buoyancy

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buoyancy

(boi`ənsē, bo͞o`yən–), upward force exerted by a fluid on any body immersed in it. Buoyant force can be explained in terms of Archimedes' principleArchimedes' principle,
principle that states that a body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid. The principle applies to both floating and submerged bodies and to all fluids, i.e., liquids and gases.
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Buoyancy

The resultant vertical force exerted on a body by a static fluid in which it is submerged or floating. The buoyant force FB acts vertically upward, in opposition to the gravitational force that causes it. Its magnitude is equal to the weight of fluid displaced, and its line of action is through the centroid of the displaced volume, which is known as the center of buoyancy. See Aerostatics, Hydrostatics

By weighing an object when it is suspended in two different fluids of known specific weight, the volume and weight of the solid may be determined. See Archimedes' principle

Another form of buoyancy, called horizontal buoyancy, is experienced by models tested in wind or water tunnels. Horizontal buoyancy results from variations in static pressure along the test section, producing a drag in closed test sections and a thrust force in open sections. These extraneous forces must be subtracted from data as a boundary correction. Wind tunnel test sections usually diverge slightly in a downstream direction to provide some correction for horizontal buoyancy.

A body floating on a static fluid has vertical stability. A small upward displacement decreases the volume of fluid displaced, hence decreasing the buoyant force and leaving an unbalanced force tending to return the body to its original position. Similarly, a small downward displacement results in a greater buoyant force, which causes an unbalanced upward force.

A body has rotational stability when a small angular displacement sets up a restoring couple that tends to return the body to its original position. When the center of gravity of the floating body is lower than its center of buoyancy, it will always have rotational stability. Many a floating body, such as a ship, has its center of gravity above its center of buoyancy. Whether such an object is rotationally stable depends upon the shape of the body.

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Buoyancy

 

of a ship, the ability of a loaded ship to float in a designated position relative to the water’s surface; one of the most important features of a ship’s seaworthiness. To ensure safe operation, every vessel must have reserve buoyancy, defined as the additional weight a ship can carry and still remain afloat. Reserve buoyancy is determined by the amount of freeboard. Standards for required freeboard are established by classification societies and depend on the design of the ship and the region and season of navigation.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

buoyancy

[′bȯi·ən·sē]
(fluid mechanics)
The resultant vertical force exerted on a body by a static fluid in which it is submerged or floating.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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An increase in Biot number from 30 to 100 produces no more effective on the flow pattern because of the buoyancy force dominating the whole domain whereas surface tension becomes insignificant at the same magnitudes of Marangoni number.
Subject to dynamic change of boundary temperature, the buoyancy force approximated by the Boussinesq model (the third term on the right hand side of Eq.
Water-to-body effects in our examples are implemented as suggested above, using the drag and buoyancy forces, but also, for example, the triangle subdivision scheme of [13] could be used.
Lorentz force and thermal buoyancy force (Gr) have no significant role in temperature distribution.
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It is further assumed that the Boussinesq approximation is valid for the buoyancy force.
The four integral characteristics, such as volume flux V, momentum flux I, buoyancy force density P, and enthalpy flux Q, were obtained by integration of the approximate distributions for each small area [DELTA]S of 0.01 m x 0.01 m (0.033 ft x 0.033 ft) in the plume cross-section according to Equations 3-6:
This is because the fluid velocity increases when the buoyancy force increases and hence increases the skin friction.
This conclusion is a direct consequence of the observation that, in an inclined duct, the buoyancy force vector has a non-vanishing projection on the plane of the duct cross-section.