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Topic: Gravity current

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June 3

	Gravity current - Wikipedia, the free encyclopedia
		In fluid dynamics, a gravity current is a primarily horizontal flow in a gravitational field that is driven by a density difference.
		Thus gravity currents may be simulated by the shallow water equations, with special dispensation for the leading edge which behaves as a discontinuity.
		The leading edge of a gravity current is a region in which relatively large volumes of ambient fluid are displaced.
	en.wikipedia.org /wiki/Gravity_current (235 words)

	Gravity Currents (Site not responding. Last check: 2007-10-08)
		Gravity currents are widespread in nature, and their common characteristics are observable in avalanches, heavy gas releases, turbidity currents, fresh and salt-water exchange, and sea breezes.
		He also further quantified previously known results, stating that the front of the gravity current moves with a speed that is proportional to the height at the front of the gravity current, and a specific ratio of the density differences between the two fluids concerned.
		The behaviour of a gravity current in a backdraft situation is dependant on several factors such as wind, opening (door/window) geometry and the temperature of the gases....
	www.firetactics.com /GRAVITY-CURRENTS.htm (489 words)

	Gravity currents
		Since gravity currents are formed in many different natural situations and may also be man-made, knowledge of their properties is of importance in many scientific disciplines.
		This gravity current in the atmosphere is the front of an outflow of cold air from a thunderstorm.
		Gravity currents appear in estuaries, where the fresh water of the river meets the salt water of the ocean.
	www.damtp.cam.ac.uk /user/fdl/people/jes14/jeshome.htm (896 words)

	Meteorologielabor
		Gravity currents (also called buoyancy or density currents) are fluid flows which arise from horizontal density gradients within the fluid.
		During the passage of a gravity current, there is a sudden drop in temperature, and an increase in the wind speed.
		Gravity currents are also observed in water, such as when lighter fresh water from rivers enter a salty sea.
	www.meteo.physik.uni-muenchen.de /~robert/meteorologielabor/labor.html (2137 words)

	AMS Glossary
		Gravity waves grow in amplitude as they propagate upward from their surface source regions into lower-density regions.
		Gravity wave drag plays an important role in explaining the zonal mean flow and thermal structure at higher atmospheric levels, particularly in the mesosphere.
		A plane gravity wave is characteristically composed of a pair of waves, the two moving in opposite directions with equal speed relative to the fluid itself.
	amsglossary.allenpress.com /glossary/browse?s=g&p=28 (957 words)

	Tristan Robinson (Site not responding. Last check: 2007-10-08)
		Gravity currents are feature often found in environmental and industry: intrusions in estuarine flows, discharges of fluids, and particle-driven currents generated by dredging.
		However, in the marine environment, the presence of progressive water waves significantly alters the spreading of a gravity current through the generation of oscillatory boundary layers near the boundaries.
		While recent work has elucidated the effect of a mean ambient flow in the spreading of gravity currents and the deposition from particle-driven gravity currents, the effect of a mean drift profile on the spreading of a gravity current have a lot of unanswered questions and uncertainties.
	www.ucl.ac.uk /~ucestor (205 words)

	Fluid Dynamics Laboratory: Glossary
		The northward flowing current along the west coast of Africa; it is one of the swiftest of ocean currents, the strongest current in the South Atlantic.
		Gravity waves include surface gravity waves, such as waves on the surface of the ocean, interfacial gravity waves, such as waves at the interface between fresh surface water and underlying salty ocean water, and internal gravity waves which propagate vertically as well as horizontally in density stratified fluid.
		The Guiana current is an extension of the south equatorial current (flowing west across the ocean between the equator and 20 degrees), which crosses the equator and approaches the coast of South America.
	taylor.math.ualberta.ca /~bruce/glossary.html (9921 words)

