波导本征问题的等几何分析方法

利用等几何分析思想通过加权余量法并结合亥姆霍兹方程推导出波导本征问题的等几何分析方程,提出了一种分析波导本征问题低自由度消耗、高精度的方法。该方法消除了传统数值方法中求解域的模型非一致性,从而实现了将问题的分析计算构架于精确的模型之上。以矩形和圆形波导的本征问题分析为例,通过与解析解和其他数值方法比较表明:在同等较细网格下,等几何分析模型仅花费1156个自由度,最大误差为0.003%,相比有限元的2245个自由度和0.03%的最大误差,此方法具有自由度少、精度高、收敛速度快等优点。     

电磁波导辛体系下的周期皱波导分析

基于Hamilton变分原理的电磁波导辛体系自建立以来解决了传统电磁有限元所不能解决的一些问题。本文在介绍这一体系之后,经半解析横向离散及辛正则化,给出了类凝聚和协调质量阵。针对常见的周期皱波导问题,引入等效折射率概念,将皱波导转化为折射率周期变化的多层薄膜,并将其对应为力学分析中的条形域问题。最后给出的数值例子中所计算的通带辛本征值与解析解很接近,表明该理论方法有很高的计算效率。     

Wave propagation in earth-ionosphere waveguide

Summary In this paper, wave propagation in a stratified medium which consists of earth, atmosphere and ionosphere, is studied. The ionosphere is described by a compressible plasma model where the earth magnetic field is neglected. The earth is considered as a highly conducting medium. The modal solutions due to the excitation of a vertical dipole have been obtained, where characteristic waves are analytically discussed and numerically determined.This work was supported by National Aeronautics and Space Administration under Grant NSG-395.     

Complex waves in a dielectric waveguide

Existence of two families of symmetric complex waves in a dielectric waveguide of circular cross section is proved. Eigenvalues of the associated Sturm–Liouville problem on the half-line are determined.     

Impedance at a rough waveguide boundary

The impedance at the randomly rough upper boundary of an ocean waveguide is derived. The sound speed of the waveguide is an arbitary function of depth. The boundary surface height is assumed to be a statistically homogeneous Gaussian process. Integral equations for the Green's function and its normal derivative on the boundary are derived. These are solved to second order in the surface interaction. The result is a rational approximation to the impedance in terms of the wave guide Green's function and the statistical properties of the surface. The special cases of small and large roughness as well as that of a constant sound speed profile are presented. For simplicity we restrict the analysis to a semi-infinite waveguide where the waveguide Green's function vanishes at the surface (Dirichlet problem).     

Laser-induced break-up of water jet waveguide

In this article, an optical method to control the break-up of high-speed liquid jets is proposed. The method consists of focusing the light of a pulsed laser source into the jet behaving as a waveguide. Experiments were performed with the help of a Q-switched frequency doubled Nd:Yag laser (=532 nm). The jet diameter was 48 µm and jet velocities from 100 to 200 m/s. To study the laser-induced water jet break-up, observations of the jet coupled with the high power laser were performed for variable coupling and jet velocity conditions. Experimentally determined wavelength and growth rate of the laser-generated disturbance were also compared with the ones predicted by linear stability theory of free jets.     

The application of three-dimensional hydroelastic analysis of ship structures in Pekeris hydro-acoustic waveguide environment简

The hydroelastic analysis and sonoelastic analysis methods are incorporated with the Green＇s function of the Pekeris ocean hydro-acoustic waveguide model to produce a three-dimensional sonoelastic analysis method for ships in the ocean hydro-acoustic environment. The seabed condition is represented by a penetrable boundary of prescribed density and sound speed. This method is employed in this paper to predict the vibration and acoustic radiation of a 1 500 t Small Water Area Twin Hull （SWATH） ship in shallow sea acoustic environment. The wet resonant frequencies and radiation sound source levels are predicted and compared with the measured results of the ship in trial.     

Near field of the open-ended parallel-plate waveguide

The near-field radiation of an open-ended parallel-plate waveguide is analyzed by the uniform asymptotic theory. The results are compared with those obtained by Keller's geometrical theory of diffraction. We demonstrate how the present solution recovers the earlier far-field results and establishes the region of validity of the latter.     

Forerunning mode transition in a continuous waveguide

We have discovered a forerunning mode transition as the periodic wave changing the state of a uniform continuous waveguide. The latter is represented by an elastic beam initially rested on an elastic foundation. Under the action of an incident sinusoidal wave, the separation from the foundation occurs propagating in the form of a transition wave. The critical displacement is the separation criterion. Under these conditions, the steady-state mode exists with the transition wave speed independent of the incident wave amplitude. We show that such a regime exists only in a bounded domain of the incident wave parameters. Outside this domain, for higher amplitudes, the steady-state mode is replaced by a set of local separation segments periodically emerging at a distance ahead of the main transition point. The crucial feature of this waveguide is that the incident wave group speed is greater than the phase speed. This allows the incident wave to deliver the energy required for the separation. The analytical solution allows us to show in detail how the steady-state mode transforms into the forerunning one. The latter studied numerically turns out to be periodic. As the incident wave amplitude grows the period decreases, while the transition wave speed averaged over the period increases to the group velocity of the wave. As an important part of the analysis, the complete set of solutions is presented for the waves excited by the oscillating or/and moving force acting on the free beam. In particular, an asymptotic solution is evaluated for the resonant wave corresponding to a certain relation between the load's speed and frequency.     

