Random Roughness Research Articles

Impact of Modelling Surface Roughness in an Arterial Stenosis

Arterial stenosis is a problem of immediate significance, as cardiovascular disease is the number one leading cause of death worldwide. Generally, the study of stenotic flow assumes a smooth, curved stenosis and artery. However, the real situation is unlikely to present an infinitely smooth-surfaced arterial stenosis. Here, the impact of surface roughness on the flow in an arterial stenosis was studied via a computational fluid dynamics analysis. A patient-specific geometry with a smooth surface was reconstructed, and a partially rough model was built by artificially adding random roughness only on the stenotic region of the smooth model. It was found that the flow was oscillatory downstream of the stenosis in the models. A slightly lower velocity near the wall and more oscillatory flows were observed due to the presence of the roughness in the stenotic region. However, the pressure distributions did not vary significantly between the smooth and rough models. The differences in the wall shear metrics were slight in the stenotic region and became larger in the downstream region of the models.

Surface Roughness Characterization and Inversion of Ultrasonic Grinding Parameters Based on Support Vector Machine

Abstract With surface roughness restricted by grinding parameters, the characterization of roughness parameters and the inversion of grinding parameters are of great significance for improving surface performance and realizing active surface machining. This research proposes a combination of statistical theory and data-driven analysis to solve the above problems. Pearson correlation analysis and multivariate variance analysis indicate the correlation characterization parameter set (CPS) consists of Sa, Vmp, Vvv, and Sz and that there are differences in the influence of grinding parameters on the parameters in CPS. Adjustment of support vector machine (SVM) core parameters makes it possible to construct expansion parameter set (EPS) optimal inversion models. By designing pseudo-surface random roughness parameters and grinding experiments, the reliability of inversion models is verified. The results show: (1) The better generalization of inversion model indicates skewness Ssk and kurtosis Sku in EPS have important implications for the optimal inversion model and surface characterization and (2) The data-driven model based on support vector machine provides machining guidance for obtaining the expected ultrasonic grinding surface.

Regression analysis of wetting characteristics for different random surface roughness of polydimethylsiloxane using sandpapers

This paper studies various wetting characteristics on different surfaces of Polydimethylsiloxane (PDMS) polymer. The random roughness of the surface is engineered by using sandpapers to introduce different order of hydrophobic properties to understand the temporal evolution of drying droplets. We develop statistical models to predict temporal evolution of the base diameter, height, surface, and contact angle of drying droplets with varying grit size or surface roughness. Five different robust polynomial regression models have been compared for the prediction of three dependent variables - base diameter, height, and surface of drying droplets for random rough surfaces. In a nutshell, we here identify the best statistical model to capture the dynamics of drying droplets on hydrophobic surfaces of random roughness characteristics.

Furthering extraction of torsional–flexural frequencies for thin-wall beams from the rocking motion of a two-wheel test vehicle

This paper proposes a furthering approach for extracting the first several flexural and torsional–flexural frequencies of thin-walled box girders from the residual contact response of a two-wheel test vehicle passing the bridge. Unlike most previous studies, the single-axle test vehicle is modeled as a two degree-of-freedom (DOF) system to account for the two wheels’ rocking motion, which relates to torsional–flexural motion of the beam. To start, a new theory for the mono-symmetric thin-walled beam subjected to a two-wheel moving vehicle is presented. The wheel contact response derived herein (which is free of vehicle frequencies) enables us in the first stance to remove the overshadowing effect on bridge frequencies brought by outstanding vehicle frequencies. The other concern in extracting the bridge frequencies is the noises posed by random pavement roughness, which is overcome through the use of the residual contact response generated by two identical connected vehicles. This paper furthers the existing ones in that the wheel response (i.e. the vehicle’s rocking motion) is utilized to extract the torsional–flexural frequencies of the bridge, making use of the linking action between the vehicle’s two wheels and the bridge’s cross section. The reliability of the theory and proposed technique is numerically validated for parameters such as damping of the vehicle and bridge, bridge/vehicle mass and frequency ratios, pavement roughness, and vehicle speed. It was confirmed that the proposed technique is capable of extracting the first several flexural and torsional–flexural frequencies of the thin-walled beam, including some higher conjugate modes, for all the cases studied herein.

