• 한국유체기계학회 논문집
• /
• 제19권4호
• /
• pp.54-62
• /
• 2016

This study presents an approach of tidal farming optimization using a numerical modelling method to simulate tidal energy extraction for 1MW scale tidal stream devices around Jangjuk-sudo, South Korea. The utility of the approach in this research is demonstrated by optimizing the tidal farm in an idealized scenario and a more realistic case with three scenarios of 28-turbine centered tidal array (named A, B and C layouts) inside the Jangjuk-sudo. In addition, the numerical method also provides a pre-processing calculation helps the researchers to quickly determine where the best resource site is located when considering the position of the tidal stream turbine farm. From the simulation results, it is clearly seen that the net energy (or wake energy yield which includes the impacts of wake effects on power generation) extracted from the layout A is virtually equal to the estimates of speed-up energy yield (or the gross energy which is the sum of energy yield of each turbine without wake effects), up to 30.3 GWh/year.

• Nuclear Engineering and Technology
• /
• 제44권5호
• /
• pp.543-550
• /
• 2012

The decrease in the fracture toughness of ferritic steels in a reactor pressure vessel is an important factor in determining the lifetime of a nuclear power plant. A surveillance program has been in place in Korea since 1979 to assess the structural integrity of RPV steels. In this work, the surveillance data were collected and analyzed statistically in order to derive the empirical relationship between the embrittlement and strengthening of irradiated reactor pressure vessel steels. There was a linear relationship between the yield strength change and the transition temperature shift change at 41 J due to irradiation. The proportional coefficient was about $0.5^{\circ}C$/MPa in the base metals (plate/forgings). The upper shelf energy decrease ratio was non-linearly proportional to the yield strength change, and most of the data lay along the trend curve of the US results. The transition regime temperature interval, ${\Delta}T_T$, was less than the US data. The overall change from irradiation was very similar to the US results. It is expected that the results of this study will be applied to basic research on the multiscale modeling of the irradiation embrittlement of RPV materials in Korea.

• Nuclear Engineering and Technology
• /
• 제49권3호
• /
• pp.569-575
• /
• 2017

One of the important requirements for the application of reduced-activation ferritic/martensitic (RAFM) steel is to retain proper mechanical properties under irradiation and high-temperature conditions. To simulate the yield strength and stress-strain curve of steels during high-temperature and irradiation conditions, a multiscale simulation method consisting of both microstructure and strengthening simulations was established. The simulation results of microstructure parameters were added to a superposition strengthening model, which consisted of constitutive models of different strengthening methods. Based on the simulation results, the strength contribution for different strengthening methods at both room temperature and high-temperature conditions was analyzed. The simulation results of the yield strength in irradiation and high-temperature conditions were mainly consistent with the experimental results. The optimal application field of this multiscale model was 9Cr series (7-9 wt.%Cr) RAFM steels in a condition characterized by 0.1-5 dpa (or 0 dpa) and a temperature range of $25-500^{\circ}C$.

• 한국물환경학회지
• /
• 제26권2호
• /
• pp.215-224
• /
• 2010

This study was carried out to estimate effects of sediment reduction with net type sediment settling pond at highland agricultural areas. Flow and sediment monitoring system with rainfall gauge were installed at the study area for real-time monitoring and analysis. It was found that amount and intensity of rainfall events strongly affect sediment yield from the study area. With net type sediment settling pond, it was expected that approximately 61% of sediment could be removed. The correlation between heavy metals and SS were analyzed in this study. $R^2$ values were 0.644, 0.876, 0.945, and 0.928 for Fe, Mn, Al, and Si, respectively. This results indicate that heavy metals also could be removed with net type sediment settling pond. As shown in this study, the sediment settling pond will be an efficient sediment reduction facility at highland agricultural areas. For maximum reduction efficiencies of sediment and other pollutants at agricultural fields, simplified sediment settling pond should be designed and implemented.

• 한국버섯학회지
• /
• 제4권3호
• /
• pp.101-105
• /
• 2006

본 연구는 볏짚을 이용한 느타리버섯 균상재배를 할 때 볏짚을 결속하고 절단하는 과정에서 많은 노동시간이 소요되어 이를 개선하고자 수행되었다. 볏짚과 폐면의 이화학적 성분은 다소차이가 있으나 폐면에서 C/N율은 84~85로 볏짚과 유사하여 혼합재료로 사용이 가능하다. 양파망 규격은 $35{\times}30cm$, 볏짚과 폐면의 배합비는 40:60(V/V)으로 하였을 때 6주기기간동안 평균수량이 양파망 1개당 1.450g 이였다. 배지재료를 준비하는 기간은 양파망재배가 볏짚 재재보다 3일정도 기간을 절감할 수 있었고 접종도 4시간정도 절략되어 전체적으로 3.5일정도 시간을 절략 5%의 경제적 이득이 있는 것으로 분석되었다.

