• Journal of Advanced Marine Engineering and Technology
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• v.31 no.2
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• pp.138-144
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• 2007

The variation of the crankshaft speed in a multi-cylinder engine is determined by the resultant gas pressure torque and the torsional deformation of the crankshaft. Under steady state operation, the crankshaft speed has a quasi-periodic variation. For the diagnosis the engine instantaneous speed versus crankshaft angle is utilized. This paper describes a simple measurement method of the engine instantaneous speed versus crankshaft angle using the teeth on the flywheel of the crankshaft. Two non-contacting magnetic pickup combinations detect the crank angle and TDC position for the data acquisition. The results from experiments on a 6 cylinder marine diesel engine demonstrate that the crankshaft speed variation are detected with good resolution. And the crankshaft speed variation is investigated according to the operation conditions. Also, it is confirmed that the engine output measured by EMS can be evaluated larger than the actual value due to TDC position error caused by instantaneous speed variation.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.284-287
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• 2005

A fluidized bed reactor made of quartz with 0.055 m I.D. and 1.0 m in height was employed for the thermocatalytic decomposition of methane to produce $CO_2 - free$ hydrogen. The fluidized bed was proposed for the continuous withdraw of product carbons from the reactor. The methane decomposition rate with the carbon black N330 catalyst was quickly reached a quasi-steady state rate and remained for several hour. The methane decomposition reaction was carried out at the temperature range of $850-925^{\circ}C$, methane gas velocity of $1.0U_{mf}\;3.0U_{mf}$ and the operating pressure of 1.0 atm. Effect of operating parameters such as reaction temperature, gas velocity on the reaction rates was investigated. The produced carbon by the methane decomposition was deposited on the surfaces of carbon catalysts and the morphology was observed by SEM image.

• Journal of Power Electronics
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• v.9 no.5
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• pp.757-771
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• 2009

This paper proposes a systematic approach to the modeling of the small-signal characteristics of three-phase bridge boost rectifiers under non-sinusoidal conditions. The main obstacle to the conventional synchronous d-q frame modeling approach is that it is unable to identify a steady-state under non-sinusoidal conditions. However, for most applications under non-sinusoidal conditions, the current loops of boost rectifiers are designed to have a bandwidth that is much higher than typical harmonics frequencies in order to achieve good current control for these harmonic components. Therefore a quasi-static method is applied to the proposed modeling approach. The converter small-signal characteristics developed from conventional synchronous frame modeling under different operating points are investigated and a worst case point is then located for the current loop design. Both qualitative and quantitative analyses are presented. It is observed that operating points influence the converter low frequency characteristics but hardly affect the dominant poles. The relationship between power stage parameters, system poles and zeroes is also presented which offers good support for the system design. Both the simulation and experimental results verified the analysis and proposed modeling approach. Finally, the practical case of a parallel active power filter is studied to present the modeling approach and the resultant regulator design procedure. The system performance further verifies the whole analysis.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.791-793
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• 2009

Hydrogen has been recognized of the energy source for the future, in terms of the most environmentally acceptable energy source. A pressurized fluidized bed reactor made of carbon steel with 0.076 m I.D. and 1.0 m in height was employed for the thermocatalytic decomposition of methane to produce amount of $CO_2$ - free hydrogen with validity from a commercial point of view. The fluidized bed was proposed for withdrawing of product carbons from the reactor continuously. The methane decomposition rate with the carbon black N330 catalyst was rapidly reached a quasi-steady state and remained for several hour. The methane thermocatalytic decomposition reaction was carried out at the temperature range of 850 - 950 $^{\circ}C$, methane gas velocity of 2.0 $U_{mf}$ and the operating pressure of 1.0 -3.0 bar. Effect of operating parameters such as reaction temperature, pressure on the reaction rates was investigated and predicted the effect of a change in conditions on a chemical equilibrium thermodynamically, according to Le Chatelier's principle.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.93-93
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• 2009

실리콘 태양전지의 효율 향상을 위한 노력의 일환으로 결정질 실리콘 웨이퍼 표면passivation 물질 중 Atomic Layer Deposition (ALD)을 이용하여 증착한 $Al_2O_3$ 박막에 대한 관심이 증가하고 있다. 본 연구에서는 $Al_2O_3$ 박막의 증착 전 실리콘 웨이퍼의 산화막 두께에 따른 passivation 효과에 대해서 연구하였다. 실리콘 산화막은 $HNO_3$ 용액을 사용하여 화학적으로 생성시켰으며 $HNO_3$ 용액과의 반응 시간을 조절하여 실리콘 산화막의 두께를 조절하였다. 실리콘 산화막 생성 후 ALD로 $Al_2O_3$ 박막을 증착하였으며 증착 후 $N_2$ 분위기에서 annealing 하였다. Annealing 후 passivation 효과는 Quasi-Steady-State Photo Conductance를 사용하여 minority carrier의 lifetime을 측정하였다. Capacitance-Voltage measurement, Transmission Electron Microscopy, Ellipsometry를 사용하여 실리콘 산화막의 두께에 따른 $Al_2O_3$ 박막의 passivation 효과를 분석하였다.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.94-94
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• 2009

