The Instrumental Error When Determining the Phase Angle Between Low-Frequency Signals with Storage and GPS Synchronization

An analytical investigation of the pressure response to forced volume oscillations of a shallow cylindrical chamber with a porous end is undertaken. Investigation is in the frequency domain. Both infinite and finite-length chambers are considered. The irreversible gas flow introduces a frequency-dependent phase angle between volume and pressure change. Pressure leads volume at low frequency, and the phase angle becomes zero at high frequency. Curve characteristics suggest applications such as gas damping of vibrating systems.

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Combustion Oscillations in Bluff Body Stabilized Diffusion Flames With Variable Length Inlet

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.3078387 ◽

2009 ◽

Vol 131 (5) ◽

Cited By ~ 1

Author(s):

M. Madanmohan ◽

S. Pandey ◽

A. Kushari ◽

K. Ramamurthi

Keyword(s):

Heat Release ◽

Phase Angle ◽

Bluff Body ◽

Diffusion Flames ◽

Combustion Process ◽

Low Frequency ◽

Pressure Oscillations ◽

Pipe Length ◽

Entry Length ◽

Low Frequency Oscillations

This paper describes the results of an experimental study to understand the influence of inlet flow disturbances on the dynamics of combustion process in bluff body stabilized diffusion flames of liquid petroleum gas and air. The results show the influence of weak disturbances created by the change in incoming pipe length on the amplitude of pressure oscillations and the phase angle between pressure and heat release. It is seen that the phase delay increases as the entry length increases. The rms value of pressure, however, generally falls with the increase in length. The phase angle is seen to be in the second quadrant, showing that the heat release oscillations damp the pressure oscillations. Therefore, the decrease in the phase angle results in the reduction in damping and hence an increase in pressure fluctuations. The dominant frequencies of combustion oscillations are found to be the low frequency oscillations, and the frequency of oscillations increases with a decrease in the inlet pipe length and an increase in the flow Reynolds number. It is suggested that such low frequency oscillations are driven by vortex shedding at the wake of the bluff body, which energizes the diffusion and mixing process.

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Transfer Function Analysis of Cerebral Hemodynamics in Patients with Carotid Stenosis

Journal of Cerebral Blood Flow & Metabolism ◽

10.1097/00004647-199904000-00012 ◽

1999 ◽

Vol 19 (4) ◽

pp. 460-465 ◽

Cited By ~ 83

Author(s):

Han-Hwa Hu ◽

Terry Bo-Jau Kuo ◽

Wen-Jang Wong ◽

Yun-On Luk ◽

Chang-Ming Chern ◽

...

Keyword(s):

Transfer Function ◽

Carotid Stenosis ◽

Phase Angle ◽

Cerebral Autoregulation ◽

Function Analysis ◽

Low Frequency ◽

High Grade ◽

Vasomotor Reactivity ◽

Transfer Function Analysis ◽

Spontaneous Fluctuations

This study evaluates the validity of the transfer function analysis of spontaneous fluctuations of arterial blood pressure (ABP) and blood flow velocity of the middle cerebral artery (MCAFV) as a simple, convenient method to assess human cerebral autoregulation in patients with carotid stenosis. Eighty-three consecutive patients with various degrees of carotid stenosis and 37 healthy controls were enrolled. The carotid stenosis was graded based on the diagnostic criteria of duplex ultrasound. Instantaneous bilateral MCAFV and ABP of all participants were assessed noninvasively using transcranial Doppler sonography and the servocontrolled infrared finger plethysmography, respectively. Spectral analyses of ABP and MCAFV were performed by fast Fourier transform. The fluctuations in ABP as well as in MCAFV were diffracted into three components at specific frequency ranges designated as high-frequency (HF; 0.15 to 0.4 Hz), low-frequency (LF; 0.04 to 0.15 Hz), and very low-frequency (VLF; 0.016 to 0.04 Hz). Cross-spectral analysis was applied to quantify the coherence, transfer phase, and magnitude in individual HF, LF, and VLF components. Transcranial Doppler CO2 vasomotor reactivity was measured with 5% CO2 inhalation. The LF phase angle (r = −0.53, P < 0.001); magnitude of VLF (r = −0.29, P = 0.002), LF (r = −0.35, P < 0.001), and HF (r = −0.47, P < 0.001); and CO2 vasomotor reactivity (r = −0.66, P < 0.001) were negatively correlated with the severity of stenosis. Patients with unilateral high-grade (greater than 90% stenosis) carotid stenosis demonstrated significant reduction in LF phase angle ( P < 0.001) and HF magnitude ( P = 0.018) on the ipsilateral side of the affected vessel compared with their contralateral side. The study also revealed a high sensitivity, specificity, and accuracy using LF phase angle and HF magnitude to detect a high-grade carotid stenosis. A strong correlation existed between the LF phase angle and the CO2 vasomotor reactivity test (r = 0.62, P < 0.001), and the correlation between the HF magnitude and the CO2 vasomotor reactivity (r = 0.44, P < 0.001) was statistically significant as well. We conclude that transfer function analysis of spontaneous fluctuations of MCAFV and ABP could be used to identify hemodynamically significant high-grade carotid stenosis with impaired cerebral autoregulation or vasomotor reserve.

