A simple piece of wave-energy-propulsion technology

.
.
.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

The arrows in the bare-bones diagram show the vertical push of the water, the function is caused by the wave or by strong current, acting on a stern-mounted rigid blade.

Simplifying the representation to stern-mounted blades only, this illustration shows the response of the system to the surface waves.

In fact, this design calls for an additional set of propulsive blades to be mounted well forward on both sides of the hull. In this top-view illustration, graduated tone is used to indicate a flexible-blade system.

The forward and aft blades function independently. When one is pushed down by the waves, the other is forced up. Similarly, the blades on each side of the boat are also free to respond differently as wave forces shift.

Thirty degrees of deviation from level is acceptable, but not over 45 degrees. The curved line indicates a "quadrant" which is a structure to limit motion inward so that the blade would not rub against the hull. As an alternative, some form of hydraulic system might be designed to enable control over the degree of tilt while eliminating this external structural detail. To achieve a more hydrodynamic shape, the goal of design refinement is to minimize the number of exterior-mounted connecting parts which can become fouled with seaweed or other debris.

.

(LOOK AT THE DIAGRAMS!)

The diagram shows support struts with a control joint restricting the amount of motion permitted. Flexible blades might not require this type of joint; in that case, the degree of flex would be that permitted by the material used.

In addition to propulsion, this method of capturing and redirecting the energy into forward motion would theoretically mitigate the infamous up-down, pitching and rolling motions that cause to sea-sickness.

--yuwei

edited and reviewed by: seokting on 17/06/08

Physics Principles involved in Ocean Wave Energy

--

23/04/08
.
.
.
.

.

.

.

.

.

.

.

.

.

.

.

.

Wave energy, is created by natural conversion of part of the wind energy above the oceans. Wind energy is created by natural conversion of part of solar energy. By heating air, the sun creates winds. This is because warmer air rises up while cooler air falls due to the difference in density. Hence, this creates movement in air, which is wind. Then, the winds blowing along the water surface create waves. Wind pressure pushes down wave troughs (lowest portion of the waves, as shown in the diagram below) and lifts up wave crests (the highest portion of the waves), due to Bernoulli's principle.

Bernoulli's principle states as the speed of a moving fluid increases, the pressure within the fluid decreases, and conversely, as the internal pressure increases, the speed of a fluid decreases proportionally.

(For more information and illustrated diagrams on Bernoulli's principle, please refer to http://home.earthlink.net/~mmc1919/venturi.html)

Hence, as the velocity of the wind increases, the pressure above the surface of the ocean decreases. This creates higher pressure under the ocean surface. The difference in pressure then pushes the water upwards and lifts it up. This is how wave is created. According to Bernoulli's principle, it also means that when the velocity of wind is higher, wavelength is also higher as wavelength determines wave power.

--yingshi

--

--

29/05/08

Both air pressure differences between the upwind and the lee side of a wave crest, as well as friction on the water surface by the wind shear stress cause the growth of the waves. The wave height increases with increasing wind speed, duration since the wind started to blow, and of the fetch (the distance of open water that the wind has blown over).

Thus, in general, wave power is determined by wave height, wave speed, wavelength and the density of water.

Oscillatory motion is the highest at the surface of the ocean and hence most devices used to extract wave energy are built on the surface.

Among different types of ocean waves, wind generated waves have the highest energy concentration. Wind waves are derived from the winds as they blow across the oceans. This energy transfer provides a natural storage of wind energy in the water near the free surface. Once created, wind waves can travel thousands of kilometres with little energy losses, unless they encounter head winds.

.

.

.

.

.

.

Ocean waves encompass two forms of energy: the kinetic energy of the water particles, that in general follow circular paths; and the potential energy of elevated water particles. On the average, the kinetic energy in a linear wave equals its potential energy. The energy flux in a wave is proportional to the square of the amplitude and to the period of the motion. The average power in long period, large amplitude waves commonly exceeds 40-50 kW per meter width of oncoming wave.

--cassandra

Edited and reviewed by the same people who wrote it:

11/06/08, 27/06/08

A random problem-- image suggestion

SO, as the title of this blog post indicates, the image above sort of explains yingshi's question in a rather comprehensive manner..

hope it helps!

--seokting

Introduction to Wave Energy

--
12/04/08

WAVES~~~

Waves are created by the progressive transfer of energy from wind currents passing over the surface of the ocean (as long as the waves propagate slower than the wind speed just above the waves, there is an energy transfer from the wind to the most energetic waves). Waves are formed from turbulence because wind pressure pushes down wave troughs and lifts up wave crests, due to Bernoulli's principle. (will be elaborated in physics principles)

Generally, large waves are more powerful. Specifically, wave power is determined by wave height, wave speed, wavelength, and water density.

