• 한국전산구조공학회논문집
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• 제16권4호
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• pp.369-376
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• 2003

본 논문에서는 가압경수로(PWR) 고준위폐기물을 깊은 지하 500m에 처분 시 사용되는 처분용기 및 이를 보호하기 위하여 50㎝ 두께로 처분용기 주위를 감싸고 있는 벤토나이트 버퍼의 복합구조물에 지진 등의 지각 변동에 의하여 갑작스럽게 10㎝의 수평한 암반 전단력이 대칭적으로 가해졌을 때, 처분용기의 안전성(붕괴)을 예측하기 위하여 「처분용기+벤토나이트 버퍼」 복합 구조물에 대한 비선형 구조해석을 수행하였다. 복합구조물을 구성하고 있는 물질들은 탄소성체로 가정하였으며, 대변형 발생 시 항복을 예측하는 항복조건식으로는 처분용기를 구성하고 있는 금속물질(구리, 주철)에 대하여 von-Mises 항복조건식을, 벤토나이트 버퍼물질에 대하여는 Drocker-Prager 항복조건식을 적용하였다. 해석 결과들을 분석하면 비록 10㎝의 수평한 대칭 암반 전단력에 대하여 벤토나이트 버퍼에는 항복점을 훨씬 상회하는 대변형이 발생하였지만, 내부의 처분용기를 구성하고있는 주철 및 구리에는 여전히 매우 작은 탄성변형 및 항복응력보다 작은 응력이 발생하고 있음을 알 수 있었다. 따라서 갑작스런 10㎝의 수평한 암반 전단력에 대하여 50㎝ 두께의 벤토나이트 버퍼는 안전하게 내부의 처분용기를 보호하고 있음을 알 수가 있다. 해석결과는 또한 벤토나이트 버퍼의 전단변형에 의하여 처분용기에 휨변형이 발생함을 보여주고 있다.

• 한국지반공학회논문집
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• 제21권3호
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• pp.43-54
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• 2005

본 연구에서는3개소의 지중연속벽(D) 시험시공에 의해 유발된 지반의 변위에 대한 분석을 실시하였다. DW의 시공은 최근에 실시된 매립에 의해 압밀이 진행중인 압측성이 높은 해성점토층 및 풍화잔적토 지반에서 실시되었다. 수평변위의 계측결과는 DW시공에 의해 최대 293mm의 매우 큰 변위가 발생함을 보여주고 있는데, 이는 약 0.8$\%$ D(D=최대굴착고)에 해당되는 값이다. DW의 시공 도중 굴착면을 의도적으로 방치하는 경우, 지반 변위가 약 50-225$\%$ 증가하였다. DW 시공 이전에 해성점토층을 제트 그라우트로 보강하게 되면 지반변위가 매우 효과적으로 감소된 것으로 관측되었다. 본 연구에서 관측된 지표침하를 유사한 조건에서 실시된 DW 시공사례에서 측정된 지표침하의 양상과 간접 비교한 결과에 따르면, 해성짐토층에 DW을 시공하는 경우 최대 0.225$\%$ D의 지표침하가 발생하는 것으로 분석되었다.

• 한국축산식품학회지
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• 제38권5호
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• pp.1080-1091
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• 2018

The eggshell, which is a complex and highly ordered structure, is very important factor for food safety and egg marketing. This study investigated the changes in eggshell structure and shell components in relationship to hen age. For this study, we examined the histological change of the endometrium of the 30-, 60-, and 72-wk-old commercial layers, and analyzed the ultrastructure and ionic composition of their eggshells. The results showed that histological deformation, fibrosis, atrophy and elimination of micro-villi in the uterus endometrium were found through microscopic observation that was associated with increasing hen age. Concentration of blood-ion components such as $Ca^{2+}$, $Na^+$, $K^+$, and $Cl^-$ ions did not change with age. Along with the results from the ultrastructure analysis of the eggshell, the palisade layer ratio and the density of mammillary knobs were significantly decreased in older hens. In addition, the type B mammillary knobs were frequently observed with increasing hen age. In the mineral element assay from the eggshell, $Ca^{2+}$, $S^{2-}$, and $Co^{2+}$ significantly decreased with increasing hen age, whereas $Na^+$, $K^+$, and $V^{2+}$ significantly increased. Therefore, the damages of endometrial tissue inhibit the processes of ion transmission and the crystallization of eggshell formation, resulting in a large and non-uniform mammillary knob formation. This means the conditions of endometrial cells affect the formation of the eggshell structure. In conclusion, hen aging causes the weakness of the eggshell and degrades the eggshell quality.

