• 한국전기전자재료학회논문지
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• 제27권11호
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• pp.702-706
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• 2014

A comparative study has been attempted for microwave and conventional sintering of lead-free $Bi_{0.5}Na_{0.5}TiO_3(BNT)$-based multilayer ceramic actuators(MLAs). It was found that microwave sintering (MWS) could be successfully applied to the co-firing of piezoceramic/AgPd MLAs with a 10 times shorter firing cycle as well as $100^{\circ}C$ lower firing temperature ($850^{\circ}C$) for sufficient densification than conventional furnace sintering ($950^{\circ}C$). Furthermore, MWS-derived specimens showed better electric field-induced strain than that of CFS-derived specimens by effectively suppressing interdiffusions between ceramic and electrode layers.

• Journal of Advanced Marine Engineering and Technology
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• 제12권1호
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• pp.28-36
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• 1988

Since the oil shocks of 1970s, the quality of the fuel oil for marine diesel engines has become more degarded than ever. When the poorer quality fuel is burned, carbon residues of the fuel oil cause blockage of the fuel injection valve nozzle and troubles of fuel injection system. The mis-firing of engine occurs due to the decrease of fuel quantity injected, the decrease of compression pressure in the slow speed range, the increase of fuel leaked and the high ignition temperature of degraded fuel etc. This paper is to investigate theoretically the effects of mis-firing on the crankshaft axial vibration of diesel engine. The cylinder pressure in operation is calculated by the computer aided simulation of closed cycle for a large two-stroke diesel engine and also the exciting force of axial vibration and the resonance amplitudes are calculated. And then, the condition of normal state, misfiring and one-cylinder cut-off operation are analyzed. The results of calculations show good agreements with those of the actual measurements.

• The Journal of Advanced Prosthodontics
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• 제3권4호
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• pp.196-203
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• 2011

PURPOSE. This study evaluated marginal fit of glass infiltrated alumina cores fabricated using two techniques and their marginal stability after firing cycles of veneering porcelain. MATERIALS AND METHODS. Fifteen standardized all-ceramic crowns were fabricated on a metal die using each technique: slip cast technique of VITA In-Ceram sprint Alumina (Group A as control) and plastic foil matrix technique of Turkom-Cera fused alumina core system (Group B). Copings were compared between groups and within groups at coping stage and after firing each layer of veneering porcelain. A device was used to standardize seating of copings on the metal die and positioning of the specimens under the microscope after each stage of fabrication. The specimens were not cemented and marginal gap was measured using an image analyzing software (Imagepro Express) on the photographs captured under an optical microscope. Two tailed unpaired 't test' was used to compare marginal gaps in two groups and one way ANOVA was used to analyze marginal distortion within each group at 95% confidence interval. RESULTS. The marginal gap was smaller at the coping stage in group B ($60+30{\mu}M$) than group A ($81+21{\mu}M$) with statistical significance. After firing of veneering porcelain the difference was insignificant. At the final stage, both groups exhibited lower mean marginal gaps than at the initial coping stage with the difference of $11.75{\mu}M$ for group A and $11.94{\mu}M$ for group B, but it was statistically insignificant due to high value of standard deviation. CONCLUSION. Within the limitations of this study, it was concluded that both techniques produced copings with comparable and acceptable marginal fit and marginal stability on firing veneering porcelain.

• 한국추진공학회지
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• 제19권5호
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• pp.22-30
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• 2015

개방형 사이클의 액체로켓엔진에서는 추진제 중 일부를 연소시켜 터빈 구동용 가스를 생성시키는 가스발생기가 사용되며, 개방형 사이클 액체로켓엔진의 주요 구성품으로서 가스발생기 자체의 연소성능 및 특성을 파악하기 위한 연소시험이 요구된다. 하지만, 가스발생기에서 생성된 연소가스는 터빈 매니폴드의 터빈 노즐에서 질식이 이루어지기 때문에 가스발생기뿐만 아니라 터빈 매니폴드 내부 부피를 고려해야만 가스발생기의 연소 성능 및 특성, 그리고 음향 특성을 정확히 파악할 수 있다. 따라서, 본 논문에서는 터빈 매니폴드 모사장치를 이용한 가스발생기 연소시험 결과를 기술하고 가스발생기 단독 연소시험 결과를 이용한 특성 예측을 설명한다.

