined and interpreted by analysts through information visualization and data mining techniques effectively. An innovative and convenient DEA solver, SmartDEA, is designed and developed in accordance with the proposed analysis framework. The developed software provides DEA results which are consistent with the framework and are ready-to-analyze with data mining tools, thanks to their specially designed table-based structures. The developed framework is tested and applied in a real world project for benchmarking the vendors of a leading Turkish automotive company. The results show the effectiveness and the efficacy of the proposed framework.