Sinusoidal Surface Research Articles

Effect of surface morphology on the deformation mechanism of Cu nanocrystal under cyclic loading at different temperatures: Molecular dynamics simulations

Micro-electromechanical systems (MEMS) are often subject to mechanical vibration or temperature, the fatigue reliability of small metal parts is a potential problem for long-term operational stability. Since the MEMS packaging is performed at a high temperature of about 600 K. Therefore, in this paper, the deformation mechanisms of copper nano-single crystals with different surface morphologies under cyclic loading were investigated by molecular dynamics calculations at room temperature (300 K) and high temperature (600 K) to provide a theoretical basis for the design of copper nanomaterials. The results show that the plastic deformation modes of the models with different surface morphologies during cyclic loading are mainly Shockley partial dislocations slipping along {111}. In contrast, the fatigue damage modes are extrusion intrusion induced by high shear strain. Compared with the surface containing a pore, the damage caused by the circular and sharp recesses through the surface is more serious. The causes of stress concentration during deformation are mainly the entanglement of Shockley partial dislocations and the generation of Lomer-Corell lock fixed dislocations. The locations of these stress concentrations will produce pores in the subsequent deformation. In addition, since periodic interfaces do not cause particularly pronounced stress concentrations and shear strain concentrations on the surface compared to other models with defects, and the resulting shear strain concentration bands are split by shear strain bands in the other direction, extrusion intrusion is prevented. Therefore, at room temperature, the model with a one-dimensional sinusoidal surface has the strongest resistance to fatigue damage, while at high temperatures, the model with a two-dimensional sinusoidal surface has the optimal resistance to fatigue damage. This provides a basis for the design of NEMS/MEMS working at high temperatures.

An Innovative Mapping Technique for Sinusoidal Frequency-Selective Surfaces in Shielding Applications

An Innovative Mapping Technique for Sinusoidal Frequency-Selective Surfaces in Shielding Applications

Experimental and numerical investigations of forced convection impingement heat transfer on plate-fin heat sinks using three different electronic cooling fans

An experimental and numerical study was conducted for plate-fin heat sinks subjected to impinging air jets produced by electronic cooling fans. One axial and two different radial fans were used and their distance to the heat sink was varied. The aluminum heat sinks had either plain fins or fins with sinusoidal surface structures, were heated by heat sources either distributed over the entire base plate or concentrated in the center. In total, temperature measurements for 264 settings were performed, and numerical simulations were carried out for 19 selected cases. The results show that the axial fan outperforms the radial fans for the investigated fan distances, that the structured fins lead to lower base plate temperatures and that significant asymmetries in the heat sink temperature distribution can occur in certain cases. The numerical simulations are used to gain a better understanding of the trends observed in the measurements. Particularly, the impact of the velocity profiles at the fan outlets and the influence of certain geometrical details of the fan design on the heat flux distributions and the airflow into the fin channels are explored. The results highlight practical problems that need to be considered when optimizing heat sink-fan combinations.

Effects of steepness on turbulent heat transfer over sinusoidal rough surfaces

We conducted a direct numerical simulation (DNS) study to investigate the impact of surface undulation steepness on rough wall turbulent heat transfer. The flow geometry was turbulent open-channel flow over three-dimensional sinusoidal rough surfaces. To examine the effects of steepness, we systematically varied the streamwise and spanwise wavelengths of the sinusoidal roughness while keeping the roughness height constant. The friction Reynolds number ranged from 180 to 600, and we considered a passive scalar with the fluid Prandtl number was 0.7, assuming air flow conditions. In the fully rough regime, the velocity roughness function is expressed as a function of the inner-scaled equivalent sand grain roughness ks+ independent of steepness, whereas the steeper surfaces with shorter wavelengths result in larger temperature roughness functions at the same ks+ value. Analysis of the physical mechanisms that increases the roughness function shows that the pressure drag primarily contributes to the increase in the velocity roughness function, while the temperature roughness function is mainly augmented by the roughness-induced wall heat transfer term, correlating with the steepness of the surface undulations. It is also suggested that the effective slope, which quantifies the steepness of rough surfaces, could improve the predictive accuracy of existing correlations for the temperature roughness function.

