• 제목/요약/키워드: CONDITION FACTOR(K)

검색결과 2,646건 처리시간 0.029초

극저온 맥동 압력 조건에서의 재생기에 관한 실험적 연구 (Experimental Study on Regenerator Under Cryogenic Temperature and Pulsating Pressure Conditions)

  • 남관우;정상권;정은수
    • 대한기계학회논문집B
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    • 제26권8호
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    • pp.1095-1101
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    • 2002
  • An experimental apparatus was prepared to investigate thermal and hydrodynamic characteristics of regenerator at cryogenic temperature under pulsating pressure condition. The regenerator was pressurized and depressurized by a compressor with various operating frequencies. Cold end of the regenerator was maintained around 100 K by means of a liquid nitrogen heat exchanger. Instantaneous gas temperature and mass flow rate were measured at both ends of the regenerator during the whole pressure cycle. Pulsating pressure drop across the regenerator was also measured to see if it could be predicted by a friction factor at steady flow condition. The operating frequency of pressure cycle was varied between 3 and 60 Hz, which are typical operating frequencies of Gifford-McMahon, pulse tube, and Stilting cryocoolers. First, the measured friction factor for typical wire screen mesh regenerator was nearly same as steady flow friction factor for maximum oscillating Reynolds number up to 100 at less than 9 Hz. For 60 Hz operations, however, the discrepancy between oscillating flow friction factor and steady flow one was noticeable if Reynolds number was higher than 50. Second, the ineffectiveness of regenerator was directly calculated from experimental data when the cold-end was maintained around 100 K and the warm-end around 293 K, which simulates an actual operating condition of cryogenic regenerator. Influence of the operating frequency on ineffectiveness was discussed at low frequency range.

부스트-플라이백 결합형 ZCS Quasi-Resonant 역률개선 컨버터 (Integrated Boost-Flyback ZCS Quasi-Resonant Power Factor Preregulator)

  • 이준영;문건우;김현수;윤명중
    • 전력전자학회논문지
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    • 제4권1호
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    • pp.91-98
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    • 1999
  • 본 논문에서는 역률개선용 단일 스위치 부스트 플라이백 결합형 ZCS quasi-resonant converter(QRC)를 제안한다. 제안된 컨버터는 입력전류를 불연속 모드로 동작시켜 역률을 개선하며 입력전류의 zero-crossing-point에서의 왜곡을 개선함으로써 고조파를 감소시켜 역률을 향상시켰으며 좋은 출력전압의 regulation 성능을 가지고 있다. 그리고 체계적인 설계를 위하여 설계식을 제안하였으며 제안된 설계식을 통하여 프로토타입 컨버터를 설계하였다. 실험결과 효율은 약 86%, 역률은 약 0.985이상을 얻었다. 따라서 본 컨버터는 스위칭 주파수가 수백 kHz이상이고 높은 regulation성능을 요구하는 낮은 전압의 소용량 컨버터에 적합하다.

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차량의 흡기부밍소음 평가지수 개발 (Development of an Index for the Evaluation of Intake Booming Noise of a Passenger Car)

  • 박영원;채장범;장한기;이종규
    • 한국소음진동공학회논문집
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    • 제14권9호
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    • pp.884-890
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    • 2004
  • In this paper, an index for the evaluation of vehicle intake booming noise is developed through a correlation analysis of objective measurement data and subjective evaluation data. First, intake orifice noise is measured at the wide-open test condition. And then, acoustic transfer function between intake orifice noise and interior noise at the steady state condition is estimated. Simultaneously, subjective evaluation was carried out with a ten-scale score by 8 engineers. Next, the correlation analysis between the psycho-acoustic parameters derived from the measured data and the subjective evaluation is performed. The most critical factor was determined and the corresponding index for the intake booming noise is obtained from the multiple factor regression method. At last, the effectiveness of the proposed index is validated.

