Effect Of Oscillation Frequency Research Articles

Effect of oscillation frequency on microstructure and properties of WC-Co cemented carbide prepared by hot oscillating pressing

In this study, a novel hot oscillating pressing (HOP) was used to prepared WC-Co cemented carbides under various oscillation frequencies. The effects of sintering frequencies on the density, microstructure, and mechanical properties of cemented carbides were systematically investigated. The results show that applying a specific oscillation frequency during the sintering process can greatly aid in the densification process, improve the uniformity of microstructure, help the grain refinement, and prevent the formation of abnormally large WC grains. The mechanical properties of the alloys showed a noticeable improvement as the oscillation frequency increased. The hardness and fracture toughness of cemented carbides were not significantly improved when the oscillation frequency was ≥5 Hz, with the optimal values reaching 1913 kg/m2 and 13.11 MPa.m1/2, in turn. The improvement in mechanical properties of cemented carbide can be mainly attributed to higher density, grain refinement, microstructure uniformity and the increase of dislocation/twins caused by plastic deformation.

Melting and Solidification Characteristics of PCM in Oscillated Bundled-Tube Thermal Energy Storage System

Phase change material (PCM) based thermal energy storage (TES) is an important solution to the waste of heat and intermittency of new energy sources. However, the thermal conductivity of most PCMs is low, which severely affects the thermal energy storage performance. Oscillation of the tube bundles in a TES unit can intensify the convection of liquid PCM and, therefore, enhance heat transfer. However, the energy storage performance of bundled-tube TES systems in response to oscillation at different amplitudes and frequencies has not been well understood yet, and the optimum time to apply the oscillation during phase transition remains unexplored. To address this issue, this present study was carried out. First, the melting behaviour of PCM with oscillation starting at different times was investigated. Then, the influences of oscillation frequency and amplitude on the melting performance were explored. Finally, the solidification behaviour of PCM with oscillation starting at different times was examined. Results show that the oscillation can accelerate the phase transition process by enhancing convective heat transfer. Compared to the case without oscillation, the complete melting and solidification times are reduced by 8.2 and 6.7% for the case with oscillation starting at 200 s, respectively. The effect of oscillation frequency on the melting enhancement is negligible, while the oscillation amplitude has an important effect on the melting enhancement.

Effect of beam oscillation frequency on porosity in laser welding of aluminum alloy lap-butt joints

Many investigations into laser oscillations for mitigating severe porosity in aluminum alloys have involved trading off penetration depth, potentially disrupting the porosity suppression mechanism. In this study, an oscillation laser butt-lap welding technique was designed, and the effect of oscillation frequency on cross-section morphologies and porosity rate was investigated while maintaining the constant weld depth. The findings unveiled that heightened oscillation frequencies led to diminished porosity levels, and this pattern remained consistent, even in cases where weld depths were extended. High-frequency laser beam oscillation enhanced the stability of the keyhole, increased the duration of the molten pool existence, and reduced porosity to 0.17%. Thus, this study offered significant insights into the impact of oscillation on laser welding of aluminum alloys.

Effects of oscillation frequency on the flow characteristics of a centrifugal pump impeller with sinusoidal flow rate

This study uses large eddy simulation to investigate the flow characteristics of a centrifugal pump impeller with sinusoidal flow rate and constant rotational speed. Five different oscillation frequencies ( f/f0 = 1.0, 1.2, 1.5, 2.0, and 3.0, where f0 indicates one-ninth of the rotational speed) are selected to isolate the influence of oscillation frequency on the flow characteristics. Studies show that the pressure deviation between dropping and rising stages concentrates at the impeller inlet at instantaneous 0.5 Qd ( Qd is the design load), and its value increases with the increase in oscillation frequency. The lowest period of many flow characteristics, including pressure fluctuation and head, equals to that of flow rate. The differences in pressure fluctuation between adjacent channels decreases with the increase in oscillation frequency. The first and second dominant frequencies of pressure fluctuation are mainly affected by the oscillation frequency in the nonstall passage, and they have an important relationship with the stall vortex in the stall passage. With the increase in oscillation frequency, the amplitude of lowest order head pulsation increases, and the high order head pulsation gradually weakens. The average head is approximately 2.36 m.

