Axial Oscillations Research Articles

Experimental and numerical investigation on the cavitation erosion effect and resonance effect of submerged water jets

ABSTRACT To analyse the cavitation erosion effect and resonance effect of submerged water jets generated by organ-pipe nozzles, experimental and numerical research is conducted in the nozzles with five different diffuser angles. The cavitation erosion intensity and the flow characteristics of submerged jets are obtained by the erosion test, high-speed photography and Large Eddy Simulation. The experimental and numerical results illustrate that the nozzle with a 60° diffuser angle is capable of producing a strong cavitation erosion effect. Compared to the fully developed submerged jet, the axial pressure oscillation of axially confined submerged jets is stronger, indicating that it has a strong resonance effect. The stress wave generated by cavitation modulates the jets after reflection from the impact wall. This modulation results in the excitation of the original main frequency oscillation of organ-pipe nozzle jets, which then gives rise to multiple frequency oscillations, thereby forming the strong resonance effect.

A study of the coupled dynamics of asymmetric absorbing clusters in a photophoretic trap

Abstract We report a study on the dynamics of absorbing asymmetric carbon clusters trapped by a loosely focused Gaussian beam using photophoretic force. At high laser powers, all the trapped clusters display rotation coupled with oscillation along the axial direction, with a majority spinning about a body fixed axis, while the rest display dual spin as well as orbital motion about a fixed point in space. The spinning and orbiting frequency is inversely proportional to the amplitude of the axial oscillation - with one growing at the expense of the other. Further, the frequencies of these rotations are not proportional to the laser power, but to the trap stiffnesses inferred from the corresponding natural frequencies. The clusters also stop rotating below a certain laser power, and execute random thermal fluctuations. Our work suggests that the dynamics of clusters trapped with photophoretic force are largely dependent on the cluster size and morphology, which could, in principle, be tuned to obtain various motional responses, and help in the design of rotating micromachines in air.

Numerical investigation of heat transfer characteristics of hydrogen flow in a randomly packed bed

In this study, two randomly packed beds with small tube-to-particle diameter (D/d) ratios of D/d = 4 (PB-4) and D/d = 5 (PB-5) are constructed using the discrete element method (DEM). The pore-scale heat transfer characteristics of hydrogen flow at low pore Reynolds numbers (Rep < 100) are investigated using a DEM-CFD simulation approach, with the temperature-dependent thermo-properties of hydrogen being considered. Distinct local channeling flow patterns are revealed by detailed analyses of the flow fields in PB-4 and PB-5. The overall friction factors for both beds are found to agree well with empirical correlations. Notably, a faster spatial temperature increase is exhibited by PB-5, with a larger D/d ratio, as evidenced by a shorter axial distance for fully-heated hydrogen flow compared to PB-4. For the pore-scale heat transfer in the packed beds, the radial temperature profiles are compared at various heights of the packed beds depending on the radial porosity oscillation, in which the wall effect should be especially considered in the near-wall region. Furthermore, the axial pore-scale Nusselt number (Nup,axial) exhibits an inverse fluctuation with the axial porosity oscillation. Finally, the global Nusselt numbers (Nu) in the packed beds are analyzed under different operating conditions, which are in good agreement with empirical correlations.

The OrbiTOF mass analyzer: Time-of-flight analysis via an orbitrap quadro-logarithmic field with periodic drift focusing

Thermo Scientific™ Orbitrap™ analyzers represent a prominent class of high-resolution mass analyzer commonly used in life sciences, and for interrogation of complex samples. Injected ions, trapped within a quadro-logarithmic field, orbit a central electrode and oscillate up and down the axis. A new class of multi-reflection time-of-flight mass analyzer has been developed based on the Orbitrap field structure plus an additional series of periodic lenses wrapped around the central axis to constrain beam dispersion. The axial and angular velocity of the injected ions was balanced so that with each axial oscillation, the ions passed through the next lens in the series, to form a tightly folded 25-m long, 3-dimensional ion path, ending with ions striking a detector surface.Performance was interrogated via experiment and simulation. 70k resolving power was observed within the relatively compact analyzer, albeit at cost to transmission. A larger design with an integrated extraction trap and greater flight energy is discussed.