지중케이블 변전소의 고장전류 분류율과 접지전위상승 특성 (Characteristics of Fault Current Division Factor & Groud Potential Rise of a Substation fed exclusively by Power Cables)

  • 최종기;정길조;김선구
    • 대한전기학회:학술대회논문집
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    • 대한전기학회 1998년도 추계학술대회 논문집 학회본부A
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    • pp.295-297
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    • 1998
  • This paper shows characteristics of fault current division factor $S_f$, which is a ratio of earth- return current to total fault current, at a substation fed exclusively by power cables under unsymmetrical fault condition, such as single line-to-ground fault. In substation grounding system design, $S_f$ is a very important factor determining GPR, touch and step voltage at a substation under fault condition. In case of substations fed by overhead lines, 40-60% of $S_f$ has been typically used, although it is a very conservative value with no other network conditions considered. It is authors' hope that $S_f$ presented in this paper could hopefully be a basic reference in designing of substation grounding system, especially for a substation fed exclusively by power cables.

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Online condition assessment of high-speed trains based on Bayesian forecasting approach and time series analysis

  • Zhang, Lin-Hao;Wang, You-Wu;Ni, Yi-Qing;Lai, Siu-Kai
    • Smart Structures and Systems
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    • 제21권5호
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    • pp.705-713
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    • 2018
  • High-speed rail (HSR) has been in operation and development in many countries worldwide. The explosive growth of HSR has posed great challenges for operation safety and ride comfort. Among various technological demands on high-speed trains, vibration is an inevitable problem caused by rail/wheel imperfections, vehicle dynamics, and aerodynamic instability. Ride comfort is a key factor in evaluating the operational performance of high-speed trains. In this study, online monitoring data have been acquired from an in-service high-speed train for condition assessment. The measured dynamic response signals at the floor level of a train cabin are processed by the Sperling operator, in which the ride comfort index sequence is used to identify the train's operation condition. In addition, a novel technique that incorporates salient features of Bayesian inference and time series analysis is proposed for outlier detection and change detection. The Bayesian forecasting approach enables the prediction of conditional probabilities. By integrating the Bayesian forecasting approach with time series analysis, one-step forecasting probability density functions (PDFs) can be obtained before proceeding to the next observation. The change detection is conducted by comparing the current model and the alternative model (whose mean value is shifted by a prescribed offset) to determine which one can well fit the actual observation. When the comparison results indicate that the alternative model performs better, then a potential change is detected. If the current observation is a potential outlier or change, Bayes factor and cumulative Bayes factor are derived for further identification. A significant change, if identified, implies that there is a great alteration in the train operation performance due to defects. In this study, two illustrative cases are provided to demonstrate the performance of the proposed method for condition assessment of high-speed trains.

박용 구조물용 일반압연강 용접부의 피로균열 전파거동에 미치는 $K_{II}$의 영향 (Effects of $K_{II}$ on fatigue crack propagation behavior of wedzone in generally rolled steel for marine structure)

  • 한문식;김상철
    • Journal of Welding and Joining
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    • 제6권3호
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    • pp.43-55
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    • 1988
  • An experimental study was carried out to identify the fatigue fractue behavior of weld zone in generally rolled steel for marine structure. The bending an shear loads were applied simultaneously on the specimens to simulate real load condition for marine structure. The effect of the stress intensity factor under mode I with II loading condition on the initiation and the propagation of a crack were investigated, with particular emphaiss on mode II. When the $K_{II}$ stress intensiy factor in mode II was applied under mode I load condition, the growth behavior of a crack seems to be affected mainly by the anisotropic characteristic of materials. Especially, when the crack was located in and near the weld zone and parallel to th weld line, the propagation behaviour was turned out to be quite different from that of the base metal along the direction transverse to the weld line. In general, the propagation veiocity of the cracks in and near the weld zone was found to be slower that the velocity in base metal.

