• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2000.09a
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• pp.133-139
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• 2000

일방향흐름의 해류나 천해파에 의한 파운동이나 해저면 가까이 경계층흐름은 주로 난류특성을 갖고 있으며, 난류특성은 완난류, 천이난류, 전난류 등 세 가지 증류로 대별된다. 그 중 완난류와 전난류로 대별하여 합성류 조건은 두 가지로 분류할 수 있다. 즉, 천해파와 해류가 합성될 때 해저면 가까이 난류특성 조건은 Table 1에 제시된 바와 같다. (중략)

• Proceedings of the Korea Water Resources Association Conference
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• 1993.07a
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• pp.115-122
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• 1993

• Korean Journal of Ecology and Environment
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• v.50 no.1
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• pp.57-69
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• 2017

Overwintering and succession of phytoplankton community with physicochemical and biological characteristics were investigated in pilot culture system. Water and phytoplankton samples were collected twice a week from February 23 to June 28, 2016. A total of 17 overwintering taxa including cyanophyceae, chlorophyceae, bacillariophyceae were identified in the experimental group in winter (February), and these overwintering species showed a marked succession pattern along with environment changes. In the process of phytoplankton succession, a total of 56 species in 28 genera were identified in two (experimental, control) pilot culture system. In the experimental group, 52 phytoplankton species in 24 genera were identified, and the number of taxa was highest in chlorophyceae (35 species), followed by Bacillariophyceae (9 species), Cyanophyceae (5 species) and others (3 species). In the control group, 25 phytoplankton species in 14 genera were classified and these taxa consisted of 17 chlorophyceae, 3 cyanophyceae, 2 Bacillariophyceae and 3 others. The standing crops ranged from 40 to $325,450cells\;mL^{-1}$ in the experimental group, and from 900 to $37,100cells\;mL^{-1}$ in the control group, respectively. The dominant species were represented by Monoraphidium minutum, Microcystis aeruginosa, Rhodomonas lacustris, Ankyra judai and Chlorella vulgaris in the experimental group; and M. minutum and Coenochloris cf. pyrenoidosa in the control group. In conclusion, overwintering and succession of predominant phytoplankton species developed due to interactions of internal environmental factors(physicochemical and biological factors) in the pilot culture system.

• Korean Journal of Environment and Ecology
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• v.27 no.4
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• pp.473-486
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• 2013

Vegetational structure and successional sere were investigated for Paryeongsan Zone in the Dadohaehaesang National Park incorporated in National Park in 2011. To do so, seventy-five plots($100m^2$) were set up and surveyed. The surveyed plots were divided into six groups according to the analysis of classification by TWINSPAN; (I) Quercus acutissima community, (II) Q. serrata-Carpinus tschonoskii var. tschonoskii community, (III) Pinus densiflora-Q. mongolica community, (IV) Q. variabilis community, (V) P. rigida-Q. variabilis-P. densiflora community, (VI) Chamaecyparis obtusa community. The results of vegetation structure analysis were. I, IICommunity, were expected that the deciduous oak trees with deciduous oak trees or Carpinus tschonoskii var. tschonoskii competing with oak trees would flourish in a deciduous broad-leaved forest. III, VCommunity, were expected that the P. densiflora and P. rigida competing with oak trees would flourish in a deciduous broad-leaved forest. IVCommunity, have expanded the influence of Q. variabilis, but understory will be developed next ecological succession by a high percentage of Machilus thunbergii in frequency of warm-temperate trees. VI Community, Chamaecyparis obtusa community were expected continue. This Chamaecyparis obtusa community is picked thinning Chamaecyparis obtusa as moving purpose of National Park, it will be inducement a plant vegetation succession to the natural forest. Frequency of warm-temperate trees in the Paryeongsan Zone of warm temperate climate zone was a total 9 species, Machilus thunbergii, Eurya japonica, Elaeagnus macrophylla, etc.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.1
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• pp.14-21
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• 2006

