Jo Nov 7, 2023
Game theory is a set of algebraic models to investigate behavior conflicting with each other. In practice, event players often have a game in uncertain conditions with lack of opponents’ strategies.
Especially, in such games as two-person zero-sum games, the payoff value of each player’s strategy is imperfect, so high accuracy of player modeling cannot be guaranteed. In general, statistical method processes uncertainty mathematically with lots of observed numerical value data, but observed data usually contain occasional fluctuation caused instantly by various reasons as well as essential information about opponents.
Being used as a technology of several variables which identifies common characteristic factors in an invariable set, statistical factor analysis uses probability methods for factor analysis. However, these methods include invariable assumptions about probability distribution so the results may not always be right. Also, there are some cases where modeling is not suitable in practice. Though modeling is not correct strictly, we can draw nearly right conclusions from those hypotheses if it is approximately suitable.
Game theoretical decision adoption is a decision-making problem which determines how the best result can be obtained when the result depends both on its own and on the opponent’s actions.
Some decision-making problems like a zero-sum game are inflexible in target weight according to the structure, so they are changed and affected by opponents. Information analysis methods used in the past are not sufficient to deal with these problems.
Kim Ok, a researcher at the Faculty of Information Science and Technology, has proposed an algorithm where a player’s model can be estimated by a small amount of game data in a two-person zero-sum game characterized by a monotonically decreasing function.
The algorithm is based on the analysis of game process profiles. First, she introduced ordered weight operators to the strategic sequence determination of players and defined a compensation function considering monotonically decreasing character of a two-person zero-sum game. Then, she evaluated the game payoff value of the strategy and conducted player modeling.
The proposed algorithm will contribute to enhancing the accuracy of player modeling in two-person zero-sum games.
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Jo Nov 2, 2023
Radiation is an important process of thermal transfer together with conduction and/or convection. Particularly, in high temperature conditions such as burning of pulverized coal, propellants of rockets and thermal plasma, it contributes significantly to overall thermal transfer. However, due to the integro-differential characteristic of a radiative transfer equation for mathematically explaining thermal radiation in absorbing, emitting and scattering media, its algebraic solution is in existence only for extremely limited geometries and conditions. Thus, numerical methods have mainly been utilized to study radiative thermal transfer. Moreover, the advance on performance of modern computers and the interest increased for understanding thermal radiation have promoted the development of numerical methods to solve the radiative transfer equation at a low cost.
Several numerical methods, such as Monte Carlo method, zonal method, discrete ordinates method, finite element method, etc. were applied to model radiative behavior.
The discrete ordinates method (DOM) is a numerical technique proposed first for analyzing radiative thermal transfer in a slab-parallel medium, which has several advantages: low dimensional approximation with sufficient accuracy, modest computational requirement, and applicability into complex geometry.
There were some attempts to use the lattice Boltzmann method (LBM) as a tool to solve the radiative transfer equation, which has developed into an alternative and promising numerical scheme for simulating fluid flows.
Kim Yong Jun, a researcher at the Faculty of Physics Engineering, has developed a discrete ordinate-lattice Boltzmann method (DO-LBM) by combining the advantages of DOM and LBM that can be utilized as a direct tool to solve the radiative transfer equation.
The discrete ordinates scheme is used for angular discretization and the lattice Boltzmann model is applied for spatial discretization.
Introducing Chapmann-Enskog method and dimensionless numbers, he analyzed accuracy of the DO-LBM and non-negativity of the equilibrium distribution function. He compared his method with numerical results by modified discrete ordinates method. The result showed that analyzing radiative transfer in geometry with complex boundaries lowers computational cost more than modified discrete ordinates method often found in literature.
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Jo Oct 30, 2023
Displacement prediction of rock mass surrounding tunnels plays an important role in displacement back analysis for determining geotechnical parameters of rock mass and in-situ stress ratio, as well as safety monitoring and quality control for tunnel construction.
Han Un Chol, a researcher at the Science Engineering Institute, has presented a method to quickly predict the tunnel closure in time-dependent rock mass by using stable deformation rate for tunnels and the non-equidistance grey Verhulst model (NGVM).
Considering preceding studies, he determined the maximum stable deformation rate as 0.05 mm/d.
The proposed method was validated fairly through a case history for a new excavated drift of -600m level in an underground coal mine.
The result showed that NGVM seems to be a more powerful tool compared with non-equidistance grey model (NGM (1, 1)) for displacement prediction of tunnels in time-dependent rock mass.
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Jo Oct 29, 2023
A research team led by Kim Ju Song, a researcher at the Faculty of Mining Engineering, has established the process of concentrating anthracite coal by a selective crusher with suspended rings (SCSR).
The main part of this process is the newly manufactured selective crusher with suspended rings.
Several rings and a gear roller are the main crushing parts of selective crushing device with suspended rings and the rings are suspended from a suspension beam.
The materials fed into the crusher through primary screening move towards the suspended rings by the action of the gear roller. Their movement is restricted by the rings and they are open to the impacts by the gear roller. Then, coal of low strength is crushed and rocks of high strength pass round along the suspended rings.
As a result, the coal in the crushed product is mostly distributed towards small particle size and the rock is distributed towards large ones.
The particle size of mined raw coal ranges from 0 to 400 mm and about 8% of it is larger than 150 mm.
As the selective crushing device can be applied to 25~150mm particles, a mass of particles larger than 150 mm is first sorted from the front part of the screening process, and a mass of particles smaller than 25 mm is sorted by a sieve installed on the front part of the selective crusher.
Because of its simple structure and low manufacturing cost, it is easy to make. It provides high stability of operation and it is affected little by moisture.
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Jo Oct 27, 2023
A research team led by Cha Song Il, a section head at the Faculty of Shipbuilding and Ocean Engineering, has developed a course control system by turning electric propulsion and helm for arbitrarily controlling the course and turning radius of a ship.
The system consists of a propulsor, a reducer, a propulsion motor and a control board, a helm and a helm motor, and a helm control board so that the course of a ship can be controlled easily and arbitrarily in different situations and conditions.
A long ship has difficulty controlling its course and entry into and departure from a port on narrow and shallow waters.
The turning electric propulsor enables convenient entry into and departure from a port without recourse to a tow rope. The helm at the stern and the propeller at the bow guarantee safe navigation in complex waters and natural environments, thus reducing fuel consumption and navigation time.
They carried out speed control of a 17kW turning propulsion motor in conformity with its hydrodynamic characteristics to prevent overload and they changed the thrust according to the change in disturbance to raise the safety of a ship.
With such advantages, this system will find wide application to large cargo ships and passenger ships.
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Jo Oct 25, 2023
Sensorless driving for PMSM is divided into two methods: one is based on stationary reference frame and the other is based on rotational reference frame.
Pak Se Yang, a researcher at the Science Engineering Institute, has presented his research results of more improved estimation performance in combination of these two methods.
First, he estimated the rotor position by using the open-loop estimation algorithm based on the stationary reference frame. Then, he evaluated the estimation error from the model based on the rotational reference frame and compensated the estimate in feedback way with differences from the current measurements.
In contrast with the sensorless field oriented control (FOC) system, the sensorless DTC has simpler construction and it is less sensitive to parameter variation.
The experimental results validate the performance of the proposed control system.
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