研究者詳細 - 芳松　克則

論文 - 芳松　克則

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Small-scale anisotropic intermittency in magnetohydrodynamic turbulence at low magnetic Reynolds numbers 査読有り

Naoya Okamoto, Katsunori Yoshimatsu, Kai Schneider, and Marie Farge

Physical Review E 89 巻 ( 3 ) 頁： 033013 2014年3月

Coherent vorticity and current density simulation of three-dimensional magnetohydrodynamic turbulence using orthogonal wavelets 査読有り

K. Yoshimatsu, N. Okamoto, Y. Kawahara, K. Schneider and M. Farge

Geophysical and Astrophysical Fluid Dynamics 107 巻 ( 1-2 ) 頁： 73-92 2013年3月

Coherent Vorticity and Current Density Simulation of Magnetohydrodynamic Turbulence 査読有り

頁： 184-189 2012年9月

Examination of the four-fifths law for longitudinal third-order moments in incompressible magnetohydrodynamic turbulence in a periodic box 査読有り

Katsunori Yoshimatsu

Physical Review E 85 巻 ( 6 ) 頁： 066313 2012年6月

Intermittency of quasi-static magnetohydrodynamic turbulence: A wavelet viewpoint

N Okamoto, K Yoshimatsu, K Schneider and M Farge

Journal of Physics: Conference Series 318 巻頁： 072035 2011年12月

Intermittency and geometrical statistics of three-dimensional homogeneous magnetohydrodynamic turbulence: A wavelet viewpoint 査読有り

Katsunori Yoshimatsu, Kai Schneider, Naoya Okamoto, Yasuhiro Kawahara, and Marie Farge

PHYSICS OF PLASMAS 18 巻 ( 9 ) 頁： 092304 2011年9月

Coherent Vorticity Simulation of Three-Dimensional Forced Homogeneous Isotropic Turbulence 査読有り

Naoya Okamoto, Katsunori Yoshimatsu, Kai Schneider, Marie Farge, and Yukio Kaneda

Multiscale Modeling & Simulation 9 巻 ( 3 ) 頁： 1144-1161 2011年9月

Columnar eddy formation in freely decaying homogeneous rotating turbulence 査読有り

K. Yoshimatsu, M. Midorikawa and Y. Kaneda

Journal of Fluid Mechanics 677 巻頁： 154-178 2011年6月

DIRECTIONAL AND SCALE-DEPENDENT STATISTICS OF QUASI-STATIC MAGNETOHYDRODYNAMIC TURBULENCE 査読有り

Naoya Okamoto, Katsunori Yoshimatsu, Kai Schneider and Marie Farge

ESAIM: Proceedings 32 巻頁： 95-102 2011年

Coherent Vorticity and Current Extraction in Three-Dimensional Homogeneous Magnetohydrodynamic Turbulence: Comparison Between Wavelet and Fourier Filtering

Naoya Okamoto, Katsunori Yoshimatsu, Yuji Kondo, Kai Schneider and Marie Farge

Procs. of V European Conference on ComputationalFluid Dynamics ECCOMAS CFD 2010, J. C. F. Pereira, A. Sequeira and J. M. C. Pereira (Eds) 頁： 01379_1-12 2010年6月

Coherent Vortex Extraction from Three-Dimesional Homogeneous Isotropic Turbulence: Comparison of Wavelet and Fourier Nonlinear Filtering Methods 査読有り

K. Yoshimatsu, N. Okamoto, M. Farge and K. Schneider

Thehoretical and Applied Mechanics Japan 58 巻頁： 227-233 2010年2月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Two nonlinear filtering methods for extracting coherent structures from direct numerical simulation data of isotropic turbulence are compared. One is based on the orthonormal wavelet decomposition, called coherent vortex extraction (CVE) method, and the other is based on the Fourier decomposition, called Fourier nonlinear filtering (FNF) method. We examine contributions of structures extracted by applying these methods to turbulent flows. Coherent structures extracted by using the CVE method, reconstructed from only 3.6 % of the degrees of freedom, preserve the vortex tubes as well as statistical quantities of turbulence. In contrast, the structures extracted by using the FNF method, represented by 7.3 % of the degrees of freedom, only well preserve low-order statistical quantities, e.g., energy, enstrophy and the energy spectrum in the inertial range, but smooth out the vortex tubes.