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Rotor Dynamic Analysis on Partial Admission Control Stage in a Large Power Steam Turbine

Volume 7: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2010-22608 ◽

2010 ◽

Cited By ~ 1

Author(s):

Lin Gao ◽

Yiping Dai

Keyword(s):

Steam Turbine ◽

Phase Angle ◽

Low Frequency ◽

Deep Understanding ◽

Labyrinth Seal ◽

Steam Turbines ◽

Large Power ◽

Stiffness Coefficients ◽

Control Stage ◽

Partial Admission

Partial admission is used widely for steam turbines to match their output power to the load demand. The occurrences or thresholds of most self-induced low-frequency vibrations are under partial admission conditions. But the destabilizing forces which cause rotor instability are seldom investigated under partial admission conditions especially for large power steam turbines. Full 3D CFD model is built for the control stage of a 600 MW steam turbine applying commercial codes. N-S equations are solved to investigate the flow fields in the control stage including all the blade passages and the labyrinth seal over the shroud. Interesting flow distributions are observed for the seal spaces at partial admission conditions. A correction formula is presented for partial admission labyrinth seal based on the classical one and a method is discussed for the estimation of partial-admission phase-angle-dependent stiffness coefficients. The destabilizing forces acting on the rotor system are calculated for different eccentricity angles and are compared with those under the concentric condition. The stiffness coefficients are solved under typical partial admission conditions. They are found to change dramatically with the phase angle. The results may be helpful for a deep understanding of the low-frequency variation problems of large power steam turbines under partial admission conditions.

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Influence of Different Modifiers on Bonding Strength and Rheological Performance of Bitumen Emulsion

Materials ◽

10.3390/ma12152414 ◽

2019 ◽

Vol 12 (15) ◽

pp. 2414 ◽

Cited By ~ 3

Author(s):

Changluan Pan ◽

Deqiang Liang ◽

Liantong Mo ◽

Martin Riara ◽

Juntao Lin

Keyword(s):

Phase Angle ◽

Bonding Strength ◽

Complex Modulus ◽

Low Frequency ◽

Epoxy Adhesive ◽

Styrene Butadiene Rubber ◽

Butadiene Rubber ◽

Modified Bitumen ◽

Bitumen Emulsion ◽

Rheological Performance

Styrene butadiene rubber latex (SBR), waterborne epoxy adhesive (WE) and colloidal silica sol (SiO2) were used to prepare modified bitumen emulsion for cold mix asphalt. The modification effects of the individual modifiers and the combination of these modifiers were investigated by using bonding strength and dynamic shear rheological property. Test results showed that the modifier dosage helped to balance the performance of modified bitumen emulsion by improving its bonding strength without compromising its rheological properties. The critical dosage at which the peak bonding strength occurred was 4%, 12% and 4% for SBR, WE and SiO2 respectively. Improved rheological performance on the master curves was well distinguished, in particular, by increased complex modulus and reduced phase angle at the low frequency region. Abrupt changes, especially on phase angle occurred when the modifier dosage was beyond 12%. The measured ratio between bonding strength and complex shear modulus could vary ranging from 10−2 to 102. Highly-modified bitumen emulsion with good adhesion, rheology and compatibility can be prepared by using the combination of SBR, WE and SiO2. It is important to carefully select the type and dosage of modifier for a particular combination to optimize the performance of modified bitumen emulsion.

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Large air pressure changes triggered by P-SV ground motion in a cave in northern Taiwan

10.21203/rs.3.rs-53321/v2 ◽

2021 ◽

Author(s):

Chieh-Hung Chen ◽

Yang-Yi Sun ◽

Li-Ching Lin ◽

Peng Han ◽

Huai-Zhong Yu ◽

...