Effect of oscillation frequency on microstructure of A356 slurry prepared by semi-solid metal forming with flow

Effect of oscillation frequency on microstructure of A356 slurry prepared by semi-solid metal forming with flow

Effect of oscillation frequency on the mechanical properties and failure behaviors of laser beam welded 22MnB5 weld

Al–Si coated 22MnB5 steel is a lightweight material that helps significantly reduce vehicle weight and fuel consumption. In this article, the effect of different oscillation frequencies on the fraction of α-ferrite, the cross-sectional shape, microstructure and mechanical properties of laser welded Al–Si coated 22MnB5 steel was investigated. The results showed that after stamping, the fraction of α-ferrite in the fusion zone can be significantly reduced from 47.9% to 2.2% by oscillating laser beam welding compared to static laser beam welding with oscillation frequency and amplitude equal to zero. When the oscillating frequency was increased from 0 to 320 Hz, the cross-sectional shape of the weld changed from “X" to “Y", and the tensile strength and elongation of the welded joint was firstly increased and then decreased from the minimum value of (426.45HV, 1159.92 MPa, 1.14%) to the maximum value of (476.98HV, 1521.39 MPa and 2.76%). The formation of α-ferrite along the strip distribution near the upper surface of the fusion zone of static laser beam welding and oscillating laser beam welding after hot stamping, which led to stress concentration and eventual failure. Under the tensile-shear load, the cracks in the weld of static laser beam welding and oscillating laser beam welding were initiated on the massive α-ferrite location in the top surface of the fusion zone and expanded to the bottom of the weld.

Effect of high-frequency beam oscillation on microstructures and cracks in laser cladding of Al-Cu-Mg alloys

This paper provides a new method to suppress solidification cracks in laser cladding of Al-Cu-Mg alloy by high-frequency beam oscillation without additional auxiliary measures. The effects of oscillation frequency on crack suppression were investigated by analyzing the microstructure evolution. The results show that the intercrystalline precipitated phase changed from coarse and continuous line to spiderweb-like morphology with the oscillation frequency (f) increased from 50 Hz to 500 Hz, and the thermal cracking tendency was completely reduced when the density of coarse intergranular precipitates was <300 μm/mm2 (f ≥ 200 Hz). The coarse Al2Cu and Al0.92Cu1.08Mg low-melting eutectic phases formed by the Cu element segregation between the columnar dendrites constituted the crack source and crack expansion channel. The rapid and periodic motion of a high-frequency oscillating laser can promote the uniform energy distribution and drive the melt flow, which will induce the columnar to equiaxed transition. The web-like eutectic liquid film between equiaxed dendrites has a smoother reflux channel and coordinated deformation ability. When the solidification shrinkage force pulls the local liquid film, the rest of the liquid phase can return to heal the crack in time, which is the main mechanism for the solidification cracks to be reduced.

Effect of Oscillation Frequency on Microstructure of A356 Slurry Prepared by Semi-Solid Metal Forming with Flow

Effect of Oscillation Frequency on Microstructure of A356 Slurry Prepared by Semi-Solid Metal Forming with Flow

Dynamics of droplet migration in oscillatory and pulsating microchannel flows and prediction and uncertainty quantification of its lateral equilibrium position using multifidelity Gaussian processes

The dynamics of a droplet in oscillatory and pulsating flows of a Newtonian fluid in a microchannel has been studied numerically. The effects of oscillation frequency, surface tension, and channel flow rate have been explored by simulating the drop within a microchannel. These types of flows introduce new equilibrium positions for the drop compared to steady flows with similar conditions. The simulation results are very sensitive to the grid resolution due to the unsteady behavior of the base flow. Therefore, a set of fine grids have been used in this study to capture the physics of this problem more accurately. However, these fine grids make the computations significantly expensive. Therefore, a multifidelity Gaussian processes method with two levels of fidelity has been used to predict the results of the remaining fine-grid simulations along with their uncertainties based on their correlations with those of the coarse-grid cases over a wide range of input parameters.

Optimal Frequency and Amplitude of Vertical Viewpoint Oscillation for Improving Vection Strength and Reducing Neural Constrains on Gait.