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부유체하부의 3차원 흐름해석을 위한 Rigid lid 경계조건의 적용 (Application of Rigid Lid Boundary Condition for Three Dimensional Flow Analysis beneath Floating Structure)

  • 홍남식
    • 한국해양공학회지
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    • 제26권5호
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    • pp.55-62
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    • 2012
  • In this paper, the rigid lid boundary condition is applied to simulate the influence of floating structures such as ships or pontoons, and the pressure term in both the momentum equations and continuity equation are modified. The pressure of a floating structure under the free surface is dependent on the draft of the structure, generally called a ship. If the free surface is covered by a floating structure, the free surface cannot move freely. The water level should be fixed, using a rigid lid boundary condition. This boundary condition is implemented by reducing the storage area of the grid cell with a factor between zero and one. The numerical model developed by Hong (2009) is verified through a comparison with experimental results, and the influence of the reduction factor is investigated using the verified numerical model.

Strength analysis of mechanical transmission using equivalent torque of plow tillage of an 82 kW-class tractor

  • Kim, Taek-Jin;Kim, Wan-Soo;Kim, Yeon-Soo;Chung, Sun-Ok;Park, Seong-Un;Hong, Soon-Jung;Choi, Chang-Hyun;Kim, Yong-Joo
    • 농업과학연구
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    • 제46권4호
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    • pp.723-735
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    • 2019
  • The power-train is the most important component of an agricultural tractor. In this study, the strength of the driving gear transmission of an 82 kW-class tractor was analyzed using equivalent torque during plow tillage. The load measurement system consisted of an engine revolution speed sensor, torque-meters, revolution speed sensors for four axles, and pressure sensors for two hydraulic pumps. The load data were measured during plow tillage for four speed stages: F2 (2.78 km/h), F5 (5.35 km/h), F7 (7.98 km/h), and F8 (9.75 km/h). Aspects of the gear-strength such as bending stress, contact stress, and safety factors were analyzed under two torque conditions: the equivalent torque at the highest plow load for the F8 speed stage and the maximum engine torque. The simulation results using KISSsoft showed that the maximum engine torque conditions had a lower safety factor than did the highest equivalent torque condition. The bending safety factors were > 1 at all gear stages, indicating that gear breakage did not occur under actual measured operating conditions, nor under the maximum torque conditions. However, the equivalent torque condition in the contact stress safety factor was > 1, and the maximum torque condition was < 1 at the first gear pair. The method of analysis using the equivalent torque showed lower stress and higher safety factor than did the method using maximum torque. Therefore, when designing a tractor by applying actual working torque, equivalent torque method would support more reliable product development.

A Novel Detection Algorithm for Instantaneous Voltage Sag Corrector Using Series Compensator

  • Lee, Sang-Hoon;Choi, Jae-Ho
    • 전력전자학회:학술대회논문집
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    • 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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    • pp.502-507
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    • 2001
  • This paper proposes a novel detection algorithm of faulted voltages under the unbalanced condition. To quantify the standard of unbalance under the faulted conditions, the 3-phase unbalanced voltages are decomposed into two balanced 3-phase symmetrical components of the positive and negative sequence voltages, which is defined by the magnitude factor (MF) and unbalance factor (MF). It is analyzed that MF and UF values are given as the dc constant values even though unbalance condition. This paper also proposes the control scheme of the instantaneous voltage sag corrector based on this detection algorithm. The validity of the proposed algorithm is verified through the EMTDC simulation and experiments.

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SOME RESULTS ON FRACTIONAL n-FACTOR-CRITICAL GRAPHS

  • Yu, Jiguo;Bian, Qiuju;Liu, Guizhen;Wang, Na
    • Journal of applied mathematics & informatics
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    • 제25권1_2호
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    • pp.283-291
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    • 2007
  • A simple graph G is said to be fractional n-factor-critical if after deleting any n vertices the remaining subgraph still has a fractional perfect matching. For fractional n-factor-criticality, in this paper, one necessary and sufficient condition, and three sufficient conditions related to maximum matching, complete closure are given.