Energy performance and pressure fluctuation in multi-stage centrifugal pump with floating impellers under various axial oscillation frequencies

A novel multi-stage centrifugal pump with floating impellers is gaining traction in energy systems because it easily links stages in series for varying high head requirements. However, the axial oscillation frequency of the floating impeller introduces uncertainties in the pump's energy performance and pressure fluctuation. To address these issues, a comprehensive analysis of multi-stage centrifugal pumps was conducted, utilizing a computational fluid dynamics simulation method that incorporats dynamic mesh and multiple reference frame techniques, validated through three experimental trials. The findings show that average head coefficient and average efficiency are not significantly affected by the axial oscillation of impeller, but that pressure fluctuations, efficiency, and head coefficient all show periodic variations that are connected to the frequency of impeller oscillation. The amplitude of variations in the head coefficient and efficiency could increase by as much as 112.3 % and 172.4 %, respectively, under the influence of impeller oscillations, thereby heightening the instability of pump operation. Trigonometric functions for the energy performance during impeller oscillations are proposed to facilitate rapid assessment of pump stability. This study offers valuable insights into the unsteady characteristics of novel multi-stage centrifugal pumps and serves as a reference for further understanding their dynamic behavior.

Fundamental properties of the gyroscope oscillation

Despite partial solutions by famous scientists during the early Industrial Revolution, gyroscope problems remained unsolvable until the beginning of the twentieth century when several fundamental physical laws were finally formulated to describe them. Today, the principles of classical mechanics enable the formulation and description of the physical processes involved in the rotation of any object. Gyroscopic devices are objects that rotate and exhibit oscillation, which has been a challenging problem in engineering mechanics. The oscillation of a gyroscope is caused by the interaction between external and inertial torques. This is different from other examples of oscillation, such as pendulums and springs, which have been well documented. The main difference in the physics of gyroscopic oscillation is that the spinning rotors of the gyroscopic devices are supported on one side, with their axes perpendicular to the axis of oscillation. The oscillation of gyroscopic devices is interrelated with the potential and kinetic energy of their components. However, the physics of oscillation of such objects has not been fully described in publications until recently. The theory of gyroscopic effects for rotating objects has now been published and provides a solution to this problem. According to this theory, gyroscopic inertial torques represent the potential energy of the external torque and kinetic energy of the spinning rotor. This paper demonstrates the distribution of inertial torques about the axes of Cartesian coordinates, which enables the computation of gyroscope motion and oscillation.

Simulation and analysis of the electro-hydraulic coordinated system for the disc brake system in mining belt conveyor

The present study aims to investigate the dynamic performance of the disk hydraulic brake system in a mining belt conveyor. To achieve this, a simulation model of the hydraulic system for the belt conveyor is designed and constructed using AMESim. It is recognized that brake disk deformation can lead to brake shock, thus an ADAMS rigid-flexible coupling model for hydraulic disk brakes is established. Furthermore, the concept of rigid-flexible coupling mechanical systems is introduced into the hydraulic system to enable interaction between physical quantities. Use fuzzy logic rules to adjust parameters in Simulink, and in response to the suboptimal control of braking and acceleration, a compact non-model-based adaptive algorithm is incorporated into the conventional PID control algorithm. Employing mechanical modeling and multidisciplinary dynamic collaborative simulation technology, a simulation system integrating electromechanical and hydraulic aspects is developed for the disk hydraulic brake of belt conveyors. This system is employed to conduct simulation studies on the closed-loop control of braking disk speed and deceleration/acceleration for belt conveyors. The study findings reveal that the non-model-based adaptive PID control algorithm, in comparison to fuzzy PID, not only demonstrates quicker and more stable responses across various dynamic performance curves but also markedly reduces the axial oscillation amplitude of the braking disk under braking conditions.

Horizontally and vertically polarized kink oscillations in curved solar coronal loops

Aims. Kink oscillations are frequently observed in coronal loops. This work aims to numerically clarify the influence of the loop curvature on horizontally and vertically polarized kink oscillations. Methods. Working within the framework of ideal magnetohydrodynamics (MHD), we conduct three-dimensional (3D) simulations of axial fundamental kink oscillations in curved density-enhanced loops embedded in a potential magnetic field. Both horizontal and vertical polarizations are examined, and their oscillation frequencies are compared with Wentzel-Kramers-Brillouin (WKB) expectations. We discriminate between two different density specifications. In the first (dubbed “uniform density”), the density is axially uniform and varies continuously in the transverse direction toward a uniform ambient corona. Some further stratification is implemented in the second specification (dubbed “stratified”), allowing us to address the effect of evanescent barriers. Results. Examining the oscillating profiles of the initially perturbed uniform-density loops, we found that the frequencies for both polarizations deviate from the WKB expectation by ∼10%. In the stratified loop, however, the frequency of the horizontal polarization deviates to a larger extent (∼25%). We illustrate the lateral leakage of kink modes through wave tunneling in 3D simulations, for the first time. Despite this, in the uniform density and the stratified loops, the damping time-to-period ratios are similar and are close to the analytical predictions for straight configurations under the thin-tube-thin-boundary (TTTB) assumption. Conclusions. The WKB expectation for straight configurations can reasonably describe the eigenfrequency of kink oscillations only in loops without an asymmetrical cross-loop density profile perpendicular to the oscillating direction. Lateral leakage via wave tunneling is found to be less efficient than resonant absorption, meaning that the latter remains a robust damping mechanism for kink motions even when loop curvature is included.

