• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.6
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• pp.26-32
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• 2016

Usually, there are many uncertainties regarding the error of an assumed load, material properties, member size, and structure analysis in a structure, and it may have a direct influence on the qualities of optimal design of structures. Probabilistic analysis has developed rapidly into a desirable process and structural reliability analysis is an increasingly important tool that assists engineers to consider uncertainties during the design, construction and life of a structure to calculate its probability of failure. This study deals with the applications of two optimization techniques to solve the reliability-based optimization problem of structures. The reliability-based optimization problem was formulated as a minimization of the structural volume subject to the constraints on the values of componential reliability index determined by the AFOSM approach. This presented method may be a useful tool for the reliability-based design optimization of structures.

• The Journal of Engineering Geology
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• v.26 no.1
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• pp.101-115
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• 2016

We carried out laboratory material tests on two cements (KS-1 ordinary Portland and Class G) with changing W/S (Water/Solid) and the content of fly ash in order to evaluate their physical and mechanical properties. The specimens of KS-1 ordinary Portland cement were prepared with varying W/S (Solid=cement) in weight, while those of Class G cement were prepared with changing the content of fly ash in volume but maintaining W/S (Solid=cement+fly ash). The results of the material tests show that as the W/S in KS-1 ordinary Portland cement and the content of fly ash in Class G cement increase, the properties (density, sonic wave velocity, elastic constants, compressive and tensile strengths, thermal conductivity) decrease, but porosity and specific heat increase. In addition, an increase in confining pressure and in the content of fly ash leads to plastic failure behavior of the cements. The laboratory data were then used in a stability analysis of cement sheath for which an analytical solution for computing the stress distribution induced around a cased, cemented well was employed. The analysis was carried out with varying the injection well parameters such as thickness of casing and cement, injection pressure, dip and dip direction of injection well, and depth of injection well. The analysis results show that cement sheath is stable in the cases of relatively lower injection pressures and inclined and horizontal wells. However, in the other cases, it is damaged by mainly tensile failure.

• Journal of the Korean Ceramic Society
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• v.41 no.10 s.269
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• pp.783-787
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• 2004

Microwave dielectric properties and the microstructure of $Ba_5Nb_4O_{15}$ ceramics with $PbO-B_2O_3-SiO_2$ glass frit were investigated to reduce the sintering temperature of $Ba_5Nb_4O_{15}$ ceramics as a function of the amount of glass frit from $0.5wt\%$ to $10wt\%$ and the sintering condition. The sintered density and the microwave dielectric properties of $Ba_5Nb_4O_{15}$ ceramics were remarkably changed with the amount of glass fit which existed as a liquid phase and assisted the densification. $Ba_5Nb_4O_{15}$ with $3wt\%$ $PbO-B_2O_3-SiO_2$ glass frit sintered at $900^{\circ}C$ for 2 h showed dielectric constant (K) of 41.4, a quality factor (Q $\times$f) of 13,485 GHz, and a Temperature Coefficient of resonant Frequency (TCF) of 9 ppm/$^{\circ}C$. Due to no trace of physical and chemical reaction between this composition and Ag electrode cofired at $900^{\circ}C$ for 2 h, this ceramics can be a good candidate for the multilayer dielectric filter.

• Journal of Korean Society of Steel Construction
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• v.9 no.4 s.33
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• pp.659-672
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• 1997

Thermal response induced from nonlinear temperature distribution in composite box gilder bridges depends on several variables(environmental conditions, physical and material properties, location and orientation of bridge, and cross-section geometry). In this paper, parametric study are conducted in order to find the effects of variations of seasons, location and orientation of bridge, sectional geometry and some material properties on the axial deformation, curvature and stresses in composite box girder bridge. A two-dimensional transient finite element model to conduct this parametric studies is briefly presented. Firstly, the effects of the parameters on the diurnal variation of curvature are considered, and for the time of maximum curvature, on the distribution of temperature and stresses of composite box girder sectional are considered. Finally, some considerations about the influence of the parameters on the daily maximum values of axial deformation, curvature and stresses are carried out. The influence of thermal effect on structures is important as much as the influence of live or dead load in some cases. In the design of steel composite bridges, the thermal stresses calculated on the supposition that the temperature difference between the concrete slab and steel girder is $10^{\circ}C$ and the temperature distributions are uniform in concrete slab and steel girder can be underestimated.

