Afzal Suleman

Modelling and design of adaptive composite structures

Recent developments in adaptive composite structures with distributed piezoelectric actuators and sensors have attracted significant attention in the research community due to their potential commercial benefits in a wide range of applications such as vibration suppression, shape control, noise attenuation and precision positioning. The complexity in the design and fabrication of the adaptive laminated composites has resulted in a need to develop reliable and refined models to study their material properties and mechanical behaviour. Here, higher order finite element formulations and an analytical closed form solution have been developed to study the mechanics of adaptive composite structures with embedded and/or bonded piezoelectric actuators and sensors. Optimization of adaptive composite structures is also an important design aspect in order to maximize actuator performance. Two optimization schemes are considered in this study where the design variables are the layer thickness, actuator size and location. To demonstrate the validity, usefulness and eAciency of the proposed models several illustrative examples are presented and discussed. ” 2000 Elsevier Science S.A. All rights reserved.

Optimization of a Morphing Wing Based on Coupled Aerodynamic and Structural Constraints

This paper presents the work done in designing a morphing wing concept for a small experimental unmanned aerial vehicle to improve the vehicles performance over its intended speed range. The wing is designed with a multidisciplinary design optimization tool, in which an aerodynamic shape optimization code coupled with a structural morphing model is used to obtain a set of optimal wing shapes for minimum drag at different flight speeds. The optimization procedure is described as well as the structural model. The aerodynamic shape optimization code, that uses a viscous two-dimensional panel method formulation coupled with a nonlinear lifting-line algorithm and a sequential quadratic programming optimization algorithm, is suitable for preliminary wing design optimization tasks. The morphing concept, based on changes in wing-planform shape and wing-section shape achieved by extending spars and telescopic ribs, is explained in detail. Comparisons between optimized fixed wing performance, optimal morphing wing performance, and the performance of the wing obtained from the coupled aerodynamic-structural solution are presented. Estimates for the performance enhancements achieved by the unmanned aerial vehicles when fitted with this new morphing wing are also presented. Some conclusions on this concept are addressed with comments on the benefits and drawbacks of the morphing mechanism design.

Structural Optimization with Frequency Constraints Using the Finite Element Force Method

A structural optimization algorithm is developed to minimize the weight of structures with truss and beam-type members under single- or multiple-frequency constraints. The cross-sectional areas of the structural members are considered as the design variables. The algorithm proposed combines the finite element technique based on the integrated force method with the mathematical programming technique. The equilibrium matrix is generated automatically using the finite element analysis, and the compatibility matrix is obtained directly using the displacement-deformation relations and the single value decomposition technique. When combining the equilibrium and the compatibility matrices with the force-displacement relations, the frequency eigenvalue equations are obtained with element forces as variables. Three structures, composed of truss and frame-type members, are studied to illustrate the procedure, and the results are compared with the literature. It is shown that, in structural problems with multiple frequency constraints, the analysis procedure (force or displacement method) significantly affects the final optimum design. The structural optimization based on the force method results in a lighter design. The proposed structural optimization method is efficient to analyze and optimize both truss and beam-type structures.

Design of a Morphing Airfoil Using Aerodynamic Shape Optimization

An in-house high-fidelity aerodynamic shape optimization computer program based on a computational fluid dynamics solver with the Spalart-Allmaras turbulence model and a sequential-quadratic-programming algorithm is used to obtain a set of optimal airfoils at the different flight conditions of a light unmanned air vehicle. For this study, the airfoil requirements at stall, takeoff run, climb gradient, rate of climb, cruise, and loiter conditions are obtained. Then, the aerodynamic shape optimization program is used to obtain the airfoil that has the optimal aerodynamic characteristics at each one of these flight conditions. Once the optimal airfoils at each flight condition are obtained, the results are analyzed to gain a better understanding of the most efficient initial airfoil configuration and the possible mechanisms that could be used to morph the single element airfoil. The results show that a very thin airfoil could be used as the initial configuration. Furthermore, a morphing mechanism that controls the camber and leading-edge thickness of the airfoil will almost suffice to obtain the optimal airfoil at most operating conditions. Lastly, the use of the optimal airfoils at the different flight conditions significantly reduces the installed power requirements, thus enabling a greater flexibility in the mission profile of the unmanned air vehicle.

Comparison of Surrogate Models in a Multidisciplinary Optimization Framework for Wing Design

The replacement of the analysis portion of an optimization problem by its equivalent metamodel usually results in a lower computational cost. In this paper, a conventional nonapproximative approach is compared against three differentmetamodels: quadratic-interpolation-based response surfaces,Kriging, and artificial neural networks. The results obtained from the solution of four different case studies based on aircraft design problems reinforces the idea that quadratic interpolation is only well-suited to very simple problems. At higher dimensionality, the usage of the more complex Kriging and artificial neural networks models may result in considerable performance benefits.

