• 조명전기설비학회논문지
• /
• 제28권12호
• /
• pp.108-115
• /
• 2014

Recently, Uninterruptible power supply(UPS) is spotlighted from concern about black out, due to reserve power problem caused by increased power consumption. When fault occurs on the grid, UPS system supplies power to loads instead of the grid. Also, it is an advantage of possible operation as Energy storage system(ESS). Bi-directional power control of AC/DC Pulse width modulation(PWM) converter is essential for grid-connected UPS system. And, mode transfer control has to be performed considering phase and dynamic characteristic under grid condition. In this paper, control of mode transfer and bi-directional power control of AC/DC PWM converter is proposed for UPS system. Also, it is verified by simulation and experimental results.

• 수산해양기술연구
• /
• 제29권1호
• /
• pp.39-55
• /
• 1993

Modal Analysis is the process of characterizing the dynamic properties of an elastic structure by identifying its modes of vibration. A mode of vibration is a global property of an elastic structure. That is, a mode has a specific natural frequency and damping factor which can be identified from response data at practically any point on a structure, and it has a characteristic mode shape which identifies the mode spatially over the entire structure. Modal testing is able to be performed on structural and mechanical structure in an effort to learn more about their elastic behavior. Once the dynamic properties of a structure are known its behavior can be predicted and therefore controlled or corrected. Resonant frequencies, damping factors and mode shape data can be used directly by a mechanical designer to pin point weak spots in a structure design, or this data can also be used to confirm or synthesize equations of motion for the elastic structure. These differential equations can be used to simulate structural response to know input forces and to examine the effects of pertubations in the distributed mass, stiffness and damping properties of the structure in more detail. In this paper the measurement of transfer functions in digital form, and the application of digital parameter identification techniques to identify modal parameters from the measured transfer function data are discussed. It is first shown that the transfer matrix, which is a complete dynamic model of an elastic plate structure can be written in terms of the structural modes of vibration. This special mathematical form allows one to identify the complete dynamics of the structure from a much reduced set of test data, and is the essence of the modal approach to identifying the dynamics of a structure. Finally, the application of transfer function models and identification techniques for obtaining modal parameters from the transfer function data are discussed. Characteristics on vibration response of elastic plate structure obtained from the dynamic analysis by Finite Element Method are compared with results of modal analysis.

• International Journal of Air-Conditioning and Refrigeration
• /
• 제14권4호
• /
• pp.131-137
• /
• 2006

The absorber in which heat and mass transfer phenomena occur simultaneously is one of the most critical components in the absorption system. It has the most significant influence on the performance and the size of the absorption system. During the absorption process, heat and mass transfer resistances exist in both liquid and vapor regions, so that the heat transfer mode should be carefully selected to reduce them. The objective of this paper is to review the previous papers analysing mathematical models of simultaneous heat and mass transfer phenomena during the absorption process. The most conventional working fluids ($H_2O$LiBr and $NH_3/H_2O$) are considered and the most common absorption modes (falling film and bubble mode) are dealt with in this review.

• 한국지반공학회논문집
• /
• 제25권6호
• /
• pp.59-72
• /
• 2009

대구경 해상 말묵의 수평 하중전이 거동 및 변형 해석을 위해 p-y 하중전이 해석법이 널리 사용되고 있다. 그러나, 본 연구에서는, 기존의 p-y 해석법의 단점을 극복하여, 지반의 연속성을 고려한 수평방향 하중전이 해석을 고찰하였으며, 3D wedge failure mode의 이론적인 해법과 재하시험을 통해 말뚝의 실제 거동에 보다 부합되도록 연약지반의 p-y 곡선을 제안하였다. 제안된 하중전이함수법의 타당성을 검증하기 위하여 현장재하시험 사례와의 비교분석을 수행하였고, 그 결과 제안된 해석방법은 기존 p-y 곡선에 비해 대구경 해상말뚝의 거동 및 변형 특성을 적절히 예측함을 알 수 있었다.

• 대한전자공학회논문지TC
• /
• 제38권4호
• /
• pp.18-26
• /
• 2001

본 논문에서는 극성 판단(Polarity Decision) PD를 이용하여 모드 변환과 루프이득(Loop Gain)의 변환시점을 자동적으로 검출해 주는 ATC(Automatic Transfer mode Control)알고리즘을 설계하고 모드 전환시 안정적으로 주파수 오프셋을 추정하는 평균방식 Gear-shift PLL을 설계하였다. 제안하는 모드 전환 시점 검출 알고리즘인 ATC 알고리즘은 종전의 QPSK방식에 적용되던 Lock Detector 알고리즘보다 구현이 매우 간단하며 정확하게 모드 전환시점을 검출한다. 또한 Shift Register에 저장했던 주파수 추정 값들을 평균하는 평균전환방식은 모드 전환시 낮은 주파수 추정 에러값으로 다음 모드에서의 빠른 추적 성능을 가능하게 한다. 본 논문에서 제안하는 알고리즘은 적은 회로 면적과 고속 처리가 가능하도록 설계되어 ASIC 설계에 매우 유용하다. 아울러 본 논문에서는 극성판단 PD를 적용하여 위상 포착 및 추적 성능평가를 수행하고 성좌도(constellation)를 각 모드별로 분석하였다.

