Sinusoidal Surface Research Articles

Surface stability in stress-assisted corrosion: a peridynamic investigation

In this paper, the stability of corrosion front of metallic material under tension is investigated by using a stress-assisted corrosion peridynamic model. The electrolyte diffusion tends to smoothen the corrosion front, while the mechanical loading tends to roughen the corrosion front and leads to higher stress concentration. We introduce a critical stress, below which the roughness of the corrosion front does not blow up, and the corrosion front is stable. Real-time surface roughness evolution is utilized to find the critical stress. Numerical results for both initially convex/concave sinusoidal and random surface contours show that corrosion without stress flattens the corrosion front, and when stress is higher than a certain value, the stress-assisted corrosion makes the corrosion front rougher. The effect of mechanochemical coefficient and applied electrical potential on the critical stress is analyzed numerically. It is found that the critical stress is less affected by the external voltage than by the mechanochemical coefficient. We also apply the model for corrosion in metal with initial holes or insulate impurities, revealing that hard impurities, such as dispersed oxides, can help maintain the stability of corrosion front, thus reducing the risk of stress-corrosion cracking.

Numerical Study of Transient Elastohydrodynamic Lubrication Subjected to Sinusoidal Dynamic Loads for Rough Contact Surfaces

Abstract The purpose of this paper is to study the behaviour of transient elastohydrodynamic contacts subjected to forced harmonic vibrations, including the effect of surface waviness for concentrated counterformal point contact under isothermal conditions. Profiles of pressure and film thickness are studied to reveal the combined effects of sinusoidal external load and surface roughness on the lubrication problem. The time-dependent Reynolds’ equation is solved using Newton–Raphson technique. The film thickness and pressure distribution are obtained at different snap shots of time by simultaneous solution of the Reynolds’ equation and film thickness equation including elastic deformation and surface waviness. It is concluded that the coupling effects of the transient sinusoidal external load and wavy surface would result in increase in modulations of the pressure and film thickness profile in comparison to the case where the smooth contact surfaces are subjected to sinusoidal external load.

Super-cooling effects and solidification of water inside a horizontal cylinder with a rough, sinusoidal surface shape

We examined how the outer shape of a cylindrical capsule, and the quantity of super-cooling, influenced the charging performance of a phase change material (water). The numerical method was validated using previous research and showed good agreement. Higher amplitude of roughness of the capsule shape was affirmed to affect solidification performance with or without super-cooling. The capsule with higher amplitude had an advantage in solidification performance, not only by increasing the heat transfer rate inside the capsule but also by reducing the quantity of super-cooling. Small super-cooling (∆TSmooth Surface = 4 °C) shows less impact (only 1%), while large super-cooling (∆TSmooth Surface = 8 °C) shows a prominent impact (10%) on the delay of solidification time. Typical results with no super-cooling and with super-cooling (∆TSmooth Surface = 8 °C) showed 10% and 15% shorter solidification time, respectively, for optimal shape with n = 6 compared to a matching smooth capsule (n = 0).

Wrinkling pattern formation with periodic nematic orientation: From egg cartons to corrugated surfaces.

Egg cartons, known as doubly sinusoidal surfaces, display a rich variety of saddles-cylinder-spherical patches organized with different spatial symmetries and connectivities. Egg carton surfaces, rich in functionalities, are observed in synthetic and biological materials, as well as across atomic and macroscopic scales. In this work we use the liquid crystal shape equationin the absence of elastic effects and normal stress jumps to predict and classify a family of uniaxial, equibiaxial, and biaxial egg cartons, according to the periodicities of the surface director field in nematic (N) and cholesteric (N*) liquid crystals under the presence of anisotropic surface tension (anchoring). Egg carton surface shape periodic solutions to the nonlinear and linearized liquid crystal shape equationspredict that the mean curvature is a linear function of the orthogonal (along the surface normal) splay and bend contributions. Mixtures of egg carton surfaces (uniaxial, equibiaxial, and biaxial) emerge according to the symmetries of the nonsingular director field, and the spatial distributions of the director escape into the third dimension; pure uniaxial egg cartons emerge when the director escape has linelike geometries and mixtures of egg cartons arise under source or sink orientation lattices. Orientation symmetry and permutation analysis are incorporated into a full curvature (Casorati, shape parameter, mean curvature, and Gaussian curvature) characterization. Under a fixed anchoring parameter, conditions for maximal nanoscale curvedness and microscale maximal shape gradient diversity are identified. The present results contribute to various pathways to surface pattern formation using intrinsic anisotropic interfacial tension.

