Jo Nov 6, 2026
The frequency is an important operating parameter of power systems and electrical equipment, and the frequency measurement is the basis of the operation and monitoring of power systems and electrical equipment and of relaying protection. The frequency of power systems is an important index of power quality, and it is very important for the fault diagnosis of power systems. Larger power system capacity increases the stability requirement of power systems, which consequently leads to higher measurement accuracy of the frequency of power systems.
Many frequency measurement theories and calculation methods have been developed so far. Although they can be used in real applications with relatively accurate frequency measurements and small measurement errors, they are all based on discrete Fourier transform (DFT) under asynchronous samples, and approximate computational methods have been employed for real frequency measurement calculations.
Im Jung Bin, a researcher at the Faculty of Electrical Engineering, used vector theory to accurately measure the frequency under asynchronous sampling conditions for sinusoidal signals with constant frequency offset. He proposed a frequency measurement principle based on the vectors at three sampling points and calculated the frequency based on the calculation of the real and imaginary parts at each sampling point using DFT transform. Likewise, he proposed a frequency calculation method under asynchronous sampling and verified through simulation that the frequency measurement method under asynchronous sampling using three sampling values is accurate.
This provides a method for accurately and quickly measuring the frequency in the development of power measuring devices and protective devices.
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Jo Nov 5, 2026
The reliability problems of shock tube initiation systems have been a focus in mining and demolition blasting. Current blasting practices widely use shock tubes as a non-electrical initiation means. Shock tube initiation systems typically consist of shock tubes coupled with a donor detonator. Shock tubes are used to transmit an initiation impulse to the target detonators. The shock tubes are initiated and detonated by the adiabatical pressing of the mixture of explosive material and air due to the explosion shock by detonators.
Reliability is the most important for any initiation system, and efficient initiation of shock tubes is an important factor.
There has been some research on initiating a bunch of shock tubes so far. However, all the researchers have concentrated on the experimental study of lateral coupling mode.
Choe Yong Chol, a researcher at the Faculty of Mining Engineering, numerically investigated the influence of coupling modes on the explosion shocks and their propagation to shock tubes, and validated it through the test results of the initiation reliability of shock tubes in bunch.
He used lateral and frontal bunch-series coupling modes for the numerical simulations and tests.
The results showed that the peak pressures of explosion shock acting on the inside of shock tubes, and initiation rates were higher for frontal bunch-series coupling mode than for lateral mode, and that the peak pressures acting on the inside of shock tubes by numerical analysis were in good relation with the initiation rate of shock tubes in bunch by tests.
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Jo Nov 3, 2026
Nowadays, rail failure in low temperature environments is a serious problem in many countries across the world. Generally, rails are often damaged due to the large amount of fluctuating stress and impact forces during operation. Rails tend to be damaged in winter when it is cold and the difference between low and high temperatures is great. In addition, the abnormal climate caused by global warming causes a rapid decline in winter temperature and the railroads in extreme regions cannot avoid rail failure at low temperatures, which is a serious problem. According to the research, 60-80% of the rails were damaged in winter from November to March, and 83-121 rails were damged between November and February with relatively low temperature conditions.
In general, different methods of heat treatment and alloying of various elements are widely used to enhance the microstructure and properties of steel. In the past, Ni and V were traditionally used to improve the low temperature properties of steel. Recently, the use of Ti and RE has also been being investigated. Therefore, research has been carried out to apply such alloying or heat treatment methods to rail steels. However, Ni, Ti, RE, etc. are resource-poor and cost-inefficient.
Jon Song Won, a researcher at the Faculty of Material Science and Technology, fabricated rails by adding barium to enhance the low temperature properties of rails and investigated the effect of barium on their microstructure and properties.
He carried out tensile, hardness and impact tests at low temperature to measure and analyze the mechanical properties of the rail steel with Ba addition. The test results showed that the tensile strength of rail steel with 0.03% Ba increased to 1 020MPa, the elongation to 8.0%, and the hardness to HB275 and impact value to 6.8J/cm2 at low temperature.
He investigated the low-temperature toughness mechanisms on the metallic structure of the samples by metal microscopy and scanning electron microscopy. At 0.025wt.% Ba, the average size of pearlite grains in the rail steel was 15μm, and grain refinement was observed in the microstructure. Changes in the size, distribution and shape of inclusions were also observed.
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Jo Oct 30, 2026
As twin-roll casting is a complex physical process, the structure and size of the metal feeding system, which supplies molten metal to the gap between two casting rolls, have a great influence on the quality of the products. In particular, the baffle is the key element for ensuring the uniformity of flow rate and temperature of molten metal at the outlet of the feeding system. The shape, size, number, and position of baffles have a significant impact on the flow characteristics of molten metal in the feeding system.