RCEMIP-II: mock-Walker simulations as phase II of the radiative–convective equilibrium model intercomparison project

Abstract. The radiative–convective equilibrium (RCE) model intercomparison project (RCEMIP) leveraged the simplicity of RCE to focus attention on moist convective processes and their interactions with radiation and circulation across a wide range of model types including cloud-resolving models (CRMs), general circulation models (GCMs), single-column models, global cloud-resolving models, and large-eddy simulations. While several robust results emerged across the spectrum of models that participated in the first phase of RCEMIP (RCEMIP-I), two points that stand out are (1) the strikingly large diversity in simulated climate states and (2) the strong imprint of convective self-aggregation on the climate state. However, the lack of consensus in the structure of self-aggregation and its response to warming is a barrier to understanding. Gaining a deeper understanding of convective aggregation and tropical climate will require reducing the degrees of freedom with which convection can vary. Therefore, we propose phase II of RCEMIP (RCEMIP-II) that utilizes a prescribed sinusoidal sea surface temperature (SST) pattern to provide a constraint on the structure of convection and move one critical step up the model hierarchy. This so-called “mock-Walker” configuration generates features that resemble observed tropical circulations. The specification of the mock-Walker protocol for RCEMIP-II is described, along with example results from one CRM and one GCM. RCEMIP-II will consist of five required simulations: three simulations with the same three mean SSTs as in RCEMIP-I but with an SST gradient and two additional simulations at one of the mean SSTs with different values of the SST gradients. We also test the sensitivity to the imposed SST gradient and the domain size. Under weak SST gradients, unforced self-aggregation emerges across the entire domain, similar to what was found in RCEMIP. As the SST gradient increases, the convective region narrows and is more confined to the warmest SSTs. At warmer mean SSTs and stronger SST gradients, low-frequency variability in the convective aggregation emerges, suggesting that simulations of at least 200 d may be needed to achieve robust equilibrium statistics in this configuration. Simulations with different domain sizes generally have similar mean statistics and convective structures, depending on the value of the SST gradient. The prescribed SST boundary condition is the only difference in the set-up between RCEMIP-II and RCEMIP-I, which enables comparison between the two; however, we also welcome participation in RCEMIP-II from models that did not participate in RCEMIP-I.

An analytical model for daily‐periodic slope winds. Part 2: Solutions

AbstractThis article presents an analytical model for the diurnal cycle of slope‐normal profiles of potential temperature and wind speed characterizing thermally driven slope winds, generated by a daily‐periodic surface energy budget. The model extends the solution proposed by Zardi and Serafin, originally formulated for a pure sinusoidal surface forcing temperature. To account for the asymmetric features characterizing the daytime and nighttime phases, a full Fourier series expansion is derived, the coefficients and phases of which are prescribed from the surface energy budget driven by the daily‐periodic radiation model described in Part 1 of the present work. The model is applicable for any slope angle () and orientation, at any latitude and elevation (up to 2500 m), and for all seasons. Despite some inherent limitations, the most remarkable being the absence of moist processes and latent heat fluxes, the model captures most key features of daily‐periodic slope wind systems, in particular the asymmetry between daytime and nighttime phases. Moreover, it allows exploration of the sensitivity of these flows to the various factors concurring in their development, and offers a basis for more realistic analytical solutions for slope winds.

Influence of activation energy and variable thermal conductivity on magneto-convective nonlinear thermo-radiative Casson nanofluid containing motile microorganisms over a sinusoidal surface