• 한국해양공학회지
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• 제25권6호
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• pp.42-48
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• 2011

The present study makes three original contributions to nanoskinned Ti-6Al-4V materials. The nanoskins were fabricated on Ti-6Al-4V material using various surface treatments: deep rolling (DR), laser shot peening (LSP), and ultrasonic nanocrystal surface modification (UNSM). These surface treatments are newly developed techniques and are becoming more popular in industrial fields. A fatigue strength comparison at up to 106 cycles was conducted on these nanoskinned Ti-6Al-4V materials. Fatigue tests were carried out using MTS under axial loading tension-compression fatigue (R = -1, RT, 5 Hz, sinusoidal wave). The analysis of the crack initiation patterns in the nanoskinned Ti-6Al-4V materials found an interior originating crack pattern and surface originating crack type. Microscopic observation was mainly used to investigate the fatigue fractured sites. These surface modification techniques have been widely adopted, primarily because of the robust grade of their mechanical properties. These are mainly the result of the formation of a large-scale, deep, and useful compressive residual stress, the formation of nanocrystals by the severe plastic deformation (SPD) at the subsurface layer, and the increase in surface hardness.

• Journal of Advanced Research in Ocean Engineering
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• 제1권2호
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• pp.106-114
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• 2015

In the fabrication of offshore oil and gas facilities, the significance of dimension control is growing continuously. But, it is difficult to determine the deformation of the structure during fabrication by simple lab tests due to the large size and the complicated shape. Strain-boundary method (a kind of shrinkage method) based on the shell element was proposed to predict the welding distortion of a structure effectively. Modeling of weld geometry in shell element is still a difficult task. In this paper, a concept of imaginary temperature pair is introduced to handle the effect of geometric factors such as groove shape, plate thickness and pass number, etc. Single pass imaginary temperature pair formula is derived from the relation between the groove area and the FE mesh size. By considering the contribution of each weld layer to the whole weldment, multi-pass imaginary temperature is also derived. Since the temperature difference represents the distortion increment, cumulative distortion curve can be drawn by integrating the temperature difference. This curve will be a useful solution when engineers meet some problems occurred in the shipyard. A typical example is shown about utilization of this curve. Several verifications are conducted to examine the validity of the proposed methodology. The applicability of the model is also demonstrated by applying it to the fabrication process of the heavy ship block. It is expected that the imaginary temperature model can effectively solve the modeling problem in shell element. It is also expected that the cumulative distortion curve derived from the imaginary temperature can offer useful qualitative information about angular distortion without FE analysis.

• 대한기계학회논문집B
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• 제39권2호
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• pp.169-176
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• 2015

생체 조직에 대한 물리적 특성은 생체공학의 주된 관심사다. 특히 뇌 조직과 같은 매우 무른 생체 조직의 특성은 아직까지 정확히 밝혀지지 않고 있는 실정이다. 이는 윤리적, 사회적인 문제로 실험이 매우 제한적이고 어렵기 때문이다. 하지만 의료 응용분야에서의 로봇 수술이 발달함에 따라 이런 매우 무른 조직에 대한 정확한 특성이 요구되어지고 있는 실정이다. 이에 본 논문에서는 뇌 조직과 유사한 거동을 보이는 젤라틴으로 시편을 제작하여 기존연구와 비교하고 유사한 거동을 보이는 시편 제작조건을 찾아내고 이 조건으로 만들어진 시편을 이용하여 반복적인 실험을 실시하였다. 이렇게 얻어진 실험 데이터를 이용하여 초탄성 모델에 적용시켜 재료 상수들을 찾고 이를 FE 해석에 적용시켜 실험데이터와 비교하여 일치함을 보였다.

• 대한기계학회논문집A
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• 제38권6호
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• pp.691-698
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• 2014

본 논문에서는 복합재료를 이용하여 플렉스빔과 토크튜브를 제작하기 위한 공정과 기본 물리량 시험과정을 소개하였다. 플렉스빔과 토크튜브는 헬리콥터에 적용되는 무베어링 로터 허브 시스템을 구성하기 위한 핵심 구성품이다. 토크튜브는 블레이드의 피치각을 변화시키기 위한 조종력을 전달하며, 플렉스빔은 구조적인 변형을 통해 플랩, 래그 및 페더링 힌지를 구현하는 기능을 담당한다. 지상회전시험을 수행하기에 앞서 플렉스빔과 토크튜브 및 블레이드의 플랩강성, 래그강성 및 토션강성을 측정하기 위한 기본 물리량 시험을 수행하였다. 또한, 해석을 통해 예측된 단면 강성과 기본 물리량을 통해 획득된 강성 값을 비교하였으며, 그 결과를 통해 복합재료로 제작된 플렉스빔과 토크튜브가 구조적인 강성 요구도를 만족함을 확인할 수 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.470-470
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• 2013

