Oscillatory and streaming flow between two spheres due to combined oscillations

2017 ◽  
Vol 826 ◽  
pp. 335-362
Author(s):  
Dejuan Kong ◽  
Anita Penkova ◽  
Satwindar Singh Sadhal
Keyword(s):  
Flow Field ◽  
Phase Difference ◽  
High Frequency ◽  
Amplitude Ratio ◽  
Dominant Role ◽  
Outer Region ◽  
Low Frequency ◽  
Frequency Oscillation ◽  
Steady Streaming ◽  
Streaming Flow

The flow induced by the combined torsional and transverse oscillations of a sphere with amplitude ratio $\unicode[STIX]{x1D6FC}$ and phase difference $\unicode[STIX]{x1D6FD}$ in a concentric spherical container is examined. Analytical solutions of the leading-order flow field and shear stress profiles have been obtained. Steady streaming flows are also analysed not only for the case of unrestricted Womersley number $|M|$, but also in the low-frequency $(|M|\ll 1)$ and high-frequency ($|M|\gg 1$) limits. At high frequency, the flow field has been divided into three regions: two boundary layers and the outer region. The streaming flow field is determined for the limiting case of the streaming Reynolds number $R_{s}\ll 1$. The results are compared with those of single torsional or transverse oscillation, and found to match very well. The amplitude ratio $\unicode[STIX]{x1D6FC}$ and phase difference $\unicode[STIX]{x1D6FD}$, in determining the streaming, are also discussed. The number and direction of steady streaming recirculation on the $r$–$\unicode[STIX]{x1D703}$ plane depend on value of the amplitude ratio $\unicode[STIX]{x1D6FC}$. The phase difference $\unicode[STIX]{x1D6FD}$ plays a dominant role in the azimuthal velocity $u_{1\unicode[STIX]{x1D719}}^{(s)}$ of steady streaming. When $\unicode[STIX]{x1D6FD}$ is approximately $(2n+1)\unicode[STIX]{x03C0}/2$, $u_{1\unicode[STIX]{x1D719}}^{(s)}$ vanishes under low-frequency oscillation, while steady streaming has a recirculation on the $r$–$\unicode[STIX]{x1D719}$ plane under higher-frequency oscillation.

Analysis of Fast-Scale Bifurcation in Peak Current Controlled Buck-Boost Inverter Based on Unified Averaged Model

2016 ◽  
Vol 26 (05) ◽  
pp. 1650074 ◽  
Author(s):  
Hao Zhang ◽  
Shuai Dong ◽  
Weimin Guan ◽  
Ye Liu
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Period Doubling ◽  
Current Control ◽  
High Frequency Oscillation ◽  
Switching Frequency ◽  
Unified Framework ◽  
Frequency Oscillation ◽  
Peak Current ◽  
Averaged Model

In this paper, a unified averaged modeling method is proposed to investigate the fast-scale period-doubling bifurcation of a full-bridge integrated buck-boost inverter with peak current control. In order to increase the resolution of the conventional classic averaged model to half the switching frequency, sample-and-hold effect of inductor current is absorbed into the averaged model, i.e. the proposed unified averaged model can capture the high-frequency dynamical characteristics of the buck-boost inverter, which is both an extension and a modification of conventional averaged model. Based on the unified mode, fast-scale bifurcation is identified, and the corresponding bifurcation point is predicted with the help of the locus movement of all the poles, and their underlying mechanisms are revealed. Detailed analysis shows that the occurrence of high-frequency oscillation means fast-scale bifurcation, while the occurrence of low-frequency oscillation leads to slow-scale bifurcation. Finally, it is demonstrated that the unified averaged model can provide not only a general method to investigate both the slow- and fast-scale bifurcations in a unified framework but also a quite straightforward design-oriented method which can be directly applicable.

