In practice, structures of metamaterials in the optical regime are restricted to planar ones. We therefore propose a topological optimisation method of electromagnetic metamaterials using the topological derivative for a cylindrical hole in periodic transmission problems for Maxwell’s equations.

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We developed a new numerical model toward simulations of human-body movements in tsunami floods. A combination of a multiphase fluid solution: CIP-CUP method and a representation method of human body: link segment model enabled human-fluid coupled analyses which are necessary for such simulations. With this model, we simulated movements of a human body model in water flows according to some experiments. Thus, we showed that our new model represents human movement well especially in whirlpools which appears behind structures.

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Improvement of computational methods for predicting the flow of droplets impingement in various industrial applications are hoped. In particular, in order to deal with industrial problems, a numerical scheme should be capable of easily deal with complicated interface topology change such as coalescence, breakup and so on. In the present paper, we investigate the possibility of DIM (diffuse interface model) as an interface tracking method to well respond to the topological change of interface. A problem of a single droplet impingement is examined to validate the performance of the DIM. Further multiple droplets impingement are investigated.

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[in Japanese]

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Thermal design with nanoscale is essential when developing miniaturized electronic devices. Whereas conventional macroscale thermal design methods have a limitation to improve the performance of an electronic device, the implementation of nanostructural designs that utilizes unique properties of heat conduction has resulted in unprecedentedly high-performance electronic devices. One of the most unique and useful properties in a nanoscale heat conduction is a temperature discontinuity on a material surface. However, few reports proposed thermal-design criteria and thermal designs have been dependent on heuristic approaches. There is a large demand for constructing the design guidelines of nanoscale thermal problems and one of the effective design criteria is a shape sensitivity which indicates how to set the material surfaces based on physics and mathematics. In this paper, we propose a shape sensitivity analysis method for a two-phase thermal design problem considering temperature discontinuities. First, we clarify the design problem of a nanoscale heat conduction based on the Boltzmann transport equation. Next, we construct a method for a shape sensitivity analysis for a heat conduction problem considering two-phase nanoscale effects by expanding the work of Pantz. The validity of our shape sensitivity analysis is demonstrated through a numerical example.

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This paper presents a topology optimization method for three-dimensional transient thermal-fluid flows, in which the state and adjoint problems are solved by using the lattice Boltzmann method and parallel computing. The local-in-time adjoint-based method is used for reducing storage cost, as time-dependent optimization problems typically require considerable memory when solving adjoint problems. A primitive numerical example that aims to maximize the heat exchange under the prescribed pressure loss is provided to confirm the efficacy of the proposed method.

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[in Japanese]

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Numerical method for analyzing pattern formation on a curved surface is investigated in this study. A multiphase-field model is applied, and the equations are solved by the finite difference method. The lattice points for the numerical integration are disposed on a spherical surface. In our previous study, several regular patterns such as barrel-shaped hexahedron and regular dodecahedron are obtained for a certain sphere. In this study, the radius of the spheres are varied, and the dependency of the pattern on the radius or curvature of the surface is examined. As a result, a drastic transition is observed at a threshold radius.

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[in Japanese]

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In this study, cellulose nanofiber (CNF) is introduced to overcome the shortcomings in waterborne epoxy resin such as low mechanical properties and applicable temperature. Benefited by the significant mechanical properties of CNF, the new composite material is supposed to possess better properties both on strength and toughness, thermal and dimensional stability etc. The composites were prepared from a waterborne epoxy emulsion and a CNF water suspension through mechanical agitation and film casting. Scanning electron microscope is used to observe the dispersion of the filler. Tensile test and tensile shear test are conducted to evaluate the mechanical performance.

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To find accurate and computationally efficient algoriths for treating boundary conditions in the Link-wise Artificial Compressibility Method proposed by Asinari et al.⁽¹⁾, we have introduced a simple method based on the extrapolation of macroscopic variables. For the extrapolation, three different immersed boundary techniques available in the literature have been considered. Then, we have conducted numerical simulation of flows around a periodic array of spheres, and have compared the obtained numerical results with the existing analytical ones to assess the accuracy and the grid convergence of the present methods.

