Nozomu Kogiso

Genetic Algorithms with Local Improvement for Composite LaminateDesign

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.

Design of Composite Laminates by a Genetic Algorithm with Memory

This paper describes the use of a genetic algorithm with memory for the design of minimum thickness composite laminates subject to strength, buckling and ply contiguity constraints. A binary tree is used to efficiently store and retrieve information about past designs. This information is used to construct a set of linear approximations to the buckling load in the neighborhood of each member of the population of designs. The approximations are then used to seek nearby improved designs in a procedure called local improvement. The paper demonstrates that this procedure substantially reduces the number of analyses required for the genetic search. The paper also demonstrates that the use of genetic algorithms helps find several alternate designs with similar performance, thus giving the designer a choice of alternatives.

Applications of Magnesium Alloys for Aerospace Structure Systems

The applications of magnesium alloys for designing aerospace structure systems are focused in this paper. As the material properties of magnesium alloys have advantages of light weight, high specific stiffness, and high damping characteristics, they are supposed to be advantageous for designing light-weight aerospace structures. Additionally, as the magnesium alloys are easily recycled with low energy costs and without environmental pollution, they are expected to be alternative materials for polymer and conventional composite materials. This paper describes the applications for aerospace structure systems with the magnesium alloys in the view point of structural design, structural reliability design, and system design of small satellites, Finally, the feasibility for applying the magnesium alloys to the space structure systems is discussed.

Reliability-based optimum design of a symmetric laminated plate subject to buckling

This study is concerned with the buckling reliability maximization of a symmetric laminated composite plate with respect to the mean ply orientation angle. The reliability is evaluated by modelling the buckling failure as a series system consisting of potential eigenmodes. The mode reliability is obtained by the first-order reliability theory (FORM), where material constants and orientation angles of individual layers, as well as the applied loads are treated as random variables. In order to keep track of the intended buckling mode during the reliability analysis, the mode tracking method is utilized. Then, the failure probability of the series system is approximated by Ditlevsens upper bound. The reliability maximization problem is formulated as a nested problem with two levels of optimization. Through numerical calculations, the reliability-based design is demonstrated to be important for the structural safety in comparison with the deterministic buckling load maximization design.

Level Set-Based Topology Optimization for the Design of an Electromagnetic Cloak With Ferrite Material

This paper presents a structural optimization method for the design of an electromagnetic cloak made of ferrite material. Ferrite materials exhibit a frequency-dependent degree of permeability, due to a magnetic resonance phenomenon that can be altered by changing the magnitude of an externally applied dc magnetic field. Thus, such ferrite cloaks have the potential to provide novel functions, such as on-off operation in response to on-off application of an external magnetic field. The optimization problems are formulated to minimize the norm of the scattering field from a cylindrical obstacle. A level set-based topology optimization method incorporating a fictitious interface energy is used to find optimized configurations of the ferrite material. The numerical results demonstrate that the optimization successfully found an appropriate ferrite configuration that functions as an electromagnetic cloak.

Lamination Parameters Applied to Reliability-Based In-Plane Strength Design of Composites

The efficiency of adopting lamination parameters as design variables for the reliability-based optimization of a laminated composite plate subject to in-plane loads is presented. The plate failure is evaluated by the first-ply failure (FPF) criterion, where the ply failure is evaluated based on the Tsai-Wu criterion. According to the FPF criterion, the laminated plate is modeled as a series system consisting of every ply failure. The system reliability of the composite plate is evaluated by Ditlevsens bounds. Each ply-failure probability is evaluated by the first-order reliability method, where the material properties and applied loads are treated as random variables. As numerical examples, two types of the reliability-based design are formulated in terms of lamination parameters. One is the reliability-maximized design of the constant-thickness plate. The other is the thickness-minimized design under the reliability constraint. Through numerical calculations, it is shown that the reliability has a single peak and a continuous distribution in the lamination parameter space. Consequently, numerical searching rapidly achieves the optimum solution.

Level Set-Based Topology Optimization for the Design of Light-Trapping Structures

This paper discusses a systematic design method for light-trapping structures that can enhance the absorption capability of thin-film solar cells. Light-trapping techniques extend the length of the light path in the active layer and thereby enhance solar cell efficiency. The level set-based topology optimization method is constructed for the structural design of a light-scattering layer that is in contact with a cladding layer above the active layer. The optimization problem is formulated to maximize the light absorption coefficient of the solar cells. Numerical results demonstrate that the optimization can successfully find an appropriate configuration of the dielectric material and air for a light-scattering layer that enhances the light absorption coefficient at the desired wavelength.

WING PLANFORM OPTIMIZATION OF HUMAN POWERED AIRCRAFT IN LOW REYNOLDS NUMBER RANGE

This study is concerned with a wing planform design of a high aspect ratio wing in a low Reynolds number range used by a human powered aircraft. In the low Reynolds number range, effect of the profile drag must be considered as well as the induced drag. For flight stability, an adequate deformation of the main spar is desirable to bring a dihedral effect. The structural problem is also incorporated into the optimization problem as a constraint concerning the tip displacement. Moreover, the spar sizing design has an effect on the weight and hence the power-required of the aircraft. Accordingly, the power-required minimized design is formulated in terms of the wing planform and the main spar dimensions. Through numerical calculations, effect of the profile drag on the wing planform design is demonstrated. The profile drag is approximated by polynomials in terms of the Reynolds number for an efficient calculation. Then, the importance of the multidisciplinary optimization is demonstrated for the wing design of the human powered aircraft.

RELIABILITY-BASED DESIGN OF SYMMETRIC LAMINATED PLATE WITH INITIAL IMPERFECTION

This study is concerned with the reliability-based design of a simply supported symmetric laminated plate with an initial imperfection under bi-axial compression load. For a plate loaded in compression, a small initial imperfection can cause large bending stresses that reduces the load at which the ply failure occurs. The failure is modeled as a series system consisting of both the buckling failure and the material strength failure. For the reliability analysis, the initial imperfection, material properties and applied loads are treated as random variables. The mode reliability is evaluated by the first order reliability method. Then, the system reliability is approximated by Ditlevsens upper bound, which is used as an objective function of the reliability maximization. The optimum laminate configuration is determined such that the reliability for the failure may be maximized in terms of the ply orientation angles of individual layers. Through numerical calculations, the reliability-based design is demonstrated to be important for the structural safety.

Level Set-Based Topology Optimization for the Design of a Ferromagnetic Waveguide

This paper discusses a level set-based topology optimization method for the design of a ferromagnetic waveguide. The optimization problem is formulated to maximize the power of transmitted waves at prescribed frequencies. A level set-based topology optimization method incorporating a fictitious interface energy is used to find optimized configurations of ferrite materials inside the waveguide. The results of the numerical examples for two different target frequencies show that the presented method successfully finds optimized configurations that maximize transmission power of waveguides for both forward and backward propagation.