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Waves

Waves. Wave Terminology. Wave Terminology. H = Height A = Amplitude = 1/2H L = λ = Wave Length ( distance 2 consecutive crests) T = Wave Period (Time between 2 consecutive crests) f = Wave Frequency = 1/T (# waves/sec) C = Wave Speed or Celerity = L/T (m/s) H/L = Wave Steepnes

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Waves

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  1. Waves

  2. Wave Terminology

  3. Wave Terminology • H = Height • A = Amplitude = 1/2H • L = λ = Wave Length (distance 2 consecutive crests) • T = Wave Period (Time between 2 consecutive crests) • f = Wave Frequency = 1/T (# waves/sec) • C = Wave Speed or Celerity = L/T (m/s) • H/L = Wave Steepnes • Waves Break = H/L = 1/7

  4. Wave Motion & Energy

  5. Wave Spectrum

  6. Ocean surface waves

  7. Wind Waves • What influences wave size? • Wind Speed • H, L, T • Duration of wind • Maximum H • Fetch • Maximum H • Wave Height (H) • Wave Interference

  8. i.e. Effect of wind speed on H

  9. Wave Interference

  10. Wave Interference – Area of Fetch

  11. Fetch Area

  12. Wave formation in storms Fetch Area: Chaotic (Rogue Waves)

  13. Wave Speed (Deep Water) C = L/T = 1.25 * √L L = 1.56 *T2 • Slow Wave Speed • long Period (T) • Short Length (L) • Fast Wave Speed • Short Period (T) • Long Length (L)

  14. Wave Dispersion Outside Fetch Area: L, T & C remain constant

  15. Waves and Currents

  16. Reduction speed = Increase steepness C=L/T Steepness = H/L

  17. Figure 9.9

  18. Orbital Motion

  19. Shallow Water Waves • Deep Water Waves (Depth > L/2) C = L/T = 1.25 * √L • Intermediate Waves (L/2 > D > L/20) C ~ D, L • Shallow Water Waves (d < L/20) C = 3.13 * √D

  20. Shallow Water Waves

  21. Shallow Water Waves • Shallow Water Waves (d < L/20) C = 3.13 * √D C = L / T • C (speed) diminishes in shallow water • T (period) remains constant • .. So L (Length) must also diminish • C & L depend on depth

  22. Figure 9.12

  23. Shallow Water Wave Height

  24. Shallow Water Waves • When D<L/20 • Speed decreases ~ D • Length decreases ~ D • Height increases ~ D • Wave steepness (H/L) • Increases very quickly • H/L = 1/7 Waves break

  25. Wave Difraction

  26. MUNDAKA VIDEO

  27. Teahupoo – Tahitisurging breakerlong wavelengthssteep slope

  28. Teahupoo Tahiti

  29. Pipeline - Oahuplunging breaker

  30. Folly Beach - SCplunging breakermoderate slope, small wavelength

  31. Rip Currents

  32. Tsunami Waves • Earthquakes • L ~ 100 – 200 Km • P ~ 10 - 30 minutes • Shallow Water Waves • C over 4000m depth = 200 m/s = 720 km/h • Refracted by topography • Height at sea = 1-2 meters • Dangerous in shallow water • H~10’s m ; T~10-30 min.

  33. Figure 9 p264 (figure 1)

  34. Figure 9.24

  35. Wave trains or ‘sets’ Train Speed = ½ wave speed = 1/C

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