• 수산해양기술연구
• /
• 제56권1호
• /
• pp.37-44
• /
• 2020

The change of fishing power index was analyzed to identify the development of the vessel and gear technology that may improve the fishing efficiency of the offshore conger eel pot fishery from 1980s to 2015. Gross tonnage per fishing vessel was rapidly increased annually. The standard of pot was maintained, but the number of pot used rapidly increased by using conger eel pot hauling devices, carrying and loading devices, main line hauler, casting devices and slide type pot. Fish finder system to identify fishing ground information and the conger eel pot hauling devices were modernized, and supply rate was also increased. Therefore, the relative fishing power index in the offshore conger eel pot fishery increased from 1.0 in 1980 to 1.3 in 1990, to 1.8 in 2000 and to 2.0 in 2015. The results are expected to contribute to reasonable fisheries stock management of the offshore conger eel pot fishery.

• Journal of Advanced Marine Engineering and Technology
• /
• 제38권3호
• /
• pp.246-252
• /
• 2014

본논문은 150마력급 선내형 소형 워터제트 추진시스템 개발에 대한 연구이다. 워터제트는 흡입부, 임펠러, 디퓨저(공기확산기), 후진부와 메인 샤프트로 구성되어 있다. 워터제트의 구성품은 사형 주조후 정밀가공을 거쳐 개발하였다. 워터제트 추진기관의 개발은 각각의 부품에 대한 설계-제작-검사의 과정을 거쳐 최종 완성하였으며, 육상 시험 풀에서는 선체의 이동 없이 워터제트의 펌프 특성을 확인한 결과, 최대 37m/s의 유속과 0.29m3/s의 유량을 배출할 수 있는 성능을 확보하였다. 본 연구에서 개발된 워터제트 추진장치를 설치한 21ft 시험선을 사용하여 실증 연구를 수행하였다. 그 결과, 국내 연안에서 시험시 선체무게와 엔진등 기타 부수적인 무게가 대략 1.2ton 가량 이였으며 이 상태에서 엔진회전수 3,700rpm에서 최대시속 45km/h의 운항속도를 기록하였다.

• 한국환경복원기술학회지
• /
• 제13권6호
• /
• pp.97-106
• /
• 2010

Earthworm, a prominent ecosystem engineer within many terrestrial ecosystems, can exert profound influences on various abiotic/biotic environments through bioturbation processes such as burrowing, casting and mixing of litter and soil. In this study, we investigated how the presence or absence of earthworm (Oligochaeta) can alter the soil physico-chemical conditions and ultimately the distribution and abundance of Collembola which constitutes a large proportion of the soil fauna. During September 2010, soil organisms along with soil samples were collected from randomly installed 20 plots in Mt. Gwan-ak. We examined the differences in the abundance of Collembola among plot samples in respect to the presence/absence of earthworm and soil physico-chemical conditions (i.e., pH, $PO_4^{3-}$, $NO_3^{2-}$, organic matter (OM), electrical conductance and water content). Analysis of soil physico-chemical environment revealed a significantly higher organic matter content and electrical conductance in plots with earthworm compared to plots without earthworm. Abundance of Collembola were not only higher in plots with earthworm than in plots without earthworm, but were also positively correlated with availability of OM present in the environment. The results suggest that positive impacts of earthworm on the abundance of Collembola in this study may have been due to their ability to effectively modify soil physico-chemical conditions favored by Collembola. Such conspicuous influence of earthworm's activity on below-ground community suggests their potential significance in forest restoration or revegetation process.