• Journal of Welding and Joining
• /
• 제25권5호
• /
• pp.58-63
• /
• 2007

The relationship between GMA welding conditions and the bead shape of overlay weld was studied by using ${\Phi}1.6mm$ hypo-eutectic metal-cored wire designed for hardfacing against the severe metal-to-metal wear. As the welding voltage increased, the dilution also increased but the sudden drop of dilution was observed at $30{\sim}33V$. It was considered to be due to the decrease of penetration resulting from the change of transfer mode, from short circuit to spray. It was also found that the behavior of penetration with welding current was dependant on the transfer mode. The short circuit mode exerted the penetration to decrease while the spray mode did it to increase with increase of welding current. The former was considered to be responsible for the remarkable decrease in dilution at low welding voltage region. The change of transfer mode also had an effect on the behavior of bead width with welding current but it did not on the bead spreadability defined as W/H ratio. It was considered that the optimal welding conditions for multi-pass overlay welding could be obtained from the bead spreadability suitable for bead lapping and the dilution as low as possible in the spray transfer mode.

• Ocean Systems Engineering
• /
• 제2권1호
• /
• pp.17-31
• /
• 2012

This study investigated the behavior of a non-isothermal $CO_2$ bubble formed through a leak process from a high-pressure source in a deep sea. Isenthalpic interpretation was employed to predict the state of the bubble just after the leak. Three modes of mass loss from the rising bubble were demonstrated: dissolution induced by mass transfer, condensation by heat transfer and phase separation by pressure decrease. A graphical interpretation of the last mode was provided in the pressure-enthalpy diagram. A threshold pressure (17.12 bar) was identified below which the last mode was no longer present. The second mode was as effective as the first for a bubble formed in deep water, leading to faster mass loss. To the contrary, only the first mode was active for a bubble formed in a shallow region. The third mode was insignificant for all cases.

• 한국유체기계학회 논문집
• /
• 제13권5호
• /
• pp.22-28
• /
• 2010

A study has been made of cool-down process on an incompressible fluid contained in a periodically oscillating cylinder when an abrupt cooling of wall temperature is imposed. Characteristics of flow and heat transfer are investigated along the variations of oscillating frequency and amplitude. One found the flow regimes are divided into 4-modes : 1 thermal island mode, 2 thermal island mode, 4 thermal island mode and asymmetry mode. Comprehensive analysis for each mode are given with a physical mechanism on cool-down process.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2009년도 춘계학술대회 논문집
• /
• pp.761-772
• /
• 2009

The introduction of KTX (Korea Train eXpress) provided passengers with a much faster mode of transport, and KTX has become a model railway system. Express railway stations are emphasized as public transit transfer centers, but their service evaluations were not performed appropriately so far. It is possible to know the level of service by developing valuation criteria for their evaluations. The evaluation of transfer centers mainly consists of two parts; connective service with other travel m odes, and transfer service inside transfer stations. Connection is defined as the inter-connection of multi-transportation vehicles, and transfer means that a passenger changes his travel mode to another. Such connective service and transfer service are evaluated by the level of service in terms of transfer facilities, the appropriateness of station layout and the quality of information throughout the facilities. We developed the service evaluation indicators of connective facilities and referred to the indicators of transfer facilities. We examined the 7 stations in Korea that are currently in operation and standardized the methodology of the evaluation process by applying the indicators suggested in this study.

• 소음진동
• /
• 제8권3호
• /
• pp.504-512
• /
• 1998

For analyzing the torsional vibration of a multiple stepped gear system containing a pair of triple gears, a transfer matrix model based on Hibner's branch method is developed and the natural properties of the branched rotor system are calculated with using the $\lambda$-matrix formulation. A Campbell diagram, in which the excitation sources caused by the mass unbalances of the rotors and the transmitted errors of thegearings are considered, shows that, at the neighborhood of the operating speed, there are the four critical speeds amplifying the first mode and the fifth mode. For the surpression of the gear box vibration, two ways are suggested by referring the mode shapes.