• Title/Summary/Keyword: 회로 모델링

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Modified Thermal-divergence Model for a High-power Laser Diode (고출력 레이저 다이오드 광원의 열저항 개선을 위한 하부층 두께 의존성 수정 모델)

  • Yong, Hyeon Joong;Baek, Young Jae;Yu, Dong Il;O, Beom Hoan
    • Korean Journal of Optics and Photonics
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    • v.30 no.5
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    • pp.193-196
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    • 2019
  • The design and control of thermal flow is important for the operation of high-power laser diodes (LDs). It is necessary to analyze and improve the thermal bottleneck near the active layer of an LD. As the error in prediction of the thermal resistance of an LD is large, typically due to the hyperbolic increase and saturation to linear increase of the thermal resistance as a function of thickness, it is helpful to use a simple, modified divergence model for the improvement and optimization of thermal resistance. The characteristics of LDs are described quite well, in that the values for simulated thermal resistance curves and the thermal cross section followed are almost the same as the values from the model function. Also, the thermal-cross-section curve obtained by differentiating the thermal resistance is good for identifying thermal bottlenecks intuitively, and is also fitted quite well by the model proposed for both a typical LD structure and an improved LD with thin capping and high thermal conductivity.

Three-dimensional micro photomachining of polymer using DPSSL (Diode Pumped Solid State Laser) with 355 nm wavelength (355nm 파장의 DPSSL을 이용한 폴리머의 3차원 미세 형상 광가공기술)

  • 장원석;신보성;김재구;황경현
    • Korean Journal of Optics and Photonics
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    • v.14 no.3
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    • pp.312-320
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    • 2003
  • The basic mechanistic aspects of the interaction and practical considerations related to polymer ablation were briefly reviewed. Photochemical and photothermal effects, which highly depend on laser wavelength have close correlation with each other. In this study, multi-scanning laser ablation processing of polymer with a DPSS (Diode Pumped Solid State) 3rd harmonic Nd:YVO$_4$ laser (355 nm) was developed to fabricate a three-dimensional micro shape. Polymer fabrication using DPSSL has some advantages compared with the conventional polymer ablation process using KrF and ArF laser with 248 nm and 193 nm wavelength. These advantages include pumping efficiency and low maintenance cost. And this method also makes it possible to fabricate 2D patterns or 3D shapes rapidly and cheaply because CAD/CAM software and precision stages are used without complex projection mask techniques. Photomachinability of polymer is highly influenced by laser wavelength and by the polymer's own chemical structure. So the optical characteristics of polymers for a 355 nm laser source is investigated experimentally and theoretically. The photophysical and photochemical parameters such as laser fluence, focusing position, and ambient gas were considered to reduce the plume effect which re-deposits debris on the surface of substrate. These phenomena affect the surface roughness and even induce delamination around the ablation site. Thus, the process parameters were tuned to optimize for gaining precision surface shape and quality. This maskless direct photomachining technology using DPSSL could be expected to manufacture tile prototype of micro devices and molds for the laser-LIGA process.

Simulation of Cholesteric Liquid Crystal Color Filter by Using User-defined Coating Property of an Illumination Design Software (조명 설계 소프트웨어의 사용자 정의 코팅 기능을 사용한 콜레스테릭 액정 컬러 필터 시뮬레이션에 관한 연구)

  • Beom, Tae-Won;Cui, Hao;Lee, Hak-Suk;Yang, Jeong-Mun;Park, Jong-Rak;Yoon, Ki-Cheol;Jang, Won-Gun
    • Korean Journal of Optics and Photonics
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    • v.19 no.4
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    • pp.294-301
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    • 2008
  • We have performed modeling and simulations of optical characteristics for a cholesteric liquid crystal (CLC) color filter. Berreman's $4{\times}4$ matrix method was used for the calculation of reflectance spectra of the CLC color filter with respect to the incident angle. The results were employed as input parameters for a user-defined coating property of an illumination design software based on the ray-tracing method, LightTools. Color shift characteristics of a planar transmission-type CLC color filter were simulated using LightTools. The results were compared with the results obtained with Berreman's $4{\times}4$ matrix method. It was found that color shift characteristics of the CLC color filter could be simulated to a reasonable accuracy when the reflectance spectra with less than 5 degrees of incremental incidence-angle were used as the input data for the user-defined coating property of LightTools. We have simulated color shift characteristics of a reflection-type CLC color filter having hemi-spherical patterns. The simulation method reported in this paper has been found to be also used for a non-planar CLC color filter structure.

