Jo Jul 17, 2025
Incline hoist skips are classified into dumping and non-dumping ones. Non-dumping skips are of two types―rear discharging and bottom discharging. They are mainly used on the slopes of 40° or more. The dumping skips are used at inclination angles below 40°, and an auxiliary rail is installed to increase the inclination of the skip for a sufficient discharging angle.
The dumping skips are of two types―rear-discharging and front-discharging. The latter is widely used. The rear wheel of a front-discharging skip is bigger in width than the front wheel. When approaching the emptying point, the front wheel tilts forward along the main rail, while the rear wheel is lifted along the profile of the unloading curve to increase the discharge angle.
The main rails on which the front wheels are placed are generally straight, which often causes complete overturning of the skip. Skip winching facilities are subjected to overwinding in unloading sections for several reasons. If the skip is out of its unloading section by overturning, the skip will be completely overturned in the direction of movement due to the increase in the angle of inclination of the skip, which causes the forward movement of the center of gravity, and the increase in the drag force exerted on the front wheels. There is also a disadvantage of poor skip restoration due to the presence of the center of gravity in the front side of the skip.
To prevent such phenomena, the main rails can be set to be curved. The curved shape of the main rails can prevent complete overturning of skips and increase the possibility of restoration. There have been many studies on dumping skips with big dip angles used in manufacturing lines of factories and enterprises in the construction and building materials industry. However, they failed to consider the unloading properties of bulk materials in the skips.
Hong Ryo Myong, a researcher at the Faculty of Mining Engineering, has analyzed the unloading properties of the front-discharging skips by combining the analysis of bulk materials and motion. He proposed that the curved shape of main rails for front wheels can eliminate full overturning of skips, and proved it by analyzing the behavior of bulk materials and motion.
He proposed a method of evaluating the overturning possibility of skips. The overturning possibility of skips can be estimated by measuring the force acting on hoisting wire ropes. If the force on hoisting wire ropes remains unchanged at zero for a while, the skips can be completely overturned.
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Jo Jul 14, 2025
Impregnated diamond bits are widely used in drilling work for geological prospecting, petroleum production and civil construction.
The most difficult problem in the application of diamond bit is the rate of penetration of diamond bit in the slipping formation. The very low rate of penetration in these slipping formations which are often encountered during drilling, is related to the mechanical characteristics of the slipping formation. The slipping formation usually has three characteristics. First, rock hardness is relatively high because of the high quartz content. Second, rock strength is high because the rock-forming mineral grains are very small and have local siliceous cementation. Third, rock abrasiveness is weak.
To overcome these shortcomings, a researcher designed a sandwich impregnated diamond bit to maintain concentric circular shape of the bottom surface of bit during drilling, remarkably improving the drilling efficiency in the slipping formation. The shortcomings of preceding studies on SIDB (sandwich impregnated diamond bit) can be found as follows. First, the effect of structural parameters (width of non-working layer) on the drilling performance of SIDB in the slipping formation is not clearly clarified. Second, the effect of sandwich structural parameters on the rock failure mode of SIDB is not clearly clarified.
Kim Il Jin, a researcher at the Faculty of Earth Science and Technology, in order to investigate the effect of structural parameters on the drilling performance of SIDB and determine suitable structural parameters, has fabricated the SIDB of ϕ59mm/41mm with different structural parameters (0, 0.5, 1, 1.5, 2, 2.5mm) and conducted a field-drilling test.
In addition, through a particle size analysis of the rock debris produced during drilling, he demonstrated that the reasonable structural parameters changed the rock breakage mode of SIDB from micro cutting to micro cutting-micro volume breakage.
The results of his study are very important to effectively overcome the slipping formation which is a challenge in the application of a diamond bit and to improve overall drilling efficiency.
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Jo Jul 13, 2025
Inverse hyperbolic problems appear in underwater sound search, geophysics, electrodynamics, etc.
In most practical applications, most of the physical phenomena are modeled by multidimensional equations. Therefore, considerable attention has been devoted to the analysis of multidimensional inverse problems. However, to the best of our knowledge, the solvability of the hyperbolic inverse source problems has only been studied for one-dimensional linear equations.
Ryom Su Jong, a post-graduate student of the Faculty of Applied Mathematics, has investigated the unique solvability of an inverse problem of determining a solely time-dependent source in a multidimensional semilinear hyperbolic equation.
