• Korean Journal of Optics and Photonics
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• v.31 no.6
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• pp.281-289
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• 2020

This paper reports a slim mobile lens design using a hybrid refractive/diffractive optical element. Conventionally a wide field of view (FOV) camera-lens design adopts a retrofocus type having a negative (-) lens at the forefront, so that it improves in imaging performance over the wide FOV, but with the sacrifice of longer total track length (TTL). However, we chose a telephoto type as a baseline design layout having a positive (+) lens at the forefront, to achieving slimness, based on the specification analysis of 23 reported optical designs. Following preliminary optimization of a baseline design and aberration analysis based on Zernike-polynomial decomposition, we applied a hybrid refractive/diffractive element to effectively reduce the residual chromatic spherical aberration. The optimized optical design consists of 6 optical elements, including one hybrid element. It results in a very slim telephoto ratio of 1.7, having an f-number of 2.0, FOV of 90°, effective focal length of 2.23 mm, and TTL of 3.7 mm. Compared to a comparable conventional lens design with no hybrid elements, the hybrid design improved the value of the modulation transfer function (MTF) at a spatial frequency of 180 cycles/mm from 63% to 71-73% at zero field (0 F), and about 2-3% at 0.5, 0.7, and 0.9 fields. It was also found that a design with a hybrid lens with only two diffraction zones at the stop achieved the same performance improvement.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.1440-1444
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• 2005

본 연구는 일반적인 수문모형 및 수자원 관련 모형들의 초기세팅시 모형별로 사용되는 각기 다른 형태의 입력자료 대한 활용성을 용이하게 하고 실제 시스템에 적용하여 모형의 활용성을 높이고자 하는데 있다. 특히 현재 한국수자원공사 데이터베이스의 수문자료는 각종 수문모형 및 수자원 관련 시스템에 직접 사용하기에는 모형의 입력 포맷 형태가 너무나 다양하기 때문에 그 한계가 있다. 자료의 형태 대부분이 Raw data의 형식으로 이루어져 있어 모형 입력을 위한 선행 자료처리가 불가피하며, 이로 인해 실질적인 유출해석의 정확성을 높이는 연구 또는 수문학적 분석을 위한 연구등의 학술적인 측면에 초점이 맞추어지기보다 오히려 입력자료 구축에 많은 시간이 투입되는 것이 사실이다. 그 예로 실시간 물관리 운영 시스템(IRWMS)에서 유역유출 모형으로 사용 중인 SSARR모형의 강우 입력자료로는 유역평균강우량(MAP)이 사용된다. 한편 데이터베이스에는 지점 강우자료가 저장되어 있으며, 이를 사용하기 위해서는 다시 티센법(Thiessen Method), 유역평균법 등을 이용하여 지점강우에서 MAP로 환산 후 활용해야한다. 또한 이러한 선행 작업들은 모형 수행자마다 반복적으로 이루어지는 작업이므로 변환 프로그램에 의해 자동으로 계산하여 DB 등에 저장하고 사용한다면 수문자료 분석에 소모되는 시간과 비용을 절감할 수 있을 것이다. 현재 데이터베이스 내부에는 이러한 자료변환 알고리즘이 포함되어 있지 않으며 원시자료인 지점 강우자료가 데이터베이스에 저장되어 활용하고 있다. 따라서 수자원 전문가들에게 분석하고자 하는 유역별 모형별로 입력자료의 형태가 변환되어 자료를 실시간으로 제공하고, 또한 전산전문가가 아닌 수자원 전문가에 의해 관리 될 수 있는 데이터베이스 관리프로그램이 필요하다. 이러한 데이터베이스 관리프로그램의 역할가운데 주요사항으로 수문 자료를 활용한 수자원 관련 프로그램에 해당 실무 차원에서 작성, 검토, 사용을 위한 수자원 공사의 Raw Data 가공이 사용자의 요구에 따라 이루어져야 한다. 사용자의 요구에 따라 가공된 데이터는 다시 데이터베이스에 저장되어 다른 모형에서 해당 자료를 필요로 하게 될 경우 사용자들은 데이터를 손쉽게 받아 사용할 수 있다. 저장된 자료들은 검$\cdot$보정 기능을 포함하여 신뢰성을 확보하고 유출모형의 입력자료를 동일한 수준으로 유지하게 된다. 특히 IRWMS(Integrated Real-time Water Manage System)를 물관리 센터에서 실질적으로 운영하기 위해서는 신뢰성 있는 수문자료의 확보가 반드시 필요하다. 초기 입력자료의 신뢰성에 따라 시스템 전체에 미치는 영향이 상당히 크기 때문이다. 따라서 이러한 수문자료 연산 프로그램(JydroDB Solution)은 수문자료의 신뢰도를 분석할 수 있을뿐만 아니라 IRWMS 내부의 여러 모형과 연동이 가능하도록 개발하였고 수자원 전문가에 의해 테이터베이스관리가 손쉽게 이루어지도록 구성하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.6
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• pp.655-662
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• 2014

