Effects Of Surface Vibrations Research Articles

Dynamic analysis of MSE wall subjected to surface vibration loading

Abstract Extensively used Mechanically Stabilized Earth (MSE) walls in Rail Transportation System (RTS) are vulnerable to surface vibrations generated by moving vehicles. Hence, it is necessary to consider the effects of surface vibrations during the design of MSE walls for RTS. Steel-reinforced panel-type MSE walls are shown to perform well during vibration loading, but costly steel materials have led to greater reliance on affordable and readily available geosynthetics for reinforcement. Limited research exists on the behavior of panel-type MSE walls with geosynthetics considering RTS-induced vibrations frequencies. Thus, this study employs Finite Element software PLAXIS 3D to simulate the impact of surface vibration frequencies on panel-type MSE walls. The qualitative study encompasses two reinforcement cases (geogrids and steel strips) of 4 m MSE wall height and four harmonic loading frequencies representing RTS-induced surface vibrations for simulation. The dynamic responses of MSE wall are presented in terms of lateral wall displacements and lateral earth pressure distributions. Furthermore, the distributions of tensile strain and the identification of potential slip surface locations are presented. The findings indicated that MSE wall and reinforcement responses are governed by RTS-induced vibrations and fundamental frequency of backfill soil. This highlights the need for consideration of both the fundamental frequency of the backfill soil and RTS-induced vibrations in the design of MSE walls.

Effects of wall vibrations on channel flows

The effect of surface vibrations on the pressure-gradient-driven flows in channels has been studied. The analysis considered monochromatic waves and laminar flows. The effectiveness of the vibrations was gauged by determining the pressure gradient correction required to maintain the same flow rate as without vibrations. Waves propagating upstream always increase pressure losses. Flow response to waves propagating downstream is more complex and changes as a function of the flow Reynolds number. Such waves reduce losses if the Reynolds number $Re <\ \sim\!\!100$ , but these waves must be sufficiently fast to reduce pressure losses for larger Re values. In general, the supercritical waves, i.e. waves faster than the reference flow, reduce pressure losses with the magnitude of reduction increasing monotonically with the wave phase speed and wavenumber. The need for an external pressure gradient is eliminated if sufficiently short and fast waves are used. Generally, the subcritical waves, i.e. waves with velocities similar to the reference flow, increase pressure losses. This increase changes somewhat irregularly as a function of the wave phase speed and wavenumber forming local maxima and minima. These waves can reduce pressure losses only if the Reynolds number becomes large enough. It is shown that subcritical waves with very small amplitudes but matching the natural flow frequencies produce significant pressure losses.

The role of vibrations for reducing the resistance in the relative movement of parallel plates

The effect of surface vibrations on the propulsion augmentation and resistance in the relative movement of parallel plates has been studied. The analysis was focused on monochromatic waves and laminar flows. The effectiveness of the vibrations was gauged by determining the external force required to maintain the movement of one of the plates at a prescribed velocity. It is shown that waves propagating upstream always increase the resistance but the flow response to waves propagating downstream is more intricate and is a function of the flow Reynolds number. In general, waves must be sufficiently fast to reduce the flow resistance. This leads to a natural division between slow and fast waves; a characterization that is helpful for flows at a sufficiently small Reynolds number Re. An increase in Re brings into play the complication of possible resonances with the natural flow frequencies. Resonances are not possible with waves faster than the plate velocity and these supercritical waves generally decrease the flow resistance. More complex flow responses can occur with slower (subcritical) waves which tend to increase the flow resistance. A complete elimination of the resistance is possible if the waves are of sufficiently short wavelength and travel quickly. This suggests that our mechanism has great potential in the development of propulsion augmentation systems. None of the waves produced net energy savings.

Effects of surface vibrations on interlayer mass transport: Ab initio molecular dynamics investigation of Ti adatom descent pathways and rates from TiN/TiN(001) islands

We carry out density-functional ab initio molecular dynamics (AIMD) simulations of Ti adatom (Tiad) migration on, and descent from, TiN <100>-faceted epitaxial islands on TiN(001) at temperatures T ranging from 1200 to 2400 K. Adatom-descent energy-barriers determined via ab initio nudged-elastic-band calculations at 0 Kelvin suggest that Ti interlayer transport on TiN(001) occurs essentially exclusively via direct hopping onto a lower layer. However, AIMD simulations reveal comparable rates for Tiad descent via direct-hopping vs. push-out/exchange with a Ti island edge atom for T >= 1500 K. We demonstrate that the effect is due to surface vibrations, which yield considerably lower activation energies at finite temperatures by significantly modifying the adatom push/out-exchange reaction pathway.