Therefore, optimizing the structure and design parameters of the feeding system is of great importance for ensuring good quality of products by adjusting the flow field of molten metal in the feeding system. In addition, the wider the strip in twin-roll casting is, the wider the feeding system gets. This increases the complexity of the flow characteristics of the molten metal, which leads to requirements for accurate structure and design parameters of the feeding system.
In order to improve the quality of strip edge in aluminum twin-roll casting, Kim Il Hyok, a student at the Faculty of Material Science and Technology, simulated the fluid flow behavior in different types of metal feeding systems (3C-type, 7C-type, and 2-split-type) by ANSYS Fluent.
Through simulations, he analyzed the effects of design parameters (shape, size, and position of baffles) of the feeding system on the distribution of fluid flow rate and temperature at the outlet of the feeding system. Based on the results, he concluded that the feeding system for the conformity of the flow rate and temperature of molten metal is of 2-split-type, and optimized its design parameters.
The optimized feeding system could ensure high quality of aluminum strips by eliminating the defects such as edge cracks.
If more information is needed, you can refer to his paper “Optimization of design parameters of metal feeding system for quality improvement of strip edge in aluminum twin-roll casting” in “The International Journal of Advanced Manufacturing Technology” (SCI).
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Jo Oct 29, 2026
Zirconium based alloys have been widely used in light water reactors due to their small neutron absorption cross sections, good corrosion resistance and excellent creep strength. Zircaloy-4 is a zirconium based Zr-Sn alloy, which is found in many applications in structural components such as fuel cladding tubes and pressure tubes.
Zircaloy-4 alloys are fabricated by several hot working methods such as hot rolling and hot extrusion, and numerical simulations are used to optimize and design the hot working process. So, predicting the hot flow stress evolution of Zircaloy-4 is of great importance for the numerical simulation of hot working processes.
Kim Hyok Song, a student at the Faculty of Material Science and Technology, constructed a modified Johnson-Cook model, a strain compensated Arrheniustype model, a modified Zerilli-Armstrong model and a microstructure-based model to predict the flow stress behavior of Zircaloy-4 in hot working. For this purpose, isothermal uniaxial compression tests had been conducted in the range of strain rates and deformation temperatures of 0.001-1s-1 and 750-1 000°C. Then, he compared the prediction accuracy of the proposed constitutive models in terms of correlation coefficient and average absolute relative error.
The results showed that the microstructure-based model is the most suitable for accurately predicting the hot deformation behavior of Zircaloy-4.
You can find the details in his paper “Constitutive Models for Predicting Flow Stress Behavior of Zircaloy-4 in Thermo-Mechanical Processing” in “Physics of Metals and Metallography” (SCI).
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Jo Oct 28, 2026
The main metallic metals used in medicine include titanium and its alloys, Co-based alloys and austenitic stainless steels. Titanium alloys are rarely used in friction contact due to their poor abrasion resistance. Austenitic stainless steels are used for short-term implants such as screws, plates and nails because austenitic stainless steels may cause allergic reactions in many patients due to their poor corrosion resistance. Meanwhile, Co-based alloys have been widely used as femoral elements because of their good corrosion and wear resistances and biocompatibility.
Chromium and molybdenum are important alloying elements of Co-based alloys. Chromium improves resistance against oxidation and corrosion at high temperature, while molybdenum of large atomic size increases the strength through solid solution strengthening.
The understanding of the hot flow stress behavior of materials is essential for the numerical simulation of thermo-mechanical processing routes such as forging, rolling, etc. So, it is quite important to develop a constitutive material model.
Ryang Chol Song, a student at the Faculty of Material Science and Technology, developed and compared several constitutive material models for accurately predicting the flow stress during hot working of Co-28Cr-6Mo alloys.
He constructed a modified Johnson-Cook (MJC) model, a strain compensated Arrhenius-type (SCAT) model and a microstructure-based constitutive (MBC) model in a wide range of temperatures (900-1 200℃) and strain rates (0.001-10s-1).
Then, he compared the average absolute relative error and correlation coefficient for the proposed models. The results are as follows. The correlation coefficient and AARE are 0.985 7 and 7.8% for the MJC model, 0.950 4 and 13.01% for the SCAT model, and 0.994 8 and 2.45% for the MBC model, respectively.
The results show that the proposed MBC model is best suited to predict the hot flow stress behavior of biomedical grade Co-28Cr-6Mo alloy.
For more information, please refer to his paper “Development of Several Constitutive Models to Predict Flow Stress of Biomedical Grade Co–28Cr–6Mo Alloy during Thermo-Mechanical Processing” in “Russian Journal of Non-Ferrous Metals” (SCI).
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