Kohei Yuge

Optimization of a frame structure subjected to a plastic deformation

An optimization method for a frame structure subjected to a plastic deformation is proposed in this paper. The method is based on the generalized layout optimization method proposed by Bendsøe and Kikuchi in 1988, where the solid-cavity composite material is distributed in the admissible domain and the cavity size is determined so that it becomes large in the area where the strain energy is small. Elasto-plastic analysis based on the homogenization method is carried out to obtain the nonlinear average stress-strain relations of a porous material first. Then the optimization algorithm of a frame structure is derived by taking plastification into account. Finally in order to demonstrate the effectiveness of the present algorithm, several numerical examples are illustrated.

Optimization of 2-D structures subjected to nonlinear deformations using the homogenization method

The generalized layout optimization method is applied to nonlinear problems. The algorithm was originally invented by Bendsøe and Kikuchi (1988), where an admissible design domain is assumed to be composed of periodic microstructures with tiny cavities; the sizes and the rotational angle of the cavities are defined as design variables which are optimized to minimize the applied work. The macroscoic material tensor of the porous material is calculated by the homogenization method for the sensitivity analysis. In order to apply it to nonlinear problems, we present a 2-D database of the material tensor calculated by the elasto-plastic homogenization method and an interpolation technique of the database for the practical computation. Several numerical examples of 2-D structures and a thin shell are shown to demonstrate the effectiveness of our algorithms. The algorithm is also extended to the finite deformation problems, and a practical optimized design is exhibited.

Dynamic analysis of ultrasonically levitated droplet with moving particle semi-implicit and distributed point source method

Numerical analysis of an ultrasonically levitated droplet with a free surface boundary is discussed. The droplet is known to change its shape from sphere to spheroid when it is suspended in a standing wave owing to the acoustic radiation force. However, few studies on numerical simulation have been reported in association with this phenomenon including fluid dynamics inside the droplet. In this paper, coupled analysis using the distributed point source method (DPSM) and the moving particle semi-implicit (MPS) method, both of which do not require grids or meshes to handle the moving boundary with ease, is suggested. A droplet levitated in a plane standing wave field between a piston-vibrating ultrasonic transducer and a reflector is simulated with the DPSM–MPS coupled method. The dynamic change in the spheroidal shape of the droplet is successfully reproduced numerically, and the gravitational center and the change in the spheroidal aspect ratio are discussed and compared with the previous literature.

Impact Injury Analysis of the Human Head

The brain is the most important organ for life activity and humanity and is also an organ that tends to have residual disabilities after an accident because neuron cells cannot repair themselves. Therefore, protecting the brain from serious damage should be one of the most important objectives in automotive safety design for both passengers and pedestrians. For this reason, the Seikei University Graduate School and others have examined head impacts and the subsequent responses.

Evaluating the Effect of Back Injury on Shoulder Loading and Effort Perception in Hand Transfer Tasks

Occupational populations have become increasingly diverse, requiring novel accommodation technologies for inclusive design. Hence, further attention is required to identify potential differences in work perception between workers with varying physical limitations. The major aim of this study was to identify differences in shoulder loading and perception of effort between a control population (C) and populations affected by chronic back pain (LBP) and spinal cord injury (SCI) in one-handed seated transfer tasks to targets. The effects of the injuries, and associated pain, are likely to produce variations in movement patterns, muscle loading and perceived effort. The main results show that a) the LBP group had the highest movement time required for an exertion; significantly higher than both the SCI and C groups, while the SCI group had significantly longer exertion times than group C, b) the SCI and LBP groups had significantly higher total, maximum, and mean shoulder torques than the C group, c) the mean shoulder effort ratings for LBPs and SCIs were significantly higher than those for Cs, d) LBPs reported higher shoulder effort ratings than SCIs, e) SCIs and/or LBPs were unable to reach some of the targets; and f) the perception of effort tended to increase as a function of the linear distance between the seat and the target shelf. Differences in shoulder loading and perception were attributed to differences in movement velocities and strategies between the groups. These results suggest that workplace adaptation must take into account population specific characteristics.