The system for adaptive control of axial tool oscillations in vibratory drilling: description and experimental study

The system for adaptive control of axial tool oscillations in vibratory drilling: description and experimental study

Hybrid Vibration Sensor for Equipment Monitoring and Diagnostics.

Vibration diagnostics based on vibroacoustic signal data belong to the most common ways to monitor the technical condition of equipment and technical structures. The paper considers the general issues of vibration-based diagnostics and shows that in general, it is required to monitor both axial and torsional oscillations, as well as the inclination angle, occurring during the operation of various technical objects. To comprehensively monitor these parameters, a hybrid vibration sensor is proposed, simultaneously implementing three operating modes: recording linear displacements of the vibrating object; recording the rotation angle of the object at its torsional oscillations; recording the object angular deviation from the vertical component of the natural local geomagnetic field, i.e., the inclinometer mode. The proposed hybrid sensor design is described, and a theoretical analysis of the sensor's operation in each of the aforementioned operating modes is performed. The authors show that in the inclinometer mode the sensor actually operates as a fluxgate meter. Generalizing the results of the sensor's operation simultaneously in all three operating modes, an equation for the total output data signal has been obtained, which allows for obtaining the required information on the current values of linear displacements and rotation and inclination angles by selectively filtering it with respective three filters tuned to specific frequencies. The experimental studies of the proposed hybrid vibration sensor confirmed its ability to record various vibrational disturbances and changes in the inclination angle of the monitored object.

Coherent High-Frequency Axial Oscillations in a Partially Magnetized Direct Current Magnetron Discharge.

High-frequency oscillations are observed in a neon plasma of a direct current magnetron discharge. At low discharge currents, we see highly coherent 60MHz fluctuations. Above a distinct current threshold, secondary 5-10MHz fluctuations emerge in addition to turbulent fluctuations in the 60-100MHz range. The oscillations in the total discharge current suggest axial wave propagation. A lower-hybrid wave theory is invoked to model the high-frequency oscillations. We attribute the low-frequency modes to a turbulence-driven inverse cascade process, as suggested by recent simulations.

Pairwise interaction of spherical particles aligned in high-frequency oscillatory flow

We present a systematic simulation campaign to investigate the pairwise interaction of two mobile, monodisperse particles submerged in a viscous fluid and subjected to monochromatic oscillating flows. To this end, we employ the immersed boundary method to geometrically resolve the flow around the two particles in a non-inertial reference frame. We neglect gravity to focus on fluid–particle interactions associated with particle inertia and consider particles of three different density ratios aligned along the axis of oscillation. We systematically vary the initial particle distance and the frequency based on which the particles show either attractive or repulsive behaviour by approaching or moving away from each other, respectively. This behaviour is consistently confirmed for the three density ratios investigated, although particle inertia dictates the overall magnitude of the particle dynamics. Based on this, threshold conditions for the transition from attraction to repulsion are introduced that obey the same power law for all density ratios investigated. We furthermore analyse the flow patterns by suitable averaging and decomposition of the flow fields and find competing effects of the vorticity induced by the fluid–particle interactions. Based on these flow patterns, we derive a circulation-based criterion that provides a quantitative measure to categorize the different cases. It is shown that such a criterion provides a consistent measure to distinguish the attractive and repulsive arrangements.

Temporal evolution of electron cloud in a cylindrical Penning trap at room temperature.

The temporal evolution of the electron cloud at room temperature has been recorded through a resonance circuit by observing the axial oscillation frequency of its center of mass. The electron cloud undergoes radial expansion by interacting with the residual gas molecules, and it is finally lost upon hitting the Penning trap electrodes. It has been confirmed through detailed experimental investigations that the unique temporal pattern of frequency variation is a consequence of the cloud's radial expansion. Consequently, this approach offers a non-destructive means for single-shot detection, enabling continuous monitoring of the electron cloud's radial expansion during the confinement time. This technique offers a significant advantage over its destructive alternatives.

