Waves

Oceanography Notes

Anatomy of a Wave

• Wave height :vertical distance between a crest and the preceding trough

• Amplitude: equal to one-half the wave height (point of equilibrium surface to the crest or trough

Sine Wave Characteristics

Diagram of a Wave: Wavelength

http://www.onr.navy.mil/focus/ocean/motion/waves1.htm

Basic Wave Diagram

Description of Periodic Motion

Motion which repeats itself precisely can be described with the following terms:

Period: the time required to complete a full cycle, T in seconds/cycle

Frequency: the number of cycles per second, f in 1/seconds or Hertz (Hz)

Amplitude: the maximum displacement from equilibrium A

https://www.youtube.com/watch?v=mEGz8Ex7jVQ

Wave Generating Forces• Sometimes waves are generated through

seismic motion or rock formations (ice too) falling (like throwing a rock into the water)

• There are three basic factors in generating surface waves (height)…

1. Wind speed

2. Wind duration

3. Fetch (the distance that the wind blows

Wave Motion

• Waves consist of orbits that are below the sea surface

Deep Water Waves• These are classified as waves that have a

depth that is at least one half of the wavelength Depth = Wavelength (L)/2

• Wave speed (C) = L/T or L = C*T

C is equal to celerity (speed of one wave)

versus v (speed of a group of waves)

Wave Equations

• For any type of water wave, the wave's wavelength (L), speed (C) and period (T) are related by the following relations:  

• L = C*T  

• L = 1.56T2  

• C = gT/2¶ 

• C = 1.56 * T

1.56 is in m/s2

Shallow Water Waves

A wave that enters water with a depth of less than one-twentieth (D < L/20)

Shallow water wavelength and speed are controlled only by the water depth (meters)

_____

C = √ g * D

(g = 9.81 m/s2)

Group Speed

• Waves can travel in groups (speed)

• Waves move as wave trains

V = C/2

http://oceanworld.tamu.edu/students/waves/index.html

Breaking Waves

http://search.live.com/images/results.aspx?q=Tsunami+diagrams%20|%20id:AE878E4D465DAB0843D7EEC20BDEFFB13B5905F7&form=IGRE1&p1=OneRow#focal=2e78f408dd2093b8c8087b736bcb8eea&furl=http%3A%2F%2Fwww.gg.uwyo.edu%2Fmedia%2Ftsunami%2Fdiagrams%2Fwave.gif

Wave Breaking Diagram

http://geology.wr.usgs.gov/parks/sea/wave.gif

Wave Steepness

For a wave to break, wave steepness is important. If the ratio of wave height to wavelength is 1:7 or more, the wave will break

Surging Breakers happen on beaches where the slope is very steep. The wave does not actually break. Instead, it rolls onto the steep beach. These kinds of breakers are known for their destructive nature

Plunging Breakers happen on beaches where the slope is moderately steep. This kind of wave normally curls over forming a tunnel until the wave breaks. Expert surfers love this type of wave!

Spilling Breakers occur on beaches with gentle slopes. These waves break far from the shore, and the surf gently rolls over the front of the wave.

http://www.onr.navy.mil/focus/ocean/motion/waves2.htm

Guess The Types of Breakers

Tsunami

Characteristics of a Tsunami

Shallow Water Wave characteristics in deep water

Large Wavelengths (kms)

Fast Wave Speeds

Depth less than one-half of the wavelength

Causes of Tsunami

Seismic disturbance causing wave impulses

Waves and the Shoreline

• Waves enter the shoreline and can exhibit the following characteristics…

Refraction

Reflection

Diffraction

Wave Diffraction

Interferences• Constructive and Destructive

Destructive

Constructive