Gravity wave (hydrodynamics)

Ripple of the gravity wave to be possible on the surface of the water when I dropped a small object underwater

An example of the simulation of the gravity wave.
It is the gravity wave that there is when I lost five times of small objects in the shallow bathtub. The first surface of the water reflects it in the wall of the bathtub and interferes surface of the water and each other later.

Gravity wave of the sea surface that I looked at from the sky

When the dynamic medium which is in equilibrium was displaced in a medium of the different density by gravitational action, a gravity wave (じゅうりょくは, gravity wave) in the hydrodynamics is a wave to occur in the interface of the medium, and to advance to along an interface in the process when I am going to return by the gravity in original equilibrium as power of restitution again. A surge occurring on the surface of the water is nominated for a phenomenon to be seen well. This is called the surface wave to become the wave going ahead through the clear appearance that is an interface. These waves became the disturbance; may grow up, and this is known as kelvin Helmholtz instability.

In addition, a wave produces buoyancy as power of restitution when difference of temperature suddenly occurs all over the water temperature front between the Stratoshere and the Troposphere to occur in wetlands on the ocean. In addition, a wave occurs equally in the large in gas and is called an atmosphere gravity wave. The billow clouds are the examples which it is imminent and can observe occurring by such a mechanism. This is called all the inside wave in the meaning called the wave spreading inside of the same medium.

Of wavelength λ and the medium of the wave which communication speed c of the gravity wave produced next-type using height (depth) h of the plumb direction, is fixed (for gravity) [¹]:

${\displaystyle c={\sqrt {{\frac {g\lambda }{2\pi }}\tanh \left({\frac {2\pi h}{\lambda }}\right)}}.}$

g is acceleration of gravity here. The upper expression shows the dispersibility which communication speed c of the wave depends on wavelength λ for.

When wavelength λ is shorter than depth h of the medium,

${\displaystyle c={\sqrt {g\lambda \over 2\pi}}}$

となる. On the contrary, when wavelength λ is longer than depth h of the medium, communication speed c does not depend on wavelength λ and is given it in the next expression:

${\displaystyle c={\sqrt {gh}}.}$

A wavelength is an extremely long gravity wave more than number 10km, and, as for the tsunami occurring on the ocean, the communication speed becomes very fast when it is transmitted through the deep bottom of the sea.

In addition, the wave to assume the surface tension of the material of the neighborhood of interface power of restitution in addition to this really increases. The surface wave that this wave became dominant appears under the zero gravity.

Footnote

1. For ^ Egon Krause "hydrodynamics" シュプリンガー Japan, 2,008 years, it is page 79. ISBN 978-4-431-10020-1. 

Allied item

• Surface of the water wave

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