Tides are the ones that occur in coastal areas Natural phenomenon , refers to the sea water in celestial bodies (mainly seleno And the sun) Tide generating force The periodic motion produced by the action. It is customary to refer to the vertical rise and fall of the sea surface as the tide, while the water in Horizontal direction The flow is called tidal current. In order to represent the time of the sea ebb and flow, the ancestors of humans called the tide of the sea during the day, and the tide of the sea at night, collectively known as the tide. This is where the tides get their name.

Chinese name: tide
Foreign name: The tides

categorize: The Earth tide, Sea tide Etc.
Development and utilization: Energy development, military applications

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Citation interpretation

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tide

Tides are the periodic rise and fall of ocean water caused by the gravitational pull of the moon and sun. In the day called tide, night called xi, the general name "tide". Generally rise and fall twice a day, there is also a rise and fall. The outer sea tidal wave follows the river upstream, and makes the river downstream tidal. On account of The lunar calendar therefore Lunar phase variation It has a major role in reflecting the tide, the tide phenomenon is the moon plays a leading role, and the Xia calendar based on the change of the moon phase is the guide to maritime activities in ancient times. The moon is attractive to the Earth's sea water, the distance between the Earth's surface and the moon is different, and the place facing the moon is attracted by gravity, and the sea water expands outward; In places facing away from the moon, the water has less gravity, more centrifugal force, and under the centrifugal force, support Where the moon expands, there will also be a high tide.

Extended meaning

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Tidal, by extension, refers to something that has similar characteristics to tidal phenomena, and is used to describe the ebb and flow of something. It is often used in positive phrases, such as: Tidal lane Tidal group, tidal passenger flow, etc.

Tidal (the property of things that, like tides, rise and fall or change periodically) means the same as tidal, and is often used in positive phrases, such as tidal lanes, tidal traffic, etc.

The Northern Qi Dynasty (550-597) Yan Zhitui "Yan's family instruction · Homecoming" : "Tide to return, who is saved?" Song Suzhe Kazuzi Zhan snow wave vegetarian "In front of the door Stone bank The tide washes away the berries and the moss." Ming Liu Ji "Jiangxing Miscellaneous Poems" seven: "The Kun spirit does not put thick Ground crack The tide should be able to help the mulberry." Ye Shengtao "Poverty" : "Gambling caves are broken, the city is noisy, the crowd to gather to see how Bo acts like people, the city is such as the tide."

Definition classification

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tide

Due to the tidal forces of the sun and the moon, the earth's lithosphere , hydrosphere and atmosphere In the respectively produced periodic movement and change, collectively known as tides. In a broad sense, tides are divided into solid tides (earth tides), liquid tides and gas tides (gas tides). In liquid tides, except ocean tides, river tides fluctuate very little and can be ignored. So the common liquid tide refers to the sea tide. As a complete tidal science, its object of study is also A surname Earth tide, sea tide and gas tide as a unified whole, but because the sea tide phenomenon is very obvious, and people's life, Economic activity , transportation The relationship is so close that it is customary to narrow the word "tide" to mean Ocean tide . Solid earth The elastic-plastic deformation caused by the tidal force of the sun and the moon is called solid tide Earth tide or Earth tide .

Tides vary from place to place, often in different areas tide Systems, all of which derive their energy from deep ocean tidal waves, but have their own unique characteristics.

The periodic rise and fall of the sea surface caused by the tidal force of the sun and the moon is called the ocean tide, referred to as the sea tide.

Atmospheric elements (e.g Barometric field , atmosphere Wind field , Earth magnetic field Etc.) produced by the action of induced tidal forces Periodic change (e.g. 8, 12, 24 hours) said Atmospheric tide , for short Air tide .

wherefrom Sun Caused by atmospheric tides Solar tide , due to seleno Induced balance Lunar tide ( Lunar tide ).

Salt tide , mainly by drought Caused by, generally occurs in the winter solstice of the previous year to the spring Qingming period of the following year, because the upstream river water volume is less, less rainfall, so that the river water level drops, resulting in coastal areas through rivers or other channels to flow back to the inland area. The effect of salt tide is mainly manifested in chloride According to the relevant national standards, if the chlorine content of water exceeds 250 mg/l, it is not suitable for drinking. The water can also harm local plants.

Salt tide It belongs to a unique monsoon in coastal areas Natural phenomenon , mostly in the dry season, drought period. Brackish water upwelling means that during the brackish tide upwelling, the pumping outlet located in the lower reaches of the river is not pumped fresh water that can be used for drinking and irrigation, but seawater that terrestrial life cannot depend on. China's salty tides mostly occur in Pearl River Estuary .