Elucidating size effects on the yield strength of single-crystal Cu via the Richtmyer–Meshkov instability

Capturing the dynamic response of a material under high strain-rate deformation often demands challenging and time consuming experimental effort. While shock hydrodynamic simulation methods can aid in this area, a priori characterizations of the material strength under shock loading and spall failure are needed in order to parameterize constitutive models needed for these computational tools. Moreover, parameterizations of strain-rate-dependent strength models are needed to capture the full suite of Richtmyer–Meshkov instability (RMI) behavior of shock compressed metals, creating an unrealistic demand for these training data solely on experiments. Herein, we sweep a large range of geometric, crystallographic, and shock conditions within molecular dynamics (MD) simulations and demonstrate the breadth of RMI in Cu that can be captured from the atomic scale. Yield strength measurements from jetted and arrested material from a sinusoidal surface perturbation were quantified as YRMI=0.787±0.374 GPa, higher than strain-rate-independent models used in experimentally matched hydrodynamic simulations. Defect-free, single-crystal Cu samples used in MD will overestimate YRMI, but the drastic scale difference between experiment and MD is highlighted by high confidence neighborhood clustering predictions of RMI characterizations, yielding incorrect classifications.

Recent Advances in Glycyrrhetinic Acid-Functionalized Biomaterials for Liver Cancer-Targeting Therapy.

Liver cancer is one of the most common causes of cancer mortality worldwide. Chemotherapy and radiotherapy are the conventional therapies generally employed in patients with liver tumors. The major issue associated with the administration of chemotherapeutics is their high toxicity and lack of selectivity, leading to systemic toxicity that can be detrimental to the patient’s quality of life. An important approach to the development of original liver-targeted therapeutic products takes advantage of the employment of biologically active ligands able to bind specific receptors on the cytoplasmatic membranes of liver cells. In this perspective, glycyrrhetinic acid (GA), a pentacyclic triterpenoid present in roots and rhizomes of licorice, has been used as a ligand for targeting the liver due to the expression of GA receptors on the sinusoidal surface of mammalian hepatocytes, so it may be employed to modify drug delivery systems (DDSs) and obtain better liver or hepatocyte drug uptake and efficacy. In the current review, we focus on the most recent and interesting research advances in the development of GA-based hybrid compounds and DDSs developed for potential employment as efficacious therapeutic options for the treatment of hepatic cancer.

Statistical Characterization of the Angle of Arrival in an Underwater Channel Due to Scattering From the Sea Surface Modeled as Sum of Sinusoids

The objective of this work is the statistical characterization of the angle of arrival (AoA) at the receiver due to scattering from a random sea surface. The sea surface is represented using the sum of sinusoids (SoS) and modeled using the JOint North Sea WAve Project (JONSWAP) sea wave spectrum. The random behavior of potential scatterers along the sea surface, surface wave height, and their impact on the distribution of AoA is evaluated. For coherent scattering, initially, the scatterer distribution is computed for a single realization of the SoS, i.e., a sinusoidal surface. The result obtained is averaged to evaluate the characteristics of the ensemble-averaged SoS surface. For incoherent scattering, the acute randomness of the sea surface leads to every point along the SoS surface acting as a potential scatterer. The overall scattering for any given channel state would be an appropriate combination of coherent and incoherent components. A similar effect manifests itself in the distribution of the overall AoA. Further, the impact of factors such as acoustic signal frequency, wind speed, and the underwater (UW) channel geometry on the parameters of the overall AoA has been studied. The AoA model proposed in this work is general and widely applicable.

Construction of three-dimensional dynamic growth TGO (thermally grown oxide) model and stress simulation of 8YSZ thermal barrier coating

A three-dimensional cylindrical numerical simulation physical and geometric model of TBCs sinusoidal surface was established based on the ultrasonic C-scan results of 8YSZ coating after thermal cycling. The stress distribution and evolution law of the TGO/BC interface and sample center and edge affected by TGO growth were simulated by the finite-element method. The results show that the stress at the TGO/BC interfaces changes from compressive stress to tensile stress with the increase of the number of thermal cycles. The center of the interface is distributed with large radial, circumferential and axial tensile stresses, while the edge of the sample is affected by thermal mismatch, which shows that shear stresses are alternately distributed in the XZ direction. The tensile stress at the center and the shear stress at the edge are the main reasons for the failure of the core and edge flakes of the thermal barrier coating. The linear elasticity, creep effect, fatigue effect and stress accumulation effect of each layer of TBCs in each thermal cycle period are fully considered by the model, which reveals the reason why the core and edges of the thermal barrier coating are most likely to form cracks.

