• 제목/요약/키워드: Transient process

검색결과 794건 처리시간 0.033초

The characteristic analysis for polymer of household macromolecule fuel cell (가정용 고분자 연료전지의 중합체에 대한 특성해석)

  • Cho, Y.R.;Kim, N.H.;Han, K.H.;Yun, S.Y.;Baek, S.H.;Kim, I.N.
    • Proceedings of the KIEE Conference
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    • 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
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    • pp.1722-1724
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    • 2005
  • The focus of this paper is to develop a mathematical model for investigating the dynamic performance of a polymer electrolyte membrane fuel cell. The model in this work is based on physical laws having clear significance in replicating the fuel cell system and can easily be used to set up different operational strategies. Simulation results display the transient behavior of the voltage within each single cell, and also within a number of such single cells combined into a fuel cell stack system. A linear as well as a nonlinear analysis of the polymer electrolyte membrane fuel cell system(PEMFC) has been discussed in order to present a complete and comprehensive view of this kind of modeling. Also, a comparison of the two kinds of analysis has been performed. Finally, the various characteristics of the fuel cell system are plotted in order to help us understand its dynamic behavior. Results indicate that there is a considerable amount of error in the modeling process if we use a linear model of the fuel cell. Thus, the nonlinearities present in the fuel cell system should be taken into account in order to obtain a better understanding of the dynamic behavior of the fuel cell system.

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Study on the Electron Injection of Newly Synthesized Organic Sensitizer in Dye-Sensitized Solar Cell

  • Gang, Tae-Yeon;Lee, Do-Gwon;Go, Min-Jae;Kim, Gyeong-Gon
    • Proceedings of the Korean Vacuum Society Conference
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    • 한국진공학회 2009년도 제38회 동계학술대회 초록집
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    • pp.310-310
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    • 2010
  • Electronic and photovoltaic characteristics of two sensitizers (TA-BTD-CA and TA-BTD-St-CA), composed of a different $\pi$-conjugation in the linker group, have been investigated by theoretical and experimental methods. The electronic structure, transition dipole moment and oscillator strengths of two sensitizers have been scrutinized by using density functional theory (DFT) and time-dependent DFT (TD-DFT) method. The LUMO level and the oscillator strength of TA-BTD-St-CA was higher than that of TA-BTD-CA, which may facilitate the electron injection process as well as increase the absorption coefficient. The relative efficiencies of the electron injection from the excited sensitizer to nanocrystalline TiO2 and SnO2 films have also been investigated by nanosecond transient absorption spectroscopy. The relative electron injection efficiency of TA-BTD-St-CA exhibited similar injection efficiency for two different semiconductors. However, in the case of TA-BTD-CA sensitizer, electron injection into SnO2 was approximately three times larger than that into TiO2. This enhancement of electron injection of TA-BTD-CA for the SnO2 is due to the increment of the driving force caused by positive shift of conduction band of semiconductor, which was also confirmed from the investigation for the photovoltaic characteristics according to the electrolyte additive, such as LiI additive.

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Analysis of the Harmonic Resonance of Primary Restorative Transmission System Using PSCAD/EMTDC PART II (PSCADI/EMTDC를 이용한 시송전계통의 고조파 공진현상 분석 II)

  • Lee H. J.;Yoo W. K.;Lee K. S.;Park S. M.
    • Proceedings of the KIEE Conference
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    • 대한전기학회 2004년도 하계학술대회 논문집 A
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    • pp.48-50
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    • 2004
  • The energization of high voltage transmission lines and transformers, that is an inevitable process in most countries as the first restorative action for wide-area blackout, may induce overvoltages such as sustained overvoltage, transient overvoltage and harmonic resonant overvoltage. And these may cause damages to power system equipments or failure of surge arresters. The harmonic resonant overvoltage originates in switching operations and nonlinear characteristics of equipments. Actually it is difficult to predict the occurrence of harmonic overvoltage, since they result from nonlinear characteristics of transformers and other equipments. This paper describes the analysis of domestic primary restorative transmission system using PSCAD/EMTDC. The harmonic resonance is verified and the solution to prevent harmonic resonance is proposed in this paper. As a result, the PSCAD/EMTBC simulation showed slightly conflictive results that had been presented by IEEE Power System Restoration Working Group report.