• Journal of the korean Society of Automotive Engineers
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• v.18 no.5
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• pp.53-68
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• 1996

마그네슘이 자동차 경량화에 관심이 되는 이유는 근본적으로 CAFE 규제와 같이 경량화를 통한 화석연료의 소모를 크게 억제해야 한다는 사회적인 규제이나, 지난 10여년간의 기술발전으로 내식성이 나쁘다거나 취급이 위험한 금속이라는 인식이 크게 개선된 데에도 있다. 다른 경량금속에 대한 Mg 지금 가격의 비교조건이 호전되었고 향후 원소 재공급의 다변화가 추진되고 있는 것도 환경을 변화시킨 중요한 요인이다. 그간 중요한 경량화 대체 재료로 연구투자가 많았던 유기고분자 재료 및 FRP 등과 같은 복합재료는 폐기부품의 재활용이 어려움 때문에 호나경친화적인 단점이 부각되어, 이 소재의 증가가 주춤해 있다. 마그네슘의 경우에는 재활용이 가능하고, 진동흡수효과가 매우 커서 소음발생을 크게 줄일 뿐만 아니라, 주행 및 내구성시험에서 치수안정성이 좋고 많은 종류의 전자기기 사용에 의한 전자파 차폐효과도 큰 장점을 가지고 있다. 본 고에서는 Mg 다이캐스팅으로 자동차부품의 경량화 현황과 선진국에서 보는 전망을 미국을 중심으로 정리하고, 이와 관련한 Mg 다이캐스팅으로 자동차부품의 경량화 현황과 선진국에서 보는 전망을 미국을 중심으로 정리하고, 이와 관련한 Mg 기술적인 이슈와 시장전망도 서술하였다. 그리고 현재 우리나라의 연구계와 부품업계에서 추진하고 있는 연구개발 동향을 자동차 업계에 소개하는 의미도 있다. 이처럼 우리나라의 현황을 정리해 보는 것은 국내 자동차 산업이 국제적인 경쟁을 하고 있고 Mg기술과 원료확보에서 일본의 견제를 받고 있는 우리의 현실에서도 필요한 작업으로 생각된다.값들로 구성되는 형상을 내구 성능, 성형성등을 고려하여 최종 형상으로 결정한다. 내구성능의 예측은 금속부품의 내구수명 예측에 널리 이용되고 있는 방법이 방진 고무부품의 경우에도 적용 가능한지를 검토하고, 방진 고무부품에도 일반적으로 적용될수 있는 내구수명 예측방안의 개발 가능성을 타진해 보았다. 본 연구의 목표는 시제품을 제작하기 이전에 설계된 부품에 대한 스프링 상수 및 내구특성을 체계적으로 규명하여 제품 시험의 횟수를 줄이고, 보다 정밀한 제품을 제작할 수 있도록 하기 위한 것이다.세포수는 초기 배반포기배에서 팽윤 배반포기배로 진행됨에 따라 두배에서 세배 정도 증가되었음을 알 수 있었다. 또한, differential labelling과 bisbenzimide기법에서 얻어진 각각의 총세포수를 비교하였을 때 총세포수는 발달의 진행 정도에 따라 증가되며 그와 동시에 동일한 군 간의 세포수도 거의 유사함을 알 수 있었다. 따라서, ICM과 TE를 differential labelling하는 기법은 수정란의 quality를 평가하는데 매우 유용한 기법으로서 착상전 embryo 발달을 연구하는데 효과적으로 이용될 수 있다는 것을 시사한다. 고도의 유의차를 나타낸 반면 비수구, 초생수로구 및 Bromegrass 목초구 간에는 아무런 유의차가 인정되지 않았다. 7. 농지보전 처리구인 배수구와 초생수로구는 비처리구에 비해 낮은 침두 유출량과 낮은 토양유실량을 나타내었다.구보다 14% 절감되는 것으로 나타났다.작용하는 것으로 사료된다.된다.정량 분석한 결과이다. 시편의 조성은 33.6 at%

