Sergio Ricci

Multilevel Structural Optimization for Preliminary Wing-Box Weight Estimation

This paper deals with the weight estimation of the wing box of a commercial aircraft by means of a procedure suitable for very large liners and/or unconventional configurations for which statistical data and empirical formulas may not be sufficiently reliable. Attention is focused on the need to account for aeroelastic interaction from a very preliminary stage of the design cycle. The procedure exploits the first of three levels of a multilevel structural optimization system conceived for the preliminary design of the wing primary structure and a simplified evaluation of the cross-sectional properties. The comparison between weight estimates obtained with the present procedure and predictions supplied by available literature shows a satisfactory agreement.

A Two-Level Approach for the Optimal Design of Morphing Wings Based On Compliant Structures

The great interest in developing morphing airfoils is mainly based on their capability to adapt their shape to optimize some specific aircraft performance indices during the mission. Nevertheless, the design of these kinds of devices requires the availability of ad hoc-developed procedures able to tackle the conflicting requirements such as the high deformability requested to change the airfoil shape coupled to the load-carrying capability and to the low weight. The article proposes an approach for optimal airfoil-morphing design based on a compactapproach to describe the airfoil geometry coupled to a two-level optimization procedure. In the first one, the best deformed airfoil configuration is determined as the most efficient aerodynamic shape which at the same time limits the requested energy to deform the airfoil skin. In the second optimization level, the best internal structural configuration is obtained using an ad hoc-developed topology optimization tool based on genetic algorithms that synthesize a compliant structure able to adapt itself in order to match the optimal shape coming out from the first level. The procedure has been applied to design the morphing leading and trailing edges for an NACA 63_2215 airfoil.

Active Aeroelastic Control over a Multisurface Wing: Modeling and Wind-Tunnel Testing

This paper presents the work that has been performed on a wind-tunnel aeroelastic wing model to implement a multisurface modal control system. Wing model realization, the control system, and experimental setup were described briefly here, together with a methodology used to numerically tune the simple control system. Usage of a multiple wind-tunnel test session has been adopted first to perform numerical-experimental correlations and then to optimize control parameters. The entire control system demonstrates the capability to damp the wing bending and torsion modes while still remaining stable within the flight envelope.

Optimization of helicopter subfloor components under crashworthiness requirements using neural networks

An optimization procedure is developed for the design of structural components under crashworthiness requirements. The optimization procedure consists of first developing a system of parallel neural networks able to reproduce the structural behavior during the crash phenomena. Training and test sets are generated by finite element analyses. Then, to find the optimal configuration, both sequential quadratic programming and genetic algorithms are implemented to evaluate the objective and constraint functions using the response surfaces generated by the neural networks. The procedure is applied for the optimization of helicopter subfloor components. In this application, the objective function is taken equal to the sum of two terms: the crush force efficiency and the specific absorbed energy. The values of maximum and mean forces are constrained to meet crashworthiness requirements, whereas other constraints are applied to define the feasibility of the structural solution. The optimal configuration, obtained measuring orders of magnitude savings in the CPU time, allows an increase of the crush force efficiency equal to 18% and a decrease of the mass equal to 8%.

Design, Manufacturing and Preliminary Test Results of an Adaptive Wing Camber Model

In the present paper, a new device developed to implement the Active Adaptive Wing Camber (AAWC) concept is analyzed in details and the results of the preliminary experimental results are reported. The AAWC concept is related to a more general concept of Mission Adaptive Wing, i.e. a wing able to adapt itself, by means of configuration and/or shape variation, to changes of flight conditions during the mission, so as to maximize some performance indices. The proposed device is based on a modification of the original idea proposed by Dr. Monner from DLR and called for sake of simplicity Rotating Ribs (RR) concept. To test the reliability of the proposed concept, a wing model has been designed and manufactured. The results of the preliminary static tests and the correlations to numerical predictions are reported in the following.

