Jo Jan 4, 2025
Among the rare and beautiful natural monuments of our country is the Isonnam Falls.
It is in the Chonthae Valley of Mt. Myohyang, a superb scenic beauty.
It was called fraternal falls as the waters had been falling in parallel with each other like good brothers for a long time.
In May, 1981, Chairman
Since then, it has been called “Isonnam Falls”.
The falls are 22 meters in height, and 6 to 10 meters and 4 to 8 meters in width, respectively.
The waters fall along the inclined rock, at the protrusion of which they spout forward.
At the bottom is a three-meter-deep pool hollowed by the waterfall.
Isonnam Falls, whose waters fall vigorously in two lines as if competing with each other, is a precious living monument that adds beauty to the natural landscape of the area for its peculiar and beautiful appearance and serves as a cultural resort for the people.
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Jo Dec 30, 2024
Generally, Least Squares (LS) Method treats only random errors of observation vector in adjustment function models. However, both observation vector and elements of coefficient matrix of adjustment function model contain random errors. Therefore, there is no guarantee that the result of adjustment by LS method is the global optimal solution.
Total Least Square (TLS) method is a primary estimation method that treats random errors of observation vector and coefficient matrix in adjustment functional models. Since TLS method takes into account both random errors of observation vector and coefficient matrix based on errors-in-variables (EVI) model, it is possible to improve the accuracy more than the result of LS method. Therefore, TLS method has been applied to different fields of science and technology including signal and image processing, computer vision, communication engineering and geodesy.
However, weighted total least square (WTLS) method has been applied less widely to geodetic network adjustment problems than to other fields.
Kim Jung Hyang, a researcher at the Faculty of Earth Science and Technology, has proposed an application method for the adjustment of triangulation network, based on the brief summarization of the algorithm of WTLS.
The key problem in the application of WTLS to the adjustment of geodetic network is to determine the weight matrix (or cofactor matrix) for the elements of coefficient matrix in the adjustment function model.
He proposed a method to determine cofactor matrix for errors of coefficient matrix and observation vector in triangulation network, and verified the effectiveness of the proposed method through an example applied to the simulation triangulation network.
You can find more information in his paper “Study on triangulation network adjustment by Total Least Square Method” in “ADVANCES IN GEODESY AND GEOINFORMATION” (SCI).
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Jo Dec 29, 2024
Airlift pumps, fluid machines for raising liquids or slurries through a vertical pipe by compressed air injected into the pipe near its mid position or lower end part, are widely used in the fields of deep seawater upwelling and seabed mining due to the advantages of simple structure, high reliability, convenient maintenance and low cost.
Therefore, many experimental studies have been conducted to clarify the air-water-solid three-phase flow characteristics of airlift pumps. Numerical and analytical studies have also been carried out to predict the performance of airlift pumps.
Rim Un Ryong, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has carried out a numerical analysis of steady air–water–solid three-phase flow as well as water–solid two-phase flow in the airlift pump, based on a one-dimensional multi-fluid model.
He calculated the depth distributions of 8 physical quantities such as volumetric fractions and axial velocities of all phases of gas, liquid and solid, air density and pressure by the governing equations or by integrating the vector form of nonhomogeneous ordinary differential equations for three-phase and two-phase flow intervals, respectively.
He applied the proposed method to the seabed mining in water depth of 2 000 meters and obtained the calculation results.
For further information, please refer to his paper “Numerical analysis of air–water–solid three-phase flow in airlift pump for seabed mining” in “Ocean Engineering” (SCI).
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Jo Dec 27, 2024
Nowadays, the numerical simulation method is an essential tool in the stability analysis of mining engineering, and it is important to ensure the accuracy and reliability of the mining engineering design to construct a numerical model used as a more realistic representation of the in situ situation.
Numerical simulation programs widely used for stability analysis of geotechnical and mining engineering structures are FLAC3D and ANSYS, etc.
Han Un Chol, a researcher at the Science Engineering Institute, has proposed a fast and convenient modeling technique by combining ANSYS and FLAC3D with unique advantages for numerical calculation and SURPAC suitable for 3D modeling.
First, he examined the relationships between the data structures of the model files for SURPAC, ANSYS and FLAC3D, and established the transformation technique of an integrated 3D solid model via Excel.
Then, he applied the proposed method to the analysis of the pillar stability for sublevel open stope method in the target mine.
Finally, he verified the validity and feasibility of the proposed model transformation technique.
You can find more information in his paper “Numerical analysis of pillar stability for safe mining of a combined mine based on three-dimensional solid model” in “CHALLENGES IN ROCK MECHANICS & ROCK ENGINEERING”, proceedings of the 15th ISRM Congress 2023 & 72nd Geomechanics Colloquium.
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Jo Dec 26, 2024
In general, convex lenses, reflectors, Fresnel lenses, and a combination of lens-reflector in the light beam-collimating system are used for floodlights, aviation obstruction lights, and lighthouse beacons. Depending on which mode is used, there are some differences in the utilization of the beam, the rate of collimating, and the resolution of the heat release problem.
According to the present study, in the cylindrical Fresnel lens used in the optical system of aviation obstruction lights, the beams going beyond the height of the Fresnel lens from the light source in the center of the cylindrical lens are not used in the collimating system, which leads to the reduction in the overall optical efficiency and shortening of the lifetime of the light source, especially in the case of high-power LEDs, due to cooling.
Ho Ji Song, a researcher at the Faculty of Electronics, has proposed a method to design a new structure of lenses that can solve the problems of light beam utilization, collimating rate, and heat release by means of a total reflection-refraction coupling.
First, he made a combination of six submodels to construct a collimating lens that can collimate light from a single LED and multiple LEDs arranged side by side on one axis in the direction of the optical axis.
Second, in order to form a whole structure, he established the relationship between the structure parameters and positions during the optimization simulation of collimating LED light into the optical axis as it is also possible for the submodels to separate from each other by changing the structure parameters.
Finally, he determined the structure parameters of optimized collimating lens using the optimization function of LightTools, an optical simulation tool.
In order to verify the effectiveness of the new method, he performed a measurement test of light intensity and divergence angle on the designed lens, and introduced a new lens into the optical system of the medium intensity aviation obstacle light.
As a result, he drew the following conclusions.
First, the paraxial lights in the light beam from the LED is collimated in parallel with the optical axis through the central part of the lens and the other lights are collimated through the TIR surface, so that the utilization of the light beam as well as the rate of collimating can be increased.
Second, the proposed method can easily increase the light intensity by layering the lenses in the lamp design, and it can realize the dispersion of the LEDs, which is effective to solve the heat release problems in the high-power lamp design.
Third, the light from a single LED can be collimated vertically and horizontally and the light from the LEDs arranged side by side on one axis can be collimated vertically.
Fourth, the proposed method can be widely used to design lenses used in optical systems that need to cast light far away, such as floodlights, aviation obstacle beacons and lighthouse beacons.
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