• Ocean Systems Engineering
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• 제8권3호
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• pp.313-327
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• 2018

Meeting the touchdown point (TDP) target box is one of the challenges during catenary riser installation, especially for deep water or ultra-deep water riser systems. TDP location mismatch compared to the design can result in variation of riser configuration, additional hang-off misalignment, and extra bending loads going into the hang-off porch. A good understanding of the key installation parameters can help to minimize this mismatch, and ensure that the riser global response meets the design criteria. This paper focuses on investigating the potential factors that may affect the touchdown point location, and addressing the challenges both in the design stage and during installation campaign. Conventionally, the vessel offset and current are the most critical factors which may affect the TDP movement during installation. With the offshore exploration going deeper and deeper in the sea (up to 10,000ft), other sources such as the seabed slope and seabed soil stiffness are playing an important role as well. The impacts of potential sources are quantified through case studies for steel catenary riser (SCR) and lazy wave steel catenary riser (LWSCR) in deep water application. Investigations through both theoretical study and numerical validation are carried out. Furthermore, design recommendations are provided during execution phase for the TDP mismatch condition to ensure the integrity of the riser system.

• 전력전자학회논문지
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• 제22권4호
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• pp.369-372
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• 2017

This paper presents a control scheme for three-level NPC inverters using small DC-link capacitors. To reduce the inverter system volume, the film capacitor with small capacitance is a promising candidate for the DC-link. When small capacitors are applied in a three level inverter, however, the AC ripple component increases in the DC-link NPV (neutral point voltage). In addition, the three-phase input grid currents are distorted when the DC-link capacitors are fed by diode rectifier. In this paper, the additional circuit is applied to compensate for small capacitor systems defect, and the offset voltage injection method is presented for the stabilization in NPV. These two proposed processes evidently ensure the quality improvement of the input grid currents and output load currents. The feasibility of the proposed method is verified by experimental results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.814-819
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• 2007

Palletizing task is well-known time consuming and laborious process in factory, hence automation is seriously required. To do this, artificial robot is generally used. These systems however, mostly user teaches the robot point to point and to avoid time-variable obstacle, robot is required to attach the vision camera. These system structures bring about inefficiency and additional cost. In this paper we propose task-oriented trajectory generation algorithm for palletizing. This algorithm based on $A^{*}$ algorithm and slice plane theory, and modify the object dealing method. As a result, we show the elapsed simulation time and compare with old method. This simulation algorithm can be used directly to the off-line palletizing simulator and raise the performance of robot palletizing simulator not using excessive motion area of robot to avoid adjacent components or vision system. Most of all, this algorithm can be used to low-level PC or portable teach pendent

• Journal of Ecology and Environment
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• 제41권2호
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• pp.34-44
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• 2017

Background: Monitoring terrestrial vegetation cover condition is important to evaluate its current condition and to identify potential vulnerabilities. Due to simplicity and low cost, point intercept method has been widely used in evaluating grassland surface and quantifying cover conditions. Field-based digital photography method is gaining popularity for the purpose of cover estimate, as it can reduce field time and enable additional analysis in the future. However, the caveats and uncertainty among field-based vegetation cover estimation methods is not well known, especially across a wide range of cover conditions. We compared cover estimates from point intercept and digital photography methods with varying sampling intensities (25, 49, and 100 points within an image), across 61 transects in typical steppe, forest steppe, and desert steppe in central Mongolia. We classified three photosynthetic groups of cover important to grassland ecosystem functioning: photosynthetic vegetation, non-photosynthetic vegetation, and bare soil. We also acquired normalized difference vegetation index from satellite image comparison with the field-based cover. Results: Photosynthetic vegetation estimates by point intercept method were correlated with normalized difference vegetation index, with improvement when non-photosynthetic vegetation was combined. For digital photography method, photosynthetic and non-photosynthetic vegetation estimates showed no correlation with normalized difference vegetation index, but combining of both showed moderate and significant correlation, which slightly increased with greater sampling intensity. Conclusions: Results imply that varying greenness is playing an important role in classification accuracy confusion. We suggest adopting measures to reduce observer bias and better distinguishing greenness levels in combination with multispectral indices to improve estimates on dry matter.

