Scattering of acoustic point‐source fields by random surfaces

While recent studies have proven an unexpected liquid–vapor phase transition of adsorbed liquid films, a comprehensive description of the mechanisms of different types of phase change regimes over realistic representations of random rough surfaces is absent in the literature. The current comprehensive study investigates the effects of a gold random rough surface, liquid film thickness, and substrate temperature on the liquid–vapor phase change regime of an adsorbed sodium liquid film, considering the evaporator section of a wicked heat pipe (WHP) using a molecular dynamics (MD) simulation. At first, to generate a realistic random rough surface, a new and promising method is proposed that is entirely based on MD simulations. Then, to simulate the evaporator section of a WHP, a unique configuration for eliminating the vapor domain is developed. The simulation results reveal that three distinct regimes, namely, normal evaporation, cluster boiling, and film boiling, could be identified, which are presented on two-dimensional diagrams with the substrate temperature and liquid film thickness as coordinates for the ideally smooth and random rough surfaces. The results also manifest that even though using the random rough surface could lead to different phase transition regimes, the type of regime depends mainly on the substrate temperature and liquid film thickness. Furthermore, this study displays two different modes for normal evaporation. Also, it is shown that the impacts of the liquid film thickness and substrate temperature on the mode of normal evaporation are much more significant than the surface roughness.

Effects of random road surface roughness and long-term deflection of prestressed concrete girder and cable-stayed bridges on impact due to moving vehicles

A statistical model of wave scattering from random rough surfaces

When a random rough surface is illuminated by light or high-frequency radio waves, the specular reflected points make an ensemble, the statistical properties of which are of great interest not only for a general theory of scattering, but also for many practical applications, ranging from real-time monitoring of man-made surface roughness to sea roughness parameter measurements using sunlight flares at the surface. Apparently, M.S. Longuet-Higgins (see J. Opt. Soc. Am., vol.50, p.838-56, 1960) was the first to employ the theory of random functions for solving this problem. In particular, the explicit equations for the spatial density of extrema and saddle points were derived for Gaussian surfaces, and the fundamental relations between them were established. We use the general theory of random field excursions (Adler, R.J., 1981; Stoyan, D. et al., 1995) to obtain the statistical characteristics of specular points arising on random surfaces at normal incidence.

Simulation of 3-D random rough surface by 2-D digital filter and fourier analysis

A rigorous three-dimensional (3-D) electromagnetic model is developed to analyze the scattering from anti-personnel (AP) nonmetallic mine-like target when it is buried near a clutter object under two-dimensional (2-D) random rough surfaces. The steepest descent fast multipole method (SDFMM) is implemented to solve for the unknown electric and magnetic surface currents on the ground surface, on the target and on the clutter object. A comprehensive numerical investigation of two clutter sources; the ground roughness and the nearby benign object, is presented based on using more than 800 random rough surface realizations which could not be achieved without using fast algorithms such as the SDFMM. The statistics of the scattered near-electric fields are computed using the Monte Carlo simulations for both polarizations. For the parameters used here, the results show that the average and the standard deviation of the target signature represent 5-7% and 3-3.5% of the total scattered signal, respectively, while they represent 16-20% and 7-12% of the signal for the clutter object, respectively. This study indicates the high possibility of a false alarm during the detection process when the target is located nearby a realistic object such as a piece of a tree root.

The physical optics approach and Lorentz transformations are combined to formulate scatter from a random rough surface in uniform motion. The perfectly conducting scatterer is excited by an elliptically polarized plane electromagnetic wave and the analysis ends in the velocity‐dependent expressions for the scattering cross section per unit area, the depolarization factor and the radial tilt. The direction of motion is considered parallel as well as normal to the scatterer's mean plane. The combined effect of roughness and motion on scattering and depolarization is investigated through a numerical example. The calculations reveal that parallel motion modifies scatter through aberration while normal motion results in scatter amplification. The depolarization factor and/or radial tilt might be used for motion estimation.

To study wave scattering from random lossy dielectric rough surfaces with large permittivities using the method of moments, a dense grid is needed for accurate results. A dense grid requires more CPU and memory. The physics‐based two‐grid (PBTG) method can reduce both CPU and memory requirements. In this paper, the PBTG is used in conjunction with the multilevel fast multipole method (FMM) to solve wave scattering from one‐dimensional random lossy dielectric rough surfaces. The proposed algorithm has the computational complexities of O(Ndg) for near‐field interactions and O(Ncg) for nonnear‐field interactions, where Ndg and Ncg are the number of sampling points on the dense and coarse grids, respectively. Using the proposed algorithm, wave scattering from Gaussian and non‐Gaussian rough surfaces is investigated and illustrated. Special emphasis is put on checking the accuracy of the algorithm and energy conservation.

