[en] In this analytical study, we are concerned about the influence of stresses produced due to a moving load on an elastic plate (which is not traveling with a moving load) under gravity lying over a semi-infinite water medium with hydrostatic stress. The elastic property of the plate is considered to be orthotropic. The water and elastic medium are bonded with an irregular interface. The type of irregularity is considered parabolic type. To discover the displacement field, the perturbation approach has been employed to solve the governing differential equations with variable coefficients. Due to moving load, closed-form normal and shear stresses are established for both elastic plate and semi-infinite water medium. The variation of non-dimensionalized shear and normal stresses with various parameters, such as gravitational coefficient, hydrostatic stress, and irregularity factor, is discussed through numerical computation and graphical demonstration. Moreover, some remarkable observations have been performed to study the influence of the frictional coefficient and depth factor on the shear and normal stresses of both mediums. Some particular cases also have been discussed for the validation of the problem. (author)

[en] Short communication

[en] Short communication

[en] The field-aligned anisotropy of the solar wind turbulence, which is quantified by the ratio of the parallel to the perpendicular correlation (and Taylor) length scales, is determined by simultaneous two-point correlation measurements during the time period 2001–2017. Our results show that the correlation scale along the magnetic field is the largest, and the correlation scale in the field-perpendicular directions is the smallest, at both solar maximum and solar minimum. However, the Taylor scale reveals inconsistent results for different stages of the solar cycles. During the years 2001–2004, the Taylor scales are slightly larger in the field-parallel directions, while during the years 2004–2017, the Taylor scales are larger in the field-perpendicular directions. The correlation coefficient between the sunspot number and the anisotropy ratio is employed to describe the effects of solar activity on the anisotropy of solar wind turbulence. The results show that the correlation coefficient regarding the Taylor scale anisotropy (0.65) is larger than that regarding the correlation scale anisotropy (0.43), which indicates that the Taylor scale anisotropy is more sensitive to the solar activity. The Taylor scale and the correlation scale are used to calculate the effective magnetic Reynolds number, which is found to be systematically larger in the field-parallel directions than in the field-perpendicular directions. The correlation coefficient between the sunspot number and the magnetic Reynolds number anisotropy ratio is −0.75. Our results will be meaningful for understanding the solar wind turbulence anisotropy and its long-term variability in the context of solar activity.

[en] This paper confines to the study of the flow of an electrically conducting incompressible viscous liquid due to the varying motion of an infinite nonconducting porous flat pjate in the presence of a transverse magnetic field under the following assumptions: (1) the fluid flows subject to uniform section, (2) the magnetic Reynold number is equai to the viscous Reynold number, (3) the plate moves in its own plane with the velocity of esup(at)tsup(n) (n is an integer and α > a), (4) the Alfven velocity is less than the suction velocity. The induced magnetic field produced by the motion is taken into account. General expressions of the velocity and skinfriction have been obtained when the plate moves with the velocity esup(at)tsup(n). Several particular cases have been studied. (authors)

[en] We consider the generation of magnetic activity—dynamo waves—in the astrophysical limit of very large magnetic Reynolds number. We consider kinematic dynamo action for a system consisting of helical flow and large-scale shear. We demonstrate that large-scale dynamo waves persist at high Rm if the helical flow is characterized by a narrow band of spatial scales and the shear is large enough. However, for a wide band of scales the dynamo becomes small scale with a further increase of Rm, with dynamo waves re-emerging only if the shear is then increased. We show that at high Rm, the key effect of the shear is to suppress small-scale dynamo action, allowing large-scale dynamo action to be observed. We conjecture that this supports a general 'suppression principle'—large-scale dynamo action can only be observed if there is a mechanism that suppresses the small-scale fluctuations.

[en] The ''Alfven paradox'' is that as resistivity decreases, the discrete eigenmodes do not converge to the generalized eigenmodes of the ideal Alfven continuum. To resolve the paradox, the ε-pseudospectrum of the resistive magnetohydrodynamic (RMHD) operator is considered. It is proven that for any ε, the ε-pseudospectrum contains the Alfven continuum for sufficiently small resistivity. Formal ε-pseudoeigenmodes are constructed using the formal Wentzel--Kramers--Brillouin--Jeffreys solutions, and it is shown that the entire stable half-annulus of complex frequencies with ρ|ω|²=|k·B(x)|² is resonant to order ε, i.e., belongs to the ε-pseudospectrum. The resistive eigenmodes are exponentially ill-conditioned as a basis and the condition number is proportional to exp(R^1/2_M), where R_M is the magnetic Reynolds number

[en] We report the observation of dynamo action in the von Karman sodium experiment, i.e., the generation of a magnetic field by a strongly turbulent swirling flow of liquid sodium. Both mean and fluctuating parts of the field are studied. The dynamo threshold corresponds to a magnetic Reynolds number R_m∼30. A mean magnetic field of the order of 40 G is observed 30% above threshold at the flow lateral boundary. The rms fluctuations are larger than the corresponding mean value for two of the components. The scaling of the mean square magnetic field is compared to a prediction previously made for high Reynolds number flows

[en] A local dynamic kinetic energy model (LDKM) for large-eddy simulation (LES) of magnetohydrodynamic (MHD) turbulence is proposed. The proposed MHD turbulence model evaluates all model coefficients locally and dynamically without any ad hoc averaging. This model also does not assume low magnetic Reynolds numbers. The turbulent residual-helicity effect (α-effect) appearing in the magnetic induction equation is successfully modeled. For validation, high-Re decaying isotropic decay turbulence with and without a mean magnetic field are studied using LES. The effect of rotation is also studied. For the case without rotation, it is observed that the energy spectrum follows a k^-5/3 law. For the case with rotation, it is shown that two mechanisms, phase scrambling due to frame rotation and Joule dissipation, are competing, and two distinct regimes with respect to rotation rate are observed. There is a critical rotation rate at which the energy decays most in MHD turbulence. It is also shown that this MHD-LDKM model is applicable to wide variety of high/low magnetic Reynolds number applications.

[en] Using steady-state resistive MHD, magnetic reconnection is reinvestigated for conditions of high resistivity/low magnetic Reynolds number, when the thickness of the diffusion region is no longer small compared to its length. Implicit expressions for the reconnection rate and other reconnection parameters are derived based on the requirements of mass, momentum, and energy conservation. These expressions are solved via simple iterative procedures. Implications specifically for low Reynolds number/high resistivity are being discussed.