阻抗劈绕射对破碎波后向散射特性的影响

海浪的破碎区会导致海面电磁散射特性发生很大改变,导致海尖峰现象的产生.本文结合阻抗劈结构模型分析了劈绕射对破碎波后向散射特性的影响.首先利用基尔霍夫近似求解破碎波的物理光学场;基于Maliuzhinets方法,从波动方程及精确阻抗边界条件出发,由谱函数的积分形式得到阻抗劈的一致性绕射系数,结合物理光学绕射系数导出阻抗劈等效边缘电磁流;利用边缘绕射场修正物理光学场,得到考虑劈绕射效应的破碎波散射总场.数值结果表明,阻抗劈的绕射场在Keller锥内出现HH极化大于VV极化的现象,因此计入绕射场的影响会使得破碎波生长到临近坍塌阶段时,小擦地角逆风观测出现总场的后向散射截面HH极化大于VV极化的现象,说明劈绕射是造成海尖峰现象产生的原因之一.     

Scattering of plane waves by a wedge with different face impedances

The scattering process of plane waves by a wedge with different face impedances is examined in terms of the closed form series solution. A new boundary condition is derived using the solution of the reflection problem of plane waves by an impedance plane. The series solution is obtained for the wedge problem. The results are investigated numerically.     

Scattering of waves by an aperture in an impedance screen

The transmission and diffraction of waves by an aperture in an impedance screen is investigated. The Senior's solution of the scattering problem of waves by an impedance half-plane is transformed into a physical optics type integral. The obtained method is applied to the transmission problem of waves by a slit in an impedance screen. The results are compared with the aperture problem in black and conducting screens numerically.     

Diffraction of sound from a dipole source near to a barrier or an impedance discontinuity

Pierce's formulation for the diffraction of spherical waves by a hard wedge has been extended to the case of the sound field due to a dipole source. The same approach is also used to extend a semiempirical model for sound propagation above an impedance discontinuity due to a dipole source. The resulting formulas have been validated by comparing their numerical solutions with that computed by summing the sound fields due to two closely spaced monopole sources of equal magnitude but opposite in phase. These new formulations are then used to develop a simple model for calculating the dipole sound field diffracted by a barrier above an impedance ground. Applications of these models relate to transportation noise prediction, particularly railway noise abatement, for which dipole sources are commonly used. The numerical predictions have been found to compare reasonably well with indoor measurements using piezoceramic transducers as dipole sources.     

Physical optics theory for the scattering of waves by an impedance strip

The physical optics integral of the scattered waves by an impedance strip is derived by using the modified theory of physical optics. The surface currents of the physical optics integral, which was introduced for the scattered waves by an impedance half-plane, are taken into account. The uniform diffracted fields of the impedance strip are evaluated asymptotically. The second order diffraction terms are also obtained. The total scattered field and its subcomponents are plotted and the effect of the second order diffraction and strip width to the scattering is investigated numerically.     

Slit radiator at the edge of an impedance wedge in a uniaxial plasma

A rigorous analytical solution is derived for the problem of the excitation of electromagnetic waves by a magnetic flux source located at the top of a wedge with impedance boundaries. The wedge is placed in a uniaxial anisotropic plasma that has been magnetized transverse to the edge of the wedge direction.Translated from Izvestiya Vysshikh Uchebnikh Zavedenii, Fizika, No. 5, pp. 88–92, May, 1987.     

Diffraction of plane Beltrami waves by a wedge with nonidentical sides showing mixed anisotropic conduction immersed in a chiral medium

The Sommerfeld–Malyuzhinets integral method is applied to solve the problem of diffraction of plane electromagnetic Beltrami waves normally incident on an edge of a wedge with the sides showing ideal mixed anisotropic conduction, the wedge being in an isotropic chiral medium. The anisotropy directions of the sides are mutually orthogonal.     

The effect of impedance boundary conditions on the potential function of the boundary diffraction wave theory

A novel potential function of the boundary diffraction wave theory is obtained for the impedance surfaces by the asymptotic reduction of the modified theory of physical integrals. The function is expressed in terms of the direction vectors of the incident and scattered rays. The application of the method is performed on the problem of diffraction of plane waves by an impedance half plane for oblique incidence.     

Diffraction Pattern Observed in Shadow Region of Thin Wedge

Diffraction patterns of wedges are studied with special attention to the finish of the samples. We assume that the sharply finished vertex should generate two hemispherical waves by the end effect of the cylindrical waves issued from two sides of the wedge under illumination of the coherent light. It is found that the assumption is valuable to the investigation of the diffraction pattern appearing in the shadow region of the wedge.     

The method of the boundary diffraction wave for impedance surfaces

The line integral of the boundary diffraction wave theory is extended for the diffraction process of waves by the impedance surfaces with edge discontinuities. With this aim, the exact diffraction field expression of Maliuzhinets is transformed into a line integral. The method is applied to the scattering problems of waves by a spherical reflector with edge discontinuity and the diffracted fields are evaluated asymptotically. The resultant expressions of the waves are examined numerically.     

Boundary diffraction wave theory of junctions between two surfaces with different face impedances

The line integral of the boundary diffraction wave theory is derived for the diffraction process of waves by a junction between two surfaces with different face impedances. The exact solution of Maliuzhinets is used with this aim. The resultant integral is applied to the diffraction of waves by a circular junction between two impedance surfaces. The results are examined numerically.     