The activation energy of convective-radiative nanoliquids with sinusoidal walls has garnered significant academic interest in recent years. This focus arises due to the pivotal applications of nanoparticles in thermal engineering, industrial processes, and medical sciences. This article investigates the magnetohydrodynamic heat transfer characteristics of Casson nanofluids containing microorganisms influenced by an oscillatory surface. The study incorporates temperature-dependent viscosity and utilizes Buongiorno’s mathematical model to account for nonlinear thermal radiation, Brownian motion, and thermophoretic effects from using nanomaterials in Casson fluids. These effects enhance thermal conductivity, improving the heat transportation phenomenon while considering gyrotactic microorganism density distributions. The boundary layer flow problem is formulated using partial differential equations and associated boundary conditions, subsequently numerically simulated using the bvp4c function. The investigation explores the thermal behavior of nanoparticles in the presence of bioconvection phenomena, Lorentz force, chemical reactions, and activation energy. As a result, this model addresses variable thermal conductivity and bioconvection aspects in Casson nanofluids over a sinusoidal surface. Numerically computed results for the Nusselt number, motile density, and Sherwood number provide insights into several essential features. The findings reveal that an increase in the Casson fluid parameter correlates with a decreased velocity profile. The assumptions of variable thermal conductivity and temperature-dependent viscosity prove more effective in raising the temperature of nanoparticles. The nanoparticle concentration profile rises noticeably for smaller Schmidt number Sc values when the activation energy parameter is higher than larger Sc values. Additionally, the presence of microorganisms in Casson nanofluids leads to increased temperatures due to an elevation in the bioconvection Rayleigh number. Moreover, heightened oscillating frequency parameters decrease nanoparticle concentration and microorganism density. Including activation energy and oscillating frequency parameters further enhances the understanding of nanoparticle concentration and microorganism density dynamics, offering valuable contributions to theoretical research and practical applications across multiple interdisciplinary fields.

On the adhesion of sinusoidal surfaces

In this work, we study the adhesive loading and unloading of a one-dimensional sinusoidal surface and use design of experiments to provide for response surface maps for the work of adhesion and the interaction length, which depend only on Johnson’s α parameter and the Maugis parameter μ. As showcased by some example, these can be used to replace the fine scale roughness by a cohesive zone model. Besides that, we provide ranges of α and μ in which the most common analytical solutions present accurate results. Finally, we characterize the presence of instabilities in the loading and unloading profiles.

Modeling of nanofluid thermophysical treatment through a permeable container under the impact of MHD

In this innovative study, a unique approach was engaged to simulate the flow characteristics of nanofluid inside a tank featuring a surface subjected to uniform flux. The testing fluid for this investigation was fabricated by incorporating alumina powders with varying shapes into water. The derivation of the final equations involved the application of Darcy’s law and the formulation of the stream function. The container experienced the combined efficacy of both the Lorentz force and gravity forces. The incorporation of additives resulted in a significant enhancement of the Nusselt number (Nu), demonstrating an increase of 19.8% and 40.28%, contingent on the magnitude of the Hartmann number (Ha). Moreover, an elevation in the shape factor led to a notable rise in Nu by 14%. Remarkably, as the Ha increased, there was a substantial reduction in the cooling rate by 51.33%. Furthermore, in the absence of the Ha, an escalation in the Rayleigh number (Ra) caused Nu to surge by 65.8%. This study holds paramount importance as it introduces a novel technique for simulating nanofluid flow with a sinusoidal surface, providing valuable insights into the complex interplay of forces within the container. The utilization of varying shapes of alumina powders adds a layer of sophistication to the experimentation, making this investigation a noteworthy contribution to the existing body of knowledge. The findings not only enhance our understanding of heat transfer dynamics but also offer practical implications for applications involving nanofluids in containers with nonuniform surfaces subjected to heat flux.

Planar oscillation-enabled deterministic magnetorheological micro-polishing

Micro-optics are attracting ever-increasing attention in advanced optical systems owing to their merits of high optical performance and high structure compactness. Although deterministic polishing is crucial for obtaining optically qualified components, the decreased micro-optic feature size imposes significant challenges on the polishing process. To proceed the post-processing technique for micro-optics, we developed a novel magnetorheological micro-polishing (μMRP) method, which features a non-contact and deterministic removal of the workpiece materials. An electromagnetic polishing tool for stiffening the MR slurry was specially designed to tightly focus the high-gradient magnetic field within a small region around the tip, thereby enabling the material removal to occur at the micro-scale. The pulse-width modulation (PWM) control strategy for the excitation currents could continuously refresh the MR slurry in the polishing, as well as precisely control the material removal. Moreover, a planar dual-axial oscillation was employed to move the tool to generate relative motions between the abrasives and workpieces for removing the materials. In practice, smooth Gaussian-shape footprints with full width at half-maximum (FWHM) around hundreds of micrometers were achieved, and the influence of the working gap, oscillation frequency, and duty ratio on the material removal was further investigated. Finally, the deterministic material removal capability was demonstrated by generating a sinusoidal micro-grid surface with an amplitude of 80 nm and a spatial period of 600 μm. The surface roughness and form error were about Sa = 1.027 nm and 6.5 nm (RMS), demonstrating that the developed μMRP is promising for figuring micro-optics.

