arXiv subjects

Hideaki Miura

Publications and source records attributed to Hideaki Miura.

6 recordsLinked to original sources

arXiv2026

Anisotropy and intermittency in drift-wave turbulence with zonal flows: a two-dimensional continuous wavelet analysis

We examine anisotropy and spatial intermittency at small scales in drift-wave turbulence with zonal flows. We use a two-dimensional directional continuous wavelet transform, which allows simultaneous localization in scale, position, and direction. This wavelet analysis is applied to vorticity fields obtained from numerical simulations of the modified Hasegawa--Wakatani model, a reduced model of resistive drift-wave turbulence in magnetized plasmas with zonal flows. Directional wavelet statistics characterize the anisotropy of the turbulence. The second-order moment is enhanced around directions perpendicular to the zonal flow. Spatial intermittency, characterized by scale-dependent flatness, is more pronounced around directions along the zonal flow.

physics.plasm-ph↗

arXiv2026

Mutual Friction in Dissipative Gross-Pitaevskii Thermal Counterflow Turbulence

We report numerical simulations of the dissipative Gross-Pitaevskii equation for a bulk region of thermal-counterflow turbulence. Quasistationary states are obtained over a range of forcing, damping, and healing-length parameters. The mutual-friction acceleration exhibits cubic scaling with the mean relative velocity between the superfluid and normal-fluid components, and the coefficient of this scaling is linked to the phenomenological damping parameter. The intervortex spacing follows the expected dimensional scaling in the weak-forcing regime. Comparison with a straight-vortex-line model suggests that the vortex-line orientations are nearly isotropic.

cond-mat.other↗

arXiv2025

Uncovering the Varieties of Three-dimensional Hall-MHD Turbulence

We carry out extensive pseudospectral direct numerical simulations (DNSs) of decaying three-dimensional (3D) Hall magnetohydrodynamics (3D HMHD) plasma turbulence at three magnetic Prandtl numbers $Pr_{m}=0.1$, $1.0$ and $10.0$. Our DNSs have been designed to uncover the dependence of the statistical properties of 3D HMHD turbulence on $Pr_m$ and to bring out the subtle interplay between three lengths, the kinetic and magnetic dissipation length scales $η_u$, and $η_b$ and the ion-inertial scale $d_i$, below which we see the manifestations of the Hall term. This interplay, qualitatively apparent from isosurface plots of the moduli of the vorticity and the current density, is exposed clearly by the kinetic-energy and magnetic-energy spectra, $E_u(k)$ and $E_b(k)$, respectively. We find two different inertial regions, In the first inertial region $k k_{i}$, the scaling of $E_b(k)$ depends upon $Pr_M$: At $Pr_{m}=0.1$, the spectral-scaling exponent is $-17/3$, but for $Pr_{m}=1$ and $10$ this exponent is $-11/3$. We then show theoretically that $E_u(k) \sim k^2 E_b(k)$ for $Pr_m \ll 1$ and $E_b(k) \sim k^2 E_u(k)$ for $Pr_m \gg 1$; our DNS results are consistent with our theoretical predictions. We examine, furthermore, left- and right-polarised fluctuations of the fields that lead, respectively, to the dominance of ion-cyclotron or whistler waves.

physics.space-ph↗

arXiv2023

Quantum vortex identification method and its application to Gross-Pitaevskii simulation

A method to identify a quantum vortex in a three-dimensional Gross-Pitaevskii simulation has been developed. A quantum vortex was identified by the use of eigenvalues and eigenvectors of the Hessian of the mass density, together with a condition to distinguish a point to constitute a swirling vortex from other confusing data points. This method has been verified to identify vortex axes in a Gross-Pitaevskii simulation appropriately, being useful to elucidate various statistics associated with turbulent quantum vortices. This method provides us with a unified approach to studying vortex statistics in the turbulence of both classic and quantum fluids. Our study reveals that the maximum radius of a swirling region of a quantum vortex can be as large as sixty times the healing length. The characterization of the vortex core radius relative to the healing length is reported for the first time in this paper. Furthermore, the geometrical natures of vortex axes such as the probability density function of the curvature are characterized by the healing length.

physics.flu-dyn↗

arXiv2021

Statistical Properties of three-dimensional Hall Magnetohydrodynamics Turbulence

The three-dimensional (3D) Hall magnetohydrodynamics (HMHD) equations are often used to study turbulence in the solar wind. Some earlier studies have investigated the statistical properties of 3D HMHD turbulence by using simple shell models or pseudospectral direct numerical simulations (DNSs) of the 3D HMHD equations; these DNSs have been restricted to modest spatial resolutions and have covered a limited parameter range. To explore the dependence of 3D HMHD turbulence on the Reynolds number $Re$ and the ion-inertial scale $d_{i}$, we have carried out detailed pseudospectral DNSs of the 3D HMHD equations and their counterparts for 3D MHD ($d_{i} = 0$). We present several statistical properties of 3D HMHD turbulence, which we compare with 3D MHD turbulence by calculating (a) the temporal evolution of the energy-dissipation rates and the energy, (b) the wave-number dependence of fluid and magnetic spectra, (c) the probability distribution functions (PDFs) of the cosines of the angles between various pairs of vectors, such as the velocity and the magnetic field, and (d) various measures of the intermittency in 3D HMHD and 3D MHD turbulence.

physics.space-ph↗

arXiv2020

Sub-grid-scale model for studying Hall effects on macroscopic aspects of magnetohydrodynamic turbulence

A new sub-grid-scale model is developed for studying influences of the Hall term on macroscopic aspects of magnetohydrodynamic turbulence. Although the Hall term makes numerical simulations extremely expensive by exciting high-wave-number coefficients and makes magnetohydrodynamic equations stiff, studying macroscopic aspects of magnetohydrodynamic turbulence together with the Hall term is meaningful since this term often influences not only sub-ion-scales but also macroscopic scales. A new sub-ion-scale sub-grid-scale model for large eddy simulations of Hall magnetohydrodynamic turbulence is developed in order to overcome the difficulties. Large eddy simulations by the use of the new model successfully reproduce statistical natures such as the energies and probability density functions of the vorticity and current density, keeping some natures intrinsic to Hall magnetohydrodynamic turbulence. Our new sub-grid-scale model enables numerical simulations of homogeneous and isotropic Hall magnetohydrodynamic turbulence with a small computational cost, improving the essential resolution of an LES from that carried out with earlier models, and retaining the ion-electron separation effects by the Hall term in the grid scales.

physics.plasm-ph↗