Simulation on Flow Field Induced by Vibration Surface of Low Frequency

2010 ◽  
Author(s):  
Ling Shen ◽  
Shuhong Liu ◽  
Yulin Wu
Keyword(s):  
Flow Field ◽  
Velocity Distribution ◽  
Numerical Computation ◽  
High Frequency ◽  
Ultrasonic Transducer ◽  
Sewage Treatment ◽  
Low Frequency ◽  
Vibration Source ◽  
Water Tank ◽  
Industrial Cleaning

Ultrasonic cavitation generated by high-frequency ultrasonic transducer is widely studied because this phenomenon could be applied in a great variety of fields, including medical therapy, industrial cleaning as well as sewage treatment. Flow field influenced by vibration source of low frequency, however, is less studied. For the present study, a water tank of 1000×600×500mm is investigated when a vibration surface that represents a transducer of less frequency vibrates in the vicinity of one wall. Numerical computation based on the method of dynamic mesh is applied. Furthermore, two different vibration patterns are simulated, i.e., piston movement and drumhead vibration. Results show different pressure and velocity distribution within water tank when vibration surface is working at various frequencies and amplitudes. Differences of the flow fields are found between these circumstances, and similarity is found with that induced by ultrasonic transducer. Analysis on differences is discussed for further study.

scholarly journals A Time-Frequency Joint Time-Delay Difference Estimation Method for Signal Enhancement in the Distorted towed Hydrophone Array

2021 ◽  
Vol 13 (22) ◽  
pp. 4586
Author(s):  
Chuanqi Zhu ◽  
Shiliang Fang ◽  
Qisong Wu ◽  
Liang An ◽  
Xinwei Luo ◽  
...  
Keyword(s):  
Time Delay ◽  
Phase Difference ◽  
High Frequency ◽  
Estimation Method ◽  
Low Frequency ◽  
Line Spectrum ◽  
Time Frequency ◽  
Radiated Noise ◽  
Estimation Performance ◽  
Delay Difference

To acquire the enhanced underwater ship-radiated noise signal in the presence of array shape distortion in a passive sonar system, the phase difference of the line-spectrum component in ship-radiated noise is often exploited to estimate the time-delay difference for the beamforming-based signal enhancement. However, the time-delay difference estimation performance drastically degrades with decreases of the signal-to-noise ratio (SNR) of the line-spectrum component. Meanwhile, although the time-delay difference estimation performance of the high-frequency line-spectrum components is generally superior to that of the low-frequency one, the phase difference measurements of the high-frequency line-spectrum component often easily encounter the issue of modulus 2π ambiguity. To address the above issues, a novel time-frequency joint time-delay difference estimation method is proposed in this paper. The proposed method establishes a data-driven hidden Markov model with robustness to phase difference ambiguity by fully exploiting the underlying property of slowly changing the time-delay difference over time. Thus, the phase difference measurements available for time-delay difference estimation are extended from that of low-frequency line-spectrum components in a single frame to that of all detected line-spectrum components in multiple frames. By jointly taking advantage of the phase difference measurements in both time and frequency dimensions, the proposed method can acquire enhanced time-delay difference estimates even in a low SNR case. Both simulation and at-sea experimental results have demonstrated the effectiveness of the proposed method.

Study of the effect of strain amplitude ratio at two-frequency cyclic loading

2018 ◽  
Vol 84 (12) ◽  
pp. 50-60 ◽  
Author(s):  
M. M. Gadenin
Keyword(s):  
High Frequency ◽  
Amplitude Ratio ◽  
Low Frequency ◽  
Frequency Component ◽  
Single Frequency ◽  
High Frequency Component ◽  
Dual Frequency ◽  
Operating Modes ◽  
Cyclic Durability ◽  
Cycle Loading

The operating modes of loading elements of machines and structures exhibit, as a rule, more complicated character of their loading cycles compared to sinusoidal used in the practice of calculations and experiments. It is noted that in a number of cases the actual conditions of load changing can be schematized by dual-frequency loading modes with superposition of the high-frequency component of the main workload attributed to the effects of vibrations, aero- and hydrodynamic impacts, regulation of the working process, etc. Testing of three steel samples which differ in their cyclic properties has shown that such two-frequency regimes lead to a decrease in the durability in comparison with single-frequency loading, equal in the amplitude of maximum stresses. This reduction depends on the parameters of the basic low-frequency and imposed high-frequency loads. Evaluation of this reduction can be performed both i) using the laws of summation of the damage expressed in the strain terms, and ii) using an analytical expression considered below, which includes calculated or experimentally determined durability for single-frequency loading with the maximum (total) amplitude of the effective stress and durability coefficient, characteristic of each type of material and determined by the ratio of amplitudes and hours of low- and high stresses. A computational-experimental analysis of the effect of the amplitude of low-frequency and superimposed high-frequency loading under two-frequency modes of stress change on the cyclic durability showed that the imposition of the high-frequency component of cyclic deformation on the main low-cycle loading process leads to a significant decrease in the cyclic durability, the level of the decrease correlates with the level of amplitudes and frequencies ratios of the summarized harmonic processes of load application.

