Water waves

1. PresentationPresentation

2. TIDES
• WHAT CAUSES THE TIDES?
• APPLICATIONS OF TIDES
• HARMFUL EFFECTS OF TIDES

3. WHAT CAUSES THE TIDES?
Tides are periodic rises and falls of large bodies of water.
Tides are caused by the gravitational interaction between the Earth and the Moon.
Tides are the cyclic rising and falling of Earth's ocean surface caused
by the tidal forces of the Moon and the Sun acting on the Earth.
Tides cause changes in the depth of the sea and produce oscillating
currents known as tidal streams, making prediction of tides important for
coastal navigation.
The strip of seashore that is submerged at high tide and exposed at low tide,
the intertidal zone, is an important ecological product of ocean tides.

4. The Earth and Moon, looking at the
North Pole
The relative distance of the Moon from the Earth also affects tide heights.
When the Moon is at perigee the range is increased and when it is at
apogee the range is reduced.

5. gravitational force
The Moon's gravity differential field at the surface of the
earth is known as the Tide Generating Force.
This is the primary mechanism that drives tidal action and
explains two bulges, accounting for two high tides per day.
Other forces, such as the Sun's gravity, also add to tidal action.

6. gravitational force
The Moon exerts its gravitational pull differently on different
parts of the earth.
The farther away the Moon, the weaker its pull.
Imagine a shell of the outer Earth, this diagram shows the
Moon's gravity differential over the thickness of the shell.

7. Spring Tides
The Sun's Interaction with
the Tides
Spring tides are especially strong tides (they do not have anything
to do with the season Spring).
They occur when the Earth, the Sun, and the Moon are in a line.
The gravitational forces of the Moon and the Sun both contribute to
the tides.
Spring tides occur during the full moon and the new moon.

8. Proxigean Spring Tide
The eccentricity of the orbit of the moon in this illustration is greatly
exaggerated.
The Proxigean Spring Tide is a rare, unusually high tide.
This very high tide occurs when the moon is both unusually close
to the Earth (at its closest perigee, called the proxigee) and in the
New Moon phase (when the Moon is between the Sun and the
Earth).
The proxigean spring tide occurs at most once every 1.5 years.
An artist's conception of spring tide

9. Neap Tides
Neap tides are especially weak tides.
They occur when the gravitational forces
of the Moon and the Sun are perpendicular
to one another (with respect to the Earth).
Neap tides occur during quarter moons.
An artist'sconception of neap tide

10. Spring Tides and Neap Tides
The Bay of Fundy at high tide The Bay of Fundy at low tide

11. Tidal range
The tidal range is the vertical difference between the
highest high tide and the lowest low tide.
In other words, it is the difference in height between high and low tides.
The most extreme tidal range will occur around the time of the
full or new moons, when gravity of both the Sun and Moon are pulling
the same way (new moon), or exact opposite way (full).
The typical tidal range in the open ocean is about 0.6 meters (2 feet).
As you get closer to the coast, however, this range gets much greater.
Coastal tidal ranges vary globally and can differ anywhere
from 1.8 meters to 3 meters (6–10 feet).

12. Tidal cycle time
Principal Types of Tides
Showing the Moon's
declinational effect in
production of semidiurnal,
mixed, and diurnal tides.

13. Tidal cycle time
The same tidal forcing has differentresults depending
on many factors,including coast orientation,
continental shelf margin,water body dimensions.

14. Tidal power
Tidal Energy sometimes called tidal power is the power achieved by capturing
the energy contained in moving water currents
tides and open ocean currents. There are two types of energy systems that
can be used to extracted energy: kinetic energy The moving water of rivers
tides and open ocean currents and the rise and fall of the tides that uses the
height difference between ebbing and surging tides and potential energy
from the difference in height (or head) between high and low tides.
The former method - generating energy from tidal currents - is considered
much more feasible today then building ocean-based dams or barrages that
flood eco systems and are expensive to build.
Tidal power is classified as a renewable energy source, because tides are
caused by the orbital mechanics of the solar system and to a lesser extent
the surface effect of winds and are considered inexhaustible within a human
timeframe.
The root source of the energy comes from the slow deceleration of the Earth's
rotation. The Moon gains energy from this interaction and is slowly receding
from the Earth. Tidal power has great potential for future power and
electricity generation because of the total amount of energy contained in this
rotation. Tidal power is reliably predictable (unlike wind energy and
solar power).

