• Solar Energy
• /
• v.17 no.4
• /
• pp.23-33
• /
• 1997

In this paper, performance of various working fluids is evaluated for the closed Ocean Thermal Energy Conversion(OTEC) power plant operating on Rankine cycle. The evaporator and condenser are modeled via UA and LMTD method while turbine and pump are modeled by specifying isentropic efficiencies. R22, Propane, Propylene, R134a, R125, R143a, R32, R410A and Ammonia are used as working fluids. Results show that newly developed fluids such as R410A and R32 that do not cause stratospheric ozone layer depletion perform as well as R22 and ammonia. The superheat at the evaporator exit and subcooling at the condenser exit do not affect the performance of the simple OTEC power cycle. Turbine efficiency and heat exchanger size influence greatly the performance of the Rankine cycle. Finally, it was shown that closed OTEC power plants can practically generate electricity when the difference in warm and cold sea water inlet temperatures is greater than $20^{\circ}C$.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.23 no.2
• /
• pp.161-167
• /
• 2017

This paper measured and evaluated the technical efficiency, pure technical efficiency and scale efficiency of port labor via three inputs and three outputs using Data Envelopment Analysis (DEA). First, the average overall technical efficiency measured about 94.18 %, with 100 % pure technical efficiency being larger than 94.18% scale efficiency. As a result, 7 ports were identified as efficient, and 4 ports were identified as inefficient. Among the 4 ineffiecient ports, Donghae had the highest Increasing Return to Scale (IRS). However, the inefficient ports were all found to be less efficient in terms of resource operation than production scale. On the other hand, the efficient ports established priorities using the super efficiency method. As a result, port efficiency was highest for Incheon, Mokpo, Pyeongtaek-Dangjin, Masan, Yeosu Gwangyang, Jeju, and Gunsan-Daesan Ports, in order. In particular, Busan Port, found to be inefficient, would benefit from using Mokpo Port and Incheon Port as benchmarks to increase trade volume and modernize equipment for full-scale commercialization to improve labor efficiency.

• Journal of Marine Bioscience and Biotechnology
• /
• v.6 no.2
• /
• pp.110-117
• /
• 2014

Recently microalgae have been proposed as a promising biodiesel feedstock, owing to their higher lipid productivity and non-arable land based cultivation system. Biomass and lipid productivities of microalgae are largely affected by various environmental and nutritional factors. In this study, the effects of nitrogen (nitrate and ammonium) and organic carbon (glucose and glycerol) sources on the cell growth and lipid production of Chlorella sp. KR-1 were examined in flask cultures. Under autotrophic culture conditions for 15 days, overall cell growth and lipid (fatty acid methyl ester, FAME) production with nitrate were better than those of ammonium, resulting in 1.06 g cell/L and 333 mg FAME/L, respectively. Maximal intracellular lipid contents (348 - 352 mg FAME/g cell) were observed at low concentrations of 1 mM for both nitrate and ammonium. In the supply of light, addition of glucose in the range of 1 - 20 g/L showed higher cell densities than the autotrophic cell growth condition. Higher lipid accumulation of 375 mg FAME/g cell could achieved at 5 g glucose/L albeit of relatively short incubation of 7 days. With glycerol, intracellular lipid contents were ~1.9 times lower than glucose cases although similar cell growths were observed for both carbon sources.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.27 no.6
• /
• pp.419-423
• /
• 2015

The flowing caused by artificial upwelling structure occurs ascending water flowing and vortex of rear side. In this moment, plentiful nutrient in the bottom water moves to the surface of the water and makes those plankton and fishing ecology promoted so that the fishing productivity can be enhanced. In this study, the changes of the upwelling flowing is included in consideration of the conditions of stratification by using CFD. In the conclusion, the closer upwelling effect is from the artificial upwelling structure, the better effectiveness comes out. Regardless of the conditions of stratification, only the upwelling feature from the bottom to the surface was shown up. But considering the conditions of stratification, the repeated flowing feature between upwelling and downwelling was verified.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.30 no.4
• /
• pp.191-199
• /
• 2018

