• Title/Summary/Keyword: Critical Load

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A study on critical load due to external force influencing on flight characteristics of a small slender body rocket. (가늘고 긴 소형로켓의 비행특성에 영향을 주는 외력에 기인한 임계하중에 관한 연구)

  • Go, Tae-Sig;Na, Seon-Hwa
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.393-397
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    • 2007
  • The aim of this study is to investigate critical load, which can influence on flight path of a small slender body rocket, due to external forces such as thrust, drag and weight. The critical load was firstly obtained from Euler column equation, and compared with analysis results using Finite Element Method to evaluate the theoretical critical load.

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Design and Control Method for Critical Load Supply Equipment using MCFC Electricity Generation Systems (대용량 MCFC 발전시스템을 이용한 비상부하 전력 공급 장치 설계 및 제어방법)

  • Kim, Dong-Hee;Kim, Jong-Soo;Choe, Gyu-Yeong;Lee, Byoung-Kuk;Kawk, Cheol-Hoon
    • The Transactions of the Korean Institute of Power Electronics
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    • v.16 no.1
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    • pp.20-29
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    • 2011
  • This paper proposes critical load following back-up system using MCFC stack. This system enables MCFC generation system to supply power to critical load without UPS and to generate rated power under grid fault state. This back-up system includes 'Load Leveler' that is connected with 3-phase inverter and is controlled by additional algorithm that includes critical load following. The proposed system and algorithm are verified by computer simulation based on 5kW system.

Optimized LCL filter Design Method of Utility Interactive Inverter (계통연계형 인버터의 LCL필터 최적 설계기법)

  • Jung, Sang-Hyuk;Choi, Se-Wan
    • The Transactions of the Korean Institute of Power Electronics
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    • v.18 no.1
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    • pp.103-109
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    • 2013
  • The conventional LCL filter design method of the utility interactive inverter considers only harmonics attenuation of the current injected to the grid. However, in case of utility-interactive inverter with critical load the voltage quality of the critical load should also be considered for LCL filter design. Also, considering cost and volume of LCL filters. it is important to have minimum values of inductance and capacitance as far as the harmonic standards are satisfied. In this paper a LCL filter design method is proposed to satisfy not only the harmonic standards of the grid current during the grid-connected mode but the voltage quality of the critical load during grid-connected mode and stand-alone mode. With the proposed method optimized values of LCL filters could be obtained by applying weighting factor to voltage ripple across the critical load, inductor volume, amount of reactive current and system bandwidth.

ADHESION STUDIES OF MAGNETRON-SPUTTERED COPPER FILMS ON INCONEL SUBSTRATES

  • Lee, G.H.;Kwon, S.C.;Lee, S.Y.
    • Journal of the Korean institute of surface engineering
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    • v.32 no.3
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    • pp.410-415
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    • 1999
  • The adhesion strength of sputtered copper films to Inconel substrates has been studied using the scratch test. The effects of substrate treatments before deposition such as chemical or ion bombardment etching were investigated by means of a mean critical load derived from a Weibull-like statistical analysis. It was found that the mean critical load was very weak unless the amorphous layer produced by mechanical polishing on the substrate surface was eliminated. Chemical etching in a nitric-hydrochloric acid bath was shown to have practically no effect on the enhancement of the adhesion. In contrast, the addition in this bath of nickel and copper sulphates allowed removal of the amorphous layer and an increase in the values of the mean critical load. However, it was observed that excessive chemical etching could cancel out the mean critical load enhancement. The results obtained in the case of ion bombardment etching pretreatments could be far higher than those obtained with chemical etching. Moreover, for a sufficiently long period of ion bombardment etching, the adhesion strength was so high that it was impossible to observe evidence of an adhesion failure.

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Elastic Critical Load of Non-symmetrically Tapered Columns by Numerical Method (수치해석법에 의한 비대칭 변단면 기둥의 탄성 임계하중)

  • 신세욱;김선혜;이수곤
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.11-18
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    • 1999
  • For the proper design of a slender compression member, the exact determination of the elastic critical load is crucial, In the cases of non-prismatic compression members, the determinations of the elastic critical load cannot be usually expressed in closed forms. h this paper, the non-symmetrically tapered compression members with arbitrary boundary conditions me analysed by using the finite element method to determine the elastic critical load. The main parameters considered in the numerical analysis are the In Parameter, $\alpha$ and the sectional property parameter, m. To generaliza the unmerical analysis, of the computed results for each sectional parameter, m are presented in algebraic equations, which agrees fairy well with those by F.E.M in most cases.