Adhesive contacts of rough elliptical punches

We numerically study adhesive contact between an elastic half-space and a rigid punch with elliptic shape and superimposed roughness. Simulation is carried out using the Fast Fourier Transform-assisted Boundary Element Method for JKR-type adhesive contact. Both regular roughness (in form of a two-dimensional wave) and random fractal roughness are studied. It is confirmed that the main governing parameter determining different modes of adhesion is the Johnson parameter. For under-critical values of the Johnson parameter (large enough amplitude of roughness), the adhesive force increases with the normal force during compression stage, until it reaches a plateau. The evolution of the contact area during the pull-off shows different configurations depending on the roughness and the pre-loading. For large Johnson parameters the detachment begins from the ends of the major axis of the ellipse and propagates to the center of the contact. In a narrow interval near the critical Johnson parameter, the detachment can also start from the center of ellipse or from the ends of minor axis, if the pre-loading is not too large (so that the complete compact contact is not established). The maximum pull-off force (force of adhesion) is also a function of the Johnson parameter. Enhanced adhesion is observed when the maximum pull-off force is larger than that for a flat-ended punch. In experiment, steel flat indenters with different elliptical shapes are indented into soft rubber sheets. It is observed that the detachment begins from the edge of minor axis of ellipse in all cases, contrary to the results of numerical simulation and analytical theory.

Evaluation Method of Soil Surface Roughness after Ditching Operation Based on Wavelet Transform

Soil surface roughness (SSR) is an important parameter affecting surface hydrology, erosion, gas exchange and other processes. The surface roughness of the farmland environment is directly related to the tillage process. In order to accurately characterize the random roughness (RR) parameters of the surface after ditching, a three-dimensional (3D) digital model of the surface was obtained by laser scanning under the conditions of an indoor ditching test, and the influence of oriented roughness components formed by removing ridge characteristics on the RR of the surface was analyzed by introducing the wavelet processing method. For this reason, four groups of ditching depths and two types of surface conditions (whether the surface was agglomerated or not) were designed in this paper. By comparing the root mean squared height (RMSH) and correlation length (CL) data calculated before and after wavelet processing under each group of tests, it was concluded that the RMSH values of the four groups before and after wavelet processing all change more than 200%, the change amplitude reached 271.02% under the treatment of 12 cm ditching depth, meanwhile, the average CL value of five cross-sections under each group of ditching depths decreased by 1.43–2.28 times, which proves that the oriented roughness component formed by furrows and ridges has a significant influence on the calculation of RR. By further analyzing the roughness value differences of clods and pits in different directions and local areas before and after wavelet transform, it was shown that the wavelet transform can effectively remove the surface anisotropy characteristics formed in the tillage direction and provide a uniform treatment method for the evaluation of surface RR at different ditching depths.

Air, Helium and Water Leakage in Rubber O-ring Seals with Application to Syringes

We study the leakage of fluids (liquids or gases) in syringes with glass barrel, steel plunger and rubber O-ring stopper. The leakrate depends on the interfacial surface roughness and on the viscoelastic properties of the rubber. Random surface roughness is produced by sandblasting the rubber O-rings. We present a very simple theory for gas flow which takes into account both the diffusive and ballistic flow. The theory shows that the interfacial fluid flow (leakage) channels are so narrow that the gas flow is mainly ballistic (the so called Knudsen limit). We compare the leakrate obtained using air and helium. For barrels filled with water we observe no leakage even if leakage occurs for gases. We interpret this as resulting from capillary (Laplace pressure or surface energy) effects.

Characterizing THz Scattering Loss in Nano-Scale SOI Waveguides Exhibiting Stochastic Surface Roughness with Exponential Autocorrelation

Electromagnetic (EM) scattering may be a significant source of degradation in signal and power integrity of high-contrast silicon-on-insulator (SOI) nano-scale interconnects, such as opto-electronic or optical interconnects operating at 100 s of THz where two-dimensional (2D) analytical models of dielectric slab waveguides are often used to approximate scattering loss. In this work, a formulation is presented to relate the scattering (propagation) loss to the scattering parameters (S-parameters) for the smooth waveguide; the results are correlated with results from the finite-difference time-domain (FDTD) method in 2D space. We propose a normalization factor to the previous 2D analytical formulation for the stochastic scattering loss based on physical parameters of waveguides exhibiting random surface roughness under the exponential autocorrelation function (ACF), and validate the results by comparing against numerical experiments via the 2D FDTD method, through simulation of hundreds of rough waveguides; additionally, results are compared to other 2D analytical and previous 3D experimental results. The FDTD environment is described and validated by comparing results of the smooth waveguide against analytical solutions for wave impedance, propagation constant, and S-parameters. Results show that the FDTD model is in agreement with the analytical solution for the smooth waveguide and is a reasonable approximation of the stochastic scattering loss for the rough waveguide.