Atmospheric flow simulation over stationary waves with various steepness using WRF-LES

We investigated the capability of the Weather Research and Forecasting (WRF) model to perform large-eddy simulations (LESs) of the structure of the marine atmospheric boundary layer and turbulence exchange between the sea surface and the atmosphere. The WRF-LES model results were compared to results from Sullivan (2008) [1] for two cases: flow over a flat surface and over an idealized stationary sinusoidal surface. We also investigated the sensitivity of the WRF-LES model in simulating turbulence through the marine atmosphere under a range of horizontal grid spacings and wave steepnesses. All simulations were performed in a conventionally neutral atmosphere with a geostrophic wind of 5 m s−1, aligned with the direction of wave propagation. The simulated wind vertical profiles from the WRF-LES model exhibit similar behavior to those of Sullivan (2008) over both wavy and flat surfaces, but the differences in Sullivan’s vertical wind profiles for the two cases are considerably larger in comparison to those derived from WRF-LES. Furthermore, spectral analysis clearly shows the effect of horizontal grid spacing. The impact of wave steepness on turbulence distribution is clearly noticeable in the vertical profiles of resolved velocity variances and covariances. The impact is largest close to the surface, but it is important throughout the bulk of the boundary layer.

Investigating journal bearing characteristics incorporating variable viscosity, couple-stress lubricant, slip-velocity, magnetic fluid, and sinusoidal surface-texturing

This study contributes to the practical understanding of journal bearings by comprehensively exploring the impact of variable viscosity, sinusoidal surface texturing, slip velocity, magnetic fluid, and couple-stress lubricants on the pressure distribution. Utilising the Barus variable viscosity formula, incorporating ferrofluid as a magnetic lubricant, and employing the Finite Difference Method for numerical analysis, this research reveals insights such as increased load-carrying capacity and pressure distribution in textured bearings. The results indicate that a small distance ratio and high magnetic parameters increase magnetic pressure. Textured bearings increased the load-carrying capacity and pressure distribution by approximately 246 % and 165 %, respectively. In addition, the magnetic, couple-stress, piezo-viscosity, and maximal slip parameters increase the load. Reducing the bearing attitude angle improves the load-carrying capacity. The magnetic parameter increases the attitude angle, as does the slip parameter. High values of the couple-stress parameter reduce friction, particularly in the presence of a textured surface, and the presence of a textured surface amplifies this effect. The study highlights the influence of magnetic, couple-stress, piezo-viscosity, and slip parameters on the bearing's performance, offering valuable insights for optimising journal bearing designs and operations in various engineering applications.

Stress concentration factor estimation for corroded steel plates using the surface gradient method

Pitting corrosion occurs in steel components as a stress-accumulating surface irregularity that is vulnerable to fatigue crack nucleation. In this study, stress distribution in sinusoidal surfaces was investigated to devise an estimation method for the stress concentration factor (SCF) fluctuations of corroded steel. An SCF equation for sinusoidal surfaces was developed from empirical data based on three parameters: wavelength, thickness, and position. For corroded surfaces, successive numerical differentiations can be performed on each point to determine the sinusoidal surface having a point sharing the same gradient information. Notably, the SCFs of corresponding points are comparable; SCF estimation is made feasible for irregular surfaces through sinusoidal surfaces. In two-dimensional sections, maximum error was below 5% at pits and 15% for the surface. In three-dimensional models, maximum error was below 20% at pits for wide-ranging corroded specimens. Therefore, the proposed method effectively estimates SCF for identifying areas at risk of fatigue cracking.

