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

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

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.

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.

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.

A statistical model of wave scattering from random rough surfaces

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.

In this paper we study the depolarized backscatter enhancement phenomenon for electromagnetic wave scattering from rough surfaces. Some new experimental data on light scattering from rough metallic surfaces shows a phenomenon of backscattering enhancement existing in the antispecular direction under some conditions, such as the surface parameters, wave polarization and operating frequency. From a roughly random surface the backscattering enhancement is predicted due to the constructive interference of multiple surfaces scattering. The study is based upon the integral equation method modified to be able to predict the phenomenon of multiple scattering and backscattering enhancement. From the study we found the backscattering enhancement takes place on the specialized surface parameters large compared with the incident wavelength. Further we also conclude that the depolarized multiple scattering makes much contribution along the plane of incidence from random rough surfaces, but depolarized single scattering makes little contributions as our expectation. In comparison of model prediction of total multiple scattering strength with measured data along the specular plane, excellent agreement is obtained.

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 novel forward method to establish the three-dimensional parametric scattering center models is developed to extract scattering centers from the combined target/rough surface models. Both scattering centers from the ship, including single-order and higher order scattering contributions, and from the multiple interactions between the ship and random rough sea surface would be described concisely with physically relevant parameters by this proposed method. Due to the statistical nature of the random rough surface for the Monte Carlo simulation, we acquire a large number of realizations for estimations of the amplitude and position parameters to overcome the problem that single realization cannot extract scattering centers effectively. This method is validated through parametric models of the ship in free space and on the sea surface, and a good agreement has been demonstrated between the constructed and simulated radar characteristics. Furthermore, we analyze the composite target/surface model's physics and feature stability in a visually spatial range and direct connections between scattering centers and scattering sources, which would be valuable to future target recognitions and classifications. Finally, we quantitatively calculate and analyze the coupling scattering centers from interactions between the ship and the ocean-like surface that provide more abundant contour information of the inverse synthetic aperture radar (ISAR) image to facilitate contour detections.

We study the electromagnetic scattering problem on a random rough surface when the height distribution of the profile belongs to the family of alpha-stable laws. This allows us to model peaks of very large amplitude that are not accounted for by the classical Gaussian scheme. For such probability distributions with infinite variance the usual roughness parameters such as the RMS height, the correlation length or the correlation function are irrelevant. We show, however, that these notions can be extended to the alpha-stable case and introduce a set of adapted roughness parameters that coincide with the classical quantities in the Gaussian case. Then we study the scattering problem on a stationary alpha-stable surface and compute the scattering coefficient under the first-order Kirchhoff and small-slope approximations. An analytical formula is given in the high-frequency limit, which generalizes the well known geometrical optics approximation. Some numerical results are given and discussed.

Rough surface scattering effects are important problem for solving emission in microwave remote sensing. Stochastically the surface length should be infinite to simulate random rough surface scattering which is possible for analytical method but not for numerical method. Generally there are two approximations to simulate real life: the tapered wave method and periodic boundary condition. Both are valid for random rough surface scattering if convergence is shown with increase of surface length for the tapered wave and if the period is large enough for periodic boundary condition. In this paper we compare the results for the four Stokes parameters between periodic boundary conditions and the tapered wave approach.

Fractal geometry function provides a practical way to simulate natural rough surface for electromagnetic scattering calculation of microwave remote sensing. In our study, we generate three-dimensional random rough surface based on band-limited Weierstrass-Mandelbrot model and carry out a series of quantitative analyses of the relation between fractal parameters and rough surface parameters. In order to eliminate the artifical reflection from the truncated boundary of rough surface model, a tapered incident wave model is built to illuminate the surface profile model with the use of sampling strategy. The tapered incident wave is introduced into the classical Two-Scale Model to calculate backscattering coefficient. The proposed model is applied to simulate the scattering of sea clutter based on the fractal sea surface model. Its simulation results are compared with real sea surface scatterometer measurement experiments in Beihai, Guangxi province and the overall deviation is less than 10%. The results validate the efficiency of the proposed model in obtaining the scattering simulation data on sea surface for parameter inversion of active microwave remote sensing.