Dynamic Stability of Externally Pressurized Gas Bearings

1980 ◽  
Vol 102 (4) ◽  
pp. 511-519 ◽  
Author(s):  
E. Blondeel ◽  
R. Snoeys ◽  
L. Devrieze
Keyword(s):  
Feedback Loop ◽  
Dynamic Pressure ◽  
Loop Model ◽  
Relative Importance ◽  
Gas Bearings ◽  
Additional Information ◽  
Transit Times ◽  
Stability Chart ◽  
Thickness Variations ◽  
Pressure Changes

A feedback loop model is presented us to study instability phenomena in externally pressurized gas bearings. The main features in the theoretical analysis are the compressibility of the fluid and molecular transit times in the bearing gap. The proposed theory is based upon a separate handling of disturbances due to gap thickness variations and pressure changes. The analysis shows, that the dynamic pressure distribution in the gap plays an important role in the overall bearing stability. Comparisons between theoretical and experimental observations are highlighted; reference is made to Turnblade’s stability chart. The proposed analysis gives some additional information with regard to the relative importance of some bearing parameters.

Identification of Compensatory Arterial Dynamics in Swine Using a Non-Invasive Sensor for Local Vascular Resistance

2018 ◽  
Author(s):  
Lu Wang ◽  
Sardar Ansari ◽  
Kevin R. Ward ◽  
Kayvan Najarian ◽  
Kenn R. Oldham
Keyword(s):  
Cardiovascular System ◽  
Vascular Resistance ◽  
Systemic Circulation ◽  
Test Subject ◽  
Loop Model ◽  
Peripheral Vascular ◽  
Dynamics Model ◽  
Non Invasive ◽  
Peripheral Arterial ◽  
Pressure Changes

Autoregulatory dynamics of the cardiovascular system play an important role in maintaining oxygenated blood transportation throughout the human body. In this work, a feedback dynamics model of the cardiovascular system with respect to heartrate and peripheral vascular resistance effects on longer-term blood pressure changes in the systemic circulation is presented. The model is identified from data taken from a swine test subject, instrumented in part with a wearable, non-invasive sensor for estimating peripheral arterial radius. Comparative simulations for the open and close loop model highlight significantly changed hemodynamics after hemorrhage.

scholarly journals Molecular mechanism of the “feedback loop” model of carcinogenesis

2012 ◽  
Vol 5 (5) ◽  
pp. 506-507
Author(s):  
Felix Rückert ◽  
Carsten Sticht ◽  
Marco Niedergethmann
Keyword(s):  
Molecular Mechanism ◽  
Feedback Loop ◽  
Loop Model

scholarly journals Diagnostics of common rail components based on pressure curves in the fuel rail

2018 ◽  
Vol 173 (2) ◽  
pp. 3-8
Author(s):  
Mirosław KARCZEWSKI ◽  
Krzysztof KOLIŃSKI
Keyword(s):  
High Pressure ◽  
Fuel Injection ◽  
Dynamic Pressure ◽  
Common Rail ◽  
Injection System ◽  
Fuel Injector ◽  
Labview Software ◽  
Cr System ◽  
Data Acquisition Module ◽  
Pressure Changes

Majority of modern diesel engines is fitted with common-rail (CR) fuel systems. In these systems, the injectors are supplied with fuel under high pressure from the fuel rail (accumulator). Dynamic changes of pressure in the fuel rail are caused by the phenomena occurring during the fuel injection into the cylinders and the fuel supply to the fuel rail through the high-pressure fuel pump. Any change in this process results in a change in the course of pressure in the fuel rail, which, upon mathematical processing of the fuel pressure signal, allows identification of the malfunction of the pump and the injectors. The paper presents a methodology of diagnosing of CR fuel injection system components based on the analysis of dynamic pressure changes in the fuel rail. In the performed investigations, the authors utilized LabView software and a µDAC data acquisition module recording the fuel pressure in the rail, the fuel injector control current and the signal from the camshaft position sensor. For the analysis of the obtained results, ‘FFT’ and ‘STFT’ were developed in order to detect inoperative injectors based on the curves of pressure in the fuel rail. The performed validation tests have confirmed the possibility of identification of malfunctions in the CR system based on the pressure curves in the fuel rail. The ‘FFT’ method provides more information related to the system itself and accurately shows the structure of the signal, while the ’STFT’ method presents the signal in such a way as to clearly identify the occurrence of the fuel injection. The advantage of the above methods is the accessibility to diagnostic parameters and their non-invasive nature.

scholarly journals Acoustic televiewer logging in glacier boreholes

2000 ◽  
Vol 46 (155) ◽  
pp. 695-699 ◽  
Author(s):  
Roger H. Morin ◽  
Guillaume E. Descamps ◽  
L. DeWayne Cecil
Keyword(s):  
Acoustic Waves ◽  
Structural Characteristics ◽  
Physical Nature ◽  
Time Data ◽  
Cross Sectional ◽  
Additional Information ◽  
Geophysical Logging ◽  
Transit Times ◽  
Acoustic Images ◽  
Deformation Processes

AbstractThe acoustic televiewer is a geophysical logging instrument that is deployed in a water-filled borehole and operated while trolling. It generates a digital, magnetically oriented image of the borehole wall that is developed from the amplitudes and transit times of acoustic waves emitted from the tool and reflected at the water–wall interface. The transit-time data are also converted to radial distances, from which cross-sectional views of the borehole shape can be constructed. Because the televiewer is equipped with both a three-component magnetometer and a two-component inclinometer, the borehole’s trajectory in space is continuously recorded as well. This instrument is routinely used in mining and hydrogeologic applications, but in this investigation it was deployed in two boreholes drilled into Upper Fremont Glacier, Wyoming, U.S.A. The acoustic images recorded in this glacial setting are not as clear as those typically obtained in rocks, due to a lower reflection coefficient for water and ice than for water and rock. Results indicate that the depth and orientation of features intersecting the boreholes can be determined, but that interpreting their physical nature is problematic and requires corroborating information from inspection of cores. Nevertheless, these data can provide some insight into englacial structural characteristics. Additional information derived from the cross-sectional geometry of the borehole, as well as from its trajectory, may also be useful in studies concerned with stress patterns and deformation processes.

