• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.1
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• pp.89-94
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• 2014

The high Young's modulus and tensile strength of carbon nanotubes has attracted great attention from the research community given the potential for developing super-strong, super-stiff composites with carbon nanotube reinforcements. Over the decades, the strength and stiffness of carbon nanotube-reinforced polymer nanocomposites have been researched extensively. However, unfortunately, such strong composite materials have not been developed yet. It has been reported that the efficiency of load transfer in such systems is critically dependent on the quality of adhesion between the nanotubes and the polymer chains. In addition, the waviness and orientation of the nanotubes embedded in a matrix reduce the reinforcement effectiveness. In this study, we carried out performed micromechanics-based numerical modeling and analysis by varying the geometry of carbon nanotubes including their aspect ratio, orientation, and waviness. The results of this analysis allow for a better understanding of the load transfer capabilities of carbon nanotube-reinforced polymer composites.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.4
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• pp.109-118
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• 2005

A concrete shear wall system is commonly adopted in high-rise residential apartment buildings. In the construction stage, a rectangular opening is often made for the convenience of horizontal movement of workers, and construction materials and equipment. In the case of safety or stability assessment of a shear wall, the cutout part can be a critical factor. Finite element method is adopted to investigate the elastic stability behavior of the perforated unit shear wall. The key analysis parameters are the cutout location and its size. The effect of out-of-plane bending and horizontal shear are also examined in the stability analysis.

• Composites Research
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• v.37 no.2
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• pp.132-138
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• 2024

In this study, a molecular dynamics simulation study was performed to investigate the size-dependent electroelastic properties of single-walled boron nitride nanotubes(BNNT). To describe the elasticity and polarization of BNNT under mechanical loading, the Tersoff potential model and rigid ion approximation were adopted. For the prediction of piezoelectric constants and Young's modulus of BNNTs, piezoelectric constitutive equations based on the Maxwell's equation were used to calculate the strain-electric displacement and strain-stress relationships. It was found that the piezoelectric constants of BNNTs gradually decreases as the radius of the tubes increases showing a nonnegligible size effect. On the other hand, the elastic constants of the BNNTs showed opposites trends according to the equivalent geometrical assumption of the tubular structures. To establish the structure-property relationships, localized configurational change of the primarily bonded B-N bonded topology was investigated in detail to elucidate the BNNT curvature dependent elasticity.

• Journal of Biomedical Engineering Research
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• v.22 no.1
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• pp.59-68
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• 2001

유체-고체 상호작용을 고려하여 다양한 복부대동맥류 모델에 대해서 맥동유동 및 구조를 동시에 해석하였다. 동맥류의 확장부 크기와 혈관벽 두께에 따라서 총 여덟 개의 축대칭 동맥류 모델을 선정하였다. 유한체적법 및 압력기반의 유한차분법을 이용하여 유동을 해석하였으며, 유한요소법을 이용하여 구조해석을 수행하였다. 동맥류의 확장부위가 클수록 최대응력은 최대확장부위와 변곡점에 해당하는 동맥류의 입구 및 출구 부분에 집중되었으며, Von Mises 응력은 최대확장부위 뿐만 아니라 동맥류의 근위부와 원위부($\pm$1D)에서도 현저하게 증가하였다. 또한 더욱 확장된 모델일수록 혈관벽은 직경방향의 변위보다 축방향의 변위가 지배적이었으며, 동맥류 원위부보다 근위부에서 큰 축방향 변위를 나타냈다. 동맥류 입구부의 미약한 와류는 한 주기동안 그 크기와 강도를 더해가며 동맥류 원외부로 이동하였고, 동맥류의 내부 유동은 압력차이가 감소하는 기간동안 더 큰 영향을 받았다. 확장정도가 심할수록 동맥류 내부에 더 크고 강한 와류가 관찰되었다. 압력차이가 최소가 된 직후 동맥류의 근위부와 원위부동맥 벽 근처에서의 역방향 유동이 관찰되었다. 대체로 혈관벽 두께가 감소한 모델과 더욱 확장된 모델일수록 벽전달률은 감소하였다. 혈관벽의 탄성에 의하여 압력차이와 벽전달률 사이에 위상차가 존재함이 확인되었다. 유체-고체의 상호작용을 고려한 연구는 다른 심혈관계를 이해하는데도 매우 유익할 것으로 생각된다.

