共查询到20条相似文献,搜索用时 15 毫秒
1.
O. V. Soloviev 《Radiophysics and Quantum Electronics》2000,43(7):557-568
This paper presents a further development of the numerical-analytical method for the solution of three-dimensional problems
in the theory of radio wave propagation. We consider a vector problem of the electromagnetic field of a vertical electric
dipole in a plane Earth-ionosphere waveguide with a local large-scale irregularity on the anisotropic ionosphere wall. The
possibility of lowering (elevating) of the local region of the upper waveguide wall with respect to the regular ionosphere
level is taken into account. The field components on the boundary surfaces obey the Leontovich impedance conditions. The problem
is reduced to a system of two-dimensional integral equations taking into account the overexcitation and depolarization of
the field scattered by the irregularity. Using asymptotic (with respect to the parameter kr ≫1) integration along the direction
perpendicular to the ray path, we transform this system to a system of one-dimensional integral equations. The system is solved
numerically in the diagonal approximation, combining direct inversion of the Volterra integral operator and the subsequent
iterations. The proposed method reduces the computer time required for solving the problem and is useful for the study of
both small-scale and large-scale irregularities. We obtained estimates of the TE field components that are not excited by
the source considered and originate entirely from field scattering by a three-dimensional irregularity disturbing the geometric
regularity of the ionospheric waveguide wall.
State University of St. Petersburg, Russia Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No.
7, pp. 617–629, July, 2000. 相似文献
2.
O. V. Soloviev 《Radiophysics and Quantum Electronics》1998,41(5):392-402
In this paper, we develop further the analytical and numerical method of solving three-dimensional problems in the theory
of radio wave propagation, including three-dimensional local inhomogeneities (ionospheric disturbances or Earth’s surface
irregularities). To model the Earth-ionosphere waveguide, we use the surface impedance concept, by which the irregularity
extending beyond one waveguide wall has an arbitrary smooth shape, and its surface can be described by the impedance. In the
scalar approximation, this problem is reduced to a two-dimensional integral equation for the irregularity surface, which,
by asymptotic (kr ≫ 1) integration over the coordinate transverse to the propagation path (with allowance for terms of the
order of (kr)−1), is reduced to a one-dimensional integral equation, in which the integration contour is the linear contour of the irregularity.
The equation is solved numerically, combining the inversion of a Volterra integral operator and successive approximations.
By reducing the computer times, this method enables one to study both small-scale and large-scale irregularities. The results
of numerical simulation of radio wave propagation in the presence of a powerful three-dimensional ionospheric disturbance
are presented as an example.
State University, St. Petersburg, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No.
5, pp. 588–604, May, 1998. 相似文献
3.
O. V. Solov'yev 《Radiophysics and Quantum Electronics》1995,38(8):520-530
The vector 3-D problem of a point-source field in a plane waveguide with a large-scale local inhomogeneity on one of its walls is considered. The field components on the boundary surfaces comply with the Leontovich conditions, which are used as a basis for obtaining expressions for the derivatives of the field vectors normal to the boundaries; these expressions reflect the 3-D nature of the inhomogeneity. The problem is reduced to a system of 2-D integral equations allowing for overexcitation and depolarization of the field scattered by the irregularity. The system of 2-D integral equations is asymptotically transformed over the inhomogeneity region on the surface of the walls bounding the waveguide space into a system of linear integral equations, for which the integration contour is represented by the line between the source and observation point, as well as by the linear geometric contour of the irregularity.State University, St. Petersburg. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 8, pp. 785–803, August, 1995. 相似文献
4.
We study the effect of striction plasma density disturbances on the generation intensity of longitudional cold and plasma
oscillations due to polarization of the magnetic field-aligned ionospheric plasma irregularities with δNo<0 by a powerful radio wave. It is assumed that the plasma density level inside the irregularity intersects the upper-hybrid
resonance level, in the vicinity of which the cold oscillations excited directly by a powerful radio wave are transformed
to shorter-wave plasma oscillations. We consider the short plasma wave limit to reduce the problem to a system of two coupled
equations for the cold wave induction and plasma wave electric field. The first equation is supplemented by a local source
equal to the integral of the plasma wave electric field in the resonance region. The second equation involves the cold wave
induction at the resonance point and describes the electric field of interacting waves in the resonance vicinity. We use simplifications
connected with the small absorption of plasma waves propagating inside the irregularity and weak radiation of these waves
outside the irregularity. These conditions correspond to the generation of eigenmodes of plasma oscillations trapped in the
irregularity. We have obtained a resonance-type nonlinear equation for the electric field intensity (or energy flux) of eigenmode
plasma waves with allowance for striction disturbances of the plasma density profile in the resonance region. It is shown
that the striction expulsion of plasma is responsible for the occurrence of coefficients describing the change in the intensity
of excitation and radiation of plasma waves at the irregularity boundary. Such an expulsion leads to variations of the efficient
generation band of plasma eigenmodes with the total phase increment of the wave in the irregularity. It also leads to a change
in the phase shift of the plasma wave reflected from the resonance. These coefficients and the nonlinear phase shift are expressed
in terms of real wave functions of the nonlinear Airy equation which describes the electric field of the excited waves in
the resonance vicinity when the dissipation is absent.
Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences, Troitsk, Moscow region,
Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 3, pp. 270–297, March, 1998. 相似文献
5.
O. V. Solov'ev 《Radiophysics and Quantum Electronics》1992,35(6-7):368-373
The author investigates effect on the field of a point source in a plane impedance waveguide of an irregularity in the form of spherical surface that projects from (or is embedded into) the plane of the, ionospheric wall of the waveguide. In a scalar approximation, the problem is reduced to a two-dimensional integral equation over the surface of the irregularity. A solution is constructed by successive approximations, for which the solution of the problem for a regular impedance waveguide is used as the initial approximation. Numerical results are given for estimation of the effect of a local ionospheric irregularity on the field of an electric dipole in the earth-ionosphere waveguide.St. Petersburg State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 6/7, pp. 569–578, June–July, 1992. 相似文献
6.
We analyze the spectra of the phase and amplitude fluctuations of radio signals recorded in the course of four ionospheric
radio-sounding sessions at altitudes from 70 to 120 km. Our study is aimed at determining the sources of these fluctuations.
Comparing the statistical properties of fluctuations measured at two wavelengths with theoretical calculations, we conclude
that only the low-frequency part of background fluctuations is of ionospheric origin, while the high-frequency fluctuations
are caused by noise of the measuring system. The amplitude fluctuations are more informative in the high-frequency region,
since they are mainly due to ionospheric irregularities.
We discuss the possibility of separation of the components of amplitude fluctuations caused by ionospheric irregularities
and the irregularities of the neutral atmosphere in the case of sounding at the altitudes at which those components have comparable
values. It is shown that this problem cannot be solved by dispersion and extrapolation methods, which are used for separation
of the regular ionospheric and atmospheric components of the amplitude and phase variations of radio signals.
A. N. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Moscow, Russia. Translated from Izvestiya Vysshikh
Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 6, pp. 511–523, June 1999. 相似文献
7.
We apply the mixed integral representation for a two-point propagator to describe propagation of waves in a randomly irregular
medium with background refraction. Combining the ideas of the Maslowe technique and the interference-integral technique, we
obtain results that generalize the technique of smooth perturbations for a smoothly inhomogeneous background. Moreover, the
proposed approach, which describes both weak and strong fluctuations, accords with the phase screen technique and generalizes
it to the case of extended media with regularly inhomogeneous background. Using the proposed method, we perform numerical
simulations of the average intensity and scintillation index near the shadow-zone boundary for oblique ionospheric propagation
of VHF radio waves.
Research Institute of Applied PHysics, Irkutsk University, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii,
Radiofizika, Vol. 43, No. 1, pp. 17–27, January 2000. 相似文献
8.
Theory for the calculation of the force characteristics of an electromagnetic suspension of a superconducting body 总被引:1,自引:0,他引:1
Yu. M. Urman 《Technical Physics》1997,42(1):1-6
A theory based on the method of secondary sources is developed for the calculation of the magnetic field and the force characteristics
of electromagnetic suspension. This method leads to a system of Fredholm vector integral equations of the second kind in the
density of the secondary sources, whose solution gives the surface currents in the superconducting bodies and then by a simple
integration, the magnetic field and the force characteristics of the suspension. It is shown how the problem can be reformulated
to apply it to the determination of the scalar secondary sources (magnetic charges), leading to integral equations of lower
dimension. Examples are given for the calculation of scalar secondary sources for a superconducting half-space and a cylinder.
Zh. Tekh. Fiz. 67, 3–9 (January 1997) 相似文献
9.
D. Habault 《Journal of sound and vibration》1985,100(1):55-67
A boundary integral equation method is used to compute the sound pressure emitted by a harmonic source above an inhomogeneous plane. First, the theoretical aspects of the problem (behaviour of the pressure around the discontinuities,…) are studied. Then, a comparison between theoretical levels and experimental levels obtained in an anechoic room is presented. It shows that the boundary integral equation (BIE) method is quite convenient for solving this kind of problem. Two interesting results are pointed out: (i) if only a prediction of maximum sound levels is needed, the attenuation is the same for a cylindrical source, a spherical source and N spherical sources, and so it is possible to transform some three-dimensional problems into two-dimensional ones; (ii) a numerical method of computation of the sound field above an inhomogeneous plane does not provide a correct prediction if each part of the plane is not accurately described by the boundary condition chosen. 相似文献
10.