	ASGSB 1998 - GRAVITY INDUCED CALCIUM CURRENTS IN GERMINATING FERN SPORES (Site not responding. Last check: 2007-10-08)
		Gravity fixes the developmental polarity in germinating spores of Ceratopteris richardii during the first 24 hours after germination is initiated by light.
		We found that during the period of polarity fixation, a strong efflux current emerges from the top of the cell, a weaker efflux current occurs at the sides of the cell, and an even weaker influx current enters from the bottom of the cell.
		The magnitude difference between the outward current at the top and the inward current at the bottom of the cell is highest in the middle of the polarity fixation period and decreases significantly toward the end of this period.
	baby.indstate.edu /asgsb/programs/1998/45.html (245 words)

	Chapter 1: Gravity and the C-R theory
		We have postulated that the true nature of gravity is caused by a significantly different mechanism than that which is currently accepted as the best explanation of gravity.
		Current theories which involve gravitons require that, in order to allow any gravitational force to be felt outside of the Black-Hole boundary, some mechanism must exist to allow the tunnelling of these hypothetical gravitational particles.
		In mathematics, the contribution to the voltage and current flow is tracked using i, or the square root of -1.
	www.geocities.com /recycling_universe/chapter1.htm (2717 words)

	Current Research (Site not responding. Last check: 2007-10-08)
		Both experimental and numerical modelisations of dense gravity currents on a slopping bottom under the influence of the Coriolis force are studied, in either homogeneous or uniformly stratified environment.
		The rotation deflects the current and the flow is stabilized into a geostrophically balanced jet along the slope.
		The aim is to determine experimentaly the depth of stabilization of the main current, its width and thickness, to measure the turbulent mixing and to observe the instabilities created (like eddies formation) from density profiles and velocity fields.
	www.coriolis-legi.org /SABINE/Sabine.htm (276 words)

	[No title]
		A gravity current originated by a power-law viscous fluid propagating in axisymmetric geometry on a horizontal rigid plane below a fluid of lesser density is examined.
		Spreading of a gravity current along a rigid horizontal surface is governed by an interplay between buoyancy, inertial, and viscous forces.
		In the process, a gravity current passes through several distinct flow regimes that are characterized by the relative balance of forces.
	www.diiar.polimi.it /franz/MFduB/NNFDiFedericoMalavasi.doc (2017 words)

	Loop quantum gravity (Site not responding. Last check: 2007-10-08)
		Loop quantum gravity (LQG), also known as loop gravity, quantum geometry and canonical quantum general relativity, is a proposed quantum theory of spacetime which attempts to blend together the seemingly incompatible theories of quantum mechanics and general relativity.
		The current position (as of 2004) is not symmetrical, in that string theorists are generally not concerned with loop quantum gravity, or they are skeptical that there is any real competition.
		The main claimed successes of loop quantum gravity are: (1) that it is a nonperturbative quantization of 3-space geometry, with quantized area and volume operators; (2) that it includes a calculation of the entropy of fl holes; and (3) that it is a viable gravity-only alternative to string theory.
	www.worldhistory.com /wiki/L/Loop-quantum-gravity.htm (2061 words)

	Gravity Current Simulations using Tecplot (Site not responding. Last check: 2007-10-08)
		This is useful for gravity current simulations as in order to simulate a gravity current you require 4 sets of data, one for velocity, one for the shape of the lower layer, one for the shape of the upper layer and one for the shape of the bottom.
		A gravity current is what forms when two fluids of different densities are put together in some container.
		Gravity currents exist in many forms and examples can be found in oceanography and meteorology.
	web.unbc.ca /hpc/tecplot_butch.html (421 words)

	Matthew Brown: Thesis Abstract (Site not responding. Last check: 2007-10-08)
		Gravity currents are common phenomena in a number of atmospheric and oceanographic contexts, with examples including dense-gas dispersion in the atmosphere and turbidity currents in the ocean.
		Clearly the terrain over which a gravity current spreads is likely to have a significant effect on its behaviour.
		At larger slopes however the forward propagating current rapidly decelerates, there is intense mixing near the slope, and the reflected wave is a turbulent bore - effectively an upstream propagating gravity current which will also cause mixing on its own account.
	www.damtp.cam.ac.uk /user/fdl/people/mab/abstract.html (408 words)

