Waves Flashcards
Transverse?
90 degrees
Longitudinal?
180 degrees
Generating force of waves?
wind, storms, earthquakes, sun and moon
Restoring force of waves?
gravity, surface tension
What does the wave form depend on?
wind speed, duration, fetch (distance over which the wind blows), original sea state.
What happens when there is a large fetch and duration?
size of wave depends only on wind speed
fully arisen sea
Hs = 0.025 u^2
bigger the speed, bigger the wave
What does Hs mean?
Significant wave height - average height of the highest 1/3rd of the waves
Particle motion beneath the waves in deep water?
wave particle orbits are circular, forwards beneath crest and backwards beneath trough
Particle motion beneath the waves with negligible depth > wavelength / 2?
Particle orbits are closed
no net flow of water
energy and momentum transferred by the waves.
What is Stokes drift?
At the surface for large waves the particle orbits are open and the netflow of water is known as stokes drift.
Particle motions in shallow water?
Particle orbits are influenced by the sea bed and often compressed in the vertical motion to ellipse
What is shallow water classified as?
depth < wavelength / 20
What is the life of an ocean wave?
storm winds - unsteady, variable direction
waves generated are - forced waves, irregular, mixed characteristics, known as ‘SEA’
How is swell produced?
Longer waves travel faster running ahead of shorter waves.
How do you calculate the wavelength?
L = gT^2 / 2 pi
How do you calculate the period?
T = L / c
How do you calculate the phase speed?
c = gT / 2 pi
What is dispersion?
progressively shorter waves follow behind
Why do waves tend to travel in groups?
propagate at group speed
arise from interaction of waves with similar characteristics
What is shoaling?
When waves steepen in shallow water
What direction are wave crests?
parallel to the shore due to refraction
Where is wave energy focused?
Towards shoals and headlands away from deep areas and bays.
What is a spilling wave?
slow release of energy - flat beach
What is a plunging wave?
rapid release of energy - steep beach
What is a surging wave?
Wave breaks at the shoreline
What does oblique incidence do?
generates longshore current.
What does normal incidence do?
piles water up on the shore leading to return flow (undertows/rip currents)
