Surface Waves
Reading
- Chapter 1 of Waves, Tides, and Shallow water processes (Open University)
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See also: Emery et al. Sec 15.1–15.3 and Stewart Chp 16 and 17.1–17.3
Things to know
Basic wave parameters
- be able to define wavelength, wave height, amplitude, period and
frequency.
- what is meant by “phase speed”?
What are waves?
- What characteristics does the text list for waves?
- What is the difference between a progressive and standing wave?
- What are the two restoring forces for surface waves on water?
- What is the difference between capillary and gravity waves?
Wind-generated waves
- Describe Jeffries’ sheltering theory for how wind waves are
generated.
- What is the average steepness of open-ocean wind generated waves?
- What ratio of wind-to-wave speed is the most efficient at generating waves?
- Why don’t the waves increase in size indefinitely?
- What is meant by a fully developed sea?
- From fig 1.4, do you expect low or high frequency waves to become more important as the wind gets stronger in a fully developed sea? Why?
Wave height and steepness
- What is meant by significant wave height? Why is such a concept used?
- Take a look over the Beaufort Scale. At what scale do whitecaps
start to form? At what scale does spindrift start to form? (What
is spindrift?)
- Have a look at the pictures at: http://en.wikipedia.org/wiki/Beaufort_Scale
Wave forms and motions
- If a wave is sinusoidal in space, and it passes you at a constant speed, how will it look in time?
- For sinusoidal waves in deep water, what is the trajectory traced out by a water parcel? How does this trajectory change with depth?
- What happens to the orbits of a water parcel if the water is “shallow”.
- What is meant by “wave speed” and how do you calculate it?
- What are the wavenumber and angular frequency? (These are often used for notational convenience).
- Wave speeds
- The wave speed of “deep” waves depends on?
- The wave speed of “shallow” waves depends on?
- What assumptions are made in linear surface wave theory?
Dispersion and Group Speed
- If a storm hits a region, an observer on a beach will encounter
long or short waves first?
- What is the difference between group speed and wave speed?
- Does the explanation of the difference on page 20 make sense to you?
- what is the group speed of shallow water waves?
- what is the group speed of deep-water waves?
- Why doesn’t the difference between group and wave speeds matter in shallow water?
Wave Energy
- What are the two forms of energy in a fluid?
- How does the energy depend of the height of the (linear) wave?
- How fast does wave energy propagate?
- Skim the section on “swell”….
Refraction and shoaling
- What is meant by refraction?
- What happens to waves as they get in shallower water?
- What is the meaning of eq, 1.13? What does it imply about the
flux of energy?
- What are the four types of breaking waves on a beach?
Special waves
- Explain what happens to the wavelength of waves propagating into a
current and with a current.
- Why are giant waves seen off the SE tip of Africa? How large do they reach?
- What causes tsunamis?
- how fast do they travel (are they shallow or deep waves?)