共查询到20条相似文献，搜索用时 15 毫秒
1.
S. Basu Mallik 《Pure and Applied Geophysics》1969,76(1):87-91
Summary The problem of disturbances in a visco-elastic medium due to Maxwell in contact with a liquid medium — both being perfectly conductive — has been investigated when an impulsive force acts along the plane of the contact. The electro-magnetic equations of Maxwell, equation of elasticity and the stress-strain relations of the material have been used in the investigation. 相似文献
2.
Summary The present note makes use of electromagnetic equations of Maxwell and those of mechanical motions to work out the problem of disturbances in two perfectly conductive media—an ideal liquid and a perfectly elastic solid-acted upon by a magnetic field perpendicular to their plane of contact. The displacement suffered by solid medium has been determined when a tangential force, exponentially decaying with time, acts in the plane of contact of the two media. The solution of the problem is achieved by using the method of Laplace transform. 相似文献
3.
P. N. Singh 《Pure and Applied Geophysics》1972,94(1):60-65
Summary The present paper studies the mechanical response of a piezoelectric composite transducer—with an elastic compliance partly constant and partly variable with time—acted upon by suitable thermal field besides the electrical voltage. The Laplace transform has been applied to solve the problem. 相似文献
4.
Timothy J. Dunkerton 《Pure and Applied Geophysics》1989,130(2-3):243-262
The body force circulation problem of Eliassen is extended to spherical geometry and a quasi-compressible atmosphere using the zonally symmetric tidal theory. The concept of body force circulation is generalized to include the effects of mechanical friction and Newtonian cooling. This viewpoint is conceptually advantageous when the circulation is driven by body forces against radiative relaxation. The resulting linear theory is qualitatively useful in middle atmosphere applications, including the equatorial momentum source for which an analytic solution has not been given previously. Further generalizations of the theory are possible by including dynamical and photochemical feedback effects. 相似文献
5.
R. S. Sidhu 《Pure and Applied Geophysics》1971,85(1):125-139
Summary The wave equations of elasticity in the presence of body forces for a semi-infinite, isotropic, heterogeneous medium with exponentially varying material properties have been solved. Using double Fourier transform the equations are first transformed to linear second order differential equations. From the solution of these equations the displacements are obtained by the use of inversion theorem for double Fourier transform. The method followed resolves the disturbance into its constitutive parts—incident and reflectedP, SV andSH type waves. Surface displacements due to a single couple, double couple and various other sources have been calculated. 相似文献
6.
Richard Maaz 《Pure and Applied Geophysics》1964,58(1):23-40
Zusammenfassung —Als Modell eines mechanischen Empfängers, der im Boden eingebettet ist, dient eine Kugelschale mit lineartranslatorisch beweglichem Gehänge. Das umgebende Medium erfüllt homogen den Vollraum und ist isotrop elastisch. Der Kontakt mit dem eingebetteten System wird entweder als haftend oder gleitend vorausgesetzt. Es ist diskutiert worden, wie sich der Empfänger in einer longitudinalen Planwelle von beliebiger Wellenform bewegt, die sich parallel zur Gehängetranslation ausbreitet. Ferner wurde die (unbekannte) Wellenform aus der Seismogrammform oder der Gestellbewegung explizit berechnet. Es ergeben sich beachtliche mathematische und physikalische Vereinfachungen, wenn das Gehänge vernachlässigbar leicht und die Gestellmasse gleich der «verdrängten Mediummasse» ist. Schliesslich wird der Zusammenhang dieses Vorgangs mit der Empfängerbewegung infolge Kräften besprochen, die nicht von der Welle herrühren und am Gestell und Gehänge gleichzeitig angreifen können. Es wurde der Kraftverlauf gesucht, der einer vorgegebenen Wellenform hinsichtlich der erzwungenen Gestellbewegung (und des Seismogramms) gleichwertig ist, und umgekehrt die zu einer bestimmten Kraftfunktion äquivalente Wellenform angegeben.
