Sinusoidal Surface Research Articles

Study on sinusoidal lapping micro-structured surface by abrasive stone with staggered abrasive particles

In order to manufacture structured surfaces, firstly, the abrasive stone model with staggered abrasive particles is established with mathematical methods. Secondly, the motion of abrasive particles on the abrasive stone is designed. Finally, the surface morphology of the workpiece is simulated. The simulated workpiece morphology under different machining parameters is compared, and the influence of different machining parameters on the workpiece surface morphology is obtained. The results indicate that the microstructured surface can be lapped by using the abrasive stone of staggered abrasive particles. As the amplitude and frequency of the abrasive stone increase, the number of protrusions increases, and the area of individual protrusions decreases.

Behavior of elastohydrodynamic lubricating film point contact problems in the unsteady state of reciprocating motion

Purpose In this study a numerical analysis of the elastohydrodynamic lubrication point contact problem in the unsteady state of reciprocating motion is presented. The effects of frequency, stroke length and load on film thickness and pressure variation during one operating cycle are discussed. The general tribological behavior of elastohydrodynamic lubrication during reciprocating motion is explained. Design/methodology/approach The system of equations of Reynolds, film thickness considering surface deformation and load balance equations are solved using the Newton-Raphson technique with the Gauss-Seidel iteration method. Numerical solutions were performed with a sinusoidal contact surface velocity to simulate reciprocating elastohydrodynamics. The methodology is validated using historical experimental measurements/observations and numerical predictions from other researchers. Findings The numerical results showed that the change in oil film during a stroke is controlled by both wedge and squeeze effects. When the surface velocity is zero at the stroke end, the squeeze effect is most noticeable. As the frequency increases, the general trend of central and minimum film thickness increases. With the same entraining speed but different stroke lengths, the properties of the oil film differ from one another, with an increase in stroke length leading to a reduction in film thickness. Finally, the numerical results showed that the overall film thickness decreases with increasing load. Originality/value General tribological behaviors of elastohydrodynamic lubricating point contact, represented by pressure and film thickness variations over time and profiles, are analyzed under reciprocating motion during one working cycle to show the effects of frequency, stroke length and applied load.

Drag reduction effect by sinusoidal superhydrophobic surface in turbulent channel flow

Drag reduction effect by sinusoidal superhydrophobic surface in turbulent channel flow

Effects of sinusoidal mid-spatial frequency surface errors on optical transfer function

Effects of sinusoidal mid-spatial frequency surface errors on optical transfer function

CONTACT OF AN ANISOTROPIC LAYER WITH A RIGID PERIODICALLY CONVEX SURFACE

By using Fourier integral transforms applied to integral equations, exact solutions are constructed for spatial problems of full contact of a transversely isotropic layer with a rigid doubly periodic sinusoidal surface. One layer face is subjected to sliding or rigid support, and isotropy planes are parallel to the layer faces. It is established that the full contact over the whole layer face is always possible except the degenerate case of isotropic incompressible layer with one face rigidly fixed. It is indicated that the full contact is also realizable for the case of isotropy planes perpendicular to the layer faces when one face is subjected to sliding support. The problems of partial contact are also considered for the transversely isotropic layer with a rigid surface relief of which is described by a doubly periodic function in the form of a system of paraboloids of revolution. On the base of the theory of generalized functions, the problems are reduced to integral equations kernels of which do not contain integrals. The complication of the problems of partial contact is that the contact domain is a priori unknown that leads us to additional inequalities and nonlinearities. With the help of the B.A. Galanov method, the system of the integral equation and inequality can be reduced to only one nonlinear integral equation for which the modified Newton numerical method can be applied. The exact solutions for the full contact are usable to check calculations. Contact domains and contact pressures are determined. Mechanical characteristics are calculated for the percolation process of initially discrete contact spots in the strengthening contact. Minimal settlements of the paraboloids of revolution are calculated to begin or complete percolation for an anisotropic material.

