Waves. Wave Terminology H = Height A = Amplitude = 1/2H L = λ = Wave Length ( distance 2...

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Transcript of Waves. Wave Terminology H = Height A = Amplitude = 1/2H L = λ = Wave Length ( distance 2...

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

– Waves Break = H/L = 1/7

Wave Motion & Energy

Wave Spectrum

Ocean surface waves

Wind Waves• What influences wave size?

– Wind Speed• H, L, T

– Duration of wind• Maximum H

– Fetch • Maximum H

– Wave Height (H)– Wave Interference

i.e. Effect of wind speed on H

Wave Interference

Wave Interference – Area of Fetch

Fetch Area

Wave formation in storms

Fetch Area: Chaotic(Rogue Waves)

Wave Speed (Deep Water)

C = L/T = 1.25 * √LL = 1.56 *T2

• Slow Wave Speed – long Period (T)– Short Length (L)

• Fast Wave Speed– Short Period (T)– Long Length (L)

Wave Dispersion

Outside Fetch Area: L, T & C remain constant

Waves and Currents

Reduction speed = Increase steepness

C=L/TSteepness = H/L

Figure 9.9

Orbital Motion

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

Shallow Water Waves

Shallow Water Waves

• Shallow Water Waves (d < L/20)C = 3.13 * √DC = L / T

– C (speed) diminishes in shallow water– T (period) remains constant– .. So L (Length) must also diminish– C & L depend on depth

Figure 9.12

Shallow Water Wave Height

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

Wave Difraction

MUNDAKA VIDEO

Teahupoo – Tahitisurging breakerlong wavelengthssteep slope

Teahupoo Tahiti

Pipeline - Oahuplunging breaker

Folly Beach - SCplunging breakermoderate slope, small wavelength

Rip Currents

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.

Figure 9 p264 (figure 1)

Figure 9.24

Wave trains or ‘sets’

Train Speed = ½ wave speed = 1/C