	Gravity current -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-08)
		In (additional info and facts about fluid dynamics) fluid dynamics, a gravity current is a primarily horizontal flow in a (A field of force surrounding a body of finite mass) gravitational field that is driven by a (The amount per unit size) density difference.
		The pressure distribution is thus approximately hydrostatic, apart from near the leading edge (this may be seen using (additional info and facts about dimensional analysis) dimensional analysis).
		The leading edge moves at a (additional info and facts about Froude number) Froude number of about unity; estimates of the exact value vary between about 0.7 and 1.4.
	www.absoluteastronomy.com /encyclopedia/g/gr/gravity_current.htm (246 words)

	GEOG 473: Lesson 23 (Site not responding. Last check: 2007-10-08)
		Gravity (density) currents are created when gravity works to undo an unstable density distribution.
		The gravity current has a distinct "nose" (at O), head (raised portion in the middle of the diagram, between O and the first billow), and "neck" (shallower area to the right of the head, beneath the billows).
		The rising air currents in the middle of the landward low are often marked by puffy white cumulus clouds, while the descending air currents just offshore are cloud free.
	www.ccrc.sr.unh.edu /~stm/AS/Teaching/GEOG473/GEOG473_23.html (1626 words)

	ANGEO - Abstracts (Site not responding. Last check: 2007-10-08)
		The passage of the shallow current was marked by a pronounced pressure disturbance and was accompanied by vertical circulations seen in the tower and profiler data.
		The gravity current is analyzed with surface observations, the wind profiler/RASS and tower-mounted instruments.
		The lee-type waves in the head region of the gravity current seem to have been generated by the gravity current acting as an obstacle to prefrontal flow.
	www.copernicus.org /EGU/annales/22/11/3937.htm?FrameEngine=false (327 words)

	Publications - James Stephens (Site not responding. Last check: 2007-10-08)
		Gravity currents are important for transporting heat, salt and momentum in oceanic, atmospheric and other environments.
		On a smaller scale, gravity currents may be observed in lakes if the deformation radius is small enough that they feel the Earth's rotation.
		A study of a two-fronted current on a slope in a one layer reduced gravity system was considered by Griffiths et al.
	www.sns.ias.edu /~jns?pagename=Publications/LINEAR (242 words)

	Physics and Astronomy Forums - Gravity = Electro-magnetism - General Physics Discussion
		If gravity were caused by the warpage of space time by mass, there would be no reason for this phenomenon -- the mass of the earth and the moon for that matter, is still the same.
		The speeding up of the orbit of the moon is due to the conservation of momentum, but the reason for the outward movement of the moon is due to the decrease in gravity (force due to the electro-magnetic current in the displacement current) because of the decrease in force of the current.
		Gravity is a special case of electro-magnetism the same as the van Der Waal attraction is in chemistry.
	www.physlink.com /Community/Forums/viewmessages.cfm?Forum=17&Topic=2833 (545 words)

	[No title]
		Further, the study of the flow of turbidity currents is used to improve the design of submarine structures such as cables and pipelines to withstand the potentially damaging effects of turbidity currents.
		The flow of turbidity currents is often accompanied by deposition of particles from the current on to the bottom surface.
		My primary objective is to calculate the thickness of the deposit from a turbidity current as a function of position, given the initial conditions of release of the current and the geometry of the bottom surface.
	www.che.utexas.edu /~vatsan/phdres.html (986 words)

	Limnology and Oceanography Abstracts (Site not responding. Last check: 2007-10-08)
		Gravity currents propagating into a heavier, uniform-density fluid are known to have near-surface velocities u that exceed the propagation speed c of the gravity current nose.
		The numerical solutions show that particles that originate in the dense fluid ahead of the gravity current are much less likely to be accumulated at the gravity current nose.
		A simple scaling criterion for the minimum vertical buoyancy velocity for efficient accumulation and transport of buoyant particles based on the gravity current and particle characteristics is developed and compares favorably with the numerical results.
	aslo.org /lo/toc/vol_48/issue_4/1509.html (276 words)