• Journal of Korea Water Resources Association
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• v.31 no.5
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• pp.539-552
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• 1998

When the pier is constructed in the cohesive be, the accuracy maynot be obtained because the equation for calculating the scour at piers is based upon the results which are analyzed through the experiments in the non-cohesive bed. In this paper, the variation of the depth of the pier scour occurred by constructing 5 types of pier in the channel having the cohesive material is examined. The experimental results are analyzed based upon Froude numbers and non-dimensional numbers which are indicated as the flow depths compared to the pier width. The results are also compared with the results obtained using the existing pier scour equations. In this paper, the shape factors, which can be used for calculating the scour depth of the pier in the cohesive channel bed, are suggested. The shape factors are indicated through the ratios between the scour depth at the circular pier and the scour depths at the different types of pier, and are suggested as two stages. In the first stage, in which the water depth compared to the pier width is less than 1.2, the shape factors are given as the equations. However, in the second stage the shape factors are given as the constant values. It is understood that the shape factors suggested in this paper can be properly usd for calculating local scour at piers in the bridges which are constructed in the cohesive channel bed having the characteristics of the bed material which is used in these experiments. Keywords : local scour, maximum scour depth, cohesive bed material, pier shape, pier, shape factor.

• Journal of the Korea Concrete Institute
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• v.21 no.2
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• pp.199-207
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• 2009

Many researches on electromagnetic (EM) properties like dielectric constant and conductivity are performed since they can be characterized in nonmetallic cement-based material such as mortar and concrete. However, they are much affected by the moisture so that the behaviors of EM properties are to be clearly understood. In this paper, measurements for saturation and EM properties are performed for cement mortar specimens with five different water to cement (W/C) ratios including basic tests like compressive strength and porosity measurement. Every saturated specimens are exposed to room condition and the changes in EM properties caused by decreasing saturation are analyzed. In the saturated condition, higher measurement of EM properties are evaluated in the specimens with higher porosity, however this relationship is adversely changed with drying process. Since the pores without filled water causes the decreases in EM properties, the measurements show stable and linear increment with the lower W/C ratios. Furthermore, the increasing ratios of EM measurements with W/C ratio are shown with saturation and the relationships between them are derived through regression analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.6
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• pp.637-644
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• 2012

In a nuclear power plant, fretting wear due to impact motion between U-tubes and support structures located in steam generators can cause serious problems. In order to guarantee the reliability of the steam generator, the damage due to fretting wear should be thoroughly investigated. The purpose of this study is to elucidate the fretting wear mechanism qualitatively and quantitatively. Hence, fretting wear simulation is performed for the environments to which the actual steam generators in nuclear power plants are exposed. Initial experimental results are obtained for various experimental parameters, and the effect of the work rate and temperature on fretting wear is evaluated. In water, the wear coefficients for $90^{\circ}C$, $200^{\circ}C$, and $340^{\circ}C$ are found to be $9.051{\times}10^{-16}\;Pa^{-1}$, $3.009{\times}10^{-15}\;Pa^{-1}$, and $2.235{\times}10^{-15}\;Pa^{-1}$, respectively. It is also found that the wear coefficient at room temperature is larger than that at low temperature in water because of the dynamic viscosity of water.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1479-1487
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• 2013

