• 한국수소및신에너지학회논문집
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• 제19권5호
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• pp.367-376
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• 2008

To obtain the data of the pressure loss and differential pressure at the inside of the stack that was composed of 126 cells with 7,500 cm2 electrode area, 75kW molten carbonate fuel cell system has been operated. Computational fluid dynamics was applied to estimate reactions and thermal fluid behavior inside of the stack that was adopted with internal manifold type separator. The pressure loss coefficient K showed 72.29 to 84.01 in anode and 6.34 to 8.75 in cathode at low part of cells at the inside of 75 kW MCFC stack respectively. Meanwhile, the pressure loss coefficient of the higher part of cells at the interior of the stack showed 15.36 and 56.44 in anode and cathode respectively. These results mean that there is no big total pressure difference between anode and cathode at the inner part of 75 kW MCFC stack. This result will be reflected in 250kW MCFC system design.

• 플랜트 저널
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• 제18권3호
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• pp.28-40
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• 2022

신재생에너지 발전 비중 확대가 예상됨에 따라 공공 발전사업자들은 바이오매스 혼소의 확대 시행을 적극적으로 검토해야 할 필요가 있다. 본 연구에서는 500MW 석탄화력에서 바이오매스 혼소율을 0wt.%에서 5.0wt.%까지 변화하며 미분기 주요 운전 특성을 측정하였다. 먼저, 목질계 바이오매스에 대한 구성성분 분석과 분쇄 특성을 알아보았고, 혼합연료의 부피 증가가 미분기 보울 압력 차이, 모터 전류, 이물질 처리횟수, 출구 온도, 내부 화재횟수에 미치는 영향을 분석하였다. 혼소율 증가에 따라 미분기 보울 압력 차이와 모터 전류, 이물질 처리횟수는 상승함을 확인하였고, 출구 온도는 상승 폭이 미미하였다. 내부 화재횟수는 명확한 상관관계를 찾기 힘드나, 다른 운전인자와 결합하여 발생할 가능성이 크다는 것을 확인하였다.

• 폴리머
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• 제31권1호
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• pp.31-36
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• 2007

플라스마 표면처리는 전체적인 물성은 유지하고 표면의 특성만을 변화시킨다고 전해지고 있다. 이번 연구에서는 플라스마 처리에 의해 높은 발수성을 나타내는 나일론 6 섬유로의 개질을 시도하였다. 발수성을 나타내는 나일론 섬유는 가스 종류, 처리시간, 인가 파워를 변수로 하여 RF 진공 플라스마 시스템에서 처리되었다. 플라스마 처리된 섬유의 표면을 scanning electron microscopy(SEM)과 atomic force microscopy(AFM)으로 모폴로지 변화를 살펴보았으며, 기계적 특성과 고분자 고유의 특성을 인장강도와 Differential scanning calorimetry(DSC), thermo-gravimetric analysis (TGA)로 각각 분석하였다. 또한 나일론 섬유의 발수성 평가는 물방울 흡수시간으로 테스트를 실시하였다. 이러한 결과들은 플라스마 표면처리로 인해서 나일론 섬유의 발수성이 향상됨을 나타내었다.

• Structural Engineering and Mechanics
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• 제42권5호
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• pp.715-728
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• 2012