Keyword(s):

Ground Motion ◽

Phase Angle ◽

Acoustic Waves ◽

Low Frequency ◽

Air Pressure ◽

Confined Space ◽

Seismic Waveforms ◽

Unusual Phenomenon ◽

Vertical Ground ◽

Pressure Changes

Abstract A barometer in the cave of the SBCB station records an unusual phenomenon of larger amplitudes in air pressure changes inside than those at the Xinwu station (outside). Accordingly, the comparison between the recorded data at the SBCB and Xinwu station can drive investigations of potential sources of the unusual phenomenon. Analytical results of phase angle differences reveal that the air pressure outside the cave at the Xinwu station often leads air pressure changes inside at the SBCB station at relatively low frequency bands. In contrast, the larger pressure changes at frequencies > 2×10-4 Hz inside the cave at the SBCB station lead smaller changes outside at the Xinwu station. To expose causal mechanisms of the unusual phenomenon, continuous seismic waveforms recorded inside the cave at the SBCB station are further conducted for examination. When the horizontal and vertical ground velocities of ground motion yield a difference in the phase angle close to 90°, amplitudes of the air pressure changes at the SBCB station are amplified accordingly. This suggests that the pressure-shear vertical ground motion can drive air pressure changes. Meanwhile, the results shed light on investigating the existence of acoustic waves near the Earth’s surface using a partially confined space underground due to that the assumptions of the waves can propagate upward in the atmosphere driving changes in the ionosphere.

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Characteristics of phase angle, extrapolated conductance and ion relaxation time in the low-frequency admittance locus plot of human palmar skin

Medical & Biological Engineering & Computing ◽

10.1007/bf02518913 ◽

1994 ◽

Vol 32 (2) ◽

pp. 161-167 ◽

Cited By ~ 1

Author(s):

Z-G. Qiao ◽

L. Mørkrid ◽

N. K. Vøllestad

Keyword(s):

Relaxation Time ◽

Phase Angle ◽

Low Frequency ◽

Palmar Skin

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Motion Simulation of Dual-Frequency Vibrating Screen

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.204-208.4916 ◽

2012 ◽

Vol 204-208 ◽

pp. 4916-4921 ◽

Cited By ~ 1

Author(s):

Yong Jun Hou ◽

Pan Fang ◽

Qi Yu Liu ◽

Jun Liang

Keyword(s):

Phase Angle ◽

Initial Phase ◽

Great Influence ◽

Low Frequency ◽

Motion Simulation ◽

Dual Frequency ◽

Vibrating Screen ◽

Mass Moment ◽

Phase Differences ◽

Screen Surface

In order to reduce screen plugging and screen pasting, improve the efficiency of screening, a kind of dual-frequency vibrating screen was introduced. It had been used three exciting motors. We established the mechanical model of this vibrating screen, and used Matlab-simulink software to analyze the trajectory changes of screen surface, influenced by mass moment rate, initial phase differences and installation position between high and low frequency exciting motors. The results of the study indicate that, the rate of mass moment and difference of initial phase angle have great influence on the motion trail pattern and amplitude of vibration of the screen, and the installation position of high-frequency exciting motor have less influence on screen surface trajectory under the condition of exciting motors’ parameters given in this article. When designing dual-frequency vibrating screen, we can use the method of this paper to select appropriate rate of mass moment, difference of initial phase angle and so on, and achieve the expected motion trajectory of vibrating screen.

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Origin of the low-frequency plateau and the light-scattering slow mode in semidilute poly(ethylene glycol) solutions

Soft Matter ◽

10.1039/c8sm02263a ◽

2019 ◽

Vol 15 (12) ◽

pp. 2666-2676 ◽

Cited By ~ 6

Author(s):

Martha Koziol ◽

Karl Fischer ◽

Sebastian Seiffert

Keyword(s):

Light Scattering ◽

Dynamic Light Scattering ◽

Ethylene Glycol ◽

Autocorrelation Function ◽

Phase Angle ◽

Polymer Solutions ◽

Low Frequency ◽

Slow Mode ◽

Poly Ethylene Glycol ◽

Poly Ethylene

The low-frequency plateau often found in the rheological spectra of semidilute polymer solutions is shown to be an artifact due to imprecise phase-angle determination; furthermore, the slow mode in the dynamic light scattering autocorrelation function of such solutions is shown to result from minor fractions of 20–200 nm sized impurities.

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