Jo Nov 28, 2022
The research team led by Kim Hyok Chol, an institute head at the Faculty of Electrical Engineering, and Kim Nam Chol, a researcher at the Faculty of Mechanical Science and Technology, who designed and manufactured our style two-way high-speed circuit breaker for underground electric vehicles, is working for further achievements.
A two-way high-speed circuit breaker was designed and fabricated by combining a digital cut-off controller.
The device can achieve reliable high-speed cutoff even under severe operating conditions of underground electric vehicles. Accurate cutoff setting current and low mass and volume are other advantages of this device. In particular, successful bidirectional blocking is guaranteed.
The high-speed circuit breaker consists of a maintenance and release device for high-speed interruption, a blanking room, a locking control unit, and a contact system, which can sense both the current entering the electric vehicle and the current entering the grid during regenerative braking, so that the circuit can be shut down within 18 ms once an accident occurs.
The shutoff coil of the hold and trip device has no vibration-induced malfunction because there is no current flow during normal operation, and it takes less than 1ms to output a shutoff signal immediately after the current-cut signal from the current sensor enters the shutoff control device.
The turn-off controller has a double current sensing and a circuit to turn off analog and digital double, and the current setting has been simplified on a button.
The contactor is a two-point open type with an inclination angle of 45° and there is an arc-extinguishing component and a main contractor at each contactor. There is little electrical wear at the main contactor because there is no structural repulsion during turn-on.
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Jo Nov 27, 2022
Pyongyang, a place of exquisite beauty, has a long history of 5 000 years.
Pyongyang was the capital of Ancient Korea founded by Tangun, the founding father of the Korean nation. Born in Pyongyang, Tangun founded a country and set up the capital in Pyongyang in the early 30th century B.C. He named it Joson, which meant a country with the sunrise in the east.
According to several old books including “Samguksagi” (Chronicles of the Three Kingdoms), “History of Koryo” and “Sejong Sillok” (Chronicles of King Sejong), Tangun held the court in Pyongyang and named the country Joson, and Pyongyang is a city with a long history which the founder king of our countrymen chose as a capital. Furthermore, a lot of names of places associated with the birth and growth of Tangun are used and the Mausoleum of King Tangun was discovered in Kangdong, Pyongyang. These prove that Pyongyang was King Tangun’s birthplace and the capital of the country.
The name “Pyongyang” is the translation in Chinese characters of the Korean native word “Puruna”, where puru referred to a large field or a walled city and na meant a place. In a word, “Puruna” means “a plain or land of fields”. The area around Pyongyang had a lot of fertile fields and a river, so it was easy of access. At that time, “Puruna” was understood as a large walled city or the capital. Pyongyang was also called other names like “Phyongchon” or “Phyongna” as a result of different translations of the same Korean word “puruna” in Chinese characters.
It is recorded in historical books “Samguksagi” and “History of Koryo” that in the period of Ancient Korea Pyongyang was also called “Wanggom Walled City”, which meant a capital city chosen by the founder king.
In the period of the Three Kingdoms, too, Pyongyang was in the position of a capital for both its natural and geographical conditions and economic and cultural conditions. The reason that Koguryo chose Pyongyang as a provisional capital in 247 and as a real capital in 427 lies in the fact that Pyongyang had enough conditions as well as a long history to be a capital.
During the Koryo dynasty, Pyongyang had other names “Sogyong” or “Sodo”, both of which meant a capital in the west. In fact, Pyongyang was not the formal capital of Koryo, but it was given as much importance as the capital. Wanggon, who founded the first unified state in 918, was planning to move the capital to Pyongyang when he recognized that Pyongyang was more important than Kaegyong in the aspects of geographical position and economical and cultural conditions.
During the feudal Joson dynasty, Pyongyang was called yet other names “Sogyong” or “Ryugyong”.
Pyongyang was famous for its scenic beauty with willows and flowers. In particular, the view of drooping branches of willows and all sorts of flowers in bloom in early spring was spectacular. Therefore, people called Pyongyang “Ryugyong”, which is translated as a capital with a lot of willows.
Pyongyang was still given importance during this period, when it was the centre of feudal rule, commodity exchange, distribution of agricultural products and feudal handicrafts.
As mentioned above, Pyongyang has been the capital or a city in the same position as a capital for as long as 5 000 years. Today, the Korean people are proud of and ardently love Pyongyang, the capital city with a long history of fifty centuries.
Kim Kwang Jo, researcher at the Academy of Social Sciences
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Jo Nov 25, 2022
Self-mixing (SM) technique has been a promising optical measurement technique for a few decades.
This technique is developing toward increasing the measurement distance and the limit of displacement measurement, enhancing the measurement accuracy and improving the real-time quality of the measurement. In addition, it is also important to drop the development cost of a sensor.
Estimation of the optical feedback factor C is the key to SM displacement measurement with a better resolution than half a wavelength. But this estimation is very complex and tricky, and it thus leads to its time-consuming nature, which is one of the important causes that increase the cost and labor for the development of a self-mixing sensor. There have been many methods reported for the C estimation, but they are very time-consuming, very sensitive to noise, or can only work in a certain feedback regime.
Kim Chol Hyon, a researcher at the Faculty of Physical Engineering, has proposed a method of the C estimation using the derivative of an SM signal. So to speak, he has solved a problem of fast estimation of the parameter of an SM interferometric system with the derivative in the jumping point of an SM signal. This method is very simple, and, what is more, it can work in all regimes including weak, moderate and strong feedback regimes.