Summary —An imbedded mechanical receiver of a seismograph may be represented by a spherical shell containing a linear oszillator. The surrounding medium is assumed to be homogeneous isotropic elastic throughout the whole space outside of the receiver. The soil may either adhere to or slide on the shell. The behaviour of the receiver under the influence of a longitudinal general shaped plane wave travelling in the oszillator direction is discussed. Furthermore the waveform corresponding to a known moving of the apparatus or a given seismogram is computed. There are noticeable mathematical and physical simplifications in the case of a negligible oszillator mass and a receiver mass equal to the displaced soil mass. Finally the connection of this problem with that of moving the receiver by forces not belonging to the wave is considered. The force function equivalent to a presumed waveform, yielding the same receiver moving, has been determined and the waveform equivalent to a given force, too.相似文献
7.
Arabinda Mukhopadhyay 《Pure and Applied Geophysics》1966,65(1):29-36
Summary The disturbances produced by time-dependent torsional body forces in a layer of elastic material lying on a rigid foundation have been discussed in this paper. Solutions have been obtained first for a general type of body force, and the solutions for an impulsive cylindrical source and an impulsive torsional line source of finite length have been deduced. It has been found that for any point in the layer, there is no disturbance up to a certain instant, after which there is a sudden displacement, which gradually falls off and tends to zero as the timet increases. 相似文献
8.
Abstract Exact solutions are obtained for a quasi-geostrophic baroclinic stability problem in which the rotational Froude number (inverse Burger number) is a linear function of the height. The primary motivation for this work was to investigate the effect of a radially-variable, dielectric body force, analogous to gravity, on baroclinic instability for the design of a spherical, synoptic-scale, atmospheric model experiment for a Spacelab flight. Such an experiment cannot be realized in a laboratory on the Earth's surface because the body force cannot be made strong enough to dominate terrestrial gravity. Flow in a rotating, rectilinear channel with a vertically variable body force and with no horizontal shear of the basic state is considered. The horizontal and vertical temperature gradients of the basic and reference states are taken as constants. Consequences of the body force variation and the other assumptions of the model are that the static stability (Brunt-Väisälä frequency squared) and the vertical shear of the basic state flow have the same functional form and that the transverse gradient of the potential vorticity of the basic state vanishes. The solutions show that the stability characteristics of the model are qualitatively similar to those of Eady's model. A short wavelength cutoff and a wavenumber of maximum growth rate are present. Further, the stability characteristics are quantitatively similar to Eady's results for parameters based on the vertically averaged Brunt-Väisälä: frequency. The solutions also show that the temperature amplitude distribution is particularly sensitive to the vertical variation of the static stability. For the static stability and shear decreasing (increasing) with height a relative enhancement of the temperature amplitude occurs at the lower (upper) surface. The other amplitudes and phases are only slightly influenced by the variation. The implication for the Spacelab experiment is that the variable body force will not significantly alter the dynamics from the constant gravity case. The solutions can be relevant to other geophysical fluid flows, including the atmosphere, ocean and annulus system in which the static stability undergoes variation with height. 相似文献
9.
Propagation of magneto-elastic waves in a perfectly conducting plate extending to infinity in vacuum
C. M. Purushothama 《Pure and Applied Geophysics》1965,61(1):60-68
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. 相似文献
10.
E. Roget J. Colomer X. Casamitjana J. E. Llebot 《Aquatic Sciences - Research Across Boundaries》1993,55(3):206-227
Because of the difference in morphometry and in the underground heating of the two lobes of Lake Banyoles there is a differential cooling that causes a density current — the denser water of the shallower lobe plunging into the deepest lobe forming a bottom current — which redistributes water between the lobes and replaces that of the northern lobe about every 5 days. This current has been studied during the mixing periods of the years 1989–1991 from temperature and current measurements and it has been found that it increases or slows down depending on the direction of the wind. Furthermore, it is observed that it mainly flows along the west shore of the lake, deflecting towards the right as an effect of the bottom morphometry. However, due to the long time scale of the density current the influence of the earth's rotation should not be neglected in advance. Finally, a simple numerical model has been used to corroborate the magnitude of this current — whose velocity has been directly measured — which is found to be the most important in the lake during the mixing period and so, it dominates the lake-wide circulation 相似文献
11.
