Linear wave theory

Question 1

Types of coast - Soft

Answer 1

• influenced by natural processes
• change at various timescales

Question 2

Types of coasts - hard

Answer 2

• resist natural forces
• change mostly at very long term timescales

Question 3

What influences coastal behaviour?

Answer 3

-geological controls (bedrock, natural features…)
- natural forcing (waves, tides, rivers…)
- interaction between different parts of a coastal system
- human intervention

Question 4

World wave mean height map

Answer 4

• large waves found in vast oceans
• waves small closer to land

Question 5

Water wave generation

Answer 5

• resulant of wind shear stress acting on the sea surface
• size dependant on; wind speed and direction

Question 6

two wave categories

Answer 6

• wind (sea) waves
• swell waves

Question 7

wind waves

Answer 7

• depend on local wind field
• shorter waves and periods
• wide frequency band`

Question 8

swell waves

Answer 8

• independant on the local wind field
• have long wave lengths and large wave periods
• all waves lengths and large wave periods
• fairly uniform

Question 9

When both sea and swell waves present

Answer 9

bi - modal sea

Question 10

linear wave theory

Answer 10

• mathematically describes water waves and their propagation
• provide wave parameters for coastal engineering applications
  -can be used to calculate sediment transport and beach change
• used to determine wave energy

Question 11

LWT assumptions

Answer 11

• fluid incompressible
• fluid is inviscid
• flow is irrotational
• surface tension negligible
• gravity waves sinusoidal (cosine) in shape
• sea bed horizontal
• wave two dimensional
• pressure at the free surface is constant

Question 12

wave number (k)

Answer 12

2(pi) / L

Question 13

wave celerity

Answer 13

the speed with which a wave crest moves

Question 14

Wave dispersion

Answer 14

water waves with different frequencies travel at different speeds
- wave period is a constant
- wave length varies with water depth

Question 15

Approximations - dispersion relationship (deep)

Answer 15

valid if the water depth h is much greater than the wavelength L

Question 16

Approximations - dispersion relationship (shallow)

Answer 16

valid if the water depth is significantly less than the wavelength

Question 17

Wave groups - speed

Answer 17

Group speed
-function of wave celerity, wavelength and water depth

Question 18

water particle velocity

Answer 18

• when in a water column, move when a progressive wave propagates at free surface
• water particles move in circular (deepwater) or elliptical (shallow water) trajectories
• direction and magnitude move in circular/ elliptical trajectories
  magnitude dependant on position with respect to wave profile and location in water column

Question 19

water particle displacement

Answer 19

• magnitude of particle displacement depends on wave height, length, postion with respect to profile and water column

Question 20

wave pressure

Answer 20

• hydrostatic pressure exerted by water in equilibrium
• water wave motion induce an additional dynamic pressure component
• total pressure under progressive waves is the sum of dynamic and hydrostatic pressure

Question 21

Wave power

Answer 21

rate of wave energy propagation over one wave period per unit width of the wave

Question 22

Wave energy

Answer 22

PE - resulting from the displacement of the free surface due to propagating wave
KE - resulting from moving water particles