Multi-objective optimization for the geometry of trapezoidal corrugated morphing skins

Morphing concepts have great importance for the design of future aircraft as they provide the opportunity for the aircraft to adapt their shape in flight so as to always match the optimal configuration. This enables the aircraft to have a better performance, such as reducing fuel consumption, toxic emissions and noise pollution or increasing the maneuverability of the aircraft. However the requirements of morphing aircraft are conflicting from the structural perspective. For instance the design of a morphing skin is a key issue since it must be stiff to withstand the aerodynamic loads, but flexible to enable the large shape changes. Corrugated sheets have remarkable anisotropic characteristics. As a candidate skin for a morphing wing, they are stiff to withstand the aerodynamic loads and flexible to enable the morphing deformations. This work presents novel insights into the multi-objective optimization of a trapezoidal corrugated core with elastomer coating. The geometric parameters of the coated composite corrugated panels are optimized to minimize the in-plane stiffness and the weight of the skin and to maximize the flexural out-of-plane stiffness of the skin. These objective functions were calculated by use of an equivalent finite element code. The gradient-based aggregate method is selected to solve the optimization problem and is validated by comparing to the GA multi-objective optimization technique. The trend of the optimized objectives and parameters are discussed in detail; for example the optimum corrugation often has the maximum corrugation height. The obtained results provide important insights into the design of morphing corrugated skins

Shape optimisation of composite corrugated morphing skins

One of the challenging parts of the morphing wing is the anisotropic skin, which must be flexible enough to allow the wing to change its shape and at the same time being stiff enough to withstand the aerodynamic loads. Composite corrugated skins have exceedingly anisotropic behaviour as they are stiff along the corrugation direction but flexible in transverse direction. Hence, elastomeric coated composite corrugated panels have been proposed as a candidate for application in morphing wings. This paper presents the shape optimisation of the corrugation with respect to better performance of the morphing skin and manufacturing constraints. The shape of the skin is optimised by minimising the in-plane stiffness and weight of the skin and maximising its flexural out-of-plane stiffness. The objective functions were obtained from homogenised model that depends on geometric and mechanical properties of the coated corrugated panel by means of finite element method for thin beams. A few methods of optimisation were considered: aggregated and genetic algorithm methods as representative of two major categories of multi-objective solving methods. A number of different approaches are proposed in order to solve the problem, such as corrugated skin with and without elastomer coating. The advantages of the new optimised shape of the corrugated skin over the typical shapes are discussed

Multi-material topology optimization for composite metal aircraft structures

This paper investigates an optimization routine for lightweight composite-metal hybrid aircraft structures. This routine is developed based on two existing topology optimization approaches, Moving Morphable Components (MMC) and level set method updated by a reaction diffusion equation. The proposed method overcomes the weakness of conventional multi-material optimizers by introducing some rules of material distribution, that enhance the manufacturability of the optimal structure. It is achieved by optimizing the main structural frame using uniform-width components first, leaving the joints as void together with the remaining design domain, and following by a conventional topology optimization using single-material level set approach. A commonly used beam model is optimized to demonstrate the key ideas of the proposed routine

Multi-objective topology optimization and structural analysis of periodic spaceframe structures

Reduction of structural weight provides significant benefits in many engineering applications. While methods to optimise structural shape and topology of both continuous solids and discrete frame structures have existed for a while, the advent of additive layer manufacturing processes has enabled more complex geometries to be feasible. In this paper, a periodic spaceframe structure is designed for minimum mass and maximum effective flexural and torsional rigidities. A method of parametrising the spaceframe through its constituent unit cells is proposed, and Genetic Algorithm (GA) multi-objective optimisation is used to optimise its topology, size and geometry as a generic structure. The superior performance of the topology optimised periodic spaceframe is highlighted in terms of structural rigidity, large deformation capability, buckling and vibrational modal analysis in compare to equivalent beam structures of identical weight and comparable domain. The results show that the proposed method can effectively generate lightweight substitute structures of great mechanical performance in many beam structures applications, such as: aircraft wing spars. The periodic spaceframe is applied into a conventional aircraft wing structure to demonstrate the possibilities of promoting weight saving in the design of civil aircraft wings