The equation here:

View: http://en.wikipedia.org/wiki/Wave_energy#Physical_concepts

where,

P the wave energy flux per unit wave crest length (kW/m),
Hm0 is the significant wave height (meter), as measured by wave buoys and predicted by wave forecast models. By definition, Hm0 is four times the standard deviation of the water surface elevation,
T is the wave period (second),
ρ is the mass density of the water (kg/m3), and
g is the acceleration by gravity (m/s2)

shows the factors affecting the size and power of a wave.

It also states that wave power is proportional to the wave period and to the square of the wave height. When the significant wave height is given in meter, and the wave period in second, the result is the wave power in kW (kilo watt) per meter wavefront length.

--yingshi

--
22/04/08

WAVES AS A SOURCE OF ENERGY

Renewable energy effectively uses natural resources such as sunlight, wind, rain, tides and geothermal heat, which are naturally replenished. Renewable energy technologies range from solar power, wind power, hydroelectricity/micro hydro, biomass and biofuels for transportation. Therefore, wave energy does have its benefits of being renewable and environmentally friendly. (This is elaborated further below)

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. Wave power generation is not a widely employed technology, and no commercial wave farm has yet been established.

The movement of waves and the rising and falling of tides can be harnessed to drive turbines that generate electricity. There are two main types of wave energy collectors. The first type directs waves into man-made channels, where the water passes through a turbine that generates electricity. The second type uses the up and down movement of a wave to push air.

Wave is a powerful source of energy. In fact, it can go up to many metres in height. The total power of waves breaking around the world’s coastlines is estimated to be 2 to 3 million megawatts.

Wave power varies considerably in different parts of the world, and wave energy cannot be harnessed effectively everywhere. Wave-power rich areas of the world include the western coasts of Scotland, northern Canada, southern Africa, Australia, as well as the northwestern coasts of United States.

Good wave power locations have a flux of about 50 kilowatts per metre of shoreline. Capturing 20 percent of this, or 10 kilowatts per metre, is plausible. Assuming very large scale deployment of (and investment in) wave power technology, coverage of 5000 kilometres of shoreline (worldwide) is plausible. Therefore, the potential for shoreline-based wave power is about 50 gigawatts. Deep water wave power resources are truly enormous, but perhaps impractical to capture.

--cassandra

--
08/05/08

BENEFITS OF WAVE ENERGY (brief overview)-- Renewable and environmentally friendly

Wave energy is a renewable and pollution-free energy source that has the potential to contribute with 2,000 TWh per year of the world's energy production.
Wave energy is free. No fuel is needed to generate the energy and thus no waste is produced. Wave energy plays a major role in the world's efforts to prevent climate change. It potentially displaces 1 to 2 billion tonnes of CO2 annually from usual fossil fuel generating sources.

--yingshi

Entire post reviewed and edited by same people who wrote it:

07/06/08

a group discussion (:

Hello there! This blog post merely consists of our group discussion in class on the information and research to include in this blog. So here it is!

Date: Tues, 8 April 2008
Time: 9.45 to 10.15am
Venue: Sec 301 Classroom

Information that our group will include in this online journal :

1) Introduction to wave energy

2) Physics principles and theories of wave energy (process of harnessing wave energy; conversion of forms of energy)

3) Devices used to harness wave energy and often, convert it into electrical energy

4) Uses of wave energy (How it helps in carrying out business within the industry)

5) General advantages and disadvantages of using wave energy as an energy source (further improvements to be made to the level of efficiency of harnessing the energy of waves to generate electricity and numerous other uses)

6) Case study on 1 country

7) Conclusion


GOOD LUCK TO US!!!!! (:

A random problem

From a report, Wave Energy Potential on the U.S. Outer Continental Shelf (2006), it states that:

“Because wind is generated by uneven solar heating, wave energy can be considered a concentrated form of solar energy. Incoming solar radiation levels that are on the order of100 W/m2 are transferred into waves with power levels that can exceed 1,000 kW/m of wave crest length. The transfer of solar energy to waves is greatest in areas with the strongest wind currents (primarily between 30° and 60° latitude), near the equator with persistent trade winds, and in high altitudes because of polar storms.”

I don't understand how wind is generated by solar heating and why it is a form of solar energy.

--yingshi