Ocean Waves – Chp 10
Newest Extreme Wave (2006) Shark Park – off Channel Islands (San Miguel), CA
• Announcements
– MIDTERM – Monday 4pm
• Covers: Chapters 1-9 (excluding Chp 7), (not Todays)
• 40 Multi Choice Qs
• 5 Short answer Qs
• All based on Lecture Notes/Qs
• Bring GREEN Scantron (Bookstore)
– #2 Pencil
• HW-3 due Wed
• HW-4, HW-5 (Nat. Bridges) due w/ Final
• See Syllabus (website) for details
• Announcements
– Your Homework
– Do it!
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If you don’t you loose 30-45% of your grade!!!
Turn it in!
DON”T WAIT TILL THE LAST MINUTE
HELP me to HELP YOU 
– FYI HW-3, Skip Question d) on Page 6
OUTLINE
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In Search of The Perfect Wave
Development of Wave Theory
What is a Wave?
Wave Theory
Analyzing Natural Waves
Wave Generation by Winds
Wave Interactions with Seafloor
Applications of Wave Theory
• In Search of The Perfect Wave (1966)
OUTLINE
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In Search of The Perfect Wave
Development of Wave Theory
What is Wave?
Wave Theory
Analyzing Natural Waves
Wave Generation by Winds
Wave Interactions with Seafloor
Applications of Wave Theory
• Development of Wave Theory
– Sir Isaac Newton (1642-1727)
• First mathematical descriptions of waves, 1687 Principia.
• Proposed motion of water particles in a wave was circular
– Franz Gerstner (1756-1832)
• Develops 1st primitive wave theory
– Particles traveling at the crest of wave move up/forward
– Particles traveling at the trough of wave move down/backward
– Motions traced a circle
» Height @ surface = Height of Wave
• Development of Wave Theory
– Ernst Weber (1795-1878) - Anatomy Professor
– Wilhelm Weber (1804-1891) - Physicist
• Built first WAVE Tank
– Confirmed Gerstener’s circular Motions.
Development of Wave Theory
WWII – Securing a Beach Head
– Commanders wanted to Known type of Sea Conditions
– Walter Munk
• (Army Corp. Engineers)
– With Harald Sverdrup (SIO)
• Undertake Surf forecasting
– Prediction of waves @
» Given location/time
– 1960s_Munk’s lifes work
• Deploys buoy devices etc.
– Alaska  New Zealand
• Munk Concludes
– “Predictions of surfing conditions @ Honolulu possible, but from what
I know of the Surfing profession I don’t suggest this as a lucrative enterprise” ???
. . .Before his time. . . But TODAY >>>>
• High Tech Surf Forecasts Now Exist
– Web Cams, Reports, Forecasts/ Conditions etc.
Surfers
How Many?
1,736,000.
-Rode a wave
Once/year
Estimates
5 -17 million. . .
Overall
1960s
≤10,000
Matt Warshaw
-Encyclopedia
of Surfing
• Development of Wave Theory
– Technology Drives the Study of Waves
• Wave Heights, Wind speeds, mea. using Satellites & Buoys
– Major Application behind Study of Waves
• Application to Coastal Engineering Problems
• Vessel Safety @ Sea
OUTLINE
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In Search of The Perfect Wave
Development of Wave Theory
What is a Wave?
Wave Theory
Analyzing Natural Waves
Wave Generation by Winds
Wave Interactions with Seafloor
Applications of Wave Theory
• What is a Wave?
– Waves result from the movement of E through a medium
• = progressive waves
– e.g. oceanic, seismic, sound waves
Challenge Qs
– What do Progressive Ocean waves arise from?
• A disturbing Force
– Force that Transmits E to the water column or surface via Wind or Earthquake
– What are Waves from Episodic Events (e.g. Winds, Earthquakes) called?
Free Waves - travel without any further influ. of Disturbing force
–What are Waves from Continual Events (e.g. tides) called?
Forced Waves - under continual influence of disturbing force
(e.g. gravity from Moon or Sun)
NOTE: Restoring Forces - Drain the Wave of it’s E
• What is a Wave?
– Anatomy of a Wave
• As E is transferred thru fluid the wave particles move in
circular motion – aka orbital
Where is the Crest (Peak)?
Where is the Trough (Valley)
What is the Wavelength (λ)?