Investigations of heat transfer and flow characteristics of wall-bounded jets on a sinusoidal wavy surface

Turbulent wall-bounded jets are used in various practical engineering and industrial applications, including cooing of electronics devices, heat exchange systems, and cooling of gas turbine blades. The aim of the present computational study is to investigate an enhancement in heat transfer using different wall-bounded jets. Detailed discussions on the effect of the amplitude of the wavy surface and offset ratio are provided. The offset ratio varies from 0 to 5.0, where the value of zero represents a turbulent wall jet. The amplitude of sinusoidal wall is ranging from 0.1 to 0.8. The computed results are validated with the reported experimental results. The validation shows that among four turbulence models used, namely, renormalization group k-ϵ (RNG), realizable k-ϵ, standard k-ω and shear-stress transport k-ω (SST), the latter provides a good agreement with the experimental results. The position of the offset ratio and amplitude of the wavy surface affect the heat transfer enhancement. An enhanced heat transfer of 29.46% for turbulent wall jet is achieved for the amplitude of 0.8. The thermal-hydraulic performance (THP) increases for the wall jet by approximately 15% for the maximum amplitude considered. The axial position of the reattachment length and primary vortex centre increase with amplitude. Correlations are developed for the average Nusselt number, vortex centre, reattachment point, and thermal-hydraulic performance parameter with the amplitude of the sinusoidal wall.

The effect of sinusoidal fins’ amplitude on the thermo-hydraulic performance of a solar air heater

Solar energy exploitation is growing consistently, as it is the cheapest and most accessible amongst all forms of renewable energies. Increasing the performance of solar air heaters can aid in developing clean energy use and subsiding the greenhouse gas emissions in the world. This study, therefore, seeks to improve the thermo-hydraulic performance of solar air heaters using sinusoidal extended surfaces. The results show that the Reynolds number increment contributes to the enhancement of Nusselt number and thermo-hydraulic performance, while it does not affect the friction factor considerably. The highest value of the Nusselt number belongs to the case with the highest fin amplitude and wavy fins configuration by about 7 times higher value in comparison to the simple solar air heater. It is shown that the wavy configuration can render higher thermo-hydraulic performance than that of raccoon fins, by about 10 percent. The finned configurations feature better fluid flow mixing at the outlet and lower maximum and gradient of temperature on the absorber plate compared to those of simple and common solar air heaters.

Heat transfer of nanomaterial with involve of MHD through an enclosure

Numerical technique was employed to present the hybrid nano-powder behavior through a permeable enclosure with considering irreversibility. Various factors of MHD (magnetohydrodynamic) and permeability have been added in velocity equations and for applying the nanomaterial properties, correlations based of single phase technique were employed. CVFEM was incorporated to achieve the amounts of scalars. With measuring the velocity and temperature, terms of irreversibility have been calculated and reported in view of contours. Water has been mixed with hybrid nano-powders (Fe3O4+MWCNT). The buoyancy force helps the carrier fluid to move faster inside the container and if the zone has higher permeability, greater velocity of fluid can be obtained. But, magnetic field makes the speed of hybrid nano-powders to decrease. Increase of Da (Darcy number) and Ra (Rayleigh number) causes the temperature of sinusoidal surface to reduce about 25% and 57.1% while impose of greater Ha leads to decrease the cooling efficiency about 33.3%. Greater Da causes the eddy to become stronger about 75% while it decreases with augment of Ha about 50%. Sgen,th grows about 70.5% with rise of Ha (Hartmann number). Rising Ra and Da makes Nu (Nusselt number) to enhance about 207.98% and 21.09% while augmenting Ha leads to reduction of Nu about 23.87%. Be decreases with rising Da about 3.77% while it augments about 9.36% with imposing stronger Lorentz force.

Experiments on natural convection in a horizontal slot with surface corrugation

In order to better understand how critically the small surface irregularity affects the formation of thermal convection, natural convection in a horizontal slot with surface corrugation was examined experimentally at Rayleigh number based on the slot half-height below 300. The sinusoidal surface corrugations whose amplitude was 2.5% of the slot full-height and wavenumber was 0.5 - 2 was applied on the bottom surface while upper surface was kept smooth. Both walls were heated uniformly at different temperature. The results showed that surface corrugation promoted the occurrence of thermal convection significantly, that is, a pair of convection rolls whose wavelength was the same as that of corrugation was observed at Rayleigh number much lower than the critical one of smooth slot. Beyond critical Rayleigh number, on the other hand, the Rayleigh-Benard convection dominated the flow regardless of corrugation wavelength examined.