15. Tidal power
1 2 3 4 5 6
0° 32.07 0 0 0 78.29
45° 32.38 22.90 23.44 -O.54 68.59
90° 33.147 33.147 33.147 0 45.191
135° 33.94 24.00 23.44 0.56 21.79
180° 34.28 0 0 0 12.10
The table shows some significant force values for the Moon:
Column 1 : Longitude along any Earth equator passing through the axis,
counted from the trans-lunar nodal point.
Column 2: The axial gravitational force of the Moon at longitudes from 0° to 180°.
Column 3: The tangential component of the gravitational force (value of Col. 2
multiplied by sin n).
Column 4: The tangential component of the centrifugal force (33.1 micronewtons
multiplied by sin n).
Column 5: The tide-raising force.
Column 6: The radial centrifugal force, having no effect on the tides, is shown for
comparison.

16. Applycation of tide to generate
electricity
Tidal Stream Turbines
The simplest of all configurations is
a rotor on a pole fixed to the seabed:
this design acquired top-sides

17. Applycation of tide to generate
electricity
Today, this twin turbine design carries two 20m rotors
is rated at 1 - 2 MW depending on current speed,
and operates in 30 - 50m water depths.
Each rotor runs in clean water upstream of its support arm.

18. Applycation of tide to generate
electricity
The tidal turbine is shown for comparison
against anoffshore wind turbine of the
samepower rating and in 25m water depth.

19. Applycation of tide to generate
electricity
Another option is to use
offshore turbines,
rather like an underwater wind farm.
This has the advantage of being much cheaper to build, and does
not have the environmental problems that a tidal barrage would bring.

20. Applycation of tide to creat barrage
The barrage method of extracting tidal energy involves building a barrage and creating
a tidal lagoon. The barrage traps a water level inside a basin. Head ( a height of water
pressure) is created when the water level outside of the basin or lagoon changes
relative to the water level inside. The head is used to drive turbines. In any design this
leads to a decrease of tidal range inside the basin or lagoon, implying a reduced
transfer of water between the basin and the sea. This reduced transfer of water
accounts for the energy produced by the scheme. The largest such installation has
been working on the Rance river
The basic elements of a barrage are caissons, embankments, sluices, turbines and
ship locks. Sluices, turbines and ship locks are housed in caisson (very large concrete
blocks). Embankments seal a basin where it is not sealed by caissons.
The sluice gates applicable to tidal power are the flap gate, vertical rising gate, radial
gate and rising sector.
Barrage systems have been plagued with the dual problems of high civil infrastructure
costs associated with what is in effect a dam being placed across two estuarine
systems, one for the high water dam storage and the other a low water dam for the
release of the storage, and, the environmental problems associated with the flooding
of two ecosystems.

21. Applycation of tide to generate
electricity
An artistic impression of a tidal
barrage, including embankments,
a ship lock and caissons housing
a sluice and two turbines.
The weir at Coburg lake in
Victoria (Australia).
A weir is a small overflow-type dam commonly used to raise the level of a river
or stream. Weirs have traditionally been used to create mill ponds in such places.
Water flows over the top of a weir, although some weirs have sluice gates which
release water at a level below the top of the weir. The crest of an overflow spillway
on a large dam is often called a weir.

22. Applycation of tide to generate
electricity
A manually operated needle dam type
weir near Revin on the Meuse River, France
A weir in Warkworth, New Zealand

23. Tidal power schemes being considered
Country Place Mean tidal range (m) Area of basin (km²) Maximum capacity (MW)
Argentina San Jose 5.9 - 6800
Australia Secure Bay 10.9 - ?
Canada
Cobequid 12.4 240 5338
Cumberland 10.9 90 1400
Shepody 10.0 115 1800
India
Kutch 5.3 170 900
Cambay 6.8 1970 7000
Korea
Garolim 4.7 100 480
Cheonsu 4.5 - -
Mexico
Rio Colorado 6-7 - ?
Tiburon - - ?
In the table, '-' indicates missing information, '?‘
indicates information which has not been decided

24. Tidal power schemes being considered
Country Place Mean tidal range (m) Area of basin (km²) Maximum capacity (MW)
United Kingdom
Severn 7.8 450 8640
Mersey 6.5 61 700
Strangford Lough - - -
Conwy 5.2 5.5 33
United States
Passamaquoddy Bay 5.5 - ?
Knik Arm 7.5 - 2900
Turnagain Arm 7.5 - 6501
Russia[7]
Mezen 9.1 2300 19200
Tugur - - 8000
Penzhinskaya Bay 6.0 - 87000
South Africa
Mozambique Channel ? ? ?