	3D Ocean Modelling (Site not responding. Last check: 2007-10-08)
		The current deflects to the right of the channel due to the effective coriolis force (or rotating frame of reference) that is applied to this example.
		The current was then rescaled so that the temperature difference (with which the density current was controlled) was effectively less, thus the current was slower and coriolis had a greater effect on the flow.
		At a later timestep the current has begun to flow down the slope whilst being advected to the right due to the coriolis effect.
	www.met.rdg.ac.uk /~sws03cb/3DOcean (722 words)

	Avalanche - Open Encyclopedia (Site not responding. Last check: 2007-10-08)
		An avalanche is caused when a build up of snow is released down a slope, and is one of the major dangers faced in the mountains in Winter.
		An avalanche is an example of a gravity current consisting of granular material.
		In an avalanche, lots of material or mixtures of diffrent types of material fall or slide rapidly under the force of gravity.
	open-encyclopedia.com /Avalanche (990 words)

	IP2A
		The development of stratification and gravity currents, and their breakdown due to tidal and wind forcing, in the Persian Gulf is described.
		The life-time of the gravity current is about 5 months, and it has an average thickness of 18 m and it travels and distance of about 150 km from the straight of Hormoz.
		The Mozambique Channel is the "melting pot" of the three water masses; the mixing ratio is 30 to 60% for the AAIW, 30 to 40% for the BIW, and 20 to 30% for the RSW, with the AAIW influence increasing rapidly to the southern limit of the channel.
	www.iugg.org /iapso/JointAssembly97/abstracts/ip2.html (12902 words)

	Mixing in Gravity Current Fronts
		Saline gravity currents were studied in a steady-state reference frame with the aid of a laboratory facility.
		A simple relationship relating the dimensionless mixing rate to the dimensionless height, or height ratio, of the currents was also set forth for physically realizable, large-scale flows.
		Parsons, J. and Garcia, M. Scale effects on the flow structure of steady-state saline gravity currents.
	www.ocean.washington.edu /people/faculty/parsons/research/mixing.html (357 words)

	USC Aerospace & Mechanical Engineering : Research Areas (Site not responding. Last check: 2007-10-08)
		When the rejected mixture of particles and upper and lower layer fluids reaches the bottom of the experimental tank it generates a secondary gravity current which in turn interacts with the primary current to further modify its behaviour.
		The constant initial speed of propagation (V) of heavy gravity currents, of density ?c, released from behind a lock and along the bottom boundary of a tank containing a linearly stratified fluid has been measured experimentally and calculated numerically.
		The distance propagated by the current before this constant velocity regime ended (Xtr), scaled by h, has been found to be a unique function of Fr for all states tested.
	ae-www.usc.edu /research/fluid_mechanics/rsp.shtml (1087 words)

	Numerical Simulation of Gravity Current Front (Site not responding. Last check: 2007-10-08)
		The present study investigates the dynamics of gravity current fronts experimentally and theoretically.
		Two typical fronts of gravity currents on the inclined boundaries are considered.
		The models consist of the conservation equations of mass and buoyancy and the momentum equation for the gravity current front.
	www.pubs.asce.org /WWWdisplay.cgi?9802357 (178 words)

	Mini-Symposium #14 (Site not responding. Last check: 2007-10-08)
		Interfacial gravity currents, or intrusions, may occur naturally along an inversion in the atmosphere as a consequence, for example, of cold thunderstorm outflows or due to rapid mixing by the collision of two fronts.
		Depending on the relative density of the upper and lower layers and the density of the intrusion, solitary waves or bores may be generated ahead of the current, as demonstrated in laboratory experiments (e.g.
		These large amplitude waves extract significant momentum from the current, and in some circumstances, the current itself is observed to stop propagating and a solitary wave is generated.
	www.math.sfu.ca /~stieu/cams-scma/ms14-sutherland.html (229 words)

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