Roughness Of Boundary Research Articles

Mathematical modeling of turbulent mixing in gas systems with a chevron contact boundary using NUT3D, BIC3D, EGAK, and MIMOSA numerical codes

The paper presents computational and experimental studies of the evolution of turbulent mixing in three-layer gas systems with the development of hydrodynamic instabilities, in particular Richtmyer-Meshkov and Kelvin-Helmholtz, under the action of shock waves. One of the contact boundaries of the gases was flat, the other with a break in the form of a chevron. Numerical calculations are performed both without initial perturbations of the contact boundaries, and in the presence of perturbations. It is shown that the roughness of the contact boundary significantly affects the width of the mixing zone.

Scarring in Rough Rectangular Billiards

We study the mechanism of scarring of eigenstates in rectangular billiards with slightly corrugated surfaces and show that it is very different from that known in Sinai and Bunimovich billiards. We demonstrate that there are two sets of scar states. One set is related to the bouncing ball trajectories in the configuration space of the corresponding classical billiard. A second set of scar-like states emerges in the momentum space, which originated from the plane-wave states of the unperturbed flat billiard. In the case of billiards with one rough surface, the numerical data demonstrate the repulsion of eigenstates from this surface. When two horizontal rough surfaces are considered, the repulsion effect is either enhanced or canceled depending on whether the rough profiles are symmetric or antisymmetric. The effect of repulsion is quite strong and influences the structure of all eigenstates, indicating that the symmetric properties of the rough profiles are important for the problem of scattering of electromagnetic (or electron) waves through quasi-one-dimensional waveguides. Our approach is based on the reduction of the model of one particle in the billiard with corrugated surfaces to a model of two artificial particles in the billiard with flat surfaces, however, with an effective interaction between these particles. As a result, the analysis is conducted in terms of a two-particle basis, and the roughness of the billiard boundaries is absorbed by a quite complicated potential.

ON SOME FEATURES OF ULTRASOUND REFLECTION WATER-SAMPLE IN AN INCLINED FALL (PHYSICAL MODELING)

In recent years, the analysis of the dependence of reflection coefficients on the magnitude of the angle of incidence of reflected waves has been successfully used in the practice of seismic research. AVO analysis is one of the methods of dynamic analysis that is used to estimate changes in the amplitude of reflected waves depending on the distance between the explosion points and the receivers. The AVO method is based on the analysis of the dependence of the reflection coefficients on the angle of incidence. In real conditions, this dependence can be determined, for example, by the roughness of the boundaries. This determines the relevance of studying the features of reflection coefficients on uneven boundaries on objects with well-controlled properties. The aim of the work is to determine the nature of the influence of different-scale roughness of seismic boundaries on the reflection coefficients of elastic waves. The work also used the technique of isolating standing waves to determine the wave velocity. As a result, graphs were obtained demonstrating the dependence of the reflection coefficients on the magnitude of the angle of incidence of reflected waves from a rough surface. Reflection coefficients were also obtained for the boundary of an isotropic medium in the direction of the isotropy plane and possible ways of applying the results were analyzed. Based on the data obtained, we can say that when the azimuth changes relative to the direction of the surface, the reflection coefficients change significantly only at the supercritical angles of incidence.

ON SOME FEATURES OF ULTRASOUND REFLECTION WATER-SAMPLE IN AN INCLINED FALL (PHYSICAL MODELING)

In recent years, the analysis of the dependence of reflection coefficients on the magnitude of the angle of incidence of reflected waves has been successfully used in the practice of seismic research. AVO analysis is one of the methods of dynamic analysis that is used to estimate changes in the amplitude of reflected waves depending on the distance between the explosion points and the receivers. The AVO method is based on the analysis of the dependence of the reflection coefficients on the angle of incidence. In real conditions, this dependence can be determined, for example, by the roughness of the boundaries. This determines the relevance of studying the features of reflection coefficients on uneven boundaries on objects with well-controlled properties. The aim of the work is to determine the nature of the influence of different-scale roughness of seismic boundaries on the reflection coefficients of elastic waves. The work also used the technique of isolating standing waves to determine the wave velocity. As a result, graphs were obtained demonstrating the dependence of the reflection coefficients on the magnitude of the angle of incidence of reflected waves from a rough surface. Reflection coefficients were also obtained for the boundary of an isotropic medium in the direction of the isotropy plane and possible ways of applying the results were analyzed. Based on the data obtained, we can say that when the azimuth changes relative to the direction of the surface, the reflection coefficients change significantly only at the supercritical angles of incidence.

