Jo Dec 28, 2022
High-efficiency electric drive systems claim not only optimally designed electric machines but also efficiency-oriented control strategies.
Taking machines and drives into synergetic consideration, Jong Hak Chol, a section head at the Faculty of Electrical Engineering, has proposed a fresh particle crowd optimization (FPCO) of efficiency-oriented control algorithm called maximum outer torque per ampere (MOPA) control and maximum efficiency per ampere (MEPA) control, aiming to maximize the efficiency of interior permanent magnet synchronous machines in operation.
Differently from conventional id = 0 or maximum torque per ampere control, MOPA and MEPA fully consider the cross effect Core loss, iron loss, supplementary loss and mechanical loss.
In order to identify the accuracy of the efficiency-oriented control algorithm, he built an efficiency-oriented controlled system based on FPCO using nonsingular terminal sliding (NTS) controller, and on the basis of this, he inspected the stabilization of current trajectory and the voltage vector from simulation and testing. After that, he verified the higher effectiveness of MOPA and MEPA through the operation experiment of IPMSM whose capacity is 82 kW.
You can find more information about it in his paper “Fresh particle crowd optimization of efficiency-oriented control in interior permanent magnet synchronous motor during operation” published in the SCI Journal “International journal of power and energy conversion”.
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Jo Dec 25, 2022
Time-dependent deformations of rock are important factors for the design and construction of tunnels in the rock masses with time-dependent strength and deformation properties. Therefore, determination of the displacement and the stable time of tunnels is an indispensable task in geotechnical engineering, especially the design and construction of underground structures.
However, in some types of rock masses, tunnel displacement may increase for months or years after excavation owing to the rheological behavior of the surrounding rock masses, which greatly influences the selection of an initial tunnel support system, excavation layout, and determination of its load-carrying capacity.
Therefore, Han Un Chol, a researcher at the Science Engineering Institute, has made it possible to predict the final displacement of rock mass surrounding a tunnel, which is gradually stabilized in the shape of an S-type saturated curve by using the improved nonequidistant grey Verhulst model (INGVM) with Fourier series.
The traditional non-equidistance grey model (NGM(1,1)) and non-equidistance grey Verhulst model (NGVM) were compared to examine the feasibility of INGVM application. He only used the monitored displacements during excavation to predict the final displacement and stable time of the tunnel excabated in time-dependent rock mass.
The results showed that the proposed model was highly accurate and adaptable.
The details of this are carried in his paper “Prediction of Final Displacement of Tunnels in Time-Dependent Rock Mass Based on the Nonequidistant Grey Verhulst Model” published in the SCI Journal “Mathematical Problems in Engineering”.
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Jo Dec 23, 2022
Ozone is one of the strongest oxidizers and disinfectants, and it does not leave any residual toxin as it is decomposed into oxygen. That is why it has been widely used in domestic and industrial areas such as disinfection of drinking water and air, wastewater treatment, pulp bleaching, food processing, decolorization and deodorization.
A research team led by Kim Jong Guk, a researcher at the Nano Physics Engineering Institute, has developed enamel ozone tubes and different types of DBD ozone generators. The most effective and practical one of all ozone generation methods is dielectic barrier discharge (DBD), which generates non-thermal equilibrium plasma.
A DBD ozone generator consists of an ozone tube and high-frequency high-voltage power supply. The ozone tube has an enameled steel tube as an internal electrode and a stainless steel tube as an external electrode. It shows stronger resistance to thermal shock and better heat dissipation than glass or ceramic material.
Addition of nano-powders as mill additive increases adhesive strength, dielectric constant and dielectric strength, which ensures a long lifespan of the generator and produces high efficiency of ozone generation. Water cooling for internal and external electrodes effectively prevents temperature rise when the ozone tube discharges, thus ensuring safe operation and high ozone concentration output. By using high-frequency power supply and intelligent control system, ozone output can be changed on demand.
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Jo Dec 22, 2022
Apatite is an important mineral resource that plays an important role in many fields such as production of phosphoric acid and phosphate fertilizer.
Flotation technology is the most important method for beneficiation of apatite, and anionic fatty acid and their salt collectors are most-commonly used collectors in the direct flotation of phosphate ores.