On the basis of Tidal cycle It can be divided into the following three categories:

Half a day Tidal regime The occurrence of two high tides and two low tides in a lunar day, the previous high tide and low tide Tidal range Roughly the same range as the last high and low water, Flood tide The duration of the process and the ebb process is also almost equal (6 hours and 12.5 minutes). China The Bohai Sea , East China Sea, The Yellow Sea Most of the places are semi-diurnal tide type, such as Dagu, Qingdao , Xiamen (in Fujian Province) Let's wait.

Diurnal tide N/A: Only one high water and one low water in a lunar day. Nhu Nanhai Shantou (a city in Guangdong Province) , the Bohai Sea Qinhuangdao Let's wait. South China Sea Beibu Gulf It is a typical diurnal tidal area in the world.

Mixed tide type: there are two high tides and two low tides on some days in a month, but the difference between the two high tides and low tides is large, and the time of the high tide process and the low tide process is different; Other days have one high tide and one low tide. Most places in the South China Sea are of mixed tide type. Such as Yulin Port Fifteen days to show up Diurnal tide The rest of the days are irregular Semi-diurnal tide , Tidal range It's larger.

Regardless of the type of tide, a spring tide with the greatest range occurs within two or three days after the first and 15th days of each lunar month, when the tide rises the highest and falls the lowest. Within two or three days after the eighth and 23rd of the lunar month, there is once a minimum tidal range Neap tide At that time, the tide is not too high, and it is not too low.

Formation reason

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tide (6 photos)

The tidal force of the moon and sun on the ocean is responsible for the rise and fall of the water, regardless of the weak effects of other planets. What kind of force is the tidal force? In physics, in Non-inertial system Below, the tidal force is the gravitational force of the moon and its corresponding inertia, and the gravitational force of the sun and its corresponding inertia Inertia force Equal the combined force of the four forces. Some sources mention that "centrifugal force" is also a tidal force Component of force One, in physics centrifugation There is no concept and definition of "centrifugal force". But the meaning of "centrifugal force" is inertia.

Flood tide

The moon's gravitational pull alone cannot explain why the phenomenon of high tides occurs at the same time in the two regions of the ocean closest to the Moon and the ocean farthest from the moon, thus making the sphere spherical Sea level Become fusiform, as shown in Figure 1. The same is true of the sun's gravity. As of 2012, the most novel concepts and definitions of gravity have emerged in physics. The definition reads: "In statics Within the range to place the support of the object or the object itself is non-inertial Reference substance Gravity is the resultant force of all gravitation and inertial forces on an object." This definition can successfully explain the cause of tides. It should be noted here that, in the case of the planets as particles, when the gravity of the object on the ground is found, only the gravitational force of the Earth on the object is combined with the object Earth rotation the Centripetal force The corresponding inertial force is calculated, and the gravitational pull of the other planets cancels out with the corresponding inertia.

Tides occur for the following reasons:

Start with the role of the moon. Consider the earth and the moon as particles, and say that the moon goes around the earth Circular motion In fact, both the moon and the Earth orbit the two barycenter In a circular motion, only the Earth's circular orbit is much smaller. ( Binary star The circumference of two planets with similar masses Orbital approximation With the center of the earth as a non-inertial reference object, the gravitational attraction of the Earth particle by the moon particle is the centripetal force of the Earth particle moving in a circle around the common center of mass, and the corresponding inertial force is equal to and opposite to the centripetal force. So the gravitational pull of the Earth particle on the Moon particle cancels out this inertial force.

Since the Earth is regarded as a particle, it is possible to classify the objects on the Earth Motion trajectory and Dynamic law Look at it exactly like an Earth particle. The gravitational pull of the Moon and its corresponding inertial force cancel each other out.

In fact, the volume of the earth is very large, the object on the ground closest to the moon, the orbit radius of circular motion around the Earth and the moon's common center of mass is significantly smaller than the orbit radius of the Earth's particle, and the object will be affected by the moon's gravity Greater than By the corresponding inertial force, the two forces can no longer be offset, and the resultant force is opposite to the direction of the object's gravitational attraction of the Earth, making the gravity of the object significantly smaller. If the "object" in question is the sea water here, then there will be a high tide. With the same Method study The object on the ground farthest from the moon, the gravitational pull of the moon on the object Less than Corresponding to the inertial force, their combined force is in the opposite direction of the Earth's gravitational attraction to the object, which also makes the gravity of the object significantly smaller. So in the farthest part of the moon, the water will also have high tides. This causes the sea level, which should be spherical, to take on a slightly spindle shape.