Inducing self-motion illusions referred as vection are critical for improving the sensation of walking in virtual environments (VE). Adding viewpoint oscillations to a constant forward velocity in VE is effective for improving vection strength under static conditions. However, the effects of oscillation frequency and amplitude on vection strength under treadmill walking conditions are still unclear. Besides, due to the visuomotor entrainment mechanism, these visual oscillations would affect gait patterns and be detrimental for achieving natural walking if not properly designed. This study was aimed at determining the optimal frequency and amplitude of vertical viewpoint oscillations for improving vection strength and reducing gait constraints. Seven subjects walked on a treadmill while watching a visual scene. The visual scene presented a constant forward velocity equal to the treadmill velocity with different vertical viewpoint oscillations added. Five oscillation patterns with different combinations of frequency and amplitude were tested. Subjects gave verbal ratings of vection strength. The mediolateral (M-L) center of pressure (CoP) complexity was calculated to indicate gait constraints. After the experiment, subjects were asked to give the best and the worst oscillation pattern based on their walking experience. The oscillation frequency and amplitude had strong positive correlations with vection strength. The M-L CoP complexity was reduced under oscillations with low frequency. The medium oscillation amplitude had greater M-L CoP complexity than the small and large amplitude. Besides, subjects preferred those oscillation patterns with large gait complexity. We suggested that the oscillation amplitude with largest M-L CoP complexity should first be chosen to reduce gait constraints. Then, increasing the oscillation frequency to improve vection strength until individual preference or the boundary of motion sickness. These findings provide important guidelines to promote the sensation of natural walking in VE.

Inertial migration of a deformable capsule in an oscillatory flow in a microchannel.

Dynamics of a deformable capsule in an oscillatory flow of a Newtonian fluid in a microchannel has been studied numerically. The effects of oscillation frequency, capsule deformability, and channel flow rate have been explored by simulating the capsule within a microchannel. In addition, the simulation captures the effect of the type of imposed pressure oscillations on the migration pattern of the capsule. An oscillatory channel flow enables the focusing of extremely small biological particles by eliminating the need to design impractically long channels. The presented results show that the equilibrium position of the capsule changes not only by the addition of an oscillatory component to the pressure gradient but it also is influenced by the capsule deformability and channel flow rate. Furthermore, it has been shown that the amplitude of oscillation of capsules decreases as the channel flow rate and the rigidity of the capsule increases.

Influence of an External Perpendicular Oscillation on Stability of a Vertical Falling Liquid Film

A vertical falling Newtonian liquid film flow is inherently unstable to surficial long-wave disturbances. Imposing external oscillation can stabilize the long-wave instability, but also triggers additional parametric instabilities. The effect of oscillation frequency on the stability is subtle. By using the “viscosity-gravity” scaling, the effect of oscillation frequency on the stability can be investigated exhaustively by separating it from other control parameters. In this paper, the effects of external perpendicular oscillation on the stability of a vertical falling liquid film are then investigated by a combination of linear stability analyses based on Floquet theory and numerical simulations with an unsteady weighted residual model (WRM). The linear analyses show that, increasing oscillation amplitude always has a stabilizing effect on the long-wave instability. On the other hand, increasing or decreasing oscillation frequency can suppress the long-wave instability, depending on whether the oscillation amplitude or the acceleration is fixed. The effect of varying oscillation frequency on the long-wave instability is opposite to that on the parametric instabilities. The long-wave and parametric instabilities compete with each other as the oscillation amplitude and frequency are varied with the Reynolds number fixed. A weakness of the long-wave instability always accompanies enhancements of the parametric instabilities, and vice versa. As a contrast, an increase of Reynolds number always results in more unstable long-wave and parametric instabilities. The numerical simulations with the WRM show that the wave amplitudes and the minimal local thickness of film are proportional to the unstable wavenumbers range rather than the growth rate of the instability. For a given oscillation frequency and Reynolds number, there exist a critical oscillation amplitude above which externally imposed oscillations perpendicular to the transversal direction of the film can also trigger a chaotic behavior in the film, just like what happens in the case where the oscillation is parallel to the stream-wise direction of the film.

Effect of oscillation frequency on the breakdown characteristics of transformer oil in a highly nonuniform field under lightning impulse voltage

Effect of oscillation frequency on the breakdown characteristics of transformer oil in a highly nonuniform field under lightning impulse voltage

Irreversible transition of amorphous and polycrystalline colloidal solids under cyclic deformation

Cyclic loading on granular packings and amorphous media leads to a transition from reversible elastic behavior to an irreversible plasticity. In the present study, we investigate the effect of oscillatory shear on polycrystalline and amorphous colloidal solids by performing molecular dynamics simulations. Our results show that close to the transition, both systems exhibit enhanced particle mobility, hysteresis, and rheological loss of rigidity. However, the rheological response shows a sharper transition in the case of the polycrystalline sample as compared to the amorphous solid. In the polycrystalline system, we see the disappearance of disclinations, which leads to the formation of a monocrystalline system, whereas the amorphous system hardly shows any ordering. After the threshold strain amplitude, as we increase the strain amplitude both systems get fluid. In addition to that, particle displacements are more homogeneous in the case of polycrystalline systems as compared to the amorphous solid, mainly when the strain amplitude is larger than the threshold value. We do not see any effect of oscillation frequency on the reversible-irreversible transition.