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Supersonic and Subsonic Projectile Overtaking Problems in Muzzle Gun Applications

  • Gopalapillai, Rajesh;Nagdewe, Suryakant;Kim, Heuy-Dong;Setoguchi, Toshiaki
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 한국추진공학회 2008년 영문 학술대회
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    • pp.711-722
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    • 2008
  • A projectile when passes through a moving shock wave, experiences drastic changes in the aerodynamic forces as it moves from a high-pressure region to a low pressure region. These sudden changes in the forces are attributed to the wave structures produced by the projectile-flow field interaction, and are responsible for destabilizing the trajectory of the projectile. These flow fields are usually encountered in the vicinity of the launch tube exit of a ballistic range facility, thrusters, retro-rocket firings, silo injections, missile firing ballistics, etc. In earlier works, projectile was assumed in a steady flow field when the computations start and the blast wave maintains a constant strength. However, in real situations, the projectile produces transient effects in the flow field which have a deterministic effect on the overtaking process. In the present work, the overtaking problem encountered in the near-field of muzzle guns is investigated for several projectile Mach numbers. Computations have been carried out using a chimera mesh scheme. The results show that, the unsteady wave structures are completely different from that of the steady flow field where the blast wave maintains a constant strength, and the supersonic and subsonic overtaking conditions cannot be distinguished by identifying the projectile bow shock wave only.

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Modeling of combined thermal and mechanical action in roller compacted concrete dam by three-dimensional finite element method

  • Abdulrazeg, A.A.;Noorzaei, J.;Mohammed, T.A.;Jaafar, M.S.
    • Structural Engineering and Mechanics
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    • 제47권1호
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    • pp.1-25
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    • 2013
  • A combined thermal and mechanical action in roller compacted concrete (RCC) dam analysis is carried out using a three-dimensional finite element method. In this work a numerical procedure for the simulation of construction process and service life of RCC dams is presented. It takes into account the more relevant features of the behavior of concrete such as hydration, ageing and creep. A viscoelastic model, including ageing effects and thermal dependent properties is adopted for the concrete. The different isothermal temperature influence on creep and elastic modulus is taken into account by the maturity concept, and the influence of the change of temperature on creep is considered by introducing a transient thermal creep term. Crack index is used to assess the risk of occurrence of crack either at short or long term. This study demonstrates that, the increase of the elastic modulus has been accelerated due to the high temperature of hydration at the initial stage, and consequently stresses are increased.

Numerical Analysis on Letdown System Performance Test for YGN 3

  • Seo, Ho-Taek;Sohn, Suk-Whun;Jeong, Won-Sang;Seo, Jong-Tae;Lee, Sang-Keun
    • Proceedings of the Korean Nuclear Society Conference
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    • 한국원자력학회 1996년도 춘계학술발표회논문집(1)
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    • pp.425-432
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    • 1996
  • Integrated performance test of Chemical and Volume Control System (CVCS) was successfully performed in 1994. However, an extensive effort to correct hardware and software problems in the letdown line was required mainly due to the lack of adequate simulation code to predict the test accurately. Although the LTC computer code was used during the YGN 3'||'&'||'4 NSSS design process, the code can not satisfactorily predict the test due to its insufficient letdown line modeling. This study developed a numerical model to simulate the letdown test by modifying the current LTC code, and then verified the model by comparing with the test data. The comparison shows that the modified LTC computer code can predict the transient behavior of letdown system tests very well. Especially, the model was verified to be able to predict the "Stiction" phenomena which caused instantaneous fluctuations in the letdown backpressure and flowrate. Therefore, it is concluded that the modified LTC computer code with the ability of calculating the "Stiction" phenomena wi11 be very useful for future plant desist and test predictions.predictions.

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Hygrothermal effect on the moisture absorption in composite laminates with transverse cracks and delamination

  • Kesba, Mohamed Khodjet;Benkhedda, A.;Adda bedia, E.A.;Boukert, B.
    • Advances in aircraft and spacecraft science
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    • 제6권4호
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    • pp.315-331
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    • 2019
  • The stiffness degradation of the cross-ply composite laminates containing a transverse cracking and delamination in $90^{\circ}$ layer is predicted by using a modified shear-lag model by introducing the stress perturbation function. The prediction shows better agreement with the experimental results published by Ogihara and Takeda 1995, especially for laminates with thicker $90^{\circ}$ plies in which extensive delamination occurs. A homogenised analytic model for average transient moisture uptake in composite laminates containing periodically distributed matrix cracks and delamination is presented. It is shown that the model well describes the moisture absorption in a cross-ply composite laminate containing periodically distributed transverse matrix cracks in the $90^{\circ}$ plies. The obtained results represent well the dependence of the stiffness degradation on the crack density, thickness ratio and moisture absorption. The present study has proved to be important to the understanding of the degradation of the material propertiesin the failure process when the laminates in which the delamination grows extensively.

