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 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 21, 2022
Chlorination leaching, one of non-cyanidation processes, which was in use until the end of 19th century after its development in the middle of the 19th century, was deprecated after the cyanidation process was born. However, in the eighties of the 20th century it was found that chlorination leaching had a good effect on fine grains of gold ores, and researchers’ interest in it revived, leading to some successes.
Compared to cyanidation leaching, chlorination leaching of gold by chlorine or hypochlorite has faster gold leaching rate and less pollution. What is more, it is cheaper and simpler.
Kim Chang Sok, a researcher at the Science Engineering Institute, has conducted thermodynamic and experimental research on chlorination leaching of refractory gold concentrates. Then, he has observed the influence of the redox potential on gold leaching and confirmed reasonable conditions for the potential.
The results demonstrate that for a higher leaching rate of gold, leaching time should be more than two hours and redox potential should be controlled at 1.0V or more. Under the conditions of the initial concentration of active chlorine 0.5%, the value of pH 4.0, the leaching time at least two hours and the redox potential more than 1.0V, the leaching rate of gold could reach over 96%.
You can find more information about this in his paper “Research on Chlorination Leaching of Pressure Oxidized Refractory Gold Concentrate” presented to the SCI Journal “Hydrometallurgy”.
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Jo Nov 17, 2022
Several works have revealed the inclusion properties between the Orlicz spaces, which are complicated in the proof process and very difficult to apply.
Kim Jin Ju, a lecturer at the Faculty of Applied Mathmatics, has formulated a necessary and sufficient condition for the existence of inclusion properties between weighted and weighted weak Orlicz spaces, which is a more generalized space than an Orlicz space, using the characteristic function of a sphere.
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Jo Nov 15, 2022
There may be potential flaws in the whole process of quality formation. The time and expenditure for their control are different according to when they are detected.
Many people found one famous principle while they were summing up their quality management. That is the Law of Ratio 1:10:100.
It means that it takes an hour and 1 won to manage a flaw of quality at the stage of development and design, 10 hours and 10 won at the stage of production, and 100 hours and 100 won at the stage of marketing. That is to say, plan: production: marketing = 1:10:100.
Kang In Song, an institute head at the Faculty of Management of Industrial Economy, has formulated 6 types related to the time of flaw detection and rectification and analyzed the influences of each type on customer satisfaction, time and cost.
Type 1-4: stages of development and design, design examination, production, and test, respectively. In each stage, quality flaws are found and controlled.
Type 5 and 6: stages when quality flaws have been transferred to customers. Type 5 gives priority to troubleshooting and maintenance and also employs refund or exchange of goods. Type 6 is when quality flaws transferred to customers cannot be controlled by enterprises.
Enterprises can choose one of these types to manage quality flaws.
The effects on customer satisfaction, time and cost are:
The enterprise which agrees to Type 1 might make the best choice by giving great satisfaction to the customers and ensuring minimum time and cost. It guarantees preventive management of quality. This enterprise can be said to have quality management level of 6σ.
Any enterprise in favor of Type 2 may give basic satisfaction to the customers and control flaws with comparatively short time and low cost. It has quality management level of 5σ. Its drawback is relative – it is not preventive but has pursuit property and delays the time of starting production.
An enterprise whose quality management goal is Type 3 may have the following advantages. It is preventive and gives partial satisfaction to the demand of the customers. It might ensure production and supply in good time and save a lot of money for equal and continuous improvement even if it needs 10 times as much expenditure. It might have quality management level of 4σ.
An enterprise in favor of Type 4 may not have good points by and large but flaws are not transferred to the customers. It might have quality management level of 3σ. It is not preventive but has pursuit property. It does not satisfy customers’ requirement but ask them for its quality level. It might delay supply and need 10 times its expenditure, in particular in the last stage.
The enterprise in Type 5 might not have good points but if any, it is responsible for flaws and takes measures even though they have already been transferred to the customers. It has quality management level of 2σ. It might always deal with the customers to fix exchange or refund the goods. It has a problem of whom to allocate extra pay – the enterprise or the customers. It might need time for fixing and servicemen and equipment for it.
Any enterprise in Type 6 may have decreased income and legal problems. It might injure its reputation, causing a lot of loss and hardly managing its own business, as flaws are transferred to customers, which makes them disappointed. It is on the verge of bankruptcy. Its quality management level is 1σ.
The 6 types mentioned above let us aware of different effects on customer’s satisfaction, time and cost.
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