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Chapter 10

Chapter 10. Waves. Ocean Waves. Anatomy of a progressive wave Orbits, orbital waves, wave crest, wave trough, wave height, wavelength, wave period, and wave frequency. Stokes drift Disturbing Force Energy that causes waves to form Energy

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Chapter 10

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  1. Chapter 10 Waves

  2. Ocean Waves • Anatomy of a progressive wave • Orbits, orbital waves, wave crest, wave trough, wave height, wavelength, wave period, and wave frequency. • Stokes drift • Disturbing Force • Energy that causes waves to form • Energy • Wind(wind wave-deep-water waves), storm surge in an enclosed body of water, seismic sea wave , or change in atmospheric pressure(seiche-rocking of water),earthquakes, landslides, or volcanic (seismic sea wave-shallow-water waves) and gravitational forces (tides)

  3. Classifying Waves/Deep-water waves/shallow-water waves • Free wave • Transmitted without additional force (wind waves/tsunami) • Force wave • Maintained by its disturbing force (tides-gravitational attraction of the moon and the sun) • Restoring force • Returns the water surface to flatness (cohesion/gravity) • Overcompensates • Capillary waves (cohesion) • Gravity waves (gravity) • Deep-water waves(1/2) • C,L,and h constant over long distances • Transitional Waves(greater than 1/20 but less than 1/2) • C and L decrease; wave height increases, rounded tops form peaks • Shallow-water waves(less than1/20) • Wave breaks • C = L/T C=speed L= wavelength T=time or period

  4. WindWaves • Wind waves • Grow from capillary waves (cohesion tugs the tiny wave troughs and crests toward flatness) • Wavelength exceeds 1.73 cm • Wave separation or dispersion • groups with similar wavelengths and speeds. (swells) • Wave trains • swells with the same origin and wavelength • Group velocity • speed with which wave energy advances in wave trains • Factors that Affect Wind Waves • Wind strength, wind duration, and fetch • Wave steepness – 1:7 ratio (7 m long/1 m high) • Higher than 1:7 ratio = whitecaps

  5. Interferences/Rogue Waves • Interference • add or subtract • Destructive • subtraction (cancellation) • Constructive • addition • “surf beat” • Constructive/destructive interferences • Rogue wave • single crest much higher than usual, caused by constructive interference

  6. Wind Waves Approaching Shore • 1. Wave train • 2. Bottom Contact • 3. Decrease wavelength/period remains unchanged • 4. Approaching the critical 1:7 ratio • 5. Shallower • 6. Wave Breaks at about 3:4 ratio

  7. Wind Waves Approaching Shore • Wave Refraction • Wave line bends • Wave Diffraction • Obstacle causes a direction change • Wave Reflection • Move away from obstruction in the direction from which they came (standing waves/sloshing back and forth)

  8. Internal Waves • Caused by layers of different densities. • Move very slow • Generated by wind energy, tidal energy, and ocean currents • Mix nutrients into surface water • Can cause structural damage (submarines and oil platforms)

  9. Tidal Waves • Harmless waves associated with the tides

  10. Storm Surge • Abrupt bulge of water • Higher in shallow waters • Short-lived • Rushes inland (looks like a windblown tide) • “Storm Tides”

  11. Seiches • Water will slosh back and forth at a specific frequency • Node • Point or line of no vertical wave action

  12. Tsunami and Seismic Sea Waves • Long-wavelength, shallow-water progressive wave caused by the rapid displacement of ocean water are called tsunami • All seismic sea waves are tsunami, but not all tsunami are seismic sea waves. Why? • Bottom-mounted pressure sensors, seismographs, and subtle changes in the expected arrival times of tide waves are analyzed to detect a tsunami

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