• 터널과지하공간
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• 제20권5호
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• pp.325-331
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• 2010

이 연구에서는 사암 벤치에 대하여 V형과 경사 V형의 두 가지 기폭 패턴으로 대규모 발파를 실시하였다. 장약량은 비슷하였다. 발파 후 디지털 이미지 프로세싱 방법으로 파쇄석의 파쇄도를 평가하였다. 10 $m^3$ 용량 로우프 쇼벨의 싸이클 시간도 계측하였다. 그 결과는 경사 V형으로 기폭한 경우 파쇄성능이나 굴착기 성과가 더 향상된다는 것을 보여준다. 이 논문에서는 경사 V형 패턴이 V 형 패턴보다 더 나은 성능을 보이는 이유에 대하여 논한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권8호
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• pp.3880-3899
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• 2019

Distributive desynchronization algorithms based on pulse-coupled oscillator (PCO) models have been proposed for achieving collision-free wireless transmissions. These algorithms do not depend on a global clock or infrastructure overheads. Moreover, they gradually converge to fair time-division multiple access (TDMA) scheduling by broadcasting a periodic pulse signal (called a 'firing') and adjusting the next firing time based on firings from other nodes. The time required to achieve constant spacing between phase neighbors is estimated in a closed form or via stochastic modeling. However, because these algorithms cannot guarantee the completion of desynchronization in a short and bounded timeframe, they are not practical. Motivated by the limitations of these methods, we propose a practical solution called PD-DESYNC that provides a short and deterministic convergence time using a flag firing to indicate the beginning of a cycle. We demonstrate that the proposed method guarantees the completion of desynchronization within three cycles, regardless of the number of nodes. Through extensive simulations and experiments, we confirm that PD-DESYNC not only outperforms other algorithms in terms of convergence time but also is a practical solution.

• 한국자동차공학회논문집
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• 제4권2호
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• pp.166-172
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• 1996

This paper presents the characteristics of the crankshaft speed fluctuations. To analyze them, the speed waveforms were measured both at the flywheel and at the front end of the engine. The speed waveform measured at the flywheel shows better result than at the front end one, because of the torsional vibration and the auxiliary components. And the patterns of the speed fluctuations are classified into three region, such as low load, middle load and high load region with the variations of the loads. Additionally, as the engine speeds increase and the loads decrease, the analysis of the speed becomes more difficult due to lower variation of the speed. And in all the regions, the main frequency component of the speed fluctuation is firing frequency.

• 한국유체기계학회 논문집
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• 제14권6호
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• pp.68-75
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• 2011

This study simulated the effect of steam injection on the performance and operation of a gas turbine combined heat and power (CHP) system. A commercial simple cycle gas turbine was analyzed. A full off-design analysis was carried out to investigate the variations in not only engine performance but also the operating characteristics of the compressor caused by steam injection. Variation in engine performance and operation characteristics according to various operation modes were examined. First, the impact of full steam injection was investigated. Then, operations aiming to guarantee a minimum compressor surge margin, such as under-firing and partial steam injection, were investigated. The former and latter were turned out to be relatively superior to each other in terms of power and efficiency, respectively.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.878-884
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• 2001

IGCC(Integrated Gasification Combined Cycle) power plant are becoming more attractive because of fuel flexibility and low emission. In this study, performances are evaluated when the low caloric value syngas fuels producted in gasification process is used a gas turbine originally designed naturel gas fuel. Using GateCycle computational thermal analysis model, performances of GE 7FA gas turbine are predicted for using four types of syngas. Also, off design performance is presented for firing syngas fuel in the gas turbine.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.665-670
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• 2004

This paper reviews the latest studies of the expander cycle Air Turbo Ramjet engine (ATREX) conducted in JAXA. First, a system analysis including the vehicle and trajectory was conducted to optimize the engine cycle and turbo-machine configuration. We selected the precooled turbo-jet cycle for a prototype engine using the near term technologies. Second, a system ground-firing test was conducted to verify a defrosting system for the precooler. Methanol injection with its particles atomization could compensate 80 % of pressure loss caused by the frost. Thirdly, a feasibility of carbon/carbon composites for the engine components was investigated by making complex shapes such as a heat exchanger and a plug nozzle. Basic technologies on the gas leakage, the junction and bonding were also studied. The end of the paper, some basic studies such as wind tunnel tests of a new type air inlet and a plug nozzle are described.