Nonlinear adaptive fault-tolerant control for full-car active suspension with velocity measurement errors and full-state constraints

This work concentrates on the vibration suppression problem for full-car active suspension in the presence of multiple actuator faults, velocity measurement errors, full-state constraints and external disturbances, simultaneously. Herein, a novel nonlinear fault-tolerant control (FTC) strategy is developed by the aid of the online estimation of fault parameters, and it can accommodate multiple actuator faults without the information obtained from costly fault detection and isolation mechanism. Then, the violation of full-state constraints can be prevented by introducing the log-type barrier Lyapunov function (BLF) into the adaptive backstepping method, and the problems related to velocity measurement errors of car body and external disturbances are handled under the robust control framework, so the complexity caused by state constraints, actuator faults and velocity measurement errors can thus be taken into consideration. The stability analysis is subsequently conducted with the assistance of Lyapunov theory, the boundness of all signals is confirmed, and the non-violation of the displacement and velocity constraints for car body motions is guaranteed. In the end, the performance of the proposed controller is evaluated under sinusoidal and random road surfaces. Importantly, the simulation results are presented to indicate the validity and advantages of the developed approach despite the existence of multiple actuator faults, velocity measurement errors and external disturbances.

Accumulation and depletion of E. coli in surfaces mediated by curvature.

Can topography be used to control bacteria accumulation? We address this question in the model system of smooth-swimming and run-and-tumble Escherichia coli swimming near a sinusoidal surface, and show that the accumulation of bacteria is determined by the characteristic curvature of the surface. For low curvatures, cells swim along the surface due to steric alignment and are ejected from the surface when they reach the peak of the sinusoid. Increasing curvature enhances this effect and reduces the density of bacteria in the curved surface. However, for curvatures larger than κ^{*}≈0.25µm^{-1}, bacteria become trapped in the valleys, where they can remain for long periods of time. Minimal simulations considering only steric interactions with the surface reproduce these results and give insights into the physical mechanisms defining the critical curvature, which is found to scale with the inverse of the bacterial length. We show that for curvatures larger than κ^{*}, the otherwise stable alignment with the wall becomes unstable while the stable orientation is now perpendicular to the wall, thus predicting accurately the onset of trapping at the valleys.

Research on precision linear displacement measurement method based on closed loop phase-shift control of single alternating light field

Abstract A high-precision linear displacement measurement method based on the digital phase shift of a single light source is proposed. In this method, the light intensity of a four-channel sinusoidal transmission surface with a 90° difference in the spatial phase is modulated by a single channel alternating light, and four-channel alternating light intensity signal with the same time phase can be obtained. Two channels of standing wave signals with a time difference of 90° are obtained through micro-control digital phase shift processing. After differential amplification, an electric travelling wave signal containing position information of measurement object is synthesized by these two standing wave signals. By measuring the phase difference between the travelling wave and the reference signal, the high precision linear displacement can be measured. The principle of displacement measurement based on the modulation of a single-alternating light field and the principle of digital phase-shift of micro-control are introduced in detail. The feasibility of the method is verified through experiments. Finally, the sensor is optimized by analyzing the causes of error, and the measurement accuracy of ±0.2 μm is achieved within the 100 mm range with a 0.6 mm grating period.

Characteristics Analysis of Influence of Multiple Parameters of Mixed Sea Waves on Delay–Doppler Map in Global Navigation Satellite System Reflectometry

Feature capture and recognition of sea wave components in radar systems especially in global navigation satellite system reflectometry (GNSS-R) using signal processing approaches or computer simulative methods has become a research hotspot in recent years. At the same time, parameter inversion of marine phenomena from the discovered characteristics plays a significant role in monitoring and forewarning the different components of sea waves. This paper aims to investigate the impact of multiple parameters, such as the wind speed, directionality variable, wave amplitude, wave length, and directions of sea wave components, on the delay waveform of the delay–Doppler map (DDM). Two types of wind waves and the 2-D sinusoidal sea surface are chosen to be analyzed. By comparing and analyzing the discrepancy of delay waveforms under different conditions, it can be concluded that the increased MSS which arises from the increase in the roughness of the sea surface can lead to the difference in the peak value or trial edges exhibited in delay waveforms. The values of delay waveforms at zero chip along the increasing direction of long-crest wind waves exhibit the periodic spikes shape, which is the opposite of the short-crest wind waves, and the fluctuation of the periodic profiles decreases with the increase in the amplitude of waves. The results and conclusions can provide a foundation for the parameter inversion, tracking, and early warning of anomalous formations of waves in bistatic radar configuration.