Cylindrical helical cell metamaterial with large strain zero Poisson’s ratio for shape morphing analysis

In this paper, a novel cylindrical metamaterial with helical cell exhibiting zero Poisson's ratio (ZPR) in two different directions is introduced. Detailed Computer-aided design modelling of a curved optimised spring element is demonstrated for numerical and experimental analysis. High fidelity finite element models are developed to assess the homogenisation study of Poisson's ratios, normalised Young's modulus and torsion behaviour, demonstrating the curvature effect and independency of mechanical behaviour of cylindrical optimised spring element metamaterial from tessellation numbers. Buckling and frequency analysis of the cylindrical metamaterial with spring element are compared with equivalent shell cylinders. Moreover, experimental analysis is performed to validate the large strain ZPR and deformation mechanism demonstrated in numerical simulations. Finally, radical shape morphing analysis under different bending conditions for cylindrical metamaterial with helical cell is investigated, including deformation and actuation energy and compared with positive and negative Poisson's ratio cylinders formed by honeycomb and auxetic cells

Crashworthiness and dimensional stability analysis of zero Poisson’s ratio fish cells lattice structures

The present article introduces Zero Poisson's Ratio (ZPR) Fish Cells metamaterial and investigates the effects of Poisson's Ratio on the crashworthiness of Positive (PPR), Negative (NPR), and Zero Poisson's Ratio lattice structures. High-fidelity Finite Element models of the proposed sandwich structures are built, based on identical domains for unit cells. Impact performances of lattice structures are addressed for low (2 m/s) and high (5 m/s) impact velocities in three orthogonal directions. The parameters investigated for crashworthiness include impactor's penetration depth, von Mises stress distribution, edges deformation and dimensional stability. Numerical results demonstrate that, unlike PPR and NPR models, the Fish Cells ZPR model possesses greater lateral stability and structural integrity with minimal edge deformations in all three directions. This leads to reduced lateral impact transfer to adjacent components and localised damaged zones, increasing the life span of structural components while reducing maintenance and repair downtime. Experimental analyses are conducted on the Fish Cells metamaterial through a drop tower test for demonstrating agreement with simulations and validation of the proposed modelling approach

Structural similitude design for a scaled composite wing box based on optimised stacking sequence

Testing appropriately-designed scaled-down structures instead of the full-size prototype structure is beneficial for quickly understanding the prototype structural behaviour in a cost-effective way. In this study, a novel approach is proposed to design scaled composite structures that can be used to predict the structural responses (e.g. static bending, modal behaviour, and compressive buckling) of the prototype. The objective is to overcome the main drawback of the conventional design method, which tends to result in low accuracy of the prototype prediction when certain variables cannot be appropriately scaled due to manufacturing constraints (e.g. ply thickness). In the present work, a set of scaling laws being independent of boundary conditions were firstly derived for plates and beams respectively based on their governing equations. The genetic algorithm (GA) was then applied to help design the stacking sequence of the scaled models, accommodating the mismatch in similarity conditions resulting from the manufacturing constraint in ply thickness. This GA-based design method was demonstrated to be effective in designing scaled plate, I-beam, and stiffened plate models, with improved accuracy in predicting the prototype structural behaviour compared with the conventional method. The application of this new design method was also extended to an A320 size wing box structure, validating its robustness for complex structures

Structural mechanics of cylindrical fish-cell zero Poisson’s ratio metamaterials

In this paper, a novel cylindrical metamaterial exhibiting zero Poisson’s ratio in two different directions is introduced. Detailed CAD modelling of a curved Fish-Cells necessary for numerical and experimental analysis are presented. High-fidelity finite element models are developed to assess the homogenisation studies of Poisson’s ratio, Young’s modulus and torsion behaviour, demonstrating the curvature effect and independency of the mechanical behaviour of cylindrical Fish-Cells metamaterial from tessellation numbers. Experimental analysis is performed to validate the zero Poisson’s ratio, deformation and fracture mechanism discussed in numerical simulations. Moreover, buckling and modal behaviours of the cylindrical Fish-Cells metamaterials are studied and compared with equivalent shell models