• Corrosion Science and Technology
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• 제11권6호
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• pp.263-269
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• 2012

Copper alloys are commonly applied to ship's propellers, pumps and valves which are serviced in seawater due to their good castability and corrosion resistance. In the environment of high flow velocity, however, erosion damage predominates over corrosion damage. In particular, the cavitation in seawater environment accelerates surface damage to copper alloys, resulting in degradation of products and economic losses and also threatening safety. The surface was coated with WC-27NiCr by high velocity oxygen fuel(HVOF) spraying technique to attain durability and cavitation resistance of copper alloys under high velocity/pressure flow. The cavitation test was performed for the WC-27NiCr coating deposited by HVOF in seawater at the amplitude of $30{\mu}m$ with seawater temperature. The cavitation at $15^{\circ}C$ caused exfoliation of the coating layer in 17.5 hours while that of $25^{\circ}C$ caused the exfoliation in 12.5 hours. When the temperature of seawater was elevated to $25^{\circ}C$ from $15^{\circ}C$, more damage was induced by over 160%. Although WC-27NiCr has good durability, corrosion resistance and eletrochemical stability, the cavitation damage rate of the coating layer could remarkably increase at the elevated temperatures under cavitation environments.

• 대한조선학회논문집
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• 제53권5호
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• pp.371-379
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• 2016

In the ship design process, ship motion and propulsion performance in sea waves became very important issues. Especially, prediction of ship propulsion performance during real operation is an important challenge to ship owners for economic operation in terms of fuel consumption and route-time evaluation. Therefore, it should be considered in the early design stages of the ship. It is thought that the averaged value and fluctuation of effective inflow velocity to the propeller have a great effect on the propulsion performance in waves. However, even for the nominal velocity distribution, very few results have been presented due to some technical difficulties in experiments. In this study, flow measurements near the propeller plane using a stereo PIV system were performed. Phase-averaged flow fields on the propeller plane of a KVLCC2 model ship in waves were measured in the towing tank by using the stereo PIV system and a phase synchronizer with heave motion. The experiment was carried out at fully loaded condition with making surge, heave and pitch motions free at a forward speed corresponding to Fr=0.142 (Re=2.55×106) in various head waves and calm water condition. The phase averaged nominal velocity fields obtained from the measurements are discussed with respect to effects of wave orbital velocity and ship motion. The low velocity region is affected by pressure gradient and ship motion.

• Journal of Welding and Joining
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• 제26권4호
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• pp.85-91
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• 2008

The grooving corrosion is caused mainly by the different microstructures between the matrix and weld which is formed during the rapid heating and cooling cycle in welding. By this localized corrosion reaction of pipes, it evolves economic problems such as the early damage of industrial facilities and pipe lines of apartment, and water pollution. So lots of researches were carried out already about grooving corrosion mechanism of ERW carbon steel pipe but there is seldom study for water hammer happened by fluid phenomenon and corrosion rate by flow velocity. In this study, the analysis based on hydrodynamic and fracture mechanics was carried out. ANSYS, FLUENT and STAR-CD were used for confirmation of flow phenomenon and stress on the pipe. As the results, fatigue failure is able to be happened by water hammer and grooving corrosion rate is increased cause by turbulent. Grooving corrosion is happened on the pipe, then friction loss of fluid is occurred from corroded part. Erosion can be happened enough in corroded region of microscopic size that wear "V" form. Also pipe is able to be damaged by water hammer effects because of corroded region is general acting as a notch effects. Corrosion depth was more than half of total thickness, it can be damaged from water hammer pressure.

• 한국농공학회논문집
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• 제56권5호
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• pp.67-75
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• 2014

In this study, the large-scale hydraulic model test was performed to investigate the hydraulic characteristics for development of the non-power soil cleaning and keeping system at the dike gate. The outlet height, outflow number, outflow discharge, and outflow cycle were compared and analyzed. The non-power soil cleaning and keeping system was most effective at 11.2 mm in the outlet height. And then the mean outflow cycle was 1.09 sec, and the mean outflow discharge was $0.00164m^3/s$. The total outflow number increased gradually as the water level of a water tank increased, and the outlet height decreased. As a level of water tank decreased, the mean outflow cycle was lengthened, and the unit outflow discharge increased. This result showed this system was most effective. To remove the silty clay deposited in facilities, the methods of excavation, dredging, high pressure washing, etc have been applied to the tidal facilities such as land reclamation, a small size fishing port, and a harbor for maintenance. However, this is extremely cost-ineffective, whereas the non-power soil cleaning and keeping system will bring about an enormously positive economic effect. In addition, when the non-power soil cleaning and keeping system is applied to the dike gate of land reclamation, a thorough examination of the local tidal data and the careful system planning are required to prevent the disaster damage caused by flooding.

