Wave Propagation In Nonuniform Medium Research Articles

A statistical model of the wave field in a bounded domain

Numerical simulations of plasma heating with radiofrequency waves often require repetitive calculations of wave fields as the plasma evolves. To enable effective simulations, bench marked formulas of the power deposition have been developed. Here, a statistical model applicable to waves with short wavelengths is presented, which gives the expected amplitude of the wave field as a superposition of four wave fields with weight coefficients depending on the single pass damping, as. The weight coefficient for the wave field coherent with that calculated in the absence of reflection agrees with the coefficient for strong single pass damping of an earlier developed heuristic model, for which the weight coefficients were obtained empirically using a full wave code to calculate the wave field and power deposition. Antennas launching electromagnetic waves into bounded domains are often designed to produce localised wave fields and power depositions in the limit of strong single pass damping. The reflection of the waves changes the coupling that partly destroys the localisation of the wave field, which explains the apparent paradox arising from the earlier developed heuristic formula that only a fraction as2(2−as) and not as of the power is absorbed with a profile corresponding to the power deposition for the first pass of the rays. A method to account for the change in the coupling spectrum caused by reflection for modelling the wave field with ray tracing in bounded media is proposed, which should be applicable to wave propagation in non-uniform media in more general geometries.

Evaluation of dependence on calculation parameters in interface settings for finite-difference time-domain analyses of acoustic fields

To date, numerical analysis for sound wave propagation in time domain has been investigated widely as a result of advances in computer technology. The finite difference time domain (FDTD) methods are very widely used for time domain numerical analysis. The following is a family of FDTD method, for example, the standard FDTD method based on Yee’s algorithm, wave equation FDTD (WE-FDTD) method, the FDTD(2,4) method, and so on. The FDTD and WE-FDTD methods cause numerical dispersion error due to using second order finite difference (FD) approximation. To overcome this problem, the FDTD(2,4) method using higher order spatial FDs have been proposed. On the other hand, the settings of the interface between different media are important issue to solve acoustic wave propagation in non-uniform media. In this study, we examine the dependence on calculation parameters in the settings of interface for some FDTD methods. The present study shows dependence on the CFL number and ratio of sound velocity and impedance between the boundaries. We demonstrate that accuracy of the interface between different media strongly depend on calculation parameters and the ratio of sound velocity. Moreover, the proposal settings of the interface for the FDTD(2,4) methods are more accurate.

Multiple-scale approximation of instabilities in unsteady boundary layers

A general procedure is developed to study the stability of unsteady boundary layers using complex-ray theory. The propagation of small disturbances is described by a high-frequency (optical) approximation similar to the one adopted for wave propagation in nonuniform media. The ray trajectories, formally defined as the characteristic lines of the eikonal equation, are described by a system of first-order differential equations. These lines are complex valued and provide the main contribution to the propagation of the wave (its Green’s function). As an application, we present the analysis of the flow past on an oscillating airfoil. The propagation of a harmonic disturbance inside the boundary layer is considered and some numerical transition-prediction results are discussed.

Wave propagation in advected acoustics within a non-uniform medium under the effect of gravity

We investigate linear wave propagation in non-uniform medium under the influence of gravity. Unlike the case of constant properties medium here the linearized Euler equations do not admit a plane-wave solution. Instead, we find a “pseudo-plane-wave”. Also, there is no dispersion relation in the usual sense. We derive explicit analytic solutions (both for acoustic and vorticity waves) which, in turn, provide some insights into wave propagation in the non-uniform case.

Numerical Method for Nonlinear Wave Propagation and Application to Laser-Plasma Interaction

A new efficient numerical scheme is presented for analyzing the nonlinear wave propagation in nonuniform medium at high accuracy. The method consists of combining the shooting method and Newton's iteration scheme. As an example, the structure resonance phenomena in laser-plasma interaction are studied as a nonlinear boundary problem. Multi-valued reflection coefficient as a function of the incident laser intensity and the associated anomalous transmission phenomena are studied.

On the wave propagation in nonuniform media

On the wave propagation in nonuniform media