Mechanisms of temporal variation in single-nephron blood flow in rats

1993 ◽  
Vol 264 (3) ◽  
pp. F427-F434 ◽  
Author(s):  
K. P. Yip ◽  
N. H. Holstein-Rathlou ◽  
D. J. Marsh
Keyword(s):  
Blood Flow ◽  
High Frequency ◽  
Laser Doppler Velocimetry ◽  
Low Frequency ◽  
Tubuloglomerular Feedback ◽  
High Frequency Oscillation ◽  
Frequency Oscillation ◽  
Acute Hypertension ◽  
Efferent Arteriole ◽  
Single Nephron

Modified laser-Doppler velocimetry was used to determine the number of different mechanisms regulating single-nephron blood flow. Two oscillations were identified in star vessel blood flow, one at 20-50 mHz and another at 100-200 mHz. Tubuloglomerular feedback (TGF) mediates the slower oscillation, and the faster one is probably myogenic in origin. Acute hypertension increased autospectral power in the 20-50 mHz and 100-200 mHz frequency bands to 282 +/- 50 and 248 +/- 64%, respectively, of control even though mean single-nephron blood flow was autoregulated. Mean blood flow increased 24.6 +/- 6.1% when TGF was inhibited by intratubular perfusion with furosemide, and it decreased 42.8 +/- 3.9% when TGF was saturated by tubular perfusion with artificial tubular fluid at high rates. Autospectral power in the low-frequency band decreased 50.5 +/- 9.6% during furosemide and decreased 74.9 +/- 5.9% during TGF saturation, consistent with a TGF origin of the slow oscillation. In contrast, autospectral power of the high-frequency oscillation increased 75.4 +/- 23.9% during TGF inhibition and decreased 35.8 +/- 11% when TGF was saturated, suggesting interactions between the two spontaneously oscillating components in efferent arteriole blood flow.

Geometry Effects on the Flow Field and the Spectral Characteristics of a Triple Annular Swirler

2003 ◽  
Author(s):  
Guoqiang Li ◽  
Ephraim J. Gutmark
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
High Frequency ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Low Frequency ◽  
Tube Length ◽  
Formation Mechanisms ◽  
Recirculation Bubble ◽  
Inlet Conditions

The dynamics of vortex breakdown are important to the performance of gas turbine combustors where swirling flows are extensively used to stabilize the flame and extend the lean flammability limit (LBO). Due to the strong interaction of vortical structures in the swirling flow with heat release and acoustical modes, vortex breakdown mechanism is essential to understanding the thermoacoustic behavior and to the development of combustion instability control strategy. This paper analyzes the vortex breakdown behavior downstream of a Triple Annular Research Swirler (TARS) based on velocity flow field data from stereoscopic PIV measurement and spectral data from hotwire/film measurements. The vortical structure is highly dependent on the different swirler combinations (swirler geometry) as well as on inlet conditions such as air flow-rate, mixing tube length and downstream conditions such as exhaust nozzle contraction ratio. The scale, location, strength, and formation mechanisms of the large-scale vortices vary for different geometries. The shape of the recirculation bubble changes with the outlet boundary conditions, suggesting that the swirling flow inside the combustion chamber remains subcritical downstream of the vortex breakdown. However, spectral analysis reveals that the dominant frequencies close to the exit of the TARS show only slight change for different outlet boundary conditions. Three ranges of frequencies characterize the spectral domain of TARS: high frequency close to the TARS exit, middle range frequency downstream of this region, and low frequency in most regions further downstream. The sources of instabilities in these three regions could be attributed to the strong shear layer, precessing vortex core and interaction between spanwise and azimuthal instabilities. The outlet boundary conditions affect the middle and low frequency range but have no effect on the high frequency. The inlet conditions have global effect on the entire flow region.