• 소성∙가공
• /
• 제32권1호
• /
• pp.12-19
• /
• 2023

The armature core is a part responsible for the skeleton of the steering wheel. Currently, in the case of commercial trucks, the main parts of the parts are manufactured separately and then the product is produced through welding. In the case of this production method, quality and cost problems of the welded parts occur, and an integrated armature core made of magnesium alloy is used in passenger vehicles. However, in the case of commercial trucks, there is no application case and research is insufficient. Therefore, this study aims to develop an all-in-one armature core that simultaneously applies a magnesium alloy material and a die casting method to reduce the weight and improve the quality of the existing steel armature core. The product was modeled based on the shape of a commercial product, and finite element analysis (FEA) was performed through Ls-dyna, a general-purpose analysis program. Through digital image correlation (DIC) and uniaxial tensile test, the accurate physical properties of the material were obtained and applied to the analysis. A total of four types of compression were applied by changing the angle and ground contact area of the product according to the actual reliability test conditions. analysis was carried out. As a result of FEA, it was confirmed that damage occurred in the spoke area, and spoke thickness (t_spoke), base thickness (t_base), and rim and spoke connection (R) were designated as design variables, and the total weight and maximum equivalent stress occurring in the armature core We specify an objective function that simultaneously minimizes . A prediction function was derived using the sequential response surface method to identify design variables that minimized the objective function, and it was confirmed that it was improved by 22%.

• 대한치과보철학회지
• /
• 제35권1호
• /
• pp.221-243
• /
• 1997

The objective of this study was to characterize the mechanical properties of $Y_{2}O_{3}$-containing glass infiltrated ceramic core material, which was made by pressureless powder packing method. A pure alumina powder with a grain size of about $4{\mu}m$ was packed without pressure is silicon mold to form a bar shaped sample, and applied PVA solution as a binder. Samples were sinterd at $1350^{\circ}C$ for 1 hour. After cooling, $Y_{2}O_{3}$-containing glass($SiO_{2},\;Y_{2}O_{3},\;B_{2}O_{3},\;Al_{2}O_{3}$, ect) was infiltrated to the sinterd samples at $1300^{\circ}C$ for 2 hours and cooled. Six different proportions $Y_{2}O_{3}$ of were used to know the effect of the mismatch of the thermal expansion coefficient between alumina powder and glass. The samples were ground to $3{\times}3{\times}30$ mm size and polished with $1{\mu}m$ diamond paste. Flexural strength, fracture toughness, hardness and other physical properties were obtained, and the fractured surface was examined with SEM and EPMA. Ten samples of each group were tested and compared with In-Ceram(tm) core materials of same size made in dental laboratory. The results were as follows : 1. The flexural strengths of group 1 and 3 were significantly not different with that of In-Ceram, but other experimental groups were lower than In-Ceram. 2. The shrinkage rate of samples was 0.42% after first firing, and 0.45% after glass infiltration. Total shrinkage rate was 0.87%. 3. After first firing, porosity rate of experimental groups was 50%, compared with 22.25% of In-Ceram. After glass infiltration, porosity rate of experimental groups was 2%, and 1% in In-Ceram. 4. There was no statistical difference in hardness between two materials tested, but in fracture toughness, group 2 and 3 were higher than In-Ceram. 5. The thermal expansion coefficients of experimental groups were varied to $4.51-5.35{\times}10^{-6}/^{\circ}C$ according to glass composition, also the flexural strengths of samples were varied. 6. In a view of SEM, many microparticles about $0.5{\mu}m$ diameter and $4{\mu}m$ diameter were observed in In-Ceram. But in experimental group, the size of most particles was about $4{\mu}m$, and a little microparticles was observed. The results obtained in this study showed that the mismatch of the thermal expansion coefficients between alumina powder and infiltrated glass affect the flexural strength of alumin/glass composite. The $Y_{2}O_{3}$-containing glass infiltrated ceramic core made by powder packing method will takes less time and cost with sufficient flexural strength similar to all ceramic crown made with slip casting technique.