MULTISCALE SIMULATION OF HYDRODYNAMIC STEP BEARING WITH ULTRA-LOW CLEARANCE INVOLVING SURFACE ROUGHNESS

The numerical calculation was carried out for the multiscale hydrodynamic step bearing with ultra-low clearance and nanoscale surface roughness based on the newly developed multiscale approach. The moving surface was assumed as perfectly smooth and the stationary surface was imposed with the sinusoidal surface roughness. Due to the surface roughness, locally the physically adsorbed boundary layer may be only present, while in other areas, the sandwich films consisting of both the adsorbed boundary layers and the intermediate continuum fluid film may be present. In this bearing, the fluid film may be locally severely squeezed so that the local film pressure is very high. In this circumstance, the influences of the film pressure on both the film viscosity and density were considered. The results show that with the increase of the surface roughness, the hydrodynamic pressure and carried load of the bearing are very significantly increased especially for a stronger fluid-bearing surface interaction; the fluid piezo-viscous effect becomes stronger with the increases of both the surface roughness and the fluid-bearing surface interaction strength.

Modification of Richtmyer–Meshkov instabilities via layered explosive charge design

In this numerical study, we investigate the effects of layered high explosive (HE) charge design on Richtmyer–Meshkov instability (RMI) in metal plates with sinusoidal surface features. The detonation wave from the HE induces a shock in the metal target that subsequently interacts with the surface features; this results in vortex formation and ultimately RMI. We seek to modify RMI by altering the detonation wave characteristics. The modification is investigated in a twofold manner: first, by varying the initial design of the unconfined surface of the target and second, by varying the charge design and composition. Within a limited scope of this design space, a wide variety of behaviors related to RMI growth are observed. Mechanistic actions, including exaggerated front curvature, behind these modifications are proposed. Charge designs, which modify RMI the most for a select target design, are then presented.

The role of interface geometry and appendages on the mesoscale mechanics of the skin.

The skin is the largest organ in the human body and serves various functions, including mechanical protection and mechanosensation. Yet, even though skin's biomechanics are attributed to two main layers-epidermis and dermis-computational models have often treated this tissue as a thin homogeneous material or, when considering multiple layers, have ignored the most prominent heterogeneities of skin seen at the mesoscale. Here, we create finite element models of representative volume elements (RVEs) of skin, including the three-dimensional variation of the interface between the epidermis and dermis as well as considering the presence of hair follicles. The sinusoidal interface, which approximates the anatomical features known as Rete ridges, does not affect the homogenized mechanical response of the RVE but contributes to stress concentration, particularly at the valleys of the Rete ridges. The stress profile is three-dimensional due to the skin's anisotropy, leading to high-stress bands connecting the valleys of the Rete ridges through one type of saddle point. The peaks of the Rete ridges and the other class of saddle points of the sinusoidal surface form a second set of low-stress bands under equi-biaxial loading. Another prominent feature of the heterogeneous stress pattern is a switch in the stress jump across the interface, which becomes lower with respect to the flat interface at increasing deformations. These features are seen in both tension and shear loading. The RVE with the hair follicle showed strains concentrating at the epidermis adjacent to the hair follicle, the epithelial tissue surrounding the hair right below the epidermis, and the bulb or base region of the hair follicle. The regions of strain concentration near the hair follicle in equi-biaxial and shear loading align with the presence of distinct mechanoreceptors in the skin, except for the bulb or base region. This study highlights the importance of skin heterogeneities, particularly its potential mechanophysiological role in the sense of touch and the prevention of skin delamination.