Numerical Simulation of CdTe Crystal Growth Using the Vertical Gradient Freeze Technique Assisted by Axial Low-Frequency Oscillations of the Melt

The problem of intensification of the melt crystal growth process has been analyzed using CdTe as an actual material. Numerical simulation of 100 mm diameter CdTe crystal growth using the VGF technique has been carried out. The heat–mass transfer was controlled by introducing low-frequency oscillating baffle into the melt, which is a so-called axial vibrational control (AVC) technique. The baffle configuration has been optimized to destroy solid “tails”, which were formed near the crucible walls at high cooling rates due to the low thermoconductivity and the corresponding latent heat. Analysis of CdTe homogeneity range showed that during fast crystal cooling, Te micro precipitations were formed, resulting from the decay of oversaturated Cd-rich nonstoichiometric solid solution during the Bridgman crystal growth technique. After full crystallization, a VGF-grown CdTe crystal stays inside the phase field of the high-temperature wurtzite polymorph. This makes it possible to go through the polymorph transition without Te micro-precipitating using the advantages of the VGF-specific feature of very slow cooling.

Polarization-controlled ultrasmall single photon emitter combining a quantum dot and an elliptical split ring metamaterial element

We propose a polarization-controlled ultrasmall single-photon emitter that combines a single photon source and an elliptical split ring (SR) type metamaterial element. Simulations using the finite difference time domain method showed that in elliptical metamaterial elements, the annular mode is suppressed and axial electric field oscillations occur preferentially, resulting in upward light emission from the photon source with controlled polarization. We fabricated prototype devices by focused ion beam lithography and PbS quantum dots. Evaluation of the optical properties of the devices revealed that the emission spectrum width was narrower and the emission lifetime was shorter than those of quantum dot ensemble, and that the polarization was controlled along the minor axis of ellipse. These suggested that the quantum dot emission and the metamaterial element resonated as expected. The combination of a single quantum dot and a single elliptical SR-type metamaterial element was shown to have the potential to operate as a polarization-controlled single-photon emitter.

MODELING OF VIBRATIONS OF A STACKED PIEZO ELEMENT MADE OF POROUS PIEZOCERAMICS

The work is devoted to a numerical study of the effectiveness of using porous piezoceramics in a stacked piezoelectric element, which can be used as a power drive element, a piezoelectric generator, or an ultrasonic emitter. The use of porous piezoceramics in stacked piezoelements has not received enough attention in the literature. The use of porous piezoceramics in stacked piezo elements has not received enough attention in the literature. The paper considers a stacked piezo element consisting of eight solid cylinders counter-polarized in the axial direction. The material of the cylinders is PZT-4 piezoceramic, the porosity of which varies from 0% to 80%. The problem of axial steady-state oscillations in the vicinity of the first resonance frequency and below it is solved. The lower end of the cylinder is fixed along the normal, excitation of oscillations is carried out by mechanical action under uniformly distributed pressure at the upper face or by the action of electric potential difference at the electrodes. The problems are solved in the framework of linear axisymmetric theory of electroelasticity. With mechanical action, the output characteristic of the device is the electrical potential of the free electrodes; with electrical action, it is the amplitude of the axial vibrations of the upper end or the reaction force if it is fixed. The finite element method implemented in the ACELAN package is used as the solution method. As a result of the numerical solution, the dependence of the percentage of porosity on the output characteristics of the piezo element is investigated: the frequencies of resonance and antiresonance, the electromechanical coupling coefficient, the output potential under mechanical loading, the amplitude of oscillations of the free upper end and the coupling reaction at its fixing when the oscillations are excited by the potential difference and the energy of the elastic element attached to this end. The analysis of the dependence of these characteristics allows us to conclude that it is reasonable to use such an element with porous ceramics as a piezoelectric generator and transmitter. It is noted that the choice of the percentage of porosity depends directly on the intensity of loads and the strength of porous piezoceramics.