*Wavelet-based coherent vorticity sheet and current sheet extraction from three-dimensional homogeneous magnetohydrodynamic turbulence 査読有り

Katsunori Yoshimatsu, Yuji Kondo, Kai Schneider, Naoya Okamoto, Hiroyuki Hagiwara, and Marie Farge

Physics of Plasmas 16 巻 ( 8 ) 頁： 082306-1 - 082306-11 2009年8月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

A method for extracting coherent vorticity sheets and current sheets out of three-dimensional homogeneous magnetohydrodynamic (MHD) turbulence is proposed, which is based on the orthogonal wavelet decomposition of the vorticity and current density fields. Thresholding the
wavelet coefficients allows both fields to be split into coherent and incoherent parts. The fields to be analyzed are obtained by direct numerical simulation (DNS) of forced incompressible MHD turbulence without mean magnetic field, using a classical Fourier spectral method at a resolution of
512^3. Coherent vorticity sheets and current sheets are extracted from the DNS data at a given time instant. It is found that the coherent vorticity and current density preserve both the vorticity sheets and the current sheets present in the total fields while retaining only a few percent of the degrees of freedom. The incoherent vorticity and current density are shown to be structureless and of mainly dissipative nature. The spectral distributions of kinetic and magnetic energies of the coherent fields
only differ in the dissipative range, while the corresponding incoherent fields exhibit near-equipartition of energy. The probability distribution functions of total and coherent fields for both vorticity and current density coincide almost perfectly, while the incoherent fields have
strongly reduced variances. Studying the energy flux confirms that the nonlinear dynamics is fully captured by the coherent fields only.

Wavelet解析による一様等方性電磁流体乱流の秩序構造抽出

近藤祐史、芳松克則、岡本直也、萩原裕之

応用力学研究所研究集会報告 20ME-S6乱流現象及び多自由度系の動力学, 構造と統計法則頁： 16－21 2009年3月

*Intermittency and scale-dependent statistics in fully developed turbulence 査読有り

K. Yoshimatsu, N. Okamoto, K. Schneider, Y. Kaneda and M. Farge

Physical Review E 79 巻 ( 2 ) 頁： 026303-1 - 026303-5 2009年2月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Fully developed homogeneous isotropic turbulent fields, computed by direct numerical simulation, are
compared to divergence-free random fields having the same energy spectrum and either the same helicity
spectrum as that of the turbulent data, or vanishing helicity. We show that the scale-dependent velocity flatness
quantifies the spatial variability of the energy spectrum. The flatness exhibits a substantial increase at small
scales for the turbulent field, but remains constant for the random fields. A diagnostic, the scale-dependent
helicity, is proposed to quantify the geometrical statistics of the flow, which shows that only the turbulent flow
is intermittent. Finally, statistical scale-dependent analyses of both Eulerian and Lagrangian accelerations
confirm the inherently different dynamics of turbulent and random flows.

Intermittency in high resolution direct numerical simulation of turbulence in a periodic box: a wavelet viewpoint 査読有り

K. Yoshimatsu, N. Okamoto, K. Schneider, Y. Kaneda and M. Farge

Advances in Turbulence XII, Proceedings of the 12th EUROMECHEuropean Turbulence Conference,September 7-10, 2009, Marburg, Germany, Springer 頁： 945 2009年

Coherent vortex simulation: application to 3D homogeneous isotropic turbulence 査読有り

N. Okamoto, K. Yoshimatsu, K. Schneider, M. Farge and Y. Kaneda

Advances in Turbulence XII, Proceedings of the 12th EUROMECHEuropean Turbulence Conference, September 7–10, 2009, Marburg, Germany, Springer 頁： 759-762 2009年

Wavelet-based statistics of energy transfer in high resolution direct numerical simulation of three-dimensional homogeneous isotropic turbulence 査読有り

K. Yoshimatsu and N. Okamoto

Journal of Turbulence 9 巻頁： No45, pp.1-25 2008年12月

Energy transfer in high Reynolds number three-dimensional homogeneous isotropic turbulence: A wavelet viewpoint 査読有り

N. Okamoto and K. Yoshimatsu

Proceedings of International Symposium onFrontiers of Computational Science 2008, Kaneda, Sasai, Tachibana (Eds), CD-ROM 頁： 173-180 2008年11月

Wavelet-Based Statistics of Energy Transfer in High Reynolds Number Three-Dimensional Homogeneous Isotropic Turbulence 査読有り

N. Okamoto and K. Yoshimatsu

IUTAM Symposium on Computational Physics and New Perspectives in Turbulence 頁： 155-160 2008年11月

担当区分：筆頭著者記述言語：英語

We examine small-scale statistics of energy transfer from a scale within grid
scales to subgrid scales localized in space and scale in high Reynolds number
fully developed turbulence. An orthonormal wavelet decomposition method
is applied to data of three-dimensional incompressible homogeneous isotropic
turbulence with Taylor microscale Reynolds number 471. We find that the
energy transfer and the kinetic energy localized in space and scale have strong
correlation in the inertial subrange though they are almost uncorrelated in the
dissipation range. The correlation is enhanced by the positive values for the
transfer, while it is reduced by the negative values for the transfer.

高レイノルズ数一様等方性乱流における秩序渦：ウェーブレットの視点から

岡本直也,芳松克則, Kai Schneider, M. Farge, 金田行雄

数理解析研究所考究録 1608 「オイラー方程式250年：連続体力学におけるオイラーの遺産」 1608 巻頁： 151-158 2008年7月

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