Effect Of Oscillation Amplitude Research Articles

Effect of Eigenmode Frequency on Loss Tangent Atomic Force Microscopy Measurements

Atomic Force Microscopy (AFM) is no longer used as a nanotechnology tool responsible for topography imaging. However, it is widely used in different fields to measure various types of material properties, such as mechanical, electrical, magnetic, or chemical properties. One of the recently developed characterization techniques is known as loss tangent. In loss tangent AFM, the AFM cantilever is excited, similar to amplitude modulation AFM (also known as tapping mode); however, the observable aspects are used to extract dissipative and conservative energies per cycle of oscillation. The ratio of dissipation to stored energy is defined as tanδ. This value can provide useful information about the sample under study, such as how viscoelastic or elastic the material is. One of the main advantages of the technique is the fact that it can be carried out by any AFM equipped with basic dynamic AFM characterization. However, this technique lacks some important experimental guidelines. Although there have been many studies in the past years on the effect of oscillation amplitude, tip radius, or environmental factors during the loss tangent measurements, there is still a need to investigate the effect of excitation frequency during measurements. In this paper, we studied four different sets of samples, performing loss tangent measurements with both first and second eigenmode frequencies. It is found that performing these measurements with higher eigenmode is advantageous, minimizing the tip penetration through the surface and therefore minimizing the error in loss tangent measurements due to humidity or artificial dissipations that are not dependent on the actual sample surface.

Experimental study on the lock-in of an oscillating circular cylinder confined in a plane channel

The results of an experimental study concerning wall boundary effects on the lock-in behavior of the shedding vortex of a circular cylinder, which is forced to oscillate transversely in a uniform flow at moderate Reynolds number Re = 2000,are presented in this paper. A height-adjustable flow channel is designed to study the boundary effect. Two sets of experiments are organized to study the lock-in behavior by changing the blockage ratio and oscillation amplitude separately. When the blockage ratio exceeds a critical value, the boundary effects are observed and the Strouhal number of the stationary cylinder increases non-linearly. As the blockage ratio increases, both the lower and upper limits of the lock-in region move to the lower value of excitation frequency, and the extent of the lock-in region decreases first and then increases. The boundary changes the effects of oscillation amplitude on lock-in behavior. When free from the boundary effect, as the oscillation amplitude increases, a V-shaped boundary of the lock-in region is observed, and the extent of the lock-in region increases monotonically. In comparison, under the influence of the boundary, the extent of the lock-in region first increases with the increase of the oscillation amplitude, and then decreases with the increase of the oscillation amplitude. Hysteresis loops are first observed near the lower limits of the lock-in region for some ranges of blockage ratio and oscillation amplitude in a forced-vibration system, and the extent of the hysteresis loop is affected by the two parameters.

Numerical study of the oscillation amplitude effect on the heat transfer of oscillatory impinging round jets

In this study, the effect of oscillation amplitude on the pulsed impinging jets in different nozzle to surface distances and Reynolds numbers investigated. Generally, the heat transfer increases by increasing frequency and amplitude. For distances smaller and longer than the length of the jet potential core the threshold frequency is highly dependent on the amplitude. As the amplitude increases, the threshold Strouhal number decreases, while for nozzle to surface distance near the end of the jet core the threshold Strouhal number is approximately independent from the oscillation amplitude and the Reynolds number and is about Also, although increasing the Reynolds number causes an enhancement in the threshold frequency, but in smaller amplitudes the heat transfer, increased relative to the corresponding steady jet.

