自动淘米式电饭煲设计与研究

设计了一种可定时、自动淘米的新型电饭煲,它是在普通电饭煲上加装电机、搅拌板和快速转换装置,此新型电饭煲可在STC12C5A60S2单片机及电磁阀控制下自动实现进水、淘米、煮饭、洗锅、排水等功能,且密封性良好。     

Alpha effect in helically forced turbulence

The effect on large-scale dynamics of small-scale helicity injection in three-dimensional resistive magnetohydrodynamic turbulence is investigated for a weak initial magnetic field. The magnetic configuration of α² dynamo prototype flows is such that, generally, the energy concentrates on one large-scale mode. However, we obtain that alpha effect is not limited to the dominant mode and that a non-local equation (in Fourier space) is more appropriate to describe it. It gives some insights into the non-local theory of Pouquet et al. [J. Fluid Mech. 77 (1976) 321] where the inverse cascade results from a competition between the helicity and Alfvén effects.     

CONTINUOUS DEPENDENCE ON VELOCITY FOR THE BACKWARD DYNAMO EQUATION ON AN EXTERIOR DOMAIN

In this paper we study solutions to a forward Dynamo equation depending continuously on the velocity on an exterior domain,using Logarithmic Convexity Methods.We obtain some more weaker conditions by introducing the unbounded domain.     

New approach to applying neural network in nonlinear dynamic model

In this work, radial basis function neural network (RBF-NN) is applied to emulate an extended Kalman filter (EKF) in a data assimilation scenario. The dynamical model studied here is based on the one-dimensional shallow water equation DYNAMO-1D. This code is simple when compared with an operational primitive equation models for numerical weather prediction. Although simple, the DYNAMO-1D is rich for representing some atmospheric motions, such as Rossby and gravity waves. It has been shown in the literature that the ability of the EKF to track nonlinear models depends on the frequency and accuracy of the observations and model errors. In some cases, just fourth-order moment EKF works well, but will be unwieldy when applied to high-dimensional state space. Artificial Neural Network (ANN) is an alternative solution for this computational complexity problem, once the ANN is trained offline with a high order Kalman filter, even though this Kalman filter has high computational cost (which is not a problem during ANN training phase). The results achieved in this work encourage us to apply this technique on operational model. However, it is not yet possible to assure convergence in high dimensional problems.     

Helicity

This short review is a contribution to an issue of Comptes Rendus Mécanique commemorating the scientific work of Jean-Jacques Moreau (1923–2014). His main contribution to fluid mechanics appeared in a brief paper in the Comptes Rendus à l'Académie des Sciences in 1961, but was not recognised till much later. It may now be seen as a significant milestone in advancing the theory of ideal fluid flow as described by Euler's equations.     

Energy fluxes in helical magnetohydrodynamics and dynamo action

Renormalized viscosity, renormalized resistivity, and various energy fluxes are calculated for helical magnetohydrodynamics using perturbative field theory. The calculation is of firstorder in perturbation. Kinetic and magnetic helicities do not affect the renormalized parameters, but they induce an inverse cascade of magnetic energy. The sources for the large-scale magnetic field have been shown to be (1) energy flux from large-scale velocity field to large-scale magnetic field arising due to non-helical interactions and (2) inverse energy flux of magnetic energy caused by helical interactions. Based on our flux results, a primitive model for galactic dynamo has been constructed. Our calculations yield dynamo time-scale for a typical galaxy to be of the order of 10⁸ years. Our field-theoretic calculations also reveal that the flux of magnetic helicity is backward, consistent with the earlier observations based on absolute equilibrium theory.     

Impact of nonlinearity on a homopolar oscillating-disc dynamo

A numerical method is developed to investigate the effect of the nonlinear factors on a homopolar oscillating-disc dynamo. Our results show that all the nonlinear factors of the oscillating-disc dynamo have no significant effect on the kinematic regime of the disc dynamo. But as the magnetic field grows larger, the nonlinear factors begin to take effect. The role of the nonlinear factor involving the cube of the magnetic flux is to make the dynamo magnetic flux tend to an oscillating solution with finite amplitude. For the case that the mean rotation rate vanishes the nonlinear factor involving the magnetic flux rate can only affect the manner of the magnetic flux tending to infinity; for another case that the disc rotation rate takes a strongly subcritical value, it may have two kinds of effects just mentioned above on the disc dynamo and its specific effect is dependent on the values of the amplitude and frequency of the oscillatory disc rotation rate.     

Effects of conductivity jumps in the envelope of a kinematic dynamo flowInfluence des discontinuités de conductivité dans l'enveloppe de l'écoulement d'une dynamo cinématique

This Note reports on numerical simulations of the kinematic dynamo action in a test flow modeling the Von Kármán Sodium (VKS) experiment performed at CEA-Cadarache. We show that the conductivity of the vessel greatly influences the critical magnetic Reynolds number. These effects are dramatically amplified as the ratio of the conductivity of the vessel to that of the sodium increases from 1 to 5. To cite this article: R. Laguerre et al., C. R. Mecanique 334 (2006).     

Homopolar oscillating-disc dynamo driven by parametric resonance

We use a simple model of Bullard-type disc dynamo, in which the disc rotation rate is subject to harmonic oscillations, to analyze the generation of magnetic field by the parametric resonance mechanism. The problem is governed by a damped Mathieu equation. The Floquet exponents, which define the magnetic field growth rates, are calculated depending on the amplitude and frequency of the oscillations. Firstly, we show that the dynamo can be excited at significantly subcritical disc rotation rate when the latter is subject to harmonic oscillations with a certain frequency. Secondly, at supercritical mean rotation rates, the dynamo can also be suppressed but only in narrow frequency bands and at sufficiently large oscillation amplitudes.