A Novel Water Index Fusing SAR and Optical Imagery (SOWI)

Continuous and accurate acquisitions of surface water distribution are important for water resources evaluation, especially high-precision flood monitoring. During surface water extraction, optical imagery is strongly affected by clouds, while synthetic aperture radar (SAR) imagery is easily influenced by numerous physical factors; thus, the water extraction method based on single-sensor imagery cannot obtain high-precision water range under multiple scenarios. Here, we integrated the radar backscattering coefficient of ground objects into the Normalized Difference Water Index to construct a novel SAR and Optical Imagery Water Index (SOWI), and the water ranges of five study areas were extracted. We compared two previous automatic extraction methods based on single-sensor imagery and evaluated the accuracy of the extraction results. Compared with using optical and SAR imagery alone, the accuracy of all five regions was improved by up to 1–18%. The fusion-derived products resulted in user accuracies ranging 95–99% and Kappa coefficients varying by 85–97%. SOWI was then applied to monitor the 2021 heavy rainfall-induced Henan Province flood disaster, obtaining a time-series change diagram of flood inundation range. Our results verify SOWI’s continuous high-precision monitoring capability to accurately identify waterbodies beneath clouds and algal blooms. By reducing random noise, the defects of SAR are improved and the roughness of water boundaries is overcome. SOWI is suitable for high-precision water extraction in myriad scenarios, and has great potential for use in flood disaster monitoring and water resources statistics.

On Average Losses of Low-Frequency Sound in a Two-Dimensional Shallow-Water Random Waveguide

For a low-frequency sound signal propagating in a two-dimensionally inhomogeneous shallow-water waveguide, the influence of random bathymetry (fluctuating bottom boundary) was considered based on the local-mode approach and statistical modeling using first-order evolution equations. The study was carried out in shallow sea conditions corresponding to the coastal waveguides of the Russian Arctic seas. Here, a feature was the presence of an almost homogeneous water layer with various characteristics of seabed sediments. To describe the latter, a random model of the impedance was adopted. For the conditions of a strongly penetrable bottom boundary, on average, the calculations predicted adequate weak effects of bathymetry fluctuations on the average sound intensity compared to the effect of fluctuations in the sediment parameters and volumetric random inhomogeneities of the water column. In addition, it was shown that, in terms of statistics, the roughness of the bottom boundary perturbed the average sound intensity in a shallow-water waveguide differently than volumetric fluctuations in the speed of sound. The dependence of the statistical effects (the first and second moments of the signal intensity) on the parameters of the waveguide and the frequency range was studied. As a result of numerical modeling, comparative quantitative estimates of the influence of both the random roughness of the bottom interface and fluctuations of bottom sediment parameters on the average losses of the propagating signal, not presented in the literature, were obtained.

Shape characterization methods of irregular cavity using Fourier analysis in tunnel

The erosion of soluble rock and transformation of groundwater result in the high geometrical irregularity of cavities in nature. The purpose of this paper is to quantitatively describe the shape of irregular cavities using Fourier transform analysis. Firstly, multi-level characterization indexes of the 2D section of cavities have been proposed, considering the high shape irregularity of cavities. The first level indexes include Shape Factor (SF), Aspect Ratio (AR) and Sphere Like (SL). The second level indexes consist of Angularity Factor (AF) and Convexity Factor (CF). The third level indexes are Roundness Factor (RF). Then, the geometric contour of cavity was transformed into a 2D waveform, with an equal-angle points sampling of the cavity boundary. The geometric boundary of irregular cavity was segmented and transformed from discrete time domain to frequency domain based on discrete Fourier transform (DFT). Furthermore, we proposed Fourier shape descriptor, which was found to control the cavity shape. The relationship between Fourier shape descriptors in different sequences and multi-level characterization indexes was determined using designed and irregular nature cavities as sample data. The results demonstrated that the Fourier shape descriptors​ D2, D3 and D8 mainly control multi-level characterization indexes including the overall shape, the irregularity and the roughness of the cavity boundary, respectively. Finally, the 3D characterization method of cavity shape was further proposed based on averaging the 2D sections, which hence offers a possible way to further quantitatively study the mechanical properties of surrounding rockmass effected by the irregular shape of cavities.

