Investigation Of Surface Roughness Effects Research Articles

Investigation of surface roughness effects on the dynamic performance of electromagnetic nano-resonators

Here, we expose the influence of surface roughness on the dynamics of electromagnetic nano-resonators. To this end, the continuum field equations of an electromechanical nano-resonator subjected to an external magnetic flux are formulated. The developed model considers surface integrity, including surface roughness, waviness, and altered layer. Also, the influence of residual stresses of the extreme surfaces of the resonator is incorporated in the proposed model. It was revealed that the surface roughness significantly tailors the dynamic stability of the resonator, as the voltage that onsets the pull-in instability of the resonator decreases as the surface roughness increases, which thus indicates the necessity of particular calibrations of nano-resonators for surface roughness. To investigate the problem and the effect of factors such as magnetic field intensity, roughness, and beam surface thickness on the pull-in voltage, we have performed an analysis using the Taguchi method and analysis of variance. The results show that the intensity of the magnetic field has the most significant effect on pull-in voltage. Also, the more accurate results show on the resonance frequency; with the increase of the input voltage to the beam, the impact of increasing the intensity of the magnetic field and other factors increases. The rest of the paper proposes a linear and non-linear model to express the pull-in voltage according to the investigated factors.

Numerical investigation of surface roughness effects on non-equilibrium flow in expansion section of rocket nozzle

To further understand the non-equilibrium flow characteristics in a rocket nozzle, we have to consider the rough wall surface caused by nozzle ablation, and explore the relative influence of surface roughness on the flow field, composition field, and wall heat transfer in the nozzle. In this study, first, the data of the inner wall morphology of the real nozzle is obtained through measurement experiments. The parameters used to characterize the inner wall morphology of the expansion section of the nozzle are determined. Then, a computational physical model is built based on these parameters. Finally, the simplified chemical reaction mechanism is used to solve the chemical non-equilibrium flow in the nozzle through the eddy dissipation conceptual model. The numerical calculation method of large eddy simulation is used to obtain the fine structure of the flow field with the shape of the inner wall of the expansion section of the nozzle. The results of the numerical study show that the influence of the wall roughness element of the nozzle expansion section caused by ablation cannot be ignored during the working process of the solid rocket motor. For the non-equilibrium flow in the supersonic nozzle, the roughness element is a crucial factor to promote the flow transition and the generation of hairpin vortices, and it also affects the wall heat transfer and gas composition near the roughness element.

Study of effects of surface preparation on carbon-fiber-reinforced-polymer (CFRP) Single Lap Joints (SLJ) using positioning of gates in ultrasonic signals

ABSTRACT Ultrasonic inspection of adhesively bonded Single Lap Joint (SLJ) with composite material as adherend is quite challenging due to very close and overlapping reflections of ultrasonic waves from multiple interfaces across the joint. This study aims to precisely identify gate positions for these reflections in the pulse-echo technique. Further, investigation of surface roughness effects in the bonded region of SLJ is attempted using reflection coefficient R. For a real-valued A-scan signal in ultrasonic pulse-echo mode, a complex-valued analytic signal with amplitude and phase was obtained from the Hilbert transform. A sudden phase change of the analytic signal and a trough in the analytic signal’s envelope was observed at the reflection plane in A-scan. Analysis of spectra of reflected signals shows variation in magnitude at peak frequencies with the surface roughness of adherend. This paper provides a technique for identifying precise gate placement for the reflected signal and R-values evaluation for composite SLJ. For each surface roughness category, reflection coefficient R was experimentally evaluated at the adherend-adhesive interface of SLJ. These R values are correlated with the shear strength of the SLJ obtained from standard destructive tests.

