Influence Of Vertical Vibration Research Articles

Influence of Different Ship Harmonic Vibration Directions on Dynamic Response of PEMFC

For the sake of study the applicability of PEMFC on ships, a three-dimensional single channel fuel cell model was established. The vibration load was loaded on the model through dynamic grid technology and user-defined function (UDF) method. The output voltage and reactive gas distribution of PEMFC loaded in different vibration directions were compared and analyzed. The results show that ship vibration will affect the transmission of components in the battery, resulting in incomplete electrochemical reaction and degradation of PEMFC performance. The influence of vertical vibration is greater than that of longitudinal vibration and lateral vibration.

Investigation of chemoconvection in vibration fields.

This study is devoted to the investigation of the chemoconvection in a two-layer miscible system caused by the neutralisation reaction proceeding in the convective-controlled (CC) regime under the influence of vertical vibrations. The CC regime without vibrational influence is characterized by the development of a density wave and vigorous convection in the upper layer, ensuring a high reaction rate and forcing the reaction front to move downwards more rapidly than in the well-known diffusive-controlled (DC) regime. It is shown that vibrations lead to some deceleration of the convection that depends both on the magnitude of the vibrational acceleration and on the initial concentrations of the reagents. Analysis of the system behaviour depending on the dimensionless parameters is carried out. It is demonstrated that the theory of thermal vibrational convection may be applied for reacting systems on quasi-steady time intervals.

Experimental investigation of flow characteristics in a vertical vibration two-phase loop thermosyphon

In this paper, flow characteristics of a two-phase loop thermosyphon under vertical reciprocating vibration are visually investigated with N-pentane as the working fluid. The tests are performed for a heating power range of 20 W to 40 W, the filling ratio of 30 % to 70%, and a 30 m?s-2, 35 Hz vertical reciprocating vibration. The effect of vertical vibration on flow characteristics of the two-phase loop thermosyphon is investigated by comparing the obtained results with those acquired in static, thereby providing a basis for explaining the heat transfer process of two-phase loop thermosyphon under vibration. The results indicate that vertical vibration promotes the rupture of a liquid plug and the transformation of the plug flow to annular flow or wavy flow. Furthermore, the vertical vibration does not change the distribution law of liquid flow velocity in the two-phase loop thermosyphon. However, it will reduce the overheating and flow velocity in the two-phase loop thermosyphon at the start-up. With an increase in the heating power, the influence of vertical vibration on liquid flow velocity is reduced due to continuous disturbance of the working medium in the two-phase loop thermosyphon.

Holding Force and Vertical Vibration of Emergency Gate in the Closing Process: Physical and Numerical Modelling

A two-dimensional unsteady fluid–structure interaction numerical model was established, based on the physical model test, to investigate the influence of vertical vibration on the holding force of an emergency gate in the closing process. Gate motion was controlled by the user-defined function in Fluent. Attention was paid to the relationship between the vertical vibration, hydrodynamic loads and flow discharge. The experiment results show that holding force has three typical forms in the closing process and it is related to the service gate height. The numerical model can reflect the gate vertical vibration and the gate-closing displacement in the form of steps. Gate vertical vibration in the closing process is a motion-induced vibration caused by gate active falling. Moreover, the transition from full-flow to open-flow behind the emergency gate has a great influence on the gate vertical vibration. With a small gate opening, gate vertical vibration makes the flow discharge fluctuation increase. Furthermore, flow discharge has an influence on the gate body loads, which is mainly concentrated in the upstream plate and gate bottom. Finally, the lift force coefficient at the gate bottom is different from the standard and is mainly controlled by the outflow boundary condition. The simulation result is in good agreement with the experiment and the relative error meets engineering requirements, suggesting that the numerical model can successfully simulate the gate fluid–structure interaction and reproduce the characteristics of physical quantities in the closing process.

Faraday instability in small vessels under vertical vibration

The formation of Faraday waves in a liquid inside a cylindrical vessel under the influence of vertical vibration is studied. The stability thresholds and its mode decomposition are obtained using a linear stability analysis. The stability model is validated with a vibration experiment in a vertical vibration table. The Faraday instability threshold is found for accelerations ranging from 0.1 to 1.0 times the gravitational acceleration. The confinement effect by the vessel introduces cut-off the low frequency modes and the allowed frequencies are discretized. The resulting acceleration stability threshold is high at low frequencies and it is the lowest at medium frequencies, , where the discretization of the mode -momenta introduces low stability regions delimited by more stable frequency ranges. The relevance of these characteristics for the agitation of liquids will be discussed.

