scholarly journals A new high-pressure technique for the measurement of low frequency seismic attenuation using cyclic torsional loading

2021 ◽  
Vol 92 (9) ◽  
pp. 093906
Author(s):  
Jean-Philippe Perrillat ◽  
Roman Bonjan ◽  
Yann Le Godec ◽  
Frédéric Bergame ◽  
Julien Philippe ◽  
...  
Keyword(s):  
High Pressure ◽  
Low Frequency ◽  
Seismic Attenuation ◽  
Torsional Loading

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

Seismic attenuation, normal moveout stretch, and low-frequency shadows underlying bottom simulating reflector events

2018 ◽  
Vol 66 (5) ◽  
pp. 857-871 ◽  
Author(s):  
José M. Carcione ◽  
Ayman N. Qadrouh ◽  
Hervé Perroud ◽  
Davide Gei ◽  
Jing Ba ◽  
...  
Keyword(s):  
Low Frequency ◽  
Seismic Attenuation ◽  
Bottom Simulating Reflector

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.

A new laboratory system for the measurement of low frequency seismic attenuation

2010 ◽  
Author(s):  
Claudio Madonna ◽  
Nicola Tisato ◽  
Sébastien Boutareaud ◽  
David Mainprice
Keyword(s):  
Low Frequency ◽  
Seismic Attenuation ◽  
Laboratory System

High-pressure Raman and Brillouin studies of single crystalline gas hydrates

2003 ◽  
Vol 81 (1-2) ◽  
pp. 127-133 ◽  
Author(s):  
H Shimizu
Keyword(s):  
High Pressure ◽  
Phase Transitions ◽  
Brillouin Scattering ◽  
Low Frequency ◽  
Visual Observation ◽  
Cage Structure ◽  
Two Phase ◽  
Single Crystalline ◽  
Open Structures ◽  
Diamond Anvil

Methane hydrate (MH) and argon hydrate (AH) single crystals were synthesized in a diamond anvil cell to investigate their intrinsic high-pressure properties by visual observation and in situ Raman and Brillouin-scattering measurements. Single crystalline MH shows clearly two phase transitions at P =0.9 and 1.9 GPa in its crystalline shape and state under a microscope, and in the change in its Raman spectra of C–H stretching vibrations of guest CH4 molecules. The first determination of the elastic properties in MH sI phase has revealed that MH is about 10% softer than the most common ice Ih, which is accounted for by MH's void-rich and open structures. For a single-crystal AH, we have observed two phase transitions from AH-I (sII) to AH-II at about P =0.65 GPa and from AH-II to AH-III at P =1.02 GPa. The breakdown of the cage structure in AH-III was confirmed by the disappearance of the O–H stretching mode of host H2O lattices. The possibility of Ar double occupancy in the large cages of sII and higher pressure phases is investigated by the low-frequency Raman peak observed around 120 ~ 140 cm–1 in view of recent MD calculations. PACS Nos.: 62.30+d, 62.50+p, 62.65+k, 64.70-p, 78.30-j, 78.35+c

Stability of High Pressure Turbine Under Partial Admission Condition

2005 ◽  
Author(s):  
Hiroshi Kanki ◽  
Akinori Tanitsuji
Keyword(s):  
High Pressure ◽  
Theoretical Analysis ◽  
Steam Turbine ◽  
High Capacity ◽  
Low Frequency ◽  
Initial Position ◽  
Experimental Results ◽  
Qualitative Description ◽  
Scale Model ◽  
Partial Admission

Subsynchronous vibration of high-pressure steam turbine is one of the difficult problems to improve the reliability of power plant. Extensive work has been done to prevent the low frequency vibration of high-capacity steam turbine and most of the problems were practically solved[1][2]. In the future, we must build up theoretical approach to design a new turbine operating under the steam condition of high-temperature and high-pressure. To design such an advanced steam turbine, it is necessary to solve the effect of partial admission on control stage of the steam turbine. This paper describes the experimental results from the scale model of the steam turbine and theoretical analysis of Alford force considered partial admission condition to solve the problem. (1) Subsynchronous vibration was reproduced in the scale model test. (2) Partial admission gave larger destabilizing force compared with full admission condition for same total flow rate. (3) Initial position of shaft center to the phase of admission arc on the partial admission had some effect on the stability of the rotor system. (4) Theoretical analysis of destabilizing force considered partial admission condition gave qualitative description of the experimental results from the scale model.

scholarly journals Prevention of Low-Frequency Vibration of High-Capacity Steam Turbine Units by Squeeze-Film Damper

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

The cause of the low-frequency vibration (subsynchronous vibration) of a high pressure turbine was investigated by the analytical study and vibration exciting test for the actual machine in operation. From the results, it is found that the low-frequency vibration is caused by the decrease of the rotor system damping at high-loading operating conditions. As a countermeasure, a squeeze-film damper is designed in order to increase the damping of the rotor system. After the verification test of the squeeze-film damper’s capability in the workshop, it was installed on the actual turbine. Vibration exciting tests for the high pressure turbine under the actual operating conditions were carried out. These field tests confirmed that the damping of the rotor system was increased as expected in the design and consequently the low-frequency vibrations disappeared completely under all operating conditions.

Sign in / Sign up

Export Citation Format

Share Document