The effect of the sun on tides is studied in the same way as the effect of the moon. If we think of the earth as moving in a circle around the center of the sun, the problem is simple. I won't go into detail here.

The occurrence of earth tide, sea tide and gas tide are all caused by the above reasons, and the three have influence on each other. Because the moon is closer to the Earth than the sun, the ratio of the moon to the Sun is 11:5, and the moon tide is more significant than the Sun tide for the ocean. The elasticity and plasticity of the crust at the bottom of the ocean Tidal deformation , will cause the corresponding sea tide, that is, for the sea tide, there is the influence of the earth tide effect; And the sea tide caused Sea water quality The migration of the earth's crust changes the load on the earth's crust, causing the crust to occur reproducibility The variation of... The air tide is above the sea tide, and it acts on the sea surface to cause additional vibration, which makes the change of the sea tide more complicated.

This energy dissipates at a rate of 1.7TW(1.7x10^12W) through friction in shallow and coastal areas.

On the fifteenth or sixteenth day of the lunar month, the sun and moon are on either side of the Earth, so there is maximum tiad-generating force and so tidal tides will occur. in Phase of the moon Is the winding sum Second quarter At the eighth and twenty-third hours of the lunar calendar, the sun's tidal force and the moon's tidal force offset one part of each other, so a "neap tide" occurred Farmer's saying There is "the first fifteen rising tide, the eighth twenty-three everywhere to see the beach" said. In addition, there is also a high tide on the first day, because the moon moves more than 13 degrees east of the Earth every day, a total of about 50 minutes, that is, every day on the moon Time of transit (is 1 Lunar day = 24:50) About 50 minutes delay, ( Lower transit There are usually two tides a day) so the daily high tide time is also delayed by about 50 minutes.

Development and utilization

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Energy development

Tidal energy

Tidal energy is used Potential energy The form appears Ocean energy "Means sea water Tide rise And the ebb and flow of the water's potential energy. The sea fluctuates Tidal phenomenon Is made up of the earth and Celestial motion And how they interact with each other. In the ocean, the moon's gravity raises the water level of the Earth towards and against the moon. Due to the rotation of the Earth, this water level rises with a period of 12 hours and 25 minutes amplitude Deep-sea wave forms smaller than 1m travel from east to west. The sun's gravity works similarly, but Applied force Smaller, with a period of 12 hours. When the sun, moon and Earth are in line, springtides occur; When they are at right angles, they create neaptides. Except for semi-diurnal tides and Monthly cycle Tidal changes outside the Earth and moon Rotational motion There are also many other cyclical cycles, which can range from days to years. At the same time, the surface water is affected Earth motion Centrifugal force The combined force of the moon's gravity and centrifugal force is the tidal force that causes the sea to rise and fall.

Contrast of tidal range

Tidal formation

In addition to the moon and the sun, other celestial bodies also produce tidal forces on the Earth. Although the sun is much more massive than the Moon, it is also much farther away from the Earth than the distance between the Moon and the Earth, so its tidal force is less than half that of the Moon. Other bodies are either far from Earth or have too small a mass to generate tidal forces. According to the equilibrium tide theory, if the Earth were completely covered by equal depth of ocean water, it would be gravitation It is calculated that the maximum tidal force generated by the moon can raise the sea surface by 0.563m, and the effect of the solar tidal force is 0.246m. The tidal range is increased by motion such as rising, converging and resonance. The energy of tidal energy is proportional to the tidal volume and range. Or, proportional to the square of the tidal range and the area of the reservoir. Compared to hydropower, tidal energy Energy density It's low. It's the equivalent of Slight water The level of hair electricity. The largest tidal range in the world is about 13 to 15m, but generally speaking, Mean range It has practical application value above 3m.

Development potential

Tides vary from place to place, and different regions often have different tidal systems, all of which originate from the deep ocean Tide wave Gain energy, but have their own unique characteristics. Despite the complexity of tides, it is possible to accurately forecast tides anywhere. Ocean tides gain energy from the rotation of the Earth and slow the rotation of the Earth as they absorb energy. But this slowing of the Earth's rotation is almost imperceptible over a human lifetime, and will not be accelerated by the exploitation of tidal energy. This energy goes through Neritic region and Coastal zone The friction dissipates at a rate of 1.7TW. Only when there are tides, when the energy is concentrated, and when Geographical condition buildable Tidal power station Where it is possible to extract energy from the tides. Although such sites are not available everywhere, countries around the world have identified a significant number of sites suitable for the development of tidal energy Site location . According to the latest estimates, the potential tidal energy is about 200TW·h per year.

