Magnetoelastic disturbances in a perfectly conducting cylindrical shell in a constant magnetic field

Summary The paper deals with the problem of determining the displacements, stresses, magnetic and the electric fields of an infinite shell placed in vacuum and subjected to an impulsive excitation load.     

Magneto-elastic shear waves in a conducting,infinite plate in vacuum

Summary The influence of an external magnetic field on the propagation of purely transverse waves polarized parallel to the plane faces in a homogeneous, initially unstressed, infinitely conducting, elastic flat plate extending to infinity has been investigated. We have found that such waves can be propagated only if the field is normal to the direction of polarization.The effects are of three fold depending on the inclination of the field to the direction of propagation. When the field is normal, it is to decrease the range of modes in which a disturbance of given frequency can be propagated; when parallel, it is to increase the velocity of each mode without decreasing the range of modes of propagation. In both these cases, the different modes can be classified into symmetric and anti-symmetric modes. In the general case, not only the phase velocity and the range of modes are affected over those of purely elastic case but the symmetric and anti-symmetric types of motion are coupled in every mode.     

Propagation of magneto-elastic waves in a perfectly conducting plate extending to infinity in vacuum

Summary The effects of a uniform external magnetic field on the propagation of waves in a homogeneous, infinitely conducting flat plate with free boundaries have been studied. It has been found that in general all the three types of waves —P, SV andSH waves—are coupled and the influence may be more pronounced in coupling the symmetric and antisymmetric types of motions in every mode.When the magnetic field is parallel to the plane faces and transverse to the direction of wave propagation, the shear wave polarized parallel to the field is purely elastic whereas the coupledP andS V waves are magnetoelastic and exhibit dispersion strikingly similar to the non-magnetic case, provided the electro-magnetic radiation into the surrounding free space is neglected.The results reported in an earlier communication [1]²) are also confirmed.     

Free convection along a non-uniformly heated vertical plate with a variable transverse magnetic field

Summary In this article, we have solved the problem of natural convection along a vertical plate with variable temperature and a transverse non-uniform magnetic field. It also represents a unified analysis of the works of other including the present author, on natural convection with or without transverse magnetic field, and with uniform or non-uniform plate temperature.The author is indebted to Prof.K. B. Ranger, Department of Mathematics, for his continuous and active interest in my research work. I am also grateful to him for offering me a fellowship from his N.R.C. (Canada) research fund.     

Electromagnetic scattering by a perfectly conducting half-plane in a conductive half-space

FollowingDmitriev (1960) a rigorous theoretical solution for the problem of scattering by a perfectly conducting inclined half-plane buried in a uniform conductive half-space has been obtained for plane wave excitation. The resultant integral equation for the Laplace transform of scattering current in the half-plane is solved numerically by the method of successive approximation. The scattered fields at the surface of the half-space are found by integrating the half-space Green's function over the transform of the scattering current.The effects of depth of burial and inclination, of the half-plane on the scattered fields are studied in detail. An increase in the depth of burial leads to attenuation of the fields. Inclination introduces asymmetry in the field profiles beside affecting its magnitude. Depth of exploration is greater for quadrature component. An interpretation scheme based on a phasor diagram is presented for the VLF-EM method of exploration for rich vein deposits in a conductive terrain.List of symbols x, y, z Space co-ordinates - Half-space conductivity - ₀ Free-space permeability - Excitation frequency (angular) - T Time - h Depth of the half-plane - a Inclination of the half-plane - E _x x-Directed total electric field - E _x ^p x-Directed primary electric field - E _xo ^p x-Directed primary electric field atz=0 directly over the half-plane - H _y y-Component of total magnetic field - H _y ^p y-Component of primary magnetic field - H _y0 ^p y-Component of primary magnetic field atz=0 directly over the half-plane - H _z z-Component of total magnetic field - H _z ^p z-Component of primary magnetic field - J _x Surface density ofx-directed scattering current - G Green's function - k ₀,K Wave numbers - u,u ₀,u ₁,u ₂ Functions - Space co-ordinate - s Variable in transform domain - Variable of integration - Normalized scattering current - Laplace transform of - N Normalized - , ₀, ₁, ₂ Functions - t Variable of integration - Skin depth - H Total magnetic field - H ^p Primary magnetic field - H ₀ ^p Primary magnetic field atz=0 directly over the half-plane - M,Q,R,S,U,V Functions - N ₁,N ₂ Functions     

Propagation ofSH waves in an infinite elastic plate with Cauchy's initial transverse stress

Summary Cauchy theory of initial stress has been applied to investigate the problem of SH waves in an initialy stressed elastic plate. The initial stress is assumed to be a uniform tension or compression along the thickness of the plate. It is found that the initial stress influences the velocities of the dispersive modes only but, it has no influence on the velocity of the non-dispersive wave.     