The estimation precision of the proposed method is not only comparable to that of the data fitting technique but also much simpler than that. Therefore, it is effective in low-cost high-precision SM displacement measurement.
You can find the details of this in his paper “Fast estimation method of feedback factor based on the derivative of the self-mixing signal” presented to the SCI Journal “Applied optics”.
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Jo Nov 24, 2022
Water spraying itself is a dynamic course, and it is affected not only by the structure of an ultrasonic gas atomizer and the compressed air pressure but also by the movement of the compressed air flow in an atomizer.
The fundamental principle of formation of fine droplets in the ultrasonic gas atomizer is that a liquid sheet is disrupted into droplets by the energy of high-velocity air. If the ultrasonic energy is supplied, finer droplets with high sphericity and uniform size distribution can be achieved.
Kim Kang Dok, a section head at the Faculty of Mining Engineering, has observed water atomization of an ultrasonic gas atomizer by numerical simulation with CFD software ANSYS Fluent, and found out about the generation of ultrasound and water fog in the ultrasonic gas atomizer with a resonance chamber together with ultrasound characters (frequency, pressure level, power level).
Recently, experimental researches to improve the features of ultrasonic atomizers by air spray have been conducted, but only a little about numerical simulation was presented except for some experimental data.
Thus, he has simulated the characters of ultrasonic air atomization using the finite volume method based on the Roe solver in the structure similar to the Hartmann resonance chamber. Then, he has looked closely at the occurrence of oscillation and the factors affecting the oscillation, and investigated the distribution character of water droplets.
The experimental conditions for the simulation were compressed air pressure 3.5~4atm, air amount 0.1㎥/min, acoustic power in the cavity resonator 242dB, acoustic power at the outlet 172dB.
The range of frequency is 20~120 kHz, where 21~28 kHz has the highest density. The acoustic power decreases with the distance when the pressure of the compressed air is 0.3MPa.
The determination of the distribution characteristics of the atomizer indicated that condensation of water droplets decreased rapidly from the distance of 3m. Thus, it is clear that the rational spray distance of the atomizer is 3m. The results show that the number density of water particles is 1.52×1010 in the center, but it is 6×108 in the diffusion region.
You can find more information about this in his paper “Numerical simulation on the generation of ultrasound and Formation of Water fog in the Ultrasonic gas atomizer” presented to the SCI Journal “ULTRASONICS”.
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Jo Nov 23, 2022
“Chonsuguksujang” is a handicraft legacy which demonstrates the high level of our national culture in the period of the Three Kingdoms.
“Chonsuguksujang”, which was produced by some craftsmen in Koguryo, Paekje and Silla in the early seventh century, is the oldest of all existing embroideries in the world. It is a long piece of cloth embroidered with a paradise. At first, it was about 4.8 meters long by 1.2~1.5 meters wide. Later, it was torn into pieces and now several pieces are found in Junggung Temple, Popryung Temple, Jongchang Temple and other places in Japan.
About 100 turtlebacks and an excellent composition of 4 letters on each one, that is, 400 letters in all, were embroidered, but now only a few turtlebacks and letters can be seen.
When Japanese Crown prince Song Tok, who was active in introducing Korean culture from the end of the sixth century to the beginning of the seventh century, died in 622, his wife had it produced wishing his happiness in the other world, stricken with grief over his death.
The original picture was painted by Ka So Il from Koguryo and its embroidery and supervisory were all done by Koreans. On the purple and yellow silk cloth of “Chonsuguksujang” are embroidered a paradise made up of characters, palaces, Buddhist images, flowers, rabbits, the moon, a phoenix, lotus flowers, liana patterns, etc. and turtles with letters on their backs in coloured thread such as white, red, green, blue, light green, etc. Several elements ― jogori and skirts worn by the characters, the moon portrayed as rabbits pounding in a mortar, the shape of lotus flowers, liana patterns, gabled belfry buildings, etc. ― are in good accordance with a number of Koguryo mural paintings.
In conclusion, “Chonsuguksujang” is a piece of handiwork that demonstrates the standard of cultural development of our country of that time.
Pak Sin Jong, researcher at the Academy of Social Sciences
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Jo Nov 22, 2022
Leather shoes called katsin in Korean were worn from long ago in our country.
Our nation did a lot of hunting, so they made shoes of animal skins from ancient times. Such shoes were called “hyoktap” in historical records.
In the period of the Three Kingdoms, shoes with very low or no ankles were called “ri” or “hye” and high boots “hwa”.
Later through the Koryo and feudal Joson dynasties, leather shoes were made better in line with the aesthetic sense of the time and the taste of the people, and subsequently their names became diverse.
Shoes and boots equivalent to the previous “ri” were also found during the feudal Joson dynasty. They were named “hye”. “Hye” was sorted into hukphihye, punthuhye, thuhye, phichohye, thaesahye, palmaksin, jinsin, etc. while “hwa” was classified into hukphihwa, mokhwa, hyopgumhwa, kijahwa, jonphihwa, tanhwa, tonghwa, etc. All these were made mainly of leather, so they were called katsin (leather shoes). Leather shoes except jinsin were also called “marunsin” (dry shoes) as they were usually worn on dry land in good weather. Jinsin (wet shoes), true to the meaning of its name, was for muddy ground when it was snowing or raining, so it was made of oil-treated leather to stop water infiltrating inside. For durability and to keep leather shoes from moth, people used to hang them on the wall above the fireplace to expose them to smoke or put hog grease on the surface of leather.
Pak Sin Jong, researcher at the Academy of Social Sciences
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