Freeform surfaces manufacturing of optical glass by ultrasonic vibration-assisted slow tool servo turning

The optical glass is a typical difficult-to-cut material for single-point diamond turning because of its high hardness and low fracture toughness. The application of high-frequency vibration-assisted technology can make it a machining method for processing optical glass materials. However, due to the lack of understanding of intermittent cutting characteristics, it is still a challenge to achieve a high-precision and crack-free freeform surface on hard-brittle glasses. Therefore, the freeform surfaces of optical glasses are processed by ultrasonic vibration-assisted slow tool servo turning (UVSTS). The crack evaluating model of UVSTS turning is established based on the theory of specific cutting energy to predict fracture formation at all cutting position points of the freeform surface. Furthermore, the mechanisms of fracture initiation are analyzed and discussed deeply according to different factors. Finally, the bidirectional sinusoidal surface as a representative freeform surface is successfully fabricated on N-BK7 glass materials. The surface roughness can reach 1 nm Sa only by UVSTS turning without requiring any subsequent processing (including grinding or polishing). The research findings show the UVSTS turning technology can be used as a new machining method with high precision and high efficiency to replace traditional grinding and polishing technology for processing the optical elements of the freeform surface of glass materials.

Effects of self-cleaning technique and nanofluid cooling on performance of photovoltaic solar unit employing sinusoidal surfaces

The urgent need for electricity generation for both commercial and residential uses can be satisfied by photovoltaic units, but the serious flaws of these units arise from the negative effects of environmental factors like dust, shadow, radiation, and wind on their performance. The present study examines how PV panels operate under dusty conditions, using ANSYS FLUENT software and focusing on steady-state and laminar conditions. This study aims to numerically examine a three-dimensional (3-D) photovoltaic thermal (PV-T) unit with sinusoidal walls (PV-T-SW). The testing fluids examined in current paper are Al2O3-H2O nanofluid and H2O. Under the same initial and boundary conditions, three configurations were tested: a PV module, a straight channel PV-T unit, and the PV-T-SW, which are numerically compared and examined. An important element that declines the power generation efficiency is the deposition of dust on photovoltaic panels. The key novelty of the current study is that it provides a numerical modeling of the impact of dust in the presence and absence of a self-cleaning coating on a photovoltaic thermal system, as well as the optimal cooling mode and configuration. First, suitable temperature management systems are critical for achieving high-efficiency solar photovoltaics, and in heat exchange devices, the employment of corrugated structures has proven to be a helpful strategy because of the benefits of extended surface area. Finally, the electrical (ηele) and thermal (ηth) efficiency are assessed by taking into account the optical properties of dust deposition and hydrophobic coating. The factors evaluated are the impacts of varying nanofluid concentration, inlet flow Reynolds number (ranging from 500 to 1500), wavy channel amplitude, and wavelengths on cooling performance. The findings revealed that using 4 % water-aluminum oxide as an operating fluid instead of H2O improved the coefficients of heat transfer in the channel by 15.7 %. In addition, at the next step, when water-aluminum oxide was used as a coolant and the sinusoidal channel was examined with different geometrical characteristics, it was discovered that the 9 mm wavelength and 0.8 mm amplitude channel, in comparison to the simple form of the system, had superior heat transfer performance. Furthermore, the obtained data indicate that the ηele decreased by 40 % as the dust deposition happens, and it was discovered that the coating reduced that negative effect on the glass used to cover solar cells. Because of rising environmental issues and the expense of energy, thermal control of sources of energy that are renewable is becoming more and more important. The findings of this investigation can be used for future PV cooling innovation unit development and optimization.

Unlocking geothermal energy for sustainable greenhouse farming in arid regions: a remote-sensed assessment in Egypt’s New Delta