This paper presents a Zero-Current Switching(ZCS) two-transformer phase-shifted full-bridge(TTFB) converter using voltage ripple. The proposed converter provides Zero-Voltage Switching(ZVS) of leading leg switches and ZCS of lagging leg switches using voltage ripple. Especially, circulating current is reduced by ZCS operation and there are no additional components required for the soft switching of power switches. Furthermore, in case of light load, ZVS operation of lagging leg can be achieved. The operations, analysis and design consideration of proposed converter are presented. To verify the validity of the proposed converter, experimental results for a 410W (205[V], 2[A]) prototype are presented.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.291-291
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• 2018

하천 및 수자원의 효율적인 관리와 더불어 다양한 수공구조물의 운영 및 관리를 위해서 구조물 주변에서 발생하는 불연속 흐름 및 급변류 등의 현상과 구조물 운영을 반영한 수치해석 기법을 이용한 모델 개발의 중요성이 커지고 있다. 본 연구에서는 하천의 불연속 흐름을 모의하기 위한 1차원 흐름해석 모형(K-River)을 개발하였다. 본 모형은 천이류와 급변류를 수치적으로 안정하게 처리하기 위하여 지배방정식을 보존형 Saint-Venant 방정식으로 선정하고, FVM과 Forward Euler 방법을 이용하여 이산화를 수행하였다. 수치흐름률을 계산하기 위해서 불규칙 단면과 하상의 급경사 등에 신뢰도가 높은 기법으로 판단되는 근사 Riemann해법 중 하나인 HLL flux를 이용하였다. 개발된 K-river 모형의 검증을 위해서 해석해가 존재하는 타원형의 하상융기가 있는 하도에 적용하였으며, 국내에서 하천 설계 및 관리를 위해서 광범위하게 이용되고 있는 1차원 흐름해석 모형인 FDM기반의 HEC-RAS 모의결과와 비교 검토를 수행하였다. 그 결과, FDM기법에서는 모의되지 않는 일부 급변류 패턴을 개발 모형을 통해 모의가능하였으며, 전체적으로 K-River가 기존 모형 보다 해석해에 근사한 결과를 나타내었다. 또한, 배수문을 비롯하여 합류부, 분류부, 펌프장, 암거 등이 설치되어 운영되고 있는 아라뱃길에 적용하여 K-River의 적용성을 평가하였다. K-River를 이용하여 아라뱃길의 흐름분석을 수행한 경우가 HEC-RAS를 이용한 경우보다 수위와 유량의 유동을 시간에 따라 세밀하게 모의하였으며, 이는 배수효과에 의한 파의 전달이 FDM기법 대비 정확히 모의되기 때문으로 판단된다. 추후 연구에서는 현재보다 시간간격을 상세화 하여 수집된 관측수위를 통해 추가적인 검증을 수행하고, 다양한 특성을 가진 타 하천 등에 적용하여 모형의 적용성을 확대하고자 한다.

• Journal of Korea Water Resources Association
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• v.38 no.2
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• pp.155-166
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• 2005

Upwind schemes are very well adapted to the discontinuous flow and have become popular for applications Involving dam break flow, transcritical Slow, etc. However, upwind schemes have been applied mainly to the idealized problems not to the natural channels with irregular geometry so far because of the error due to source terms. In this paper, the new type of upwind discretization of source terms, which uses the normalized Jacobian to discretize the source terms, is proposed. As results of tests to flows with source terms by the upwind models, the method proposed in this paper is proved as efficient and accurate. This generalized method for differencing source terms is simple and might beapplicable to diverse type of flux upwind discretization scheme in finite difference method.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.389-389
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• 2022