Experimental study on effect of surface vibration on micro textured surfaces with hydrophobic and hydrophilic materials

Artificial hydrophobic surfaces have been studied in the last ten years in an effort to understand the effects of structured micro- and nano-scale features on droplet motion and self-cleaning mechanisms. Among these structured surfaces, micro-textured surfaces consisting of a combination of hydrophilic and hydrophobic materials have been designed, fabricated and characterized to understand how surface properties and morphology affect enhanced self-cleaning mechanisms. However, use of micro textured surfaces leads to a strong pinning effect that takes place between the droplets and the hydrophobic-hydrophilic edge, leading to a significant contact angle hysteresis effect. This research study focuses on the effects of surface vibrations on droplet shedding at different inclined angles on micro-textured surfaces. Surface vibration and shedding processes were experimentally characterized using a high speed imaging system. Experimental results show that droplets under the influence of surface vibration depict different contour morphologies when vibrating at different resonance frequencies. Moreover, droplet sliding angles can be reduced through surface vibration when the proper combination of droplet size and surface morphology is prescribed.

Effect of deformation and vibration on theαdecay half-life

In this work, we expand upon our previous study, the effect of surface vibrations (low-lying vibrational states) on the calculation of penetration probability in alpha decay of spherical isotopes [Phys.Rev.C91,034611(2015)]. To this aim, the Coulomb and proximity potential model, taking in to account the ground state deformations of the involved nuclei along with the surface vibrations in the daughter nucleus, is used to evaluate the alpha decay probability. The results are compared with those obtained by spherical potential barrier, which shows the dramatic effect of employing the ground state deformations in case of deformed nuclei. As well, including of surface vibrations give rise to an increase in the value of tunneling probability in better agreement with experimental data.

Half-life of sphericalαemitters and intrinsic properties of nuclei

The quantum mechanical effects are investigated on the half-life of $\ensuremath{\alpha}$ decay. To this aim the penetration probability in $\ensuremath{\alpha}$ decay of spherical isotopes of $^{146}\mathrm{Sm},\phantom{\rule{0.16em}{0ex}}^{148}\mathrm{Sm},\phantom{\rule{0.16em}{0ex}}^{148}\mathrm{Gd}$, and $^{224}\mathrm{Ra}$ is calculated by employing coupled channel formalism by considering the effects of surface vibrations in the daughter nucleus; the obtained results are compared with those calculated by the semiclassical WKB approximation using two versions of the proximity potential. It is shown that by including low-lying excitation states the results are modified, in better agreement with experimental data.

Structural and dynamical properties of Ru(0 0 0 1) surface

I performed density functional theory (DFT) calculations combined with MD simulations to study the structural relaxation of Ru(0001) surface. The surface relaxation of the topmost layer is found to be about −4% at absolute zero temperature. Using MD simulations in the temperatures range of 50 K and 900 K, the effect is found to be minor on the surface relaxation as compared to Pd (1 1 1) clean surface. The effect of surface vibration is also investigated using a LEED code and shows no effect of the vibrational level on the IV curves, which rules out any disagreement between proper theory and LEED results of well prepared surfaces.

Effects of surface vibrations on quadrupole response of nuclei

The effect of quadrupole-type surface vibrations on the quadrupole response function of heavy nuclei is studied by using a model based on the solution of the linearized Vlasov equation with moving-surface boundary conditions. By using a separable approximation for the residual interaction, an analytical expression is obtained for the moving-surface response function. Comparison of the fixed- and moving-surface strength functions shows that surface vibrations are essential in order to achieve a unified description of the two characteristic features of the quadrupole response: the giant resonance and the low-lying states. Calculations performed by setting the surface tension equal to zero shows that the low-lying strength is strongly affected by the surface tension.

A theoretical investigation of microscopic dynamics and time scales of predesorption processes

When an internal mode of an absorbate is excited with enough energy to break the absorbate–surface bond, the adsorbate may desorb in a manner similar to predissociation (or unimolecular reaction) in isolated molecules. In this article, we set up a simple, microscopic model for this ‘‘predesorption’’ process and investigate the influence of various aspects of the model on the time scale of predesorption. These comparisons include quantum mechanical vs classical treatment, and the inclusion vs neglect of surface vibrations. For this simple analog of a ‘‘unimolecular reaction,’’ we find that classical mechanics predicts shorter lifetimes; and that the effect of surface vibrations is far less pronounced in quantum mechanics.