• 대한기계학회논문집A
• /
• 제25권3호
• /
• pp.353-361
• /
• 2001

Recently the boundary element method has been developed swiftly. The boundary element method is an efficient and accurate means for analysis of two dimensional elastic crack problems. This paper is concerned with the evaluation and the prediction of the stress intensity factor(SIF) for the crack emanating from the circular hole using boundary element method-neural network. The SIF of the crack emanating from the hole was calculated by using boundary element method. Neural network is used to evaluate and to predict SIF from the results of boundary element method. The organized neural network system (structure of four processing element) was learned with the accuracy 99%. The learned neural network system could be evaluated and predicted with the accuracy of 83.3% and 71.4% (in cases of SIF and virtual SIF). Thus the proposed boundary element method-neural network is very useful to estimate the SIF.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
• /
• pp.500-504
• /
• 1997

Current source inverter drives of auto sequentially commutated type are very popular in high power applications, because of simple power circuit configuration with four quadrant operation. But the six-step current output create harmonic problems and the input power factor of such a drive is not always good. In this respect pulse width modulated drives using gate turn off thyristors ( GTO ) are finding application, especially in traction drives. However the switching and snubber loses of a GTO do not permit the inverter switching frequency go beyond a few hundred hertz.This will again introduce low frequency harmonic problems. Multi level inverters of the 3-level and 5-level can be considered as an alternative to overcome the low switching frequency harmonic problem of the 2-level GTO inverters. But with multi level inverters the complexity of the power circuit increases. In this paper a combination of multi level ( 2-level and 3-level ) inverters and multi phase induction motor ( 3-phase and 6-phase) configurations are presented for high power VSI drives for traction applications with reduced inverter switching frequency requirements coupled with reduced voltage rating for the power switch.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1995년도 추계학술대회 논문집 학회본부
• /
• pp.268-270
• /
• 1995

In crane drives, DC motor has been most widely used due to simple control characteristic and favorable transient behavior. Nowadays, however, the squirrel cage induction motor is known as an attractive candidate due to elimination of all sliding electrical contacts, resulting in an exceedingly simple and rugged construction. Especially, in hoist application, the smooth torque control and four quadrant operation are essential. In this paper, an operation of dual inverters with common DC bus fed by vector controlled induction motor is described. Single DSP is employed as a main processor to control dual inverters and communicates each input/output signal with PLC. As well as giving a detailed expression, full simulation and experimental results are presented.

• 한국통신학회논문지
• /
• 제11권5호
• /
• pp.340-348
• /
• 1986

변환을 이용한 2차원 zero-phase FIR 디지털 필터의 설계는 인기가 있고 잘 발전된 기술이나, 현재 설계된 4상한 대칭 필터의 형태는 원점에서 원거리의 주파수에서 정확하게 환상 대칭이 되지 못하는 단점을 가지고 있다. 적절한 급수의 확장 방법에 의한 변환을 이용하여 어떻게 다차원 필터에 대해 임의의 정확성을 갖는 대칭의 필요성이 만족되게 할 수 있는가를 보인다. 이러한 변환 방법으로써 일반적으로 McClellan 변환이 알려져 왔다. 본 논문에서는 원점으로부터 원거리의 주파수에서 훌륭한 환상 대칭이 되는 간단한 방법을 제시하였다. 이 방법은 1차원 필터로부터 2차원 환상 대칭 FIR디지탈 필터의 설계를 위해서 변형된 McClellan 변환을 이용하는 것으로써 band-pass 필터와 같은 다수의 cut-off 영역을 갖는 2차원 FIR필터의 설계에 매우 유용하다.

• 대기
• /
• 제25권4호
• /
• pp.591-600
• /
• 2015

We have analyzed wind and eddy covariance data collected within roughness sublayer over sloping terrain. The study site is located on non-flat terrain with slopes in both south-north and east-west directions. The surface elevation change is smaller than the height of roughness element such as building and tree. This study examines the directional wind shear for data collected at three levels in the lowest 10 m in the roughness sublayer. The wind direction shear is caused by drag of roughness element and terrain-induced motions at this site. Small directional shear occurs when wind speed at 10 m is strong and wind direction at 10 m is southerly which is the same direction as upslope flow near surface at this site during daytime. Correlation between vertical shear of lateral momentum and lateral momentum flux is smaller over steeply sloped surface compared to mildly sloped surface and lateral momentum flux is not down-gradient over steeply sloped surface. Quadrant analysis shows that the relative contribution of four quadrants to momentum flux depends on both surface slope and wind direction shear.

