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 12, 2025
From childhood, the people of Koguryo possessed of exceptional martial habit were all good at horse riding and they accepted it as an important requirement of life.
The mural paintings of Koguryo tombs including murals of dancing, Yaksuri mural paintings and murals of hunting give a lifelike portrayal of the life of Koguryo people who enjoyed riding with excellent horsemanship. In particular, the delightful scenes depicting some people hunting wild animals with bows and arrows while dashing vigorously on horseback show master horsemanship and archery of the Koguryo people in an intensive way.
Through such hunting, the Koguryo people further refined their riding skills and trained courage and matchless capability to defeat any aggressors at a single blow without fear.
The Koguryo people learned riding skills through their routine martial arts training as well as from hunting wild beasts.
The mural painting of Tokhungri tomb vividly depicts the horse-riding archery training on a fixed target. The wall is painted with 4 competitors, 2 judges and one scorer.
Although the mural shows the scene of horse-riding archery only, the Koguryo people further improved their riding skills through various martial arts training including racing, fencing and spearing on horseback.
As a result, the distinguished horsemanship of the Koguryo people played a decisive role in the war to defend the land and the dignity and sovereignty of the country and nation.
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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 9, 2025
Kangso Mineral Water is not only unique in its taste but also efficacious for treating various diseases and protecting health.
Our people already started using Kangso Mineral Water hundreds of years ago.
“Kangsogunji”, published in 1936, says the following.
There was a mineral spring in Jonghwa ri of Kangso myon. Over 250 years ago, a crane which got hurt in the leg flew down to the spring to drink the water and wash its body with it every morning. After a few days, it was fully recovered and flew away. Thus, the mineral water was discovered to be of medicinal value.
It tastes refreshing and stimulates the tip of the tongue, which tastes just like a fizzy drink. In addition, habitual drinking of it helps cure many diseases including gastric disorder, anemia, constipation, inflammation of the bladder, etc.
This tells us that Kangso Mineral Water has hundreds of years of use history and it has been one of our country’s specialties well known from long ago for its unique taste and mysterious and marvelous medicinal effect.
On December 7, 1947, when he visited the Kangso Mineral Water spring, President
Today, the modern Kangso Mineral Water Factory near the spring is producing a huge amount of bottled mineral water to supply to every part of the country including Pyongyang City.
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