• Nuclear Engineering and Technology
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• 제24권2호
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• pp.111-120
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• 1992

본 논문은 안전정지지진에 대한 spacer grid충격하중의 동적특성을 고찰한 것이다. 안전정지지 진 (SSE： Safe Shutodown Earthquake)을 가진력으로 사용하였고 모델로는 가장 긴 15 row의 핵연료집합체 모델을 사용하였다. 외부에서 제공되는 입력데이타의 불확실성을 보상하기 위하여 흔히 사용되는 10%증가된 입력값과, NRC 권고사항인 입력응답스펙트럼의 이동효과의 영향이 평가되었다. 평가대상으로는 spacer grid의 충격력이 사용되었다. 해석결과로서 입력응답 스펙트럼의 이동효과의 영향은 거의 무시할 수 있으나 증가된 입력값의 영향은 spacer grid의 충격력에 큰 영향을 줌을 알 수 있었다. 따라서 원자로노심의 동적응답을 위해서는 입력응답 스펙트럼을 이동시키면서 해석할 필요가 없음을 확인하였다.

• 수산해양기술연구
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• 제52권2호
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• pp.88-95
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• 2016

Most grid sorting has been used to sort out flatfish in shrimp fisheries, while double grid systems have been tested to separate smaller shrimp. The escape of juvenile red seabream through separating panels made with steel grids or large mesh tested for masking effects in a two-species system. Fish behavior was observed in a circulating water tank. The escape rate was 20% greater with the separating codends than with the normal codend in the single-species experiments. The rates in the two-species experiments were 30% or 20% greater than the single-species rates for the normal or separating codends, respectively. The seabream retention rates in the grid separator codend decreased as rockfish retention increased, possibly due to a threat effect. Conversely, the retention rate of both species increased concurrently in the net separator, possibly due to a masking effect. The escape rates of juvenile red seabream varied by compartment in the mesh separating codend. These results suggest that grid separating codends can be used in the field as towed fishing gear to reduce juvenile catch.

• Nuclear Engineering and Technology
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• 제52권11호
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• pp.2479-2490
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• 2020

We performed experiments to measure a single-phase upward flow in a 5 × 5 rod bundle with spacer grids using a particle image velocimetry, focusing on the crossflow. The Reynolds number based on the hydraulic diameter and the bulk velocity is 10,000. The ratio of pitch between rods and rod diameter is 1.4 and spacer grid is installed periodically. The turbulence in the rod bundle results from the combination of a forced mixing and natural mixing. The forced mixing by the spacer grid persists up to 10D_h from the spacer grid, while the natural mixing is attributed to the crossflow between adjacent subchannels. The combined effects contribute to a sinusoidal distribution of the time-averaged stream-wise velocity along the lateral direction, which is relatively weak right behind the spacer grid as well as in the gap. The streamwise and lateral turbulence intensities are stronger right behind the spacer grid and in the gap. Based on these findings, we newly defined a modified mixing coefficient as the ratio of the lateral turbulence intensity to the time-averaged streamwise velocity, which shows a spatial variation. Finally, we compared the developed model with the measured data, which shows a good agreement with each other.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1998년도 가을 학술발표회 논문집
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• pp.283-290
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• 1998

• 대한디지털의료영상학회논문지
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• 제9권2호
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• pp.23-30
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• 2007

This study attempts to propose an appropriate method of using digital medical imaging equipments, by studying the effects of automatic exposure control(AEC), grid ratio and the change of radiography distance on the patient dose and detertor acquisition dose during the procedure of acquiring image through a digital medical imaging detector. The change of dose following the change of grid ratio's exposure and radiography distance was measured, by using an abdominal phantom organized with tissue equivalent materials in an amorphous silicon thin film transistor detecter installed with AWC. The case to use grid ratio 12 : 1, focal distance 180cm to radiography distance 110cm in AEC, the patient dose increased rather when we used grid ration 10 : 1, focal distance 110cm. When AEC was not used,the dose necessary for image acquisition decreased as the grid ratio became higher and the distance became further. but detector acquisition dose was not reduced when in applied AEC. When purchasing digiral medical imaging equipments, optional items such as AEC and grid shall be accurately selected to satisfy the use of the equipments. Radiography error made by radiation technologist and unnenessary patient dose can be reduced by selecting equipments with a radiography distance marker equipment when it did not apply AEC. These equipments can also be helpful in maintaining high imaging quality, one of the merits of digital detectors.

• 한국수자원학회논문집
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• 제31권2호
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• pp.199-208
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• 1998

유역의 지형특성에 근거를 두고 유출기여면적의 변화를 고려한 분포형 모형인 TOPMODEL을 이용하여 홍수유출해석에 대한 적용성을 연구하였다. 건설교통부에서 설치운영중인 위천대표시험유역의 소유역인 동곡 및 고로지점을 분석대상유역으로 선정하였으며, 1/25,000 지형도를 이용하여 수치고도지도를 작성하였고 지형인자분석은 지리정보 시스템 도구인 Arc/Info를 이용하였다. 두 소유역의 지형상수가 서로 비슷하였고 각 연도별 동일호우사상에 대한 모형매개변수도 서로 유사한 특성을 나타내었다. TOPMODEL을 이용한 홍수유출에 대한 첨두유량의 모의 결과는 관측치와 비교할 때 그 재현성이 매우 우수하였다. 격자의 크기별로 유역을 분할하고 그에 따른 첨두유량과 발생시각의 변화를 동곡소유역은 100,120,240m, 고로유역은 120,200,360m 격자로서 분석한 결과 두 유역 모두 격자 크기의 증가에 따라 첨두유량은 증가하고 발생시각은 격자의 크기와 관계없이 일정한 것으로 나타났다.