This paper deals with determining the fundamental frequency of tall buildings that consist of framed tube, shear core, belt truss and outrigger systems in which the framed tube and shear core vary in size along the height of the structure. The effect of belt truss and outrigger system is modeled as a concentrated rotational linear spring at the belt truss and outrigger system location. Many cantilevered tall structures can be treated as cantilevered beams with variable cross-section in free vibration analysis. In this paper, the continuous approach, in which a tall building is replaced by an idealized cantilever continuum representing the structural characteristics, is employed and by using energy method and Hamilton's variational principle, the governing equation for free vibration of tall building with variable distributed mass and stiffness is obtained. The general solution of governing equation is obtained by making appropriate selection for mass and stiffness distribution functions. By applying the separation of variables method for time and space, the governing partial differential equation of motion is reduced to an ordinary differential equation with variable coefficients with the assumption that the transverse displacement is harmonic. A power-series solution representing the mode shape function of tall building is used. Applying boundary conditions yields the boundary value problem; the frequency equation is established and solved through a numerical process to determine the natural frequencies. Computer program has been developed in Matlab (R2009b, Version 7.9.0.529, Mathworks Inc., California, USA). A numerical example has been solved to demonstrate the reliability of this method. The results of the proposed mathematical model give a good understanding of the structure's dynamic characteristics; it is easy to use, yet reasonably accurate and suitable for quick evaluations during the preliminary design stages.

• 정보보호학회논문지
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• 제32권2호
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• pp.155-162
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• 2022

CHES 2020에서 제안된 SITM (See-In-The-Middle) 공격은 차분 분석과 부채널 분석이 조합된 분석 기법의 일종으로 SNR (Signal-to-Noise Ratio)이 낮은 열악한 환경에서도 적용할 수 있다. 이 공격은 부분 1차 또는 고차 마스킹으로 구현된 블록암호를 공격대상으로 하여, 마스킹 되지 않은 중간 라운드의 취약점을 이용한다. 블록암호 PRESENT는 CHES 2007에 제안된 경량 블록암호로, 저전력 환경에서 효율적으로 구현 가능하도록 설계되었다. 본 논문에서는 차분 패턴들을 이용하여 14-라운드 부분 마스킹으로 구현된 PRESENT에 대한 SITM 공격을 제안한다. 기존 공격은 4-라운드 부분 마스킹 구현된 PRESENT에 적용 가능했지만 본 공격은 더 많이 마스킹된 구현에도 유효하며, 이는 PRESENT가 본 공격에 내성을 가지기 위해서는 16-라운드 이상의 부분 마스킹이 필요함을 보인다.

• Ocean and Polar Research
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• 제28권4호
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• pp.385-393
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• 2006

Screening performance of the existing intake screens (drum and travelling screen) on mass impingement of marine animals, a euphausiid, Euphausia pacifica and a scyphozoan medusae, Aurelia aurita that have often clogged intake screens of the Uljin Nuclear Power Plant, was tested. The maximum tolerable densities of marine animals in the inflowing seawater upon the screen were estimated with two different approaches. First the maximum density of jellyfish was calculated from (1) passing amount of seawater per unit time through the screens and (2) the covered area of animals on the screens clogged. The maximum density of krill tolerable in the drum screen was cited from a simulated record of Uljin NPP, then those in the travelling screens were also calculated using the data of drum screen and ratio of seawater amount passing through the screens under the condition of 0.5m water column (W.C.) of the differential pressure (AP) produced by screens, an established permissible limit of ${\Delta}P$. Secondly, the screening performances were also tested by hydrodynamic measurements with various screen models in a circulating water channel equipped with a speed-controlling pump and a differential pressure gauge. From the first approach, the maximum tolerable densities of drum and travelling screen were calculated as 2.0 and $1.5ind/m^3$ for the Jellyfish and 900 and $680ind./m^3$ for the euphausiid, respectively. These densities estimated from the second approach were 2.1 and $0.8ind/m^3$ for the jellyfish and 1059 and $504ind/m^3$ for the euphausiid, respectively. These estimates were compared with the data from historic clogging events to evaluate the practical performance of these intake screens. The comparisons suggest a newly improved intake-screen of which performance should be at least seven times (approximately) better than the existing ones ior the krill and 3.2 times for the jellyfish, respectively, for preventing mass impingement, and for maintaining the condition of the differential pressure between the screens below 0.3 m W.C.

