Jo Jul 19, 2026
The precise orbit of a satellite is determined from the exact position and velocity estimated by the dynamic solution obtained from the motion differential equation of a satellite in the inertial space satisfying the Newton second law and by the data measured by some means such as on-board GPS. Because the dynamic solution is from GCRF and the measurement data is from ITRF, coordinates transformation is needed. Therefore, the uncertainty of the coordinates transformation affects the accuracy of position determination of satellites.
Precise ITRF/GCRF transformation is generally conducted using the earth originate parameter (EOP) provided by international earth rotation service (IERS). EOP data is updated every day. ITRF/GCRF transformation methods using the EOP data are classified into the classical equinox-based method and the modern CIO-based approach.
The latter is simpler in procedure than the former as it needs neither ecliptic nor equinox, and it is considered as a suitable method for improving the calculation speed as it can tabulate data necessary for coordinates transformation.
CIO-based approaches include precise theory method, series method and numerical interpolation method. The method using the series can improve the calculation speed by decreasing the order of the series, but it degrades the accuracy of coordinates transformation. Therefore, necessary data in the astrodynamics calculations are tabulated and interpolated to improve the calculation accuracy and speed.
Cha Pong Il, a section head at the Faculty of Aerospace Engineering, proposed a method for reducing the calculation time in precise ITRF/GCRF transformation and verified its effectiveness through simulation.
The simulation results show that the calculation time by the classical equinox-based method is equal to about 195s, while the time by the precise theory method is about 98s, but the numerical interpolation method maintains its accuracy with the calculation time of less than 1s. It means that the numerical interpolation method decreases calculation load and improves calculation speed significantly.
If further information is needed, you can refer to his paper “A Method for the Reduction of the Calculation Cycle in Precise ITRF/GCRF Transformation using the Numerical Interpolation Technology” in “Proceedings of KUTIC-2025”.
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Jo Jul 17, 2026
A nozzle is a device that splits liquid into fine droplets to spray them into the surrounding space. It has been widely used in various systems and devices including cooling, dust collection and spray systems. The tangential pressure swirl nozzle finds particularly wide use in various industrial and agricultural fields such as combustion engines, spray drying, cooling, plating, etc., due to its simple structure and good spray properties. Therefore, investigating the factors influencing the water spray characteristics of tangential pressure swirl nozzles is of great importance for proper installation and use of nozzles.
So far, the effect of the swirl chamber diameter, outlet diameter and swirl chamber cone angle on the water spray characteristics of a tangential pressure swirl nozzle has been studied, but that of the liquid incidence angle has not been considered.
Kim Song Won, a section head at the Faculty of Thermal Engineering, has experimentally studied the spray distribution, spray angle, etc. of a tangential pressure swirl nozzle and carried out a CFD simulation to analyze the effect of liquid incidence angle on the spray characteristics and determine the optimum incidence angle.
Through the study, he has concluded that it is necessary to take measures to prevent U-tube bundles from sagging down in the design and manufacture of reheater bundles.
For more information, you can refer to his paper “Experimental and CFD Study on Spray Characteristics of Tangential Pressure Swirl Nozzle” in “Proceedings of KUTIC-2025”.
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Jo Jul 16, 2026
Many programs have been in use for accurate evaluation of the efficiency of thermal systems and for their optimal design. Cyclepad is a good example. It has been developed for an analysis and the optimal design of different thermodynamic cycles.
However, Cyclepad has the disadvantage of needing the input and output of each computational module to be single phase only. Therefore, it failed to support accurate analyses of systems using wet steam and accurate calculation of the thermal properties of the working fluid at the transition points.
In addition to Cyclepad, some other programs for optimizing a second-order system using different optimization algorithms have also been developed, but they have not proved to be useful.
Pak Myong Guk, an institute head at the Faculty of Thermal Engineering, has proposed an improved random tunneling algorithm (RTA) to effectively solve a constrained mixed-variable global optimization problem, and based on it, he has conducted a thermal sequence efficiency analysis of the Rankine cycle and developed an optimization system for it.