Convergence Comparison of Linear Oscillating Electric Machines (리니어 오실레이팅 전기기기의 비교 연구)

  • Jeong, Sung-In;Eom, Sang In
    • Journal of the Korea Convergence Society
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    • v.12 no.12
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    • pp.273-280
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    • 2021
  • This paper presents the results of study of linear oscillating electric machine; Cartesian, cylindrical type with permanent magnet, flux reversal, cylindrical reluctance, and transverse flux type. The focus of the work is the suggestion of the characteristics and design process of propose topology, respectively. First of all, there are five types of the proposed to this study on the basis of the existing literatures; Cartesian type, cylindrical type, flux reversal type, cylindrical reluctance type, and transverse flux type. All topology is achieved using equivalent magnetic circuit considering leakage elements as initial modeling. Cartesian type is investigated by number of phases and number of pole pairs using optimal process. A cylindrical type is described by number of phases and displacement of stroke. The flux reversal type is proposed based on the symmetrical and non symmetrical stator cores of the surface mounted PMs mover, and non slanted PMs and slanted PMs of the flux concentrating PMs mover. A cylindrical reluctance type is studied by the shape of mover teeth in geometric aspect to reduce force ripple and increase magnetic flux. A transverse flux type is considered by dividing the transverse flux electric excited and the transverse flux permanent magnet excited. It is significant that the study gives a design rules and features of linear oscillating electric machine.

Construction of Logic Trees and Hazard Curves for Probabilistic Tsunami Hazard Analysis (확률론적 지진해일 재해도평가를 위한 로직트리 작성 및 재해곡선 산출 방법)

  • Jho, Myeong Hwan;Kim, Gun Hyeong;Yoon, Sung Bum
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.31 no.2
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    • pp.62-72
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    • 2019
  • Due to the difficulties in forecasting the intensity and the source location of tsunami the countermeasures prepared based on the deterministic approach fail to work properly. Thus, there is an increasing demand of the tsunami hazard analyses that consider the uncertainties of tsunami behavior in probabilistic approach. In this paper a fundamental study is conducted to perform the probabilistic tsunami hazard analysis (PTHA) for the tsunamis that caused the disaster to the east coast of Korea. A logic tree approach is employed to consider the uncertainties of the initial free surface displacement and the tsunami height distribution along the coast. The branches of the logic tree are constructed by reflecting characteristics of tsunamis that have attacked the east coast of Korea. The computational time is nonlinearly increasing if the number of branches increases in the process of extracting the fractile curves. Thus, an improved method valid even for the case of a huge number of branches is proposed to save the computational time. The performance of the discrete weight distribution method proposed first in this study is compared with those of the conventional sorting method and the Monte Carlo method. The present method is comparable to the conventional methods in its accuracy, and is efficient in the sense of computational time when compared with the conventional sorting method. The Monte Carlo method, however, is more efficient than the other two methods if the number of branches and the number of fault segments increase significantly.

Roll Angle Estimation of Slowly Rolling Guided Munition With Time-delayed Measurement and Its Verification Through Flight Experiment (지연된 측정치를 가진 저속 회전 유도형 탄약의 롤각 추정 및 비행 실험을 통한 검증)

  • Park, Junwoo;Ahn, Hyungjoo;Jung, Sungmin;Noh, Junyoung;Hong, Kyungwoo;Jang, Kwangwoo;Kim, Sungjoong;Bang, Hyochoong;Kim, Jin-Won;Heo, Junhoe;Pak, Chang-Ho;Seo, Songwon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.49 no.5
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    • pp.373-381
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    • 2021
  • This paper details the result of flight experiment that examines performance of roll angle estimation algorithm of slowly rolling munition taking time delay of measurement into account when measurement comes in delayed fashion. As the measurement is passed through low pass filter for numerical stabilization and de-noising purpose which induces time delay, we design augmented state Kalman filter that incorporates distribution models of stochastic delay over time. Flight experiment was conducted to verify the algorithm at around 250m high AGL(Above Ground Level) conveying velocity of 28m/s from fixed-wing mother plane to the munition. Munition was made spun with respect to its roll axis using internal reaction wheel afterward. Numerical comparison of proposing method's roll estimation performance with that of commercial aerospace graded GPS/INS shows that proposed filter design can effectively compensate time delay of measurement.

Field Observation of Morphological Response to Storm Waves and Sensitivity Analysis of XBeach Model at Beach and Crescentic Bar (폭풍파랑에 따른 해빈과 호형 사주 지형변화 현장 관측 및 XBeach 모델 민감도 분석)

  • Jin, Hyeok;Do, Kideok;Chang, Sungyeol;Kim, In Ho
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.32 no.6
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    • pp.446-457
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    • 2020
  • Crescentic sand bar in the coastal zone of eastern Korea is a common morphological feature and the rhythmic patterns exist constantly except for high wave energy events. However, four consecutive typhoons that directly and indirectly affected the East Sea of Korea from September to October in 2019 impacted the formation of longshore uniform sand bar and overall shoreline retreats (approx. 2 m) although repetitive erosion and accretion patterns exist near the shoreline. Widely used XBeach to predict storm erosions in the beach is utilized to investigate the morphological response to a series of storms and each storm impact (NE-E wave incidence). Several calibration processes for improved XBeach modeling are conducted by recently reported calibration methods and the optimal calibration set obtained is applied to the numerical simulation. Using observed wave, tide, and pre & post-storm bathymetries data with optimal calibration set for XBeach input, XBeach successfully reproduces erosion and accretion patterns near MSL (BSS = 0.77 (Erosion profile), 0.87 (Accretion profile)) and observed the formation of the longshore uniform sandbar. As a result of analysis of simulated total sediment transport vectors and bed level changes at each storm peak Hs, the incident wave direction contributes considerable impact to the behavior of crescentic sandbar. Moreover, not only the wave height but also storm duration affects the magnitude of the sediment transport. However, model results suggest that additional calibration processes are needed to predict the exact crest position of bar and bed level changes across the inner surfzone.