Analysis of an ultrasonically rotating droplet by moving particle semi-implicit and distributed point source method in a rotational coordinate

Numerical analysis on the rotation of an ultrasonically levitated droplet in centrifugal coordinate is discussed. A droplet levitated in an acoustic chamber is simulated using the distributed point source method and the moving particle semi-implicit method. Centrifugal coordinate is adopted to avoid the Laplacian differential error, which causes numerical divergence or inaccuracy in the global coordinate calculation. Consequently, the duration of calculation stability has increased 30 times longer than that in a the previous paper. Moreover, the droplet radius versus rotational acceleration characteristics show a similar trend to the theoretical and experimental values in the literature.

Shape and rotation analysis on an ultrasonically levitated droplet using distributed point source method and least square moving particle semi-implicit method

Ultrasonic droplet levitation has recently been drawing attention as a way of non-contact transportation. Many experiment revealed that the shape changes or streaming field on the levitating droplets, however, quite small number of numerical simulation have discussed this phenomenon including fluid dynamics within the droplet. In this paper, coupled analysis using the distributed point source method (DPSM) and the least square moving particle semi-implicit (LS-MPS) method, both of which do not require grids or meshes to handle the moving boundary with ease, is suggested. The acoustic radiation force including viscoacoustic torque, which emerges from the viscous boundary layer, is calculated from the distributed point source method result using the idea of boundary layer normal velocity and input to the LS-MPS surface particles. A droplet levitated in an acoustic chamber is simulated using the proposed calculation method. The droplet is vertically supported by a plane standing wave from an ultrasonic drive...

Analysis of ultrasonically rotating droplet using moving particle semi-implicit and distributed point source methods

Numerical analysis of the rotation of an ultrasonically levitated droplet with a free surface boundary is discussed. The ultrasonically levitated droplet is often reported to rotate owing to the surface tangential component of acoustic radiation force. To observe the torque from an acoustic wave and clarify the mechanism underlying the phenomena, it is effective to take advantage of numerical simulation using the distributed point source method (DPSM) and moving particle semi-implicit (MPS) method, both of which do not require a calculation grid or mesh. In this paper, the numerical treatment of the viscoacoustic torque, which emerges from the viscous boundary layer and governs the acoustical droplet rotation, is discussed. The Reynolds stress traction force is calculated from the DPSM result using the idea of effective normal particle velocity through the boundary layer and input to the MPS surface particles. A droplet levitated in an acoustic chamber is simulated using the proposed calculation method. The droplet is vertically supported by a plane standing wave from an ultrasonic driver and subjected to a rotating sound field excited by two acoustic sources on the side wall with different phases. The rotation of the droplet is successfully reproduced numerically and its acceleration is discussed and compared with those in the literature.

Tangential streaming analysis on ultrasonically levitated droplet through the boundary layer approximation with moving particle semi-implicit and distributed point source method

Ultrasonic droplet levitation has recently been drawing attention as a way of non-contact transportation. Many experiment revealed that the shape changes or streaming field on the levitating droplets, however, quite small number of numerical simulation have discussed this phenomenon including fluid dynamics within the droplet. In this paper, the calculation result on a streaming field on the levitated droplet with rotational acoustic driver is discussed. The visco-acoustic torque originated in Reynolds stress as well as acoustic radiation force is input on a coupled analysis using distributed point source method (DPSM) and moving particle semi-implicit (MPS) method.

Maximization of Strengthening Effect of Microscopic Morphology in Duplex Steels

An inverse analysis method based on nonlinear finite element analysis is developed to find an optimized morphology of periodic microstructure for improving the macroscopic mechanical properties in duplex elastoplastic solids. Here a gradient-based computational optimization method and two types of homogenization methods are employed. In this study, the optimization problem is defined as the maximization of the sum of macroscopic external works for several macroscopic deformation modes, enabling us to obtain a high strength material. The morphologic strengthening effect is discussed through a comparison with experiments and classical theories.