Ocean Waves – Chp 10

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! • 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

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 OUTLINE

In Search of The Perfect Wave (1966)

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 OUTLINE

Development of Wave Theory • Sir Isaac Newton (1642-1727) • First mathematical descriptions of waves, 1687Principia. • 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

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 What is the Wavelength (λ)? Dist. b/w peaks (crests) Where is the Crest (Peak)? Where is the Trough (Valley) 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? • Period • Wavelength • Frequency • Distributing force

What is a Wave? • Summary int

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 = T2g/2π • T = period time • g = Acceleration of gravity 9.8 m/s-2 or (32 feet/sec) • π = Pi ~ 3.1415 λ

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 • P = water Density • g = accel. of gravity • H = height of Wave • 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 ~> 20 feet ~ 10 feet

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

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 • What are Swells? • Long wavelength - surface waves (group) • traveled long distances • (more stable then wind waves) Coming to a Shore Near YOU!!!!

From Calm to Fully Developed Sea What is Wave Steepness ~ S ? • S = H/ λChallenge 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

Wave Interactions with Seafloor • When deep water waves hit seafloor what happens? • 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-big-waves

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

Ocean Waves – Chp 10