• Korean Chemical Engineering Research
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• 제51권5호
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• pp.602-608
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• 2013

$CO_2$를 포집, 수송, 저장하는 기술에 있어서 경제적이고 친환경적 혁신기술로 주목받고 있는 가스 하이드레이트 이용기술의 연구가 활발히 진행되고 있다. 본 연구에서는 가스 하이드레이트를 이용한 $CO_2$ 수송/저장기술의 핵심이 되는 자기보존효과(self-preservation effect)가 발현하는지를 확인하고자 하였다. 특히 $CO_2$ 하이드레이트 입자의 직경에 대한 효과 정도를 실험적으로 살펴보았다. 밀리미터, 마이크론, 그리고 나노 크기의 각각 다른 직경을 갖는 세 종류 $CO_2$ 하이드레이트 샘플을 준비하였고, 3주간 $-15{\sim}-30^{\circ}C$의 온도 및 대기압 조건에서 각각의 샘플 무게 변화를 측정하였다. 실험연구 결과 $CO_2$ 하이드레이트의 자기보존효과를 최대한 얻기 위해서는 온도는 가능한 낮아야 하며, 샘플의 직경 크기가 클수록 좋고, 샘플은 치밀한 구조로 조직되어 높은 밀도를 갖는 방식으로 제조하는 것이 매우 향상된 결과를 얻을 수 있음을 확인하였다.

• 한국전자통신학회논문지
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• 제6권5호
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• pp.703-708
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• 2011

본 논문에서는 대형 교회를 제외한 대부분의 교회가 협소한 공간에 많은 청중을 수용하고자 발코니 층을 설치하여 음의 사각지역 및 음상 정위가 어긋난 지역이 발생하는 문제를 경제적 관점에서 컴퓨터 시뮬레이션을 이용하여 음의 사각지역 및 음상의 개선하는 해결방안을 제시한다. 본 연구에서는 특정교회에 대하여 컴퓨터 시뮬레이션 툴로 경제적으로 쉽게 구할 수 있는 Mapp online으로 사용하였으며, 서브 스피커의 추가 설치 및 메인 스피커 대비 서브 스피커의 -10 dB 이득조절로 명료도를 실측값과 비교한 결과 약 52% 상승하여 명료도가 "보통"에서 "아주 좋음" 단계로 개선됨을 확인할 수 있었다.

• 디지털융복합연구
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• 제11권10호
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• pp.527-536
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• 2013

논문은 대학생의 자기완벽성, 우울, 절망이 자살생각 미치는 영향을 검증하였다. 검증을 위해 무작위로 선택한 서울 소재 3개 대학으로부터 240명을 편의 추출하였다. 조사 기간은 2011년 5월부터 6월까지이며, 분석방법은 SPSS 15.0을 가지고 집단간 차이 분석을 위해서는 t-test, ANOVA를 시행하였으며, 자살생각에 독립변인이 미친 영향을 분석하기 위해서는 위계적 회귀분석을 실시했다. 연구결과는 첫째, 경제상황이 좋지 않은 그룹에서 자살생각이 큰 것으로 나타났으며, 친한 친구의 수가 적을수록 우울, 절망, 자살생각이 높은 것으로 나타났다. 둘째, 자기완벽성의 수준, 우울과 절망의 수준이 높을수록 자살생각 수준이 높은 것으로 나타났다. 본 연구를 통해 대학생들의 완벽성 수준, 우울, 절망, 자살생각을 줄이기 위해서 학우들간의 상호 멘토링을 통한 인간관계 형성 프로그램의 운영, 가족과 학교를 통해 대학생들이 심리적 안정을 이룰 수 있도록 정책적, 법적 지원이 필요하다고 판단된다.