Numerical Modeling of Optical Energy Transfer Based on Coherent Beam Combination under Turbulent Atmospheric Conditions (대기 외란 상황에서 결맞음 빔결합을 통한 광학 에너지의 전달 방법 수치 모델링)

  • Na, Jeongkyun;Kim, Byungho;Cha, Hyesun;Jeong, Yoonchan
    • Korean Journal of Optics and Photonics
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    • v.31 no.6
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    • pp.274-280
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    • 2020
  • In this paper, the effect of atmospheric turbulence is numerically modeled and analyzed via a phase-screen model, in regard to long-range optical energy transfer using coherent beam combination. The coherent-beam-combination system consists of three channel beams pointing at a target at a distance of 1-2 km. The phase and propagation direction of each channel beam are assumed to be corrected in an appropriate manner, and the atmospheric turbulence that occurs while the beam propagates through free space is quantified with a phase-screen model. The phase screen is statistically generated and constructed within the range of fluctuations of the structure constant Cn2 from 10-15 to 10-13 [m-2/3]. Particularly, in this discussion the shape, distortion, and combining efficiency of the 3-channel combined beam are calculated at the target plane by varying the structure constant used in the phase-screen model, and the effect of atmospheric turbulence on beam-combination efficiency is analyzed. Analysis with this numerical model verifies that when coherent beam combination is used for long-range optical energy transfer, the received power at the target can be at least three times the power obtainable by incoherent beam combination, even for maximal atmospheric fluctuation within the given range. This numerical model is expected to be effective for analyzing the effects of various types of atmospheric-turbulence conditions and beam-combination methods when simulating long-range optical energy transfer.

Numerical Modeling for Region of Freshwater Influence by Han River Discharge in the Yeomha Channel, Gyeonggi Bay (경기만 염하수로에서의 한강 유량에 따른 담수 영향범위 수치모델링)

  • Lee, Hye Min;Song, Jin Il;Kim, Jong Wook;Choi, Jae Yoon;Yoon, Byung Il;Woo, Seung-Buhm
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.33 no.4
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    • pp.148-159
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    • 2021
  • This study estimates the region of freshwater influence (ROFI) by Han River discharge in the Yeomha channel, Gyeonggi Bay. A 3-D numerical model, which is validated for reproducibility of variation in current velocity and salinity, is applied in Gyeonggi Bay. Distance of freshwater influence (DOFI) is defined as the distance from the entrance of Yeomha channel to the point where surface salinity is 28 psu. Model scenarios were constructed by dividing the Han River discharge into 10 categories (200~10,000 m3/s). The relation equation between freshwater discharge and DOFI was calculated based on performing a non-linear regression analysis. ROFI in Yeomha channel expands from the southern sea area of Ganghwa-do to the northern sea area of Yeongheung-do as the intensity of Han River discharge increases. The discharge and DOFI are a proportional relationship, and the increase rate of DOFI gradually decreases as discharge increases. Based on the relation equation calculated in this study, DOFI in the Yeomha channel can be estimated through the monthly mean Han River discharge. Accordingly, it will be possible to respond and predict problems related to damage to water quality and ecology due to rapid freshwater runoff.

Analysis of Problems in the Phase Diagram of the 2015 Revised Curriculum Chemistry II Textbook (2015 개정 교육과정 화학II 교과서의 상평형 그림에 대한 문제점 분석)

  • Youngha, Hwang;Seoung-Hey, Paik
    • Journal of the Korean Chemical Society
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    • v.67 no.1
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    • pp.54-63
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    • 2023
  • In this study, six types of 2015 revised curriculum ChemistryII textbooks were analyzed for conditions, definitions, whether or not critical points were displayed, and real-life examples of phase diagram. In this study, it was confirmed that the problems pointed out in several previous studies were not reflected in the 2015 revised curriculum ChemistryII textbook. The same as the situation defining the phase diagram, the translation of the phase diagram into a phase equilibrium diagram, the distinction between phase and state being unclear, the critical point not being shown in the phase diagram, real life examples are very limited what is being presented as is suggested as a problem. Therefore, it is necessary to reflect the results of various previous studies in the revised curriculum ChemistryII textbook that will be made in the future, specify the conditions under which the phase diagram is drawn, newly model the situation defining the phase diagram, and translate the phase diagram as a 'phase diagram'. It is necessary to use the term, clarify the distinction between phase and state, mark the critical point in the phase diagram, and develop various real-life examples.