최근 실리콘 태양전지는 점점 얇아 지는 추세에 있다. 실리콘 태양전지에 있어 실리콘의 두께를 감소시키는 것은 실리콘 소모량을 줄이는데 있어 필수적인 조건이 되었다. 이에 따라 실리콘 표면의 passivation도 더욱 중요하게 여겨지고 있다. 실리콘 태양전지의 passivation막의 한 종류인 $Al_2O_3$는 다른 산화막 물질들과는 달리 negative fixed charge를 가지고 있고 charge의 양이 다른 산화막의 density보다 높아 p-type 실리콘의 경우 후면 passivation막으로 이용이 고려되고 있다. 본 연구에서는 atomic layer deposition으로 $Al_2O_3$막을 실리콘 위에 증착하여 열처리에 따른 그 특성을 비교하고 태양전지를 제작하였다. $Al_2O_3$막을 rapid thermal annealing을 통해 서로 다른 분위기에서 열처리 한 결과를 capacitance-voltage를 통해 측정하여 비교, 분석하였고 ellipsomety 분석을 통해 광학적 특성을 비교하였다. 또한 열처리 온도의 변화에 따른 $Al_2O_3$내에 charge에 변화가 있다는 것을 관찰하였다. 이러한 charge의 변화가 태양전지의 passivation에 영향을 주는지 관찰하기 위해 Quasi-steady state photoconductace를 통해 lifetime의 변화를 관찰 하였다. 이러한 실험결과로부터 열처리 분위기와 온도를 최적화 하여 태양전지 passivation 특성을 증가시킬 수 있었다.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.57-60
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• 2007

A fluidized bed reactor made of quartz with 0.055 m I.D. and 1.0 m in height was employed for the thermocatalytic decomposition of methane to produce $CO_{2}$ - free hydrogen. The fluidized bed was proposed for the continuous withdraw of product carbons from the reactor. The methane decomposition rate with the carbon black N330 catalyst was quickly reached a quasi-steady state rate and remained for several hour. The methane and propane mixture decomposition reaction was carried out at the temperature range of 850 - 900 $^{\circ}C$, methane and propane mixture gas velocity of 1.0 $U_{mf}$ ${\sim}$ 3.0 $U_{mf}$ and the operating pressure of 1.0 atm. Effect of operating parameters such as reaction temperature, gas velocity on the reaction rates was investigated. The produced carbon by the methane decomposition was deposited on the surfaces of carbon catalysts and the morphology was observed by SEM image.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.687-687
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• 2013

In rearpoint contact solar cell and the PERC (passivated emitter rear contact) type cell, surfaces were passivated by SiO2 or Al2O3 to increase solar cell efficiency. Therefore, we have investigated the effect of surface passivation for crystalline silicon solarcell using mass-production atomic layer deposited (ALD) Al2O3. The patttern which consists of cylinders with 100um diameter and 5um height was formed by PR patterning on Si (100) substrate and then Al2O3 of about 10nm and 20nm thickness was deposited by ALD. The pattern in 10 nm Al2O3 film was removed by dipping in aceton solution for about 10 min but the pattern in 20 nm Al2O3 film was not. The influences of process temperature and heat treatment were investigated using microwave photoconductance decay (PCD) and Quasi-Steady-State photoconductance (QSSPC). The solar cell process used in this work combines the advantage of using the applicability of a selective deposition associated with a ALD passivation and the use of low-cost screen print for the contacts formation.

• Computers and Concrete
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• v.26 no.3
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• pp.227-237
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• 2020

Strain rate investigations are needed to calibrate strain-rate-dependent material models and numerical codes. An appropriate material model, which considers the rate effects, need to be used for proper numerical modeling. The plastic concrete cut-off wall is a special underground structure that acts as a barrier to stop or reduce the groundwater flow. These structures might be subjected to different dynamic loads, especially earthquake. Deformability of a structure subjected to dynamic loads is a principal issue which need to be undertaken during the design phase of these structures. The characterization of plastic concrete behavior under different strain rates is essential for proper designing of cut-off walls subjected to dynamic loads. The Cowper-Symonds model, as one of the most commonly applied material models, complies well with the behavior of a plastic concretes in low to moderate strain rates and will be useful in explicit dynamics simulations. This paper aims to present the results of an experimental study on mechanical responses of one of the most useful types of plastic concrete and Cowper-Symonds constant determination procedures in a wide range of strain rate from 0.0005 to 107 (1/s). For this purpose, SHPB, uniaxial, and triaxial compression tests were done on plastic concrete samples. Based on the results of quasi-static and dynamic tests, the dynamic increase factors (DIF) of this material in different strain rates and stress state conditions were determined for calibration of the Cowper - Symonds material models.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.3
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• pp.27-34
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• 2001

This experimental study is to investigate the intermittent spray characteristics of the multi-hole diesel nozzle with a 2-spring nozzle holder. Without changing the total orifice exit area, its hole number varied from 3($d_n=0.42mm$) to 8($d_n$=0.25mm). Through the use of the 2-D PDPA(phase Doppler particle analyzer), the droplet diameter and the velocity of the diesel spray injected intermittently from the multi-hole nozzle into the still ambient were measured. And the calculations of time-resolved diameters, SMD and AMD were made. The results can be summarized as follows. The spray of the multi-hole nozzle consisted of three parts. These are the leading edge, the central part and the trailing edge. And most of droplets produced at the trailing edge of spray. In the spray flow field, the measuring position which represented the intermittent spray characteristics well was near the nozzle tip. But at the downstream of the spray, its characteristics disappeared, and spray behavior showed a quasi steady state regardless of the time evolution of the spray. The overall mean SMD of the spray increased with the spray development, and showed their maximum value near 1.5ms regardless of hole number.