Aero-structural Design Optimization of a Morphing Wingtip

Over the past few years, better knowledge of aerodynamics and structures and the permanent need to improve the performance and efficiency of aircraft have led to the generalized adoption of wingtip devices. The requirements faced by wingtip devices throughout the various flight conditions are, however, different. A static wingtip device (as is the case with existing designs) must be a compromise of these various conflicting requirements, resulting in less than optimal effectiveness in each flight condition. A morphing device, on the other hand, can adapt to the optimum configuration for each flight condition, leading to improved effectiveness. This article presents a morphing wingtip mechanism based on a servo-actuated articulated winglet, able to rotate about two different axes: vertical axis (toe angle) and aircraft’s longitudinal axis (cant angle). These can be controlled independently by servo-actuators. The wingtip behavior is a function of aerodynamic and structural loads which, in turn, are interdependent, requiring a multidisciplinary design optimization procedure in order to determine the ideal wingtip configuration for each case. The proposed concept is applied to a multi-mission unmanned aerial vehicle and the results show that a morphing wingtip can outperform an optimum fixed design. The optimum geometries for the different flight missions are presented and the feasibility of such a morphing wingtip is confirmed by a prototype. The performance metrics of the morphing wingtip are compared to those of a fixed wingtip to quantify the gain associated with the use of the morphing concept and it is seen that the improvement can reach 25%.

AERO-STRUCTURAL OPTIMIZATION AND PERFORMANCE EVALUATION OF A MORPHING WING WITH VARIABLE SPAN AND CAMBER

An aero-structural design and analysis study of a telescopic wing with a conformal camber morphing capability is presented. An aerodynamic analysis of a telescoping wing, first with a high speed airfoil followed by an analysis with a low speed airfoil is performed. The data obtained from these analyses is used to determine the optimum polar curves for drag reduction at different speeds. This information in turn provided the background for devising an optimal morphing strategy for drag reduction assuming that the telescoping wing airfoil has the capability to step morph between the high and low speed airfoils. Next, a conformal camber morphing concept is introduced. The concept is based on a non-uniform thickness distribution along the chord of a wing shell section that deforms from a symmetrical airfoil shape into a cambered airfoil shape under actuation. Structural optimization based on finite element models is used to obtain the shell thickness distribution for minimum shell section weight and best airfoil shape adjustment. Finally, a comparison study between the performance of an aircraft equipped with a morphing wing (telescopic wing combined with conformal camber morphing) and the performance of the same aircraft equipped with an optimized fixed wing for 30 m/s cruise speed and 100 N weight is presented. Aerodynamic optimization based on computational fluid dynamics models is used for the optimum fixed wing geometric parameters calculations. The optimal wing configurations for various performance parameters are calculated. The morphing wing generally outperforms the optimum fixed wing with the exception of a 10% reduction in rate of climb and 4% drag penalty at 30 m/s cruise speed.

Optimal Design of Ultralow-Platinum PEMFC Anode Electrodes

A computational, two-dimensional agglomerate anode electrode model is presented. The model provides insight on the mass and charge transport in the anode and implements the recent proposed dual-pathway kinetics for the hydrogen oxidation reaction. Results from this model highlight the potential for platinum reduction on the anode. In order to systematically assess the possible reductions on platinum loading, an optimization problem is formulated to minimize platinum loading while maintaining performance of typical state-of-the-art electrodes. The results reveal that platinum loading can be reduced by more than one order of magnitude, from 0.4 to less than 0.018 mg/cm 2 , by changing the gas diffusion layer (GDL) and catalyst layer (CL) composition. Furthermore, if the CL thickness and the GDL and CL compositions are optimized simultaneously, the amount of platinum can be further reduced by an extra order of magnitude by depositing a catalyst layer of 1.25 μm with a platinum loading of 0.0026 mg/cm 2 .

A Robust and Reliability Based Design Optimization Framework for Wing Design

This paper presents the outline of a framework for simultaneous analysis and robustness and reliability calculations in aircraft design optimization, with the option of employing surrogate models. Robust Design Optimization and Reliability Based Design Optimization are merged into a unied formulation which simplies the setup of optimization problems and aims at preventing foreseeable implementation issues. The code in development expands upon and, in some cases, completely rewrites a previous version of a Multidisciplinary Design Optimization tool that was solely oriented to deterministic problems.

Topology Optimization of a Reinforced Wing Box for Enhanced Roll Maneuvers

In this paper, the aileron reversal speed of a wing torsion box is maximized by reinforcing its upper skin. We propose a topology optimization approach using the spectral level set methodology. This is based on the level set methods,which represent theinterface describing thereinforcements asthe zerolevel setofafunction. Accordingto the proposed methodology, this function is discretized using its Fourier coefficients. These coefficients become the design variables of the optimization problem assigned to define the reinforcing layout. Results show that approximately the sameoptimal reinforcement layout isobtained from topologically different initialconfigurations. The two underlying ideas of the present work are to propose the spectral level set methodology as a framework for topology optimization, given its potential for reducing the design space dimension, and, considering the possibilities of new custom-made materials, to readdress the reinforcement perspective in aircraft structures without the weight penalty. Nomenclature ai,bi = problem domain boundaries corresponding to componenti ofx at = � t smoothness parameter aV = � V smoothness parameter a0 = lift curve slope bt = minimum thickness C = positive constant Cl� = derivative of the rolling moment coefficient of the rigid airplane with respect to� C �� � y;n� = twist aty produced by a unit moment at