• 한국농림기상학회지
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• 제6권3호
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• pp.149-163
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• 2004

Evapotranspiration (ET) is a critical component of the hydrologic cycle which influences economic activities as well as the natural ecosystem. While there have been numerous studies on ET estimation for homogeneous areas using point measurements of meteorological variables, monitoring of spatial ET has not been possible at landscape - or watershed - scales. We propose a site-specific application of the land surface model, which is enabled by spatially interpolated input data at the desired resolution. Gyunggi Province of South Korea was divided into a regular grid of 10 million cells with 30m spacing and hourly temperature, humidity, wind, precipitation and solar irradiance were estimated for each grid cell by spatial interpolation of synoptic weather data. Topoclimatology models were used to accommodate effects of topography in a spatial interpolation procedure, including cold air drainage on nocturnal temperature and solar irradiance on daytime temperature. Satellite remote sensing data were used to classify the vegetation type of each grid cell, and corresponding spatial attributes including soil texture, canopy structure, and phenological features were identified. All data were fed into a standalone version of SiB2(Simple Biosphere Model 2) to simulate latent heat flux at each grid cell. A computer program was written for data management in the cell - based SiB2 operation such as extracting input data for SiB2 from grid matrices and recombining the output data back to the grid format. ET estimates at selected grid cells were validated against the actual measurement of latent heat fluxes by eddy covariance measurement. We applied this system to obtain the spatial ET of the study area on a continuous basis for the 2001-2003 period. The results showed a strong feasibility of using spatial - data driven land surface models for operational monitoring of regional ET.

• 대한조선학회논문집
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• 제44권1호
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• pp.16-25
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• 2007

Studies of unsteady-airfoil flows have been motivated mostly by efforts to avoid. or reduce such undesirable effects as flutter, noise and vibrations, dynamic stall. In this paper, we carry out a computational study of viscous flows around a two-dimensional oscillating airfoil to investigate unsteady effects in these important and challenging flows. A fully implicit incompressible RANS solver has been used for calculating unsteady viscous flows around an airfoil. The cell-centered End order finite volume method is utilized to discretize governing equations. in order to ease the flow computation for fluid region changing in time, improve the qualify of solution and simplify the grid generation for an oscillating airfoil flow, the computational method adopts a moving and deforming grid generation technique based on the multi-block grid topology. The numerical method is applied for calculating viscous flows of an oscillating NACA 0012 in uniform flow. The computational results are compared with available experimental data. Computed results are compared with experimental data and flow characteristics of the experiment are reproduced well In the computed results.

• Journal of Power Electronics
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• 제11권4호
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• pp.471-478
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• 2011

This paper addresses the establishment of a kVA-range plug-in hybrid electrical vehicle (PHEV) integration test platform and associated issues. Advancements in battery and power electronic technology, hybrid vehicles are becoming increasingly dependent on the electrical energy provided by the batteries. Minimal or no support by the internal combustion engine may result in the vehicle being occasionally unable to recharge the batteries during highly dynamic driving that occurs in urban areas. The inability to sustain its own energy source creates a situation where the vehicle must connect to the electrical grid in order to recharge its batteries. The effects of a large penetration of electric vehicles connected into the grid are still relatively unknown. This paper presents a novel methodology that will be utilized to study the effects of PHEV charging at the sub-transmission level. The proposed test platform utilizes the power hardware-in-the-loop (PHIL) concept in conjunction with high-fidelity PHEV energy system simulation models. The battery, in particular, is simulated utilizing a real-time digital simulator ($RTDS^{TM}$) which generates appropriate control commands to a power electronics-based voltage amplifier that interfaces via a LC-LC-type filter to a power grid. In addition, the PHEV impact is evaluated via another power electronic converter controlled through $dSPACE^{TM}$, a rapid control systems prototyping software.

• Journal of Power Electronics
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• 제17권5호
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• pp.1231-1243
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• 2017

Grid-interactive power converters are normally synchronized with the grid using phase-locked loops (PLLs). The performance of the PLLs is affected by the non-ideal conditions in the sensed grid voltage such as harmonics, frequency deviations and the dc offsets in single-phase systems. In this paper, a single-phase PLL is presented to mitigate the effects of these non-idealities. This PLL is based on the popular second order generalized integrator (SOGI) structure. The SOGI structure is modified to eliminate the effects of input dc offsets. The resulting SOGI structure has a high-pass filtering property. Hence, this PLL is termed as a high-pass generalized integrator based PLL (HGI-PLL). It has fixed parameters which reduces the implementation complexity and aids in the implementation in low-end digital controllers. The HGI-PLL is shown to have the lowest resource utilization among the SOGI based PLLs with dc cancelling capability. Systematic design methods are evolved leading to a design that limits the unit vector THD to within 1% for given non-ideal input conditions in terms of frequency deviation and harmonic distortion. The proposed designs achieve the fastest transient response. The performance of this PLL has been verified experimentally. The results agree with the theoretical prediction.