scholarly journals Study on dynamic characteristics of gas films of spherical spiral groove hybrid gas bearings

2019 ◽  
Vol 233 (8) ◽  
pp. 1169-1181
Author(s):  
Chenhui Jia ◽  
Haijiang Zhang ◽  
Shijun Guo ◽  
Ming Qiu ◽  
Wensuo Ma ◽  
...  
Keyword(s):  
Pressure Effect ◽  
Dynamic Pressure ◽  
Iteration Algorithm ◽  
Unstable State ◽  
Gas Bearings ◽  
Damping Coefficients ◽  
The Stability ◽  
Stiffness And Damping ◽  
Film Stiffness ◽  
Gas Bearing

According to the gas film force variation law, when the bearing axis is slightly displaced from the static equilibrium position, displacement and velocity disturbance relation expressions for the gas film force increment are constructed. Moreover, combined with the bearing rotor system motion equation, calculation model equations for the gas film stiffness and damping coefficients are established. The axial and radial vibration and velocity of the gas bearings during operation are collected. The instantaneous stiffness and damping coefficients of the gas film are calculated by the rolling iteration algorithm using MATLAB. The dynamic changes in the gas film stiffness and damping under different motion states are analyzed, and the mechanism of the gas film vortex and oscillation is studied. The results demonstrate the following: (1) When the gas bearing is running in the linear steady state in cycle 1, the dynamic pressure effect is enhanced and the stability is improved by increasing the eccentricity; when the gas supply pressure is increased, the static pressure effect is enhanced and the gas film vortex is reduced, but the oscillation is strengthened. (2) With the increase in rotational speed, the gas film vortex force gradually exceeds the gas film damping force, and the stability gradually worsens, causing a fluctuation in the gas film stiffness and damping, following which singularity occurs and a half-speed vortex is formed. Meanwhile, the gas film oscillation is intensified, and the rotor enters the nonlinear stable cycle 2 state operation. (3) As the fluctuation of the film force increases, the instantaneous stiffness and damping oscillation of the film intensifies, most of the stiffness and damping coefficients exhibit distortion, and the rotor operation will enter a chaotic or unstable state. Therefore, the gas bearing stiffness and damping variation characteristics can be used to study and predict the gas bearing operating state. Finally, measures for reducing the vortex and oscillation of the gas film and improving the stability of the gas bearing operation are proposed.

The effect of solar wind dynamic pressure changes on low and mid-latitude magnetic records

1992 ◽  
Vol 19 (12) ◽  
pp. 1227-1230 ◽  
Author(s):  
C. T. Russell ◽  
M. Ginskey ◽  
S. Petrinec ◽  
G. Le
Keyword(s):  
Solar Wind ◽  
Dynamic Pressure ◽  
Solar Wind Dynamic Pressure ◽  
Pressure Changes

scholarly journals Feedback loop and upwind-propagating waves in ideally expanded supersonic impinging round jets

2017 ◽  
Vol 823 ◽  
pp. 562-591 ◽  
Author(s):  
Christophe Bogey ◽  
Romain Gojon
Keyword(s):  
Flat Plate ◽  
Acoustic Waves ◽  
Feedback Loop ◽  
Supersonic Jet ◽  
Vortex Sheet ◽  
Impinging Jets ◽  
Loop Model ◽  
Turbulent Structures ◽  
Fourier Decomposition ◽  
Pressure Fields

The aeroacoustic feedback loop establishing in a supersonic round jet impinging on a flat plate normally has been investigated by combining compressible large-eddy simulations and modelling of that loop. At the exit of a straight pipe nozzle of radius $r_{0}$, the jet is ideally expanded, and has a Mach number of 1.5 and a Reynolds number of $6\times 10^{4}$. Four distances between the nozzle exit and the flat plate, equal to $6r_{0}$, $8r_{0}$, $10r_{0}$ and $12r_{0}$, have been considered. In this way, the variations of the convection velocity of the shear-layer turbulent structures according to the nozzle-to-plate distance are shown. In the spectra obtained inside and outside of the flow near the nozzle, several tones emerge at Strouhal numbers in agreement with measurements in the literature. At these frequencies, by applying Fourier decomposition to the pressure fields, hydrodynamic-acoustic standing waves containing a whole number of cells between the nozzle and the plate and axisymmetric or helical jet oscillations are found. The tone frequencies and the mode numbers inferred from the standing-wave patterns are in line with the classical feedback-loop model, in which the loop is closed by acoustic waves outside the jet. The axisymmetric or helical nature of the jet oscillations at the tone frequencies is also consistent with a wave analysis using a jet vortex-sheet model, providing the allowable frequency ranges for the upstream-propagating acoustic wave modes of the jet. In particular, the tones are located on the part of the dispersion relations of the modes where these waves have phase and group velocities close to the ambient speed of sound. Based on the observation of the pressure fields and on frequency–wavenumber spectra on the jet axis and in the shear layers, such waves are identified inside the present jets, for the first time to the best of our knowledge, for a supersonic jet flow. This study thus suggests that the feedback loop in ideally expanded impinging jets is completed by these waves.

Sign in / Sign up

Export Citation Format

Share Document