• Journal of Electrical Engineering and Technology
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• 제12권4호
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• pp.1376-1385
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• 2017

This paper proposes a method for estimating the expected frequency of voltage swells caused by asymmetrical faults in a power system. Although voltage swell is less common than voltage sag, repeated swells can have severe destructive impact on sensitive equipment. It is essential to understand system performance related to voltage swells for finding optimal countermeasures. An expected swell frequency at a sensitive load terminal can be estimated based on the concept of an area of vulnerability (AOV) and long-term system fault data. This paper describes an effective method for calculating an AOV to voltage swells. Interval estimation for an expected swell frequency is also presented for effective understanding of system performance. The proposed method provides long-term performance evaluation of the frequency and degree of voltage swell occurrences.

• 정보과학회 논문지
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• 제42권7호
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• pp.846-851
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• 2015

풍파와 너울은 바다 표면 시뮬레이션에 있어 가장 기본이 되는 파도로 해상 공간 배경의 시뮬레이터 구축에 매우 중요한 요소이다. 본 논문에서는 선박운항 시뮬레이터와 같은 실시간 시뮬레이터에 활용을 목적으로 서로 다른 시각적 특성을 가진 풍파와 너울에 대해 각각의 특성을 사실적으로 재현할 수 있는 실시간 시뮬레이션 방법을 제안하였다. 풍파에 비해 파장이 길고 마루가 둥근 너울은 절차적 방법을 통해 전역적으로 가시화 하였으며, 너울 가시화에 필요한 파라미터는 해양파 스펙트럼으로부터 추출하여 적용 하였다. 그리고 근거리에서 관측 시 그 특징이 잘 나타나는 풍파는 적용 가능 범위는 좁으나 사실적 시뮬레이션에 강점을 가진 해양파 스펙트럼 기반의 통계적 파도 모델을 활용하여 가시화 하였다.

• Journal of Ship and Ocean Technology
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• 제9권2호
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• pp.21-28
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• 2005

Recently moored offshore vessels like as FPSO(Floating Production Storage Offloading) are frequently deployed in seas for a long time. For successful operation, the motion behavior of such a vessel in waves must be clarified in advance either theoretically or experimentally. It is of particular interest to examine the behavior, when swells are superposed to seas with different incident angle. Such a situation is actually reported in some offshore oilfield. In this paper, the motion of a FPSO in irregular waves including swells is studied in time domain. Hydrodynamic coefficients and wave forces are calculated in frequency domain using three-dimensional singularity distribution method. Time memory function and added mass at infinite frequency are derived by Fourier transform utilizing hydrodynamic damping coefficients. In the process, the numerical accuracy of added mass at infinite frequency is carefully examined in association with free decay simulations. It is found from numerical simulations that swells significantly affect the vertical motion of FPSO mainly because of their longer period compared to the ordinary sea waves. In particular, the roll motion is largely amplified because the dominant period of swell is closer to the roll natural period than that of seas.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권4호
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• pp.312-319
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• 2016

Measured wave data covering two years simultaneously at 3 locations along the eastern Arabian Sea reveals the presence of long-period (peak wave period > 18 s) low-amplitude waves (significant wave height < 1 m) and the characteristics of these waves are described in this article. In a year, 1.4-3.6% of the time, the low-amplitude long-period swells were observed, and these waves were mainly during the nonmonsoon period. The wave spectra during these long-period swells were multi-peaked with peak wave period around 18.2 s, the secondary peak period around 13.3 s and the wind-sea peak period at 5 s. The ratio of the spectral energy of the wind-sea peak and the primary peak (swell) was slightly higher at the northern location (0.2) than that at the southern location (0.15) due to the higher wind speed present at the northern location.

• 한국해양학회지:바다
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• 제15권2호
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• pp.62-67
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• 2010

2008년 2월 24일 동해안에 출현한 너울은 3명의 인명 사고를 발생시켰으며 또한 일본의 서쪽 해안에서도 피해가 나타났다. 최근에 그 강도가 점점 강해지는 동해의 너울에 의한 사고를 줄이기 위해서는 향후 그 발생 시간과 위치에 대한 보다 정확한 예보가 필요하다. 본 연구에서는 동해에서의 파랑 예보의 정확성을 검증하기 위하여 SWAN 파랑 모델을 이용하여 2008년 2월 발생한 동해의 너울을 예측하고 검증하였다. 모델 결과는 파랑 관측 자료뿐만 아니라 한국기상연구소가 ReWW3를 사용하여 생산한 자료와도 비교 하였으며 특히 동해안의 두개의 파랑 관측소에서 획득한 주파수 스펙트럼과의 비교 분석도 수행하였다. 그 결과 파고 분포와 발생 시간은 유사하게 나타났지만 주파수 스펙트럼의 형태에 있어서는 차이가 나타났다. 너울에 대한 보다 정확한 예보를 위해서는 보다 많은 현장 관측 자료와의 비교 분석이 필요하며 특히 동해에서의 너울 특성 연구를 위해서는 파향 스펙트럼 관측 자료가 필요하다.