Research on the Hydrodynamic Performance of a Vertical Axis Current Turbine with Forced Oscillation

For a current turbine fixed on a floating platform, the wave-induced motion responses of the platform change the hydrodynamic performance of the current turbine. In this paper, a numerical simulation method based on commercial computational fluid dynamics software-CFX is established to systematically analyze the turbine loads condition and power output efficiency of the turbine subject to the wave-induced motion. This method works well in terms of 2D hydrodynamic performance analysis and is verified by an experiment. In addition, the method is applied to investigate the hydrodynamic performance of a vertical axis current turbine under forced oscillation by a combining sliding mesh with moving mesh technique. This research mainly focusses on the effects of oscillation frequency and oscillation amplitude on the hydrodynamic performance and the flow field. It is found that a wake flow similar to the Von Karman Vortex Street appears under sway oscillation. Spacing between vortex in the wake flow changes under surge oscillation. The fluctuations of the blade load coefficients can be decomposed into a low frequency part and a high frequency part. The low frequency part is related to the frequency of the forced oscillation, while the high frequency part is a consequence of the rotational frequency of the turbine. The oscillation amplitudes of the turbine load coefficients increase linearly with the growth of oscillation frequency and oscillation amplitude. This paper can provide a useful reference for similar research on the turbine loads condition and power out efficiency of the turbine subject to wave-induced motion. This paper can also provide a reference on the structural design or electronic control of vertical axis current turbines.

Effect of oscillation amplitude on the residence time distribution for the mesoscale oscillatory baffled reactor

&lt;p&gt;A recent development in oscillatory baffled reactor technology is down-scaling the reactor, so that it can be used for the applications such as small-scale continuous production of bioethanol. A mesoscale oscillatory baffled reactor (MOBR) with central baffle system was developed and fabricated at mesoscales (typically 5 mm diameter). This present work aims to analyse the mixing conditions inside the MOBR by evaluating the residence time distribution (RTD) against the dynamic parameters of net flow Reynolds number (&lt;em&gt;Re&lt;/em&gt;&lt;em&gt;&lt;sub&gt;n&lt;/sub&gt;&lt;/em&gt;) at 4.2, 8.4 and 12.6 corresponding to flow rates of 1.0, 2.0 and 3.0 ml/min respectively, oscillatory Reynolds number (&lt;em&gt;Re&lt;/em&gt;&lt;em&gt;&lt;sub&gt;o&lt;/sub&gt;&lt;/em&gt;) between 62 to 622, and Strouhal number (&lt;em&gt;Str&lt;/em&gt;) between 0.1 to 1.59. The effect of oscillation frequency and amplitude on RTD performance were studied at frequency, amplitude, and velocity ratio ranging from 4 to 8 Hz, 1 to 4 mm and 1 to 118, respectively. Effect of oscillation frequency has resulted in the variance of the RTD increased as the oscillation frequency increased from 5 Hz to 8 Hz and peak at 6 Hz of 0.264. A further increase in the frequency above 5 Hz caused the RTD to slightly broaden and positively skewed. At frequency of 5 Hz, the RTD profiles were close to Gaussian form for all tested amplitude values from 1 mm to 4 mm. At low amplitudes, i.e. xo = 1 mm, the variance exhibited its minimum around 0.842 at &lt;em&gt;Re&lt;/em&gt;&lt;em&gt;&lt;sub&gt;o&lt;/sub&gt;&lt;/em&gt;&lt;em&gt; &lt;/em&gt;=156. An increase in &lt;em&gt;Re&lt;/em&gt;&lt;em&gt;&lt;sub&gt;o&lt;/sub&gt;&lt;/em&gt;&lt;em&gt; &lt;/em&gt;above 300 resulted in increased in the variance rapidly to 1.28, and later eliminated the plug flow behaviour and the reactor behaved similar to a single continuous stirred tank reactor.&lt;/p&gt;&lt;p&gt;Chemical Engineering Research Bulletin 19(2017) 111-117&lt;/p&gt;

