Important Announcement
• The first prelim will be held during regular
class time on Thursday 21 February
• A short in-class review will be held Tuesday
19 February to go over student submitted
questions
• Submit review questions to Yianna Samuel
(ys88@cornell.edu) by Friday 15 February
Why Study Waves?
Wave Prediction and Shipping
Wave Prediction and Construction of Coastal
Structures
Wave Prediction and Construction of
Off-Shore Structures
Wave-Induced Beach Erosion
and Sediment Transport
Wave Prediction and Recreation
Fundamental Principles
Wave Parameters
•
Wave Period = Time it Takes a Wave Crest to Travel one
Wavelength (units of time)
•
Wave Frequency = Number of Crests Passing A Fixed
Location per Unit Time (units of 1/time)
•
Wave Speed = Distance a Wave Crest Travels per Unit
Time (units of distance/time)
•
Wave Steepness = Wave Height/Wavelength
Constructive, Destructive and
Mixed Addition of Two Waves
Constructive
Destructive
Mixed
Ideal Deep-Water
Waves Propagate
Energy not Mass
Two Critical Points to Note About Wave Speeds
• Deep-Water Waves (Bottom Depth > L/2)
– Speed is a Function of Wavelength Only
– Waves with Longer Wavelength move faster than
Waves with Shorter Wavelength
• Shallow-Water Waves (Bottom Depth < L/20)
– Speed is a Function of Depth Only
– Waves Travel Slower in Shallower Water Irrespective
of Wavelength as long as Depth < L/20
Note: L = wavelength
_________________
Note that there is also an intermediate region (L/20 < Depth < L/2) where
Wave Speed is a Function of Both Wavelength & Depth
Speed of Deep-Water and ShallowWater Waves as a Function of
Wavelength and Depth
Deep-Water and Shallow-Water
Wave Regions
The Size of Wind Generated
Waves is a Function of:
1. Wind Speed
2. Duration of Wind
3. Fetch - the distance over which
wind can blow without
obstruction
The Importance of Fetch
Full Developed Waves
(Unlimited by Fetch and Duration)
Lateral Spreading of Wave Energy from a
Storm Source
(95% of Energy Contained Within ±45o of Storm Direction)
Wave Measurement Methods
Wave Height Measured with
Bottom-Moored Pressure Sensor
Significant Wave Heights Derived from
the Shape of the Returned Beam on the
Topex-Poseidon Altimeter
The Distribution of Wave Energy as a Function
of Wave Period or Wavelength…
Distribution of Wave Energy in the Ocean as a Function of Wave
Frequency or Wavelength
Some Interesting Things
About Waves…
Wave Dispersion: Self Sorting of Deep-Water
Waves Leaving a Storm Region based on Wavelength.
It Occurs Because Longer Wavelength Waves Travel
Faster than Shorter Wavelength Waves (for Deep
Water).
Wave Refraction:
Bending of Shallow-Water
Wave Fronts Due to
Change in Bottom Depth.
The Leading Edge of a
Wave Front Enters
Shallower Water and Slows
While the Remaining Front
Continues at Higher Speed.
The Net Result is a
Rotation of Wave Fronts To
Become Parallel with
Bottom Depth Contours.
Consequence of Wave Refraction
Focusing and Defocusing of Wave Energy on
Headlands and Bays, Respectively
Wave Diffraction
Wave Diffraction
Along
Shore
Sediment
Transport
Along-Shore Sediment Transport
Obstructed by Groins
Initiation and
Propagation
of a Tsunami
Motion of Seiche Caused by a Storm
Over a Semi-Enclosed Body of Water
Internal Waves Travel along Density
Discontinuities in the Ocean Interior
Thin Layers of Phytoplankton
Oscillating with an Internal Wave
Formed along the Continental Shelf
Kelvin and Rossby Waves
- Planetary Waves -
Rossby Waves in the Equatorial
Pacific
QuickTime™ and a
decompressor
are needed to see this picture.
Summary Points
1. Waves Propagate Energy and not Mass
2. Waves Add Constructively or Destructively
3. Deep-Water Wave Speed is a Function of
Wavelength
4. Shallow-Water Wave Speed is a Function of
Bottom Depth
5. Wave Dispersion: Sorting of Deep-Water Waves
Based on Wavelength
6. Wave Refraction: Bending of Shallow-Water
Waves Based on Depth
7. Wave Height Determined by: Wind Speed, Wind
Duration and Fetch
8. Waves Hitting a Shore Obliquely Will Cause
along Shore Transport of Sediment
9. Constructed Structures such a Groins will Block
the Along Shore Sediment Transport
10. Tsunami are Generated by Underwater
Earthquakes or Landslides and Propagate across
Whole Ocean Basins
11. Seiches are Standing Waves formed in SemiEnclosed Bodies of Water
12. Internal Waves Propagate along Density
Discontinuities (Pycnoclines) in the Ocean
Interior
13. Kelvin and Rossby Waves are Important
Planetary Wave