Diffraction of cylindrical waves by an ideally conducting wedge in an anisotropic plasma

The problem of diffraction of cylindrical waves by an ideally conducting wedge in an anisotropic plasma is formulated and solved. The integral equations for the field are reduced to function equations, which are solved with the aid of a special function that is introduced. The properties of this function are studied. The general solution is represented as a double contour integral in the plane of a complex variable. The radiation field and surface waves for a number of special cases are analyzed: a source of cylindrical waves on an edge; at infinity; etc. Diffraction in a half-plane is studied separately.     

Schardin问题的数值研究

激波绕过三角楔(Schardin问题)时会产生激波马赫反射与绕射、 三角楔尾涡与涡串等复杂物理现象. 本文利用三阶精度加权基本无振荡(WENO)格式、 结构化矩形网格的自适应加密方法与沉浸边界法对Schardin问题进行了数值模拟. 数值结果清晰地显示了激波与三角楔相互作用, 在楔面发生马赫反射以及在楔角绕射诱导主涡的过程, 并与Schardin等的实验结果及相关数值结果完全符合. 另外, 数值结果还详细反映了先前实验与数值结果没有详细讨论的主涡滑移层上的涡串生成机理, 以及激波与涡串相互作用和产生声波的     

Spherical Wave Diffraction by a Slit in an Impedance Screen

An exact solution is developed for the problem of diffraction of an E-polarized and an H-polarized spherical waves by a slit in an impedance screen. This consideration is important in the sense that point sources are regarded as better substitutes for real sources than line sources/plane waves. The two independent problems are solved using the Fourier transform, the Wiener-Hopf technique and asymptotic approximations.     

Schardin问题的数值研究

激波绕过三角楔(Schardin问题)时会产生激波马赫反射与绕射、 三角楔尾涡与涡串等复杂物理现象. 本文利用三阶精度加权基本无振荡(WENO)格式、 结构化矩形网格的自适应加密方法与沉浸边界法对Schardin问题进行了数值模拟. 数值结果清晰地显示了激波与三角楔相互作用, 在楔面发生马赫反射以及在楔角绕射诱导主涡的过程, 并与Schardin等的实验结果及相关数值结果完全符合. 另外, 数值结果还详细反映了先前实验与数值结果没有详细讨论的主涡滑移层上的涡串生成机理, 以及激波与涡串相互作用和产生声波的过程.     

Diffraction of plane electromagnetic waves by a wedge with perfect mixed anisotropic conductivity sides in a chiral medium

The Sommerfeld–Malyuzhinets integral method is used to solve the problem of the diffraction of plane circlepolarized electromagnetic waves normally incident on the edge of a wedge with the sides possessing perfect mixed anisotropic conductivity, which is immersed in an isotropic chiral medium.     

Fringe waves in wedge diffraction

Explicit expressions for the non-uniform currents of the physical theory of diffraction are derived in terms of Fresnel functions for wedge diffraction by taking into account the surface integrals of the modified theory of physical optics. The obtained fringe waves are compared numerically by the asymptotic representations, found in the literature.     

Diffraction of a plane wave from a wedge in a chiral medium

In a rigorous electrodynamic formulation, we have investigated diffraction of a plane wave in a chiral medium from a wedge with ideally conducting faces. The boundary-value problem is reduced to a system of functional equations which are transformed to Fredholm integral equations and singular integral equations. We have carried out an asymptotic analysis of the diffraction fields. The scattered field contains plane waves reflected by the faces and cylindrical waves due to the edges, having two opposite types of circular polarization, and also two refraction waves whose polarization corresponds to polarization of the slower characteristic wave in the chiral medium.This paper is dedicated to the memory of Professor M. S. Bobrovnikov.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 108–116, October, 1993.     

Nonlinear Elastic Waves in a Solid Isotropic Wedge with Defects

The paper presents experimental data for linear and nonlinear elastic waves in an acute-angled wedge made of D16 isotropic polycrystalline alloy with defects. The localization of waves at the edge of the wedge has been studied using laser vibrometry. The velocities of wedge waves have been measured by a pulse method in the frequency range 0.25–1.50 MHz. Measurements have not revealed any dispersion. The second harmonic of the wedge waves has been found. The dependences of the velocity and amplitude of the second harmonic on the amplitude of the first harmonic have been studied. It is noted that nonlinear effects observed in wedge waves may be explained in terms of the Murnaghan classical five-constant theory of elasticity. They are attributed to a defect-induced structural nonlinearity present in the wedge.     

Propagation of sound over grassland and over an earth barrier

A model for the calculation of effects of ground and a screen or a wedge shaped barrier on the transmission of sound has been tested by comparing calculated transmission losses with losses measured in real situations. With the model presented in this paper, the effect of a homogeneous ground with a finite or an infinite impedance, the effect of diffraction at a discontinuity in the impedance of the ground (e.g., the transition between road surface and adjacent grassland), and the combined effect of ground surface and a barrier with a finite or an infinite surface impedance can be handled. The incorporation of the effects of a discontinuity in the impedance of the ground and of the finiteness of the height of a barrier led to an additional improvement of the agreement between calculated and measured transmission losses.