A vibration model of a rotor system with the sinusoidal waviness by using the non-Hertzian solution

The nonlinear contact forces and deformations between the balls and raceways can cause very complex vibration behaviours of rotor systems with the waviness in the support bearings. However, almost all previous works that used sinusoidal waviness took the Hertzian solution as the calculation method, which is not an accurate method based on Johnson’s formulation since the changes in the curvature at the sinusoidal contact surfaces. To overcome this issue, a new dynamic model of a rigid rotor system with the waviness in the support bearings is proposed. To provide a more accurate nonlinear contact force formulation for the sinusoidal waviness profile, the model used the Johnson’s extended Hertzian contact model to replace Hertzian contact model. This model can consider the time-varying curvature between the mating sinusoidal surfaces. The lubricating condition in the support bearing is also considered. A comparative study on the effects of Hertzian contact model, simplified Hertzian contact model, and Johnson's extended Hertzian contact model on the nonlinear vibrations of the rotor system is developed. The effects of the waviness amplitude and orders on the vibrations of the rotor system are discussed. The comparative simulations show that the proposed model can provide a more reasonable approach for predicting the vibrations of the rigid rotor system. Moreover, the simulations give that the nonlinear contact forces in the support bearings can greatly affect the system vibrations.

Effects of TGO growth on the stress distribution and evolution of three-dimensional cylindrical thermal barrier coatings based on finite element simulations

Based on the ultrasonic C-scan results of 8YSZ coatings after thermal cycles, three-dimensional cylindrical numerical simulations of the physical geometry model of the thermal barrier coating (TBC) sinusoidal surfaces were conducted with finite elements to estimate the stress distribution and evolution law of the top coat (TC)/bond coat (BC) interface, including the centre and edge of the specimen affected by the dynamic growth of the thermally grown oxide (TGO). The results show that when a layer of TGO is grown on the TC/BC interface, compressive stress is uniformly distributed on the TGO interface, and the stress value decreases as a function of the TGO layer thickness. When the thickness of the TGO exceeds a certain value, the compressive stress of all parts of the interface gradually changes to tensile stress; meanwhile, the edges of the model affected by the crest and trough effects of the wave are reflected in the radial and circumferential directions, especially along the axial direction, with alternating concentrated tensile and compressive stresses. TGO growth imposes a minor influence on the magnitude and distributions of the radial and circumferential stresses at the BC interface. The linear elasticity, creep, fatigue, and stress accumulation effects of each layer of TBCs in each thermal cycle were fully considered in this model. The model not only interprets the crest and trough effects of the TC/BC surface interface during the growth of TGO, but also interprets the effects of the core and edge of the cylindrical model, further revealing the reason for which the core and edge of the TBC will most likely form cracks.

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.

Evaluation of overall thermal performance for conjugate natural convection in a trapezoidal cavity with different surface corrugations

The effects of various surface corrugations and wall materials of the thick base wall of a trapezoidal cavity on conjugate natural convection have been examined in this study. Pinewood, plexiglas, dry concrete and glass fiber are considered as the materials of the solid bottom wall. In this cavity, both sidewalls are kept adiabatic, while the top wall is kept isothermally cold, and isothermal heating is applied at the bottom wall. Four types of regular surface corrugation, such as flat, rectangular, sinusoidal, and triangular-shaped corrugated surfaces are considered at the inner side of the base wall. The mathematical solutions of Navier-Stokes and thermal energy equations are obtained using Galerkin finite element method. Parametric simulation is carried out by varying Rayleigh number within laminar regime. The computed results are presented in terms of isotherm and streamline plots. The average Nusselt numbers along the solid-fluid interface, the average fluid temperature inside the cavity and the overall thermal performance ratio are also observed to assess the impact of wall materials and shapes of corrugation on convective heat transfer mechanism. From the viewpoint of overall heat transfer performance, the present results reveal that the surface material as well as the shape of the corrugation plays critically on the heat transfer enhancement of the trapezoidal cavity.

Electric Transverse Emissivity of Sinusoidal Surfaces Determined by a Differential Method: Comparison with Approximation of Geometric Optics

We present in this paper a numerical study of the validity limit of the optics geometrical approximation in comparison with a differential method which is established according to rigorous formalisms based on the electromagnetic theory. The precedent studies show that this method is adopted to the study of diffraction by periodic rough surfaces. For periods much larger than the wavelength, the mechanism is analog to what happens in a cavity where a ray is trapped and undergoes a large number of reflections. For gratings with a period much smaller than the wavelength, the roughness essentially behaves as a transition layer with a gradient of the optical index. Such a layer reduces the reflection there by increasing the absorption. The code has been implemented for TE polarization. We determine by the two methods such as differential method and the optics geometrical approximation the emissivity of gold and tungsten cylindrical surfaces with a sinusoidal profile, for a wavelength equal to 0.55 microns. The obtained results for a fixed height of the grating allowed us to delimit the validity domain of the optic geometrical approximation for the treated cases. The emissivity calculated by the differential method and that given on the basis of the homogenization theory are satisfactory when the period is much smaller than the wavelength.

