Jo Jan 8, 2025
More than ten old Kwangmyong Zelkova trees are growing by Jogye Gate of the Sogwang Temple about twenty kilometers north of the seat of Kosan County, Kangwon Province, DPRK.
These trees are said to have been planted in 1386, when the Sogwang Temple was being built.
The largest one is 27 meters tall, with the root collar of 9.8 meters round, the chest-height of 8 meters round and the canopy of 25 meters in diameter. The smallest one is 12 meters tall, with the root collar of 2.4 meters round, the chest-height of 2.3 meters round and the canopy of 8 meters in diameter.
These large old trees are designated as a living monument and in good preservation and care as they are of academic and educational significance and add beauty to the Sogwang Temple.
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Jo Jan 7, 2025
Induction heating (IH) converters commutate close to resonant frequency to supply maximum power to the workpiece. Therefore, the correct identification of the tank’s resonant frequency is a matter of vital importance in most IH converters. Detection of resonant frequency is based on the calculation of the phase-shift between two electric variables. In order to control this phase-shift between two electric variables, most IH converters use a PLL system.
Most PLL systems used in IH converters are analog PLLs that use integrated circuits from the CD4046 circuit family and analog low pass filters. Although analog control has demonstrated to be effective and accurate, it is less flexible and robust to the degradation of the components than digital control. Due to the advantages of digital control presented above, DSPs or field-programmable gate arrays (FPGAs) have been used to implement PLLs. But as hardware components are used, the change of components is needed in the case of changing parameters. In software PLL systems, many of the parameters used during the control, like frequency, dead time or filters, can be adjusted with no changes in hardware.
Kwon Chang Hyok, a researcher at the Faculty of Mechanical Science and Technology, has proposed a method for implementing the resonant frequency tracking control, the main control in IH systems used in various sectors of the national economy, by using a software PLL algorithm, conducted a simulation to evaluate the stability and reliability of control, and verified them through several experiments in the IH system with LLC.
The proposed software PLL algorithm can be applied to induction heating systems as well as to various fields where phase-shift control of both signal waveforms is necessary.
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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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