A general methodology is outlined for a complete seismic soil—pile-foundation—structure interaction analysis. A Beam-on-Dynamic-Winkler-Foundation (BDWF) simplified model and a Green's-function-based rigorous method are utilized in determining the dynamic response of single piles and pile groups. The simplified model is validated through comparisons with the rigorous method. A comprehensive parameter study is then performed on the effect of pile group configuration on the dynamic impedances of pile foundations. Insight is gained into the nature of dynamic pile—soil—pile interaction. The results presented herein may be used in practice as a guide in obtaining the dynamic stiffness and damping of foundations with a large number of piles. 相似文献
12.
Expansion of a Plane Wave into Gaussian Beams 总被引：6，自引：0，他引：6
Magnetic susceptibility measurements on topsoils have often been used during the last few years to detect anthropogenic pollution. In most cases, a Bartington susceptibility meter for field measurements was used. However, up to now, no standard procedure has been developed for carrying out such investigations. The purpose of our study was to test the compatibility of different set-ups of instruments used for this purpose and the possible influences of subjective (human) factors. Field magnetic susceptibility measurements, carried out with four different Bartington MS2D instruments in strictly defined positions, are very consistent both for low and high values. The correlation coefficient between the magnetic susceptibility values recorded with different Bartington MS2D probes reached 97–98%. A test area was mapped independently by two groups, without any restrictions concerning the choice and distribution of the measured points, but respecting a few standard conditions (e.g., measuring at a distance from tree trunks; on the flattest place possible; recording between 10–30 values per point). The resulting susceptibility maps show the same general features in both cases, suggesting that the measuring strategy applied is suitable for topsoil magnetic screening. The methodology proposed can be used to map magnetic susceptibility on a larger scale—for example Europe—providing large sets of representative data and eliminating border-transition biases and human errors. 相似文献
13.
The problem of migration of a hydrocarbon liquid through aeration zone to groundwater table is formulated and solved analytically. The aeration zone is represented by fractured–porous rocks, and the pollution source is a shallow pool that has formed due to a spill. Two schemes of liquid infiltration from fractures into rock blocks—piston-like and kinetic—are considered. The trajectory of pollution front in fractures and its distribution in the rock blocks are found. 相似文献
14.
Fred Ward 《Pure and Applied Geophysics》1966,63(1):196-204
Summary The longitudinal proper motion of sunspot groups has been shown to be a function of their size and relative extension in longitude. Two theories are proposed to explain these effects, which theories assume that the wind circulation of the spots and the wind field surrounding the spots are intimately connected, and dynamically interact. The retardation in the motion of large spot groups is hypothesized to be due to the effect of the latitudinal variation of the Coriolis parameter (on a rotating spherical body) and an assumed vortical circulation around the spots. The more rapid longitudinal motion of extended spot groups is suggested to be the result of the preferential occurrence and development of such groups in regions of above-average horizontal wind and wind shear. If these theories are essentially correct, the real solar rotation rate—i.e., the longitude- and time-averaged fluid motion field—should be derived from the motions of small spot groups, and is 1% to 11/2% higher than the usually accepted rate whichNewton andNunn derived. 相似文献
15.
Summary The paper is dealing with the separation problem of weak intensity anomalies from the perturbation background. By means of the Shannon's form and based on the values estabilished for a measured gravitational field, g, the mean quantity of information sent forth at the source — perturbating body — is calculated in order to intercept the g set. This quantity takes a maximum value above the perturbating body, while for the remainder a deadening of the perturbations is obtained. 相似文献
16.
