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13.9–17.1 m/s 13–19 ft 4–5.5 m Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind; spindrift begins to be seen Whole trees in motion; inconvenience felt when walking against the wind 8 Gale, fresh gale 34–40 knots 39–46 mph 62–74 km/h 17.2–20.7 m/s 18–25 ft 5.5–7.5 m
In hurricane-force winds with V (3 m) = 40-m/s (≈78 knots) the speed at 15 m would be V (15 m) = 49 m/s (≈95 knots) with p = 0.128. [26] This suggests that sails that reach higher above the surface can be subject to stronger wind forces that move the centre of effort ( CE ) higher above the surface and increase the heeling moment.
Wave turbulence; Wingtip vortices; ... 40 (4): 511 – 544. doi: 10.1515 ... v is a characteristic velocity of the fluid with respect to the object (m/s)
Turbulence kinetic energy is then transferred down the turbulence energy cascade, and is dissipated by viscous forces at the Kolmogorov scale. This process of production, transport and dissipation can be expressed as: D k D t + ∇ ⋅ T ′ = P − ε , {\displaystyle {\frac {Dk}{Dt}}+\nabla \cdot T'=P-\varepsilon ,} where: [ 1 ]
Airy wave theory is often used in ocean engineering and coastal engineering. Especially for random waves, sometimes called wave turbulence, the evolution of the wave statistics – including the wave spectrum – is predicted well over not too long distances (in terms of wavelengths) and in not too shallow water.
A wind speed gradient of 4 (m/s)/km can produce refraction equal to a typical temperature lapse rate of 7.5 °C/km. [51] Higher values of wind gradient will refract sound downward toward the surface in the downwind direction, [52] eliminating the acoustic shadow on the downwind side. This will increase the audibility of sounds downwind.
40–50 knots (21–26 m/s) is the threshold for survivability at some stages of low-altitude operations, and; several of the historical wind shear accidents involved 35–45 knots (18–23 m/s) microbursts. Wind shear is also a key factor in the formation of severe thunderstorms.
If the length of waterline is given in metres and desired hull speed in knots, the coefficient is 2.43 kn·m −½. The constant may be given as 1.34 to 1.51 knot·ft −½ in imperial units (depending on the source), or 4.50 to 5.07 km·h −1 ·m −½ in metric units, or 1.25 to 1.41 m·s −1 ·m −½ in SI units.