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In
fluid dynamics In physics, physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids – liquids and gases. It has several subdisciplines, including (the study of air and other gases in motion ...
, the Froude–Krylov force—sometimes also called the Froude–Kriloff force—is a hydrodynamical
force In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...
named after
William Froude William Froude (; 28 November 1810 – 4 May 1879) was an English engineer, hydrodynamicist and naval architect. He was the first to formulate reliable laws for the resistance that water offers to ships (such as the hull speed equation) and for ...
and Alexei Krylov. The Froude–Krylov force is the force introduced by the unsteady
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...
field generated by ''undisturbed''
waves United States Naval Reserve (Women's Reserve), better known as the WAVES (for Women Accepted for Volunteer Emergency Service), was the women's branch of the United States Naval Reserve during World War II. It was established on July 21, 1942, ...
. The Froude–Krylov force does, together with the
diffraction Diffraction is the deviation of waves from straight-line propagation without any change in their energy due to an obstacle or through an aperture. The diffracting object or aperture effectively becomes a secondary source of the Wave propagation ...
force, make up the total non-
viscous Viscosity is a measure of a fluid's rate-dependent resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for example, syrup h ...
forces acting on a floating body in regular waves. The diffraction force is due to the floating body disturbing the waves.


Formulas

The Froude–Krylov force can be calculated from: : \vec F_ = - \iint_ p ~ \vec n ~ ds, where *\vec F_ is the Froude–Krylov force, *S_w is the wetted surface of the floating body, *p is the pressure in the undisturbed waves and *\vec n the body's
normal vector In geometry, a normal is an object (e.g. a line, ray, or vector) that is perpendicular to a given object. For example, the normal line to a plane curve at a given point is the infinite straight line perpendicular to the tangent line to the cu ...
pointing into the water. In the simplest case the formula may be expressed as the product of the wetted surface area (A) of the floating body, and the dynamic pressure acting from the waves on the body: : F_ = A \cdot p_ The dynamic pressure, p_, close to the surface, is given by: : p_ = \rho \cdot g \cdot H/2 where *\rho is the sea water density (approx. 1030 kg/m3) *g is the acceleration due to the earth's gravity (9.81 m/s2) *H is the wave height from crest to
trough Trough may refer to: In science * Trough (geology), a long depression less steep than a trench * Trough (meteorology), an elongated region of low atmospheric pressure * Trough (physics), the lowest point on a wave * Trough level (medicine), the l ...
.


See also

*
Response Amplitude Operator Response may refer to: *Call and response (music), musical structure * Reaction (disambiguation) * Request–response **Output or response, the result of telecommunications input * Response (liturgy), a line answering a versicle * Response (music ...


References

* Shipbuilding Naval architecture Fluid dynamics {{fluiddynamics-stub