Recently, active materials such as amorphous silicon (a-Si), poly crystalline silicon (poly-Si), transition metal oxide semiconductors (TMO), and organic semiconductors have been demonstrated for flexible electronics. In order to apply flexible devices on the polymer substrates, all layers should require the characteristic of flexibility as well as the low temperature process. Especially, pentacene thin film transistors (TFTs) have been investigated for probable use in low-cost, large-area, flexible electronic applications such as radio frequency identification (RFID) tags, smart cards, display backplane driver circuits, and sensors. Since pentacene TFTs were studied, their electrical characteristics with varying single variable such as strain, humidity, and temperature have been reported by various groups, which must preferentially be performed in the flexible electronics. For example, the channel mobility of pentacene organic TFTs mainly led to change in device performance under mechanical deformation. While some electrical characteristics like carrier mobility and concentration of organic TFTs were significantly changed at the different temperature. However, there is no study concerning multivariable. Devices actually worked in many different kinds of the environment such as thermal, light, mechanical bending, humidity and various gases. For commercialization, not fewer than two variables of mechanism analysis have to be investigated. Analyzing the phenomenon of shifted characteristics under the change of multivariable may be able to be the importance with developing improved dielectric and encapsulation layer materials. In this study, we have fabricated flexible pentacene TFTs on polymer substrates and observed electrical characteristics of pentacene TFTs exposed to tensile and compressive strains at the different values of temperature like room temperature (RT), 40, 50, $60^{\circ}C$. Effects of bending and heating on the device performance of pentacene TFT will be discussed in detail.

• 한국자동차공학회논문집
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• 제12권3호
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• pp.192-203
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• 2004

The AA5182/polypropylene/AA5182 (AA/PP/AA) sandwich sheets have been developed for the application for automotive body panels in the future light weight vehicles with significant weight reduction. It has been reported that the 5182 aluminum sheet shows Luders band because of dissolved Mg atoms that causes fabrication process problem, especially surface roughness. The examination of serration behavior has been made after the tensile deformation of the AA/PP/AA sandwich sheets as well as that of the 5182 aluminum skin at room and elevated temperatures. All sandwich sheets and the 5182 aluminum skin showed serration phenomena on their flow curves. However, the magnitude of the serration was significantly diminished in the sandwich sheet with the high volume fraction of the polypropylene core. According to the results of the surface roughness analysis after the tensile test, the sandwich sheet evidently showed lower Luders band depth than the 5182 aluminum skin. Strain rate sensitivity, m-value, of the 5182 aluminum skin was -0.006. By attaching this skin with polypropylene core which has relatively large positive value, 0.050, m-value of the sandwich sheets was changed to the positive value. The serration reduction of the sandwich sheets was quantitatively investigated in the point of the effect on the polypropylene core thickness variation, that on the strain rate sensitivity. It was found that the serration reduction degree from the experimental results of the sandwich sheet was higher than that from the calculated values by the rule of mixture based on volume fraction of the skins and the core.

• Earthquakes and Structures
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• 제10권5호
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• pp.1143-1179
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• 2016

Offshore wind turbines are considered as a fundamental part to develop substantial, alternative energy sources. In this highly flexible structures, monopiles are usually used as support foundations. Since the monopiles are large diameter (3.5 to 7 m) deep foundations, they result in extremely stiff short monopiles where the slenderness (length to diameter) may range between 5 and 10. Consequently, their elastic deformation patterns under lateral loading differ from those of small diameter monopiles usually employed for supporting structures in offshore oil and gas industry. For this reason, design recommendations (API and DNV) are not appropriate for designing foundations for offshore wind turbine structures as they have been established on the basis of full-scale load tests on long, slender and flexible piles. Furthermore, as these facilities are very sensitive to rotations and dynamic changes in the soil-pile system, the accurate prediction of monopile head displacement and rotation constitutes a design criterion of paramount importance. In this paper, the Fourier Series Aided Finite Element Method (FSAFEM) is employed for the determination of static impedance functions of monopiles for OWT subjected to horizontal force and/or to an overturning moment, where a non-homogeneous soil profile has been considered. On the basis of an extensive parametric study, and in order to address the problem of head stiffness of short monopiles, approximate analytical formulae are obtained for lateral stiffness $K_L$, rotational stiffness $K_R$ and cross coupling stiffness $K_{LR}$ for both rough and smooth interfaces. Theses expressions which depend only on the values of the monopile slenderness $L/D_p$ rather than the relative soil/monopile rigidity $E_p/E_s$ usually found in the offshore platforms designing codes (DNV code for example) have been incorporated in the expressions of the OWT natural frequency of four wind farm sites. Excellent agreement has been found between the computed and the measured natural frequencies.