Tidal energy reserves

Theory of tidal energy around the world reserves It is approximately 3×10^9kw. China's coastline twists and turns, a total length of about 1.8×10^4km, there are more than 6,000 islands along the coast, composed of 1.4×10^4km of coastline, the long coast contains very rich tidal energy resources. The theoretical reserves of tidal energy in China reach 1.1×10^8kw, of which Zhejiang and Fujian provinces have the largest reserves, accounting for about 80.9% of the country, but these are theoretical estimates, the actual available is far less than the above figures.

Power generation principle

Tidal power generation Similar to the principle of ordinary hydropower, through the reservoir, in At high tide The seawater is stored in the reservoir, stored in a potential energy situation, and then, in Low water time The sea water is released, using the drop between high and low tide to push Water turbine Spin, turn the generator to generate electricity. The difference is that the seawater is different from the river, the accumulated seawater drop is not large, but the flow is large and intermittent, so the turbine structure of tidal power generation should be suitable for the characteristics of low head and large flow.

Power station

Tidal power station

Countries around the world have selected a considerable number of sites suitable for the development of tidal energy. According to the latest estimates, the potential tidal energy is about 200TW·h per year. 1912, the first in the world Tidal power station It was built in Busum, Germany. In 1966, the world's largest capacity tidal power station was in France Lens Built. Our country has been in succession since 1958 Guangdong Province the Shunde and East Bay , Shandong Province the Rushan , Shanghai Municipality the Chongming And so on, established Tidal power generation Stand.

Canada Annapolis Tidal Power Station, France Longs Tidal power Station Kisraya Tidal Power Station is one of the world's three famous tidal power stations.

Military application

tide

On April 21, 1661, Zheng Chenggong With 25,000 men and women Kinmen Island Depart, arrive Penghu Islands Enter Taiwan to attack Crimson Embedding City . Zheng Chenggong's army chose instead of the harbour waterway, which was wide, deep and easy to access but heavily guarded on shore Luermen A waterway. There were many shallow reefs in the Luermen channel, and the channel was not only narrow but also blocked by the Dutch scuttled ships, so the Dutch army was poorly fortified here. Zheng Chenggong led his army on the ride Flood tide Channel widens and Deep hour Take them by surprise, and quickly pass the deer ear gate along the current, in Holiao Hong Kong landing, straight to the Chifeng city, landing success.

In 1939, the Germans laid mines to block entry and exit at night English Channel The British ships. The German army determined by accurately calculating the size and direction of the current change Mooring mine The depth, bearing, with Drifting mine The tactics achieved great results. The year 1950 Korean War In the early days, Korean People's Army Like the wind rolling stone, straight into the hit Busan Around. The United States scrambled to rally The United Nations Multinational force The North was aggressively killed, but it was difficult to choose a landing site - the ports suitable for landing were heavily guarded by the Korean People's Army, and the forced landing was bound to be costly. After careful consideration, General MacArthur led the successful landing of American troops at Incheon. Turns out, Port of Incheon Located on the west coast of North Korea, 28 km west of the capital Seoul, it serves as a gateway to Seoul. The sea level is Asia Tidal range The largest, up to 9.2 m, is close to shore at low tide Mud flat More than 5,000 meters long, landing ships, amphibious vehicles and landing soldiers are easily stranded; The shore is built of stone 4 meters high breakwater Constitutes an obstacle to the boarding of soldiers and amphibious vehicles; There is only one channel for ships entering the harbor, the Flying Fish Gorge, and if a ship sinks, it blocks the channel; Shore artillery can destroy all ships, amphibious vehicles and landing troops near shore. The Korean People's Army thinks it's impossible for the Americans to withdraw Incheon landing In addition, the front was too long, so the defense of the port of Incheon was neglected, and the troops were weak. However, the Incheon Port area has the highest spring tide three times a year, the highest time Tidal range It can reach 9.2 meters, including September 15. After analysis and calculation, the US army used the high tide on September 15 to pass through the normally narrow and silt-piled Flying fish Gorge waterway Reef flat It unexpectedly landed at the port of Incheon. As a result, the Korean People's Army was cut off at the waist, the front line logistics completely lost the guarantee, the back and belly of the enemy, heavy losses, almost into a desperate situation. MacArthur commanded American troops and United Nations forces In just 1 month, it almost swept Korean peninsula , Army Presence The Yalu River Edge, an unprecedented victory.