This study introduces a novel approach for assessing geothermal potential in arid regions, specifically Egypt’s New Delta Agriculture Mega Project area. The challenge of limited sub-soil temperature profile data was addressed by integrating Global Land Data Assimilation System (GLDAS) weather data. Using the Earth-to-Air Heat Exchanger (EAHE) model, the extracted air and sub-soil temperature profiles the potential for geothermal energy production was estimated. We modeled the annual sinusoidal soil surface periodic heating pattern by utilizing GLDAS ambient air temperature (AAT) and land surface temperature (LST). Using either AAT or LST yielded a Root-Mean-Square Error (RSME) of 0.2°C. The generated sub-soil profiles for the New Delta region showed a temperature variation of no more than 1.5°C at a 4-m depth, making it an optimal depth for EAHE installation. One-pipe EAHE demonstrated a cooling/heating capacity ranging from 400 W (cooling) to −300 W (heating). The study highlights the New Delta region’s strong geothermal potential for greenhouse cooling and heating, underlining its suitability as a sustainable energy source in arid areas. It also offers a practical guide for the EAHE application and it emphasizes the global potential for geothermal energy exploration, using innovative GLDAS data to expand sub-soil temperature profile accessibility.

Complex Fourier Surfaces by Superposition of Multiple Gratings on Azobenzene Thin Films

AbstractDiffractive optical elements (DOE) are integral components for lightweight and ultra‐thin optical elements due to their ability to manipulate light efficiently and accurately. However, conventional DOEs are static and cannot be altered after fabrication, which hinders their adaptability to changing requirements. To overcome this limitation, the potential of surface patterning on azobenzene thin films to fabricate reconfigurable DOEs is investigated. Using holographic lithography, surface topographies with sinusoidal surface relief gratings (SRG) are created and the superposition of up to 80 SRGs with high accuracy and minimal information loss in subsequent inscriptions is demonstrated. This is enabled by a surface patterning tool combining holographic lithography and digital holographic microscopy. Reconfigurable and adaptive optical elements can improve the efficiency of optical coupling and increase the sensitivity and selectivity of sensors, especially in applications such as near‐eye displays and plasmonic sensors. These results demonstrate the ability to create complex azobenzene‐based DOEs for advanced photonic applications, where the ability to alter optical elements is of high importance.

Slow motion of a sphere near a sinusoidal surface

Particle motion near non-plane surfaces can exhibit intricate hydrodynamics, making it an attractive tool for manipulating particles in microfluidic devices. To understand the underlying physics, this work investigates the Stokesian dynamics of a sphere near a sinusoidal surface, using a combination of perturbation analysis and boundary element simulation. The Lorentz reciprocal theorem is employed to solve the particle mobility near a small-amplitude surface. Compared with a plane wall, the curved topography induces additional translation and rotation velocity components, with the direction depending on the location of the sphere and the wavelength of the surface. At a fixed distance from the surface, the longitudinal and vertical mobilities of the sphere are strongly affected by the wavelength and amplitude of the surface, whereas its transverse mobility is only mildly influenced. When a sphere settles perpendicular to a sinusoidal surface, the far-field hydrodynamic effect drives the particle towards the local hill, while the near-field effect attracts the particle to the valley. These results provide valuable insights into the particle motion near surfaces with complex geometry.

Effect of laser preparation strategy on surface wettability and tribological properties under starved lubrication

The preparation strategy determines the microstructure of surface textures, influencing the lubrication properties of surface. This paper proposes three laser scanning strategies aimed at achieving a sinusoidal textured surface, and discussed the evolution of surface structure and chemical composition. The subsequent investigation focuses on the impact of the transition in surface wettability on friction performance. The findings reveal that the ridge structures enhance surface anti-wear properties but concurrently elevates the friction coefficient. However, the oil cover preparation method prevents the formation of ridges and increases the water contact angle to 138°. The shift in wettability is determined by the combined effects of structure and the adsorption of organic compounds. Furthermore, the hydrophobic surface exhibits superior tribological properties in friction tests.