On the influence of a surface roughness on propagation of anti-plane short-length localized waves in a medium with surface coating

We discuss the propagation of localized surface waves in the framework of the linear Gurtin–Murdoch surface elasticity and taking into account a roughness of a free boundary. We derive a boundary-value problem for anti-plane motions with curvilinear boundary and surface stresses. Using the asymptotic technique developed earlier, we obtain the form of a localized wave and analyze its amplitude evolution. As the main result we present the dependence of the wave amplitude on the roughness magnitude. The presented results could be used for non-destructive evaluation of the surface microstructure using surface waves-based devices. In particular, measuring the decay rate with the depth one can estimate roughness of a surface and appearance of new surface defects.

Моделирование течения тонкого слоя жидкости с учетом разрывов и шероховатости границ

Моделирование течения тонкого слоя жидкости с учетом разрывов и шероховатости границ

Intelligent prediction of engine failure through computational image analysis of wear particle

The present study is focused on studying the morphological characteristics of wear particles. The raw image captured from the CCD microscope is processed through a series of image processing techniques to obtain the final image. Fractal computation is performed to estimate the surface roughness of the particle boundary, which indicates the wear rate failure. An intelligence-based ANN model has been created using feed-forward backpropagation to predict outputs such as Form Factor, Convexity, Aspect Ratio, Solidity, and Roundness with respect to Running Hour, Engine RPM and Engine Oil temperature. The propound ANN model is seen as equipped to map the input-output patterns of failure under the engine parameter platform. Statistical analysis of combined error and correlation factor provides a powerful mapping tool for failure prediction. Subsequent ANN models have been seen as practical tools for predicting the performance of wear properties with the nominal inspection.

Electrodynamic Model of the Signal Scattered by the Multilayer Structure with the Use of Physical Optics and Ray Tracing Technique

Introduction. Remote monitoring of layered underlying surfaces is an urgent task. To assess the performance of new algorithms for processing the radar signal reflected from the surfaces, full-scale tests are required. As their carrying out demands big expenses, simulation modeling is actual. There are many methods of estimating an electromagnetic field (EMF) scattered by the earth's surface. However, there are no proven methods and algorithms for engineering calculation of the reflected radio signal in the conditions of this problem.Aim. The aim is to develop and to verify a software model to simulate the reflected multilayer extended structure of the radio signal received on board the aircraft.Materials and methods. The core of the model was based on high-frequency electrodynamics' methods, which allowed rapid calculation for large areas of targets with any number of layers. Simulation was produced using the MATLAB software package. The developed simulation model represented the result in the form of the normalized radar cross-section (RCS) of the multilayer structure. Since the layered structure had rough boundaries, the model provided triangulation of the boundaries of the volume-distributed object. The resulting EMF was calculated using the superposition principle. Each partial EMF value on the facet was calculated taking into account the phase and the polarization of the locally incident EMF.Results. In the paper the comparison of simulation results with theoretical calculations for the normalized RCS of a two-layer structure (difference is less than 10 percent) was presented. Verification for the coefficient of variation of the envelope of the reflected radio signal from the depth of groundwater (critical error was 7 percent) was performed. RCS modeling of the absorbing layer with different degrees of roughness of the layer boundaries was carried out. The upper boundary roughness (for maximal height deviation 0.1 m) affected on specific EPR more than lower boundary. It manifested itself in decreasing of RCS down to 30 dB.Conclusion. The developed model is intended to reduce expenses for designing synthesis of subsurface imaging systems with comparison of scheme "model of device development – field tests – completion – etc". The model is designed to verify the new signal processing algorithms for subsurface radar.

The roughness calculation of the basal boundary for the ice-sounding data collected at Princess Elizabeth Land (PEL)

In this paper, we calculated the roughness of the basal boundary collected at Princess Elizabeth Land (PEL) to evaluate the topographic structure via the ice-sounding data collected during 32ndand 33rdChinese Antarctic Research Expeditions (CHINARE 32 and 33). The calculation is achieved by a two-parameter roughness index method, which could differentiate different classes of subglacial landscape, in particular between erosional and depositional settings. Finally, the calculation results of partial regions of PEL are illustrated to describe the roughness of the detected regions.

