Jo Jan 14, 2025
Water is an important basic material in the chemical industry and indispensable for human life. The world has witnessed a lot of progress in the research on the disinfection of water, which is closely related to the human life.
Generally, sterilizers used for water disinfection and wastewater treatment contain chlorine, hydrogen chloride, chlorine dioxide, ozone, hydrogen peroxide and ferrate. These sterilizers have been degraded due to the high cost and the release of substances harmful to the human body. In addition, their low disinfection effectiveness and short duration restrict their usage.
At present, there is a worldwide research to develop new chemical water treatment reagents with a strong disinfection effect and no harm to the human body, especially with a focus on potassium ferrate, one of the green multifunctional water treatment reagents.
Currently, commonly accepted methods for producing potassium ferrate include melting, electrolysis and wet methods. Among them, the wet methods are most widely used since the electrolytic and melting methods have some disadvantages such as high production cost, high power consumption and explosion risk.
One of the most important problems arising in the production of potassium ferrate is that it is stable in dry air but very unstable in aqueous or humid environments and it is easily decomposed. It is rapidly decomposed to release oxygen in acidic solutions and slowly decomposed in neutral or weak basic solutions. The rate of decomposition decreases as the salinity of the solution increases.
The main focus of the research on the production of potassium ferrate is to maximize its stability.
Ri Su Ryon, a researcher at the Faculty of Chemical Engineering, has examined the stability of the production of potassium ferrate widely used for water disinfection by using KI, K2SiO3 and K3PO4 as stabilizers. The experimental results show that the production of potassium ferrate is stabilized most when the amounts of KI, K2SiO3 and K3PO4 are 0.1%, 0.4%, and 0.4% of the total amount of reactants, respectively. She has also found that having dimethyl sulfoxide, methanol, diethyl ether as a detergent, it is effective to dehydrate first by using dimethyl sulfoxide and, subsequently remove the impurities such as KCl and KOH by using methanol before finally removing the remaining water and methanol by using diethyl ether. It has also been proved that when the washing temperature is lower than 20℃ and the number of washing is three, the potassium ferrate can be kept for a long time.
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Jo Jan 10, 2025
Time delay is one of the common cases in industrial processes such as chemical and metallurgical industries. The controlled value cannot reflect the dynamic change of systems under disturbances because of the existence of time delay. It also results in significant overshoot, longer settling time and even instability of the system. Therefore, the time-delay system (TDS) is more difficult to control.
A lot of control methods have been proposed to overcome the impact of time delay. The complexity of time-delay systems such as long time delay, nonlinearity, stochastic uncertainty and multivariable coupling characteristics limit the application of the existing control theories and methods to actual systems.
ADRC (active disturbance rejection control) is an effective method to solve the control problem of complex structure (nonlinearity, uncertainty, coupling, etc.) systems. The core idea of ADRC regards the integral form as a standard form of feedback system. System dynamics different from the standard form are treated as total disturbance including internal disturbance and external disturbance. A complex system with full disturbance, uncertainty and nonlinearity can be reduced to a linear, canonical form.
Several control strategies based on ADRC have been proposed to handle time delay. According to those strategies, it can be concluded that time delay parameter τ is of vital importance. However,τ may be a time-varying parameter changing with working conditions in real industrial processes.
Kim Ha Su, a researcher at the Faculty of Metal Engineering, has proposed a predictive active disturbance rejection control with adaptability (AD-PADRC) to solve the control problem of a time-varying delay system.
The proposed method is based on the integration of a PADRC and an estimation module for adaptive delay. First, a time-delay system is controlled by PADRC. Then, the time-varying delay is estimated via correlation technique. The minimum variance principle is used as a benchmark to monitor the control performance of a time-varying delay system under AD-PADRC.
The simulation results have proved the efficiency of AD-PADRC when the time delay changes on a large scale.
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Jo Jan 7, 2025
Induction heating (IH) converters commutate close to resonant frequency to supply maximum power to the workpiece. Therefore, the correct identification of the tank’s resonant frequency is a matter of vital importance in most IH converters. Detection of resonant frequency is based on the calculation of the phase-shift between two electric variables. In order to control this phase-shift between two electric variables, most IH converters use a PLL system.
Most PLL systems used in IH converters are analog PLLs that use integrated circuits from the CD4046 circuit family and analog low pass filters. Although analog control has demonstrated to be effective and accurate, it is less flexible and robust to the degradation of the components than digital control. Due to the advantages of digital control presented above, DSPs or field-programmable gate arrays (FPGAs) have been used to implement PLLs. But as hardware components are used, the change of components is needed in the case of changing parameters. In software PLL systems, many of the parameters used during the control, like frequency, dead time or filters, can be adjusted with no changes in hardware.
