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? Ripples on lake, waving your hand, sound, light etc 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 Wave elevation profile: deep water = sine wave Wavelength Crest amplitude Height 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)

Velocity (C): distance divided by time 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

So, waves transport energy, NOT matter. 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 Question: If a wave amplitude is doubled, what happens to the energy? Ans: it quadruples.

where h is the water depth WAVE PARAMETERS Water particle motion within a wave train decays exponentially with depth and varies in shape depending on relative depth. “Shallow” “Intermediate” “Deep” where h is the water depth Dean and Dalrymple Coastal Engineering textbook

This suggest that the water particle motion changes with depth. 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” “Intermediate Water” “Shallow Water” Wavelength (L) Wave velocity (C) Intermediate requires iteration and too hard to solve at this level.

WAVE PARAMETERS T = 10 seconds, H = 6 ft. Intermediate region

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.

A typical depth for an ocean basin may be 3 miles. 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

Example: it usually gets deeper as you go farther offshore. 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

The profile shape is governed by variable waves and currents 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 WINTER coastalchange.ucsd.edu

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.