Effect of vertical vibration on the stability of Side-Suspending HTS Maglev Rotating System with trimodal structure PMG

By changing the vibration amplitude, side-suspending gap and load of side-suspending maglev system, respectively, the influence of vertical vibration on the bearing stability of the side-suspending high temperature superconducting (HTS) maglev system with trimodal structure permanent magnetic guideway (PMG) is investigated. The results show that the attenuation of the side-suspending height increases with the increase of the vibration amplitude, side-suspending gap and load, respectively. However, the overall decrease of the side-suspending height is not larger than 1.5 mm under all situations, and it will not affect the stability of the side-suspending maglev system apparently.

Influence of Vertical Vibrations on the Stability of a Binary Mixture in a Horizontal Porous Layer Subjected to a Vertical Heat Flux

We present an analytical and numerical stability analysis of Soret-driven convection in a porous cavity saturated by a binary fluid mixture and subjected to vertical high-frequency and small-amplitude vibrations. Two configurations have been considered and compared: an infinite horizontal layer and a bounded domain with a large aspect ratio. In both cases, the initial temperature gradient is produced by a constant uniform heat flux applied on the horizontal boundaries. A formulation using time-averaged equations is used. The linear stability of the equilibrium solution is carried out for various Soret separation ratios $$\varphi $$ , vibrational Rayleigh numbers Rv, Lewis numbers Le and normalized porosity. For an infinite horizontal layer, the critical Rayleigh number $$\mathrm{Ra}_c$$ is determined analytically. For a steady bifurcation to a one-cell solution (the critical wavenumber is zero), we obtain $$\mathrm{Ra}_{c}={12}/{({\varphi }(\mathrm{Le}+1)+1)}$$ for all Rv. When the bifurcation is a Hopf bifurcation or when the critical wavenumber is not zero, we use a Galerkin method to compute the critical values. Our study is completed by a nonlinear analysis of the bifurcation to one-cell solutions in an infinite horizontal layer that is compared to numerical simulations in bounded horizontal domains with large aspect ratio.

Analytical and numerical stability analysis of Soret-driven convection in a horizontal porous layer: The effect of vertical vibrations.

The authors studied the effect of vertical high-frequency and small-amplitude vibrations on the separation of a binary mixture saturating a porous cavity. The horizontal bottom plate was submitted to constant uniform heat flux and the top one was maintained at constant temperature while no mass flux was imposed. The influence of vertical vibrations on the onset of convection and on the stability of the unicellular flow was investigated for positive separation ratio [Formula: see text]. The case of high-frequency and small-amplitude vibrations was considered so that a formulation using time averaged equations could be used. For an infinite horizontal porous layer, the equilibrium solution was found to lose its stability via a stationary bifurcation leading to unicellular flow or multicellular one depending on the value of [Formula: see text]. The analytical solution of the unicellular flow was obtained and separation was expressed in terms of Lewis number, separation ratio and thermal Rayleigh number. The direct numerical simulations using the averaged governing equations and analytical stability analysis showed that the unicellular flow loses its stability via oscillatory bifurcation. The vibrations decrease the value of [Formula: see text], which allows species separation for a wide variety of binary mixtures. The vibrations can be used to maintain the unicellular flow and allow species separation over a wider range of Rayleigh numbers. The results of direct numerical simulations and analytical model are in good agreement.

О влиянии вертикальных вибраций на устойчивость перманентных вращений твердого тела вокруг осей, лежащих в главной плоскости инерции

О влиянии вертикальных вибраций на устойчивость перманентных вращений твердого тела вокруг осей, лежащих в главной плоскости инерции

Influence of Vertical Vibration on Surface Velocity of a Liquid Bridge

In this paper, the vertical vibration influence on the surface velocity of a 5cSt silicone oil liquid bridge has been investigated numerically. The Navier-Stokes equations coupled with the energy conservation equation are solved on a staggered grid, and the two-phase surface is captured by using the mass conserving level set method. The present results indicate that the axial and radial surface velocities of the liquid bridge are suppressed by the external vertical vibration.

Influence of vertical vibrations on the separation of a binary mixture in a horizontal porous layer heated from below

We study the influence of vertical high-frequency and small-amplitude vibrations on the separation of a binary mixture saturating a shallow horizontal porous layer heated from below. The monocellular flow obtained for a separation ratio ψ > ψ mono > 0 leads to a migration of the species towards the two vertical boundaries of the cell. The 2D direct numerical simulations and the linear stability analysis of the averaged governing equations show that the vertical vibrations delay the transition from monocellular flow to multicellular flow. The vibrations also decrease the value of ψ mono, which allows species separation for a wide variety of binary mixtures.

