• Journal of Power Electronics
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• v.13 no.2
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• pp.304-312
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• 2013

The most common power quality problems in distribution systems are related to unbalanced voltage sags. Voltage sags must be detected quickly and corrected in a minimum amount of time. One of the most widely used methods for sag detection is based on the d-q transformation. This method has the disadvantage of missing the detection of unbalanced faults, because this method uses a voltage sag level signal obtained from the average of 3 phases for sag detection. In this paper, an adaptive filter sag detection method is proposed for Dynamic Voltage Restorers (DVR) under unbalanced fault conditions. The proposed DVR controller is able to detect balanced, unbalanced and single phase voltage sags. A novel reference voltage generation method is also presented. To validate the proposed control methods, a 3-phase DSP controlling a DVR prototype with a power rating of 1.5-kVA has been developed. Finally, experimental results are presented to verify the performance of the proposed control methods.

• Journal of Power Electronics
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• v.15 no.3
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• pp.721-729
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• 2015

A sensorless control method was recently investigated in the robot and automation industry. This method can solve problems related to the rise of manufacturing costs and system volume. In a vector control method, the rotor position estimated in the sensorless control method is generally used. This study is based on a conventional full-order flux observer. The proposed full-order flux observer estimates both currents and fluxes. Estimated d- and q-axis currents and fluxes are used to estimate the rotor position. In selecting the gains, the proposed full-order flux observer substitutes gain k for the speed information in the denominator of the gain for fast convergence. Therefore, accurate speed control in a low-speed region can be obtained because gains do not influence the estimation of the rotor position. The stability of the proposed full-order flux observer is confirmed through a root-locus method, and the validity of the proposed observer is experimentally verified using a surface permanent-magnet synchronous motor.

• Journal of the Korean Society for Marine Environment & Energy
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• v.16 no.4
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• pp.255-262
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• 2013

The boltzmann equation is based on the particle distribution function while the Navire-Stokes equation based on the continuum theory. In order to simulate free surface flow, this paper used the Lattice Boltzmann Method of which is the discretized form. The detail study on the characteristics of the Lattice Boltzmann Method for the free surface simulation was investigated. The developed code was validated with the traditional dam breaking problem by tracking the front position of the water. A basic roles of density functions in the Lattice Boltzmann Method is discussed. To have an engineering applications, the simulation is also conducted the free surface behavior with an arbitrary wall geometry.

• Geomechanics and Engineering
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• v.5 no.6
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• pp.541-564
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• 2013

In this study, artificial neural networks (ANNs) were used to predict the settlement of pad footings on cohesionless soils based on standard penetration test. To achieve this, a computer programme was developed to calculate the settlement of pad footings from five traditional methods. The footing geometry (length and width), the footing embedment depth, $D_f$, the bulk unit weight, ${\gamma}$, of the cohesionless soil, the footing applied pressure, Q, and corrected standard penetration test, $N_{cor}$, varied during the settlement analyses and the settlement value of each footing was calculated for each method. Then, an ANN model was developed for each traditional method to predict the settlement by using the results of the analyses. The settlement values predicted from the ANN model were compared with the settlement values calculated from the traditional method for each method. The predicted values were found to be quite close to the calculated values. It has been demonstrated that the ANN models developed can be used as an accurate and quick tool at the preliminary designing stage of pad footings on cohesionless soils without a need to perform any manual work such as using tables or charts. Sensitivity analyses were also performed to examine the relative importance of the factors affecting settlement prediction. According to the analyses, for each traditional method, $N_{cor}$ is found to be the most important parameter while ${\gamma}$ is found to be the least important parameter.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.2
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• pp.124-129
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• 2005

This paper presents an advanced method for an initial pole position estimation of a Permanent Magnet Linear Synchronous Motor(PMLSM) that has an accurate incremental encoder for servo applications but does not have Hall sensors as a magnetic pole sensor. By appropriately using the secant method as a numerical method the proposed algorithm finds either of two zero force positions and then the correct d-axis by applying a q-axis test current. It only requires the tuned current controller and the relative position information md so it can be simply applicable to a rotary PMSM. The experimental results show the validity of the proposed method, which has an excellent performance with respect to an accurate pole position estimation under the minimal moving distance(average of about 85㎛) during the estimation process.

• Magazine of the Korean Society of Agricultural Engineers
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• v.8 no.1
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• pp.1011-1034
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• 1966

This thesis is the final report which has long been studied by the author to obtain the design basis for various hydrological constructions with the specific system suitable to the natural environmental conditions in Korea. This report is divided into two parts: one is to estimate runoff volume from watersheds and the other to estimate the peak discharge for a single storm. According to the result of observed runoff record from watersheds, it is known that Kajiyama formula is useful instrument in estimating runoff volume from watersheds in this country. But it has been found that this formula shows us 20-30% less than the actual flow. Therefore, when wihed to bring a better result, the watershed characteristics coefficient in this formula, that is, f-value, should be corrected to 0.5-0.8. As for the method to estimate peak discharge from drainage basin, the author proposes to classify it in two ways; one is small size watershed and the other large size watershed. The maximum -flood discharge rate $Q_p$ and time to peak Pt obtained from the observed record on the small size watershed are compared by various methods and formulas which are based upon the modern hydrological knowledge. But it was fou.d that it. was not a satisfied result. Therefore, the author proposes. tocomputate $Q_p$, to present 4.0-5.0% for the total runoff volume ${\Sigma}Q$.${\Sigma}Q$ is computed under the assumption of 30mm 103s in watershed per day and to change the theoritical total flow volume to one hour dura tion total flow rate when design daily storm is given. Time to peak Pt is derived from three parameters which are u,w,k. These are computed by relationship between total runoff volume (ha-m unit)and $Q_p$. (C.M.S. unit). Finally, the author checked out these results obtained from 51 hydrographs and got a satisfied result. Therefore the author suggested the model of design dimensionless unit-hydrograph. And the author believes that this model will be much available at none runoff record river site. In the large size watersheds in Korea when the maximum discharge occurs, the effective rainfall is two consequtive stormy days. So the loss in watershed was assutned as 6Omm/2days,and the author proposed 3-hour-daration hydrograph flow distribution percentage. This distribution percentage will be sure to form the hydrograph coordinate.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.9
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• pp.6-12
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• 1999