Turbulent boundary layer flow over regularly and irregularly arranged truncated cone surfaces

Aiming to study the rough-wall turbulent boundary layer structure over differently arranged roughness elements, an experimental study was conducted on flows with regular and random roughness. Varying planform densities of truncated cone roughness elements in a square staggered pattern were investigated. The same planform densities were also investigated in random arrangements. Velocity statistics were measured via two-component laser Doppler velocimetry and stereoscopic particle image velocimetry. Friction velocity, thickness, roughness length and zero-plane displacement, determined from spatially averaged flow statistics, showed only minor differences between the regular and random arrangements at the same density. Recent a priori morphometric and statistical drag prediction methods were evaluated against experimentally determined roughness length. Observed differences between regular and random surface flow parameters were due to the presence of secondary flows which manifest as high-momentum pathways and low-momentum pathways in the streamwise velocity. Contrary to expectation, these secondary flows were present over the random surfaces and not discernible over the regular surfaces. Previously identified streamwise-coherent spanwise roughness heterogeneity does not seem to be present, suggesting that such roughness heterogeneity is not necessary to sustain secondary flows. Evidence suggests that the observed secondary flows were initiated at the front edge of the roughness and sustained over irregular roughness. Due to the secondary flows, local turbulent boundary layer profiles do not scale with local wall shear stress but appear to scale with local turbulent shear stress above the roughness canopy. Additionally, quadrant analysis shows distinct changes in the populations of ejection and sweep events.

Single potential step chronoamperometry for EC′ reaction at rough electrodes: Theory and experiment

• Rough electrode shows anomalously enhanced current response. • Intermediate time regime has anomalous power-law relationship. • Enhancement is observed both in transient and steady-state time regimes. • Steady-state response is dependent on rate constant and RMS roughness. • Diffusion and diffusion-kinetics lengths govern roughness influence. The theory is developed for the chronoamperometry of first order homogeneous catalytic chemical reaction coupled with electron transfer ( EC ′ ) on a rough electrode. We obtained a solution for the diffusion problem on an arbitrary and random topography of the electrode to generalize Danckwerts’ equation. Derived equation of random electrode roughness is used for developing theory of (statistically isotropic) self-affine fractal on limited length scales. The characteristics fractal morphological parameters, viz. D H , ℓ and ℓ τ , are varied for detailed analysis of current transient. The current transient shows anomalously enhanced response for a rough electrode. Our theoretical results explain both transient and steady-state behavior of the current response under the influence of roughness. The anomalous enhancement of steady-state current is only observed when RMS roughness is greater than bulk reaction–diffusion length ( L k ). Finally, the theory is compared and validated with experimental data of ferrocyanide and ascorbic acid coupled system on rough Pt electrodes.

ON RANDOM EXPECTED VALUES VARIATIONS OF TRIBOLOGY PARAMETERS IN HUMAN HIP JOINT SURFACES

This paper presents recent progress in the knowledge concerning the stochastic theory of bio- hydrodynamic lubrication with a phospholipids bilayer. On the basis of experimental measurements and analytical solutions, the research concerns the determination of the random expectancy values of load carrying capacity, the friction coefficient, and synovial fluid dynamic variations. After numerous measurements, it directly follows that the random density function of the gap height in the human joint usually indicates a disorderly increases and decreases in the height. Such irregular gap height variations have an important influence on the random synovial bio-fluid dynamic viscosity. This finally leads to the friction coefficient and cartilage wear changes of cooperating bio- surfaces. The main topic of this paper relates to the expectancy values of the tribology parameters localized inside the variable stochastic standard deviation intervals of the human joint gap height. The results obtained finally indicate the influence of the random roughness and growth of living biological cartilage surfaces on the expectancy values of the synovial fluid dynamic viscosity, load carrying capacity and friction forces in human hip joints.

A Stochastic Rockfall Model Related to Random Ground Roughness Based on Three-Dimensional Discontinuous Deformation Analysis

