• 한국철도학회:학술대회논문집
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• 한국철도학회 1999년도 추계학술대회 논문집
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• pp.558-565
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• 1999

Rubber wheel-type AGT has two major kinds of bogie; one is the bogie type and the other and passenger loads. This paper deals with the statics analysis for two types of bogie frame subjected to combined external forces, as well as independent ones specified in UIC 515-4. Furthermore, the dynamics analysis is performed under vibrational loading conditions so as to compare dynamic characteristics, Numerical results by using commercial packages, Ⅰ-DEAS and NASTRAN show that maximum stresses do not exceed the yielding level of material used for both bogies. From an overall viewpoint of strength, the bogie type turns out to be superior to the steering type except the case of a lateral loading. It is also observed that the steering type shows a be stiffened. It is strongly anticipated that vibrational fatigue analysis should be carried out under realistic loading conditions closely matching to situations such as running surface and lateral clearances along the guideway.

• 한국지반공학회논문집
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• 제30권1호
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• pp.103-116
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• 2014

본 논문에서는 석션파일의 하중지지력 및 압밀 거동에 대한 수치해석 내용을 다루었다. 수치해석에서는 파일-지반 간 인터페이스 거동이 고려된 3차원 모델을 적용하여 석션파일의 길이 대 직경 비, 하중 형태(수직하중, 수평 및 조합하중)를 변화시키며 해석을 수행하고 그 결과를 토대로 수직 및 수평지지력 거동 특성을 고찰하였다. 아울러 임의의 수직하중이 작용하는 조건에 대해 응력-간극수압 연계해석을 수행하여 석션파일의 하중재하 후 압밀거동을 고찰하였다. 해석 결과 석션파일의 지지력은 석션파일과 지반간의 상호작용 모델링 여부에 따라 큰 차이가 발생하는 것으로 검토되어 인터페이스 모델링의 중요성이 부각되었으며 산정된 하중지지력 결과를 토대로 제시된 조합하중에 대한 파괴포락선을 제시하였다. 아울러 응력-간극수압 연계해석에 근거한 압밀해석 결과를 분석한 결과 석션파일은 주면마찰이 주 하중지지 구조인 관계로 수직하중 재하시 과잉간극수압 발생량 및 압밀침하량은 미미한 것으로 검토되었다.

• Structural Engineering and Mechanics
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• 제74권2호
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• pp.283-296
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• 2020

The coupled hydro-mechanical loading conditions commonly occur in the geothermal and petroleum engineering projects, which is significantly important influence on the stability of rock masses. In this article, the influence of flaw inclination angle of fracture behaviors in rock-like materials subjected to both mechanical loads and internal hydraulic pressures is experimentally studied using the 3-D X-ray computed tomography combined with 3-D reconstruction techniques. Triaxial compression experiments under confining pressure of 8.0 MPa are first conducted for intact rock-like specimens using a rock mechanics testing system. Four pre-flawed rock-like specimens containing a single open flaw with different inclination angle under the coupled hydro-mechanical loading conditions are carried out. Then, the broken pre-flawed rock-like specimens are analyzed using a 3-D X-ray computed tomography (CT) scanning system. Subsequently, the internal damage behaviors of failed pre-flawed rock-like specimens are evaluated by the 3-D reconstruction techniques, according to the horizontal and vertical cross-sectional CT images. The present experimental does not only focus on the mechanical responses, but also pays attentions to the internal fracture characteristics of rock-like materials under the coupled hydro-mechanical loading conditions. The conclusion remarks are significant for predicting the rock instability in geothermal and unconventional petroleum engineering.