25. World energy resources and consumption
Fuel type Power in TW Energy/year in ZJ
Oil 5.6 0.18
Gas 3.5 0.11
Coal 3.8 0.12
Hydroelectric 0.9 0.03
Nuclear 0.9 0.03
Geothermal, wind,
solar, wood
0.2 0.006
Total 15 0.5
The estimated 15TW total energy consumption of 2004 was divided as follows:

26. World energy resources and consumption
World energy consumption
in TW (=1012
Watt),
1980-2004. Source: Energy
Information Administration
World energy consumption
in TW, 1965-2005. Source:
BP 2006 Statistical review

27. World energy resources and consumption
Global energy consumption in
successively increasing detail Source:
BP 2006 Statistical review and Renewables,
Global Status Report 2006.

28. Renewable resources
World renewable energy in 2005 (except 2004 data for items marked* or **).
Source Renewables, Global Status Report 2006.

29. Renewable resources
Available renewable energy. The volume of the cubes represent the amount of
available wind and solar energy. The small red cube shows the proportional global
energy consumption. Values are in TW =1012
Watt. The amount of available renewable
energy dwarfs the global consumption.

30. Renewable resources
Solar energy as it is dispersed on the planet and radiated back to space.
Values are in PW =1015
Watt. Data to produce this graphic was taken from
a NASA publication.

31. WAVES
• WHAT CAUSES THE WAVES?
• APLYCATIONS OF WAVES
• HARMFUL EFFECTS OF WAVES

32. What Causes Waves?
The winds cause waves on the surface of the ocean (and on lakes).
The wind transfers some of its energy to the water,
through friction between the air molecules and the water molecules.
Stronger winds (like storm surges) cause larger waves.
You can make your own miniature waves by blowing across the surface
of a pan of water.
Waves of water do not move horizontally, they only move up and down
(a wave does not represent a flow of water). You can see a demonstration
of this by watching a floating buoy bob up and down with a wave;
it does not, however, move horizontally with the wave.

33. Motion of a particle in a ocean wave
Motion of a particle in a ocean wave.
A = At deep water.
B = At shallow water (ocean floor is now at B).
The circular movement of a surface particle
becomes elliptical with decreasing depth.
1 = Progression of wave
2 = Crest
3 = Trough

34. Wave motion
Waves are oscillations in the water's surface. For oscillations to exist and to
propagate, like the vibrating of a guitar string or the standing waves in a flute,
there must be a returning force that brings equilibrium. The tension in a string
and the pressure of the air are such forces.

35. Wave motion
These two diagrams show the relationships between wave speed and period for
various depths (left), and wave length and period (right), for periodic, progressive
surface waves. (Adapted from Van Dorn, 1974) Note that the term phase velocity
is more precise than wave speed.
The period of waves is easy to measure using a stopwatch, whereas wave length
and speed are not. In the left picture, the red line gives the linear relationship
between wave speed and wave period. A 12 second swell in deep water travels at
about 20m/s or 72 km/hr. From the red line in the right diagram, we can see that
such swell has a wave length between crests of about 250m.

36. Waves and wind
How wind causes water to form waves is easy to understand although many
Intricate details still lack a satisfactory theory. On a perfectly calm sea, the wind
has practically no grip. As it slides over the water surface film, it makes it move.
As the water moves, it forms eddies and small ripples.

37. how do we measure waves objectively?
Scientists do this by introducing a value E which is derived from the energy
component of the compound wave. In the left part of the drawing is shown
how the value E is derived entirely mathematically from the shape of the wave.
Instruments can also measure it precisely and objectively. The wave height is
now proportional to the square root of E.
The sea state E is two times the average of the sum of the squared amplitudes
of all wave samples.