It is difficult to realize adaptive main carrier rejection circuit in feedforward-type LPA(Linear Power Amplifier) because the gain and nonlinear characteristics of power amplifier are changed according to operating frequency, voltage, temperature. Usually, pilot tones are used for adaptive LPA operation. but in this paper, the relative phase, which in obtained through I&Q demodulator using input signals as LO signals and main-path & sub-path signals as RF signals, and the magnitude of main-path & sub-path signals are compared, so main carrier rejection is obtained. The proposed method rejects main carriers by 28.34 ~ 34.66dB (@Po=36.2 ~ 28.2 dBm/tone) with two tones at 877MHz, 882MHz and also rejects main carriers by 31.3dB despite changing condition of operating voltage.

• Journal of Animal Reproduction and Biotechnology
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• v.37 no.4
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• pp.246-254
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• 2022

Current studies have revealed the capacity of mesenchymal stem cells (MSCs) in term of immunomodulatory properties, and this distinct potential is downgraded according to the disease duration of patients-derived MSCs. In order to enhance the immunomodulatory and anti-tumorigenic properties of the rheumatoid arthritis (RA) joints-derived MSCs, we aggregate synovial fluid-derived MSCs from RA joints (RA-hMSCs) into 3D-spheroids by the use of hanging drop culture method. Cells were isolated from synovial fluids of RA joints with longstanding active status over 13 years. For aggregation of RA-hMSCs into 3D-spheroids, cells were plated in hanging drops in 30 μL of advanced DMEM (ADMEM) containing 25,000-30,000 cells/drop and cultured for 48 h. To analyze the comparative immunomodulatory effects of 3D-spheroid and 2D monolayer cultured RA-hMSCs and then cells were cultured in ADMEM supplemented with 20% of synovial fluids of RA patients for 48 h and were evaluated by qRT-PCR for their expression of mRNA levels of inflammatory and anti-inflammatory markers. Cellular aggregation of RA-hMSCs was observed and cells were aggregate into a single sphere. Following treatment of RA patient's synovial fluids into the RA-hMSCs, spheroids formed RA-hMSCs showed significantly (p < 0.05) higher expression of TNFα stimulated gene/protein 6 (TSG-6) than the monolayer cultured RA-hMSCs. Therefore, the 3D-spheroid culture methods of RA-hMSCs were more effective than 2D monolayer cultures in suppressing inflammatory response treated with 20% of RA-synovial fluids by expression of TNFα (TSG-6) according to the immune response and enhanced secretion of inflammatory factors.

• Design & Manufacturing
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• v.13 no.2
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• pp.54-59
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• 2019

CNC(Computer Numerical Control) machine tools are being used in various industrial fields such as aircraft and automobiles. The machining conditions used in the mold industry are used, and the simulation and the experiment are compared. The tool used in the experiment was carried out to increase the reliability of the simulation of the cutting machining. The program used in the 3D-FEM (finite element method) was the AdvantEdge and predicted by down-milling. The tool model is used 3D-FEM simulation by using the cutting force, temperature prediction. In this study, we carried out the verification of cutting force by using a 3-axis tool dynamometer (Kistler 9257B) system when machining the plastic mold Steel machining of NAK-80. The cutting force experiment data using on the charge amplifier (5070A) is amplified, and the 3-axis cutting force data are saved as a TDMS file using the Lab-View based program using on NI-PXIe-1062Q. The machining condition 7 was the most similar to the simulation and the experimental results. The material properties of the NAK-80 material and the simulation trends reflected in the reverse design of the tool were derived similarly to the experimental results.

• Steel and Composite Structures
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• v.21 no.1
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• pp.177-194
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• 2016

The cable-supported ribbed beam composite slab structure (CBS) is a new type of pre-stressed hybrid structure. The standard construction method of CBS including five steps and two key phases are proposed in this paper. The theoretical analysis and experimental research on a 1:5 scaled model were carried out. First, the tensioning construction method based on deformation control was applied to pre-stress the cables. The research results indicate that the actual tensile force applied to the cable is slightly larger than the theoretical value, and the error is about 6.8%. Subsequently, three support dismantling schemes are discussed. Scheme one indicates that each span of CBS has certain level of mechanical independence such that the construction of a span is not significantly affected by the adjacent spans. It is shown that dismantling from the middle to the ends is an optimal support dismantling method. The experimental research also indicates that by using this method, the CBS behaves identically with the numerical analysis results during the construction and service.