• 제목/요약/키워드: critical impulse

검색결과 64건 처리시간 0.029초

A Numerical Approach for Lightning Impulse Flashover Voltage Prediction of Typical Air Gaps

  • Qiu, Zhibin;Ruan, Jiangjun;Huang, Congpeng;Xu, Wenjie;Huang, Daochun
    • Journal of Electrical Engineering and Technology
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    • 제13권3호
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    • pp.1326-1336
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    • 2018
  • This paper proposes a numerical approach to predict the critical flashover voltages of air gaps under lightning impulses. For an air gap, the impulse voltage waveform features and electric field features are defined to characterize its energy storage status before the initiation of breakdown. These features are taken as the input parameters of the predictive model established by support vector machine (SVM). Given an applied voltage range, the golden section search method is used to compute the prediction results efficiently. This method was applied to predict the critical flashover voltages of rod-rod, rod-plane and sphere-plane gaps over a wide range of gap lengths and impulse voltage waveshapes. The predicted results coincide well with the experimental data, with the same trends and acceptable errors. The mean absolute percentage errors of 6 groups of test samples are within 4.6%, which demonstrates the validity and accuracy of the predictive model. This method provides an effectual way to obtain the critical flashover voltage and might be helpful to estimate the safe clearances of air gaps for insulation design.

The buckling of a cross-ply laminated non-homogeneous orthotropic composite cylindrical thin shell under time dependent external pressure

  • Sofiyev, A.H.
    • Structural Engineering and Mechanics
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    • 제14권6호
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    • pp.661-677
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    • 2002
  • The subject of this investigation is to study the buckling of cross-ply laminated orthotropic cylindrical thin shells with variable elasticity moduli and densities in the thickness direction, under external pressure, which is a power function of time. The dynamic stability and compatibility equations are obtained first. These equations are subsequently reduced to a system of time dependent differential equations with variable coefficients by using Galerkin's method. Finally, the critical dynamic and static loads, the corresponding wave numbers, the dynamic factors, critical time and critical impulse are found analytically by applying a modified form of the Ritz type variational method. The dynamic behavior of cross-ply laminated cylindrical shells is investigated with: a) lamina that present variations in the elasticity moduli and densities, b) different numbers and ordering of layers, and c) external pressures which vary with different powers of time. It is concluded that all these factors contribute to appreciable effects on the critical parameters of the problem in question.

패션제품의 충동구매행동에 관한 구조방정식 모델분석 (Analysis of Structural Equation Model on Impulse Buying Behavior for Fashion Products)

  • 박은주
    • 한국의류학회지
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    • 제29권9_10호
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    • pp.1306-1315
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    • 2005
  • Impulse buying has been considered a pervasive and distinctive phenomenon in the modern lifestyle and has been receiving increasing attention from consumer researchers and theorists. In the modern marketplace, spontaneous urges to buy and consume often compete with the practical necessity to delay the immediate gratification that purchasing provides. The purpose of this study is to conceptualize and test the framework of impulse buying behavior for fashion products using structural equation model. Data were obtained from 413 students attending universities during schedules classes in Busan. Analysis of the data, utilizing AMOS 4.1, supported most of the predictions. The results showed that situational variable(time available) and individual variable(fashion involvement) have direct effects on consumers' shopping emotions, including positive and negative emotion. Positive emotions had effects on all types of impulse buying(planned impulse buying, reminded impulse buying, and fashion-oriented impulse buying), while negative emotion affected two types of impulse buying(reminded impulse buying and fashion-oriented impulse buying). These emotional experiences influence impulse buying behaviors for fashion products serving as critical mediators. The findings suggest that time available and fashion involvement are good predictors mediated by shopping emotion to impulse buying behavior for fashion products. The implications of this research for future work on the shopping emotion and impulse buying behavior are discussed.

Study on the Chirped Waveform of the USPR Pulse using the Impulse Response of a Waveguide

  • Roh, Young-Su
    • 조명전기설비학회논문지
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    • 제24권3호
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    • pp.20-26
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    • 2010
  • In ultrashort-pulse reflectometry (USPR), a chirped waveform transformed from the USPR source impulse signal via waveguide makes it possible to employ millimeter-wave mixers for the frequency up-conversion process. Consequently, the frequency bandwidth of the USPR system is sufficiently wide to cover a large portion of the electron density profile of the plasma. Some physical aspects of the chirped waveform, such as maximum amplitude and length, are critical factors to determine the performance of the system. In this paper, the propagation of the USPR impulse signal through a rectangular waveguide is numerically studied to derive the chirped waveform using the impulse response of the waveguide. The results of numerical computation show that the chirped waveform significantly depends on the waveguide cutoff frequency as well as the waveguide length.

국부충격에 의한 전단건물의 손상곡선 (Damage Curves for the Shear Building to the Local Impact)

  • 이상호;황신우
    • 한국구조물진단유지관리공학회 논문집
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    • 제8권4호
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    • pp.247-256
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    • 2004
  • 하층충격에 의한 2층 전단건물의 손상곡선을 엄계변위를 발생시키는 하중최대치 비와 임펄스 비를 이용하여 작성하였다. 손상곡선 작성에 필요한 구조물의 거동파악은 하중과 임펄스 응답행렬의 합성곱을 이용하여 구하였으며, 합성곱에 필요한 임펄스응답행렬은 모드중첩법을 이용하여 구하였다. 작성된 손상곡선으로부터 하층충격에 의한 각층의 안전성은 상층은 하중의 최대치에 그리고 하층은 임펄스의 크기에 민감한 것으로 파악되었다.

