带铁磁薄膜悬臂板的磁场微感应器磁弹性特征研究

对于在可变形非磁材料悬臂梁式板单表面粘贴可磁化材料薄膜所构成的磁场微传感器件结构,研究了其处在磁场环境中的磁弹性弯曲变形的磁场-力学特征.为此,建立了由有限元方法分析磁场与有限差分法计算挠曲变形相结合来计算其结构在磁场中产生磁弹性变形的定量分析程序.在此基础上,对于这一微传感结构的算例给出了其结构变形随外加磁场环境变化的磁场-挠度特征关系等定量结果.结果表明:微传感器件不仅可以测量出磁场的大小,而且给出了测量磁场矢量方向的可能性.     

Effect of a rotating magnetic field on convection in a horizontal fluid layer

The stability of mechanical equilibrium of a horizontal layer of conducting fluid in the presence of a magnetic field rotating in a horizontal plane is considered. Both finite field rotation frequencies and the limiting case of high frequencies are investigated. It is shown that the magnetic field stabilizes the equilibrium. The dependence of the critical perturbation wavelength on the field strength is non-monotonic, and with increase in the magnetic field strength the mode of most dangerous perturbations changes from long-to short-wave type. Nonlinear three-dimensional convection regimes are calculated numerically. It is found that at finite supercriticalities and a sufficiently strong magnetic field the rolls and the hexagonal cells may be stable simultaneously.     

Two-fluid magnetohydrodynamic model of plasma flows in a quasi-steady-state accelerator with a longitudinal magnetic field

This paper reports the results of numerical studies of axisymmetric flows in a coaxial plasma accelerator in the presence of a longitudinal magnetic field. The calculations were performed using a two-dimensional two-fluid magnetohydrodynamic model taking into account the Hall effect and the conductivity tensor of the medium. The numerical experiments confirmed the main features of the plasmadynamic processes found previously using analytical and one-fluid models and made it possible to study plasma flows near the electrodes. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 3, pp. 44–55, May–June, 2009.     

An analysis on three-dimensional effects near the tip of a crack in an elastic plate

An infinite plate containing a finite through crack under tensile loading is analysed by Fourier transform based on the Kane-Mindlin kinematic assumptions for the quasi-three-dimensional deformation of plates in extension. The asymptotic expressions of stress and displacement fields near the crack tip, the variation of the stress intensity factor with the plate-thickness and the three-dimensional deformation zone near the crack tip are investigated. The results of the analysis show that, (a) the crack-tip stress and displacement fields accounting for the plate-thickness effects are different from the plane stress solutions and this is true even for extremely small parameter (=1–vh/6 a). In a very small region near the crack tip, plane strain solutions prevail; (b) the ratio of the stress intensity factor K_I to the corresponding plane stress one K_I, K_I/K _I ^o , approaches 1/(1–v²) as tends to zero; (c) plane stress solutions can give satisfactory results for points a distance from the crack tip greater than about three-fourths of the plate-thickness; (d) the linear elastic result for the zone of three-dimensional effects is approximately valid for an elasto-plastic material with linear strain-hardening when the plastic tangential mudulus E_t is not very small.The Project Supported by National Natural Science Foundation of China.     

Torsional vibration of functionally graded nano-rod under magnetic field supported by a generalized torsional foundation based on nonlocal elasticity theory

Abstract

This article contains the nonlocal elasticity theory to capture size effects in functionally graded (FG) nano-rod under magnetic field supported by a torsional foundation. Torque effect of an axial magnetic field on an FG nano-rod has been defined using Maxwell’s relation. The material properties were assumed to vary according to the power law in radial direction. The Navier equation and boundary conditions of the size-dependent FG nano-rod were derived by the Hamilton’s principle. These equations were solved by employing the generalized differential quadrature method (GDQM). Presented model has the ability to turn into the classical model if the material length scale parameter is taken to be zero. The effects of some parameters, such as inhomogeneity constant, magnetic field and small-scale parameter, were studied. As an important result of this study can be stated that an FG nano-rod model based on the nonlocal elasticity theory behaves softer and has smaller natural frequency.