상수도 관망에서의 유량 측정은 유수율을 결정하는 데 있어서 중요한 평가 수단이다. 따라서, 유량 측정을 위해 유량계를 활용하는데, 높은 빈도의 자료를 획득할 수 있는 수압계는 시중에서 저가로 활용 가능하지만, 상수도관망 예산의 상당부분을 차지하고 있는 유량계는 수압계보다 고가에도 낮은 빈도의 자료만을 획득하는 비용 대비 낮은 효율을 가진다. 만약 수압계의 측정자료를 유량자료로 고속전환하는 기술을 개발하면 기존의 유량계보다 적은 비용으로 고빈도의 유량자료를 획득할 수 있다. 상수도 관망에서 수압자료를 유량 자료로 전환하는 기술은 기존 관망에서 유도된 지배방정식에서 임의 관망에서 일련의 유도과정을 거쳐 상하류 단사이 수압과 유량의 관계를 형성하고, 이러한 관계를 활용하여 간단한 저수조-관망-밸브 체제에서 관망 내의 특정지점에서의 시간상 수압자료와 시간상 유량자료의 비를 정의한 다음, 임의의 지점에서 측정된 수압자료를 정의한 비로 나타나는 임피던스 역수를 역푸리에 전환하면 시간상의 유량자료를 획득할 수 있는 원리이다. 이러한 수압-유량 전환기술의 원리를 가지고 개발된 기술의 정확도를 확인하는 과정을 수행하였으며, 이는 전통적 천이류 해석 방법인 특성선 모델로 비교하는 수치해석적인 방법 그리고 실제 설치된 관망을 사용해서 수압을 측정하고, 지정된 지점에서 유량을 정밀측정하여 비교하는 실험적인 방법을 통해 정확도를 비교해봄으로써 개발된 기술을 검증해보고자 한다.

• Microbiology and Biotechnology Letters
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• v.30 no.3
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• pp.282-286
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• 2002

Seasonal succession of algae and water quality parameters were studied in artificial reservoirs in Daegu city from 2000 to 2001. The algal succession was evaluated with respect to dom-inant class and their frequencies. Succession order of algae in two reservoirs was : Bacillariophyceae longrightarrow Chlo-rophyceae longrightarrow Cyanobacteria longrightarrow Bacillariophyceae longrightarrow Bacillariophyceae longrightarrow Cyanobacteria longrightarrow Cyanobacteria longrightarrow Cyanobacteria. This succession order was different from other studies. The local environment condition maybe affects the succession of algae in these reservoirs. As result of correlation analysis between algal biom-ass and water quality parameters, we got low correlation coefficients. Also we got low correlation coefficients between chlorophyll-a and algal biomass. Between chlorophyll-a and water quality parameters, we got high correlation coefficients. An approach having attention to cell biovolume rather than cell number is made to understand the algal community and the ecosystem of reservoir.

• Korean Journal of Environmental Biology
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• v.33 no.3
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• pp.330-337
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• 2015

Pre-monsoon dynamics of zooplankton community were investigated in Yongwol West River tributary; wetland shaped Korean Peninsula. Zooplankters were collected at three sites (stn 1: Yongwol West River, stn 2: Pyungchang River, stn 3: Jucheon River) monthly during the period between March and July 2014 except April. Totally 58 taxa of zooplankton occurred, consisting of 27 species of rotifer, 18 species of cladoceran, eight species of copepod, four kinds of aquatic insect larvae and one nematod. Lotic cladocerans of Alona spp. belonging to Chydoridae occurred frequently while typical lentic ones of Bosmina spp. and Daphnia spp. were not distributed, then sampling sites may be located in lotic waters. Zooplankton abundance recorded as $4,451-8,011indiv{\cdot}m^{-3}$ in Jucheon River but never exceeded $500indiv{\cdot}m^{-3}$ in other rivers. In Yongwol West River, dominant taxa were aquatic insect larvae from March through June and succeeded to cladocerans and copepods in July. Similar succession was observed in Jucheon River where aquatic insect larvae dominated in March and changed to cladocerans and copepods from May with high abundance. No such succession of zooplankton community was detected in Pyunchang River. Species diversity indices were the highest in Yongwol West River except in March. High values of dissolved oxygen ($9.0-11.0 mg{\cdot}liter^{-1}$) may show the characteristics of mountain streams. Water temperature increased gradually from $10.1^{\circ}C$ to $27.9^{\circ}C$ and pH varied within generally high range between 7.9-8.9, respectively. High value of pH seems to be derived from lime stone mines and cement factories around the studied area.