• 한국해양공학회지
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• 제22권6호
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• pp.13-19
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• 2008

Abnormally large swells that appeared on the coast of the East Sea in October in 2005 and 2006 were simulated using SWAN model to examine the accuracy of the model for future forecasting Seawind data calculated based on the weather chart ant bottom topography were used for input data, and the model was operated more than 20 days before the observed swells to avoid the problems from the cold start of the model. The comparisons with observed wind and wave data were unsatisfactory and neededmore improvement in terms of swell component in the wave model as well as the quality of seawind data. The satellite wind and wave data can be good candidates for future comparison of the wave model results in the East Sea.

• 소성∙가공
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• 제16권4호
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• pp.260-265
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• 2007

Rubber compounds have high viscoelastic property. One of the viscoelastic behaviors during profile extrusion is the swelling of extrudate. In this study, die swells of rubber compounds at the capillary die have been investigated through experiment and computer simulation. Experiments and simulations have been performed using fluidity tester and commercial CFD code, Polyflow respectively. Die swells of rubber compounds in a capillary die were predicted using non-linear differential viscoelastic model, Phan-Thien-Tanner(PTT) model for various relaxation times and relaxation modes. The results of simulation were compared with the experiments. Pressure and velocity distribution, and circulation flows at the comer of capillary die have been investigated through computer simulation. It is concluded that the PTT model successfully represented the amount of the die swell of rubber compounds for various relaxation times at different modes.

• 한국자원식물학회:학술대회논문집
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• 한국자원식물학회 2002년도 춘계 학술발표대회
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• pp.29-30
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• 2002

• 전기학회논문지
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• 제61권2호
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• pp.199-208
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• 2012

This paper proposes a quasi Z-source DVR(Dynamic Voltage Restorer) system with a series connection of the output terminals, to compensate the voltage variations in the 6.6[kV]/60[Hz] power distribution system. The conventional DVR using one quasi Z-source AC-AC converter has the advantage which it can compensate the voltage variations without the need for the additional energy storage device such as a battery, but it is impossible to compensate for the 50[%] under voltage sags. To solve this problem, a DVR system using two quasi Z-source AC-AC converters with the series connection of the output terminals is proposed. By controlling the duty ratio D in the buck-boost mode, the proposed system can control the compensation voltage. For case verification of the proposed system, PSIM simulation is achieved. As a result, in case that the voltage sags-swells occur 10[%], 20[%], 60[%] in power distribution system, and, in case that the 50[%] under voltage sags-swells continuously occur, all case could compensate by the proposed system. Especially, the compensated voltage THD was examined under the condition of the 10[%]~50[%] voltage sags and the 20[${\Omega}$]~100[${\Omega}$] load changes. The compensated voltage THD was worse for the higher load resistances and more severe voltage sags. Finally, In case of the voltage swells compensation, the compensation factor has approached nearly 1 regardless of the load resistance changes, while the compensation factor of voltage sags was related to the load variations.

• 한국수자원학회논문집
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• 제41권8호
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• pp.785-795
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• 2008

너울은 항만활동 및 선박운행을 방해하며, 연안지역의 인명사고와 지형 변화 등을 야기키는 주요 원인이다. 이러한 너울의 관측 및 예측은 장기간에 걸친 파랑 및 바람 관측자료와 주변외해 기상자료의 거시적인 검토가 필요하기 때문에 자료 수집 및 분석에 많은 시간과 노력을 필요로 한다. 이러한 어려움 때문에 지금까지는 너울에 관한 연구가 활발히 이루어지기 어려웠다. 이에 본 연구는 인터넷 기반의 실시간 모니터링 시스템인 필드박스를 개발하고 이로부터 수집한 파랑자료, 선형파이론과 국내 기상청과 NASA의 기상자료 등을 이용하여 우리나라에서 발생하는 너울의 특성과 원인을 분석하였다. 2004년부터 2006년 동안 광안타워에서 관측된 자료를 이용하여 너울의 빈도와 총발생시간을 월별로 통계 분석하였다. 따라서 우리나라의 분기별 너울 발생의 특징을 규명할 수 있었으며 국내에 발생하는 너울의 원인과 위치적 특징 등을 도출하였다.