Low‐frequency instabilities in the high‐pressure regime of Penning discharges

1978 ◽  
Vol 49 (12) ◽  
pp. 5809-5815 ◽  
Author(s):  
S. K. Guharay ◽  
S. N. SenGupta ◽  
M. R. Gupta
Keyword(s):  
High Pressure ◽  
Low Frequency ◽  
Pressure Regime

Erratum: Low‐frequency instabilities in the high‐pressure regime of Penning discharges

1979 ◽  
Vol 50 (9) ◽  
pp. 6032-6032
Author(s):  
S. K. Guharay ◽  
S. N. SenGupta ◽  
M. R. Gupta
Keyword(s):  
High Pressure ◽  
Low Frequency ◽  
Pressure Regime

Compressibility of water in magma and the prediction of density crossovers in mantle differentiation

2008 ◽  
Vol 366 (1883) ◽  
pp. 4239-4252 ◽  
Author(s):  
Carl B Agee
Keyword(s):  
High Pressure ◽  
Compressible Liquid ◽  
Silicate Melt ◽  
Liquid Density ◽  
Low Velocity ◽  
Oxide Component ◽  
The Earth ◽  
Liquid Oxide ◽  
Planetary Differentiation ◽  
Pressure Regime

Hydrous silicate melts appear to have greater compressibility relative to anhydrous melts of the same composition at low pressures (<2 GPa); however, at higher pressures, this difference is greatly reduced and becomes very small at pressures above 5 GPa. This implies that the pressure effect on the partial molar volume of water in silicate melt is highly dependent on pressure regime. Thus, H 2 O can be thought of as the most compressible ‘liquid oxide’ component in silicate melt at low pressure, but at high pressure its compressibility resembles that of other liquid oxide components. A best-fit curve to the data on from various studies allows calculation of hydrous melt compression curves relevant to high-pressure planetary differentiation. From these compression curves, crystal–liquid density crossovers are predicted for the mantles of the Earth and Mars. For the Earth, trapped dense hydrous melts may reside atop the 410 km discontinuity, and, although not required to be hydrous, atop the core–mantle boundary (CMB), in accord with seismic observations of low-velocity zones in these regions. For Mars, a density crossover at the base of the upper mantle is predicted, which would produce a low-velocity zone at a depth of approximately 1200 km. If perovskite is stable at the base of the Martian mantle, then density crossovers or trapped dense hydrous melts are unlikely to reside there, and long-lived, melt-induced, low-velocity regions atop the CMB are not predicted.

Prevention of Low-Frequency Vibration of High-Capacity Steam Turbine Units

1997 ◽  
Author(s):  
H. Kanki ◽  
Y. Kaneko ◽  
M. Kurosawa ◽  
T. Yamamoto ◽  
Y. Yamamoto ◽  
...  
Keyword(s):  
High Pressure ◽  
High Capacity ◽  
Low Frequency ◽  
Field Tests ◽  
Operating Conditions ◽  
Squeeze Film ◽  
High Pressure Turbine ◽  
Solution Approach ◽  
Vibration Excitation ◽  
Low Frequency Vibration

Abstract The causes of low-frequency vibration (subsynchronous vibration) of a high pressure turbine were investigated analytically and also via vibration excitation tests on actual machines under operation. From the results, it was concluded that low-frequency vibrations may be caused by either the decrease of the rotor system damping or by external forces, such as flow disturbance in the control stage and the rubbing between the rotor and casing. After identifying the cause of the low-frequency vibration, appropriate countermeasures such as installation of a squeeze-film damper and modification of valve opening sequence were taken. Vibration measurements and vibration excitation tests for the high pressure turbine under actual operating conditions were carried out in order to verify the validity of the countermeasures. These field tests confirmed that the problems of low-frequency vibration can be solved completely by taking the appropriate countermeasure depending on the cause of the vibration. This paper presents some field experiences of low-frequency vibration and the effective solution approach.

scholarly journals The Enhancement of Lump Coal Percentage by High-Pressure Pulsed Hydraulic Fracturing for Sustainable Development of Coal Mines

2019 ◽  
Vol 11 (10) ◽  
pp. 2731 ◽  
Author(s):  
Hao Yan ◽  
Jixiong Zhang ◽  
Nan Zhou ◽  
Junli Chen
Keyword(s):  
High Pressure ◽  
Water Injection ◽  
Low Frequency ◽  
Injection Pressure ◽  
Pulse Amplitude ◽  
High Amplitude ◽  
Hard Coal ◽  
Fracture Width ◽  
Mining Face ◽  
Lump Coal