The river levee collapse and flood damages are dramatically increased due to the floods which caused by abnormal weather nowadays. The counterplan like TDR(Time Domain Reflectometry) river levee leaking exploration technique is needed to that levee failure causes of levee failure such as levee failure by penetration, piping, inadequate levee materials selection, poor compaction are almost 52% of the failure. This research practiced various comparing experiments of existing TDR(probe and tube types) and developing CAP type TDR to evaluate acrylic small CAP mould and low-cost TDR levee leaking monitoring system which was used probe type TDR. As the result, evaluated TDR system had 20cm critical exploration performance which was a leaking exploration performance, The functional ratio of TDR exploration sensitivity of dry density was sensitive more than 3 times than dry density, and weathered granite soil foundation water contents(w)-dielectric constant(${\epsilon}$) corelation formula was suggested to measure functional ratio on developing cap type TDR system.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.389.1-389.1
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• 2014

최근의 환경 및 에너지에 대한 관심으로 수요가 증가하고 있는 하이브리드 및 전기 자동차나 태양광발전, 풍력발전용의 인버터기기에는 고에너지밀도 커패시터가 필수적이 되었다. 높은 에너지 밀도를 요구하는 전력전자, 펄스파워 등의 응용분야에 사용되는 고에너지밀도 커패시터는 PET (Polyethylene terephtalate)와 PP (Polypropylene)와 같은 폴리머 유전체를 사용하는 범용 필름 커패시터가 사용되었으나 사용 요구 조건의 한계에 도달하여, 새로운 유전체를 적용하는 커패시터가 절실히 필요한 상황이다. PET와 PP와 같은 유전체는 유전상수가 2~3의 낮은 값을 가지고 있어 고에너지밀도를 구현하기가 어렵다. 본 연구에서는 새롭게 요구되고 있는 고에너지 밀도 커패시터의의 성능을 만족시키기 위하여 $20{\sim}50{\mu}m$ 두께의 PET 필름상에 세라믹 유전체인 $ZrO_2$ 박막을 스퍼터(Sputter) 증착법에 의해 코팅하여 종래의 필름 커패시터와 세라믹 커패시터의 장점을 갖는 커패시터를 제조하기 위한 박막 유전재료의 개발을 목표로 하였다. 수백 nm~수 ${\mu}m$ 두께의 $ZrO_2$ 박막을 스퍼터링 공정조건에 따라 증착한 후 박막의 결정성, 기판과의 부착성, 증착속도, 유전상수, 절연파괴강도, 온도안정성 등을 XRD, SEM, AFM, EDS, XPS, Impedance analyzer 등에 의해 평가하였다. $ZrO_2$ 유전체막은 상온에서 증착하였음에도 정방정(tetragonal)구조의 결정질로 성장하였고 증착압력이 증가함에 따라 주피크의 세기가 감소하였다. 증착 중 산소가스를 주입하였을 경우에도 결정질막으로 성장하였다. 증착막들은 산소가스의 양이 증가함에 따라 짙은 흰색으로 변하였으며 PET 기판과의 접착력도 약해졌다. 또한 거칠기는 Ar가스만으로 증착한 경우보다 증가하였으며 24~66 nm의 평균 거칠기값을 보였다. PET위에 Ar가스만으로 증착한 $ZrO_2$의 비유전율은 1kHz에서 116~87의 비유전율을 보여 PET에 비해 매우 우수한 특성을 보였다. $ZrO_2$ 막들은 300kV/cm의 전계에서 대략 10-8A 이하의 누설전류를 보였다. 증착가스비를 달리하여 제조된 시편에서도 유사한 누설전류값을 나타내었다. 300 kV/cm 전후의 전계까지 측정한 $ZrO_2$ 막의 P-E (polarization-electric field) 특성을 확인하였는데, 5 mTorr의 압력에서 증착한 막은 253 kV/cm에서 $5.5{\mu}C/cm^2$의 분극값을 보였다. P-E커브의 기울기와 분극량에 따라 에너지밀도가 달라지므로 공정조건에 따라 에너지밀도가 변화됨을 예측할 수 있었다. PET위에 스퍼터 증착한 $ZrO_2$ 유전체막은 5mTorr의 Ar가스분위기에서 제조할 때 가장 안정적인 구조를 보였으며, 고에너지밀도 커패시터에의 적용가능성을 보였다.