• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2007년도 춘계학술대회 논문집
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• pp.473-477
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• 2007

The development of advanced Insulated Gate Bipolar Transistor(IGBT)has enabled high-frequency switching operation and has improved the performance of PWM inverters for motor drive. However, the high rate of dv/dt of IGBT has adverse effects on motor insulation stress. In many motor drive applications, the inverter and motor are separated and it requires long motor feds. The long cable contributes high frequency ringing at the motor terminal and it results in hight surge voltage which stresses the motor insulation. The inverter output filter and RDC snubber are conventional method which can reduce the surge voltage. In this paper, we propose the new low loss snubber to reduce the motor terminal surge voltage. The snubber consists of the series connection of charging/discharging capacitor and the voltage-clamped capacitor. At IGBT turn-off, the snubber starts to operate when the IGBT voltage reaches the voltage-clamped level. Since dv/dt is decreased by snubber operating, the peak level of the surge voltage can be reduced. Also the snubber operates at the IGBT voltage above the voltage-clamped level, the snubber loss is largely reduced comparing with RDC snubber. The proposed snubber enables to reduce the motor terminal surge voltage with low loss.

• 해양환경안전학회지
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• 제20권3호
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• pp.323-333
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• 2014

In this paper, the wakes behind a square cylinder were simulated using two kinds of different turbulence models for the eddy viscosity concept such as the zero- and the one-equation model in which the former is the mixing length model and the latter is the k-equation model. For comparison between numerical and analytical solutions, we employed three skill assessments: the correlation coefficient(r) for the similarity of the wake shape, the error of maximum velocity difference(EMVD) for the accuracy of wake velocity and the ratio of drag coefficient(RDC) for the pressure distribution around the structure. On the basis of the numerical results, the feasibility of each model for wake simulation was discussed and a suitable value for the empirical constant was suggested in these turbulence models. The zero-equation model, known as the simplest turbulence model, overestimated the EMVD and its absolute mean error(AME) for r, EMVD and RDC was ranging from 20.3 % to 56.3 % for all test. But the AME by the one-equation model was ranging from 3.4 % to 19.9 %. The predicted values of the one-equation model substantially agreed with the analytical solutions at the empirical mixing length scale $L=0.6b_{1/2}$ with the AME of 3.4 %. Therefore it was concluded that the one-equation model was suitable for the wake simulation behind a square cylinder when the empirical constant for eddy viscosity would be properly chosen.

• Journal of Oral Medicine and Pain
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• 제41권2호
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• pp.48-53
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• 2016

Purpose: The purpose of this study was to compare the differences in clinical signs and symptoms, and psychological profiles of temporomandibular joint osteoarthritis (TMJ OA) between juvenile and adult patients. Methods: Two-hundred eighty-three TMJ OA patients who visited the Orofacial Pain Clinic of Seoul National University Dental Hospital were classified by juvenile (153 patients; mean age $14.2{\pm}1.7$ years, range 9-16 years) and adult (130 patients; mean age $34.0{\pm}2.8$ years, range 30-40 years) groups, and compared the clinical symptoms based on the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) axis I guidelines including Graded Chronic Pain (GCP) scale, mandibular range of motion, and the associated symptoms. Psychological profiles were also evaluated using the Symptom Checklist 90-Revision (SCL-90-R). Results: Juvenile patients reported lower pain intensity and a lower prevalence of headache and clenching than adult patients. Their mandibular range of motion was also higher than adult patients. Juvenile patients showed a lower percentage of patients with T-score above 50 in somatization (SOM), obsessive-compulsive (O-C), interpersonal sensitivity (I-S), and paranoid ideation (PAR) than adults. Based on the GCP scale, the percentage of the high disability group was lower in juveniles. Conclusions: Juvenile TMJ OA patients generally showed milder clinical symptoms than adults. Adult patients showed higher prevalence of psychological problems and higher disability than juvenile patients. Age should be considered in evaluation and treatment of TMJ OA patients to achieve better treatment results and understanding its pathophysiology.

• 해양환경안전학회지
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• 제25권3호
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• pp.344-353
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• 2019

The wakes behind a square cylinder were simulated using two-equation turbulence models, $k-{\varepsilon}$ and RNG $k-{\varepsilon}$ models. For comparisons between the model predictions and analytical solutions, we employed three skill assessments:, the correlation coefficient for the similarity of the wake shape, the error of maximum velocity difference (EMVD) of the accuracy of wake velocity, and the ratio of drag coefficient (RDC) for the flow patterns as in the authors' previous study. On the basis of the calculated results, we discussed the feasibility of each model for wake simulation and suggested a suitable value for an eddy viscosity related constant in each turbulence model. The $k-{\varepsilon}$ model underestimated the drag coefficient by over 40 %, and its performance was worse than that in the previous study with one-equation and mixing length models, resulting from the empirical constants in the ${\varepsilon}-equation$. In the RNG $k-{\varepsilon}$ model experiments, when an eddy viscosity related constant was six times higher than the suggested value, the model results were yielded good predictions compared with the analytical solutions. Then, the values of EMVD and RDC were 3.8 % and 3.2 %, respectively. The results of the turbulence model simulations indicated that the RNG $k-{\varepsilon}$ model results successfully represented wakes behind the square cylinder, and the mean error for all skill assessments was less than 4 %.