Anionic fatty acid collectors have been proven both theoretically and in plant practice to be highly efficient in the flotation of apatite. Under basic conditions (pH10), fatty acid is saponified, which results in a negatively charged carboxylate ion. The negatively charged carboxylate ion then reacts with calcium on the apatite surface to form calcium carboxylate. This chemisorption method is generally considered to be the primary method of fatty acid adsorption onto the apatite surface in alkaline conditions.
Although a flotation mechanism of apatite using sodium oleate as a collector has been studied by several investigators, the flotation mechanism, reaction processes and associated surface reaction products still remain controversial.
Jong Kwang Sok, a researcher at the Faculty of Mining Engineering, synthesized a new collector for apatite flotation by a series of reactions including sulfation and amidation, using sodium oleate as raw material. Then, he carried out an investigation on the flotation behavior and mechanism of oleic acid amide onto apatite by micro flotation tests, zeta potential measurements, and XPS analysis.
The flotation results showed that mixing sodium oleate and oleic acid amide could float apatite well in a pH range of 7.5–9.5 even at the acid number of 120 mgKOH/g and it exhibited better collecting capacity on apatite than a sodium oleate collector. The XPS analysis data correlated with zeta potential showed that the zeta potential of apatite became more negatively charged at around pH8.5 and the oleic ions (C17H33COO−, (C17H33COO)22− and C17H33CONH−) in the mixing collector suspension could get chemisorbed by Ca-O bond formation on the apatite surface, and that the molecular (C17H33CONH2) and micelles ((C17H33CONH2)m) in oleic acid amide could get chemisorbed on the apatite surface by Ca-O or Ca-N bond formation.
You can find more information about this in his paper “Flotation mechanism of oleic acid amide on apatite” published in the SCI Journal “Colloids and Surfaces A: Physicochemical and Engineering Aspects”.
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Jo Dec 20, 2022
Kim Jang Hak, a section head at the Faculty of Distance Education, has proposed a new learning content model and a communication interface with interactivity and feedback structure considering the requirements and levels of learners while meeting the pedagogical requirements for distance education.
Generally, distance education system consists of three components, namely, learner, learning content and learning management system.
Learning-based interaction is mainly of three types, i.e. learner-content, content-management system and learner-management system.
Learning content consists of a content object and an interaction object with communication interface. The content object is Sharable Content Object (SCO) for teaching activities like lecture, experiment, practice, etc. The interface object is for interaction with learners through the communication interface and standardized communication with the management system.
If the structure of content is properly defined and standardized for interaction and feedback control, the reusability, extension and inter-operability of content can be ensured and it can be used in other management systems. The design of the content in hierarchical structure allows reuse of some of the content object in other contents.
On the basis of SCORM, the content model and learning object metadata are defined in the figure above. In the figure, “organization” is a learning unit and “item” is learning resources. “Resource” is a reference set, that is, SCO or asset of minimum unit. The root folder of the content has index.html, imsmanifest.xml, XSD and DTD, metadata.xml and resources. The content model is in imsmanifest.xml and metadata files.
Finally, he managed to form the content by adding communication interface with four control objects for interactivity and feedback control to the content model in hierarchical structure. The communication interface is made up of display control object, learning control object, communication control object and evaluation control object.
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Jo Dec 16, 2022
A research team led by Kim Tok Su, head of the Electric Power System Institute, and Mun Yong Guk, a section head at the same institute, has developed a flow meter which measures flow in real time in hydropower plants by using Winter Kennedy method.
Winter-Kennedy method utilizes a static pressure difference between the outside and the inside of a turbine spiral due to the centrifugal force acting on the curved streams of liquid in the spiral case.
The flow calculation formula in the flow meter using Winter Kennedy is Q=khn, where K is a constant coefficient and n is a power exponent which is theoretically equal to 0.5, but could be chosen between 0.48~0.51.
Generally, the values of the constant K can be determined experimentally by using flow Q measured by other standard flow meter. However, they have established a method of determining the coefficient K through FLUENT simulation.
They have introduced and examined the proposed flow meter in a generator. The result was n=0.497 9, K=0.057 and the maximum error compared with a standard flow meter was 0.616%.
As this simulation method is helpful to estimate power exponents and flow coefficients for any spiral cases, the flow meter can be used for all hydro power plants with a spiral case. It is simple in installation and it does not disturb fluid flow. Moreover, real-time measurement is possible with low cost but high accuracy.
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