Importance of sign conventions on analytical solutions to the wave-induced cyclic response of a poro-elastic seabed

This paper discusses the influence of different sign conventions for strains and stresses, i.e. the solid mechanics sign convention and the soil mechanics sign convention, on the form of governing partial differential equations (the static equilibrium equations and the continuity equation) used to describe the wave-induced cyclic response of a poro-elastic seabed due to propagation of a sinusoidal surface water-wave. Some selected analytical solutions, obtained by different authors and published in specialist literature in the form of complex functions describing the wave-induced pore-fluid pressure, effective normal stress and shear stress oscillations in the seabed, have been analysed and compared with each other mainly with respect to different sign conventions for stains and stresses and also with regard to different orientations of the positive vertical axis of the two-dimensional coordinate system and different directions of surface water-wave propagation. The performed analyses of the analytical solutions has indicated many inaccuracies, or even evident errors and exemplary mistakes of wrong-signed values of basic wave-induced response parameters (the shear stress in particular), thereby disqualifying these solutions and their final equations from practical engineering applications. Most of the mistakes found in the literature must be linked to authors’ lack of understanding and consistency in an uniform application of a certain sign convention for strains and stresses in the soil matrix at both stages of mathematical formulation of the governing problem and correct interpretation of equations of the final analytical solution. The present paper, based mostly on a thorough literature review, ought to draw attention and arouse interest among coastal scientists and engineers in proper identification and use of the existing analytical solutions to the wave-induced cyclic seabed response – solutions which differ very often in the applied sign convention for stresses in the soil matrix.

Three dimensional interface normal prediction for Volume-of-Fluid method using artificial neural network

In the numerical simulations of multi-phase flow using Volume-of-Fluid (VOF) method, the calculation of the interface normal is a crucial point. In this paper, a machine learning method is used to develop an artificial neural network (ANN) model to make more accurate prediction of the local normal vector from neighboring volume fractions. Spherical surfaces with different radii are intersected with a structural background grid to generate 84328 groups of data: 3×3×3 neighboring volume fractions are used as input, and normal vector as output. Using 90% data as training dataset, the ANN model is well trained by optimizing the number of hidden layers and the number of neurons on each layer. Using the remaining 10% data, normal predictions are made using ANN-VOF and the most used YOUNG and HEIGHT-FUNCTION methods. The RMSE of the ANN-VOF/YOUNG/ HEIGHT-FUNCTION methods are 0.008/0.022/0.045 respectively. In the reconstruction of a sinusoidal surface, the MSE of the ANN-VOF/YOUNG/ HEIGHT-FUNCTION methods are 0.008/0.018/0.041. It is demonstrated that the ANN-VOF method has better performance for interface normal prediction. The proposed method has a simple computational logic and does not need to deal with complex geometric topology, which lays the foundation for application in other more complex grids.

Study on the influence of pore water pressure on shear mechanical properties and fracture surface morphology of sandstone

To further investigate the weakening effect of pore water pressure on intact rock mechanics properties and characteristics of fracture surface after failure, direct shear tests of sandstone were conducted under different pore pressure. A 3D scanner was employed to digitize the morphology of the post-shear fracture surface. The variogram function was applied to quantify the anisotropic characteristics of post-shear fracture surface. The relationship between deformation during shear failure of intact rock and quantitative parameters of fracture surface after shear failure was initially established. It can be found that amplitudes of the sinusoidal surface determine the maximum value of variogram, and period affect lag distance that reach the maximum value of variogram. Test results revealed that the increase of pore pressure has obvious weakening effect on shear strength and deformation of rock. Moreover, the increase of pore pressure makes the shear fracture surface flatter. It can be obtained that both Sillmax and Rangemax are positively related to shear strain, but negatively related to normal strain.