• Biotechnology and Bioprocess Engineering:BBE
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• 제9권4호
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• pp.309-312
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• 2004

Aspergillus sojae B-l0 was immobilized and used to treat model dye compounds. The model wastewater, containing 10 ppm of azo dyes such as Amaranth, Sudan III, and Congo Red, was treated with cells attached to a rotating disc contactor (RDC). Amaranth was decolorized more easily than were Sudan III and Congo Red. Decolorization of Amaranth began within a day, and the dye was completely decolorized within 5 days of incubation. Both Sudan III and Congo Red were almost completely decolorized after 5 days of incubation. Semicontinuous decolorization of azo by reusing attached mycelia resulted in almost complete decolorization in 20 days. This experiment indicated that decolorization was successfully conducted by removing azo dyes with Aspergillus sojae B-10.

• 한국농공학회:학술대회논문집
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• 한국농공학회 1998년도 학술발표회 발표논문집
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• pp.287-292
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• 1998

The phenomena of local scour due to a current from a seadike closure gap which is protected by rock, then on to an erodible bed, have been studied. Based on the data of hydraulic model test, the scour characteristics have been investigated for the variation of maximum scour depth with time until reaching equilibrium stage and the shape of ultimate scour hole. A brief evaluation of DHL formula for the relationship between maximum scouring depth and time and a dimensionless form leading to time-scale introduced. On the basis of DHL formula, modified DHL formula denoted DHL-RDC formula is extend to the range of estimation of scour depth compared to DHL formula verified by model test.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.876-877
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• 2011

Variable Reluctance(VR) 레졸버는 엔코더를 대신해 Hybrid Electric Vehicle (HEV) / Electrical Vehicle(EV) 및 자동화 산업 전반에서 위치센서로써 사용되고 있다. VR 레졸버는 두 개의 출력신호(SIN, COS)를 발생시키며, Resolver-to-Digital Convert(RDC) 알고리즘을 통하여 위치신호로써 변환된다. 위치센서로써의 VR 레졸버는 무엇보다도 회전자의 정확한 위치를 찾아내는 것이 중요하다. 위치 정보의 오류를 발생시키는 원인으로는 다양한 것들이 있다. 본 논문에서는 VR 레졸버 형상을 변화시킴으로써 인해 레졸버를 통해 나온 출력신호에 포함된 각도정보의 정밀도 향상을 위해 FEM 해석을 통해 연구 및 분석 하였다.

• 산업경영시스템학회지
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• 제17권31호
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• pp.59-72
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• 1994

This paper deals with ordering policies of consumable goods which have large demand rates in a multi-level distribution system. The system we are concerned consists of one Central Distribution Center(CDC) and N non-identical Regional Distribution Centers(RDCs) which have different demand rates, minimum fillrates, leadtimes, etc. The customer demand on the RDC is stationary poisson and the RDCs demand on the CDC is superposition of Q-stage Erlang distributions. We approximate the RDCs and CDC demand distribution to nomal in order to enhance the efficiency of algorithm. The relevant costs include a fixed ordering cost and inventory holding cost, and backorder cost. The objective is to find a continuous-review ordering policy that minimizes the expected average costs under constraints of minimum fill rates of RDCs and maximum allowable mean delay of CDC. We developed an algorithm for determining the optimal ordering policies of the CDC and the RDCs. We verified and compared the performance of the algorithm through the simulation using the algorithm result as the input parameters.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2015년도 제46회 하계학술대회
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• pp.778-779
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• 2015

전동기의 위치센서로 Variable Reluctance(VR) 레졸버의 구동 방식은 1차 권선에 여자신호가 인가됨과 동시에 2차 권선 COS, SIN의 유기된 기전력을 발생시키며, RDC(Resolover-to-Digital Converter)를 이용함으로써 위치 신호를 출력한다. 위치센서로서의 레졸버는 전동기 회전자의 정확한 위치를 정밀하게 측정하는 것이 중요하다. 그러나 다양한 외란으로 인해 위치 정보의 오차가 발생하며 레졸버 설계시 회전자 형상에 따라 오차가 다르게 나타난다. 본 논문은 레졸버의 설계 및 특성 해석을 용이하게 하기 위해 Visual Basic tool을 이용하여 자동화 설계 및 특성 해석 프로그램을 구성하였다. 또한 프로그램을 이용하여 레졸버 회전자 형상 변화에 따른 인덕턴스 변화로 유기된 전압의 크기변화와 그에 따른 위치 오차율을 분석하였다.

• 한국작물학회:학술대회논문집
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• 한국작물학회 1998년도 21세기 한반도 농업전망과 대책(한국작물학회.한국육종학회 공동주관 심포지움 회보)
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• pp.24-40
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• 1998

This study attempts to make an observation on the problems and prospects for overseas agricultural investment(OAI) through the insights of farming and farmed companies abroad and through secondary data. OAI mainly aims at the securing steady supplies of crops, which could be anticipated to have increased foreign dependence, and to prepare for crop price fluctuations in the international markets. These functions of OAT are classified with the public and private sector. The public sector needs are largely crops supply for national food consumption and bilateral collaboration between nations. The private sector needs are to gain maximum profits from agricultural investments and to produce raw material for self-consumption in overseas farming companies. The problems in OAI are legal and institutional restrictions in the project area or nation; generally economical unfeasibility in the farm projects, and technical limitations of the farming companies. The prospects of OAI are not very promising. The reason why those many companies which previously planned on OAI changed their investment plans after what is called IMF system with financing difficulties.