• Wind and Structures
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• 제18권5호
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• pp.511-528
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• 2014

The characteristics of wake galloping phenomenon for two parallel/unparallel circular cylinders were investigated via wind tunnel tests. The two cylinders were initially deployed in parallel and wake galloping phenomena were observed by varying the center-to-center distance. The effect of an unparallel arrangement of two cylinders was next investigated by fixing the spacing ratio of one side of the cylinders at 5.0D and the other side at 3.0D, in which D represents the diameter of the cylinder. For the unparallel disposition, the 5.0D side showed a small, limited vibration while the 3.0D side produced much larger amplitude of vibration, resulting in a rolling motion. However, the overall amplitude appeared to decrease in unparallel disposition when compared with the amplitude of the 3.0D - 3.0D parallel case. This represents the mitigation effect of wake galloping due to the unparallel disposition between two cylinders. Flow visualization tests with particle image velocimetry were conducted to identify flow fields between two cylinders. The test results demonstrate the existence of a complex interaction of the downstream cylinder with the shear layer generated by the upstream cylinder. When the spacing ratio was large enough, the shear layer was not observed and the downstream cylinder showed only limited random vibration.

• Fisheries and Aquatic Sciences
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• 제1권1호
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• pp.30-34
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• 1998

Rotifer culture fed on five types of artificial microparticle diets were evaluated to substitute the natural diets such as Chlorella or w-yeast. These microparticle diets including solidified blood using squid oil (SBSO), solidified blood using soybean oil (SBSB), nylon protein walled particle (NPW) simple coacervation oil capsule (SCO), complex coacervation oil capsule(CCO), were tested for the evaluation of feeding efficiency. The prepared micro particle diets had diameters ranging from 3 to 30 Jim. Rotifer culturing experiments were carried out in 3-liter beakers for 13-16 days. The initial inoculum density of rotifers was 10 ind./ml. The rotifers fed on Chlorella or $\omega-yeast$ showed maximal densities of 2,000 ind./ml in 9 days or 500 ind./ml in 7 days, respectively. Those fed on SBSO, SBSB or NPW showed maximal densities of 1568 ind./ml, 586 ind./ml or 503 ind./ml, respectively and the reproductive rates for those diets were equivalent to or better than w-yeast. However, the coacervated oil capsule showed lower maximal densities of 400 ind./ml for SCO and less than 100 ind./ml for CCO due to the unbalanced diet formulation and indigestibility.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2009년도 정보통신설비 학술대회
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• pp.36-39
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• 2009

We developed an optimal design interface based on VBA(Visual Basic Application) that takes advantage of API(Application Program Interface) function of commonly used EM analysis software. The developed interface is adopted for an optimal design of a septum in a waveguide tee junction using PSO(Particle Swarm Optimization) algorithm. The objective function of the optimal design is defined by $S_{11}$-parameter of the waveguide tee junction Design variables are established as position of the septum, that are changed to satisfy the design goal Using the developed design interface and PSO algorithm, the objective function converged to the smallest value, showing the validity of the proposed method. The design interface was developed using Microsoft Excel software, enabling easy control of design parameters for user. Also, various analysis parameters can be set in the Excel interface, including waveguide input mode and frequency. After completion of the design, field solutions at user-specified positrons can be extracted to the output files in complex number form.

• 한국환경과학회지
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• 제19권2호
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• pp.157-170
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• 2010

Air mass recirculation is a common characteristic in the coastal area as a result of the land-sea breeze circulation. This study simulates the recirculation of air mass over the Gwangyang Bay using WRF-FLEXPART and offers a basic information about the effective domain size that can reflect recirculation. For this purpose, WRF is set up four nested domains and three cases are selected. Subsequently FLEXPART is operated on the basis of WRF output. During the clear summer days with weak wind speed, particles that emitted from Yeosu national industrial complex and Gwangyang iron works flow into emission sources because of the land-sea breeze. When land-sea breeze is strengthen, the recirculation phenomena appears clearly. However particles aren't recirculated under weak synoptic condition. Also plume trajectory is analyzed and as a consequence, the smallest domain area have to be multiplied by 1.3 to understand recirculated dispersion pattern of particles.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.517-520
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• 2002

Stereoscopic particle image velocimetry is a measurement technique to acquire of three dimensional velocity field by two cameras. With a laser sheet illumination, the third velocity component can be deduced by out-of-plane velocity components using a stereoscopic matching method. Industrial fluid flows are almost three dimensional turbulent flows, so it is necessary to use the stereoscopic PIV measurement method. However the existing stereoscopic PIV system seems hard to use since it is very expensive and complex. In this study we have developed a Stereoscopic Miniature PIV(MPIV) system based on the concept of the Miniature PIV system which we have already developed. In this paper, we address the design and some first experimental results of the stereoscopic PIV system. The Stereoscopic MPIV system features relatively modest performances, but is considerably smaller, cheaper and easy to handle. The proposed Stereoscopic MPIV system uses two one-chip-only CMOS cameras with digital output. Only two other chips are needed, one for a buffer memory and one for an interfacing logic that controls the system. Images are transferred to a personal computer (PC) via its standard parallel port. No extra hardware is required (in particular, no frame grabber board is needed).

