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, 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.

SurfersHow Many?

1,736,000. -Rode a waveOnce/year

Estimates5 -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

• 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

• 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?– Period

– Wavelength

– Frequency

– Distributing force

• What is a Wave?– Summary

int

• 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

• 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 Theorycalculating 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

1/20 > h/ λh/λ > 1/2

or Velocity (V)

• 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

~ 10 feet

~> 20 feet

• 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

• 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

• 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

WIND WIND WIND WIND

• Wave Generation by Winds– From Atm. Winds to sea surface. . . .– Some wind E causes surface currents

• Most Wind E waves

• 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 SeaWhat 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

0.16

Discovered aboard FLIP

• 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

• 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

http://www.youtube.com/watch?v=7BOhDaJH0m4&feature=related

TUBE – a product of an ocean floor

• WAVES– Now the Whole Package Comes together

– A SUMMARY of Some Concepts & Big Waves– http://www.kqed.org

/quest/television/science-of-big-waves

• 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

• 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?

So Locate the best Possible Surf break?

1600’

• 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 levelhttp://www.youtube.com/watch?v=4Xebwzb3dDE&feature=related

ANIMATION / Summary

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

http://www.youtube.com/watch?v=ElpzfM5knYA&feature=related

Tsunami CBS

http://www.youtube.com/watch?v=g15sZ_d2WUY&feature=related

http://www.youtube.com/watch?v=4Xebwzb3dDE&feature=related

Tsunami Graphic

http://www.youtube.com/watch?v=deX7R9RbmX0&NR=1

ROGUE waves