Urs M. Schaudt 《Communications in Mathematical Physics》1998,190(3):509-540
In suitable coordinates Einstein's field equations for a rigidly rotating perfect fluid in equilibrium can be written as a
semilinear system of purely elliptic partial differential equations of second order. Therefore, the formulation of a boundary
value problem is appropriate in this situation. It is shown that the Dirichlet problem for the vacuum region outside a ball,
and for a ball inside the matter region, has a unique regular solution if the boundary data are in a characteristic way limited
by the “diameter” of the ball. This restriction seems to be closely connected with stability limits for rotating stars. Furthermore,
the used mathematical methods are directly related to a numerical solution technique for such physical systems.
Received: 30 November 1995/ Accepted: 15 April 1997 相似文献
11.
Using the method of parabolic equation (MPE), we obtain transfer equations for the mean field, the space-coherence function,
and the ray intensity of a radiowave beam as it is reflected from a plasma layer with random inhomogeneities. The general
solutions of these equations are found. Special attention is given to the case of radiowave beam reflection from a linear
plasma layer with large-scale electron-density inhomogeneities. If a weakly directed transceiving SW antenna is used, the
shortwave scattering can lead to a pronounced (of the order of 3 dB) decrease in the intensity of a vertical-sounding signal
reflected from the ionospheric F2 layer only under the conditions of abnormally strong ionospheric electron-density perturbations.
Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika,
Vol. 41, No. 8, pp. 955–965, August, 1998. 相似文献
12.
V. A. Alimov L. M. Erukhimov E. N. Myasnikov A. V. Rakhlin 《Radiophysics and Quantum Electronics》1997,40(4):294-300
The problem of defining the spectral form of ionospheric irregularities with dimensions from hundreds to thousands of meters
is considered. A generalized model is proposed for the ionospheric turbulence spectrum, taking into account both the anisotropic
properties of the large-scale fraction of irregularities and the dependence of the anisotropy (elongation) of small-scale
irregularities of the upper ionosphere along the Earth magnetic field direction on the transverse scale of those irregularities.
Relations have been derived to determine the basic parameters of the irregularity spectrum of the uppers ionosphere (anisotropy
indices for large-scale and small-scale fractions) and the depth of a thin ionospheric layer through measurement of the spectral
characteristics of amplitude and phase fluctuations of orbital satellite signals. Using this model of the plasma irregularity
spectrum, we can explain consistently many well-known experimental data on spectral characteristics of the phase and amplitude
fluctuations of orbital satellite signals both in the high-latitude and midlatitude ionosphere.
Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika,
Vol. 40, No. 4, pp. 446–456, April, 1997. 相似文献
13.
In the paper we give a method for calculating the tractions (local forces) of the fluid motion determined by an incoming plane pressure wave on an artificial hair cell transducer structure. The sensing element of the transducer is a standing high aspect ratio cilium in the shape of a narrow thin curved beam (tape-like), which can be easily fabricated in micro-/nanotechnology. The method is based on considering the system of partial differential equations describing the motion of the compressible viscous fluid in an acoustic linearized approximation, and representation of the velocity field as a viscous acoustic single-layer potential. The boundary conditions, stating the cancellation of the velocity components on the solid beam, yield a two-dimensional (2-D) system of three integral equations over the beam's surface for the traction components. In the case of a narrow cilium, the system of integral equations furnishes a system of two 1-D integral equations over the symmetry curve of the structure for obtaining the tangential and normal components of the traction. This system is solved numerically by a finite (boundary) element method. The numerical code written for solving the problem was applied to some particular structures. The last structure is similar to the trichobothrium of a spider Cupiennius salei. The results obtained show that the curvature of the hair is enhancing sensitivity to flows directed normal to the main shaft of the hair confirming the assertion of Barth et al. [Philos. Trans. R. Soc. London, Ser. B 340, 445-461 (1993)]. 相似文献
14.