Numerical investigation of resonators in a waveguide

A technique for numerically investigating resonators based on their exposure to broadband noise with a subsequent analysis of the input and output signal spectra is proposed. Resonance chambers connected with a waveguide through its wall are numerically investigated using both linear (linearized Euler equations) and nonlinear (Euler and Navier-Stokes equations) models. The general features of the linear resonance and the influence of nonlinear effects and dissipation on sound-absorbing properties are studied. The dependence of the resonator parameters on the presence of an axial flow and the boundary layer thickness is investigated for the model based on the Navier-Stokes equations.     

Two nonmixed symmetric end-loadings of an elastic waveguide

This investigation treats the response of the semi-infinite plate with free faces subjected to suddenly applied normal loads on its end. The plate is elastic and in plane strain. The normal loads are symmetric and act in the absence of shear stress, i.e. the plate has nonmixed end conditions. A double Laplace transform technique is used to obtain long-time information for two particular normal loads; the uniform load and the line-load. Near-field and far-field approximations are found. Results in the long-time near-field for the uniform load reduce to elementary forms; for the line-load however, the corresponding forms are quite complex entailing singular terms and some numerically evaluated contributions. The far-field approximations give rise to integral of the Airy function forms for both loads and, if the forces applied under the two loadings are equal, these far-field responses are shown to be identical.     

Broadband optimization of a pentamode-layered spherical acoustic waveguide

Transformational acoustics offers the theoretical possibility of cloaking obstacles within fluids, provided metamaterials having continuously varying bulk moduli and densities can be found or constructed. Realistically, materials with the proper, continuously varying anisotropies do not presently exist. Discretely layered cloaks having constant material parameters within each layer are a viable alternative, but due to their discrete nature, may become ineffective outside of narrow frequency ranges. Because of such limitations, there is interest in finding discretely layered systems that can be effective in as wide as possible bandwidth without the need for unrealizable material properties within each layer. The present work introduces a novel methodology for finding optimal material parameters for use in such layered cloaks. In principle, the technique could be applied to any acoustic or electromagnetic scattering problem, but for purposes of demonstration, this paper considers a fluid-loaded acoustically hard sphere with a cloak that comprised layered pentamodes, whose material properties are constrained to lie within reasonable ranges relative to the density and bulk modulus of water.     

Summation of Gaussian beams in a surface waveguide

The Gaussian beams summation method is applied to a surface waveguide problem in the parabolic approximation. It is shown by means of numerical comparison with an exact solution that the method is effective for computations. Its accuracy does not depend on the complication of the ray field, but the method fails for long distances from the source because of the beam's spreading if a large parameter of the problem is fixed.     

TE modes of a layered nonlinear optical waveguide

The general theory is given of the propagation of electromagnetic TE modes in a layered structure consisting of a homogeneous dielectric layer between two homogeneous optically nonlinear semi-infinite dielectrics. Allowance is made for the nonlinear coefficients of the nonlinear media to be different and a detailed analysis is given, together with the appropriate formulae for the power flow down the guide, as a function of guide wave number, and layer thickness. Detailed consideration is given to the existence conditions for surface waves.     

Stability of an inhomogeneous vibrationally-nonequilibrium flow in a waveguide

The stability of an inhomogeneous subsonic vibrationally-nonequilibrium flow is examined in the linear approximation. It is shown that the nonequilibrium flow stability is reduced with increase in the initial flow velocity and the energy pumping zone width. This is attributed to the effect of the feedback due to acoustic disturbances propagating counter to the flow. Calculations are carried out for different pumping models.     

一种基于硅基波导的新型谐振式集成光学陀螺

介绍了一种基于单偏振波导环形谐振腔的新型集成光学陀螺及单偏振环形波导谐振腔的实现方法。其中单偏振光波导由SiO2衬底层、锗掺杂SiO2波导芯层和SiO2上包层组成,整个结构可用硅热氧化技术和PECVD技术生长在硅衬底上。用BPM(束传播法)对设计的单偏振环形谐振腔的传输特性进行仿真分析。结果表明,当入射光波长为1550nm时,此单偏振波导谐振腔对TM模式传输光的消光比是25dB/cm,而对TE模式传输光的传输损耗是0.05dB/cm,谐振腔的精细度可达到35。单偏振波导谐振腔的这些特点适于集成光学陀螺的应用要求,由其研制的集成光学陀螺的分辨率可达到16(°)/h。