The enhancement of lump coal percentage (LCP) is of great significance for most aging mines to achieve the production reduction and quality improvement. In order to enhance the LCP of hard coal seam in fully mechanized mining face and prolong the service life of aging mines, this paper puts forward the technological path of LCP enhancement using high-pressure pulsed hydraulic fracturing (HPPHF) based on the detailed analysis of the main factors controlling LCP. By analyzing the correlation between coal fracturing and LCP, the enhancement mechanism of LCP through HPPHF was concluded. Using the extended finite element method, a fluid–solid coupling numerical model of high-pressure pulsed water injection into coal seam was established, and effects of the fracturing method, pulse amplitude, pulse frequency, and water injection pressure on fracturing performance were assessed. Simulation results demonstrate that HPPHF can effectively reduce the required maximum pressure in fracturing, thus providing a higher percentage of coal lumps with lower energy consumption through the repeated pulsed loading of coal masses. Variations in pulsed pressure amplitude and frequency, as well as water injection pressure were positively correlated with fracturing performance. By their effect on the fracturing performance, we found that water injection pressure had the greatest influence, and the pulse amplitude and frequency had similar effects. At the same time, “high amplitude-high frequency” and “high amplitude-low frequency” had characteristics of short initiation time, large initiation pressure, but small fracture width, while “low amplitude-high frequency” and “low amplitude-low frequency” had characteristics of slow initiation speed, low initiation pressure, but large fracture width. Through the field test results in the fully mechanized mining face of Shichangwan Coal Mine, it was found that LCP with a diameter range of 13–100 mm was significantly enhanced by HPPHF. The present study is considered quite instrumental in providing a theoretical foundation for enhancing the LCP of hard coal seams and the sustainable development of coal mine enterprises.

Mantle-derived dunite and lherzolite nodules from Ubekendt Ejland, west Greenland Tertiary province

1982 ◽  
Vol 46 (340) ◽  
pp. 329-336 ◽  
Author(s):  
Jørgen Gutzon Larsen
Keyword(s):  
High Pressure ◽  
Partial Melting ◽  
High Temperatures ◽  
Mantle Material ◽  
West Greenland ◽  
Coexisting Phases ◽  
Pressure Regime ◽  
Very High

AbstractScattered dunite and lherzolite nodules occur in one of the youngest basanitoid lavas on Ubekendt Ejland. They have protogranular to porphyroclastic textures. The dunites are composed of olivine (Fo93.2−91.9b), enstatite (En93.4−92.8) low in Al2O3 and CaO, and Cr-spinel (61-13% Cr2O3 and 3–55% Al2O3). A solitary lherzolite module has olivine (Fo94.7–94.1), enstatite (En94.7–94.2), Cr-rich spinel, Ti-phlogopite (11% TiO2), and hyalophane. Petrographic evidence suggests that the two latter minerals have not been introduced by magmatic injection from the host in spite of the refractory nature of the coexisting phases, and metasomatic processes prior to the last deformation are therefore indicated. Partial melting of such mantle material would presumably produce small amounts of alkaline liquids even at very high temperatures. Another lherzolite nodule from a lamprophyre dyke has minerals with lower Mg/(Mg + Fe) ratios which, together with its preserved igneous textures, suggest a high-pressure precipitate. The lowest well-esablished equilibrium temperatures of 700–830°C for both dunites and lherzolites indicate a pressure regime of 12-17 kbar, according to the oceanic geotherm, whereas unrealistically high pressure (20–5 kbar) are suggested using the continental shield geotherm.

Observations of low-frequency oscillations during relativistic-electron-beam-plasma interactions

1991 ◽  
Vol 46 (2) ◽  
pp. 237-246
Author(s):  
A. S. Paithankar ◽  
G. P. Gupta
Keyword(s):  
Electron Beam ◽  
Relativistic Electron ◽  
Relativistic Electron Beam ◽  
Low Frequency ◽  
Hydrogen Gas ◽  
The Novel ◽  
Low Frequency Oscillations ◽  
Wave Forms ◽  
Beam Parameters ◽  
Pressure Regime

During propagation of a relativistic electron beam in hydrogen gas at sub-torr pressures using a foil-less diode, low-frequency oscillations in the megahertz range are observed in the net current wave forms, and continue even after passage of the beam. The novel feature of the experiment is that both beam generation and propagation take place in the same low-pressure regime, and hence the beam parameters are functions of gas pressures. Analysis of the experimental results shows that the low-frequency oscillations result from the resistive-hose instability.

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