• Geomechanics and Engineering
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• 제31권2호
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• pp.223-235
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• 2022

Bearing capacity of shallow foundations is often determined for either dry or saturated soils. In some occasions, foundations may be subjected to external loading which is inclined and/or eccentric. In this study, the ultimate bearing capacity of shallow foundations resting on partially saturated coarse-grained cohesionless and fine-grained cohesive soils subjected to a wide range of combined vertical (V) - horizontal (H) - moment (M) loadings is rigorously evaluated using the well-established limit equilibrium method. The unified effective stress approach as well as the suction stress concept is effectively adopted so as to simulate the behaviour of the underlying unsaturated soil medium. In order to obtain the bearing capacity, four equilibrium equations are solved by adopting Coulomb failure mechanism and Bishop effective stress concept and also considering a linear variation of the induced matric suction beneath the foundation. The general failure loci of the shallow foundations resting on unsaturated soils at different hydraulic conditions are presented in V - H - M spaces. The results indicate that the matric suction has a marked influence on the bearing capacity of shallow foundations. In addition, the effect of induced suction on the ultimate bearing capacity of obliquely-loaded foundations is more pronounced than that of the eccentrically-loaded footings.

• 대한기계학회논문집A
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• 제38권11호
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• pp.1207-1214
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• 2014

균열이 존재하는 구조물의 균열 선단에서 과도한 소성 상태에 도달하게 되면 파괴역학 매개변수에 의하여 예측되는 균열 선단의 응력장이 실제와는 매우 다르게 나타난다. 구조물의 크기와 형상 그리고 하중의 형태에 따라 균열 선단의 응력장이 유일하지 않다. 이는 균열 선단의 구속 효과가 단일 매개변수 파괴역학으로 표현 될 수 없기 때문이다. 따라서 전통적으로 사용되었던 K, J를 이용한 단일 매개변수 파괴역학을 보완하기 위하여 다양한 시도가 있었고, 대표적으로 Q-응력이 있다. 본 논문에서는 Q-응력을 이용하여 원주방향으로 완전히 발달한 표면 균열이 있을 경우의 균열 선단의 구속 효과를 확인하였다. 고려된 하중은 일차하중으로 축 방향 인장하중과 반경방향 열구배에 의한 이차하중의 복합하중이다. 이차하중이 일차하중보다 구속효과가 더 심하며 기계하중보다 열하중이 뒤에 가해지는 열충격조건에서 구속효과가 더 심하게 나타남을 확인하였다.

• 대한기계학회논문집A
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• 제39권5호
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• pp.453-460
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• 2015

후쿠시마 원전 사고 이후로 원자력 발전 플랜트의 배관 시스템에 가해지는 비틀림 하중의 영향에 대한 연구가 여러 연구자들에 의해서 수행되었다. 발전 플랜트의 원주방향 균열을 포함한 배관은 정상운전 조건이나 갑자기 발생한 사고에 의해서 굽힘과 비틀림과 같은 하중을 받을 수 있다. ASME 코드에서는 균열 배관의 구조건전성 확보를 위해서 한계하중 기법을 사용해서 완전소성 파단에 대한 결함평가를 제공한다. 최근 개정된 코드에 따르면, 복합하중은 막응력과 굽힘 응력만을 포함하고 있다. 실제로 운전 환경에서 비틀림 하중이 가해질 수 있음에도 불구하고, 비틀림 하중을 평가하는 방법론에 대해서는 언급하지 않았다. 본 논문에서는 한계하중 분석을 기반으로 원주방향 균열 존재하는 배관에 단순 굽힘과 단순 비틀림, 인장을 포함한 굽힘 비틀림 복합하중이 가해질 경우에 대한 유한요소해석 결과를 포함하고 있다. 전단면 완전항복 기준을 만족하는 한계하중 이론해를 제안하고 유한요소해석을 통해서 이를 검증하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.1-4
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• 2005

