Ionospheric Storms and Small Pressure Fluctuations at Ground Level

Nature ◽  
1966 ◽  
Vol 210 (5040) ◽  
pp. 1032-1034 ◽  
Author(s):  
G. G. BOWMAN ◽  
K. L. SHRESTHA
Keyword(s):  
Pressure Fluctuations ◽  
Ground Level ◽  
Small Pressure

A Brief Review of Wind Effects on Buildings and Structures

1966 ◽  
Vol 70 (665) ◽  
pp. 553-560 ◽  
Author(s):  
C. Scruton
Keyword(s):  
Air Flow ◽  
Pressure Fluctuations ◽  
Ground Level ◽  
Vertical Gradient ◽  
Proximity Effects ◽  
Wind Tunnels ◽  
Wind Loading ◽  
Local Pressure ◽  
Wind Speeds ◽  
Random Forcing

SummaryPresent day structural forms and methods of fabrication have considerably increased the importance of wind as a design consideration. For estimations of the overall stability of a structure and of the local pressure distribution on the cladding, a knowledge of the maximum steady or time-averaged wind loads is usually sufficient. Mind tunnel tests to determine the wind loading coefficients are often made in smooth uniform flow, but for more accurate data account must be taken of the effects of the vertical gradient of wind speed and the turbulence of natural winds. Further research is needed into these effects and also into methods of obtaining a sufficient representation of the natural wind in the wind tunnel.There are a number of ways by which wind excites structures into oscillation; among these are vortex excitation, galloping, proximity effects including buffeting, stalling flutter and classical flutter. The vortex and galloping excitation might be expected to be especially sensitive to the turbulence properties of the air flow. Also, in the absence of any mechanism for instability, atmospheric turbulence may directly excite oscillations through the random forcing by the pressure fluctuations which it produces. Further understanding of this problem must come through research into the effects of turbulence (and to the extent to which these effects may be disregarded), but the range of the conditions is so vast and complicated that it seems unlikely that sufficient aerodynamic and wind data will be accumulated to permit the response of a proposed structure to be calculated with reasonable certainty, and for major projects it is anticipated that comprehensive tests on aeroelastic models in wind tunnels with appropriate turbulent air flow will continue to offer the more reliable predictions.The air flow around buildings is of concern inasmuch as it influences the dispersal of combustion and other gases from the smokestack and also in its effect on the speeds and turbulence of the wind over areas used by pedestrians. The erection of a tall building may cause an increase in wind speeds and gustiness at ground level. These problems of the external flow over buildings are readily examined in wind tunnels. For this purpose tunnels with large working sections are desirable to permit a sufficiently wide area of the neighbourhood to be represented.

scholarly journals Internal Structure of a Jet Nozzle for Coalbed Methane Mining Based on Airfoil Curves

2018 ◽  
Vol 2018 ◽  
pp. 1-17
Author(s):  
Jian Chen ◽  
Liwen Guo ◽  
Yanwei Hu ◽  
Yong Chen
Keyword(s):  
Water Column ◽  
Coalbed Methane ◽  
Pressure Fluctuations ◽  
Axial Direction ◽  
Shock Pressure ◽  
Conical Nozzle ◽  
Small Pressure ◽  
Jet Nozzle ◽  
Column Pressure ◽  
Variation Rule

Based on airfoil curves that can effectively balance the rectification and drag reduction effects in flight hydrodynamics, we designed an internal streamline structure of jet nozzle for coalbed methane (CBM) mining. The three types of nozzles originating from three typical airfoil curves are compared with the conical nozzle. Results showed that the thin-type streamlined nozzle had the largest effective shock range and least radial divergence and was thus selected as the best nozzle. Moreover, the pressure distribution at the outlet of the nozzle was found to be related to the range and number of small-pressure fluctuations near the wall. A larger number of small-pressure fluctuations and a larger range caused faster pressure of the jet water column to decay along the axial direction. Rectification with a concentrated effect also slowed down the attenuation velocity of the jet-water-column pressure between the concentration point and the nozzle. The variation rule of shock pressure with range was further determined experimentally. We found that the shock pressure of jet water column initially increased within a short distance and then decreased rapidly. The effective shock range of the thin-type streamlined nozzle in air was 1.417 times that of the conical nozzle, and the effective reaming area was 1.104 times greater. Thus, the effect of reaming was effectively improved. The length of the water column at high pressure was larger than that of the conical nozzle, and the shock efficiency was relatively high.