• Journal of Electrical Engineering and Technology
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• 제13권3호
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• pp.1251-1264
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• 2018

The systematic and effective design method of a Class-D current-source resonant inverter for use in an induction cooker with zero-ripple line current is presented. The design procedure is based on the principle of the Class-D current-source resonant inverter with a simplified load network model that is a parallel equivalent circuit. An induction load characterization is obtained from a large-signal excitation test-bench based on parallel load network, which is the key to an accurate design for the induction cooker system. Accordingly, the proposed scheme provides a systematic, precise, and feasible solution than the existing design method based on series-parallel load network under low-signal excitation. Moreover, a zero-ripple condition of utility-line input current is naturally preserved without any extra circuit or control. Meanwhile, a differential-mode input electromagnetic interference (EMI) filter can be eliminated, high power quality in utility-line can be obtained, and a standard-recovery diode of bridge-rectifier can be employed. The step-by-step design procedure explained with design example. The devices stress and power loss analysis of induction cooker with a parallel load network under large-signal excitation are described. A 2,500-W laboratory prototype was developed for $220-V_{rms}/50-Hz$ utility-line to verify the theoretical analysis. An efficiency of the prototype is 96% at full load.

• 정보처리학회논문지B
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• 제9B권4호
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• pp.421-428
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• 2002

지금까지 삽입(Embedding)백터를 이용한 국소적예측방법은 고차미분방정식으로부터 생성된 카오스 시계열을 예측할 때, 파라메타 $\tau$의 추정이 정확하지 않으면 예측성능은 떨어졌다. 지금까지 지연시간 ($\tau$)의 값을 추정하는 방법은 많이 제안되어있지만 실제로 고차원미분방정식부터 생성되어진 수많은 시계열에 모두 적용 가능한 방법은 아직 없다. 이것을 기울기 백터를 이용한 기울기 선형모델을 도입하는 것에 의해 정확한 지연시간 ($\tau$)의 값을 추정하지 않아도 예측성능에 만족할 수 있는 결과를 표시했다. 이것을 이론뿐이 아니고 경제시계열에도 적용해서 종래의 예측방법과 비교해서 그 유효성을 표시했다.

• 한국소음진동공학회논문집
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• 제26권1호
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• pp.75-81
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• 2016

In this study, a transfer matrix method in which can produce an infinite number of accurate natural frequencies using a single element for the bending vibration of rotating Bernoulli-Euler beam with linearly reduced width, is developed. The roots of the differential equation in the proposed method are calculated using the Frobenius method in the power series solution. To demonstrate the accuracy of the method, the calculated natural frequencies are compared with the results given by using the commercial finite element analysis program(ANSYS), and the comparison results between these two methods show the excellent agreement. Based on the comparison results, a parametric study is performed to investigate the effect of the centrifugal forces on the non-dimensional natural frequencies for rotating beam with the variable width.

• International Journal of Advanced Culture Technology
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• 제6권3호
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• pp.163-172
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• 2018

The power train of hydro-mechanical continuously variable transmission(HMCVT) for the middle class forklift makes use of an hydro-static unit, hydraulic multi-wet disc brake & clutches and complex helical & planetary gears. The complex helical & planetary gears are a very important part of the transmission because of strength problems. The helical & planetary gears belong to the very important part of the HMCVT's power train where strength problems are the main concerns including the gear bending stress, the gear compressive stress and scoring failures. The present study, calculates specifications of the complex helical & planetary gear train and analyzes the gear bending and compressive stresses of the gears. It is necessary to analyze gear bending and compressive stresses confidently for an optimal design of the complex helical & planetary gears in respect of cost and reliability. This paper not only analyzes actual gear bending and compressive stresses of complex helical & planetary gears using Lewes & Hertz equation, but also verifies the calculated specifications of the complex helical & planetary gears by evaluating the results with the data of allowable bending and compressive stress from the Stress - No. of cycles curves of gears. In addition, this paper explains actual gear scoring and evaluates the possibility of scoring failure of complex helical & planetary gear train of hydro-mechanical continuously variable transmission for the forklift.