• 한국수산과학회지
• /
• 제47권6호
• /
• pp.997-1005
• /
• 2014

We analyzed annual and seasonal variations in fish species composition and distribution patterns using both daily catch and quantitative analysis data collected from a set-net fishery over a period of two years (2011-2012) on the coast of Dapo, Geoje Island. Set-net fishing season in this area is from May to November, and the annual yield based on the daily catch data was 171,412 kg in 2011, and 102,611 kg in 2012. In total, there were 46 species (belonging to 36 families and 12 orders) in 2011, and 41 species (belonging to 25 families and 9 orders) in 2012. The dominant species in terms of numbers were Trachurus japonicus, Engraulis japonicus, Clupea pallasii, Scomber japonicus, and Sphyraena pinguis. The range in fork length for T. japonicus and E. japonicus was from 3.2 to 23.9 cm, and from 2.6 to 13.3 cm, respectively. The fork length of recruiting juveniles to the Dapo set-net fishing ground ranged from 4.6 to 7.8 cm (median) for T. japonicus, and from 4.1 to 5.0 cm (median) for E. japonicus. The fact that most of the fish caught from the two species were at immature growth stages implies that the coast of Dapo can act as a nursery area for these migratory species.

• 화훼연구
• /
• 제19권1호
• /
• pp.1-7
• /
• 2011

본 연구는 나리 하계 고온기 고품질 절화생산 및 경영비 절감을 위한 도입 소구의 비대증식에 유리한 환경조건을 찾아내기 위해 수행하였다. 종구비 절감을 위해 소구를 도입하여 양구하는데 효과적인 환경조건을 찾아내고자 재배형태를 비가림, 망실, 무피복으로 나누고 다시 절화 재배시 많이 사용하는 30% 차광처리와 무처리로 구분하여 시험하였다. 모든 처리구에서 비가림 재배가 우수하였고 차광의 효과도 다소 있었다. 특히 양구에 있어서는 대관령 등의 고랭지에서 주간과 야간온도의 차이가 커서 동화산물의 전류 및 축적이 많아 평지에 비해 구비대가 유리하여 시비 및 관수방법에 따라 보통 3년 정도인 양구 기간을 단축할 수도 있을 것으로 기대된다.

• 열처리공학회지
• /
• 제14권3호
• /
• pp.155-159
• /
• 2001

The thermal shock resistance has been investigated and compared in three hot-work tool steels. The resistance to thermal shock is first of all a matter of good toughness and ductility. Therefore, a proper hot-work tool steel should be characterized by high fracture strength and high temperature toughness. In this study, new test method is proposed to measure the thermal shock resistance. New method is basically based on Uddeholm' thermal shock test but some modification has been properly applied. Based on these results, some critical temperature($T_{fractures}$) at which fracture occur can be measured to characterize the thermal resistance of the materials. The specific values of ${\Delta}T$, the temperature difference between holding temperature and $T_{fractures}$, has been successfully used as a measure of the thermal shock resistance in this study, the results showed that the thermal shock method used in this study was properly modified.

• 대한기계학회논문집A
• /
• 제27권11호
• /
• pp.1897-1906
• /
• 2003

A finite element analysis for near-net-shape forming of A16061 powder was performed under warm rubber isostatic pressing and warm die pressing. The advantages of warm compaction by rubber isostatic pressing were discussed to obtain a part with better density distributions. The shape of rubber mold was designed by determining a cavity shape that provides a desired shape of the final powder compact. To simulate densification and deformed shape of a powder compact during pressing, the elastoplastic constitutive equation based on yield function of Shima-Oyane was implemented into a finite element program(ABAQUS). The hyperelastic constitutive equation based on the Ogden strain energy Potential was employed to analyze nonlinear elastic response of rubber. Finite element results were compared with experimental data for Al6061 powder compacts under warm die pressing and warm isostatic pressing.

• 한국농공학회지
• /
• 제40권5호
• /
• pp.37-42
• /
• 1998

This study was performed to evaluate the characteristics of volume change is unsaturated clayed soil. The medium-plastic clay was selected and compacted by 50% of Proctor standard compaction energy at 6% higher moisture content than its OMC. A series of isotropic compression tests and triaxial shear tests were performed. The results of the study are summarized as follows. At each matric suction, when the matric suction was increased, the yield stress was increased and slope of volume change was decreased. The more net mean stress was, the less the quantity of volume change was. In shear test, the volumetric strain was much rapidly changed in large matric than in low matric suctions. But the effect of matric suction to volume change disappeared under high net mean stress. At lower deviator stress the more matric suction was, the higher volume change was. But As the matric suction was increasing, the behavior of the unsaturated clayey soil was similar to that of saturated clayey soil. Volume change in the unsaturated clayey soil can be represented as a unique plane in three-dimensional space, which is the axes of net mean stress, matric suction and void ratio.