This paper is concerned with a numerical procedure to estimate two parameters, amplitude modification factor α and propagation order of distance β, for electromagnetic (EM) propagation in complicated natural environments such as random rough surface (RRS). These two parameters are key parameters when we simulate field distributions along various types of RRS based on 1-ray model. We assume that the former parameter α can be evaluated by the visual planar angles of illuminated lines in case of 1D RRS and by the visual solid angles of illuminated planes in case of 2D RRS. We also assume that the latter parameter β can be estimated not only by base station (BS) antenna height, similar to Okumura-Hata model simulating EM propagation in urban and suburban areas, but also by mobile station (MS) antenna height. In order to demonstrate validity of the proposed parameter estimation, we compare the numerical field distributions obtained by the 1-ray model using estimated two parameters with those computed by discrete ray tracing method (DRTM) which is an effective EM field solver. It is shown that both numerical results are in good agreement.

Flow accelerated corrosion generates not only pipe-wall thinning but also roughness on an inside wall. In some flow conditions, the increase in roughness can increase the mass transfer coefficient by up to 80%. It is then very important to have an evaluation tool to monitor and quantify the roughness of a pipe. This study aims to estimate the roughness by using ultrasonic attenuation. The advantage of using ultrasonic attenuation is that it utilizes the signals measured by existing ultrasonic probes, and does not require significant changes to the equipment. To evaluate the inner rough surface, this study compares ultrasonic attenuations on random and periodic rough surfaces. We used an ultrasonic broadband probe on specimens with random and periodic rough surfaces in experiments. The results indicate a significant difference between the attenuation values estimated on random and periodic roughness. In addition, attenuation of amplitude at specific frequencies also was observed. These specific frequencies implied having the potential to estimate the pitch of periodic flaws on the rough surface.

In this paper, the model developed for predicting the scattering characteristics from statistically rough surfaces is based upon the integral-equation model with multiple scattering. Its objective is to examine the bistatic scattering characteristics from randomly rough surfaces along different azimuth angles. For a better understanding of the scattering behavior from randomly rough surfaces, information about scattering must be known omnidirectionally, not just in the specular or backscatter direction. Comparisons between the model prediction and the experimental measurements are made for both like and cross polarizations. This model prediction demonstrates good agreement with the experimental data. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 271–275, 2000.

We investigate static and dynamic aspects of the demagnetizing factor N in magnetic thin films with random rough surfaces which are described by the rms amplitude Δ, the correlation length ξ, and the roughness exponent H (0⩽H⩽1). The demagnetizing factor decreases as the surface smoothens (increasing H and/or decreasing ratio Δ/ξ), with the exponent H yielding a comparable contribution to N as the roughness ratio Δ/ξ. Moreover, for growing films with self-affine surfaces, N decreases with film thickness, closely as a power law for large roughness exponents (H∼1). Finally, estimates of the demagnetizing factor based on sinusoidal models are shown to be inadequate since they neglect fine roughness details at short wavelengths (<ξ) as depicted by the roughness exponent H.

Backscattering enhancement of electromagnetic wave scattering from a perfectly conducting two-dimensional random rough surface (three-dimensional scattering problem) is studied with Monte Carlo simulations. The magnetic-field integral equation formulation is used with the method of moments. The solution of the matrix equation is calculated exactly with an efficient method known as the sparse-matrix flat-surface iterative approach. Numerical examples are illustrated with 32,768 surface unknowns, surface areas between 256 and 1024 square wavelengths, rms heights of 0.5 and 1 wavelength, and as many as 1000 realizations. The bistatic scattering simulations show backscattering enhancement for both copolarized and cross-polarized components. Comparisons are made with controlled laboratory experimental data for which the random rough surfaces are fabricated with prescribed properties of a rms height of 1 wavelength and a correlation length equal to 2 wavelengths. Comparisons are made between simulations and experimental data for the absolute value of the bistatic scattering coefficient. The copolarized scattering coefficient is in good agreement, and the cross-polarized scattering coefficient is in excellent agreement.

In a series of papers, the first in 1994, Sánchez-Gil et al [1] and in 1997 Madrazo and Maradudin [2] studied the scattering of electromagnetic waves from a wave guide film on a perfect conductor with a random rough surface. They found the enhanced backscattering and satellite peaks in the incoherent part of the mean differential reflection coefficient (DRC) as a function of the scattering angle when the system supports several guided waves modes.

The emissivity is an important surface property parameter in many fields, including infrared temperature measurement. In this research, a symmetry theoretical model of directional spectral emissivity prediction is proposed based on Gaussian random rough surface theory. A numerical solution based on a matrix method is determined based on its symmetrical characteristics. Influences of the index of refraction n and the root mean square (RMS) roughness σrms on the directional spectrum emissivity ε are analyzed and discussed. The results indicate that surfaces with higher n and lower σrms tend to have a peak in high viewing angles. On the contrary, surfaces with lower n and higher σrms tend to have a peak in low viewing angles. Experimental verifications based on infrared (IR) temperature measurement of Inconel 718 sandblasted surfaces were carried out. This model would contribute to understand random rough surfaces and their emitting properties in fields including machining, process controlling, remote sensing, etc.