Intensification of the ozone-water mass transfer in an oscillatory flow reactor with innovative design of periodic constrictions: Optimization and application in ozonation water treatment

Ozone-water mass transfer was investigated in continuous mode using a macroscale oscillatory flow reactor provided with smooth periodic constrictions (OFR-SPC). The effects of oscillation amplitude (x0) and frequency (f) on the mass transfer coefficient (kLa) were assessed through a Doehlert experimental design. Different gas and liquid flow rates were also studied. The results show that kLa increases with f (up to 4 Hz), x0 (up to 15 mm), and the gas flow rate (up to 150 Ncm3 min−1). No significant changes in kLa were observed over a wide range of liquid flow rates (up to 180 mL min−1) and for Re0 < 1000. In all conditions studied, and among different reactor configurations tested, the higher kLa values were observed with the OFR-SPC, achieving kLa values up to 35 times higher than those obtained in a conventional bubble column. Moreover, the enhancement on the mass transfer efficiency (MTE) promoted by the oscillatory movement was more pronounced as the gas (ozone) flow rate decreases and liquid (water) flow rate increases, which is another advantage of this system when looking for large-scale implementation of the ozonation process in water treatment. Ozonation experiments using a mixture of fluoroquinolones in different matrices (distilled water, surface water and urban wastewater) were also performed, the results demonstrating that OFR-SPC is an interesting reactor alternative for ozone-driven water treatment.

Effects of oscillation amplitude on motion-induced forces for 5:1 rectangular cylinders

While the 5:1 rectangular cylinder is a benchmark section, studied extensively, there are limited experimental studies commenting on any amplitude-dependence of its motion-induced forces. To this goal, such a cylinder is tested in wind tunnel through a forced vibration protocol for extracting distributed simultaneous pressure measurements under smooth flow conditions and for different heaving, pitching and coupled motion amplitudes. Ordinary flutter derivatives are extracted, and discrepancies due to oscillation amplitude are scrutinized. Spectral analysis is performed for the developing motion-induced forces, and it is found that torsional amplitudes above a threshold would increase higher harmonic frequency content. The phenomenon was also confirmed by means of Probability Density Functions and (PDFs) the Proper Orthogonal Decomposition (POD) of the unsteady wind force. In order to understand the link between the observed amplitude dependence and the flow field variation, the movement of the reattachment point on the cylinder surface is investigated by interpreting statistics of the recorded pressure measurements. The response in terms of instantaneous angle of attack is proven to be incompatible with respect to observations, since equal amplitudes of this variable result to different motion-induced forces.

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;

Flow over an inline oscillating circular cylinder in the wake of a stationary circular cylinder

Flow interference between an upstream stationary cylinder and an inline oscillating cylinder is studied with the lattice Boltzmann method. With a fixed Reynolds number Re = 100 and pitch ratio L/D = 4, the effects of oscillation amplitude A/D = [0.25, 1] and frequency fe/fs = [0.5, 2] are investigated. The wake response state is categorized into lock-in and non-lock-in. The lock-in zone in the bifurcation diagram of amplitude versus frequency is discontinuous. Response states of upstream and downstream wakes are similar under the conditions of small amplitude or low frequency. However, with large oscillating parameters, the two wakes are prone to be in different states as the flow field becomes irregular. Two distinct flow regimes have been identified, i.e., single-cylinder and two-cylinder shedding regimes. The presence of single-cylinder shedding regime is attributed to the low shedding frequency of the downstream cylinder at large amplitude. Hydrodynamic forces of the oscillating tandem system are discussed. The results reveal that forces on the two cylinders behave differently and that the absence of vortices in the gap flow significantly reduces the forces exerting on the tandem system.

Grain refining of magnesium welds by arc oscillation

Grain refining is known to improve the solidification-cracking resistance and mechanical properties of welds. Mg alloys are increasingly used for vehicle weight reduction. The present study was conducted to grain refine Mg welds by arc oscillation, which has not been investigated so far. First, significant grain refining was demonstrated by transverse arc oscillation. The effects of oscillation amplitude, oscillation frequency and torch travel speed on grain refining were shown. The effect of the alloy composition on grain refining was also demonstrated. Second, by using an overlap welding procedure, the grain refining mechanism was identified as dendrite fragmentation. Third, cooling curves recorded during welding showed that transverse arc oscillation caused reheating during solidification, which has been shown in casting/solidification to cause dendrite fragmentation by melting off dendrite arms. The cooling curves also showed that transverse arc oscillation significantly reduced the temperature gradient G along the torch travel direction, which suggested constitutional supercooling was increased. Thus, transverse arc oscillation not only caused dendrite fragmentation but also increased constitutional supercooling to help dendrite fragments survive and grow into fine equiaxed grains. Dendrite fragmentation by remelting, instead of mechanical breakup, of dendrites was discussed in the context of welding.