• Journal of Electrical Engineering and Technology
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• 제12권6호
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• pp.2099-2105
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• 2017

In a power system that has a high wind penetration, the output power fluctuation of a large-scale wind turbine generator (WTG) caused by the varying wind speed increases the maximum frequency deviation, which is an important metric to assess the quality of electricity, because of the reduced system inertia. This paper proposes a stable power-smoothing scheme of a doubly-fed induction generator (DFIG) that can suppress the maximum frequency deviation, particularly for a power system with a high wind penetration. To do this, the proposed scheme employs an additional control loop relying on the system frequency deviation that operates in combination with the maximum power point tracking control loop. To improve the power-smoothing capability while guaranteeing the stable operation of a DFIG, the gain of the additional loop is modified with the rotor speed and frequency deviation. The gain is set to be high if the rotor speed and/or frequency deviation is large. The simulation results based on the IEEE 14-bus system demonstrate that the proposed scheme significantly lessens the output power fluctuation of a WTG under various scenarios by modifying the gain with the rotor speed and frequency deviation, and thereby it can regulate the frequency deviation within a narrow range.

• 대한전자공학회논문지SD
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• 제37권12호
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• pp.79-90
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• 2000

본 논문에서는 고성능 수퍼스칼라 마이크로프로세서에 적합하고, IEEE 754 표준을 준수하는 고성능 부동 소수점 유닛의 구조를 설계한다. 부동 소수점 AU에서는 비정규화 수 처리를 모두 하드웨어적으로 지원하면서 추가적인 지연 시간이 생기지 않도록 점진적 언더플로우 예측 기법을 제안 구현한다. 부동 소수점 제산/제곱근기는 기존의 고정적인 길이의 몫을 구하는 방식과 달리 매 사이클마다 가변적인 길이의 몫을 구하는 구조를 채택하여 성능과 설계 복잡도 면에서 SRT 알고리즘에 의한 구현 보다 우수하도록 설계한다. 또한, 수퍼스칼라 마이크로프로세서에 이식이 용이하도록 익셉션 예측 기법을 세분화하여 적용하며, 제산 연산에서의 익셉션 예측에 필요한 스톨사이클을 제거하도록 한다. 설계된 부동 소수점 AU와 제산/제곱근기는 부동 소수점 유닛의 구성요소인 명령어 디코더, 레지스터 파일, 메모리 모델, 승산기 등과 통합되어 기능과 성능을 검증하였다.

• 한국통신학회논문지
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• 제27권10C호
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• pp.963-972
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• 2002

DMT 기반의 VDSL 모뎀, OFDM 방식의 DVB 모뎀 등 다중 반송파 변조 시스템에서 핵심 블록으로 사용되는 8192점 FFT/IFFT 프로세서를 설계하였다. 새로운 2단계 수렴 블록 부동점 (two-step convergent block floating-point; TS_CBFP) 스케일링 방법을 제안하여 설계에 적용하였으며, 이를 통해 FFT/IFFT 출력의 신호 대 양자화 잡음 비 (signal-to-quantization-noise ratio; SQNR)가 크게 향상되도록 하였다. 제안된 TS_CBFP 스케일링 방법은 별도의 버퍼 메모리를 사용하지 않아 기존의 방법에 비해 메모리를 약 80% 정도 감소시키며, 따라서 칩 면적과 전력소모를 크게 줄일 수 있다. 입력 10-비트, 내부 데이터와 회전인자 14-비트, 그리고 출력 16-비트로 설계된 8192점 FFT/IFFT 코어는 약 60-㏈의 SQNR 성능을 갖는다. 0.25-$\mu\textrm{m}$ CMOS 셀 라이브러리로 합성한 결과. 약 76,300 게이트와 390K 비트의 RAM, 그리고 39K 비트의 ROM으로 구현되었다. 시뮬레이션 결과, 50-MHzⓐ2.5-V로 안전하게 동작할 것으로 평가되었으며, 8192점 FFT/IFFT 연산에 약 164-$\mu\textrm{s}$가 소요될 것으로 예상된다. 설계된 코어는 Xilinx FPGA에 구현하여 정상 동작함을 확인하였다.

