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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Jo Oct 20, 2023
Ti2AlNb-based alloys have expansive application prospects in advanced automotive and aerospace fields because of their excellent mechanical properties such as high specific strength, good creep resistance at elevated temperature, low thermal expansion and inimitable combination of strength and elongation.
The deformation process of Ti2AlNb-based alloys is inevitably performed at high temperatures because of their limited plasticity at room temperature. Therefore, predicting the hot deformation behavior of Ti2AlNb-based alloys is quite important for numerical modeling of hot working processes.
In recent years, some scholars have constructed some constitutive models to predict the hot deformation behavior of Ti2AlNb-based alloys. Unfortunately, however, few endeavors have been devoted to developing and improving ZA model and KHL model for P/M Ti-22Al-25Nb alloys.
Sim Kyong Ho, a researcher at the Faculty of Materials Science and Technology, has developed improved m-ZA and KHL models which can accurately predict the hot deformation behavior of a fine-grained (FG) Ti-22Al-25Nb alloy fabricated from mechanically alloyed powder by spark plasma sintering.
First, in order to obtain true stress-strain curves of P/M Ti-22Al-25Nb alloy, he conducted isothermal uniaxial compression tests at different deformation conditions of 950 ~ 1 070 ℃ and 0.001 ~ 1 s-1.
Second, using the friction-corrected experimental data, he developed a modified Zerilli-Armstrong model and a Khan-Huang-Liang model in the α2+β/B2 + O triple-phase and α2 + B2 two-phase fields, respectively, and evaluated the predictability of the models.
Finally, based on the analysis of the reason for large deviation, he modified Zerilli-Armstrong and Khan-Huang-Liang models to consider the coupled effects of deformation parameters.
Conclusively, he drew the following conclusions.
First, the m-ZA and KHL models for the P/M Ti-22Al-25Nb alloy showed relatively good predictability at the reference deformation conditions. However, the prediction accuracy of the models was lowered in other deformation conditions.
Second, the improved versions of the m-ZA and KHL models exhibited enhanced prediction accuracy. R2 and AARE of the improved constitutive models were 0.989 6 and 6.14%, 0.989 1 and 6.82%, respectively.
Finally, in comparison with other constitutive models, the improved versions of the m-ZA and KHL models are very appropriate for engineering applications including numerical simulation and control for hot working processes of P/M Ti-22Al-25Nb alloy.
The details of this are found in his paper “Modified Zerilli-Armstrong and Khan-Huang-Liang constitutive models to predict hot deformation behavior in a powder metallurgy Ti-22Al-25Nb alloy” in “Vacuum” (SCI).
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Jo Oct 17, 2023
Han Un Chol, a researcher at the Science Engineering Institute, studied the structural influence of a connection block on the pressure impulse generated by the detonator and transmitted to a large number of shock tubes via a numerical simulation by using ANSYS AUTODYN code.
He employed two modes of connection block for initiating a bundle of shock tubes for his numerical simulations and experiments: One is a lateral initiation mode widely used in blasting practice, in which each shock tube surrounds the detonator, extending in parallel to the axis of the detonator body. The other is a frontal initiation mode where entrances of shock tubes are aligned at certain distances from the firing end of the detonator.
He compared the strength of a pressure impulse within the shock tubes numerically obtained for frontal initiation mode with that for lateral initiation mode.
Then, for frontal initiation mode, he observed the relationship between structural factors such as strength of a pressure impulse, materials and thickness of connector block bodies, and standoff distance between the firing end of the detonator and the inlets of shock tube.
The results showed that his study is useful for designing connector blocks of a frontal initiation mode for simultaneously initiating a large number of shock tubes.
His paper was presented in the 10th International Conference on Advanced Technologies.
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