A unified approach for nonlinear vibration analysis of curved structures using non-uniform rational B-spline representation

A novel procedure for the nonlinear vibration analysis of curved beam is presented. The Non-Uniform Rational B-Spline (NURBS) is combined with the Euler−Bernoulli beam theory to define the curvature of the structure. The governing equation of motion and the general frequency formula, using the NURBS variables, is applicable for any type of curvatures, is developed. The Galerkin procedure is implemented to obtain the nonlinear ordinary differential equation of curved system and the multiple time scales method is utilized to find the corresponding frequency responses. As a case study, the nonlinear vibration of carbon nanotubes with different shapes of curvature is investigated. The effect of oscillation amplitude and the waviness on the natural frequency of the curved nanotube is evaluated and the primary resonance case of system with respect to the variations of different parameters is discussed. For the sake of comparison of the results obtained with those from the molecular dynamic simulation, the natural frequencies evaluated from the proposed approach are compared with those reported in literature for few types of carbon nanotube simulation.

Investigation of Airfoil Unsteady Aerodynamic Characteristics Based on Finite Macro-Element and TFI Hybrid Dynamic Mesh Correction

The hybrid dynamic mesh method combining finite macro-element with transfinite interpolation (TFI) is adopted in this paper which ensures mesh quality for large deformations and high efficiency. Besides, TFI is modified to preserve the grid orthogonality near the boundary using rotation correction and weighted approach in order to solve its orthogonal problem. The numerical simulation of oscillating airfoil is performed by solving Reynolds Averaged Navier-Stokes (RANS) equations with hybrid dynamic mesh method. The influences of oscillation parameters and Mach number on the hysteresis effect are investigated and the separation vortex pattern and evolution procedure are presented. Moreover, numerical results show the occurrence of lock-in zone. The effect of oscillation amplitude and frequency on it and the characteristics of vortex shedding are discussed.

Modelling the effect of Pliocene–Quaternary changes in sea level on stable and tectonically active land masses

ABSTRACTA mathematical model was used to examine the effect of Pliocene and Quaternary changes in sea level on the development of tectonically active and inactive rock coasts. The model calculated rates of mechanical wave erosion according to such factors as the deep water wave regime, bottom topography and surface roughness, and the resistance of the rocks. Subaerial terraces were truncated or eliminated by subsequent terrace formation at lower elevations, especially on steeply sloping landmasses experiencing slow rates of uplift. Submarine terraces formed during glacial stillstands were best preserved when rapid subsidence quickly carried them below the level of wave action. On slowly subsiding landmasses, submarine terraces formed during interglacials and glacial periods experienced repeated erosional modification during subsequent periods of rising and falling sea level and were generally less distinctive. On rapidly rising or subsiding (&gt;5 mm yr‐1) landmasses, terraces that formed during interglacial stages alternated, above and below present sea level, with terraces formed during glacial stages. Despite some differences in terrace occurrence and elevational distribution, it may be difficult to distinguish profiles cut during accelerating or decelerating uplift. The amount of erosion during sea level oscillations increases with oscillation amplitude and the larger oscillations in the middle to late Quaternary were therefore more conducive to erosion than the smaller oscillations of the Pliocene and early Quaternary. The effect of oscillation amplitude may have been countered during the earlier stages of profile development, however, by steeper submarine gradients and reduced rates of wave attenuation. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Numerical aerodynamic analysis of bluff bodies at a high Reynolds number with three-dimensional CFD modeling

This paper focuses on numerical simulations of bluff body aerodynamics with three-dimensional CFD (computational fluid dynamics) modeling, where a computational scheme for fluid-structure interactions is implemented. The choice of an appropriate turbulence model for the computational modeling of bluff body aerodynamics using both two-dimensional and three-dimensional CFD numerical simulations is also considered. An efficient mesh control method which employs the mesh deformation technique is proposed to achieve better simulation results. Several long-span deck sections are chosen as examples which were stationary and pitching at a high Reynolds number. With the proposed CFD method and turbulence models, the force coefficients and flutter derivatives thus obtained are compared with the experimental measurement results and computed values completely from commercial software. Finally, a discussion on the effects of oscillation amplitude on the flutter instability of a bluff body is carried out with extended numerical simulations. These numerical analysis results demonstrate that the proposed three-dimensional CFD method, with proper turbulence modeling, has good accuracy and significant benefits for aerodynamic analysis and computational FSI studies of bluff bodies.