• 천문학논총
• /
• 제30권2호
• /
• pp.103-105
• /
• 2015

The 22 m diameter Mopra telescope in Australia is being used to undertake an improved survey of the CO J = 1-0 line at 3mm along the 4th quadrant of the Galaxy, achieving an order of magnitude better spatial and spectral resolution (i.e. 0.6 and 0.1 km/s) than the Dame et al. (2001) survey that is publically available for the Southern Galactic plane. Furthermore, the Mopra CO survey includes the four principal isotopologues of the CO molecule (i.e. $^{12}CO$, $^{13}CO$, $C^{18}O$ and $C^{17}O$). The survey makes use of an 8 GHz-wide spectrometer and a fast mode of on-the-fly mapping developed for the Mopra telescope, where the cycle time has been reduced to just 1/4 of a second. 38 square degrees of the Galaxy, from $l=306-344^{\circ}$, $b=0{\pm}5^{\circ}$ have currently been surveyed, together with additional 9 sq. deg. regions around the Carina complex and the Central Molecular Zone. We present new results from the survey (see also Burton et al., 2013, 2014). The Mopra CO data are being made publically available as they are published; for the latest release see the project website at www.phys.unsw.edu.au/mopraco.

• 대한치과의사협회지
• /
• 제9권12호
• /
• pp.791-795
• /
• 1971

Thirty-four children who were patients at the Pedodontic Department of Infirmary of Dental College, S.N.U., aged from 3 years 1 month to 6 years 10 months. One quadrant jaw was measured for each child, Each of the 5 teeth was measured in 6 specific areas, therefore, a total of 1,020 measurements were observed. The results were as follows: 1. Facial surface was the shallowest of all. It was 0.14 mm. shallower than lingual, 0.62mm. shallower than mesial, 0.98mm. shallower than distal. 2. The sulcus generally increased in depth from anterior to posterior. 3. The anterior segment in the maxilla was the shallowest of all. It was 0.68mm. shallower than posterior of maxilla, 0.08 mm. shallower than anterior of mandible, 0.63 mm. shallower than posterior of mandible. 4. The most frequent measurement observed in the both jws was 1.4mm. 5. The mean for the complete anterior segment in the maxilla was 1.3±0.50 mm. In the posterior segment of the maxilla, the mean was 2.0v0.74mm. In the mandible, the mean for the anterior segment was 1.4±0.46 mm. In the posterior segment of the mandible, the mean was 2.0±0.56 mm. 6. The mean gingival sulcus depth for the entire Primary Dentition was 1.7±0.59 mm.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
• /
• 제54권12호
• /
• pp.592-600
• /
• 2005

In this paper, a low loss magnetic levitation(Maglev) system is suggested and tested. The suggested Maglev system includes four hybrid magnets which consist of permanent magnet and coil. In the steady state, the levitated module system can be supported by attraction force generated by permanent magnet. The coil current controls only dynamic loads due to external disturbances. The module systems are designed by using finite element method(FEM) software tools such as MAXWELL and ANSYS. Also, digital control systems are designed to keep the magnet airgap at a constant value. The control systems include a VME(versa module europa)-based CPU(central processing unit) board, AD(analog to digital) board, PWM(pulse width modulation) board, 4-quadrant chopper, and sensors. In order to estimate the vertical velocity of the magnet, we use second order state observer with acceleration and gap signals as input and output signals, respectively. The characteristics of the suggested low loss Maglev system are demonstrated by experimental results showing coil current of 0A in the steady state of 3m airgap and performance specifications are satisfied for reference gap and force disturbance.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2015년도 추계학술대회 논문집
• /
• pp.225-226
• /
• 2015

이 논문에서는 ITER 초전도 코일 전원 장치 중 진공 용기내에 형성된 자장의 오차를 보정해주는 CCU/L 컨버터의 4 상한 운전을 위한 제어 알고리즘을 설명하고, 제어 알고리즘을 실제 컨버터에 적용하여 구현하였다. ITER CCU/L 컨버터는 4 상한 제어를 통해 영 전류 불연속 구간 없이 Correction Coil에 전압(${\pm}85V$), 전류(${\pm}10kA$)를 공급해야 하고, 이를 위해선 4 상한 운전을 위한 제어가 매우 중요하다. 4 상한 운전은 다섯 가지 모드에서 동작된다. 본 논문에서, 각 모드에 대해 설명하고, 컨버터가 각 모드에서 정상적으로 제어되는지 시뮬레이션 및 실제 시험을 통해 검증하였다.

• Pediatric Gastroenterology, Hepatology & Nutrition
• /
• 제22권6호
• /
• pp.619-623
• /
• 2019

We report the case of a seven-year-old boy with an ingested foreign body, which was retained within the appendix for a known duration of ten months, ultimately requiring appendectomy. The ingested foreign body was incidentally discovered by abdominal x-ray at an emergency room visit for constipation. Despite four bowel cleanouts, subsequent x-rays showed persistence of the foreign body in the right lower quadrant. While the patient did not have signs or symptoms of acute appendicitis, laparoscopic appendectomy was performed due to the risk of this foreign body causing appendicitis in the future. A small metallic object was found within the appendix upon removal. This case highlights the unique challenge presented by foreign body ingestions in non-verbal or developmentally challenged children and the importance of further diagnostic workup when concerns arise for potential retained foreign bodies.