Dist. b/w peaks (crests)
What is the Wave height (h)?
Dist. b/w Crest - Trough
λ
h
• What is a Wave?
– Anatomy of a Wave
• What is the Period of a Wave?
– Amount of Time passing b/w wave peaks
» (how far are the peaks apart in time)
• What is the Wave frequency?
– How often peaks are passing same point in time
• What is a Wave?
– Classification of Waves
• According to their?
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Period
Wavelength
Frequency
Distributing force
• What is a Wave?
– Summary
int
OUTLINE
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In Search of The Perfect Wave
Development of Wave Theory
What is a Wave?
Wave Theory
Analyzing Natural Waves
Wave Generation by Winds
Wave Interactions with Seafloor
Applications of Wave Theory
• Wave Theory
• Mathematical description of waves allows us to?
– Predict behavior under diff. circumstances
– Forecast their arrival on beaches
• Surf forecasters make use of Wave theory to predict:
– When & Where ocean waves have their greatest impact on shore.
• Wave Theory
– Wave Speed (Velocity ~ V)
• V = Wavelength / Period (Time) or
V=λ/T
– Waves with different wavelengths and periods travel @ diff speeds
– Since λ /T are proportional increases in Wind speed (C) lead to?
» Increases in either Wavelength or Period or both
» Note: the PERIOD does NOT change once Wave is formed
• Wave Theory
calculating wavelength (λ)
λ
λ = T2g/2π
– T = period time
– g = Acceleration of gravity 9.8 m/s-2
– π = Pi ~ 3.1415
or (32
feet/sec)
• Wave Theory
– What are Shallow water waves?
• Waves traveling in H2O whose depth is less than one-twentieth (1/20) of the
wavelength of the wave
– What are deep water waves?
• Waves whose propagation is NOT affected by the seafloor
– What are intermediate water waves?
• Surface waves in b/w the deep and shallow water approximations
or Velocity (V)
h/λ > 1/2
1/20 > h/ λ
• Wave Particle Motions
– For Deep-water waves
• Diameter of wave orbital
– Based on Height
• Challenge Question?
– What happens to the diameter of
» wave orbitals with depth?
– They shrink (diminish)
» disappear
• Wave Particle Motions
– For Shallow-water waves
• Diameter of wave orbital hits bottom
– Becomes ovular b/c of:
» friction/ drag effects etc.
» e.g. notice Kelp moving
Back/ fourth
• Wave Energy (E)
E = 1/8 p g H2
~> 20 feet
• P = water Density
• g = accel. of gravity
• H = height of Wave
~ 10 feet
– WHAT TO KNOW
– Equation states that:
• E increases as the Square of the waves Height
– i.e. if you 2X the wave height  4X Wave E!!!
– e.g. 6 m (20 foot) wave has 4 Xs as much E as 3 m (10 foot) wave
OUTLINE
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•
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In Search of The Perfect Wave
Development of Wave Theory
What is a Wave?
Wave Theory
Analyzing Natural Waves
Wave Generation by Winds
Wave Interactions with Seafloor
Applications of Wave Theory
• Analyzing Natural Waves
• Wave Interference
– Challenge Questions
• What is produced when Crests/ troughs of Waves are offset?
– Destructive interference
» Cancel each other out
• What is produced when two wave Crests overlap exactly?
– Constructive interference
» Doubling of wave height!
• Wave Interference
– Summary
• Wave E Spectrum
– Knowing H and frequency of Waves  wave E spectrum
• @ given location / set of conditions exist?
Wave E spectrums
OUTLINE
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In Search of The Perfect Wave
Development of Wave Theory
What is a Wave?
Wave Theory
Analyzing Natural Waves
Wave Generation by Winds
Wave Interactions with Seafloor
Applications of Wave Theory
• Wave Generation by Winds
– From Atm. Winds to sea surface. . . .
– Some wind E causes surface currents
• Most Wind E  waves
WIND
WIND WIND
WIND
• Wave Generation by Winds
– Challenge Qs
• What factors of wind determine the severity of the waves?
– Speed of Wind
– Length of Time in Blows (duration)
– Distance over which it travels aka?
» Fetch
»Fetch
• From Calm to Fully Developed Sea
– IT all starts with the Wind  swells
Coming to a Shore
Near YOU!!!!
– What are Swells?