A higher order zig-zag shell theory is developed to refine accurately predict deformation and stress of smart shell structures under the mechanical, thermal, and electric loading. The displacement fields through the thickness are constructed by superimposing linear zig-zag field to the smooth globally cubic varying field. Smooth parabolic distribution through the thickness is assumed in the transverse deflection in order to consider transverse normal deformation. The mechanical, thermal, and electric loading is applied in the sinusoidal distribution function in the in-surface direction. Thermal and electric loading is given in the linear variation through the thickness. Especially, in electric loading case, voltage is only applied in piezo-layer. The layer-dependent degrees of freedom of displacement fields are expressed in terms of reference primary degrees of freedom by applying interface continuity conditions as well as bounding surface conditions of transverse shear stresses. In order to obtain accurate transverse shear and normal stresses, integration of equilibrium equation approach is used. The numerical examples of present theory demonstrate the accuracy and efficiency of the proposed theory. The present theory is suitable for the predictions of behaviors of thick smart composite shell under mechanical, thermal, and electric loadings combined.

• 한국자동차공학회논문집
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• 제12권1호
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• pp.122-129
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• 2004

Finite element analysis was performed to analyze structural safety of a new heavy-duty direct injection diesel engine. A half section of the in-line 6-cylinder engine was selected as a computational domain. A mapping method was used to project heat transfer coefficients from CFD results of engine coolant flow onto the FE model. The accurate setting of thermal boundary condition on the FE model was expected to result in improved prediction of temperature, cylinder bore distortion, and stresses. Characteristics of high cycle fatigue were investigated by assuming the engine was operated under the following five loading conditions repeatedly; assembly force, assembly force with thermal loading, alternating maximum gas pressure loading at each cylinder combined with assembly force and thermal loading. Distribution of fatigue safety factor was calculated by using it Haigh diagram in which the maximum and the minimum stresses were selected from the five loading cases.

• 대한의용생체공학회:의공학회지
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• 제39권3호
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• pp.109-115
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• 2018

Obesity is a worldwide disease caused by the excessive proliferation of adipocytes. Multiple factors, including melatonin and physical loading, are involved in the control of obesity. Melatonin has been shown to induce apoptosis on preadipocytes while physical loading such as fluid shear stress (FSS) affects the proliferation and differentiation of adipocytes. Here, we studied the combined effects of melatonin and FSS on 3T3-L1 preadipocytes. For physical loading, preadipocytes were stimulated with a maximum dynamic fluid shear stress of 1 Pa at 1 Hz for 2 hours with/without melatonin. The experiment conditions were divided into four groups: (1) control, (2) 1 mM melatonin treatment, (3) FSS, and (4) combined 1 mM melatonin and FSS. All groups had a fixed duration time of 2 hours. ERK, p-ERK, COX-2, $C/EBP{\beta}$, $PPAR{\gamma}$, osteopontin, Bax, caspase-3 and caspase-8 proteins were assessed by Western blot analysis. GAPDH was used as a control. Results showed that combined melatonin and FSS treatment activated the ERK/MAPK pathway but not COX-2. Furthermore, combined melatonin and FSS treatment significantly decreased $C/EBP{\beta}$ and $PPAR{\gamma}$ compared to other groups. However, caspase-3 and caspase-8 did not result in significant changes. In summary, combined melatonin and FSS appears to have the potential to inhibit adipogenesis and treat obesity.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.233-236
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• 2002

An efficient method was developed in this study to obtain optimal stacking sequences, thicknesses, and minimum weights of stiffened laminated composite shells under combined loading conditions and stiffener layouts using genetic algorithms (GAs) and finite element analyses. Among many parameters in designing composite laminates determining a optimal stacking sequence that may be formulated as an integer programming problem is a primary concern. Of many optimization algorithms, GAs are powerful methodology for the problem with discrete variables. In this paper the optimal stacking sequence was determined, which gives the maximum critical buckling load factor and the minimum weight as well. To solve this problem, both the finite element analysis by ABAQUS and the GA-based optimization procedure have been implemented together with an interface code. Throughout many parametric studies using this analysis tool, the influences of stiffener sizes and three different types of stiffener layouts on the stacking sequence changes were throughly investigated subjected to various combined loading conditions.