• 대한기계학회논문집
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• 제16권11호
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• pp.2159-2168
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• 1992

본 연구에서는 CWS 액적의 가열 및 연소에 관한 현상규명에 있어서 액적크기, CWS 석탄함량 및 연소분위기 가스온도, CWS 액적중의 미분된 석탄입자의 크기와 특히 분위기중의 산소농도의 변화에 의한 영향을 파악하고자 한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권1호
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• pp.61-80
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• 2018

Location information of individual nodes is important in the implementation of necessary network functions. While extensive studies focus on localization techniques in 2D space, few approaches have been proposed for 3D positioning, which brings the location closer to the reality with more complex calculation consumptions for high accuracy. In this paper, an effective range-free localization scheme is proposed for 3D space localization, and the sensitivity of parameters is evaluated. Firstly, we present an improved algorithm (MDV-Hop), that the average distance per hop of the anchor nodes is calculated by root-mean-square error (RMSE), and is dynamically corrected in groups with the weighted RMSE based on group hops. For more improvement in accuracy, we expand particle swarm optimization (PSO) of intelligent optimization algorithms to MDV-Hop localization algorithm, called PMDV-hop, in which the parameters (inertia weight and trust coefficient) in PSO are calculated dynamically. Secondly, the effect of various localization parameters affecting the PMDV-hop performance is also present. The simulation results show that PMDV-hop performs better in positioning accuracy with limited energy.

• 한국도로학회논문집
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• 제6권3호
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• pp.55-64
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• 2004

최대건조단위중량은 노상토 재료 특성으로서 매우 중요한 인자이다. 최대건조단위중량을 예측하는 기존의 모델들은 많은 변수를 포함하고 있어 다소 복잡해 보인다 본 논문에서는 사질토의 최대건조단위중량을 예측할 수 있는 간편한 식을 제안하였다. 이를 위해 36개 시료를 체분석하여 입도분포를 구하고, 다짐시험 한 후 그 결과를 회귀 분석하였다. 제안식은 변수로 노상토의 기하평균과 기하표준편차 또는 입도분포계수를 포함한다. 제안식의 검증을 위해 전국16개 지역의 채취 시료에 대한 최대건조단위중량의 실측치와 예측치를 비교한 결과 잘 맞는 것으로 밝혀졌다.

• 한국화재소방학회논문지
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• 제16권3호
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• pp.1-7
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• 2002

Diffusion and dispersion of injected $CO_2$gas into the $N_2$ gas flow are complex. In the packed column with porous particles the axial dispersion and the extra-particle mass transport as well as the intra-particle mass transport are involved. The pulse spreads by stationary diffusion during the period of arrested flow. Hence, the effect of axial dispersion, and of entrance and exit, as well as that of intraparticle convection should be eliminated during the period. The effective diffusivity was determined experimentally by using the gas chromatography, which is to arrest the gas flow during the period after injecting the pulse. This experiment method hasn't been used often in the field. Effective diffusivities are raised with temperature increasing, and it is quite satisfied com-pared to literature values. In this study, the calculated data of gaseous chemical for extinguish fires could be helpful to appreciate several physical phenomenons. Also, it could be expected that, the calculated data of this study might be very useful for development of excellent gaseous chemical for extinguish fires and improvement of its efficiency.

• 자원환경지질
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• 제33권3호
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• pp.195-204
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• 2000

order to investigate physical characteristics and element concentrations of sediments, coastal bottom sediments were collected at 20 stations in the vicinity of Youngkwang Nuclear Power Plant. After air drying of samples in the laboratory. article size distribution was examined by Master sizer (X-350F), radio-activity by HPGe ${\gamma}$-spectrphotometer, and element concentrations by ICP-AES and AAS. According to particle size analysis , sediments are mainly composed of silt fraction weith 23% of sand, 65% of silt and 12% of clay on average. Most sediments are derived from muddy environment that silt dominates with the characteristics of 5.3${\varsigma}$ mean particle size, poorly sorted, very fine skewed and lepto-kurtic. Only two sediments are well sorted with sandy silt owing to wind, winnowing action, tide and current andits complex reactions. Element concentrations in the coastal bottom sediments are relatively high at finer sediment and show significant relationship with grain size. Index of geoaccumulation by heavy metals at every sampling station is classified as practically unpolluted. The radioactivities of the sediments were measured for 15 isotope elements, and 2 elements of K-40 and Cs-137 were detected in most sediments. The K-40 is the natural nuclide and the artificial nuclide of Cs-137 was thought to be derived from the fallout of past nuclear weapon test. The results of correlation coefficient between grain size and radioactivity shows that the activity of Cs-137 significantly increases in finer grain.