A natural low-frequency oscillation of the flow over an airfoil near stalling conditions

1989 ◽  
Vol 202 ◽  
pp. 403-442 ◽  
Author(s):  
K. B. M. Q. Zaman ◽  
D. J. Mckinzie ◽  
C. L. Rumsey
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Flow Field ◽  
Bluff Body ◽  
Low Frequency ◽  
Two Dimensional ◽  
Frequency Oscillation ◽  
Low Frequency Oscillation ◽  
Unsteady Forces ◽  
Flow Fluctuations

An unusually low-frequency oscillation in the flow over an airfoil is studied experimentally as well as computationally. Wind-tunnel measurements are carried out with two-dimensional airfoil models in the chord Reynolds number (Rc) range of 0.15 × 105−3.0 × 105. During deep stall, at α [gsim ] 18°, the usual ‘bluff-body shedding’ occurs at a Strouhal number, Sts ≈ 0.2. But at the onset of static stall around α = 15°, a low-frequency periodic oscillation is observed, the corresponding Sts being an order of magnitude lower. The phenomenon apparently takes place only with a transitional state of the separating boundary layer. Thus, on the one hand, it is not readily observed with a smooth airfoil in a clean wind tunnel, while on the other, it is easily removed by appropriate ‘acoustic tripping’. Details of the flow field for a typical case are compared with a case of bluff-body shedding. The flow field is different in many ways from the latter case and does not involve a Kármán Vortex street. The origin of the flow fluctuations traces to the upper surface of the airfoil and is associated with a periodic switching between stalled and unstalled states. The mechanism of the frequency selection remains unresolved, but any connection to blower instabilities, acoustic standing waves or structural resonances has been ruled out.A similar result has been encountered computationally using a two-dimensional Navier–Stokes code. While with the assumption of laminar flow, wake oscillation akin to the bluff-body shedding has been observed previously, the Sts is found to drop to about 0.03 when a ‘turbulent’ boundary layer is assumed. Details of the flow field and unsteady forces, computed for the same conditions as in the experiment, compare reasonably well with the experimental data.The phenomenon produces intense flow fluctuations imparting much larger unsteady forces to the airfoil than that experienced in bluff-body shedding, and may represent the primary aerodynamics of stall flutter of blades and wings.

scholarly journals Steady streaming in a two-dimensional box model of a passive cochlea

2014 ◽  
Vol 753 ◽  
pp. 254-278 ◽  
Author(s):  
Elisabeth Edom ◽  
Dominik Obrist ◽  
Leonhard Kleiser
Keyword(s):  
Basilar Membrane ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Travelling Wave ◽  
Steady Streaming ◽  
Compliant Structure ◽  
Physiological Relevance ◽  
Theoretical Predictions ◽  
New Phenomena ◽  
Streaming Flow

AbstractAcoustic stimulation of the cochlea leads to a travelling wave in the cochlear fluids and on the basilar membrane (BM). It has long been suspected that this travelling wave leads to a steady streaming flow in the cochlea. Theoretical investigations suggested that the steady streaming might be of physiological relevance. Here, we present a quantitative study of the steady streaming in a computational model of a passive cochlea. The structure of the streaming flow is illustrated and the sources of streaming are closely investigated. We describe a source of streaming which has not been considered in the cochlea by previous authors. This source is also related to a steady axial displacement of the BM which leads to a local stretching of this compliant structure. We present theoretical predictions for the streaming intensity which account for these new phenomena. It is shown that these predictions compare well with our numerical results and that there may be steady streaming velocities of the order of millimetres per second. Our results indicate that steady streaming should be more relevant to low-frequency hearing because the strength of the streaming flow rapidly decreases for higher frequencies.

scholarly journals On the steady streaming flow due to high-frequency vibration in nearly inviscid liquid bridges

1998 ◽  
Vol 354 ◽  
pp. 147-174 ◽  
Author(s):  
JOSÉ A. NICOLÁS ◽  
DAMIÁN RIVAS ◽  
JOSÉ M. VEGA
Keyword(s):  
Reynolds Number ◽  
High Frequency ◽  
Asymptotic Model ◽  
Steady Streaming ◽  
Capillary Bridges ◽  
Axial Vibrations ◽  
Vibration Parameters ◽  
Limiting Case ◽  
Quantitative Response ◽  
Streaming Flow

The steady streaming flow due to vibration in capillary bridges is considered in the limiting case when both the capillary Reynolds number and the non-dimensional vibration frequency (based on the capillary time) are large. An asymptotic model is obtained that provides the streaming flow in the bulk, outside the thin oscillatory boundary layers near the disks and the interface. Numerical integration of this model shows that several symmetric and non-symmetric streaming flow patterns are obtained for varying values of the vibration parameters. As a by-product, the quantitative response of the liquid bridge to high-frequency axial vibrations of the disks is also obtained.

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