Enhancing heat transfer in a high Hartmann number magnetohydrodynamic channel flow via torsional oscillation of a cylindrical obstacle

An approach is studied for side-wall heat transfer enhancement in the magnetohydrodynamic flow of fluid in a rectangular duct that is damped by a strong transverse magnetic field. The mechanism employs the rotational oscillation of a cylinder placed inside the duct to encourage vortex shedding, which promotes the mixing of fluid near a hot duct wall with cooler fluid in the interior. The effectiveness of the heat transfer enhancement is investigated over a wide range of oscillation amplitudes and forcing frequencies. The motivation for exploring this mechanism is inspired by the transient growth response of this flow, which indicates that the optimal disturbances feeding the vortex shedding process are localized near the cylinder, and are characterized by an asymmetrical disturbance with respect to the wake centreline. The results show that a considerable increase in heat transfer from the heated channel wall due to rotational oscillation of the cylinder can be achieved, with the maximum enhancement of more than 30% over a zone extending 10d downstream of the cylinder. As the angular velocity amplitude of oscillation is increased, the range of oscillation frequencies for effective enhancement is widened, and the frequency at which the peak Nusselt number occurs is shifted slightly to lower frequencies. As the amplitude is increased, the formation of strong discrete wake vortices draws fluid from the wall boundary layers into the wake, enhancing heat transfer. The effect of oscillation amplitude on the distribution of local Nusselt number \documentclass[12pt]{minimal}\begin{document}$\textit {Nu}_w$\end{document}Nuw along the heated wall is significant. With an increase in Reynolds number, scope for additional heat transfer enhancement is possible.

Effect of oscillation amplitude on velocity distributions in an oscillatory baffled column (OBC)

This paper presents a numerical study of the effect of oscillation amplitude in oscillatory baffled column (OBC) using computational fluid dynamics. The numerical work was carried out for single phase liquid flow for an unsteady 3-D model using commercial software, Fluent (2006). This work was concentrated on the effect of oscillation amplitude. Three amplitudes of 5, 10 and 15mm with constant frequency of 1Hz are applied. Vortex and cycle average velocities at different points are analyzed. The studies show the maximum velocity for 5mm, 10mm and 15mm in an OBC are 0.11m/s, 0.25m/s and 0.40m/s respectively in the first cycle of oscillation. At a constant frequency, greater oscillation amplitude displaces the liquid to a further distance and builds a larger vortex. Vortex length was 1.5 times bigger when oscillation amplitude changes from 5mm to 10mm and 2 times when the amplitude is triple from 5mm. The detailed validation is presented somewhere else; this research is focused on the effect of oscillation.

Application of Harmonic Balance Method to Numerical Model Unsteady Viscous Flow around Oscillating Cascade

A harmonic balance approach has been developed to compute nonlinear viscous unsteady flows around oscillating blades. The computed results using two orders harmonic balance method are compared with those by conventional dual-time stepping method. Results obtained with the present method agree well with those from dual-time stepping method, which demonstrate the ability of the present analysis method to model accurately the unsteady flow. Furthermore，the present method is highly efficient. It is about 36 times fast than conventional dual-time stepping method in the present computation. Then the effects of oscillation amplitude and reduced frequency on unsteadiness of flows are studied. The analysis exploits the fact that, (1) the hysteresis effect of unsteady flow is hardly affected by oscillation amplitude, but the first harmonic unsteady pressure across the blade is proportional to oscillation amplitude; (2) the higher the reduced frequency, the wider the range of unsteady aerodynamic forces, the more intense the hysteresis effect.