• 대한조선학회지
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• 제22권1호
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• pp.21-30
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• 1985

This paper deals whth the buckling as well as postbuckling analysis of axisymmertric shells taking the initial deflection effects into account. Incremental equilibrium equations, based on the principle of virtual work, were derived by the finite element method, the successive step-by-step Newton-Raphson iterative technique was adopted. To define the transition pattern of postbuckling behavior from the prebuckling state more accurately, a simple solution method was developed, i.e. the critical load was calculated by the load extrapolation method with the determinant of tangent stiffness matrix and the equilibrium configuration in the immediate postbuckling stage was obtained by perturbation scheme and eigenvalue analysis. Degenerated isoparametric shell elements were used to analyse the axisymmetric shell of revolution. And by the method developed in this paper, the computer program applicable to the nonlinear analysis of both thin and moderately thick shells was constructed. To verify the capabilities and accuracies of the present solution method, the computed results were compared with the results of analytical solutions. These results coincided fairly well in both the small deflection and large deflection ranges. Various numerical analyses were done to show the effect of initial deflection and shape of shells on buckling load and postbuckling behavior. Futhermore, corrected directions of applied loads at every increment steps were used to determine the actual effects of large deflection in non-conservative load systems such as hydrostatic pressure load. The following conclusions can be obtained. (1) The method described in this paper was found to be both economic and effective in calculating buckling load and postbuckling behavior of shell structure. (2) Buckling and postbuckling behavior of spherical caps is critically dependent upon their geometric configuration, i.e. the shape of spherical cap and quantities of the initial deflection. (3) In the analysis of large deflection problems of shells by the incremental method, corrections of the applied load directions are needed at every incremental step to compensate the follower force effects.

• Journal of Preventive Medicine and Public Health
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• 제49권3호
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• pp.143-152
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• 2016

Objectives: Metabolic syndrome is a cluster of risk factors for type 2 diabetes mellitus and cardiovascular disease. Associations between metabolic syndrome and several types of cancer have recently been documented. Methods: We analyzed the sample cohort data from the Korean National Health Insurance Service from 2002, with a follow-up period extending to 2013. The cohort data included 99 565 individuals who participated in the health examination program and whose data were therefore present in the cohort database. The metabolic risk profile of each participant was assessed based on obesity, high serum glucose and total cholesterol levels, and high blood pressure. The occurrence of cancer was identified using Korean National Health Insurance claims data. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazards models, adjusting for age group, smoking status, alcohol intake, and regular exercise. Results: A total of 5937 cases of cancer occurred during a mean follow-up period of 10.4 years. In men with a high-risk metabolic profile, the risk of colon cancer was elevated (HR, 1.40; 95% CI, 1.14 to 1.71). In women, a high-risk metabolic profile was associated with a significantly increased risk of gallbladder and biliary tract cancer (HR, 2.05; 95% CI, 1.24 to 3.42). Non-significantly increased risks were observed in men for pharynx, larynx, rectum, and kidney cancer, and in women for colon, liver, breast, and ovarian cancer. Conclusions: The findings of this study support the previously suggested association between metabolic syndrome and the risk of several cancers. A high-risk metabolic profile may be an important risk factor for colon cancer in Korean men and gallbladder and biliary tract cancer in Korean women.

• 가정과삶의질연구
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• 제23권3호
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• pp.25-33
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• 2005

This study examines socio-demographic characteristics of married couples and their desire for a second child. Questionnaires were completed by 355 married men and women who have only one child currently. The participants were classified into four groups by their desire, or a lack thereof, for a second child. Group I consisted of married people who wanted to have another child, and whose spouse wanted the same. Members of Group II were in a marriage where only the wife wanted to have another child. Members of Group III were in a marriage where only the husband wanted a second child. Group IV consisted of participants who did not want another child, and whose spouse agreed with thor The research questions were (1) how different those four groups are in terms of socio-demographic characteristics, (2) what are the reasons to stop having children and to have another child, and (3) what are the perceptions of the current low fertility rate in Korea, and the policies designed to increase birth rata The results indicate that wife' age, husband's educational level, expectant level of household economy, age at marriage, marriage duration and the time length between marriage and birth of the first child were significantly different among the four groups. The reasons to stop having children were expected constraint of privacy and time, physical and psychological burden and economic pressure. The most pronounced reason for wanting another child was the desire to give their first child a sibling. Group III had more serious disagreement about having another child than did Group II. There were significant differences among the four groups in the perceptions of possible consequences of the low birth rate. These perceptions included: undermined competitiveness of the nation and weakened family ties.