4.7.08 - Waves

# 4.7.08 - Waves - ג/T = gT/2pi = 1.56T Speed depends on...

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Waves Orbital motion Water (and things in water) follow circular path At surface: orbital diameter = wave height At depth = ½ ג Orbital diameter = 4% height wave base Shallow vs. deep-water waves Water depth > ג / 2 : Waves do not “feel” bottom deep-water waves Water depth > ג / 2 : Waves do feel bottom Orbitals become elliptical intermediate waves Water depth > ג / 20 : Orbitals flattened shallow-water waves shallow-water waves move sediment on seafloor Simple waves in deep water have rounded crests Mass-transport in waves Theory: Orbitals are closed, no net forward movement of water Real world: Viscous interactions and large wave heights Velocity at top of orbital greater than at base Small net forward transport of water Wave speed Deep-water waves (depth > / ג 2 ): Velocity (m/sec) =

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Unformatted text preview: ג /T = gT/2pi = 1.56T Speed depends on wavelength and period Shallow-water waves (depth < / ג 20 ) ג /T still true but also: velocity (m/sec) = sq.rt(gD) = 3.1 * sq.rt(D) (D is in m) What happens as waves approach the coast? Water depth decreases and keeps decreasing Deepwater waves become shallow-water waves Interaction with bottom decreases orbital velocity…but Period does not change. Wavelength becomes compressed Height must increase Steepness must increase Also: top of wave has greater velocity than base Waves slow, grow, cusp, and break D = / ג 2 : Waves feel bottom Slow down (at base!) ג decreases h increases (water is shoved upward) D = 1.3 h: wave steepness = 1/7:...
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4.7.08 - Waves - ג/T = gT/2pi = 1.56T Speed depends on...

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