This inverse problem models the identification of underwater sound source when its position is known. She addressed a numerical scheme together with the existence and uniqueness of the weak solution by means of Rothe’s time-discretization method. Moreover, she evaluated the error of the semi-discretization scheme.
The time-discretization method she applied is a powerful and efficient tool for solving a wide range of evolution equations.
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Jo Jul 11, 2025
Cold pilger mills include a roll cold-pipe rolling mill and a roller cold-pipe rolling mill. As the roll cold-pipe rolling mill involves difficult roll processing, the roller cold-pipe rolling mill is now in wide use.
Determination of rolling force during periodic rolling in roller cold pilger mills is one of the important problems in determining the design parameters. In particular, the roller cold pilger mill is subject to periodic reciprocating motion so that the deformation zone and rolling force continue to change during one cycle, and thus it is important to determine the maximum rolling force.
Han Myong Jin, a researcher at the Faculty of Materials Science and Technology, has determined the average pressure and contact area between the rolling roller and the workpiece as one of the basic data for determination of the design parameters of two-row roller cold pilger mills, and investigated the rolling force.
First, he derived a formula of the maximum rolling force and performed a comparison using the finite element analysis tool Deform-3D. Then, he installed a force sensor under the inclined support plate and compared it with the measured results to confirm the accuracy of calculation.
When producing a copper tube of ϕ24mm×0.5mm in size from a workpiece of ϕ30mm×3mm in size in a two-row roller cold-pipe rolling mill, the rolling force analysis by the computer-coupled rolling force measuring device and the rolling force calculation confirmed that the rolling force formula is relatively accurate, with 3% in the first row and 0.73% in the second row. In the same way, the comparison of the rolling force by the simulation analysis data with Deform-3D and the rolling force determined by the rolling force formula showed that the rolling force formula is relatively accurate, with 2.8% in the first row and 1.96% in the second row.
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Jo Jul 10, 2025
A turbogenerator is one of the main equipment for large-capacity power stations such as nuclear power plants. In order to design a turbogenerator of high operational reliability, thermal characteristics should be analyzed exactly.
The direct gas-cooled rotor winding in large power turbogenerators is cooled by gas (hydrogen) that flows along the U-type or radial ventilation duct. Many researchers and experts have published their research results on the temperature characteristics of winding of direct gas-cooled rotor in large turbine generators larger than 1 000MW. However, the detailed research results on the cooling duct dimension at the radial cooling rotor windings are rarely mentioned in the literature.
An Se Gwang, a researcher at the Faculty of Electrical Engineering, has determined the reasonable cross section of an axial ventilation duct that makes the distribution of flow velocity uniform in the radial cooling slot of a 1 000MW 4-pole turbogenerator and the reasonable value of the width coefficient of cooling duct and segment length.
First, he proposed a mathematical model to analyze the temperature feature of radial cooling rotors and confirmed the range of practical value to determine the reasonable number and dimension of radial ventilation ducts.
Then, he proved that the gas velocity distribution has an equal value along the axial length when the input cross section of the axial ventilation duct is increased 1.67 times the output cross section, with the effect of revolution in consideration.
The research result is helpful for the design standard of large 4-pole turbine generators, and it can be applied to the design and building of 1 000 MW 4-pole turbine generators.
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Jo Jul 8, 2025
Manganese is an important alloying element indispensable in the metallurgical industry and it is widely deposited in the form of oxides in nature.
The reduction reaction of manganese oxides in the production of metallic manganese or ferromanganese from these manganese raw materials is of great importance, and there have been many thermodynamic and kinetic studies on it. In particular, several kinetic models describing the carbothermic reduction reaction of MnO have been proposed and experimentally examined.
However, there are some errors in the calculation and experimental results in the models proposed by the previous authors, and no studies have yet applied the fractional order to the kinetic modeling of the reduction reaction of MnO by solid carbon.
Kim Un Dok, a researcher at the Faculty of Metal Engineering, has developed a kinetic model for the reduction process by solid carbon of MnO in high-carbon ferromanganese slags using fractional differential equations (FDE), determined the relationship between fractional order, fractional rate constant and temperature, and verified the accuracy of the fractional order model through the comparison with the results of previous studies.
Comparing the preset values calculated from the FDE and previous models with the experimental values, the root-mean-square errors (RMSE) were 0.005 and 0.029, respectively, and the coefficients of determination were 0.999 and 0.980, respectively, which shows that the proposed model is more accurate.
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