Subpore‐Scale Trapping Mechanisms Following Imbibition: A Microfluidics Investigation of Surface Roughness Effects

AbstractSurface roughness is ubiquitous in subsurface formations due to weathering and diagenesis. Yet micromodel studies of porous media have not sufficiently addressed the impact of pore‐wall roughness on multiphase fluid displacement. We investigate the influence of pore‐wall roughness on capillary trapping by implementing surface roughness into glass micromodels and conducting imbibition experiments. Time‐lapse fluorescence microscopy, micromolding in capillaries, and scanning electron microscopy are used to examine flow behavior during spontaneous and forced imbibition experiments with capillary numbers between 10−6 and 10−4. It is found that surface roughness causes interface pinning and irregular displacement fronts within a single pore, promotes latent pore filling following imbibition, enhances snap‐offs, and contributes to interface relaxation. Furthermore, we verify a cooperative effect between corner flow and surface roughness that causes pore filling to occur at over 10 times the channel width ahead of the main bulk front. Consequently, a significant increase in trapped air saturation of up to 60% is observed, especially at lower capillary numbers and narrower pores. Effects of surface roughness also decrease the rate of spontaneous imbibition, which is slower than the prediction from Washburn's equation. Our results emphasize the importance of surface roughness in building conceptual models for capillary trapping when the ratio of surface roughness‐to‐pore size reaches a critical value of about 0.1. Above this critical threshold value, subpore‐scale trapping mechanisms contribute significantly to capillary trapping, which theoretical and numerical models should consider for accurate quantification of fluid‐transport processes.

Investigation of surface roughness effects on microstructural and mechanical properties of diffusion bonding between dissimilar AZ91-D magnesium and AA6061 aluminum alloys

The effects of surface roughness were studied on microstructural and mechanical properties of solid-state diffusion bonding between two dissimilar alloys of magnesium AZ91-D and aluminum 6061 by means of hot pressing. Although applied pressure, temperature, and duration of diffusion bonding are known as the most effective parameters, surface roughness can alter the mechanical and microstructural properties remarkably, which is usually neglected. To investigate the effect of surface roughness between 0.06 and 0.15 μm, the width of the diffusion bond in the interfacial transition zone (ITZ) and the presence of intermetallic phases were analyzed. Moreover, microhardness, shear strength, and fracture surfaces were evaluated. The results exhibit that in the applied roughness range, the bond width and the microhardness of the joints improved by increasing the surface roughness of the both metals; however, the shear strength decreased. It may be attributed to more disruption of the oxide films on the metal surfaces in the rougher samples and also increase in the effective interface boundary during the process. Consequently, there would be more chance for aluminum-magnesium contacts, resulting in more diffusion, further formation of brittle intermetallic phases (such as Al12Mg17 and Al3Mg2), and therefore more hardness and less shear strength.

Experimental investigation of Surface Roughness effects and Transition on Wind Turbine performance

Aerodynamic experiments have been executed in the wind tunnel and on a wind turbine blade to measure the impact of roughness on the airfoil characteristics and the associated effect on rotor performance and to establish the transition location on a rotating blade. The wind tunnel tests have been performed in the low-speed, low-turbulence wind tunnel of TUDelft. The wind turbine tests were carried out at ECN’s Wind Turbine Test Site. Roughness simulation material has been installed on the airfoil leading edge to measure the impact on airfoil performance. Microphones were mounted on the airfoil surface to detect the boundary layer laminar to turbulent transition position both on the wind tunnel model and on the wind turbine blade.

Experimental investigation of surface roughness effects on flow behavior and heat transfer characteristics for circular microchannels

This paper experimentally investigates the effect of surface roughness on flow and heat transfer characteristics in circular microchannels. All test pieces include 44 identical, parallel circular microchannels with diameters of 0.4mm and 10mm in length. The surface roughness of the microchannels is Ra=0.86, 0.92, 1.02μm, and the Reynolds number ranges from 150 to 2800. Results show that the surface roughness of the circular microchannels has remarkable effects on the performance of flow behavior and heat transfer. It is found that the Poiseuille and Nusselt numbers are higher when the relative surface roughness is larger. For flow behavior, the friction factor increases consistently with the increasing Reynolds number, and it is larger than the constant theoretical value for macrochannels. The Reynolds number for the transition from laminar to turbulent flow is about 1500, which is lower than the value for macrochannels. For the heat transfer property, Nusselt number also increases with increasing Reynolds number, and larger roughness contributes to higher Nusselt number.