In this paper, wind data at 20 locations are collected and analyzed in order to review optimal candidate site for offshore wind farm around Korean marginal seas. Observed wind data is fitted to Rayleigh and Weibull distribution and annual energy production is estimated according to wind frequency. As the model of wind turbine generator, seven kinds of output of 1.5~5 MW were selected and their performance curves were used. As a result, Repower-5 MW turbines showed high energy production at wind speeds of 7.15 m/s or higher, but G128-4.5 MW turbines were found to be favorable at lower wind speeds. In the case of Marado, Geojedo and Pohang, where the rate of occurrence of wind speeds over 10 m/s was high, the capacity factor of REpower's 5 MW offshore wind turbine was 56.49%, 50.92% and 50.08%, respectively.

• Journal of Marine Bioscience and Biotechnology
• /
• v.8 no.2
• /
• pp.45-53
• /
• 2016

Most of microalgae shift their metabolic pathways toward the fatty acid biosynthesis following nitrogen deprivation. Recent studies on Nannochloropsis species, oleaginous microalgae, have been performed to investigate the regulation of contents and compositions of fatty acids under stressful condition. The objective of this experiment is to identify the effect of nitrogen on cell growth and fatty acids production in Nannochloropsis oculata K-1281 and compare fatty acid composition response to nitrogen deficiency between N. oculata LB2164 and K-1281. The fatty acids content in N. oculata K-1281 was increased up to 210%, while the growth rate was decreased under nitrogen deficient condition. The contents of C16:0 and C16:1 increased dramatically in both N. oculata K-1281 and LB2164, while the contents of C20:4 and C20:5 increased in N. oculata LB2164. The fatty acids content and composition in N. oculata K-1281 returned following addition of nitrogen after nitrogen starvation. These results demonstrated that fatty acid contents and compositions under nitrogen deficiency will provide the understanding of fatty acid synthesis in microalgae.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.43 no.1
• /
• pp.1-11
• /
• 2007

It is the basic studies for productivity improvement and laborsaving of purse seine fishery. Because the seine shape is apt to be transformed in seine shooting process due to the effect of tide, this study is intended to establish 4 steps, whose flow velocity are 0, 2, 4 and 6cm/sec, in flume tank and perform the experiment to review the character. We used two model seines designed on the scale of 1 to 180 based on the power block seine, which is the mackerel purse seine generally used in the near sea of Jeju Island and triplex seine, which is the mackerel purse seine of one boat system fishing expected in the future, for the experiment, analyzed of the sinking movements on the two seines and its results are as follows. In the setting over the flow velocity 6cm/sec, experiment was impossible because of flying and transformation of seine were severe. The sinking movements of P seine and T seine generally showed linear phenomenon and the sinking speed showed gentle curve shape. Sinking tendency was distinguished by existence of flow velocity. When there is flow velocity, it showed the phenomenon that it sinking by similar type. Although sinking depth and sinking speed did not show distinguished classification, P seine shows bigger than T seine. When there was in flow velocity, the elapsed time(Et) and sinking depth (PDp, TDp) of P seine and T seine can be shown such experimental equations as PDp=(0.21V+4.96)Et-(0.62V-0.10) and TDp=(0.19V+4.95)Et-(0.72V+0.34). When there was in flow velocity, the elapsed time and siking speed (PSp, TSp) of P seine and T seine can be shown such experimental equations as $PSp=-0.11Et^2+1.42Et+1.75\;and\;TSp=-0.11Et^2+1.41Et+1.37$.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2017.05a
• /
• pp.360-360
• /
• 2017