막냉각에 의한 액체로켓엔진의 비추력 변화 (Specific Impulse Variation of a Liquid Rocket Engine by Film Cooling)

  • 조원국;박순영;설우석
    • 항공우주기술
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    • 제8권2호
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    • pp.133-139
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    • 2009
  • 가스발생기 사이클 액체로켓엔진의 비추력 성능 해석을 수행하였다. 본 해석 방법은 공개된 문헌의 추력 300톤급 엔진에 대한 개념설계와 비교하여 검증을 마쳤다. 막냉각을 증가시킴으로써 연료가 연소에 참여하는 비율이 감소될 수 있지만 재생냉각에 필요한 연료 펌프의 소요동력 감소를 통하여 엔진의 비추력이 증가될 수 있다. 개선된 조건은 막냉각의 도움을 통하여 연료펌프 헤드를 감소시키고 연소 압력을 높일 수 있음을 예시한다.

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Pulmonary Functions and Inflammatory Biomarkers in Post-Pulmonary Tuberculosis Sequelae

  • Shanmugasundaram, Kumar;Talwar, Anjana;Madan, Karan;Bade, Geetanjali
    • Tuberculosis and Respiratory Diseases
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    • 제85권2호
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    • pp.175-184
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    • 2022
  • Background: Post-tuberculosis (TB) sequelae is a commonly encountered clinical entity, especially in high TB burden countries. This may represent chronic anatomic sequelae of previously treated TB, with frequent symptomatic presentation. This pilot study was aimed to investigate the pulmonary functions and systemic inflammatory markers in patients with post-TB sequelae (PTBS) and to compare them with post-TB without sequelae (PTBWS) participants and healthy controls. Methods: A total of 30 participants were enrolled, PTBS (n=10), PTBWS (n=10), and healthy controls (n=10). Pulmonary function tests included spirometry and measurement of airway impedance by impulse oscillometry. Serum levels of matrix metalloproteinase (MMP)-1, transforming growth factor-β, and interferon-γ were estimated. Results: Slow vital capacity (SVC), forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), FEV1/FVC, and peak expiratory flow were significantly lower in PTBS as compared to controls. SVC and FEV1 were significantly less in PTBS as compared to PTBWS. Total airway impedance (Z5), total airway resistance (R5), central airway resistance (R20), area of reactance (Ax), and resonant frequency (Fres) were significantly higher and respiratory reactance at 5 and 20 Hz (X5, X20) were significantly lower in PTBS as compared to PTBWS. Spirometry parameters correlated with impulse oscillometry parameters in PTBS. Serum MMP-1 level was significantly higher in PTBS as compared to other groups. Conclusion: Significant pulmonary function impairment was observed in PTBS, and raised serum MMP-1 levels compared with PTBWS and healthy controls. Follow-up pulmonary function testing is recommended after treatment of TB for early diagnosis and treatment of PTBS.

웨이퍼 가공기에서 회전 원판의 동특성에 미치는 불균일 장력의 영향 분석 (Analysis of Non-uniform Tension Effect on Dynamic Characteristics of Spinning Circular Plates in the Wafer Cutting Machine)

  • 임경화
    • 소음진동
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    • 제8권2호
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    • pp.324-330
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    • 1998
  • The forced vibration analysis of the outer-clamped spinnig annular disk with arbitrary in-plane is formulated to investigate the influence of non-uniform tension on the cutting accuracy of wafer cutting machine. The arbitrary in-plan force along the outer edge of an annular plate is expressed as a Fourier series. Galerkin method and modal superposition method are employed to obtain the forced responses under the static force and the impulse force in astationary coordinate. Through qualitative and quantitative analyses, it can be found that forced and impulse responses are sensitive to the non-uniformity of in-plane force, which can bring a bad effect to the accuracy of wafer cutting process. Also, in case of a spinning disk with non-uniform in-plane force, critical speed is required to define in a different way, compared with conventional definition in axi-symmetrical spinning disk.

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동축 고온 초전도 케이블의 전류분포 및 mini-model 케이블의 전기절연 (The Characteristics of Current Distribution of a Coaxial HTS Cable and Insulation of Mini-model Cable)

  • 김영석;곽동순;백승명;김해종;김상현
    • 한국초전도저온공학회:학술대회논문집
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    • 한국초전도저온공학회 2003년도 학술대회 논문집
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    • pp.47-50
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    • 2003
  • In order to verify the extended theory, we have fabricated a two layers cable with the same twisting layer pitch. It was observed that almost all the operational current less than the critical current flowed on the outer layer because of its lower inductance. In case of operational current more than critical currents of layers, the flux flow resistances affect strongly current waveform and thereby the currents of layers were determined by the flux flow resistances. And we investigated withstand voltage, impulse voltage and breakdown characteristics of mini-model cable. In these test, the withstand voltage and impulse voltage test was satisfied and the breakdown voltage was 110kV.

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폴리머재료의 파괴인성치에 관한 연구 (A study on the Dynamic Fracture Toughness for Polymeric Materials)

  • 최영식;박명균
    • 대한안전경영과학회:학술대회논문집
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    • 대한안전경영과학회 2001년도 춘계학술대회
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    • pp.311-317
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    • 2001
  • The notched Charpy and Izod impact tests are the most prevalent techniques used to characterize the effects of high impulse loads on ploymeric materials. An analysis method for rubber toughened PVC is suggested to evaluate critical strain energy release rates(Gc) from the Charpy impact energy measurements. An Instrumented Charpy Impact tester was used to extract ancillary information concerning fracture properties in addition to total fracture properties and maximum critical loads. The stress intensity factor Kd was computed for varying amounts of rubber contents from the obtained maximum critical loads and also toughening effects were investigated as well.

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