Optical Characterization of Non-Stoichiometric Silicon Nitride Films Exhibiting Combined Defects

The study was devoted to optical characterization of non-stoichiometric silicon nitride films prepared by reactive magnetron sputtering in argon-nitrogen atmosphere onto cold (unheated) substrates. It was found that these films exhibit the combination of three defects: optical inhomogeneity (refractive index profile across the films), uniaxial anisotropy with the optical axis perpendicular to the boundaries and random roughness of the upper boundaries. The influence of the uniaxial anisotropy was included into the corresponding formulae of the optical quantities using the matrix formalism and the approximation of the inhomogeneous layer by a multilayer system consisting of large number thin homogeneous layers. The random roughness was described using the scalar diffraction theory. The processing of the experimental data was performed using the multi-sample modification of the least-squares method, in which experimental data of several samples differing in thickness were processed simultaneously. The dielectric response of the silicon nitride films was modeled using the modification of the universal dispersion model, which takes into account absorption processes corresponding to valence-to-conduction band electron transitions, excitonic effects and Urbach tail. The spectroscopic reflectometric and ellipsometric measurements were supplemented by measuring the uniformity of the samples using imaging spectroscopic reflectometry.

Effect of Aggregation and Adsorption Behavior on the Flow Resistance of Surfactant Fluid on Smooth and Rough Surfaces: A Many-Body Dissipative Particle Dynamics Study.

To study the effect of surfactant on the resistance of wall-bound flow, the adsorption and aggregation behaviors of surfactant fluid on both smooth and groove-patterned rough surface are investigated through many-body dissipative particle dynamics (MDPD) simulation. The MDPD models of surfactants were carefully parametrized and have been validated to be able to simulate the aggregation and adsorption behavior of surfactants. The simulation results show that the surfactant in laminar flow can only increase the flow resistance on the smooth surface. On the rough surface, surfactant with strong adsorption performance on the channel wall shows a drag reduction effect at moderate concentration. The surfactant with weak adsorption properties can enhance the flow resistance, which is even more significant than that of those surfactants with no adsorption capacity. Although heating (high temperature) can generally reduce the viscosity and flow resistance of surfactant fluid, it would cause a poor drag reduction efficiency. It may arise from the destruction of the adsorption layer and the interruption of the fluid/boundary interface. Surfactant adsorption can tune the roughness of the fluid boundary on either the smooth or rough surface in a different manner, which turns out to be highly correlated to the change in flow resistance. Compared with the adsorption layer, surfactant in the bulk fluid makes a greater contribution to enhancing the flow resistance as the concentration rises. This study is expected to be helpful in guiding the application of surfactants on the micro- and nanoscale such as lab-on-a-chip nanodevices and EOR in a low-permeability porous medium.

Inferring blocked mantle convection

Geophysics The boundaries between rocks with different physical properties in Earth's interior come from either a change in crystal structure or a change in chemical composition. Wu et al. examined the roughness of the boundary between Earth's upper and lower mantle, thought to form from a change in mineral structure (see the Perspective by Houser). To their surprise, in some locations, the boundary has small-scale roughness that requires some chemical difference above and below the boundary. This observation provides evidence of partially blocked mantle circulation that leads to some chemical differences between the upper and lower mantle. Science , this issue p. [736][1]; see also p. [696][2] [1]: /lookup/doi/10.1126/science.aav0822 [2]: /lookup/doi/10.1126/science.aaw4601

Efficient method to calculate the optical quantities of multi-layer systems with randomly rough boundaries using the Rayleigh–Rice theory

An efficient and numerically stable method for calculating the optical quantities of multi-layer systems with slightly rough boundaries using the second order Rayleigh–Rice theory is developed. It is assumed that the mean planes of the boundaries are parallel and all the media forming the system are nonmagnetic, isotropic and homogeneous. The perturbation series is formulated using the four-dimensional formalism inspired by the Yeh matrix formalism, but the final result is written using the two-dimensional formalism which is more efficient for the numerical calculations. The final formulae, which are expressed using an arbitrary power spectral density function (PSDF), include the mixing between the p and s polarizations occurring for anisotropic roughness. Although in the general case the calculation of optical quantities requires evaluation of double integrals, it is shown that for the PSDF given by the isotropic Gaussian function some integrals can be calculated analytically and only single integrals have to be evaluated numerically. The random roughness of boundaries is a defect that occurs frequently in practice, and it must be taken into account in the optical characterization and synthesis of thin film systems exhibiting this defect. The presented method is suitable for these purposes, since both of the mentioned applications require methods that are very fast.

