• Journal of Electrical Engineering and Technology
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• 제1권2호
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• pp.170-176
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• 2006

This paper proposes a topological locating algorithm to determine the location of the power quality event source. This algorithm makes use of the information on the topology of the monitored network and on the direction of PQ events. As a result, the bus incidence matrix is modified using monitor location and the direction matrix is constructed. With this information, the algorithm determines the suspected locations of the PQ events. To reduce suspicious areas, it utilizes event cause and related equipment. In case of line fault event, it calculates the distance from the monitor to the location of event source. The overall algorithm is applied to the IEEE test feeder and accurately identifies the event source location.

• 한국유체기계학회 논문집
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• 제13권2호
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• pp.36-40
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• 2010

Tidal current power system is the energy converter which converts the kinetic energy of tidal stream into electric energy. The performance of the rotor which initially converts the energy is determined by various design factors and it should be optimized by the ocean environment of the field. Flow direction changes due to rise and fall of the tides, but horizontal axis turbine is very sensitive to direction of flow. To investigate the rotor performance considering the interaction problems with incidence angle of flow, series of experiments have been conducted. The results and findings are summarized in the paper.

• Journal of Mechanical Science and Technology
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• 제20권2호
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• pp.185-190
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• 2006

An ultrasonic self-calibrating technique for the characterization of a ceramic which was fabricated by change pressing time during the HIP process has been applied by using the ratio of the reflection and transmission coefficients of normal incidence longitudinal waves. The ratio is self-compensated, in that it is independent of the characteristics for transmission and reception of ultrasound by the transducer and the condition of the couplant. The insensitive direction in parameter space is defined as the direction in which the variation of the ratio to changes of two parameters vanishes. For inverse problem the distribution of minima in an error surface is investigated.

• 한국해안해양공학회지
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• 제15권1호
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• pp.21-32
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• 2003

본 연구에서는 1996년에 Hanzawa et al.이 수평혼성방파제 피복 블록의 기대피해를 계산하기 위해 개발한 신뢰성 설계법을 방향 불규칙 파의 방향 분산, 심해 설계 주파향이 해안선에 직각 방향으로부터 기울어진 각도, 심해 주파향의 설계치에 대한 편차 등과 같은 파향의 변동성을 고려할 수 있도록 확장하였다. 심해로부터 방파제 설치 위치까지의 파랑 변형을 계산하기 위하여 Hanzawa et al.은 평행한 등심선을 갖는 직선 해안에 직각으로 입사하는 일방향 불규칙파를 가정하여 1975년에 Goda가 개발한 모형을 사용하였다 본 연구에서는 방향 불규칙파의 변형을 계산하기 위하여 1997년에 Kweon et al.이 개발한 모형을 사용하였다 계산 결과. 파향의 변동성이 피복 블록의 기대피해 계산에 큰 영향을 미치는 것을 알 수 있었다. 만일 본 연구에서 가정한 바와 같이, 방파제에 직각으로 입사하는 파랑에 대한 피복석의 안정공식이 비스듬히 입사하는 파랑에 대해서도 유효하다. 면 파랑의 방향성을 무시한 종래의 설계법은 수심과 바닥경사에 따라 기대피해를 두 배 정도까지도 과대산정 혹은 과소산정 할 수 있을 것이다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2004년도 Proceedings of ISRS 2004
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• pp.582-585
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• 2004

Oyster fanning structures in tidal flats are well detected by SAR system. Each frame of these artificial structures is composed of two vertical and one horizontal wooden pole. We investigate characteristics of polarimetric features in the target structures. In this paper, the results of AIRSAR L-band POLSAR data and experiments in laboratory are discussed. The ratio of single bounce to double bounce scattering depends of vertical pole height, direction of horizontal pole to radar look direction, and incidence angle as well as sea surface condition. We have conducted laboratory experiments. According to target scale, Ku-band and targets downsized by scale of 10 are used. The results of the experiments are summarized as: i) total power of the backscattering is more affected by vertical poles than a horizontal pole; ii) and backscattering from a horizontal pole is sensitive to the relative radar look direction to target array. We conclude that water level can be effectively measured by using interferometric phase and backscattering intensity if vertical poles in the water are observed by L-band HH- or VV-polarization. Measurement of tide height can be further improved if double bounced components are separated from fully polarized SAR data.

• 한국해양공학회지
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• 제24권4호
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• pp.8-12
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• 2010

The use of a tidal-current power system is one source of renewable energy that can minimize the environmental impact of power production and offer many other advantages compared to conventional energy sources. Unlike other energy production approaches, rate of energy production can be precisely predicted and the operational rate is very high. The performance of the rotor, which has a vital role in energy production using tidal currents, is determined by various design factors, and it should be optimized for the specific ocean environment in the field. The horizontal-axis turbine is very sensitive to the direction of flow, and flow direction changes due to rise and fall of the tides. To investigate the performance of the rotor considering the interaction problems with incidence angle of flow, a series of experiments were conducted, and a 3D CFD model was designed and analyzed by ANSYS CFX. The results and findings are summarized in the paper.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 1999년도 Proceedings of International Symposium on Remote Sensing
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• pp.485-490
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• 1999