This study conducted tensile tests on an Alloy 690TT tube at room temperature (RT) and at $343^{\circ}C$ using tube- and ring-type specimens to investigate the stress-strain behavior and tensile properties of a steam generator (SG) tube in the axial and circumferential directions at RT and at the design temperature of a nuclear power plant (NPP). The results of the axial tensile test showed that yield point phenomena appeared at both RT and $343^{\circ}C$, and serrated flow in the stress-strain curve appeared at $343^{\circ}C$. Yield and tensile strengths for both directions were clearly lower at $343^{\circ}C$ compared to RT; however, the elongations were approximately the same at both test temperatures. Regardless of the test temperature, the strengths in the circumferential direction were lower by approximately 5~10 % than those in the axial direction. In addition, the test data revealed that the reduction in the yield and tensile strengths of the Alloy 690TT SG tube with the test temperature was more significant than that estimated by the temperature correction factor of ASME Sec.II.

• Journal of Korean Society of Transportation
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• v.30 no.1
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• pp.75-83
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• 2012

This study is to find a shortcoming embedded in the current Korean Highway Capacity Manual (KHCM) on reflecting a heavy vehicle effect to the highway capacity. The KHCM suggests to handle the percent heavy vehicle to deal with its effect to a capacity regardless of density levels. Authors hypothesized in this study that the effect of heavy vehicles would vary at different levels of traffic density - the effect would be comparably insignificant when a density is low and it becomes comparably significant when it becomes high. Field data from a freeways located in Seoul were collected for 360 hours (15 days) and categorized them into a set of operation conditions grouped by 15 minutes and by the LOS density levels. Comparison between the field measured and the estimated by the KHCM method showed that the KHCM method overestimated the effect of heavy vehicles in LOS B and C but underestimated in LOS E. The results suggested that there be a difference pattern from the one the KHCM expected and brought discussion on further studies.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.1
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• pp.53-58
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• 2011

Ultra-precision miniaturized machine tools essential for manufacturing accurate machine components in micro/meso-scale have been developed. To realize high accuracy using mMTs, geometric errors, which are considered as the main sources of inaccuracy should be identified and compensated. The conventional systems for measuring geometric errors, such as a laser interferometer, can measure only one geometric error in a single setup and they involve complicated measurement procedures. A measurement system using PSDs is a promising alternative but the measurable range of such systems is limited to the active range of the PSDs. The proposed measurement system using PSDs can overcome the limit of small measurable range. Further, the mounting errors that could occur during set-up process can be avoided. In this paper, an algorithm corresponding to the system was analyzed and experiments were carried out.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.6
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• pp.794-801
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• 2012

Finite Element Method is a strong tool to analyse static and dynamic problem of a structure. FEM is a good method for static problem, but for dynamic problem there are some differences between real phenomena and analyzed phenomena. Therefore some modifications are needed to identify two results. In this paper authors propose a genetic algorithm method 1) to adjust dimensions of plate for identifying natural frequencies, 2) to fit amplitude of FEM Frequency Response Function(FRF) onto it of real FRF. Analysis by raw FEM data gave questions if the results were for the same object. By only adjusting Young's modulus much better accordances were obtained, but limitation existed still. Very good agreements were achieved by shape modification and damping coefficient identification.