Damping characteristic of Ni-coated carbon nanotube/copper composite

In this paper, the damping capacity and mechanical strength of Ni-coated carbon nanotube (CNT) reinforced copper-matrix nanocomposites (Ni-coated CNT/CMNc) and single-crystal copper are investigated using molecular dynamics (MD). It is found that the mechanical strength of copper can be significantly improved by the embedded Ni-coated CNT. However, a relatively higher dissipation rate is observed for the Ni-coated CNT/CMNc compared with single-crystal copper. To have a better understanding of the augmented dissipation rate for Ni-coated CNT/CMNc, the effects of oscillation frequency and temperatures on the quality factor (Q factor) are explored. The simulation results show that the Q factor decreases with the increase in angular frequency or temperature for both single-crystal copper and Ni-coated CNT/CMNc. In addition, a weaker frequency and temperature dependence is obtained for the case of Ni-coated CNT/CMNc compared with single-crystal copper. Furthermore, by tracing the source of dissipated energy, we demonstrate that the distorted Cu lattice structure caused by the attraction of Ni is the dominant factor for the high damping rate of Ni-coated CNT/CMNc.

Numerical simulation of circular particles migration in oscillatory Poiseuille flow

The present work reports on the simulation of one and two circular particles migration in a two-dimensional channel subjected to oscillatory Poiseuille flow using a finite element arbitrary Lagrangian-Eulerian method. The effects of oscillation frequency on terminal angular velocity, drag force, motion trajectory, vortex structure and relative displacement during sedimentation have been investigated. The results show that the oscillation can cause a strong modification of the eddy formation and shedding behind the particle, and there is a critical oscillation frequency for the flow pattern of particles motion related to the blockage ratio. When the frequency is below the critical value, the single particle increases its rotation speed with alternate oscillation and discharge of vorticity, and eventually approaches the channel wall with one side vortex shedding; otherwise the particle is rotation shift with swinging wake near the channel center. The fluctuating velocities have little impact on the turning couples on the body, while the average vertical velocity decreases with the rising oscillation frequency. Moreover, the hydrodynamic interaction between the particles has a close association with the oscillatory effect. The horizontal distance reaches the maximum and the two particles separate as falling forward at the critical frequency; while the pairs in a low or high frequency oscillatory flow always settle in the horizontal line despite their different rotation characteristics. The final configuration of the pairs is sensitive to the attractor between the particles, and is caused by the Magnus type of lift balancing the wall repulsion and the interplay between particles.

Measurement of unsteady transition on a pitching airfoil using dynamic pressure sensors

Unsteady boundary layer transition on a pitching OA209 airfoil in a wind tunnel was detected by using pressure fluctuation measurement at different oscillation frequency. Thirty Kulite dynamic pressure transducers flush-mounted on the airfoil surface recorded pressure signatures, and root mean square of pressure signatures were calculated. Results indicated that the criterion of transition for static airfoil defined as the peak of root mean square of pressure fluctuation was still suitable for detection of transition on a pitching airfoil. Fixed transition experiment for pitching airfoil was performed to validate the conclusion. Effect of oscillation frequency on transition was investigated. For small reduced frequency, the hysteresis loop is larger near leading edge. With increasing in the oscillation frequencies, the transition was promoted and relaminarization was enhanced.

Dynamic of one and two elliptical particles settling in oscillatory flow: Period bifurcation and resonance state

The inertial migrations of one and two elliptical particles in a two-dimensional channel under oscillatory pressure driven flow are investigated by a finite element arbitrary Lagrangian-Eulerian (ALE) method. The effects of oscillation frequency on rotation behavior, vortex structure, pressure distribution and relative displacement during sedimentation have been studied. The results show that the oscillation can accelerate the eddy formation and shedding behind the particle, and cause a strong modification of the turning couples on the ellipse with lateral displacement. As the frequency increases, the initial ‘zigzag migration’ at the channel side goes through a period bifurcation transition to the resonance state with ‘anomalous rotation’ near the wall, and further induces ‘rotation shift’ near the channel center. The angular velocity increases before the resonance state, while the average vertical velocity decreases with the rising frequency. Moreover, the hydrodynamic interaction between the particles has a close association with the oscillatory effect. In the period bifurcation regions, the higher the oscillation frequency, the bigger the horizontal distance of the opposite rotation particles, and the particles separate fastest at the resonance state. In contrast, an attractor is formed between the pairs in the high frequency, and the two particles are exchanging the lead as settling forward. The final configuration of the pairs is shown to be caused by the Magnus type of lift balancing the wall repulsion and the interplay between particles, and is sensitive to the dynamic drag statistically corresponding to the oscillation in the wake and the periodic discharge of vorticity.