The equation of the modulator's passing cross-section area in the pulsation device with the vibrating rotor

The article provides an analysis of the existing analytical models of the change in the cross-sectional area of the modulator in rotary-pulsation devices. The peculiarities of the application of such functions for the pulsation devices with the vibrating rotor are determined, taking into account the predominant mechanism of dispersion of emulsions. Using classical hydraulic and mathematical dependencies, in order to fulfill the requirement of creating harmonic pulsations of the emulsion in the modulator holes for synchronization with the axial oscillations of the rotor and the equality of the conditions of pulsations of the speed of the emulsion in each channel of the stator and rotor, the equation of the change in the cross-sectional area of the modulator in the pulsation devices with the vibrating rotor is determined in the form of a continuous function. This greatly simplifies the mathematical description of the function, and the subsequent analytical model of the movement of the emulsion in devices of this type. The resulting equation is necessary in determining such characteristics as the instantaneous speed and acceleration of the emulsion and the diameter of the dispersed phase after treatment.

A Transverse Velocity Spectral Estimation Method for Ultrafast Ultrasound Doppler Imaging.

A novel transverse velocity spectral estimation method is proposed to estimate the velocity component in the direction transverse to the beam axis for ultrafast imaging. The transverse oscillation was introduced by filtering the envelope data after the axial oscillation was removed. The complex transverse oscillated signal was then used to estimate the transverse velocity spectrum and mean velocity. In simulations, both steady flow with a parabolic flow profile and temporally varying flow were simulated to investigate the performance of the proposed method. Next, the proposed approach was used to estimate the flow velocity in a phantom with pulsatile flow, and finally, this method was applied in vivo in a small animal model. Results of the simulation study indicate that the proposed method provided an accurate velocity spectrogram for beam-to-flow angles from 45° to 90°, without significant performance degradation as the angle decreased. For the simulation of temporally varying flow, the proposed method had a reduced bias ( % versus 73.3%) and higher peak-to-background ratio (PBR) (>15.6 versus 10.5 dB) compared to previous methods. Results in a vessel phantom show that the temporally varying flow velocity can be estimated in the transverse direction obtained using the spectrogram produced by the proposed method operating on the envelope data. Finally, the proposed method was used to map the microvascular blood flow velocity in the mouse spinal cord, demonstrating the estimation of pulsatile blood flow in both the axial and transverse directions in vivo over several cardiac cycles.

Investigation of unsteady engulfment flows in a cross‑shaped mixer by particle image velocimetry

An experimental study was conducted to characterize flow fields in a cross-shaped mixer by particle image velocimetry technique (PIV). Instantaneous flow fields describe the formation and development of secondary flows at 20 ≤ Re ≤ 400, with focus on the dynamic evolution of vortices for periodic unsteady engulfment flows. Three stages are detected during one flow period, i.e., vortex merging, growing, and splitting. Vortex characteristics including populations, distributions, and strengths, are evaluated by a vortex identification and vorticity distributions. Reversal flow regions triggered by vortex breakdown are identified in merging and splitting vortices, which periodically shed downstream, thus causing an axial oscillation. The statistical properties and proper orthogonal decomposition (POD) modes of unsteady engulfment flows are analyzed. The peak of turbulent kinetic energy appears near the chamber corners where two co-rotating vortices are observed, and it decreases with Re. The second and third-order POD modes describe large-scale coherent structures in unsteady engulfment flows.

Based on Wavelet and Windowed Multi-Resolution Dynamic Mode Decomposition, Transient Axial Force Analysis of a Centrifugal Pump under Variable Operating Conditions

This study analyzes the transient axial force of a centrifugal pump under variable operating conditions using wavelet analysis and a novel technique called windowed multi-resolution dynamic mode decomposition (wmrDMD). Numerically simulating the sampled time series allows the reconstruction of the impeller’s axial force information, providing validation for this innovative data-driven analysis technique. The comparison between the reconstructed results and the original axial force data demonstrates a remarkable agreement, as all data points exhibit error values below 2.49%. The wmrDMD technique systematically decomposes the impeller’s axial force field into dynamically significant modes across various time scales. Removing the mean flow field in this study resolves the transient motion of the impeller’s axial force, facilitating the identification of positions with high-frequency axial force oscillations and fluctuations in intensity amplitude. The high-frequency axial force of the impeller exhibits stable periodic variations within the operating range of 1.0nr-1.0Qr, whereas the changes are insignificant within the range of 0.4nr-0.4Qr. However, within the operating range of 1.0nr-0.4Qr, both the position and intensity amplitude of the axial force exhibit significant variations without a stable trend. Furthermore, cross-wavelet and wavelet coherence analyses reveal that within the operating range of 0.4nr-0.4Qr, the axial forces on the front and rear cover plates show the strongest correlation at the periodic scale. Within the operating range of 1.0nr-1.0Qr, the next highest correlation is observed, whereas the correlation is lowest within the 1.0nr-0.4Qr operating range.