Experimental investigation of surface roughness effects on the flow boiling of R134a in microchannels

This study experimentally investigates the effect of surface roughness on the hydrodynamic and thermal performance of microchannel evaporators. Three micro-evaporators of the same dimensions and different surface roughness have been fabricated by micro-WEDM. Each micro-evaporator consists of forty rectangular microchannels of 700μm height, 250μm width, and 19mm length. A microscale vapor compression refrigeration cycle has been constructed to carry out the experiments. R134a is used as the refrigerant. Heat transfer coefficient, pressure drop and COP results are presented at variously imposed heat fluxes, and at mass fluxes of 85 and 200kg/(m2s). The results demonstrate up to 45% enhancement in the two-phase heat transfer coefficient at low to moderate heat flux values as the surface roughness increases. Considering the surface roughness effect of the microchannel walls, a new correlation is developed to predict the heat transfer coefficient of R134a boiling in microchannels.

Wavelet based decoupled method for the investigation of surface roughness effects in elastohydrodynamic lubrication problems using couple stress fluid

Abstract In this paper, we developed the wavelet based decoupled method for the numerical solution of elastohydrodynamic lubrication problems. The standard decoupled method with Newton-generalized minimum residual procedure performs poorly or may break down when it is used to solve such type of problems. Zargari et al. (2007) presented decoupled and coupled methods, in which for the limitations of decoupled method for some set of physical parameters and slight variation in these values the non-convergence solution was tabulated. The wavelet based decoupled technique is used to overcome these limitations. Residual errors are presented in comparison with the existing methods to demonstrate the versatility and applicability of the proposed method. And also investigations of the effects of couple stress fluids on elastohydrodynamic lubrication behavior in smooth and rough contacts at low-speed-high load and high-speed-low load conditions are discussed. The elastohydrodynamic lubrication characteristics computed for couple stress fluids are found to have strong dependence on couple stress parameter.

Investigation of surface roughness effects on fluid flow in passive micromixer

Surface roughness effects are dominant at microscale. In this study, microchannels are fabricated on Silicon substrate. The roughness morphology is modeled for the fabricated structure using Weierstrass-Mandelbrot function for self-similar fractals. A two dimensional model of hexagonal passive micromixer is analyzed with surface roughness present on inner walls of channels using parallel Lattice Boltzmann method, implemented on sixteen node cluster. The results are compared by simulating this micromixer structure using Navier---Stokes equations. The experimental results on the fabricated micromixers are also presented. The effects of relative roughness, fractal dimension and Reynolds number are discussed on laminar flow in hexagonal passive micromixers. The study concludes the importance of modeling surface roughness effect for better mixing efficiency.

Combining AFM and EQCM for the in situ investigation of surface roughness effects during electrochemical metal depositions

In this communication we clearly show that the surface roughness of Cu films strongly influences the signal of an EQCM. These effects were studied with a novel combination of AFM and EQCM, which proved to be a powerful tool for the in situ investigation of surface roughness effects during electrochemical metal depositions and dissolutions.

Normal Impact Model of Rough Surfaces

An elastic-plastic impact model for spheres is introduced as the basis to study the normal impact of rough surfaces. Statistics is applied to arrive at the ensemble behavior of many unit events alluded above, allowing the investigation of surface roughness effects. Dissipation of kinetic energy increases such as surface roughness, material compliance, and impact velocity is increased. The rebound velocity is shown to be dependent on surface topography and material properties, in addition to impact velocity.

Investigation of surface roughness effects on adiabatic wall temperature

Les resultats numeriques montrent que la rugosite a un effet important sur la temperature de paroi adiabatique