МЕЗОСКОПІЧНА МОДЕЛЬ ДИФУЗІЙНОЇ ВЗАЄМОДІЇ ТА РОСТУ ФАЗ В СИСТЕМІ Cu-Sn

The model of interdiffusion in system Cu - Cu 8 at.% Sn depending on the form of interface was made in this work. The model sample is a diffusion pair of Cu and Cu 8 at.% Sn, which was thermally annealed at the temperature of 741°C. In this simulation was used the kinetic-thermodynamic approach, which included the calculation of diffusion flux, chemical potentials and Onzager coefficients for the Cu-Sn system phases Calculations of Gibbs potentials for pure components and a solid solution of the Cu-Sn system were carried out using CALPHAD technology.Simulation of diffusion evolution in the sample allows us to calculate the concentration profiles, the positions of the interphase boundaries, the width of the diffusion zone, to estimate the change in the roughness of the interphase boundary during the diffusion reaction. The following roughness parameters are calculated: arithmetical mean deviation of the assessed profile, root mean squared, maximum valley depth, maximum peak height, maximum height of the profile, the skewness and kurtosis. We investigated influence diffusion interaction on the change of roughness of the interphase boundary in model samples. As the size of the projections increases, namely maximum valley depth and maximum peak height, the thickness of the resulting diffusion zone increases. The diffusion annealing smoothes out the interphase limits and reduces their roughness (sample 2-4). In the future we plan to develop a two-dimensional model of diffusion interaction in the Cu-Sn pair in the presence of intermediate phase Cu-Sn in diffusion zone and the presence of initial interfaces with different roughness and structure.

Mathematical modeling of Stokes flow in petal shaped pipes

A theoretical model is developed to characterize fully developed laminar flow (Stokes flow) in idealized petal shaped pipes by regarding the pipe wall as a circular boundary having sinusoidal perturbation (or, equivalently, surface roughness). Built upon the method of perturbation, the model quantifies the effects of the relative roughness and wave number of the pipe boundary on the Stokes flow. Approximate solutions of the velocity field, pressure gradient, and static flow resistivity are obtained. The same approach together with the method of Fourier transform is used to deal with low Reynolds flow in pipes having other cross-sectional morphologies such as triangle and square. Results obtained from computational fluid dynamics simulations are used to validate the theoretical model predictions, with good agreement achieved. The presence of surface roughness causes periodic fluctuation and global offset of velocity distribution and enlarges both the pressure gradient and static flow resistivity in petal shaped pipes.

Modeling interface shear behavior of granular materials using micro-polar continuum approach

Recently, the authors have focused on the shear behavior of interface between granular soil body and very rough surface of moving bounding structure. For this purpose, they have used finite element method and a micro-polar elasto-plastic continuum model. They have shown that the boundary conditions assumed along the interface have strong influences on the soil behavior. While in the previous studies, only very rough bounding interfaces have been taken into account, the present investigation focuses on the rough, medium rough and relatively smooth interfaces. In this regard, plane monotonic shearing of an infinite extended narrow granular soil layer is simulated under constant vertical pressure and free dilatancy. The soil layer is located between two parallel rigid boundaries of different surface roughness values. Particular attention is paid to the effect of surface roughness of top and bottom boundaries on the shear behavior of granular soil layer. It is shown that the interaction between roughness of bounding structure surface and the rotation resistance of bounding grains can be modeled in a reasonable manner through considered Cosserat boundary conditions. The influence of surface roughness is investigated on the soil shear strength mobilized along the interface as well as on the location and evolution of shear localization formed within the layer. The obtained numerical results have been qualitatively compared with experimental observations as well as DEM simulations, and acceptable agreement is shown.

NUMERICAL MODELING OF BREAKING SOLITARY WAVE RUN UP IN SURF ZONE USING INCOMPRESSIBLE SMOOTHED PARTICLE HYDRODINAMICS (ISPH)

This paper presents a numerical model for simulating wave run-up on rough sloping surfaces. Incompressible smoothed particle hydrodynamics (ISPH) has been utilized, which is capable of efficient tracking of free surface deformation in a Lagrangian coordinate system. Many of the existing models have focused on inviscid wave run-up on a smooth surface, but few numerical models and especially experimental studies have investigated the effect of beach roughness on the run up. In the present study two methods have been deployed to study the effect of roughness on wave run up. In the first method, the mass unit force, which is a coefficient of the fluid viscosity, and is dependent on the roughness of the solid boundary, has been used. In the second method, mass unit force obtained from the wall functions was utilized to enforce the friction on the particles near the boundaries. The comparisons of the numerical simulations with the analytical solutions and experimental data confirmed the capability of the model in simulating wave propagation and wave breaking. It was also concluded that the effect of roughness on wave run up depends on both the roughness itself and the beach slope. The results also indicated small roughness effect on waves running up over steep slopes.