However, this successful landing example also has a failure, the U.S. military miscalculated the day of Incheon port high tide time, the real high tide arrived earlier. Therefore, although the front American troops have landed successfully in advance, the artillery has carried out pre-landing bombing according to the scheduled time, and the result has been the landed army to blow flesh and blood, and lost a battalion of officers and soldiers in vain.

Effect on celestial bodies

1.
Tides and slow Earth rotation Due to the relative motion of each layer of sea water will produce viscous force and the friction between sea water and the land and seabed, tides have a kind of brake effect on the earth's rotation, making the Earth's rotation gradually slow down. Studies have shown that the Earth's rotation period is getting longer by 1-2 milliseconds per century, and if this slowing effect is applied to long time spans, the number of days in the year 370 million years ago (the Devonian period) is about 400 days, which is consistent with the number of growth rings in the Devonian coral fossils (coral rings last every day).
2.
People find that the moon always faces us with the same face. We can't see the other side of the moon from the earth. This is because the period of the moon's rotation is exactly the same as the period of the moon's rotation around the Earth, and the two periods are the same because of the long-term effect of the tides. It is calculated that the tidal force of the earth on the moon is 22.17 times that of the Moon on the Earth. With such a strong tidal force, the moon's moment of inertia is much smaller than Earth's, so the slowing down of the rotation caused by tides is particularly significant for the moon. It can be assumed that the early moon had a large rotation speed, under the action of tides, the moon's rotation gradually slowed down, and finally, the moon's rotation period was equal to the moon's rotation period around the Earth, at this time, the moon's tide disappeared, the moon's rotation period no longer changed, so the moon always faced the Earth with the same side.
3.
The increasing distance of the tides from the moon to the Earth slows the Earth's rotation, resulting in a decrease in the angular momentum of the Earth's rotation. Since the total angular momentum of the Earth-January system should remain unchanged, and the direction of the moon's rotation around the Earth is basically the same as that of the Earth's rotation, the reduction of the angular momentum of the Earth's rotation will inevitably increase the angular momentum of the moon's centroid of the Earth-January system, so as to maintain the conservation of the total angular momentum of the Earth-January system. The practical effect of this effect is to slowly increase the distance between the moon and the Earth. According to recent observations, the moon is moving away from the Earth at a rate of 3.81 centimeters per year. The slow movement of the moon away from the Earth can also be explained by the lunar acceleration formed by the tidal bulge of the Earth. Because the bulge of the tides is carried east by the Earth's rotation, bulge A is closer to the Moon than bulge B, so the two parts have different gravitational forces on the Moon, causing the Earth's gravitational center to drift to the east of the line between the Earth and the Moon's center of mass. As a result, the moon generates a small acceleration in the direction of its orbital motion, causing the moon to pick up speed and slowly spiral outward.

World famous tide

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Qiantang River spring tide

Qiantang River spring tide map

The great tides of the Qiantang River are the three largest in the world bore One is the gravitational attraction of celestial bodies and Earth rotation The centrifugal action, plus Hangzhou Bay Horn mouth The special terrain caused by the extraordinary surge. The mouth of Qiantang River It is wide on the outside and narrow on the inside, showing a distinct trumpet shape. The river out of the mouth of the river is 100 kilometers wide, and the narrower the river becomes Heining Yanguan Town The river suddenly dropped to only 3 kilometers wide.

Qiantang River Rising tides and deep inland more than 600 kilometers Yangtse River Tide. It is mainly formed by the tidal current flowing upward along the channel of the river entering the sea. Tidal influx triangle In the bay, the tidal level is piling up and the tidal range is increasing. When the tide comes, the tide end stands sharply, splashing all around, like an upright water wall advancing at high speed, the front has not been dredged, and the waves behind catch up, a Wave height After a wave, it is spectacular, forming a "towering Muddy waves emptying Here we go. It's a spectacular sight.

Yu Yafei poetry cloud: "Qiantang a look at waves, an instant wild waves across the eyes; Seemingly ordinary river water, contains energy can be shocking." At the beginning of the tide, the river flashed a white line, accompanied by a rumbling sound, the tide from far and near, galloping, the tide pushed, the sound was like thunder, and in an instant, the tide peak raised a three or four meters high water wall standing on the river, spraying pearls and splashing jade, the potential was like ten thousand horses galloping. Tide watching began in the Han and Wei dynasties. Flourish in Tang and Song dynasties, after more than 2000 years, have become local customs.

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