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Kadowaki, Satoshi; Thwe, T. A.; Furuyama, Taisei*; Kawata, Kazumasa*; Katsumi, Toshiyuki; Kobayashi, Hideaki*

Journal of Thermal Science and Technology (Internet), 16(2), p.20-00491_1 - 20-00491_12, 2021/00

Times Cited Count：3 Percentile：35.94(Thermodynamics)Effects of pressure and heat loss on the unstable motion of cellular-flame fronts in hydrogen-air lean premixed flames were numerically investigated. The reaction mechanism for hydrogen-oxygen combustion was modeled with seventeen reversible reactions of eight reactive species and a diluent. Two-dimensional unsteady reactive flow was treated, and the compressibility, viscosity, heat conduction, molecular diffusion and heat loss were taken into account. As the pressure became higher, the maximum growth rate increased and the unstable range widened. These were due mainly to the decrease of flame thickness. The burning velocity of a cellular flame normalized by that of a planar flame increased as the pressure became higher and the heat loss became larger. This indicated that the pressure and heat loss affected strongly the unstable motion of cellular-flame fronts. In addition, the fractal dimension became larger, which denoted that the flame shape became more complicated.

Thwe, T. A.; Kadowaki, Satoshi; Hino, Ryutaro

Journal of Thermal Science and Technology (Internet), 13(2), p.18-00457_1 - 18-00457_12, 2018/12

Times Cited Count：0 Percentile：0.01(Thermodynamics)Two dimensional unsteady calculations of reactive flows were performed in large domain to investigate the unstable behaviors of cellular premixed flames at low Lewis numbers based on the diffusive-thermal (D-T) model and compressible Navier-Stokes (N-S) equations. The growth rates obtained by the compressible N-S equations were large and the unstable ranges were wide compared with those obtained by the D-T model equations. When the length of computational domain increased, the number of small cells separated from large cells of the cellular flame increased drastically. The stronger unstable behaviors and the larger average burning velocities were observed especially in the numerical results based on the compressible N-S equations. In addition, the fractal dimension obtained by the compressible N-S equations was larger than that by the D-T model equations. Moreover, we confirmed that the radiative heat loss promoted the instability of premixed flames at low Lewis numbers.

Chikazumi, Shimpei*; Iwamoto, Akira

Chaos, Solitons and Fractals, 23(1), p.73 - 78, 2005/01

Times Cited Count：0 Percentile：0.02(Mathematics, Interdisciplinary Applications)To seek for a possible origin of fractal pattern in nature, we perform a molecular dynamics simulation for a fragmentation of an infinite fcc lattice. The fragmentation is induced by the initial condition of the model that the lattice particles have the Hubble-type radial expansion velocities. As time proceeds, the average density decreases and density fluctuation develops. By using the box counting method, it is found that the frequency-size plot of the density follows instantaneously a universal power-law for each Hubble constant up to the size of a cross-over. This cross-over size corresponds to the maximum size of fluctuation and is found to obey a dynamical scaling law as a function of time. This instantaneous generation of a nascent fractal is purely of dynamical origin and it shows us a new formation mechanism of a fractal patters different from the traditional criticality concept.

Ito, Shinichi*; Kajimoto, Ryoichi; Adams, M. A.*

Journal of the Physical Society of Japan, 74(1), p.279 - 282, 2005/01

Times Cited Count：3 Percentile：27.03(Physics, Multidisciplinary)Magnetic fractons in the near-percolating three-dimensional (3D) Heisenberg antiferromagnet, RbMnMgF, have been studied using inelastic neutron scattering with high energy resolution (eV) and at low temperature ( K). It is demonstrated that the fractons follow the dispersion relation of (q being the wave number). The observed exponent, , is in good agreement with the fractal dimension of the 3D system (), as predicted by theory.

Bak, P. E.; Asakura, Nobuyuki; Miura, Yukitoshi; Nakano, Tomohide; Yoshino, Ryuji

Physics of Plasmas, 8(4), p.1248 - 1252, 2001/04

Times Cited Count：1 Percentile：3.56(Physics, Fluids & Plasmas)The temporal losses of confinement during Edge Localised Modes in JT-60U show multifractal scaling and the spectra are generally smooth, but in some cases there are signs of discontinuous derivatives. Dynamics of the Sugama-Horton Model, interpreted as Edge Localised Modes, also display multifractal scaling. The spectra display singularities in the derivative, which can be interpreted as a phase transition. We argue that the multifractal spectra of Edge Localised Modes can be used to discriminate between different experimental discharges and validate Edge Localised Mode models.

Suzudo, Tomoaki; Hayashi, Koji

Proc. of a Symp. on Nuclear Reactor Surveillance and Diagnostics,Vol. 1, 12 Pages, 1991/00

no abstracts in English

Ueki, Taro

no journal, ,

A new methodology has been developed to make the reliable estimation of statistical errors in Monte Carlo criticality calculation (MCCC). The methodology developed is directly based on the convergence process in the functional central limit theorem and is shown to perform well in the evaluation of reactor power distribution. The theoretical backbones are described within the general context as framed in the operations research. The requisite basics of statistics are reviewed in terms of output analysis in MCCC. Numerical results are presented for the initial core model of a 1200 MWe pressurized water reactor. Preliminary results of fractal dimension analysis are shown to discuss a potential for convergence assessment.