• Spatial Information Research
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• 제20권3호
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• pp.83-93
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• 2012

최근 환경문제로 인해 보행, 자전거, 대중교통과 같은 친 환경 교통수단에 대한 관심이 높아지고 있다. 하지만 보행과 자전거는 경우에 따라 장거리 이동이 불가능하기 때문에 이용범위가 제한적이라는 단점이 있다. 반면에 대중교통은 교통체증이라는 사회적 문제점까지 해결할 수 있는 교통수단이다. 이러한 대중교통은 시간에 따라 운행여부가 달라진다는 특징을 갖고 있다. 하지만 현재 웹상에서 서비스중인 대중교통정보 안내 서비스는 이러한 특징을 반영하지 못하기 때문에 경우에 따라 사용자에게 잘못된 정보를 제공할 수 있다. 이러한 한계점을 해결하고 대중교통의 운행정보를 고려한 정보제공을 위해 본 연구에서는 STP(Space Time Point)데이터 모델을 제안하였다. STP데이터 모델은 객체의 최하위 개념을 포인트 단위로 인식하고 이들을 계층적으로 구성하여 객체를 표현할 수 있으며, 기존의 시공간 데이터 모델과는 달리 시간에 따라 객체정보가 변하는 다양한 동적 공간객체의 구현이 가능하다. 대전지역을 대상으로 대중교통 운행정보로 버스 및 지하철에 대한 STP모델을 설계 및 구축하고 이를 이용하여 동적 경로 안내 기능을 구현하였다. 구현한 경로안내 기능을 통해 대전국립현충원에서 한남대학교로 가는 경로를 시간대별로 탐색해 본 결과 대중교통의 운행에 제한이 발생하는 심야시간에는 운행이 제한되는 노선을 우회하는 경로를 안내함으로써 시간에 따라 서로 다른 경로를 나타내었다. 이는 기존 데이터 모델에서는 제공할 수 없는 결과로 실시간 운행정보를 고려한 경로안내가 가능함을 확인하였다. 이러한 기능은 실시간 교통정보나 통행이력정보등과 같은 다양한 데이터 모델의 적용을 통해 추가적인 기능 확장이 가능할 것으로 기대한다.

• 통상정보연구
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• 제6권2호
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• pp.107-127
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• 2004

The rapid development of internet information technology has increased interest in e-Trade these days, but it is not activated greatly up to now. In order to promote e-Trade, it is essential to construct cooperative process such as connecting systems among trade related parties. Building e-Trade platform which is based on the infrastructure of the past trade automatic system is key point of promoting e-Trade. To do this, a study on the basic concept and specific components of e-Trade platform is needed absolutely. At this point of view, after this paper has examined domestic and foreign studies on the fundamental technologies about electronic commerce, it drew several key technologies that could be applied to e-Trade considering the current IT trend. Then it evaluates these technologies according to Technology Reference Model(TRM) of the National Computerization Agency. This will help us to show the operation strategy as well as the concept of future e-Trade platform and its composition. On the basis of the theoretical background, this paper classified NCA's technology model into 6 fields, which are application. data, platform, communication, security and management. Considering the key technologies, e-Trade platform has to be mutually connected and accept international standards such as XML. In the aspect of business side, trade relative agencies' business process as well as trading company's process has to be considered. Therefore, e-Trade platform can be classified into 3 parts which are service, infrastructure and connection. Infrastructure part is compared of circulating and managing system of electronic document, interface and service framework. Connecting service (application service) and additional service (application service) consist of service part. Connecting part is a linking mutual parts and can be divided into B2B service and B20 service. The organization operating this e-trade platform must have few responsibilities and requirements. It needs to positively accept existing infrastructure of trade automatic system and improving the system to complete e-trade platform. It also have to continuously develop new services and possess ability to operate the system for providing proper services to demanders. As a result, private sector that can play a role as TTP(Third Trust Party) is adequate for operating the system. In this case, revising law is necessary to support the responsibility and requirement of private sector.

• 전기학회논문지
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• 제56권7호
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• pp.1211-1217
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• 2007

In this paper, a 10kVA PV inverter applying Incremental Conductance(IncCond) method for maximum power point tracking WIS developed and its performance tests were carried out. Modeling and simulation of PV array and system controller was performed using PSCAD/EMTDC, an electromagnetic transient analysis program. After comparison and analysis of Perturbation & Observation (P & O) and IncCond method, a PV inverter based on IncCond method was designed and manufactured. Grid interface transient characteristics including start-up, normal operation, and fault operation were tested, which verified the usefulness of the proposed system. In the near future, commercialization process will proceed through additional extensive tests of transients.