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Anti-islanding Method by Harmonic Injection for Utility Interactive Inverter with Critical Load (중요부하를 갖는 계통연계형 인버터의 고조파주입에 의한 단독운전방지 기법)

  • Oh, Hyeong-Min;Choi, Se-Wan;Kim, Tae-Hee;Lee, Gi-Pung;Lee, Tae-Won
    • The Transactions of the Korean Institute of Power Electronics
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    • v.17 no.4
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    • pp.315-321
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    • 2012
  • The utility-interactive inverter with critical loads should supply continuous and stable voltage to critical loads even during the grid fault. The conventional control method which performs current control for grid-connected mode and voltage control for stand-alone mode undergoes the critical load voltage variation during grid fault. The critical load voltage may have large transient when the inverter performs mode transfer after the islanding detection. Recently, the indirect current control method which does not have the transient state during not only islanding detection but also the mode transfer has been proposed. However, since the voltage control is maintained even during the grid-connected mode it is difficult to detect the islanding. This paper proposes an active anti-islanding method suitable for the indirect current control method which does not have NDZ(Non-Detection Zone).

The Dynamic Buckling and Critical Load of the Spatial Truss under the Beating-wave Load (맥놀이하중을 받는 공간구조물의 동적좌굴과 임계하중)

  • Ha, Jun-Hong;Shon, Su-Deok;Lee, Seung-Jae
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.32 no.7
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    • pp.23-31
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    • 2016
  • In this study, the dynamic unstable phenomenon and critical load variation of the spatial truss under the beating-wave load were researched. For this purpose, a non-linear governing equation of a shallow spatial truss was derived. In addition, a dynamic analysis and a characteristic analysis of the buckling phenomenon were conducted using the numerical method. The analysis model was selected considering the number of free nodes and the rise-span ratio, and the response to the periodic parameter that determines the period of the beating function was analyzed. To compare the results, a analysis for the step load and sinusoidal-wave load were also conducted. Resonance was observed in the analysis results for both the sinusoidal-wave load and the beating-wave load. The patterns of critical load level were similar in the area lower than the natural frequency, but they were different in the area above it. Furthermore, the critical level of the beating-wave load changed more sensitively than the sinusoidal-wave load did and was much lower than the step load.

Evaluation of Joint Reaction Forces for a Hydraulic Excavator Subjected to a Critical Load (가혹하중이 작용하는 경우의 굴삭기 연결부의 반력계산)

  • Kim, Oe-Jo;Yu, Wan-Seok;Yun, Kyeong-Hwa;Gang, Ha-Geun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.4
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    • pp.1154-1163
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    • 1996
  • This paper presents a three dimensional modeling and dynamic anlaysis of a hydraulic excavator. An excavator is composed of a ground, an under-frame, two idlers, two spockets, an upper-frame, a boom, an arm, a bucket two yokes, two connecting rods, two boom cylinders, an arm cylinder, and a bucket cylinder. Each cylinder is modeled with two separate bodies which are linked to each other by a translational joint. The three dimensioanl model of the excavator consists of 22 bodies and each body is assumed as rigid. This paper suggested the maximum lifting capability, a critical load and reaction forces at joints form the DADS simulation. It was presumed that the reaction forces due to a critical load are three times bigger than those due to the maximum lifting capacity.

Effect of the WC particle size and Co content on the adhesion property between AIP-TiN coating and WC-Co substrate (AIP-TiN/WC-Co계에서 WC입자크기와 Co함량이 밀착력에 미치는 영향)

  • 한대석;류정민;권식철;김광호
    • Journal of the Korean institute of surface engineering
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    • v.35 no.3
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    • pp.165-171
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    • 2002
  • TiN coating were deposited onto different WC-Co substrates using arc ion plating (AIP) technique. The structure and morphology for the deposited coating were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The adhesion behavior of the deposited TiN coating was investigated with a conventional scratch test. Effects of WC particle size and Co content on the adhesion strength between the deposited TiN coating and substrate were studied. During the scratch test, the value of critical load was dependent of WC particle size and Co content on substrate. As the WC particle size and Co content on substrate decreased, the critical load increased. The highest critical load, approximately 110N, was obtained at WC particle size of 1$\mu\textrm{m}$ and Co content of 10wt.%.

The Relationship between Critical Load and Frequency of Sinusolidally Non-symmetrically Tapered Member (정현상 비대칭으로 Taper진 부재의 임계하중과 고유진동수와의 관계)

  • Lee, Hyuck;Hong, Jong-Kook;Lee, Soo-Gon
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.59-66
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    • 2000
  • It is generally known that the lateral frequency( ω) of the vibration of a prismatic beam-column decreases according to the rele (equation omitted) (ω/sub 0/=natural frequency). In the cases of tapered members, the determination of P/ sub/ cr/(elastic critical load) and ω/ sub 0/ are not easy. Furthermore, the relationship between the compressive load and frequency can not be determined by the conventional analytical method. The axial force-frequency relationship of sinusolidally non-symmetrically tapered members with different shapes were investigated using the finite element method. To obtain the two eigenvalues, the axial thrust was increased step by step and the corresponding frequency was calculated. The result indicated that the axial thrust of the elastic critical load ratio and the square of the frequency ratio can be approximately represented in any case by a straight line. Finally, the linear relationship is also applicable to the sinusolidally non-symmetrically tapered member.

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