Jo Jul 24, 2026
The mixture formation process in diesel engines consists of injection by which fuel is divided into small droplets, heating and evaporation of fuel, and mixing of fuel droplets and air in the combustion chamber. In other words, the shape and position of combustion chamber, fuel injection and air motion play a crucial role in the formation of mixture. Thus, many studies have been carried out in order to improve the mixing performance of fuel and air in the cylinder and improve combustion efficiency.
However, it was not fully taken into account that mass flow rate of intake air could be reduced when air swirl intensity was increased, while changing the inlet channel profile and the helical spiral shroud (HSS) shape of the intake valve. In addition, some attempts have been made to increase the air swirl and turbulent kinetic energy (TKE) by changing the shape of combustion chamber, but little study has been focused on improving the in-cylinder airflow characteristics by changing the eccentricity of combustion chamber.
Sin Mun Hak, a researcher at the Faculty of Mechanical Science and Technology, investigated the variation of in-cylinder swirl intensity and TKE depending on the eccentricity of combustion chamber. To this end, he conducted simulations of six series of eccentric combustion chambers.
The results showed that the air swirl intensity and turbulent kinetic energy in the combustion chamber increases as the y-axis eccentricity of combustion chamber is placed on the eccentric direction of injector and the x-axis eccentricity increases gradually from the centre of cylinder to the direction of injector. It was also shown that when the eccentricity is too large, there will be a drop in the fuel spray jet velocity or airflow separation in the region of mixture formation, resulting in a gradual increase in power and torque and then a decrease over a certain limit.
For more information, please refer to his paper “Effect of Combustion Chamber Eccentricity on In-Cylinder Air Flow and Combustion Process in Direct Injection Diesel Engine” in “Proceedings of KUTIC-2025”.
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Jo Jul 23, 2026
Nowadays, most spacecraft use solar array continuously facing the sun by solar array drive assembly (SADA) to increase the energy efficiency. However, in spacecraft with rotating flexible appendages, system dynamics and control are very difficult.
There has been an extensive study on suppressing the vibration caused by flexible appendages in such spacecraft across the world. What is attracting a great deal of attention is a method by the robust controller design. However, almost all robust control systems considered only fixed flexible appendages and neglected their rotation dynamics.
Sonu Kwang, a post-graduate student at the Faculty of Aerospace Engineering, proposed an attitude control method to suppress the vibration of flexible spacecraft with rotating solar array.
First, he simplified the singular dynamic model of spacecraft with rotation of flexible appendages by introducing extended state and modal identities into a non-singular state space-formed dynamic model. Based on this simplified dynamic model, he developed a PD-type static output feedback controller that essentially guarantees asymptotic stability and disturbance rejection. Then, he designed a compensator for the extended system including a static output feedback controller in order to ensure the stability of the control system under the influence of rotations of solar array, variation of natural frequency and damping coefficients, high-order flexible modes and measurement noises.
Through computer simulations, he found that the proposed attitude control system with and without compensators stabilized the attitude within 60s and suppressed flexible vibration.
You can find the details in his paper “Vibration Suppression for Flexible Spacecraft with Rotating Solar Array” in “Proceedings of KUTIC-2025”.
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Jo Jul 22, 2026
High accuracy and machining capability are the main requirements for metal cutting operations, and high cutting speed and feed rate increase the quality of machining parts, machining accuracy and metal removal per unit time. However, tool life and material removal rates are contradictory because of higher tool temperature, accelerated wear, shorter tool life, and lower machining efficiency with increasing tool replacement time and replacement rate.
Since both material removal rate and tool life are related to cutting conditions, it is necessary to choose appropriate cutting conditions.
Ham Kum Chol, a section head at the Faculty of Mechanical Science and Technology, developed an optimization model with maximum tool wear life at constant metal removal rate (efficiency) per unit time and proposed a method of optimizing the cutting conditions affecting tool life.
The tool wear model was constructed as a polynomial regression model from the simulation data using Deform3D finite element software, and the optimization solution was performed by MATLAB’s fmincon function.
The proposed method was applied to the cutting of high-temperature alloy Ti6A14V as a machining objective, which showed improved machining accuracy and machining time of center machine.
The proposed method can be applied to the selection of cutting conditions for maximizing tool life when machining various hard-working materials.
If more information is needed, please refer to his paper “Optimization of Cutting Parameters in Milling Based on Model of Tool Wear” in “Proceedings of KUTIC-2025”.
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Jo Jul 21, 2026
The impact energy, which is the main performance index of a rock drill, was estimated by many researchers in an indirect way because of the difficulty of direct measurements.
Those measurement methods are difficult to apply to the performance tests of mass-produced drills as they require modification of the structure of percussion drills or preparation of standardized rock samples.
In view of these practical requirements, Han Tok Hyong, an institute head at the Faculty of Mining Engineering, proposed a new structure of impact energy measurement device and analyzed its performance and availability through simulation.
The analysis results show that the stress wave transmitted through the drill rod is converted into the pressure wave of oil filled inside the cylinder. Its maximum value is 15-28MPa, varying with position. Therefore, a suitable location of the measurement point can raise measurement accuracy while extending the service life of the sensor.
The proposed device can be used effectively in the field of impact energy measurement of rock drills due to its simple structure and high reliability. Especially, as it is possible to estimate impact energy without altering the structure of rock drills, it can be used in performance testing processes in rock drill plants.
For more information, please refer to his paper “Simulation Study of Hydraulic Measuring Device for Impact Energy Estimation in Performance Test of Rock Drill” in “Proceedings of KUTIC-2025”.
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Jo Jul 20, 2026
Electric motors and drives consume approximately 40% of the electrical energy generated worldwide. In industrial applications, electric motors account for about 70% of energy consumption. Thus, it can be said that one way to save electrical energy is to increase the efficiency of electric motors.
SynRMs have been preferred in industry for their low cost, simple structure, field weakening capability, small loss, and high torque-to-volume ratio. High efficiency, power factor and torque-to-volume ratio depend on the saliency. It is determined by the synchronization and steady state performance according to starting winding parameters and barrier dimension.
An Se Gwang, a researcher at the Faculty of Electrical Engineering, designed a line-start synchronous reluctance motor (LS-SynRM) with reference to a 1kW induction motor, and determined the optimum rotor structure parameters.
The comparison of the rotor structure of these two motors with the same stator showed that the LS-SynRM has lighter rotor structure by 27.1%.
He determined the optimum dimensions for good synchronization performance and high power factor to be as follows: the diameter of starting winding ds2=4mm, the bridge thickness H=5.5mm, the yoke thickness Y0=5mm, and the barrier thickness B0=3mm.
You can find details in his paper “Determination of Reasonable Rotor Structure Parameters of Line Start Synchronous Reluctance Motor with Round Bar” in “Proceedings of KUTIC-2025”.
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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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