Performance Assessment of Different Turbulence Models for a Dual Jet Flowing Over a Heated Sinusoidal Wavy Surface

Abstract An enhancement in heat transfer is the key objective in any thermal system where an efficient cooling is needed. This requirement becomes more important for turbulent flow. A turbulent dual jet is associated with entrainment and mixing processes in several applications. This article aims at enhancing the heat transfer rate by utilizing the wavy surface of a heated plate. Heat transfer and flow characteristics are studied using five low Reynolds-Averaged Navier–Stokes (RANS) turbulence models, namely, Yang and Shih k − ɛ (YS), Launder and Sharma k − ɛ (LS), realizable k − ɛ, renormalization group k − ɛ (RNG), and shear-stress transport k − ω (SST) models. The amplitude of the wavy surface is varied from 0.1 to 0.8 for the number of cycles fixed to 7. The Reynolds number and offset ratio are set to 15,000 and 3, respectively. An isothermal wall condition is used at the wavy wall. An experimental validation has been performed. An enhancement of 55.94% in heat transfer is achieved by the RNG k − ɛ model. Furthermore, it is noticed that the YS model fails to predict the flow separation as the amplitude of the sinusoidal wavy surface increases. However, the SST model reveals that the flow separates when the amplitude increases beyond 0.6. The thermal hydraulic performance (THP) is found to increase for the RNG model by approximately 13.9% for the maximum amplitude considered. As the profiles of the bottom walls change, various turbulence models predict different fluid flow characteristics.

Direct numerical simulation of flow-induced vibrations of a wavy cable at a low Reynolds number

Previous studies have revealed that fluid induced forces and wake structure of a cylinder can be significantly modified by varying the cross-section size along its axis. However, the fluid dynamic characteristics behavior of a flexible cable with a sinusoidal wavy surface remains unclear. The current study endeavors to present a systematic investigation of flow-induced vibrations (FIV) of an infinitely long wavy cable with different wave amplitude (A=0.1D to 0.3D) and a constant spanwise wavelength λ=4π, by using a highly resolved direct numerical simulation employing a high-order spectral/hp element method at a Reynolds number of 100, corresponding to laminar flow state. A tensioned beam model with a tension value can trigger a single wave is selected to govern the dynamics of the wavy cables. In addition, the structural dynamics are initialized from a standing wave. The present study focuses on the effects of the wave amplitude on the cable wake and the structural dynamic response, including the transverse displacement, wake pattern, vortex formation length, energy transfer, vortex shedding frequency and flow separation angle. Two completely different vibration modes are identified from the numerical cases studied, and hence the wavy cable are divided into control failure (A<0.2D) and optimal wavy cable (0.2D⩽A⩽0.3D) classes, respectively. It is also revealed that the counter-rotating vortices observed in the optimal wavy cables play an important role in stabilizing the shear layer and elongating the vortex formation length. Furthermore, the three-dimensional wake patterns of the wavy cable are mainly caused by the variations of flow separation angle along its spanwise direction. For the optimal wavy cables, the separation point is almost fixed along its spanwise direction while is variable for the control failure cases.

Speed Oscillations of a Vehicle Rolling on a Wavy Road

Every driver knows that his car is slowing down or accelerating when driving up or down, respectively. The same happens on uneven roads with plastic wave deformations, e.g., in front of traffic lights or on nonpaved desert roads. This paper investigates the resulting travel speed oscillations of a quarter car model rolling in contact on a sinusoidal and stochastic road surface. The nonlinear equations of motion of the vehicle road system leads to ill-conditioned differential-algebraic equations. They are solved introducing polar coordinates into the sinusoidal road model. Numerical simulations show the Sommerfeld effect, in which the vehicle becomes stuck before the resonance speed, exhibiting limit cycles of oscillating acceleration and speed, which bifurcate from one-periodic limit cycle to one that is double periodic. Analytical approximations are derived by means of nonlinear Fourier expansions. Extensions to more realistic road models by means of noise perturbation show limit flows as bundles of nonperiodic trajectories with periodic side limits. Vehicles with higher degrees of freedom become stuck before the first speed resonance, as well as in between further resonance speeds with strong vertical vibrations and longitudinal speed oscillations. They need more power supply in order to overcome the resonance peak. For small damping, the speeds after resonance are unstable. They migrate to lower or supercritical speeds of operation. Stability in mean is investigated.