Jo Apr 17, 2023
Hong Phyong Il, a section head at the Faculty of Applied Mathematics, has provided a new condition for the existence of fixed points of contractive mapping which maps a non-set into a compact subset on a b-metric space, and on this basis, he has introduced a condition for the existence of fixed points of contractive mapping on a complete b-metric space.
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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 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 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 3, 2023
The knotty problems in displacement reconstruction based on self-mixing (SM) technique are estimation of self-mixing interferometry parameters and normalization of SM signals (SMSs) since they are all very time-consuming and based on complex algorithms. This has an unfavorable effect on the real-time and low-cost natures of an SM displacement sensor.
Kim Chol Hyon, a researcher at the Faculty of Physical Engineering, has presented a simple method of displacement retrieval with a high resolution, which does not require any parameter estimation and normalization.
According to his study, when C changes during the operation of a self-mixing sensor, a single fringe, in a strict sense, does not correspond to a half wavelength and, therefore, this causes inaccuracy in displacement reconstruction. On the basis of it, he has proposed a very simple method called fringe scaling for displacement reconstruction, which does not require any normalization of SMSs and parameter estimation. This method provides a high resolution of λ0/10 and in addition, it can be employed for all feedback regimes including weak, moderate and strong regimes.
The proposed method is based on the scaling of individual fringes in SMSs and speckle noise proof. The simplicity of the method will make a great contribution to lowering the cost of SM displacement sensors and improving their reliability and resolution.
For more information, please refer to his paper “Normalization-free displacement reconstruction method based on fringe scaling” in “Applied optics” (SCI).
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Jo Mar 30, 2023
A research team led by Kye Myong Ho, an institute head at the Faculty of Metal Engineering, has developed an energy dispersive X-ray fluorescence (EDXRF) analyzer.
The analyzer has several advantages: nondestructive analysis without any chemical reagents, simultaneous analysis of several elements in a short time, very simple structure, wide range of concentration standardless analysis and convenience in use.
It is made up of a high voltage power unit, an x-ray tube, a semiconductor detector, a multi-channel pulse height analyzer, a control circuit, a vacuum pump and analysis software.
The maximum power of the x-ray tube is 50W and the energy resolution of the semiconductor detector is 149eV. The analyzer enables measurement in the vacuum and its measuring time is below 5 minutes.
The analytical software is used for instrument control, qualitative analysis, semi-quantitative analysis, calibration curve drawing and quantitative analysis.
In the software, the voltage and current of the x-ray tube are set according to elements, and fluorescence spectrum is collected. Semi-quantitative analysis is available by standardless analysis. For semi-quantitative analysis, the kind of sample must be selected before measuring. You can also make a quantitative analysis by a standard curve. First, you should select the standard curve for a sample, and then quantitative analysis result is presented.
EDXRF analyzer can be widely used for analysing element concentration of substances such as alloy, mineral, cement, precious metals and catalyzers in the fields like metal, chemical, building materials, mining industries, prospecting and archaeology.
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