Effect of Structural Parameter on Drilling Performa...

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.

Reconstruction of Solely Time-Dependent Source in S...

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.

Master Horsemanship of Koguryo People Reflected by ...

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.