The Computed Sinusoid

Hepatic sinusoids are lined with thin endothelial cells with transcellular pores, termed fenestrations. These fenestrations are open channels that connect the sinusoidal lumen to the underlying Space of Disse (SoD) and the hepatocytes of the liver parenchyma. Fenestrations range from 0.05 to 0.35 µm in diameter and cover 5–15% of the sinusoidal endothelial surface area, depending on their location along the sinusoids. The direct measurement of hemodynamic parameters, such as pressure and flow velocity, remains challenging within the narrow sinusoids. Such knowledge would increase our understanding of the physiology of the hepatic niche and possible implications in aging or diseases in which fenestrations are reduced or lost. Few simulations of liver blood flow focus on the level of the individual sinusoid, and fewer still include the transcellular pores (fenestrations) of the sinusoidal endothelium. Furthermore, none have included (i) a porosity gradient along the sinusoid wall, modeled using through-all pores rather than a porous medium, (ii) the presence of the SoD, or (iii) lymphatic drainage. Herein, computed fluid dynamics (CFD) simulations were performed using a numerical model with relevant anatomical characteristics (length, diameter, porosity, inlet/outlet pressure, and lymphatic outflow from the portal region of the SoD). The greatest contribution to luminal velocity magnitude and pressure was the overall shape of the vessel. Divergent-radius models yielded velocity magnitudes 1.5–2 times higher than constant-radius models, and pressures were 5–8% lower in the divergent-radius models compared to the constant-radius models. Porosity only modestly contributed to luminal pressure. The luminal velocity magnitude was largely unaffected by the presence or absence of lymphatic drainage. Velocity magnitudes through fenestrations were lower in higher-porosity models (20%) vs. lower-porosity models (5%) across all models (0.4–0.55-fold lower). Velocity magnitudes through the space of Disse were increased 3–4 times via the addition of lymphatic drainage to the models, while pressures were decreased by 6–12%. The flow velocity in the SoD was modified via differences in porosity, while the flow velocity in the lumens of the sinusoids was largely unaffected. The overall shape of the vessel is the single most important factor in the pressure flow behavior of the sinusoidal lumen. The flow rate over hepatocytes and the SoD is modestly affected by the distribution of porosity along the sinusoid and greatly affected by the lymphatic drainage, parameters that would be of interest for modeling the exchange of blood with the hepatic parenchyma.

Surrogate‐based optimization for active drag reduction of turbulent boundary layer flows

AbstractTwo surrogate‐based optimization strategies using support vector regression (SVR) and Gaussian process regression (GPR) as surrogates are investigated to guide the design of actuation parameters for active drag reduction techniques in turbulent boundary layer flows encountered at civil airplanes in cruise flight and high‐speed trains. As an approximation, the turbulent flow over a flat plate subjected to spanwise traveling transversal sinusoidal surface waves is simulated by wall‐resolved large‐eddy simulations (LESs). These simulation data are used to model the dependence of the objective drag reduction on the actuation parameters, that is, the optimization variables. In this work, the previous purely exploitative approach of SVR‐based ridgeline optimization is extended to GPR‐based Bayesian optimization to further automate the simulation‐driven tuning of the actuation parameters.

Enhancing heat-driven acoustic characteristics of standing wave thermoacoustic engines by using corrugated stack

The present work considers the heat-driven acoustic characteristics and dynamic thermal-fluid flow fields of a standing-wave thermoacoustic engine (SWTAE) by using sinusoidally shaped corrugated stack surfaces. 3-D numerical SWTAE models are developed and validated, aiming to examine the heat-driven acoustic effects caused by different corrugation amplitudes and wave-lengths of the sinusoidal stack surface. The results demonstrate that corrugated-shaped stack channels increase the contact area of the working gas in the stack area, and the thermos-acoustic conversion is more amplified. Compared to the SWTAE with uniform-shaped stack, the corrugated-shaped stack exhibit enhanced acoustic power output while maintaining a constant acoustic oscillation frequency. With the corrugation peak and wave-length of the sinusoidal stack are 2 and 0.2 mm, respectively, the amplitude and acoustic power of the acoustic pressure oscillations increase by 10.12% and 17.31%, respectively, in comparison with that of the conventional SWTAE. However, when the corrugation peak exceeds 0.4 mm, stronger nonlinear acoustics and flow effects are observed in the stack channels, leading to a reduction in the heat-driven acoustic power output, and thermo-acoustics energy conversion efficiency. The developed model highlights the effects of the corrugated-shaped stack on enhancing acoustic power output and thermo-acoustic conversion efficiency.