38. Fully Developoled Sea energy
spectrum for various wind speeds
When the wind blows sufficiently long from the same direction, the waves it creates,
reach maximum size, speed and period beyond a certain distance (fetch) from the
shore. This is called a fully developed sea. Because the waves travel at speeds
close to that of the wind, the wind is no longer able to transfer energy to them and
the sea state has reached its maximum. In the picture the wave spectra of three
different fully developed seas are shown. The bell curve for a 20 knot wind (green) is
flat and low and has many high frequency components (wave periods 1-10 seconds).
As the wind speed increases, the wave spectrum grows rapidly while also expanding
to the low frequencies (to the right)

39. Waves entering shallow water
As waves enter shallow water, they slow down, grow taller and change shape.
At a depth of half its wave length, the rounded waves start to rise and their crests
become shorter while their troughs lengthen. Although their period (frequency)
stays the same, the waves slow down and their overall wave length shortens.
The 'bumps' gradually steepen and finally break in the surf when depth becomes
less than 1.3 times their height. Note that waves change shape in depths depending
on their wave length, but break in shallows relating to their height!

40. Wave groups
Part of the irregularity of waves can be
explained by treating them as formed
by interference between two or more
wave trains of different periods, moving
in the same direction. It explains why
waves often occur in groups.
The diagram shows how two wave
trains (dots and thin line) interfere,
producing a wave group of larger
amplitude (thick line).

41. Wave power
Wave power refers to the energy of ocean surface waves and the
capture of that energy to do useful work - including electricity
generation, desalination, and the pumping of water (into reservoirs).
Wave power is a form of renewable energy.
Though often co-mingled, wave power is distinct from the diurnal
flux of tidal power and the steady gyre of ocean currents.
When an object bobs up and down on a ripple in a
pond, it experiences an elliptical trajectory.

42. An Ocean Wave Energy Converter
The novel ocean wave energy converter consists of an array of parallel Savonius
rotors with elastic blades, which are arranged to form a plane and are mounted on
tensioned axes in a rectangular frame.
The diameter of the rotors is small compared to their length, and compared to the
height of the waves. The rotors are made of rubber or plastic on a core of aluminium
and rotate around tensioned axes of carbon fibres or coated steel.
At the ends of each rotor sit small dynamos which transform the rotational movement
of the rotors into electricity. In order to capture energy from waves the proposed
converter must be positioned right beneath the water surface and oriented parallel to it.
(1) Savonius rotor, (2) dynamo,
(2) (3) frame, (4) anchor and
(3) length-variable pole,
(4) (5) ocean wave, (6) sea ground.

43. An Ocean Wave Energy Converter
The basis of the wave converter is the omni-directional Savonius rotor with
elastic blades shown below. Savonius rotors are driven by any local water flow
that has a directional component perpendicular to their axis, no matter from
which direction the water comes. Under the ocean waves there is an oscillating
flow field that locally changes its direction all the time.

44. An Ocean Wave Energy Converter
Using a multitude of small rotors instead of a big one has several advantages.
Small rotors can be placed much closer to the water surface,
where most of the wave energy is. An array of small rotors covering the same
water flux as a big rotor requires much less material to harvest the same flow power.

45. An Ocean Wave Energy Converter
(1) rotors, (2) frame, (3) floating body, (4) stabilizer plate, (5) connecting chain,
(6) anchor chain, (7) anchor, (8) ocean waves, (9) sea ground.
The ocean wave energy converter
can be installed floating offshore
as well as be fixed to poles near
the coast - invisibly submerged under
the water surface. The figure below
shows a floating converter and how
it is anchored to the ground.

46. An Ocean Wave Energy Converter
The Pelamis Wave Energy
Converter (Ocean Power
Delivery Ltd.)
Pelamis ?prototype (Ocean
Power Delivery Ltd.)

47. R&D ?The Way Forward
Roadmap of R&D targets and associated events and activities
One effective way of planning future R&D needs is by use of the Roadmap ?
a diagram with a timeline, showing the main R&D targets and the associated
events and activities, set against the timeline as a high-level plan. It displays
the generic issues that must be addressed if wave power is to become
commercially realisable in the next few years.

48. Thank you for listening
THE END