• Applied Chemistry for Engineering
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• v.19 no.4
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• pp.421-426
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• 2008

Multi-walled carbon nanotube/polystyrene (MWCNT/PS) composites with various MWCNT contents were prepared by using a solution process with an aid of surfactant. Particularly, PS's with 3 different molecular weights (${\bar{M}}_n$ = 101500 g/mole for PS-1, ${\bar{M}}_n$ = 89900 g/mole for PS-2, and ${\bar{M}}_n$ = 85000 g/mole for PS-3) were used in this study. Thermal behavior of these composites was examined by using an oscillator rheometer at $210^{\circ}C$ and $180^{\circ}C$, of above and below the critical flow temperature ($T_{cf}{\sim}195^{\circ}C$) of PS matrix, respectively. The storage and loss modulus, and the complex viscosity of these composites increased with increasing MWCNT content at both temperatures. Largest increases in the frequency-dependent moduli and complex viscosity were observed between 2 wt% and 5 wt% of MWCNTs at $210^{\circ}C$ and $180^{\circ}C$. Only the composite at $210^{\circ}C$ showed the rheological phase transition from a viscous-dominant to an elastic-dominant behavior of the composites at a certain MWCNT content. The MWCNT content at the rheological phase transition of MWCNT/PS composites generally increased with decreasing molecular weight of PS, and was measured to be 3.5 wt% for MWCNT/PS-1, 3.2 wt% for MWCNT/PS-2, and 3.0 wt% for MWCNT/PS-3 composites.

• Computational Structural Engineering
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• v.8 no.4
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• pp.159-171
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• 1995

The parameters describing a complete hysteresis loop include pinch force, drift offset, effective stiffness, unloading and reloading trangential stiffness. Analytical equations proposed to quantify the nonlinear, inelastic behavior of reinforced shear walls can be used to predict these parameters as a function of axial load and drift ratio. For example, drift offset, effective stiffness, and first and second unloading and reloading tangential stiffness are calculated using equations obtained from test data for a desired drift ratio or ductility level. Pinch force can also be estimated for a given drift ratio and axial load. The effective virgin stiffness at the first yield and its post yield reduction can be estimated. The load deflection response of flexural reinforced concrete shear walls can now be estimated based on the effective wall stiffness that is a function of axial force and drift ratio.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.3
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• pp.107-116
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• 1990

The liquid sloshing in an elastic tank is a fluid-structure interaction problem. It requires nonlinear analysis to solve the complicated physics involved in the large interaction of fluid-structure, the variation of dynamic characteristics of structure due to hydrodynamic loading, and the distorsion of fluid flow due to structural vibration. In this paper a Lagrangian FEM is introduced to analyze the liquid sloshing in an elastic tank assuming that the elastic wall is one degree of freedom rigid wall. Numerical integration is performed using an implicit-explicit algorithm, which is formed by mixing the predictor-corrector method and the Runge-Kutta 4th order method. The influence of dynamic characteristics of the sloshing tank on the fluid flow is discussed. The numerical method is also applied for the simulation of the wall generated wave in the tank.

• Proceedings of the Korean Nuclear Society Conference
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• 2004.05a
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• pp.453.2-453.2
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• 2004

• Proceedings of the Korean Nuclear Society Conference
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• 1999.10a
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• pp.371.1-371
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• 1999

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.5
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• pp.187-197
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• 2004

This paper presents the effects of cylinder shell elasticity on effective bulk modulus of oil $K_e$ in automotive hydraulic dampers. A theoretical model of cylinder shell bulk modulus $K_c$ based on the elasticity theory of thick-walled cylinder incorporating not only radial but longitudinal deformation is proposed. In a cylinder, values of $K_c$ by the new model and traditional models are computed and the discrepancies among them are discussed. In a twin-tube type automotive damper, the variation of $K_e$ under different pressure values in chambers of the damper cylinder, based on different theoretical models for $K_c$ is computed. Through these computations, it is shown that remarkable discrepancies in computed values of $K_e$ might occur according to the $K_e$ models in connection with $K_c$ models.