Wind vector information over the ocean is currently obtained using multiple beam scatterometer data. The scatterometers on ERS-1/2 generate wind vector information with a spatial resolution of 50km and accuracies of $\pm$2m/s in wind speed and $\pm$20$^{\circ}$ in wind direction. Synthetic aperture radar (SAR) data over the ocean have the potential of providing wind vector information independent of weather conditions with finer resolution. Finer resolution wind vector information can often be useful particularly in coastal regions where the scatterometer wind information is often corrupted because of the lower resolution system characteristics which is often contaminated by the signal returns from the coastal areas or ice in the case of arctic environments. In this paper we tested CMOD_4 and CMOD_IFR2 algorithms for extracting the wind vector from SAR data. These algorithms require precise estimation of normalized radar cross-section and wind direction from the SAR data and the local incidence angle. The CMOD series algorithms were developed for the C-band, VV-Polarized SAR data, typically for the ERS SAR data. Since RADARSAT operates at the same C-band but with HH-Polarization, the CMOD series algorithms should not be used directly. As a preliminary approach of resolving with this problem, we applied the polarization ratio between the HH and VV polarizations in the wind vectors estimation. Two test areas, one in front of Inchon and several sites around Jeju island were selected and investigated for wind vector estimation. The new results were compared with the wind vectors obtained from CMOD algorithms. The wind vector results agree well with the observed wind speed data. However the estimation of wind direction agree with the observed wind direction only when the wind speed is greater than approximately 3.0m/s.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.465-471
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• 2000

The flow characteristics around an elliptic cylinder with axis ratio of AR=2 located near a flat plate were investigated experimentally to study the interaction between the cylinder wake and the turbulent boundary layer. The pressure distributions on the cylinder surface and on the flat plate were measured with varying the angle of attack of the cylinder. In addition, the velocity profiles of wake behind the cylinder were measured using a hot-wire anemometry As the angle of attack increases, the location of peak pressure on the windward and leeward surfaces of the cylinder moves toward the rear and front of the cylinder, respectively. At positive angles of attack, the position of the minimum pressure on the flat plate surface is moved downstream, but it is moved upstream at negative angles of attack. With increasing the angle of attack, the vortex shedding frequency is gradually decreased and the critical angel of attack exists in terms of the gap ratio. By installing the elliptic cylinder at negative angle of attack, the turbulent boundary layer over the flat plate is disturbed more than that at positive incidence. This may be attributed to the shift of separation point on the lower surface of the cylinder according to the direction of the angle of attack.

• 한국산업정보학회논문지
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• 제4권1호
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• pp.102-109
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• 1999

본 논문에서는 접지평면위에 2개의 유전체 층을 가지는 완전도체 격자구조에서의 전자파 산란문제를 간단한 방수치해석 방법으로 잘 알려진 PMM방법을 적용하여 입사각에 따라 수치해석하였다. 산란전자계는 Floquet 모드 함수의 급수로 전개하였다. 경계조건은 미지의 계수를 구하기 위하여 적용하였고, 도체의 경계조건은 접선성분의 전계와 스트립 위의 전류와의 관계를 위해 적용하였다. 입사각이 수직일 때 비유전율이 증가함에 따라 기하광학적 반사전력의 변하는 최소점은 스트립 폭이 높은 값으로 이동한다는 것은 주목되며, 이때 수직입사시 대부분의 전력은 다른 각도의 방향으로 산란된다.

• 대한전자공학회논문지TC
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• 제40권1호
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• pp.15-23
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• 2003

본 논문에서는 입사 신호의 근사 공분산 행렬을 이용하여 신호의 입사각을 빠르게 추정하는 입사각 추정 알고리듬을 제안한다. MUSIC(MUltiple Signal Classification) 알고리듬과 같은 기존의 부분공간 입사각 추정 알고리듬은 입력 공분산 행렬을 구하기 위해서 다수의 표본 신호를 필요로 하며, 입력 공분산 행렬을 획득하기 위한 표본 신호의 수신시간 동안 입사각 추정이 수행될 수 없으므로 빠른 신호처리가 불가능하다. 또한 코히어런트 신호가 입사하는 경우에 코히어런트 신호간의 간섭으로 신호의 입사각을 정확하게 추정할 수 없다. 제안한 입사각 추정 알고리듬은 빔 형성기를 이용하여 매 표본 신호의 공간적인 빔 형성을 먼저 수행하여 신호간의 간섭을 제거한 후에 센서의 출력 값을 이용하여 방위각 응답(bearing response)과 방향 스펙트럼(directional spectrum)을 구한다. 방위각 응답으로 대략적인 신호의 입사각을 추정한 후에 방향 스펙트럼을 이용하여 정착하게 신호의 입사각을 추정한다. 제안 입사각 추정 알고리듬은 공분산 행렬을 구하기 위하여 그 순간의 각 어레이 소자에 입사되는 표본 신호만을 사용하고 방위각 응답을 구하기 위해서 몇 순간 동안의 표본 신호만 필요로 하므로 기존 입사각 추정 알고리듬에 비하여 크게 향상된 입사각 추정 속도를 갖는다.