• Journal of Korean Society of Transportation
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• v.35 no.6
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• pp.525-544
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• 2017

With the advent of the big data era, the interest in the development of land using traffic data has increased significantly. However, the current research on traffic big data lingers around organizing or calibrating the data only. In this research, a novel method for discovering the hidden values within the traffic data through data mining is proposed. Considering the fact that traffic data and network structures have similarities, network analysis algorithms are used to find valuable information in the actual traffic volume data. The PageRank and HITS algorithms are then employed to find the centralities. While conventional methods present centralities based on uncomplicated traffic volume data, the proposed method provides more reasonable centrality locations through network analysis. Since the centrality locations that we have found carry detailed spatiotemporal characteristics, such information can be used as an objective basis for making policy decisions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.11
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• pp.3066-3073
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• 2009

Joint paths of master and branch pipes are induced mathematically for many kinds of joint patterns between both pipes in 3-axis pipe profile-cutting machines. By compensating them with a kerf width, the real cutting paths are determined, and their CL-data are generated, and the tool paths generated by CL-data are verified by a ghost function. A bevelling of welds is implemented through tilting a cutting torch in the $\beta$-axis direction for 8 sections in the chuck rotation of $\alpha$-axis. A PLC controls simultaneously position and velocity in a real time for $\alpha$, X, $\beta$-axis by loading CL-data generated. We developed the PLC-controlled 3-axis pipe profile-cutting system which can cut a master or branch pipe along the cutting path and simultaneously do a bevelling process.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1784-1788
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• 2010

APEC 기후센터(APEC Climate Center, APCC)에서 제공하는 다중모형앙상블(Multi-model Ensemble, MME) 형태의 계절예측정보를 이용하여 3개월 가뭄전망을 수행하였다. APCC MME는 기후예측모형이 가지는 불확실성을 최소화하기 위한 방법으로, 아시아 태평양 지역 내 9개 회원국 16개 기관 21개 기후모형의 계절예측정보를 활용하여, 개별 모형이 가지는 계통오차(Systematic error)를 앙상블 기법을 통하여 상쇄함으로써 최적의 예측자료를 도출한다. 또한, 기후예측 모형이 예측한 대기순환장은 관측 지점변수와 경험적 통계적 관련성을 가지므로, 이를 바탕으로 상세지역의 이상기후에 대한 정보를 도출할 수 있다. 본 연구에서는 가뭄 관리 및 전망을 위한 입력 자료로서, 기상전문 기관인 APEC 기후센터 (APEC Climate Center, APCC)에서 제공하는 전구 규모의 기온 및 강수 전망자료를 기상청 산하 59개 지점의 전망자료로 통계적 규모 축소화 기법을 통해 3개월 예보를 실시하였다. APCC 계절예측자료를 가뭄모니터링시스템의 자료입력 포맷에 따라 적절히 가공한 뒤, 가뭄 관리 및 전망을 위하여 SPI(Standard Precipitation Index) 및 PDSI(Palmer Drought Severity Index)지수의 입력자료로 사용하여 SPI 및 PDSI 지수를 산정하였다. 또한 분위사상법(Quantile Mapping)을 이용하여 총 59개 지점의 과거 월평균 관측값과 최근 2009년에 대한 모의값의 누적확률분포값을 계산하고 모의값의 확률분포를 관측값의 확률분포에 사상시켜 가뭄 전망을 위한 기상변수의 오차를 보정하고자 하였다. 이러한 계절예측정보를 이용하여 가뭄 전망에 대한 신뢰도가 높아진다면, 사전예방 및 피해완화로 가뭄상황에 대한 신속한 대처 및 피해의 경감이 이루어질 수 있을 것이다.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.7 no.4
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• pp.13-24
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• 2008

Real-time traffic data are readily obtainable by traffic surveillance systems of intelligent transportation systems (ITS). Such data greatly support further applications in the field of traffic operations, planning, and safety. However, traffic data should be appropriately processed to fully exploit the benefits of data collection capability. Rather than developing individual data processing techniques, which is major concern of existing studies, this study proposes a novel methodology for evaluating data processing techniques in an integrated manner. Also, a tool for implementing the proposed methodology is developed. Users can extract useful and more reliable traffic data based upon their ultimate purpose of data usage by the evaluation tool developed in this study. Actual freeway traffic data are, as an example, fed into the evaluation tool, and results are discussed.