The existence of force-free magnetic fields in the exterior domain of some compact simply connected surface S is proved via an iteration scheme. The iteration starts with an arbitrary exterior vacuum field, which contains flux tubes
originating and ending on S. At one cross-section of such a flux tube with S an arbitrary function α is prescribed. For small values of α (in the H?lder-norm 1, λ; 0 < λ < 1) the iteration is shown
to converge to a force-free field with the prescribed values of α in a flux tube which is close to the vacuum flux tube and
α≡ 0 outside. The force-free field is close (in the H?lder- norm 1,λ) to the starting vacuum field, in particular, it has
the same field line topology, the same boundary values on S and satisfies the same decay conditions in spatial infinity. It is in general three-dimensional and requires no continuous
symmetries.
Received: 20 June 1999 / Accepted: 25 October 1999 相似文献
15.
研究了以近场声压重建任意边界条件的轴对称振动体表面声场的一类逆问题.提出了解决该类问题的能克服奇异积分的基于正交函数展开(OFE)与边界元积分(BEI)相结合的数值重建算法.通过对结构在对称或非对称振动下的表面声场的非共形数值重建的精度分析,提供了一种关于轴对称体表面场重建的工程化方法,数值结果也表明了该方法的有效性. 相似文献
16.
提出了一种基于边界元法求解变系数瞬态热传导问题的特征正交分解(POD)降阶方法,重组并推导出变系数瞬态热传导问题适合降阶的边界元离散积分方程,建立了变系数瞬态热传导问题边界元格式的POD降阶模型,并用常数边界条件下建立的瞬态热传导问题的POD降阶模态,对光滑时变边界条件瞬态热传导问题进行降阶分析.首先,对一个变系数瞬态热传导问题,建立其边界域积分方程,并将域积分转换成边界积分;其次,离散并重组积分方程,获得可用于降阶分析的矩阵形式的时间微分方程组;最后,用POD模态矩阵对该时间微分方程组进行降阶处理,建立降阶模型并对其求解.数值算例验证了本文方法的正确性和有效性.研究表明:1)常数边界条件下建立的低阶POD模态矩阵,能够用来准确预测复杂光滑时变边界条件下的温度场结果;2)低阶模型的建立,解决了边界元法中采用时间差分推进技术求解大型时间微分方程组时求解速度慢、算法稳定性差的问题. 相似文献
17.
D.W. Mueller Jr 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,92(4):457-477
The topic of this work is the generalized X- and Y-functions of multidimensional radiative transfer. The physical problem considered is spatially varying, collimated radiation incident on the upper boundary of an isotropically scattering, plane-parallel medium. An integral transform is used to reduce the three-dimensional transport equation to a one-dimensional form, and a modified Ambarzumian's method is used to derive coupled, integro-differential equations for the source functions at the boundaries of the medium. The resulting equations are said to be in double-integral form because the integration is over both angular variables. Numerical results are presented to illustrate the computational characteristics of the formulation. 相似文献
18.
S. N. Shul’ga 《Radiophysics and Quantum Electronics》1997,40(10):841-847
We have constructed a physicomathematical model of scattering of electromagnetic waves by a homogeneous object immersed in
a material halfspace, which allows for anisotropy of electromagnetic properties of the scatterer and surrounding medium. This
model is motivated by the need for remote sensing, nondestructive testing, and microwave devices and is based on the numerical
solution of a system of integral equations for the electric field components inside an inclusion using the method of moments.
We present numerical examples that illustrate wave scattering by an inhomogeneity in sea ice and polymer composite.
State University, Khar’kov, Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 10,
pp. 1249–1259, October, 1997. 相似文献
19.
A model of a shielded asymmetric two-slot transmission line is constructed on the basis of the method of almost total inversion
of the integral operator. In the case of symmetric location of the slots, the boundary-value problem for the given structure
is reduced to two independent systems of integral equations corresponding to different types of natural waves. The results
of numerical computation of the dispersion characteristics and distributions of tangential components of the electric field
intensity on the slots are given.
Povolzhskii Institute of Informatics and Communication, Samara; Institute of Radio Engineering and Electronics, Russian Academy
of Sciences, Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 4, pp. 507–518,
April, 1998. 相似文献
20.
P. Politi A. Torcini 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(3):401-404
We consider a class of unstable surface growth models,
?t z = -?x J\partial_t z = -\partial_x {\cal J}
,
developing a mound structure of size λ and displaying a
perpetual coarsening process, i.e. an endless increase in time of λ.
The coarsening exponents n,
defined by the growth law of the mound size λ with time,
λ∼tn, were previously found by numerical integration of the
growth equations [A. Torcini, P. Politi, Eur. Phys. J. B 25, 519 (2002)].
Recent analytical work
now allows to interpret such findings as finite time effective
exponents. The asymptotic exponents are shown to appear at so large
time that cannot be reached by direct integration of
the growth equations. The reason for the appearance of effective exponents
is clearly identified. 相似文献