Jo Apr 20, 2023
Pak Song Chol, a researcher at the Faculty of Physical Engineering, has determined agitation factors of reactants for coal liquefaction, set up an experimental process, and studied their effects on the treatment through an experiment.
It is the mixing ratio in COWM(coal-oil-water mixture) production for liquefaction that should provide an environment for coal powder particles bonding into crude oil molecules and allow enough electric current for HVHF discharge. Here, the bonding environement depends on the ratio of oil while discharge current depends on the ratio of water.
At the begining, coal:oil:water =5:1:4 in w.t. ratio was adopted. However, self-oganization of coal powder particles needed higher ratio of oil so that different mixing experiments were conducted with different factors. As a result, it was concluded that coal:oil:water =1:(1~2):(0.5~1) in w.t. ratio is more effective for self-organization of coal powder particles of the mixture in post-reaction, as well as during discharge accompanied by continuous flow.
The experiments were conducted both in static and dynamic manners. The static experiment was for estimation of yield while the dynamic one was for quality assessment in addition to yield with different raw materials.
The measured factors and results showed that the diesel oil distilled out of the products in his ratio is as good as commercial diesel oil in terms of moisture content, ash content, sulfur content, aqui-soluble acid-alkali.
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Jo Apr 18, 2023
Sin Tong Jun, a researcher at the Faculty of Information Science and Technology, developed a tactic supporting system for small size robot soccer.
The robot soccer tactics simulation system covers formation design, strategic positioning of players, a situation-based intentional cooperative attacking tactic, an aid-obligatory array-based dynamic cooperative defending method and a genetic-reinforcement learning-based online tactics learning method.
In the formation design, you can set initial positions and movement ranges of each player in formations like 4-3-3, 4-4-2 and 4-2-4. For dynamic transformation of formations, you can select any formation table when necessary.
In the strategic positioning, the positioning of team players without a ball is modeled for 40-metre stonewall defense, which supports all-out attack and all-in defense and the numerical superiority of the team around the ball at the same time.
In the situation-based intentional cooperative attacking tactic, preconditions and stoppage conditions for passing a ball among players in such situations with high stochastic presence as a kick-off or a corner kick are designed so that intentional cooperative attacks among players can be made.
In aid-obligatory array-based dynamic cooperative defense tactic, an assistant player is selected when it is impossible for a single player to change the current situation so as to support unified cooperation among players, and problems of task sharing among players are solved to ensure dynamic defense.
The genetic-reinforcement learning-based online tactic learning is divided into tactic rule generation and tactic selection control. In tactic selection control, you control parameters for kicking, dribbling and passing. In tactic rule generation, determination of attacking and defensive situations, determination of the main robot and an assistant robot, and determination of ball handling of the main robot and the movement point of the assistant robot are completed by genetic-reinforcement learning so that tactic rules for a goal can be found automatically.
Formation designing and strategic positioning can increase shooting success rate by 12%. Intentional cooperative attacking tactic and dynamic cooperative defense tactic can improve the average attacking rate by more than 3% and the average ball possession rate by more than 10%. Genetic-reinforcement learning helps to find a new team tactic against opponents within 1000ms after the kick-off of the first half.
The system is available for small size Robot League and for control of intelligent robots working for automated factories. It also finds use in the measurement and assessment of techniques newly arising in the distributed AI field.
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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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