The use of feasible 3-D numerical methods has become essential for addressing problems related to rockfall hazard. Although several models with various degrees of complexity are available, certain trajectories and impact dynamics related to some model inputs could fall in the rockfall observations area but are rarely calibrated against reflecting its range, especially the lateral deviations. A major difficulty exists in the lack of simulating the apparent randomness during the impact-rebound process leading to both ground roughness and block irregularities. The model presented here is based on three-dimensional discontinuous deformation analysis (3-D DDA). Despite similarities to previous simulations using 3-D DDA, the model presented here incorporates several novel concepts: (1) ground roughness is represented as a random change of slope angle by height perturbation at a grid point in DEM terrain; (2) block irregularities are modelled directly using polyhedron data; (3) a scaled velocity restitution relationship is introduced to consider incident velocity and its angle. Lateral deviations of rebound velocity, both direction and value, at impact are similarly accounted for by perturbing the ground orientation laterally, thus inducing scatter of run-out directions. With these features, the model is capable to describe the stochastic rockfall dynamics. In this study, 3-D DDA was then conducted to investigate the dynamic behavior of the rockfall and examine the role of sphericity of the rock block travelling on bench slopes with different ground roughness levels. Parametric analyses were carried out in terms of cumulative distribution function (CDF) to investigate for spatial distribution (both runout distance and lateral displacement), velocity and jumping height. The effects of block shape and ground roughness revealed by these factors were discussed. It suggests that ground roughness amplifies the randomness and plays important roles on the dynamic behavior of the system; irregularity from block sphericity will further amplify the randomness especially when the size of the rock is relatively small compared to the roughness level. Both irregularities should be taken into consideration in simulating rockfall problems. Further calibration of the new model against a range of field datasets is essential.

Strength Model of Backfill-Rock Irregular Interface Based on Fractal Theory

In the two-step open stope subsequent filling mining method, the determination of the strength model for the backfill-rock interface is of great engineering significance to study the stress distribution and stability of the backfill in the stope. Considering the deformation mechanism of the interface and the interaction of the asperities, a strength model for backfill-rock with irregular interface has been proposed based on fractal theory, which can effectively describe the shear mechanical behavior of interfaces with random roughness. The model has been compared with the two-body mechanistic model and good agreements have been achieved. The results show that the shear strength of the interface changes non-linearly with increasing fractal dimension D, when the fractal dimension D is in the range of 1∼1.12. The complete relationship between the interface shear strength and the fractal dimension is given, as the fractal dimension increases from 1 to 2 based on the presented model. At the same time, the quantitative relationship between the interface and backfill friction angles during direct shear testing is analyzed.

Numerical Simulation of Flow Through Microchannels with Random Roughness

The aim of the study is to determine the effect of a randomly generated rough surface on the laminar flow of a fluid in a microchannel. Two-dimensional axially symmetric microchannels with a circular cross-section in the range of Reynolds number Re = 100-1700 were considered. Flow numerical simulations were performed using the Ansys / Fluent software.

Impact of random and periodic surface roughness on P- and L-band radiometry

L-band passive microwave remote sensing is currently considered a robust technique for global monitoring of soil moisture. However, soil roughness complicates the relationship between brightness temperature and soil moisture, with current soil moisture retrieval algorithms typically assuming a constant roughness parameter globally, leading to a potential degradation in retrieval accuracy. This current investigation established a tower-based experiment site in Victoria, Australia. P-band (~40-cm wavelength/0.75 GHz) was compared with L-band (~21-cm wavelength/1.41 GHz) over random and periodic soil surfaces to determine if there is an improvement in brightness temperature simulation and soil moisture retrieval accuracy for bare soil conditions, due to reduced roughness impact when using a longer wavelength. The results showed that P-band was less impacted by random and periodic roughness than L-band, evidenced by more comparable statistics across different roughness conditions. The roughness effect from smooth surfaces (e.g., 0.8-cm root-mean-square height and 11.1-cm correlation length) could be potentially ignored at both P- and L-band with satisfactory simulation and retrieval performance. However, for rougher soil (e.g., 1.6-cm root-mean-square height and 6.8-cm correlation length), the roughness impact needed to be accounted for at both P- and L-band, with P-band observations showing less impact than L-band. Moreover, a sinusoidal soil surface with 10-cm amplitude and 80-cm period substantially impacted the brightness temperature simulation and soil moisture retrieval at both P- and L-band, which could not be fully accounted for using the SMOS and SMAP default roughness parameters. However, when retrieving roughness parameters along with soil moisture, the ubRMSE at P-band over periodic soil was improved to a similar level (0.01‐0.02 m3/m3) as that of smooth flat soil (0.01 m3/m3), while L-band showed higher ubRMSE over the periodic soil (0.03‐0.04 m3/m3) than over smooth flat soil (0.01 m3/m3). Accordingly, periodic roughness effects were reduced by using observations at P-band.