Vibration-induced granular segregation in a pseudo-2D column: The (reverse) Brazil nut effect

The segregation of nine different disk-shaped intruders in a pseudo-2D granular bed consisting of 0.85 mm polystyrene beads under the influence of vertical vibrations was studied. The intruders used were all fabricated of brass and were much denser than the polystyrene particles. Depending on the vibration amplitude and frequency, intruders were able to segregate to the top or bottom of the granular bed as long as the vibration intensity Γ was greater than 1. At a fixed vibration amplitude, upward segregation, also known as the Brazil nut effect, occurred at a much higher frequency than downward segregation, which is also known as the reverse Brazil nut effect. Segregation to the top was always much quicker than segregation to the bottom irrespective of size and mass of the intruder used. By the use of high-speed video movies, it was found that the disk-shaped intruders rose along the bed height by a void filling mechanism.

Air-driven Brazil nut effect.

A large heavy object may rise to the top of a bed of smaller particles under the influence of vertical vibration, the "Brazil nut effect." Recently it has been noted that interstitial air can influence the Brazil nut rise time. Here we report that the air movement induced by vertical vibration produces a very strong Brazil nut effect for fine granular beds. We use a porous-bottomed box to investigate the mechanism responsible for this effect and to demonstrate that it is related to the piling of fine beds, first reported by Chladni and studied by Faraday. Both effects are due to the strong interaction of the fine particles with the air, as it is forced through the bed by the vibration.

Influence of vertical vibration on heart rate of pigs.

Pigs with a body weight between 15 and 20 kg were vibrated in the vertical direction for 1 h at 2, 8, and 18 Hz, in combination with root mean square (RMS) acceleration magnitudes of 1 or 3 m/s2. Welfare and stress were quantified by comparing heart rate characteristics during a control period (2200 to 0600) before vibration exposure and during vibration (1000 to 1100). The level of maximum heart rate and number of ventricular ectopic beats during vibration at 2 and 8 Hz in combination with a RMS acceleration of 3 m/s2 indicated a larger fear response than at 1 m/s2. Isocomfort contours based on mean heart rate during vibration showed the greatest specific sensitivity of the pigs to vibration at a frequency of 8 and 18 Hz, especially in combination with a RMS acceleration of 3 m/s2. During transport, RMS acceleration should be less than 3 m/s2 to protect pigs' welfare. Pigs were more sensitive to acceleration than to frequencies within the range of treatments in this investigation. Although the response of the pigs in this experiment fit within the model concept for adult humans and for domestic fowl, changes in heart rate are dependent on body weight.

Liquid sloshing phenomenon accompanying solidification.

The liquid sloshing phenomenon accompanying solidification was studied experimentally. The influence of vertical vibration on the convection flow by cooling the central inner cylindrical wall was investigated. The solidification rate of melting paraffin in the vibrating and cooling field was also measured quantitatively. The experiment revealed that the free surface wave motion disturbed the natural convection and decreased the rate of solidification. Possible control of the solidification rate by vibrating the container with the suitable input frequency or amplitude was also suggested.

Development of a steady relief at the interface of fluids in a vibrational field

The vibrations of a vessel strongly influence the behavior of the interface of the fluids in it. Thus, vertical vibrations can lead both to the parametric excitation of waves (Faraday ripples) and to the suppression of the Rayleigh-Taylor instability [1–2]. At the present time, the influence of vertical vibrations on the behavior of a fluid surface have been studied in sufficient detail (see, for example, review [3]). The behavior of an interface of fluids in the case of horizontal vibrations has been studied less. An interesting phenomenon has been revealed in the experimental papers [4, 5]: in the case of fairly strong horizontal vibrations of a vessel containing a fluid with a free surface, the fluid collects near one of the vertical vessel walls, the free surface being practically plane and stationary with respect to the vessel, while its angle of inclination to the horizon depends on the vibration rate. But if there is a system of immiscible fluids with comparable but different densities in the vessel, horizontal vibrations lead to the formation of a steady wave relief at the interface. An explanation of the behavior of a fluid with a free boundary was given in [6] on the basis of averaged equations of fluid motion in a vibrational field. The present paper is devoted to an analysis of the behavior of the interface of fluids with comparable densities in a high-frequency vibrational field.