Jo Apr 13, 2023
A research team led by Im Jung Bin, a researcher at the Faculty of Electrical Engineering, proposed a scheme of a relay protection device based on Field Programmable Gate Array (FPGA) for high-speed operation of protection, one of the basic demands of relay protection.
Unlike in all conventional relay protection devices based on a microprocessor that realizes a protection algorithm by using the sequentiality of software architecture, they took advantage of the features of parallelism of FPGA in order to configure multi-function protective relays that promptly process multi-channel input signals in real time and concurrently estimate and process protective logics of different functions, in one FPGA.
They made a protection relay combined with functions of protection, control and communication by involving a data acquisition and control module, protection and warning modules, control modules for operation of protective relays of hardware architecture, a hardware checking module and a data transmission module, with a 64-point FCDFT module for multi-channel as the core.
The protective relay of a new scheme can operate within a 1.1 cycle of power frequency.
With plenty of hardware resources available on the FPGA board, this approach can be updated to a multi-function hardware relay with metering and protective capabilities and can be applied to different equipment of electric power systems in the future.
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Jo Apr 11, 2023
Ryom Chol Ung, a researcher at the Faculty of Mining Engineering, has been adding sci-tech knowledge of cross-disciplinary sciences to physical beneficiation of minerals so as to help his students to get a deep knowledge about it by means of preparation and discussion.
First, he has enriched the teaching content with cross-disciplinary sciences.
For instance, ways and methods of optical separation of minerals by differences from optical spectrum, a branch of cross-disciplinary sciences, were added to gravity separation of minerals that attaches importance only to the differences in the density of minerals, while such cross-disciplinary knowledge as cryogenic temperature physics, magnetic fluid, etc. were to magnetic separation of minerals.
Second, he has made preparations oriented to the acquisition of cross-disciplinary knowledge.
For example, he gives preparation tasks of consulting international scientific journals on the ways and methods of beneficiation of different kinds of minerals so that the students come to know that if ultraviolet separation is combined in the preseparation of scheelite, they can avoid excess grinding and reduce the amount of beneficiation reagents by using the differences from an ultraviolet luminescent colour and in the falling velocity of mineral particles in air media.
Third, he has consolidated student’s cross-disciplinary knowledge through debates and discussions.
Students have had a wide knowledge of several branches of cross-disciplinary sciences through discussions and debates on their tasks ― modeling, setting boundary conditions and result analysis for motion characteristics of mineral particles in a jigger, for example.
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Jo Apr 10, 2023
Blast-induced vibration produces very complex signals, and it is very important to work out environmental problems induced by blasting.
Some researchers applied wavelet analysis theory to the signal process of blasting vibration to determine the delay time of short-delay blasting, and suggested variation characteristics of blasting vibration frequency. Some others analyzed the time-frequency distribution characteristics of blasting vibration to determine their main frequency and peak vibration velocity.
Wavelet analysis has been widely used to understand the frequency characteristics of blasting vibration by estimating vibration energy characteristics applied to civil structures, to identify time errors during blasting, and to appreciate vibration characteristics of geological structures and so on.
Pak Thae Un, a section head at the Faculty of Mining Engineering, has made a wavelet analysis of measured blasting vibration signals to identify frequency bands reflecting the changes of blasting vibration parameters such as vibration velocity and energy in different frequency bands. Then, he has discussed frequency characteristics in view of blast source distance and charge weight per delay.
From the analysis results, it can be found that peak velocity and energy of blasting vibration in frequency band of 62.5~125Hz are larger than those in other bands, indicating the similarity to the characteristics in the distribution band (31~130Hz) of main vibration frequency. And most frequency bands are affected by blasting source distance, and the frequency band of 0~62.5Hz reflects the change of charge weight per delay.
If further information is needed, please refer to his paper “Prediction of characteristic blast-induced vibration frequency during underground excavation by using wavelet transform” in “Frontiers of Structural and Civil Engineering” (SCI).
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Jo Apr 9, 2023
Kuryong Falls is a famous waterfall in the zone of Kuryong Pool in Outer Kumgang of Mt. Kumgang, a world-famous scenic spot.
From ancient times, it has been accepted as one of the three famous waterfalls of our country along with Pakyon Falls in Kaesong and Taesung Falls on Mt. Solak, and what is more, it is known as number one of the four famous waterfalls on Mt. Kumgang.
At the bottom of the waterfall is a pool shaped like a large stone mortar dug by the falling waters.
The pool got the name Kuryong as legend has it that there lived nine dragons defending Mt. Kumgang in old days, and the water falling down into the pool was called Kuryong Falls (“Kuryong” means “nine dragons”). Above the falls is Sangphaltam (eight pools), which is well known for the legend about “eight fairies of Mt. Kumgang”.
Pak Sin Jong, researcher at the Academy of Social Sciences
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Jo Apr 6, 2023
Recently, large floating structures such as oil storage facilities and floating airports have appeared for the purpose of utilizing sea space and exploiting ocean resources. Many researchers have been developing artificial protective structures such as submerged breakwaters to prevent or decrease the actions of incident wave towards a coast. Therefore, it is necessary to estimate wave motion at a place where such structures are installed, and it is also important to consider the cases of undulated seabeds or bathymetric regions.
Rim Un Ryong, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has studied three-dimensional water wave motion over undulated seabeds. For wave motion in sea water of finite depth, a fluid domain is usually unbounded horizontally but bounded vertically by free water surfaces and seabeds.
To study local wave motion over undulated regions only, he suggested a novel Dirichlet-to-Neumann (DtN) boundary condition on an artificial cylindrical surface by which a fluid domain is divided into an interior region with finite volume and an exterior region. Then, he applied the DtN boundary condition and other boundary conditions on mean free water surfaces and undulated seabeds in order to determine the solution to wave motion in the interior region by using Boundary Integral Equation (BIE). Upon verification of a submerged square cylinder, he extended the present model to the case of an array of rounded-rectangular cylinders or circular paraboloidal shoals.
The proposed model can be applied to assess wave motion over an undulated seabed when an undulated region is local and its surrounding region is horizontal and unbounded.
More information about this is found in his paper “An exact DtN artificial boundary condition for motion analysis of water wave with undulated seabed” in “Wave Motion” (SCI).
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Jo Apr 5, 2023
A catapult, a bow that works in a mechanical way, was one of the excellent weapons of Koguryo.
It was made up of two parts ― a bow and a body. The bow was for loading shooting force on the arrow and the body was for holding and directing the arrow.
Our country has the longest history of a catapult in the East. A catapult was of two types ― single-shot and multi-shot.
The most well-known multi-shot catapult was a three-arrow-shot catapult of our country in the middle ages.
Upgraded from the Koguryo’s single-shot catapult, the three-arrow-shot catapult could hold many arrows and discharge three arrows at a time.
Other countries did not have such a multi-shot catapult in those days.
The catapults invented by our resourceful ancestors were absolutely unique in structure, way of working and manufacturing technique, so they are still attracting admiration of people.
A great number of people are particularly impressed by the line of sight inscribed on the catapult that can be seen only on modern weapons.
That is why even weapon experts from other countries praised, “The simple but clever construction of a catapult amazes modern people. It is so interesting since it works like a today’s rifle. As an invention 2 000 years ago, it is absolutely amazing.”
Indeed, the catapult of Koguryo demonstrates our ancestors’ extraordinary creative wisdom and talent.
Kim Kwang Jo, researcher at the Academy of Social Sciences
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