• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.5
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• pp.479-487
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• 2023

Recently, the destructive power of typhoons is continuously increasing owing to global warming. In a situation where the installation of floating wind turbines is increasing worldwide, concerns about the huge loss and collapse of floating offshore wind turbines owing to strong typhoons are deepening. A new type of disconnectable mooring system must be developed for the safe operation of floating offshore wind turbines. A new submersible mooring pulley considered in this study is devised to more easily attach or detach the floating of shore wind turbine with mooring lines compared with other disconnectable mooring apparatuses. To investigate the structural safety of the initial design of submersible mooring pulley that can be applied to an 8MW-class floating type offshore wind turbine, scale-down structural models were developed using a 3-D printer and structural tests were performed on the models. For the structural tests of the scale-down models, tensile specimens of acrylonitrile butadiene styrene material that was used in the 3-D printing were prepared, and the material properties were evaluated by conducting the tensile tests. The finite element analysis (FEA) of submersible mooring pulley was performed by applying the material properties obtained from the tensile tests and the same load and boundary conditions as in the scale-down model structural tests. Through the FEA, the structural weak parts on the submersible mooring pulley were reviewed. The structural model tests were conducted considering the main load conditions of submersible mooring pulley, and the FEA and test results were compared for the locations that exceeded the maximum tensile stress of the material. The results of the FEA and structural model tests indicated that the connection structure of the body and the wheel was weak in operating conditions and that of the body and the chain stopper was weak in mooring conditions. The results of this study enabled to experimentally verify the structural safety of the initial design of submersible mooring pulley. The study results can be usefully used to improve the structural strength of submersible mooring pulley in a detailed design stage.

• Ocean Systems Engineering
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• v.6 no.2
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• pp.143-159
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• 2016

Cargo, such as a Tension Leg Platform (TLP), Semi-submersible platform (Semi), Spar or a circular Floating Production Storage and Offloading (FPSO), are frequently dry-transported on a Heavy Lift Vessel (HLV) from the point of construction to the point of installation. The voyage can span months and the overhanging portions of the hull can be subject to frequent wave slamming events in rough weather. Tie-downs or sea-fastening are usually provided to ensure the safety of the cargo during the voyage and to keep the extreme responses of the cargo, primarily for the installed equipment and facilities, within the design limits. The proper design of the tie-down is dependent on the accurate prediction of the wave slamming loads the cargo will experience during the voyage. This is a difficult task and model testing is a widely accepted and adopted method to obtain reliable sea-fastening loads and extreme accelerations. However, it is crucial to realize the difference in the inherent stiffness of the instrument that is used to measure the tri-axial sea fastening loads and the prototype design of the tie-downs. It is practically not possible to scale the tri-axial load measuring instrument stiffness to reflect the real tie-down stiffness during tests. A correlation method is required to systematically and consistently account for the stiffness differences and correct the measured results. Direct application of the measured load tends to be conservative and lead to over-design that can reflect on the overall cost and schedule of the project. The objective here is to employ the established correlation method to provide proper high-frequency responses to topsides and hull design teams. In addition, guidance for optimizing tie-down design to avoid damage to the installed equipment, facilities and structural members can be provided.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.153-153
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• 2022

Large-scale and accurate observations at fine spatial resolution through a means of remote sensing offer an effective tool for capturing rainfall variability over the traditional rain gauges and weather radars. Although satellite rainfall products (SRPs) derived using two major estimation approaches were evaluated worldwide, their practical applications suffered from limitations. In particular, the traditional top-down SRPs (e.g., IMERG), which are based on direct estimation of rain rate from microwave satellite observations, are mainly restricted with their coarse spatial resolution, while applications of the bottom-up approach, which allows backward estimation of rainfall from soil moisture signals, to novel high spatial resolution soil moisture satellite sensors over South Korea are not introduced. Thus, this study aims to evaluate the performances of a state-of-the-art bottom-up SRP (the self-calibrated SM2RAIN model) applied to the C-band SAR Sentinel-1, a statistically downscaled version of the conventional top-down IMERG SRP, and their integration for a targeted high spatial resolution of 0.01° (~ 1-km) over central South Korea, where the differences in climate zones (coastal region vs. mainland region) and vegetation covers (croplands vs. mixed forests) are highlighted. The results indicated that each single SRP can provide plus points in distinct climatic and vegetated conditions, while their drawbacks have existed. Superior performance was obtained by merging these individual SRPs, providing preliminary results on a complementary high spatial resolution SRP over central South Korea. This study results shed light on the further development of integration framework and a complementary high spatial resolution rainfall product from multi-satellite sensors as well as multi-observing systems (integrated gauge-radar-satellite) extending for entire South Korea, toward the demands for urban hydrology and microscale agriculture.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.12
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• pp.1-8
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• 2005

The gate length-dependence of cutoff frequency is modeled by using scaling parameter equations of equivalent circuit parameters extracted from measured S-parameters of Nano-scale MOSFETs. It is observed that the modeled cutoff frequency initially increases with decreasing gate length and then the rate of increase becomes degraded at further scale-down. This is because the extrinsic charging time slightly decreases, although the intrinsic transit time greatly decreases with gate length reduction. The new gate length-dependent model will be very helpful to optimize RF performances of Nano-scale MOSFETs.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.527-528
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• 2010

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.71-72
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• 2014

• Proceedings of the KSRS Conference
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• 2007.03a
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• pp.138-141
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• 2007

본 논문에서는 제작이 간편하고, 저렴하여, 설치가 용이한 Trihedral comer reflector를 연결하여 전방향(omni-directional)에서 전파를 입사방향으로 반사하도록 전파반사기를 설계한다. Scale-down된 사각(Square) 형태와 원형(circular) 형태의 Retroreflector를 제작하고 RCS(radar cross section)의 각도별 패턴 특성을 측정하여 이론적, 수치 해석적 계산과 비교한 결과를 보인다. 측정된 RCS 절대 값과 패턴을 이론식 및 시뮬레이션 수치 해석 값과 비교하여 데이터의 적정성을 분석한다.

• 한국ITS학회:학술대회논문집
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• v.2006 no.10
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• pp.179-181
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• 2006

톨게이트에서 사용되는 UHF RFID 비발디 배열 안테나를 설계하였다. 안테나의 주파수 대역은 미국 기준의 RFID UHF 대역으로 $902{\sim}928MHz$이다. 안테나 설계는 먼저 단일소자 비발디 안테나를 설계한 후, 전력분배 비율 0.3:1:1:0.3으로 $1{\times}4$ 배열한 안테나로 설계하였다. 설계된 배열 안테나는 VSWR 2:1이하에서 $850{\sim}942MHz$인 S11 특성을 보였다. 이득은 최대방사 9.93dBi를 얻었다. 안테나 제작은 주파수를 높여 scale down하여, 1소자 비발디를 제작하고 이의 특성을 측정하였다.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.22-23
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• 2008

As technology continues to scale down dramatically into 130nm and below, the impacts of process-induced variations on interconnect as well as device become more severe and significant in 130nm and below design. In order to predict changes of circuit characteristics due to process-induced variations accurately and efficiently, the DFM-Aware design environment has been developed and verified.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.05a
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• pp.109-113
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• 1996

In this work, a scaling methodology to scale down to or below 0.1$\mu\textrm{m}$ is presented, considering a current process technology. 0.12$\mu\textrm{m}$ nMOSFET's with both good performance and reliability is designed by this methodology