Prediction of Environmentally Assisted Cracking on Gas and Liquid Pipelines

2006 ◽  
Author(s):  
J. Been ◽  
R. Eadie ◽  
R. Sutherby
Keyword(s):  
Crack Growth ◽  
Growth Rates ◽  
Pressure Fluctuations ◽  
Low Frequencies ◽  
Small Pressure ◽  
Environmentally Assisted Cracking ◽  
Pressure Time ◽  
Growing Crack ◽  
Small Cracks ◽  
Crack Growth Rates

A model has been developed to predict crack growth on pipelines from environmentally assisted cracking in near-neutral pH environments (often-termed low-pH stress corrosion cracking (SCC)). The model is based on the results of cyclic loading experiments and is used in conjunction with pressure time variations in the pipeline determined from the operating SCADA records to predict the growth of an assumed existing crack in the pipe. The crack grows through different crack growth regimes, which are determined by the size of the pressure variations and the instantaneous crack dimensions. For a growing crack that experiences relatively high pressure fluctuations, as often encountered on liquid lines, reasonable crack growth predictions were made based on corrosion fatigue. An approach based on crack tip strain rate appears more suitable for the prediction of crack growth of small cracks and for cracks on gas lines with small pressure fluctuations. The model is designed so that the effect of stress intensifiers (like the long seam weld crown) that are often associated with these failures can be included. The model can be used in its present format for prioritizing inspections on both gas and liquid pipelines. Whereas predicted crack growth rates compare favorably with rates measured in the field, further work is required to incorporate additional mechanical and environmental effects, in particular to improve the prediction of small crack growth rates. Low crack velocities may be possible in the presence of small pressure fluctuations and low frequencies, but they may be less probable.

A microbarograph for internal gravity wave studies in Antarctica

1992 ◽  
Vol 4 (2) ◽  
pp. 241-248 ◽  
Author(s):  
P.S. Anderson ◽  
S.D. Mobbs ◽  
J.C. King ◽  
I. McConnell ◽  
J.M. Rees
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Pressure Fluctuations ◽  
Internal Gravity Wave ◽  
Internal Gravity Waves ◽  
Small Pressure ◽  
Prototype Instrument ◽  
Antarctic Environment

Measurement of pressure fluctuations provides the best means of detecting atmospheric internal gravity waves at the Earth's surface. We have developed an instrument which is sufficiently sensitive to detect the small pressure fluctuations associated with such waves yet robust enough for deployment in an Antarctic environment. The instrument incorporates several novel features, both in its design and in the method of deployment used. A prototype instrument has been successfully deployed at the British Antarctic Survey's Halley Station during 1989. The design of an experiment using an array of six improved instruments is briefly described.

Development of Differential PSP Technique for Detecting Small Pressure Fluctuations

2022 ◽  
Author(s):  
Yasuhiro Egami ◽  
Masashi Takizawa ◽  
Saki Watanabe ◽  
Yu Matsuda
Keyword(s):  
Pressure Fluctuations ◽  
Small Pressure

scholarly journals Plucking as an Effect of Water-Pressure Variations at the Glacier Bed

1981 ◽  
Vol 2 ◽  
pp. 57-62 ◽  
Author(s):  
Hans Rӧthlisberger ◽  
Almut Iken
Keyword(s):  
High Pressure ◽  
Water Supply ◽  
Laboratory Experiments ◽  
Water Pressure ◽  
Pressure Fluctuations ◽  
Drainage System ◽  
Temperature Fluctuations ◽  
Small Pressure ◽  
Rock Fragments ◽  
Lake Drainage

A rapid displacement of glaciers occurs at times when the water supply from melting or lake drainage surmounts the capacity of the subglacial drainage system. It is explained by the hydraulic action of water at high pressure in cavities which open up on the lee side of undulations or steps of the glacier bed. It is suggested that, because of pressure-induced temperature fluctuations, rock fragments may freeze on to the glacier sole and be lifted out into an opening cavity. Laboratory experiments have shown that small pressure fluctuations of a few bars* only are sufficient for rock slabs of a considerable thickness to be moved in this way.

Effects of Vibration on the Preparation of Ultrathin Sections

1973 ◽  
Vol 31 ◽  
pp. 358-359
Author(s):  
Joseph M. Blum ◽  
Edward P. Gargiulo ◽  
J. R. Sawers
Keyword(s):  
Cutting Speed ◽  
Ground Level ◽  
Environmental Vibration ◽  
Block Face ◽  
Ultrathin Sections ◽  
Embedding Medium ◽  
Thickness Variations ◽  
Building Walls ◽  
Cutting Direction ◽  
Diamond Knife

It is now well-known that chatter (Figure 1) is caused by vibration between the microtome arm and the diamond knife. It is usually observed as a cyclical variation in “optical” density of an electron micrograph due to sample thickness variations perpendicular to the cutting direction. This vibration might be induced by using too large a block face, too large a clearance angle, excessive cutting speed, non-uniform embedding medium or microtome vibration. Another prominent cause is environmental vibration caused by inadequate building construction. Microtomes should be installed on firm, solid floors. The best floors are thick, ground-level concrete pads poured over a sand bed and isolated from the building walls. Even when these precautions are followed, we recommend an additional isolation pad placed on the top of a sturdy table.

A global perspective of ground level, 'ambient' carbon dioxide for assessing the response of plants to atmospheric CO2

2001 ◽  
Vol 7 (7) ◽  
pp. 789-796 ◽  
Author(s):  
L. H. Ziska ◽  
O. Ghannoum ◽  
J. T. Baker ◽  
J. Conroy ◽  
J. A. Bunce ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Ground Level ◽  
Global Perspective ◽  
Atmospheric Co2
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