이상기상현상의 발생횟수가 지속적으로 증가함에 따라 기상 예측은 국가 재난 관리에 중요한 요소로써 부상하고 있다. 계절예측 또한 재난관리의 한 부분으로, 농업, 에너지, 수자원 그리고 공공보건 등 다양한 분야에서 잠재적 위험을 파악하는데 도움이 되는 보조 자료로 활용이 가능하다. 본 연구에서는 ICON(ICOsahedral-Nonhydrostatic) 모델을 이용하여 2015년 여름철(JJA) 강수를 예측하였다. 2015년은 장마기간을 포함한 여름철 동안 평년대비 약 절반수준(54%)에 그치는 비가 내렸으며, 태풍으로 인한 강수량도 적어 연 강수량이 평년대비 72%로 역대 최저 3위를 기록하였다. 지역별로 보면 제주도와 남해안 지방을 제외한 대부분 지방에서 강수량이 적게 나타났으며, 수도권을 중심으로는 60% 미만의 강수량을 보였다. ICON 모델은 독일 기상청(DWD)과 막스플랑크 연구소(MPI-M)에서 공동 개발하여 현업 운영중인 전 지구 모델로 비정역학 코어를 사용한다. 전 지구를 정 20면체의 삼각형으로 격자화 시켜 모든 격자의 크기가 동일하고, 극점은 1개의 꼭짓점으로 구성되어 CFL(Courant-Friderich-Lewy) 문제가 해소될 수 있다. 또한 hybrid의 병렬구조를 사용하여 전산사용 효율성을 극대화 하는 특징이 있다. 강수의 계절 예측 수행 과정은 다음과 같다. 우선, 계절예측 자료 분석 시 활용할 ICON모델의 기후값을 생산하기 위해 30년(1980년~2009년)간의 AMIP기반 규준실험을 수행한다. 다음으로, SST와 Sea ice의 평년대비 현재 변동량을 계산하고, 이 자료는 모델 적분을 수행할 때 경계 자료로서 활용하게 된다. 계절 예측은 시간 지연기법(Time-lagged method)를 이용한 앙상블예측으로 수행하며, 예측하고자 하는 계절이 시작하기 약 1개원 이전부터 1일 간격으로 전 지구 모델의 초기자료를 다르게 선택하여 총 10개의 앙상블 멤버를 구성한다. 모델의 해상도는 수평 40km, 수직 90개 층으로 구성하였으며, 적분이 완료되면 AMIP기반 실험을 통해 모의된 기후값을 토대로 예측된 계절전망 자료의 변동성을 분석한다.

• Journal of Fisheries and Marine Sciences Education
• /
• v.11 no.1
• /
• pp.59-68
• /
• 1999

The effectiveness of fishery resources enhancement of artificial reef settled in the coast of Cheju Island was determined by using the samples collected by scuaba and caught by the trammel net. The obtained results are summarized as follows; 1. Six types of shellfish were found in the artificial reef area, and the amount of shellfish living in that area was $490{\sim}3,483g/m^2$ according to our research. This shows a high density of shellfish in that area. 2. Ten types of seaweeds were found in the artificial reef area, and the reef living in that area was abundant, with $3,556{\sim}10,550g/m^2$. 3. The amount of a catch of fish in the artificial reef area was 3.5~21.4 times more than in the control area. This result shows the high productivity in that area.

• Journal of Ocean Engineering and Technology
• /
• v.32 no.6
• /
• pp.502-510
• /
• 2018

In order to accumulate data to lower the friction coefficient of a press mold, tribological tests were performed before and after coating SM45C with a PVC/PO film and plasma coating (CrN, concept). The ultrasonic nanocrystal surface modification (UNSM)-treated material had a nano-size surface texture, high surface hardness, and large and deep compressive residual stress formation. Even when the load was doubled, the small amount of abrasion, small weight of the abrasion, and width and depth of the abrasion did not increase as much as those of untreated materials. A comparison of the weight change before and after the tribological test with the CrN and the concept coating material and that of the untreated material showed that the wear loss of the concept coating material and P-UNSM treated material (that is, the UNSM treated material treated with the concept coating) showed a tendency to decrease by approximately 55-75%. Concept 100N had a lower friction coefficient of about 0.6, and P-UNSM-30-100N showed almost the same curve as concept 100N and had a low coefficient of friction of about 0.6. The concept multilayer coating had a thickness of $5.32{\mu}m$. In the beginning, the coefficient of friction decreased because of the plasma coating, but it started to increase from about 250-300 s. After about 350 s, the coefficient of friction tended to approach the friction coefficient of the SM45C base metal. The SGV-280F film-attached test specimen was slightly pushed back and forth, but the SM45C base material was not exposed due to abrasion. The friction coefficient was 0.22, which was the lowest, and the tribological property was the best in this study.