Estimated performance of an adaptive trailing-edge device aimed at reducing fuel consumption on a medium-size aircraft

This paper deals with the estimation of the performance of a medium-size aircraft (3-hour flight range) equipped with an adaptive trailing edge device (ATED) that runs span-wise from the wing root in the flap zone and extends chord-wise for a limited percentage of the MAC. Computations are calculated referring to the full wing and do not refer to the complete aircraft configuration. Aerodynamic computations, taking into account ideal shapes, have been performed by using both Euler and Navier- Stokes method in order to extract the wing polars for the reference and the optimal wing, implementing an ATED, deflected upwards and downwards. A comparison of the achieved results is discussed. Considering the shape domain, a suitable interpolation procedure has been set up to obtain the wing polar envelop of the adaptive wing, intended as the set of “best” values, picked by each different polar. At the end, the performances of the complete reference and adaptive wing are computed and compared for a symmetric, centered, leveled and steady cruise flight for a medium size aircraft. A significant fuel burn reduction estimate or, alternatively, an increased range capability is demonstrated, with margins of further improvements. The research leading to these results has gratefully received funding from the European Union Seventh Framework Programme (FP7/2007- 2013) under Grant Agreement n° 284562.

Ground modal tests of space-structure components using boundary masses

A method for performing ground modal vibration tests of structural components, such that the resulting natural frequencies and vibration modes can be combined with those of neighboring components, is presented. The cost and technical difficulties associated with testing large and multiple-configuration structures can be greatly reduced with this approach. The method is based on testing the components with the interface coordinates loaded with rigid, heavy dummy masses supported by soft springs. With these boundary masses, the low-frequency modes contain local deformations near the interface and thus can be used to obtain accurate dynamic properties of the assembled structure. The method is demonstrated with measured natural frequencies and modes of a 19-m spacetype truss, loaded at one end with a dummy mass. The measured data are used to predict the frequencies and modes of the original truss with free and damped boundary conditions, and those of the double-length truss. The good agreement of the predicted results with test results on the unloaded structure and with analytical results on a tuned finite element model indicates that low-cost applications of the method to more complex structures are feasible.

Integrated Servostructural Optimization in the Design of Aerospace Systems

Multidisciplinary optimization is playing a fundamental role in the design of aerospace vehicles because of the need to simultaneousl y take into account the strong interactions among different disciplines to ensure an efficient design. This paper presents a multimodel, multiobjective formulation of the servostructural optimization problem specifically tailored toward airplane preliminary design. Structural and control design variables are simultaneously treated along with constraints and objective functions related to different aeroservoelastic and structural performances. Reduced-order models, based on finite element method/ boundary element method, are adopted to reduce the computational burden of the optimization process.

Conceptual Design of an Adaptive Wing for a Three-Surfaces Airplane

The article describes the activities developed by Politecnico di Milano, as partner of Active Aeroelastic Aircraft Structures (3AS) EU project, focused on the preliminary investigations on the Active Adaptive Wing Camber (AAWC) concept, based on a device able to continuously change the camber angle of a wing. After a short description of the device, a preliminary investigation on the possible advantages of that device on the performances of a reference aircraft is reported. The investigation is formulated solving an optimization problem where the induced drag is minimized.

Compliant structures-based wing and wingtip morphing devices

Purpose The purpose of this paper is to provide an overview of the design and experimental work of compliant wing and wingtip morphing devices conducted within the EU FP7 project NOVEMOR and to demonstrate that the optimization tools developed can be used to synthesize compliant morphing devices. Design/methodology/approach The compliant morphing devices were “designed-through-optimization”, with the optimization algorithms including Simplex optimization for composite compliant skin design, aerodynamic shape optimization able to take into account the structural behaviour of the morphing skin, continuum-based and load path representation topology optimization methods and multi-objective optimization coupled with genetic algorithm for compliant internal substructure design. Low-speed subsonic wind tunnel testing was performed as an effective means of demonstrating proof-of-concept. Findings It was found that the optimization tools could be successfully implemented in the manufacture and testing stage. Preliminary insight into the performance of the compliant structure has been made during the first wind tunnel tests. Practical implications The tools in this work further the development of morphing structures, which when implemented in aircraft have potential implications to environmentally friendlier aircrafts. Originality/value The key innovations in this paper include the development of a composite skin optimization tool for the design of highly 3D morphing wings and its ensuing manufacture process; the development of a continuum-based topology optimization tool for shape control design of compliant mechanisms considering the stiffness and displacement functions; the use of a superelastic material for the compliant mechanism; and wind tunnel validation of morphing wing devices based on compliant structure technology.