With CAD technique introduced, the newly-developed program is effective for designing various Rankine cycles and for optimizing the efficiency of the Rankine cycle by applying improved IRTA.
For further details, you can refer to his paper “Development of Rankine Cycle Optimization CAD” in “Proceedings of KUTIC-2025”.
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Jo Jul 15, 2026
In recent years, many modal identification methods based on continuous wavelet transform have been developed. The time variation of the instantaneous amplitude and phase of each mode component within measured signals can be observed on time-frequency planes, where measured signals are decomposed to a series of curves called ridges which directly express the amplitude and phase of each mode component at the time of wavelet analysis. Thus, the extraction of ridges and the value of the CWT along the ridges are used to identify modal parameters.
What is important here is to determine ridges. When the frequency window of a wavelet function includes only one natural frequency, ridges accurately represent modal parameters. Therefore, ridges have to be considered carefully in the application of this method.
Ri Yong Ho, a researcher at the School of Science and Engineering, mathematically investigated the distortion of a ridge when the frequency window of wavelet function includes two closely-spaced natural frequencies.
He demonstrated the correctness of the analytical result in detail through numerical simulation.
If further information is needed, you can refer to his paper “Research of Characteristics of a Ridge for the Closely Spaced Two Modes in Time-Frequency Domain” in “Proceedings of KUTIC-2025”.
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Jo Jul 14, 2026
Ultrafine-grained pure titanium is characterized by its exceptional mechanical properties, among which high ultimate strength and high yield value are of utmost importance. Equal channel angular pressing (ECAP) and ECAP+cold extrusion (CE) have been used to process ultrafine-grained pure titanium.
Though many aspect studies on the mechanical deformation behavior of ultrafine-grained (UFG) pure titanium have been carried out, there is little study on systematic qualitative and quantitative characterizations on the temperature-dependent deformation and fracture features of pure titanium processed by ECAP and CE.
The study on the temperature-dependent deformation and fracture features of ultrafine-grained materials is of great interest because of their limited application temperature.
Yun Jong Guk, a section head at the Faculty of Mechanical Science and Technology, investigated the tensile deformation and damage behavior and microstructures of ultrafine-grained (UFG) pure titanium processed by ECAP and ECAP+CE at different temperatures, and carried out quantitative fractal analyses of deformation and damage morphologies by the yard-stick method based on Mathematica.
The results show that as the temperature increases, the diameter and depth of dimples on the fracture surfaces of ultrafine-grained pure titanium increase significantly with corresponding increase in the fractal dimensions. The microstructure observation results of the tensile deformation show that the dislocation density decreases significantly with increasing temperature and the grain boundaries become clear.
For more information, please refer to his paper “Temperature-Dependent Tensile Deformation and Fracture Features of Commercially Pure Ti Processed by ECAP and Cold Extrusion” in “Proceedings of KUTIC-2025”.
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Jo Jul 13, 2026
Coal processing is the most effective method for removing unwanted minerals and pollutants from coal, and there are several techniques for it including physical, chemical and physicochemical separation.
Among various physical separation methods, the selective crushing separation is a promising method for reducing specific energy consumption during the early stages of classification and for treating low-grade ores and tailings disposal.
Currently, toothed roll crushers are commonly used in various stages of mineral processing. The toothed roll crushers can be designed to be with either a single toothed roll or a double toothed roll.
The selective crushing device with hanging rings and a toothed roll is a kind of a single toothed roll crusher in which many hanging rings are supported by the supporting structure including a beam and a supporting rod. The supporting structure for hanging rings not only stands the weight of the rings and the dynamic loads during crushing processes but also constricts the freedom degree of the rings. The supporting structure may have a great influence on the crushing performance of this selective crushing device.
Jon Chol Min, a researcher at the Faculty of Mining Engineering, has proposed a new type of toothed roll based selective crushing device, and investigated the effect of the supporting structure to improve the crushing performance of the device.
The analytical result of the interaction of hanging rings and feed particles shows that the placement of the supporting rod has the greatest influence on the interaction force, and that the placement angle of the supporting rod for hanging rings is a critical design parameter for the improvement of crushing performance of the selective crushing device.
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