The Effect of External Attributes of Eco-Friendly Product on Perceived Values, Perceived Risk and Purchasing Intention : Focus on Organic Milk Product in China (친환경 제품의 외재적 속성이 지각된 가치, 지각된 위험 및 구매의도에 미치는 영향: 중국 유기농우유를 중심으로)

  • Piao, Xuexu;Park, Sang-Moon
    • Asia-Pacific Journal of Business
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    • 제10권1호
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    • pp.55-72
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    • 2019
  • Natural disasters and transient resource extraction cause new environmental problems and the waste of resources has also become a big problem. Because these kinds of environmental damage and pollution are harmful to human beings, the problem of environmental protection has become a global issue. In this situation, most consumers prefer Eco-Friendly products that benefit their health and can reduce environmental pollution as well. Businesses also try to develop marketing strategies that position products focused on the environment. At this point, the study has categorized extrinsic properties of Eco-Friendly products into brand images, the reliability of Eco-marks, advertisement views, and researches how the properties have effects on the perceived values and perceived risk in the process of consuming and how the perceived values and perceived risk have implications for purchasing intention. The consumer's perceived values are classified into emotional, social and Eco-friendly values. On the research of existing Chinese consumers or organic milk products, this study explains how the Chinese consumers make an assessment of the extrinsic property of Eco-Friendly products in the Chinese market and provide strategic implications to the Chinese market entrants.

Design, modelling and analysis of a new type of IPMC motor

  • Kolota, Jakub
    • Smart Structures and Systems
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    • 제24권2호
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    • pp.223-231
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    • 2019
  • The properties of Electroactive Polymer (EAP) materials are attracting the attention of engineers and scientists from many different disciplines. From the point-of-view of robotics, Ionic Polymer Metal Composites (IPMC) belong to the most developed group of the EAP class. To allow effective design of IPMC-actuated mechanisms with large induced strains, it is necessary to have adequate analytical tools for predicting the behavior of IPMC actuators as well as simulating their response as part of prototyping methodologies. This paper presents a novel IPMC motor construction. To simulate the bending behavior that is the dominant phenomenon of motor movement process, a nonlinear model is used. To accomplish the motor design, the IPMC model was identified via a series of experiments. In the proposed model, the curvature output and current transient fields accurately track the measured responses, which is verified by measurements. In this research, a three-dimensional Finite Element Method (FEM) model of the IPMC motor, composed of IPMC actuators, simultaneously determines the mechanical and electrical characteristics of the device and achieves reliable analysis results. The principle of the proposed drive and the output signals are illustrated in this paper. The proposed modelling approach can be used to design a variety of controllers and motors for effective micro-robotic applications, where soft and complex motion are required.

Short-term activation of synaptic transmission by acute KCl application significantly reduces somatic A-type K+ current

  • Song, Jung-Yop;Kim, Hye-Ji;Jung, Sung-Cherl;Kang, Moon-Seok
    • Journal of Medicine and Life Science
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    • 제15권2호
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    • pp.62-66
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    • 2018
  • A-type $K^+$ ($I_A$) channels are transiently activated in the suprathreshold membrane potential and then rapidly inactivated. These channels play roles to control the neuronal excitability in pyramidal neurons in hippocampi. We here electrophysiologically tested if regulatory functions of $I_A$ channels might be targeted by acute activation of glutamatergic synaptic transmission in cultured hippocampal neurons(DIV 6~8). The application of high KCl in recording solutions(10 mM, 2 min) to increase presynaptic glutamate release, significantly reduced the peak of somatic $I_A$ without changes of gating kinetics. This indicates that neuronal excitation induced by the enhancement of synaptic transmission may process with distinctive signaling cascades to affect voltage-dependent ion channels in hippocampal neurons. Therefore, it is possible that short-lasting enhancement of synaptic transmission is functionally restricted in local synapses without effects on intracellular signaling cascades affecting a whole neuron, efficiently and rapidly enhancing synaptic functions in hippocampal network.