Application of biomachining on copper for a minichannel heat exchanger

Studies have established a random surface roughness found on the surface of copper after immersion in an Acidithiobacillus ferooxidans-containing culture medium during the biomachining process. In this study, a heat exchanger system was built by employing the biomachining process to manufacture the copper-based minichannel parts for the system. This study investigates the effect of the surface roughness of the minichannel obtained from the biomachining process upon the pressure drop and heat transfer of a fluid flowing through the system. These parameters were also compared to another system possessing minichannel parts with a lower surface roughness made by conventional milling. The result shows that the system containing the biomachined minichannels tends to increase the pressure drop and heat transfer rate of the fluid flow compared to the milled example due to the effect of the roughness average (Ra), which consistently occurred with flow rates (Q) of 32 and 64 mL/min. A novel finding revealed in this study is that the biomachining method can contribute to fluidic channel and heat transfer applications, due to its naturally unique surface roughness.

Evaluating the Dynamic Response of the Bridge-Vehicle System considering Random Road Roughness Based on the Moment Method

The bridge-vehicle interaction (BVI) system vibration is caused by the vehicles passing through the bridge. The road roughness has a great impact on the system vibration. In this regard, poor road roughness is known to affect the comfort of the vehicle crossing the bridge and aggravate the fatigue damage of the bridge. Road roughness is usually regarded as a random process in numerical calculation. To fully consider the influence of road roughness randomness on the response of the BVI system, a random BVI model was established. Thereafter, the random process of road roughness was expressed by Karhunen–Loeve expansion (KLE), after which the moment method was used to calculate the maximum probability value of the BVI system response. The proposed method has higher accuracy and efficiency than the Monte Carlo simulation (MCS) calculation method. Subsequently, the influences of vehicle speed, roughness grade, and bridge span on the impact factor (IMF) were analyzed. The results show that the road roughness grade has a greater impact on the bridge IMF than the bridge span and vehicle speed.

Numerical study of laminar forced convection heat transfer in a rough mini-channel fabricated by Additive Manufacturing

This study investigates laminar convective heat transfer of water flowing in a mini-channel with a rough surface fabricated by Laser-based Powder Bed Fusion (L-PBF) technology. A Gaussian model was used for generating random roughness, and then the three-dimensional numerical simulation was performed in ANSYS-Fluent 19.1. The numerical results indicated a more than double increase in the Nusselt number of rough channels than that of smooth ones with a marginal pressure drop penalty compared to smooth channels, showing the potential benefits of using rough channels fabricated by L-PBF for heat transfer applications.

Control of variable rate system of a rotary tiller based on real-time measurement of soil surface roughness

It is required to employ variable rate (VR) tillage because the soil is not uniform and immense spatial variability is available inside the agricultural fields. A conventional rotary tiller was instrumented to instantly vary the tillage intensity based on the tilled soil surface roughness measurement. The random roughness (RR) was estimated as the standard deviation of surface peaks and depressions which were measured using an infrared sensor. The tilling intensity was adjusted based on rising off and lowering down the tiller soil shield that was controlled by a hydraulic actuator. The soil shield could be adjusted from 0° to 80° in 20° increments with an average response time of 0.26 s. The field tests were performed in order to recognize whether the VR tiller can create predefined soil roughness which was assigned in three ranges of 0.5 ≤ RR1 ≤ 1.5, 1.5 < RR2 ≤ 2.5, and 2.5 < RR3 ≤ 3.5 cm. As a reference, a pin-type profiler was utilized to measure the soil roughness created by the VR tiller. The results showed the soil shield tended to be closer when finer predefined roughness was requested. There were no significant differences in RR over the experimental subplots which received similar adjustments, verifying the tiller performance. The results also showed that different surface roughness could be statistically separated when they were created by the tiller at different travel speeds of 2.6, 3.5, and 4.8 km/h (p < 0.01), because the soil shield tends to be closer when the travel speed increases. The tiller developed in this study could perform VR tillage across the field with an overall success of 83.3%.

Modal analysis and dynamic shimmy behavior of vehicle–road system

To analyze the influence of the road roughness excitation on vehicle shimmy, a 12 degrees-of-freedom dynamic model of vehicle–road system is developed. The Hopf bifurcation theory is used to study the system stability. On this basis, the natural frequency and modal properties of the vehicle system are elaborated. It can be found that the roll mode plays a crucial role in the vehicle stability. Then, the dynamic shimmy behavior exposed to the sinusoidal and random road roughness excitations is investigated with the help of the modal analysis and the largest Lyapunov exponent. Furthermore, the numerical results are verified through the measurement results, and the influence of the front wheel track on vehicle shimmy is also examined. The results show that the decrease of the front wheel track is an effective way to attenuate vehicle shimmy for different road roughness excitations.