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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Jo Oct 24, 2023
Han Un Chol, a researcher at the Science Engineering Institute, has presented a new method of intelligent back analysis (IBA) using grey Verhulst model (GVM) to identify geotechnical parameters of rock mass surrounding a tunnel, and on this basis, he has validated the accuracy of this method via a test for the main openings of -600m level in a mine.
Displacement components used for back analysis are the crown settlement and sidewalls convergence monitored at the end of openings excavation, and the final closures predicted by GVM.
First, he obtained the nonlinear relation between displacements and back analysis parameters by artificial neural network (ANN) and Burger-creep viscoplastic (CVISC) model of FLAC3D.
Then, he determined the optimal parameters for rock mass surrounding a tunnel by genetic algorithm (GA) with both groups of measured displacements at the end of the final excavation and closures predicted by GVM.
The maximum absolute error (MAE) and standard deviation (Std) between calculated displacements by numerical simulation with back analysis parameters and in situ ones were less than 6 mm and 2 mm, respectively.
Therefore, it was found that the proposed method could be successfully applied to determination of design parameters and stability for tunnels and underground cavities, as well as mine openings and stopes.
For more information, please refer to his paper “Intelligent back analysis of geotechnical parameters for time-dependent rock mass surrounding mine openings using grey Verhulst model” in “Journal of Central South University” (SCI).
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Jo Oct 23, 2023
Fluorite (CaF2) is an important mineral resource that is used in many industries as a fluxing agent for production of hydrofluoric acid and steel making, as building materials, etc. As the demand for fluorite continues to increase, there has been a steady rise in the price of higher-quality fluorite ores.
Flotation technology is the most commonly used method for beneficiation of fluorite, that is, for production of fluorite concentrates of up to 98% purity. In flotation of fluorite ores, fatty acids are the most popular collectors. However, the flotation performance of these collectors is highly dependent on the pulp temperature. At low pulp temperatures, their collecting ability declines due to their low water solubility and activity. To improve flotation efficiency, pulp heating is generally applied, with the pulp heated to 35~85℃. Pulp heating inevitably increases production cost. Therefore, developing new collectors with good collecting ability at low temperature is of great economic interest.
Although fatty acids have been employed as collectors in fluorite flotation, flotation mechanisms of fluorite using fatty acid amide have not yet been revealed.
Jong Kwang Sok, a researcher at the Faculty of Mining Engineering, has succeeded in synthesizing a new collector for fluorite flotation from EvodiaeFructus oil by mixing sodium fatty acid and fatty acid amide. He evaluated the relationship between the flotation behavior and mechanism of the collector onto fluorite through micro-flotation tests, zeta potential, AFM measurements and quantum mechanics simulations. The flotation results showed that this synthesized collector could float fluorite very well in a pH range of 8.5~9.5 at the acid number of 120mgKOH/g and it exhibits excellent collecting capacity for fluorite even at low slurry temperature (6.5℃). AFM analysis data correlated with quantum mechanics simulation results showed that compared to sodium oleic acid or oleamide, their mixture has better chemical adsorption ability on fluorite surfaces.
You can find more information about this in his paper “Flotation Mechanism of a Novel Synthesized Collector from Evodiaefructus onto Fluorite Surfaces” in “Minerals Engineering” (SCI).
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