• 한국추진공학회지
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• 제21권6호
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• pp.21-31
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• 2017

본 연구에서는 모드 천이가 발생하는 동안 상세한 유동 특성을 조사하기 위해, 이론분석과 수치해석을 수행하였다. 이론분석은 기존의 기체역학과 종래 보고된 이론식들 재정립하였으며, 수치해석은 2차원 비정상 압축성 Navier-Stokes 방정식을 풀기 위해 fully implicit finite volume scheme을 사용해 수행하였다. 해석의 검증을 위하여 실험 결과와 비교하였다. 격리부 입구 전온도와 수소 연료의 당량비를 변화시키면서 모드 천이에 미치는 영향을 조사하였다. 해석과 실험 결과는 정성적으로 잘 일치하였다. 당량비가 증가하면 스크램제트 모드에서 램제트 모드로 천이가 발생하였다. 이 때, 천이는 당량비에 따라 불연속적으로 나타나며, Non-allowable region이 존재하였다. 한편 격리부 입구에서 전온도의 증가는 모드 천이 경계를 변화시켰다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.814-819
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• 2003

Machine tool design concepts have evolved towards high efficiency, accurate precision. high structural integrity, and multi-functional systems. Like many other structures, machine tools are also composed of many parts. When these parts are assembled, many kinds of joints are used. In the finite element analysis of these assembled structures, most joints are commonly considered as rigid joints. But, to get the more accurate solution, we need to model these joints in a appropriate manner. In this study, rational dynamic modeling and analysis method for complex structures are studied with special attention to slide way joints. For modeling of slide way joints, a general modeling technique is used by influence coefficients method which is applied to the conversion of detailed finite element model to the equivalent reduced joint model. The theoretical part of this method is illustrated and the method is applied to the structure with slide way joint. In this method. the non-linearity of the contact surfaces is considered within a proper range and the boundary effect of the joint model can be eliminated. The proposed method was applied to finite element modal analysis of a clamp jointed cantilever beam and slide way joints of the vertical type lathe. The method can also be used to other kinds of joint modeling. The results of these analysis were compared with those of Yoshimura models and rigid joint models. which demonstrated the practical applicability of the proposed method.

• 한국전자파학회지:전자파기술
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• 제3권2호
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• pp.66-78
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• 1992

본 논문에서는 레이다 클러터 자료와 실험적 또는 이론적 모델을 모아 분서가였다. 원격탐사에 대한 자료와 모델이 폭넓게 연구되었는데 이는 비교적 세부적인 목표물에 대한 자료가 풍부한 장점이 있기 때문이다. 실제 레이다 설계에는 원격탐사에 사용되는 입사각 보다 큰 영역(near grazing angle)의 클러터 자료 및 모델이 필요한데 이에 대한 연구는 더 계속 되어야 한다.

• 대한전기학회논문지
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• 제35권12호
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• pp.560-566
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• 1986

In the design of an RF discharge system, the electrical equivalence of the gas discharge must be known. With this knowledge, one can design a suitable matching network for a maximum power transfer from the RF generator into the discharge. For this purpose, an experiment has been conducted in which the electrical impedance (conductance and capacitance) was determined as a function of power. In parallel with this, a detailed theoretical analysis has been done and the results are in accord with those of our experiment. Design equations are also given for a simple matching network, and a design example is presented to demonstrate its application. During the actual operation of an RF discharge system, however, it has been often observed that the reflected power tends to vary in small values due to the changes in the impedance of the system. This problem can be relieved by adding an automatic impedance matching circuit to the system and this paper presents such an automatic impedance matching network.

• Journal of Mechanical Science and Technology
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• 제15권5호
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• pp.656-664
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• 2001

A theoretical analysis is performed to describe the qualitative behavior of transient buoyant flows in a vertical channel. Consideration is given to the case of a fluid with a pre-existing stratification. The fluid motion is generated by giving impulsive anti-symmetric step-changes in temperature at the vertical left ad right sidewalls. The qualitative character of the flow is shown to be classified in the Rayleigh number (Ra)-Prandtl number ($sigma$) diagram. The transitory approach to the steady state can be monotonic or oscillatory, depending on ($sigma$-1)$^2$$pi$$^4$ 4$sigma$$R_a$. The prominent characteristics of time-dependent flow are discussed for large $R_a$. The profiles of temperature and velocity in the transient phase are depicted, which disclose distinctive time scales of motion. The transient process is shown to be sensitive to the Prandtl number. The detailed evolutions of flow and temperature fields are illustrated for large $R_a$.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.3-4
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• 2011

In this paper, a new pickup with compensation winding for KAIST OLEV is proposed. The proposed compensation winding increases induced voltage at a pickup and can be used for tuning of a pickup. The detailed theoretical analysis is given. It is expected to enhance the performance of OLEV pickup,

• 한국경영과학회지
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• 제41권2호
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• pp.1-16
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• 2016

Yield management, which originated from the U.S. service industry, uses pricing techniques and information systems to make demand management decisions. Demand uncertainty is an important factor in the area of demand management. A key strategy to reduce the effects of demand uncertainty is substitution. The most generally known type of substitution is inventory-driven substitution, in which consumers substitute an out-of-stock product by buying a similar or other type of product. Another type of substitution is the price-driven substitution, which occurs as a result of price changes. In this research, we consider two market segments that have unique perishable products. We develop yield management optimization models with stochastic demand based on the newsvendor model where inventory-driven and price-driven substitutions are allowed between products in the two market segments. The most significant contribution of this research is that it develops analytical procedures to determine optimal solutions and considers both types of substitution. We also provide detailed theoretical analysis and numerical examples.

• 한국자동차공학회논문집
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• 제7권7호
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• pp.136-148
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• 1999

Detailed mathematical models of hybrid drivertrain components are presented and numerical simulations are carried out to analyze the shift characteristics and to improve the driving comfortability when the hybrid drivetrain is applied at the vehicle . Theoretical results are compared with experimental ones from the dynamometer as same condition in order to prove the appropriateness of modeling . Adding the vehicle body modeling, included in the suspension and the engine mount, it is possible to predict the dynamic behavior and shift characteristics more actually when shifts are occurred by automated manual transmission(AMT). these additional results are also compared with the same simulation ones of internal combustion engined vehicle equipped conventional manual transmission. Hence, it can be expected that the hybrid vehicle with AMT has a good shift quality.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 B
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• pp.1079-1081
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• 2001

A propulsion system apparatus is needed for a railroad vehicle to test and estimate propulsion performance. The electrical inertia simulator to facilitate the development and testing of propulsion systems, is presented in this paper. It is based on a vector-controlled induction motor drive supplied from the AC mains through a double PWM converter that provides desirable features such as bi-directional power flow, nearly unity power factor and low harmonic factor at the AC mains. A theoretical analysis is first presented, followed by a detailed simulation study to assess the overall system performance under dynamic conditions.

• Current Optics and Photonics
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• 제2권1호
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• pp.96-100
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• 2018

A tunable low-phase-noise microwave generation structure that utilizes an optoelectronic oscillator (OEO) and a fiber Bragg grating (FBG) is proposed and experimentally demonstrated in this article. This structure has no particular requirement for the band width of the laser, and its tunability is realized through adjusting the central frequency of the tunable FBG. A detailed theoretical analysis is established and confirmed via an experiment. A high-purity microwave signal with a frequency tunable from 6 to 12 GHz is generated. The single-sideband phase noise of the generated signal at 10.2 GHz is -117.2 dBc/Hz, at a frequency offset of 10 kHz.