• Long wavelength - surface waves (group)
– traveled long distances
– (more stable then wind waves)
• From Calm to Fully Developed Sea
What is Wave Steepness ~ S ?
• S = H/ λ
Challenge Q
• What happens when steepness exceeds 1/7 or (0.142) ?
– e.g. wavelength = 7m, wave height ≥ 1m
the formation of White caps
Discovered aboard FLIP
0.16
OUTLINE
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•
•
•
•
•
•
•
In Search of The Perfect Wave
Development of Wave Theory
What is a Wave?
Wave Theory
Analyzing Natural Waves
Wave Generation by Winds
Wave Interactions with Seafloor
Applications of Wave Theory
• Wave Interactions with Seafloor
– When deep water waves hit seafloor what happens?
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1) Friction slows down wave, decreases wavelength
2) Orbitals become ovular
3a) Height/steepness of Wave increases
3b) Wave overly steep: S > 1/7  Breaks!
• Wave Interactions with Seafloor
– Bathymetry Matters
• RECALL
TUBE – a product of an ocean floor
http://www.youtube.com/watch?v=7BOhDaJH0m4&feature=related
• WAVES
– Now the Whole Package Comes together
– A SUMMARY of Some Concepts & Big Waves
– http://www.kqed.org/quest/television/science-of-bigwaves
OUTLINE
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•
•
•
•
•
•
•
In Search of The Perfect Wave
Development of Wave Theory
What is a Wave?
Wave Theory
Analyzing Natural Waves
Wave Generation by Winds
Wave Interactions with Seafloor
Applications of Wave Theory
• SURF Forecasting
– Confirming your knowledge
• What are the major factors u need to form Considerable Waves?
• Fetch (long distance for wind to blow)
• Sustained High winds
• Bathymetry effects
– Most intense waves occur where?
» It gets Very shallow Very fast
» And or the wave bends around an obstruction
Pipeline, HI
Challenge Question
– Could Anyone really surf Lake Tahoe?
• ?
– What conditions would be needed?
• Sustained High Winds
• Lots of Fetch
– What direction?
• Bathymetric
Obstruction
where?
1600’
So Locate the best Possible Surf break?
• 11/29/2009- Powerful Winter Storm Hits Tahoe Basin
– 60-100 mph Winds from South!
– It Can been done! and Was!!!
Munk would be proud
• Applications of Wave Theory
– Tsunamis
• A real Serious Threat!
• Warning System (when earthquake registers – Send the Alert)
• Few minutes all you need – get to Higher Ground (2nd story)
• Applications of Wave Theory
– Tsunamis
• Generated by vertical displacement of seafloor
– (earthquakes)
– Landslides
– Eruptions
• Do they Have Large or Small Wavelengths?
– Very Large: When reach shore, What Happens?
– a Big WAVE!
• Challenge Question?
– If out to see in row boat earthquake/ Tsunami Hits
» Could you notice a change in sea level change?
» NO – b/c the very longggggg wavelength –
» Small sea surface height change/time
• Applications of Wave Theory
– Tsunamis
• Generated by vertical displacement of seafloor
– Creates upsurge of Water
Propagates outward
» Very Tall waves
Exceed sea level
ANIMATION / Summary
http://www.youtube.com/watch?v=4Xebwzb3dDE&feature=related
http://www.youtube.com/watch?v=g15sZ_d2WUY&feature=related
• Applications of Wave Theory – Final Thoughts
– Knowing what we Know about Waves
• What can we do?
• Early detection of Earthquakes etc.
–  Tsunami Warning System
• Erosion – Next Time (Beaches/ Tides etc.)
• Can we make our own surf?
• Applications of Wave Theory
– Human Made Surf Breaks?
– A potential Reality
Will Bournemouth Surf Reef Ever Produce Waves? Australia
JUST NEED THE RIGHT conditions
-Pending . . .
http://www.kqed.org/quest/television/science-of-big-waves
• Remember Midterm Monday –
– Green Scantron
– Study your notes
• Have a Peaceful Weekend
ROGUE waves
http://www.youtube.com/watch?v=deX7R9RbmX0&NR=1
http://www.youtube.com/watch?v=ElpzfM5knYA&feature=related
Tsunami Graphic
http://www.youtube.com/watch?v=4Xebwzb3dDE&feature=related
Tsunami CBS
http://www.youtube.com/watch?v=g15sZ_d2WUY&feature=related