• 콘크리트학회논문집
• /
• 제25권6호
• /
• pp.657-665
• /
• 2013

이 연구는 알칼리 활성 슬래그(alkali-activated slag, AAS) 결합재를 이용하여 자기충전성을 갖는 콘크리트 개발을 위한 기초 연구로서 자기충전 콘크리트에 사용될 AAS 결합재 및 고성능 감수제의 유동성능 평가를 통해 선정하고, 선정된 결합재 및 고성능 감수제를 사용하여 자기충전 콘크리트를 배합한 후 굳기 전 콘크리트의 유동특성을 평가하였다. 높은 pH에서 폴리카르본산계 고성능 감수제의 성능이 저하됨에 따라 비교적 강도가 낮은 약알칼리성 활성화제를 사용한 AAS 결합재를 선정하였다. 시험 결과 일본토목학회(JSCE) 기준인 고유동성, 재료분리 저항성, 간극 충전성은 대부분 만족시켰으나, AAS 페이스트의 기본점성이 OPC에 비해 높은 이유로 유럽통합기준의 간극 통과성은 만족시키지 못했다. 하지만, AAS 결합재를 이용하면 증점제의 사용 없이 재료분리가 발생되지 않는 자기충전 콘크리트 제조가 가능함을 확인하였다. 이 연구는 AAS 결합재를 이용한 자기충전 콘크리트 개발의 기초연구로서 앞으로 현장적용이 가능한 AAS 자기충전 콘크리트 개발을 위해 더 높은 강도의 고유동 결합재와 간극 통과성을 높이기 위한 콘크리트 배합비의 연구가 필요하다.

• 수산해양기술연구
• /
• 제39권1호
• /
• pp.50-55
• /
• 2003

자원관리형 자망$.$통발 어구어법 기술개발을 위한 연구의 일환으로 서해구의 자망$.$통발어업에 대한 현황을 파악하고, 서해구의 대표적인 어종 중의 하나인 민어를 어획대상으로 하는 민어 연안 유자망어업과 피뿔고둥을 주 어획대상으로 하는 기타 통발어업을 연구대상으로 선정하여 현장조사 등을 통하여 조업실태와 대상어종의 체장조성 등을 조사한 결과는 다음과 같다. 1. 서해구의 연안어업 총 허가건수는 12,944건(조업건수 7,558건; 2001년 12월말 현재)이며, 그 중에서 자망어업이 5,154건(조업건수 3,724건)으로 39.8%, 통발어업이 1,025건(조업건수 662건)으로 7.6%를 차지하였으며, 서해구에서의 조업율은 연안 자망어업과 연안 통발어업이 각각 72.3%와 64.6%로서 타 업종에 비해 비교적 높은 편이었다. 2. 민어 유자망어업의 주어기는 7월 중순부터 9월 초순까지이며, 주어장은 서해 남부 연안의 섬주변의 수심 약 15∼50m(주로 30m 이내)이고, 조업은 저질이 펄 또는 사니질인 해역에서 사리때를 전후하여 1일 1∼2회 1주일 정도 창조시 투망하여 1∼2시간 정도 어구가 조류에 표류하도록 한 후 양망하는 것으로 조사되었다. 3. 민어 유자망어업의 현장조사 결과 어획된 139마리의 체장 범위는 43.0∼120cm이고, 모우드(mode)는 85cm였으며, 꽃게$.$병어$.$가오리 등이 소량 혼획되었다. 4. 서해구에서의 피뿔고둥을 주대상으로 하는 기타 통발어업은 꽃게 어기(9월 초순∼10월 중순)를 제외한 시기에 연중 조업하며, 서해 연안의 수심이 10∼20m이고 저질이 사니질인 해역에서 보통 전날 투망하여 다음 날 양망하는 것으로 조사되었다. 5. 기타 통발어업의 현장조사 결과 조사기간 중 어획된 피뿔고둥 5,372마리의 갑장 범위는 4.5∼8.5cm이고, 모우드(mode)는 7.5cm였으며, 피뿔고등 91.7%, 배꼽고등 4.8%, 민꽃게$.$쥐노래미$.$조피볼락 등이 3.5% 정도 혼획되었다.