Shinji Kawamoto

Particle-in-cell plus direct simulation Monte Carlo (PIC-DSMC) approach for self-consistent plasma-gas simulations

The particle-in-cell (PIC) and direct simulation Monte Carlo (DSMC) approaches have been combined into a PIC-DSMC model for self-consistent simulations of low-temperature collisional plasmas and the background gas. This novel approach is based on the weighting collision simulation scheme allowing for disparate number densities and time scales of different species. The applicability of the developed algorithm is illustrated by simulations of one-dimensional direct current and two-dimensional magnetron sputtering discharges in argon. An appreciable effect of the energetic discharge species on the density, temperature, and flow field of the background gas shows the importance of the coupled plasma-gas simulation for such technologies as sputtering, dry etching, plasma enhanced vapor deposition, etc.

Numerical prediction of wind loading on buildings and structures : Activities of AIJ cooperative project on CFD

This study presents the activities of the Architectural Institute of Japan (AIJ) concerning the Computational Fluid Dynamics (CFD) for a numerical prediction of wind loading on buildings and structures. In the AIJ project, the flows and the pressures around a low-rise building (breadth : depth : height = 1 : 1 : 0.5) have been computed by 10 members of the working group, who mainly employed the κ-e model or the large eddy simulation for turbulent flows. Here, on the basis of the results of the AIJ project, future subjects for further development of the CFD technique are discussed. Also we present how to find the way to realize the practical use of the CFD technique on prediction of wind loading.

Improved turbulence models for estimation of wind loading

Abstract The objective of this work is to develop a cost efficient and accurate turbulence model for the estimation of wind loading on buildings. This paper presents two types of k−e−φ turbulence model, which are stable, simple, cost efficient and high-accuracy turbulence models, for estimation of wind loading on a bluff body. The variable φ, an anisotropy parameter of the Reynolds stresses, decreases due to the deceleration effect through an adverse pressure gradient, and increases due to the acceleration effect through a favorable pressure gradient. The coefficient of the kinematic eddy viscosity, Cμ, is defined by a function of φ and the helicity H, and the coefficient of production term of turbulence energy dissipation rate in the conventional standard k−e turbulence model, Ce1, is defined by a function of φ. The favorable pressure gradient flow and the flows around a square prism are used for adjusting each coefficient, and the flows around a low-rise building in a 1 4 shear flow are used for adjusting the coefficient of the helicity effect and for the verification of these models. The distributions of the mean pressure coefficient using these two types of k−e−φ turbulence model are improved dramatically compared with those using the standard k−e turbulence model.

Numerical experiments in Monte Carlo modeling of polarization, diffraction, and interference phenomena

We present the numerical tests for a Monte Carlo ray-tracing model. The model has been extended to simulate not only geometrical but also physical optics phenomena, including polarization, diffraction, and interference of light. Light beams are represented by a flux of simulated particles (photons) carrying a complex vector characteristic that contains information about amplitude and phase of electromagnetic field oscillations. The model allows simulations of polarization phenomena in global coordinates. It has been verified by predicting the results that perfectly match those derived from the Fresnel formulae for unpolarized light reflection/refraction at the interface of two media. The capability of handling diffraction and interference has been tested on the problems of Fraunhofer diffraction at an infinite slit and circular aperture, and Fresnel diffraction at a semi-infinite knife-edge plane. The results obtained for the former compare fairly well with the analytical solutions from the wave theory, whereas, for the latter, there is only a qualitative agreement with the fringe pattern deduced from the Cornu spiral.

Polarizers designed by FEM for electromagnetic simulation

FEM for electromagnetic simulation with absorbing boundary condition is applied to the design of polarizers, and the characteristics of metal sheet polarizers has been studied numerically. The dimensions of Au and Al metal sheet polarizers, which give enough performance as practical polarizers with much thinner structure than conventional polarizers, are presented. An Al metal sheet polarizer with comparable performance to Au metal sheet polarizer can be achieved by applying thinner Al metal sheets than the thickness of Au metal sheets. However, the performance given by Al metal sheet polarizer should be taken care, because the relative permittivity of Al film varies largely according to the film condition. Though Au and Al metal sheet polarizers exhibit high performance, the reflectance of TE polarization is higher than that of conventional polarizers. Therefore, the stray light should be paid attention more than conventional ones. The metal sheet polarizer exhibits enough high polarization performance for wide range of wavelength over 5 times as large as the distance between the metal sheets. The characteristics of metal fiber polarizers are also simulated. The metal fiber polarizers need much finer and thicker structure than metal sheet polarizers to exhibit enough performance.

Numerical analysis of wind around building using high-speed GSMAC-FEM — Validation of differential stress model —

Abstract A stable and cost-efficient finite element formulation, the high-speed GSMAC-FEM (generalized simplified marker and cell finite-element method), for unsteady incompressible viscous flow analysis is developed. In this paper, the high-speed GSMAC-FEM with the differential stress turbulence model, which includes curve effect in Rottas term as a pressure-strain correlation, is validated by computing the channel flow and the flow over a backward-facing step. After that, the superiority of the differential stress model to the k - ϵ turbulence model for the prediction of the pressure distributions on a building in a turbulent stream is demonstrated.