Random gaussian rough surfaces for full-wave electromagnetic simulations

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.

Soil Roughness Measuring System Combined With Image Processing

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.

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 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.

A statistical model of wave scattering from random rough surfaces

A random medium is used to investigate reservoir heterogeneities in this study. Random media are characterized by autocorrelation functions that allow a construction of spatially anisotropic random structures with different correlation lengths and fluctuation standard deviations. Based on the analysis, we calculate a power spectrum using fast Fourier transform (FFT), which is observed in spatial wavelengths ranging from a few metres to a few thousand metres. Correlation distance and root mean square (RMS) height are directly obtained from the power spectrum. Numerical experiments show that the correlation length and fluctuation standard deviation can cause correlation distance and RMS height undergoing variations. Combining the characteristics of statistical parameters and sonic-log data, we quantitatively analyse the reservoir heterogeneities in the Yanchang Basin. The correlation distance and RMS height of coarse lithofacies in fluvial sandstones interpret a high-energy deposit and strong heterogeneity, affected by different lithological combinations. The correlation lengths decrease gradually from shales, tight sands to gas-bearing sands. Using the sonic-log data from 28 wells in the Yanchang Basin, we compute the isolines of correlation distances and RMS heights for both the He-8 and Shan-1 members in the studied area, which present a correlation with the distribution of gas. This offers an improved foundation for reservoir lateral prediction.

A new approach of numerically generating a microtube with three-dimensional random surface roughness is presented. In this approach, we combined a bi-cubic Coons patch with Gaussian distributed roughness heights. Two random roughness generation methods are studied. A computational fluid dynamic solver is used to solve the 3-D N–S equations for the flow through the generated rough microtubes with D = 50 μm and L = 100 μm. The effects of the peak roughness height, H, asperities spacing in the θ direction, S θ , and Z direction, S Z , standard deviation of the Gaussian distribution, σ, arithmetical mean roughness, R a, on the Poiseuille number, Po are investigated. It is found that when H/D < 5% the Po number can still be predicted by the conventional flow theory if the mean diameter of rough microtubes, D m, is used to be the hydraulic diameter D h. When H/D = 10%, the main flow is strongly affected by the roughness at Reynolds number Re = 1,500. The Po number increases with Re and deviates from the prediction up to 11.9%. The Po number does not change a lot with S θ and S Z because D m almost keeps constant when the spacing is changed. For the rough microtubes with different R a values, the Po numbers can be almost the same, which prove that only with the R a value we can not determine the friction in the rough microtube. The mean value μ, the maximum and minimum values of the random roughness are found to be critical to determine the Po number.

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.

A mechanistic study of the effect of pigment loading on the appearance of powder coatings: The effect of surface topography on the optical properties of powder coatings: Modelling and experimental results

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.

Estimates are obtained for the pressure field reflected from random rough surfaces when the surfaces are insonified by a high‐frequency, omnidirectional point source. A geometric acoustics or ray‐tracing approach is taken together with the assumptions that there is no shadowing of the surface and that each ray undergoes a single reflection. A stationary phase approximation of the Helmholtz integral is used to estimate the field associated with each ray. The emphasis of the paper is on accounting for the phase differences, that is, the interference effects, between the possibly very many geometric rays from source to surface to receiver.Subject Classification: 20.30.

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