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[in Japanese]

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[in Japanese]

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Influence of misfit dislocations on mechanical properties of fine pearlite is investigated via uniaxial tensile deformation tests of multilayered composite models composed of ferrite and cementite phases with the Bagaryatsky relation by using molecular dynamics simulations. The analysis models have various spacing of misfit dislocations. First, we show the relationship between the misfit dislocation spacing and each component of phase stress in ferrite and cementite under no applied stress. Second, it is found that the misfit dislocation spacing influences tensile yield stresses and the dominant non-elastic phenomena, i.e. phase stresses and misfit dislocation structures influence the resolved shear stress and the critical resolved shear stress for each slip system, respectively. Therefore, the misfit dislocation spacing has a potential to be a controlling parameter of the resolved stress and the critical resolved stress for non-elastic phenomena. In addition, it has been also found that the flow stresses of the lamellar models are affected by the misfit dislocation density. That is, the misfit dislocation spacing influences the mechanical properties of fine pearlite.

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[in Japanese]

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In the analysis of unsteady flow field, low-dimensionalization methods have been often used. Those methods are based on a linearization method and have several issues in application to a flow field with a strong nonlinearity. In this paper, we focus on deep learning, which is a state-of-the-art nonlinear mapping method, and apply it to a low-dimensionalization method for unsteady flow field. In addition, we extend the dynamic network visualization method proposed by Elzen et al to a visualization of a time series data of unsteady flow field. Our proposed method is applied to the analysis of 3D unsteady flow around a sphere, and we shows the effectiveness in analyzing the unsteady flow.

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[in Japanese]

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In this study, we simulate compression of graphite and bending of graphene using molecular dynamics to explain the mechanism of kink-band deformation and mechanical characteristics of them. The results show that kink-band is formed under compressing of graphite with l_x : l_y aspect ratio 2:3 when the strain equal approximately 0.02 and the potential energy of graphene proportionately increases as the curvature of kink-band deformation increases.

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[in Japanese]

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[in Japanese]

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FTMP-based realizations of ductile fracture modes in single crystal and polycrystals models are presented. The fracture modes in the current context stem from destabilized dislocation substructure spontaneously evolved in the deformationinduced manner, strongly depending on the crystallographic orientations and their combination. Duality diagram representations enable us not only to visualize the associated energy flow but also how the excessively-stored strain energy are redistributed into incompatibility-related underlying degrees of freedom.

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Successful reproduction of inhomogeneous recovery-triggered accelerated creep rupture modes is achieved with FTMPbased lath martensite hierarchical models, wherein designated set of interaction fields play critical roles. A systematic “manhunt” for the determinant implies the climb-related mechanisms as the key process.

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[in Japanese]

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Microwave atomic force microscopy (M-AFM) is designed to realize the non-contact measurement of topography and electrical property at nanoscale simultaneously. For the evaluation of dielectric materials, since the detected reflected signal depends strongly on the probe-sample distance, in non-contact mode the quantitative evaluation regardless of the effect of distance is difficult. In this study, the effect of microwave on the force between the probe and dielectric materials was investigated. A theoretic model based on the reflection of electromagnetic wave was established to describe the distance dependence of microwave intensity between sample and probe. The relationship between the force gradient and sample permittivity was obtained and the permittivity of Al₂O₃, Ge, and ZrO₂ was evaluated using this theoretical model.

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In this study, the topology optimization was applied to structural lightening of the core layers in sandwich composite beams. Then, the optimized core layer which achieved both the highest weight reduction and rigidity was molded with a FDM 3D printer. Three point flexural test was carried out for experimentally evaluating mechanical properties of the present topology-optimized sandwich beam. In addition, finite element method (FEM) numerical analysis was also conducted for the flexural test. As a result, both of the compliances of experimental and numerical results were found to be in a good agreement, which shows the present topology optimization for composite sandwich beams is very effective for the structural lightening design.

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Today fiber reinforced composites such as CFRP (carbon fiber reinforced plastics) have been more and more used for light-weight structural components in various industrial fields such as aerospace. Although there are several sophisticated and practical processing techniques for manufacturing fiber reinforced composite, promise and possibility of additive manufacturing, or 3D printing of those materials like CFRP are indispensable because such newcomers of material and structural processing obviously allow design methodologies widen beyond their conventional design and optimization approaches. Topology optimization designs are very attractive for additive manufacturing product designs. However, this method still seems to be not perfect in case that one tries to apply it to fiber reinforced composite design, in which one should take into consideration of orthotropic and graded material and physical properties. In this preliminary report, the present author tries to raise awareness of this issue and also attempts to formulate an extension or a generalization of the existing density-based topology optimization scheme, that is, SIMP (Solid Isotropic Material with Penalization) method.

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