Science Modules using the Mini Wave Tank (working document)
Jack A. Puleo, Ph.D.
University of Delaware, Center for Applied Coastal Research
What are Waves
Wave Description
Period and Frequency
Energy Transport
Wave Speed
Shallow versus Deep Water
Tsunami
Beach Profile
View of a breaking wave
from below the surface
What is a Wave?
Waves are everywhere in nature
Most people think of waves on the ocean when someone mentions waves
But, they exist in many other places:
Here are a few examples: Can you think of more?
http://image.tutorvista.com
http://www.dermawave.com
http://lh3.ggpht.com
Wave Description
A wave is a disturbance that travels through some medium (typically
air or water) from one place to another.
There are a variety of wave types, but here we will only discuss
surface waves
Surface waves travel on the surface of a fluid where particle undergo a
circular motion
For simple surface waves, the water particles have no net
displacement. The individual particles return to where they started
from.
WAVE PARAMETERS
Wavelength
Crest
Height
amplitude
Wave elevation profile: deep water = sine wave
Rest position
Trough
Crest: location of maximum upward displacement
Trough: location of maximum downward displacement
Amplitude (a): amount of maximum displacement from rest position
Height (H): vertical distance between trough and crest
Wavelength (L): The horizontal length of a complete wave cycle
WAVE PARAMETERS
Period (T): time is takes for one cycle to complete
Frequency (f): refers to how often something happens, usually cycles
per second. The unit cycles per second is called Hertz (Hz)
1
T
f
and
1
f 
T
WAVE PARAMETERS
Moving with velocity, C
Velocity (C): distance divided by time
Crests can be seen to move along the ocean, how long it takes the crest
to get from one point to another is the velocity.
Velocity (C) = Wavelength/Period = L/T
Or
Velocity (C) = Wavelength * frequency = L*f
WAVE PARAMETERS
Low energy
High energy
Energy (E): From the movie we saw that particles return to their
original position.
So, waves transport energy, NOT matter.
Wave energy is proportional to the amplitude of a wave SQUARED
E a
2
WAVE PARAMETERS
Water particle motion within a wave train decays exponentially
with depth and varies in shape depending on relative depth.
L
h
20
L
L
h
20
2
“Shallow”
“Intermediate”
L
h
2
“Deep”
where h is the water depth
Dean and Dalrymple Coastal Engineering textbook
WAVE PARAMETERS
This suggest that the water particle motion changes with depth.
It also suggests that parameters such as velocity and wavelength
change with depth
g is gravity; g = 32.2 ft/s2.
“Deep Water”
Wavelength (L)
gT
L
2
“Intermediate
Water”
2
“Shallow Water”
gT 2
 2h 
L
tanh

2
L


L  T gh
gT
 2h 
tanh

2
 L 
C  gh
Wave velocity (C)
gT
C
2
C
WAVE PARAMETERS
Intermediate
region
Intermediate
region
T = 10 seconds, H = 6 ft.
TSUNAMI
Tsunami are waves that often cause destruction.
They are often incorrectly referred to as tidal waves, but they are
not associated with the moon or sun that forces tides.
Tsunamis typically occur after an earthquake where parts of the
ocean floor are raised or lowered very rapidly.
They can also be caused by a landslide where lots of dirt and
rock quickly enter the ocean.
TSUNAMI
The wavelength of a tsunami as it travels across the ocean can be
300-500 MILES.
A typical depth for an ocean basin may be 3 miles.
Tsunami height can
increase drastically
when the water
depth becomes
very shallow
http://www.jobsletter.org.nz
BEACH PROFILE
The beach profile is the change in elevation or depth as a
function of cross-shore distance.
Example: it usually gets deeper as you go farther offshore.
Imagine staring straight offshore and taking a slice down through
the beach.
http://myweb.cwpost.liu.edu/vdivener/notes
BEACH PROFILE
The profile shape is governed by variable waves and currents
During large waves, sand tends to move offshore. Sometimes
termed “winter” profile
During small, long period waves sand tends to move onshore.
Sometimes termed “summer” profile
SUMMER
coastalchange.ucsd.edu
WINTER
BEACH PROFILE
Changes in the beach profile can be simulated in the wave tank
by running waves of different size for periods of time.
BEACH PROFILE SPREADSHEET
Screen shot of the Excel spreadsheet.