"wave energy"

Wave energy refers to the kinetic energy and potential energy of waves on the surface of the ocean. The energy of a wave is proportional to the square of the wave height, the wave motion cycle, and the width of the wavefront. Wave energy is the most unstable energy source in marine energy. Wave energy is generated by the wind transferring energy to the ocean. It is essentially formed by absorbing wind energy. The rate of energy transfer is related to the wind speed and is also related to the distance of wind-water interaction. Waves can be described by features such as wave height, wavelength, and wave period.

Introduction

The destructive power of the waves is amazing. The great waves that took tossing shores have thrown dozens of tons of megaliths to a height of 20 meters and have also put 10,000 tons of ships on the coast. The waves used to invert the two to three thousand tons of reinforced concrete components on the revetment. Many seaport projects, such as breakwaters, piers, and harbors, are designed according to wave standards.

In the ocean, the big wheel in the waves can only drift up and down like a small piece of wood. Big waves can overturn the wheel, and they can also break or twist the wheel. If the wavelength of the wave is exactly equal to the length of the ship, when the wave crest is in the middle of the ship, the bow of the bow is just a trough, and at this time the ship will have a "middle arch." When the wave peak is at the bow and stern, the trough is in the middle. At this time, the boat will have a "sag". One arch is like a folding iron. A few times, the big wheel is broken. In the 1950s, there had been a shipwreck of an American ship in the Italian waters. At this time, experienced captains can avoid doom as long as they change the direction of navigation. Because the change of course changes the "relative wavelength" of the wave, the middle arch and sag of the ship will not occur.

Development

The wave energy is so huge. It exists so extensively that it has attracted coastal craftsmen since ancient times and has tried every means to control the waves for human use. Hydraulic power can meet three times the world's energy.

The energy contained in waves is mainly the kinetic energy and potential energy of waves on the ocean surface. The energy of a wave is proportional to the square of the wave height, the wave motion cycle, and the width of the wavefront. Wave energy is the most unstable energy source in ocean energy. The typhoon-induced waves have a power density of up to several thousand kW per meter of the wavefront, and the wave-rich North Sea region of Europe has an average annual wave power of only 20 to 40 kW/m^2. The wave power density is 2~7kW/m^2.

The theoretical estimate of wave energy worldwide is also on the order of 109 kW. Using the data from China's coastal ocean observation stations, we estimate that the average annual average wave power of China's coastal theoretical waves is about 1.3×10 7 kW. However, since many of the observation stations of the ocean stations are located in inner bays or locations where wind waves are relatively small, the actual coastal wave power is greater than this value. Among them, Zhejiang, Fujian, Guangdong, and Taiwan are rich in wave energy.

Wave energy devices that collect wave energy and convert it into electrical energy or other forms of energy have two types of waves installed on shore and floating in the sea. According to the form of energy transmission, there are 4 direct mechanical transmissions, low pressure hydraulic transmissions, high pressure hydraulic transmissions and pneumatic transmissions. The pneumatic transmission adopts an air turbine wave power generator to convert the energy of the reciprocating air flow generated by the wave motion compressed air into electric energy. The rotating parts are not in contact with seawater and can be rotated at a high speed, and thus develop rapidly. Various wave power generation devices, eclectic, a little head type, wave type, wave power ship type, atoll type, rectifier type, jellyfish type, soft bag type, oscillating water column, multi-shaking water column, There are more than ten kinds of wave-type, pendulum-type, water-column-type oscillating wave type and shrinkage waterway type.

use

Thousands of mechanical designs of waves are used throughout the world, and hundreds of patent certificates have been obtained. Therefore, the use of wave energy is called the "inventor's paradise."

The earliest wave energy use of mechanical invention patents was obtained in 1799 by the French Gillard and his son. In the 119 years between 1854 and 1973, the United Kingdom registered 340 patents for wave energy inventions and 61 for the United States. In France, 600 specifications for wave energy utilization technology can be found.

The early ocean wave power generation utility is a pneumatic wave power device. The reason is very simple, that is, using the power of the waves up and down, through the compressed air, to promote the reciprocating motion of the piston in the pump and do work. In 1910, the Frenchman Bousso Blasek built a pneumatic wave power station near his beachfront residence, supplying 1,000 watts of electricity to his residence. The principle of this power station device is that the air in the sealed vertical pipe that communicates with seawater is compressed or evacuated due to undulations, and the piston is driven to make a reciprocating motion, and then converted into a rotational motion of a generator to generate electricity.

In the 1960s, Japan successfully developed a pneumatic wave power generation device used on a floating body of navigation lights. This device has been put into mass production, the product rated power from 60 watts to 500 watts. In addition to its own use in Japan, the product was also exported and became one of the few commercialized wave energy equipment.

The principle of power generation of this product is like an inverted pump, which draws and presses the air by the force of the wave reciprocating up and down to drive the turbine to generate electricity.

Relevant experts estimate that there are billions of dollars of market demand for wave power equipment used for maritime navigation and island power supply. This estimate has greatly promoted the study of wave power in some countries. Since the 1970s, Britain, Japan, Norway, and other countries have invested a lot of manpower and material resources for wave power generation research, and their performance is also the most significant. The United Kingdom had planned to deploy a "nodding duck" type wave power plant on the wave field outside the Scottish Sea to supply electricity for the entire country at that time. This ambitious plan was later put on hold because the device structure was too large and the cost was too high. In the 1980s, the Japanese “Haiming” wave power generation pilot ship achieved good results of 190,000 kWh per year, and achieved a small-scale power transmission of offshore floating wave power stations to the land. Japan has listed the “Haiming” wave power generation vessel as the preferred solution for the “island power supply” and continues to study and improve it.

China's wave power generation research results are also very significant. Since the 1970s, five or six research units in Shanghai, Qingdao, Guangzhou, and Beijing have carried out this research. Wave power generation devices for navigation lights have also been put into mass production. Shore-wave power stations that provide power to the island are also being tested.

distributed

The southernmost hemisphere and the northern hemisphere have the strongest winds between 40° and 60° latitude. Xinfeng District (within 30° on both sides of the equator)

Waves also produce attractive waves, because the low-velocity winds here are more regular. In the coastal areas of Shengfeng District and Changfeng District, the density of wave energy is generally high. For example, the coastal areas of the United Kingdom, the western coast of the United States, and the southern coast of New Zealand are all wind districts and have particularly good wave conditions. The coastal regions of Zhejiang, Fujian, Guangdong, and Taiwan are rich in wave energy.

Although the wave energy in the ocean is difficult to extract, the available wave energy resources are limited only to the shoreline. However, even if this is the case, the reserve of wave energy resources in the coastal areas with better conditions will probably exceed 2TW. It is estimated that the world can develop and use 2.5TW of wave energy. The effective wave height in China's coastal areas is about 2 to 3 m and the wave period is 9 s. The wave power can reach 17 to 39 kw/m and the Bohai Bay can reach 42 kw/m.

Energy estimation

The size of the wave energy can be estimated by the change in the potential energy of seawater fluctuations, ie, P=0.5TH2 (P is the wave power per unit wavefront width in kw/m; T is the wave period, unit s; H is the wave height, unit m, actually the size of the wave power is also related to many factors such as wind speed, wind direction, continuous blowing time, flow velocity, etc.). Therefore, the wave energy level is generally expressed in kw/m, which represents the rate at which energy passes through a 1m long line parallel to the wavefront.