Kwon Chang Hyok, a researcher at the Faculty of Mechanical Science and Technology, has proposed a method for implementing the resonant frequency tracking control, the main control in IH systems used in various sectors of the national economy, by using a software PLL algorithm, conducted a simulation to evaluate the stability and reliability of control, and verified them through several experiments in the IH system with LLC.
The proposed software PLL algorithm can be applied to induction heating systems as well as to various fields where phase-shift control of both signal waveforms is necessary.
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Jo Dec 30, 2024
Generally, Least Squares (LS) Method treats only random errors of observation vector in adjustment function models. However, both observation vector and elements of coefficient matrix of adjustment function model contain random errors. Therefore, there is no guarantee that the result of adjustment by LS method is the global optimal solution.
Total Least Square (TLS) method is a primary estimation method that treats random errors of observation vector and coefficient matrix in adjustment functional models. Since TLS method takes into account both random errors of observation vector and coefficient matrix based on errors-in-variables (EVI) model, it is possible to improve the accuracy more than the result of LS method. Therefore, TLS method has been applied to different fields of science and technology including signal and image processing, computer vision, communication engineering and geodesy.
However, weighted total least square (WTLS) method has been applied less widely to geodetic network adjustment problems than to other fields.
Kim Jung Hyang, a researcher at the Faculty of Earth Science and Technology, has proposed an application method for the adjustment of triangulation network, based on the brief summarization of the algorithm of WTLS.
The key problem in the application of WTLS to the adjustment of geodetic network is to determine the weight matrix (or cofactor matrix) for the elements of coefficient matrix in the adjustment function model.
He proposed a method to determine cofactor matrix for errors of coefficient matrix and observation vector in triangulation network, and verified the effectiveness of the proposed method through an example applied to the simulation triangulation network.
You can find more information in his paper “Study on triangulation network adjustment by Total Least Square Method” in “ADVANCES IN GEODESY AND GEOINFORMATION” (SCI).
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Jo Dec 29, 2024
Airlift pumps, fluid machines for raising liquids or slurries through a vertical pipe by compressed air injected into the pipe near its mid position or lower end part, are widely used in the fields of deep seawater upwelling and seabed mining due to the advantages of simple structure, high reliability, convenient maintenance and low cost.
Therefore, many experimental studies have been conducted to clarify the air-water-solid three-phase flow characteristics of airlift pumps. Numerical and analytical studies have also been carried out to predict the performance of airlift pumps.
Rim Un Ryong, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has carried out a numerical analysis of steady air–water–solid three-phase flow as well as water–solid two-phase flow in the airlift pump, based on a one-dimensional multi-fluid model.
He calculated the depth distributions of 8 physical quantities such as volumetric fractions and axial velocities of all phases of gas, liquid and solid, air density and pressure by the governing equations or by integrating the vector form of nonhomogeneous ordinary differential equations for three-phase and two-phase flow intervals, respectively.
He applied the proposed method to the seabed mining in water depth of 2 000 meters and obtained the calculation results.
For further information, please refer to his paper “Numerical analysis of air–water–solid three-phase flow in airlift pump for seabed mining” in “Ocean Engineering” (SCI).
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Jo Dec 27, 2024
Nowadays, the numerical simulation method is an essential tool in the stability analysis of mining engineering, and it is important to ensure the accuracy and reliability of the mining engineering design to construct a numerical model used as a more realistic representation of the in situ situation.
Numerical simulation programs widely used for stability analysis of geotechnical and mining engineering structures are FLAC3D and ANSYS, etc.
Han Un Chol, a researcher at the Science Engineering Institute, has proposed a fast and convenient modeling technique by combining ANSYS and FLAC3D with unique advantages for numerical calculation and SURPAC suitable for 3D modeling.
First, he examined the relationships between the data structures of the model files for SURPAC, ANSYS and FLAC3D, and established the transformation technique of an integrated 3D solid model via Excel.
Then, he applied the proposed method to the analysis of the pillar stability for sublevel open stope method in the target mine.
Finally, he verified the validity and feasibility of the proposed model transformation technique.
You can find more information in his paper “Numerical analysis of pillar stability for safe mining of a combined mine based on three-dimensional solid model” in “CHALLENGES IN ROCK MECHANICS & ROCK ENGINEERING”, proceedings of the 15th ISRM Congress 2023 & 72nd Geomechanics Colloquium.
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