Vibration and stability of an axially moving Rayleigh beam

In this paper, the vibration and stability of an axially moving beam is investigated. The finite element method with variable-domain elements is used to derive the equations of motion of an axially moving beam based on Rayleigh beam theory. Two kinds of axial motions including constant-speed extension deployment and back-and-forth periodical motion are considered. The vibration and stability of beams with these motions are investigated. For vibration analysis, direct time numerical integration, based on a Runge–Kutta algorithm, is used. For stability analysis of a beam with constant-speed axial extension deployment, eigenvalues of equations of motion are obtained to determine its stability, while Floquet theory is employed to investigate the stability of the beam with back-and-forth periodical axial motion. The effects of oscillation amplitude and frequency of periodical axial movement on the stability of the beam are discussed from the stability chart. Time histories are established to confirm the results from Floquet theory.

Gaseous Cavitation and Wear in Lubricated Fretting Contacts

Fretting phenomena operating in the presence of grease was investigated experimentally and analytically. A fretting test rig was designed, developed, and equipped with a microscope and high-speed video camera to observe the effects of the lubricant entrainment within the contact during the fretting phenomena. A mixed elastohydrodynamic lubrication model was used to analytically investigate lubricated fretting and corroborate with experimental results. An analytical approach is also presented to determine the amount of lubrication entrained within the fretting contact. The results of fretting wear operating in the presence of grease are presented for case-hardened steel in the crossed cylinder configuration and hardened steel ball-on-sapphire flat configuration. The roles of lubrication, oscillation amplitude, and cavitation in fretting are presented and discussed. Lubrication was found to mitigate the effect of fretting on a surface while the effect of oscillation amplitude on fretting was more complex. The results indicate that frequency increases the amount of material transfer between fretting surfaces. Gaseous cavitation was observed to occur in the trailing edge of the fretting contact and increased with speed. A closed form equation was derived to approximate the volume of the lubricant entering the fretting contact area during the fretting motion and explain the effect of test conditions on fretting wear.

A study of velocity and residence time of single bubbles in a gassed oscillatory baffled column: effect of oscillation amplitude

AbstractIn this paper, the experimental evaluation of velocity and residence time of single bubbles of different sizes in a gassed oscillatory baffled column (OBC) using a high‐speed imaging technique is reported. This work is particularly concentrated on the effect of oscillatory amplitude. The results show that the instantaneous axial bubble velocities vary up to four times with respect to the mean value at an oscillatory amplitude greater than 2 mm. The ratio of the radial to axial bubble velocity increases beyond unity for the highest oscillation amplitude investigated. The direct measurement of residence time of the bubbles within a baffled cell is also reported.© 2003 Society of Chemical Industry

Effects of oscillation amplitude on aerodynamic derivatives

In this paper, the effects of oscillation amplitude on the aerodynamic derivatives of the thin rectangular cylinder with B/ D=13 and 150 were investigated. It was clear that the torsional amplitude affected strongly the aerodynamic derivatives H 2 * and A 2 *. This effect reduced the critical velocity of flutter by about 10%. The cause of this effect was investigated by the measurement of the unsteady surface pressure. This investigation made it clear that the variation of A 2 * is caused by the movement of the acting point of the resultant lift force. These results indicate that these effects cannot be disregarded for such a simple thin plate but for a real bridge girder with a more complex cross-section and with delicate aerodynamic control devices.

Effects of Oscillatory Speed and Mutual Overlap on the Tribological Behavior of PTFE and Selected PTFE-based Self-Lubricating Composites

The wear reducing actions of bronze, graphic powder and discontinuous glass fiber within a PTFE matrix have been demonstrated in oscillatory contact with stainless steel, at two different amplitudes, over a range of speeds. The secondary effects on the friction of the PTFE have also been investigated. The effects of oscillation amplitude on frictional surface morphology have been observed for these composites. The friction and wear of the unfilled PTFE matrix were both found to increase as speed increased, with wear going through a transition from a low- to high-rate regime. The speed at which this transition occurs increases with decreasing oscillatory amplitude.