On disturbances in a semi-infinite medium traversed by a transverse magnetic field

Summary The method of operational calculus has been used to deal with the disturbances in an elastic medium traversed by a magnetic field.     

On the propagation of a reflected radiative shock in a transverse magnetic field

Summary The paper considers a shock wave to be reflected from a wall in the presence of a transverse magnetic field when the radiation pressure and radiation energy are taken into account. It has been shown that under certain physical conditions, the velocity of the reflected radiative shock would be greater than the corresponding velocity when the magnetic field and radiation effects are neglected.     

On the propagation of disturbances in a composite viscoelastic layer in a magnetic field

Summary The propagation of disturbances in a composite viscoelastic layer when subjected to an impulsive force in the presence of a primary magnetic field, has been investigated in this note. The mechanical displacement has been derived from the electro-magnetic equations of Maxwell, the equation of motion and the stress-strain relations of the materials considered and has been computed for small values of time.     

On longitudinal vibration of an elastic bar in a magnetic field

Summary The equations of elasticity, electromagnetic equations of Maxwell have been applied to investigate the longitudinal vibration of a partly homogenous, partly inhomogeneous elastic bar permeated by a magnetic field.     

On longitudinal disturbances in a viscoelastic solid of Reiss type placed in a magnetic field

Summary The propagation of longitudinal disturbances in a viscoelastic solid of Reiss type subjected to a magnetic field has been obtained in the present note.     

Deflection of an elastic plate on a viscoelastic foundation under the influence of a variable temperature field

Summary In this research the differential equation governing the deflection of an elastic plate on a viscoelastic foundation, where the foundation is under the influence of a variable temperature field, has been obtained. The relaxation moduli and creep compliances are considered to be temperature-dependent. The discussion has been illustrated with a particular case of a temperature field.     

On disturbances in an inhomogeneous viscoelastic bar of Reiss type in a magnetic field

Summary This paper deals with the study of the disturbances in an inhomogeneous semi-infinite viscoelastic bar of Reiss type acted upon by an impulsive force at its finite end, under the influence of a primary static magnetic field.     

On disturbances in a viscoelastic solid rod of Burger's type subjected to a magnetic field

Summary The propagation of disturbances in a semi-infinite visco-elastic rod of Burger's type has been investigated, when the rod is subjected to an initially static magnetic field, making use of the electro-magnetic equations of Maxwell, equations of elasticity and the stress-strain relations of the material.     

Radial vibration of a composite cylindrical shell subjected to a magnetic field

Summary The radial vibration in a composite cylindrical shell under the effect of a magnetic field has been investigated by solving the equations of elasticity, taking into account electromagnetic equations of Maxwell. The frequency equation has been obtained at the final stage.     

Induced currents in a conducting sphere placed in the field of an oscillating magnetic dipole

Summary Expressions are obtained for the currents induced inside a conducting sphere placed in the field of an oscillating magnetic dipole. Interesting conclusions can be drawn from an analysis of the formulas for the current induced due to different orientations of the dipole.     

瞬变电磁横磁场响应特征与探测能力分析

瞬变电磁法是重建地下电阻率等电性结构的重要方法.传统磁性源和电性源瞬变电磁法主要观测横电极化场,横电极化场仅对良导目标敏感,对高阻目标的分辨能力有限.横磁极化场对高阻目标具有较强的分辨能力,但未得到有效利用.双线源瞬变电磁法可以增强观测电场中横磁极化场的占比,但对该方法的响应特征和分辨能力缺乏系统性的研究.为此,本文以双线源为例开展瞬变电磁横磁场响应特征与分辨能力分析.双线源瞬变电磁水平电场的响应强度要小于传统接地导线源,在发射源的中垂线上,层状大地模型的响应为零,观测的水平电场响应只能由地下的三维目标体产生.分别提取双线源和传统接地导线源激发电磁场中的横磁场和横电场,双线源瞬变电磁场中的横磁场占比要大于传统接地导线源,特别是在中晚期,横磁场远大于横电场,横磁场占比得到明显增强.通过均方根差和三维数值模拟的计算,双线源瞬变电磁水平电场显示出相较于传统接地导线源更强的高阻目标分辨能力,特别是在赤道向,水平电场对高阻目标分辨能力的增强效果更加明显.

     

Longitudinal vibration of a slender bar with nonuniform characteristics in presence of a magnetic field

Summary In the present article the magnetic influence on the free vibrations of a slender bar with characteristics slightly different from those of a uniform one has been discussed. It presents a simple approximate solution to this problem. Moreover the frequency equation has been derived.