Jo Sep 16, 2025
In order to actively develop marine resources for sustainable economic development, it is necessary to identify the types, distribution locations and reserves of seabed mineral resources. All seabed work is impossible without seabed sample exploration, whether it is a study of seabed geological structure or seabed resource exploration.
Ri Jong Chol, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has designed a gravity corer with a spring release mechanism for re-identification of a seabed phosphorite distribution area, and determined the critical velocity before the free fall of the corer designed for sample seabed phosphorites at the depths of 1 000-2 000m.
He has found that the range of critical velocity increases with the increase in the mass of the corer and the decrease in the stiffness of the spring, and that it decreases with the length of a lever arm.
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Jo Sep 15, 2025
Calculation of riser for steel casting is more important than that for other alloy castings because of the high shrinkage and pouring temperature of cast steels, which leads to severe shrinkage defects.
Among the different calculation methods, the cubic equation method can be used to calculate the shape and dimensions of riser in parametric forms, but it is not widely used due to the large computational amount.
Numerical simulations of the solidification process of cast are more and more used in the design of casting process because of the economy of time and effort as well as the increased accuracy. Many researchers have studied the process of the flow and solidification processes of castings using ProCAST. Most of them, however, found the optimum values by constructing initial design schemes and repeating simulations and modifications. Also, the inclusion of excess mass in the riser is unavoidable, which reduces casting yield.
Hence, it is necessary to establish a methodology to determine the optimum size of the riser while saving the time for simulations.
Ri Hak Song, a researcher at the Faculty of Materials Science and Technology, has set the hydro-powered Pelton turbine blade casting as the main research project, and optimized the riser by combining the numerical simulation analysis by ProCAST with the cubic equation method.
He performed a calculation of the riser by the cubic method and a numerical simulation by ProCAST, a simulation tool for casting processes, to identify the most suitable riser.
The results of the study show that the yield of riser calculated by the cubic method does not differ significantly with the change in the shape of riser, but the elliptical shape is the optimum shape of the riser, with the ratio of height to width of 1.3 and the yield of riser of 67.5%.
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Jo Sep 14, 2025
Ozone water is made by dissolving into water the gaseous ozone generated during the discharge of oxygen or air or the electrolysis of water.
There are several methods for ozone water production from generated ozone gas, such as porous, bubble tower, U-tube, spray tower, Venturi tube, etc. Among them, venturi-based ozone mixers are widely used, due to their excellent features such as cost, performance, installation area, power consumption, etc.
One of the important ways to increase the concentration of ozone water in the venturi ozone mixer is to increase the amount of ozone gas inhalation into the gas intake. Previous studies only considered the pressure change or velocity change inside the venturi, but not much work has been done on the inhalation volume at the intake.
Rim Chol Bom, a researcher at the Institute of Nano Science and Technology, has determined the optimum geometry of a venturi tube for ozone water production through computational fluid dynamics (CFD) simulations.
The numerical results are inlet diameter of 40mm, throat diameter of 12mm, converging angle of 27° and gas inlet diameter of 7mm, with inhalation rate of 0.100 6g/s.
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Jo Sep 12, 2025
Polyester fibers currently represent more than half of fibers in global use, and the most commonly-used of them is polyethylene terephthalate (PET), which has continued to increase in its production. In addition, with the improvement in the people’s living standard, the use cycle of textiles is getting much shorter, which leads to the production of textile waste, reaching 90% of global fiber production. On the other hand, resource depletion and environmental pollution have become a serious problem, and people have been better aware of the environmental system, which has encouraged positive efforts to recycle textile waste.
There are three main ways to reuse waste textiles, namely, mechanical, physical and chemical methods. In the chemical method, polyester is decomposed into monomers or oligomers before being separated and purified to obtain desired chemical products. This is a complete fiber-fiber cycle technique that can produce new textile fibers from waste textiles. In the 2010s, some countries synthesized PET for textile fibers by applying the chemical method to PET waste plastics to produce clothing such as suits, shirts, etc. Chemical recycling methods of post-consumer PET include glycolysis, hydrolysis and others. In glycolysis, in particular, Bis(2-hydroxyethyl terephthalate) monomer (BHET) and oligomer are obtained by trans-esterification between diol and ester groups of PET.
Since BHET is used as a PET synthetic feedstock, many studies have been carried out on glycolysis of PET. However, previous studies addressed glycolysis of relatively clean PET waste, and little attention has been paid to PET waste fibers containing various impurities such as dyes.
Ri Myong Chol, a researcher at the Faculty of Materials Science and Technology, has investigated the preparation of BHET by glycolysis of PET textile waste under microwave irradiation.
The experimental results show that high purity BHET used as a precursor for PET synthesis can be prepared by pre-decolorization of PET textile and glycolysis of PET before recrystallization of BHET.
When PET textile and PET plastics are glycolyzed under the same reaction conditions, the conversion of PET and the yield of BHET are higher in the fiber than in the plastics. The reason lies in the fact that the depolymerization reaction rate gets faster in the PET fiber because the specific surface area of fiber is much larger than that of plastics and the molecular weight of PET fiber is lighter than that of PET plastics.
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Jo Sep 9, 2025
A converter that changes one AC power to another is called an AC/AC converter. The AC/AC converter has become a research topic in the field of power electronics because of its applications converting one AC voltage to another, including lighting control, soft start of induction motors, blowers and pumps.
An AC/AC converter has several conversion modes, among which the method of directly changing the input AC voltage to another AC voltage based on the operating principle of a direct buck-type DC/DC converter can implement PWM (Pulse Width Modulation) control to smoothly control the amplitude value of the output voltage.
O Yong Hun, a researcher at the Robotics Institute, has proposed a circuit planning for a buck-type direct AC/AC converter that can directly change AC voltage to lower AC voltage without the help of a transformer, based on the operation principle of a buck-type DC/DC converter. In addition, he has investigated the correlation between the several factors affecting the input and output waveforms under constant load conditions by means of MATLAB simulations.
The theoretical study and simulations of a buck-type direct AC/AC converter can be concluded as follows: The buck-type direct AC/AC converter is theoretically possible and is applicable at small-scale yield power levels (500W), but in order to achieve high power, efforts should be directed to circuitry and space isolation problems to prevent harmonic production rather than enlarging the capacitance of the output device.
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Jo Sep 5, 2025
Wind or solar power generation systems are at an early stage of equipment or technical cycle life, but hydroelectric facilities are typically older and operate with a mismatched assortment of hardware and controls, which are not optimized to work as a unified system.
The changes of many parameters that affect the efficiency of a plant make it difficult for operators to fully optimize it. Thus, if hydropower plants are operated and maintained by operators, they may affect the efficiency of the generating equipment.
This is the reason why the operation and maintenance management system of hydroelectric power plants should have high control performance, be reliable and inexpensive, and minimize personal intervention.
Ri Kyong Hyok, a researcher at the Faculty of Electrical Engineering, has built a fieldbus control system by CAN and an SCADA system by Ethernet using the CAN interface function, Ethernet interface function and 485 interface function of a microcomputer, and integrated these systems to realize an automation system for hydroelectric power plants.
To improve real-time control, he installed two CAN networks, and further enhanced the reliability of the field bus system by checking the measurement accuracy of control parameters and monitoring the communication status of CAN bus in real time.
His research results have laid a foundation for implementing an integrated automation system using CAN bus in various fields of industry as well as in hydropower plants.
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