Analysis and compensation for the dominant tool error in ultra-precision diamond ball-end milling

Diamond ball-end milling is an enabling technology to fabricate complex curved surfaces with a nanometer level roughness. However, limited by the errors of tool manufacturing and installation, the cutting edge profile of a single-bladed diamond milling tool cannot form an ideal sphere crown in rotation, which will significantly worsen the machining accuracy. Although a titled milling method and a tool error reduction method based on milling-test have been proposed to improve the machining accuracy, a complete analysis of the effects of multiple tool errors on the machining accuracy have not been performed. Therefore, the present work contributes an analytical model to accurately calculate the tool rotation profile under various position and orientation errors. The results reveal that the horizontal off-center error of tool cutting edge is the dominant error among all the tool errors. According to the results, a novel high precision identification process is developed to evaluate the horizontal off-center error in view of the cutting-mark, and subsequently a tool center shift method is proposed to compensate for such error. Finally, experiments on millimeter scale spherical surface, micro sphere array and micro sinusoidal surface confirm that the proposed tool error compensation method can significantly improve the form accuracy. The average form errors (PV) of three test surfaces are reduced from 2.29 μm, 0.90 μm and 0.88 μm to 0.61 μm, 0.28 μm and 0.18 μm, respectively.

Numerical modeling of Van der Waals interaction between a spherical particle and rough surfaces with different planar asperity distributions

Roughness and microstructures at the micro and the nano scales have significant influence on the van der Waals forces between the adhering particles and the surface. Previous theoretical models may treat the particle-asperity interactions in an unprecise manner, which may result in inaccurate estimations of the van der Waals force especially when the sphere is much larger than the asperities. In this paper, we proposed a numerical model to calculate the van der Waals force between a spherical particle and a rough surface with periodic nanostructures. The 3D sinusoidal rough surfaces are simplified with their asperities modelled as hemispheres, and the contact is within the Derjaguin-Muller-Toporov (DMT) regime. The proposed model calculates the van der Waals forces between the sphere and all the asperities in the contact surface, which will provide more accurate estimations of the van der Waals force. Moreover, the effect of the planar distribution of asperities on the van der Waals forces is considered, which includes the cases when asperities have close-packed hexagonal lattice, square, and hollow-centered hexagonal packing distributions. The theoretical results calculated using the proposed model are verified by comparing the results to previous theoretical and experimental results and the comparison shows that the proposed numerical model predicts the van der Waals force accurately.

Laser repairing of FeCoCrNiV high-entropy alloy and its mechanical and cutting characteristics

High-entropy alloys (HEAs) are promising structural and functional materials owing to their superior mechanical and chemical properties. High surface quality and good machinability are essential for micro-machining high-end precision equipment. Here, laser repairing (LR) was firstly employed to eliminate surface defects and improve the machinability of FeCoCrNiV. After LR, the microstructures and mechanical properties of FeCoCrNiV were investigated. The results show that the surface morphology and chemical composition uniformity of FeCoCrNiV were significantly improved after LR, in which the high melting-point V-rich precipitates concentrated on the original surface were homogeneously distributed throughout the substrate. The surface hardness decreased from 10.5 to 4.5 GPa due to the growth of grains, and the hardness distribution became more homogeneous after LR, providing the opportunity to improve its machinability. In ultrasonic vibration diamond turning tests, the machined surface quality, tool wear, and cutting chips indicated that the laser-repaired material exhibited superior machinability. A sinusoidal free-form surface with high surface quality was then constructed by ultrasonic vibration-assisted diamond turning on the laser-repaired surface. This study provides a method to repair surface defects of HEAs and improve their machinability, which is beneficial to their practical applications.