Summary Elastic wave propagation problem has been studied in the composite medium — a gravitating liquid layer overlying an elastic half-space. Assuming moving normal pressure load on the free surface, an attempt has been made to study the order of disturbance on the earth's surface. In the discussion asymptotic values of the displacement, components have been considered for small values of the parameter. 相似文献
17.
Arabinda Mukhopadhyay 《Pure and Applied Geophysics》1967,67(1):43-53
Summary The disturbances produced in a semi-infinite visco-elastic medium and in a layer of visco-elastic material resting on a rigid foundation by transient torsional body forces have been considered. Formal solutions have been obtained for a general type of body force, and this solution has been used to obtain the displacements for a transient torsional point source in the case of a semiinfinite medium, and for a cylindrical source of finite dimensions and a line source in the case of the layer of visco-elastic material mentioned above. Solutions have also been obtained for a transient shearing stress applied at the free surface of the layer mentioned above. 相似文献
18.
The Rainier Mesa ash-flow is a large (1200 km3), 11.6 My old, chemically zoned unit that ranges in composition from 55 to 76% SiO2 — one of the largest chemical ranges ever observed in a large volume ash-flow sheet. Two chemical trends occur in this sheet, a low silica (55–66% SiO2) and a high silica (>66% SiO2) trend. Ninety per cent of the Rainier Mesa sheet occurs in the high silica trend. Immediately beneath the Rainier Mesa sheet is a thick tephra sequence. The chemical variation of this sequence is nearly equivalent to the high silica portion of the Rainier Mesa ash-flow sheet (about 66–78% SiO2). Throughout the tephra sequence numerous small ash-flow layers occur, and each ash-flow layer is chemically zoned from more evolved at the base to less evolved at the top. This is consistent with having been erupted from a zoned magma body. The lowest silica tephra units are at the base of the sequence and the highest silica units are at the top — that is, the large-scale chemical trend of the entire sequence is opposite to that of the individual ash-flow layers. These ash-flow layers are of very small volume. The tephra sequence provides a unique record of the incremental development of the zoned, high silica portion of the Rainier Mesa magma body. 相似文献
19.
We invert 2D surface gravity data constrained both by geological and seismic information. We use a number of pre-processing tools in order to reduce the general multi-body inversion into several single-body inversions, whereby we can reduce the overall complexity of the inversion task. This is done with as few assumptions as possible. Furthermore, for a single-body inversion we uncouple the determination of the shape of the causative sources from the determination of their mass density contrast to the surroundings. The inversion for the geometrical shape of the source body is done in steps. Firstly, a rough 3D shape of the source is modelled—a model consisting of the vertical mass columns of equal height. The horizontal extension is implied by the surface gravity signal. Subsequently, the shape of each source body is modified to obtain a better fit to the surface gravity data. In each modification step, the overall change of the shape of the source body is followed by an update of the mass density contrast to the surroundings. The technique was applied to a set of gravity data from the Eastern Goldfield area in Western Australia. The area has been widely studied in the past. In 1999, two seismic profiles that cross-sect the area were measured. Furthermore, an extensive geological modelling for the area has been conducted. The practical goal of this work was to verify the geological interpretation using the potential field data (mainly the gravity data although magnetic data were also available) and only weakly constrained by the seismic information. The result was the reconstruction of the ‘rough’ 3D geometry of the source bodies and the estimation of a constant mass density contrast to the surroundings. A possible extension of this technique for detailed studies of the geological model is briefly discussed. 相似文献
20.
Summary Three dimensional magneto-elastic equations pertaining to the problem of propagation of axial Rayleigh waves on the surface of elastic cylinder of isotropic material have been solved. Two cases have been considered — first, when the density varies linearly and second, when it varies inversely as the radius vector and frequency equations for both the cases have been obtained. 相似文献