• Korean Chemical Engineering Research
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• v.53 no.6
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• pp.709-716
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• 2015

In this study, structural developments of polypropylene / ionomer / clay ternary composites were investigated depending on the dispersion and localization of clay. The changes in physical properties were observed adding organoclays 1~10wt% to 90% polypropylene and 10% ionomer blends. The organoclays were localized inside of the dispersed phase under the composition of 3wt%, however, over that composition, clay particles formed stiff network structure in the dispersed phase and additional clays were localized at the interface between two phases. According to the developments of microstructure, the interaction of ternary composites changed from polypropylene-ionomer to polypropylene-ionomer and ionomer-clay which affected rheological properties. The storage modulus (G') of the composites was similar to the blends when clays were localized inside of dispersed phase but increased when clays were localized at interface. Also, the fractured morphology of the composites showed phase boundary and growing radius of dispersed phase depending on addition of fillers when clays were found inside. However, when fillers found at the interface between blends, the radius of the dispersed phase decreased and compatibilized morphology were observed. The interfacial interaction of the ternary composite was quantified depending on the structural development of dispersed phase and localization of clay particles by the rheological properties. The interaction of composites at solid state which was measured through peel adhesion strength increased by growth of interfacial interaction of each component. Furthermore, the crystallinity of the composites was decreased when the clay particles were localized at the interface.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.114-122
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• 2015

In the high convective gas flow condition, irregular shaped water waves from which droplet entrainment occurs are generated under horizontally stratified two-phase flow condition. KAERI proposed a new mechanistic droplet entrainment model based on the momentum balance equation consisting of the shear stress, surface tension, and gravity forces. However, this model requires correlation or experimental data of several physical parameters related to the wave characteristics. In the present study, we tried to measure the physical parameters such as wave slope, wave hypotenuse length, wave velocity, wave frequency, and wavelength experimentally. For this, an experiment was conducted in the horizontal rectangular channel of which width, height, and length are, respectively, 40 mm, 50 mm, and 4.2 m. In the present test, the working fluids are chosen as air and water. The PIV technique was applied not only to obtain images for phase interface waves but also to measure the velocity field of the water flow. Additionally, we developed the parallel wire conductance probe for the confirmation of wave height from PIV image. Finally, we measured the physical parameters to be used in the validation of new droplet entrainment model.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1991.07a
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• pp.93-97
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• 1991

수표면에 방류되는 온배수등의 흐름과 같은 표층방류밀도분류는 자유난류의 전단류 효과와, 방류수와 주위수의 밀도차에 기인하는 부력효과를 동시에 받는 흐름장을 형성한다. 또한, 이 흐름은 수표면 및 밀도계면에 의해 2 개의 자유경계에 둘러싸인 특이한 경계조건때문에 개수로 흐름으로 대표되는 자유전단류와 구별된다.(중략)

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2015.10a
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• pp.100-103
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• 2015

본 연구에서는 선박의 내항 및 조종성능평가를 위해 사용되는 2차원부가질량계수와 파랑감쇠계쉬를 desingularized indirect boundary integral method를 이용하여 주파수영역에서 계산하였다. 본 방법을 Rankine source를 유체경계면 전체에 분포하는 방법으로 수학적으로 간단하고 경계조건의 변경 및 적용이 용이하다는 장점이 있다. 하지만 물체표면, 자유수면 그리고 방사경계면의 계산영역 및 요소의 배치에 따라 계산정확도에 차이가 발생한다. 따라서 본 연구에서는 수치시험을 통해, 자유수면과 방사계면의 적절한 계산영역과 요소의 개수를 결정하였다. 계산의 정도와 효율성을 확보하기 위하여, 자유수면과 방사경계면의 계산영역과 요소의 분포를 파의주파수에 따라 달리 적용하였다. 본 연구에서 제안된 수치방법을 활용하여 계산된 동유체력과 실험에서 계측된 동유체력을 비교하여 본 방법의 정도를 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.7
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• pp.695-701
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• 2013

The suppression of a thermocapillary flow (Marangoni flow) by a nonionic surfactant is experimentally investigated for evaporating pure water droplets on hydrophobic substrates. The experiment shows that as the initial concentration of the surfactant increases, the velocity and lifetime of the flow monotonically decrease. The result confirms the no-slip boundary condition at a liquid-air interface, which is explained on the basis of the previous model regarding the effect of surfactants on the no-slip condition. Interestingly, at an initial concentration much less than a critical value, it is found that depinning of the contact line occurs during the early stage of evaporation, which is ascribed to a reduction in the contact angle hysteresis owing to the presence of the Marangoni flow.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.10a
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• pp.380-385
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• 2000

In this study, geometric shape and crack in welded interface of the air cooled heat exchanger Fin-Tube of Dissimilar Meterials was analysed. The object of study is to understand the behavior of Stress Intensity Factor for fin length, flash thickness, flash length, symmetric and asymmetric cracks of comming from the manufacturing process. Stress Intensity Factor was analysed by BEM. Kelvin's solution was used as a fundamental solution in BEM analysis and stress extrapolation method was used to determine Stress Intensity Factor.

• Proceedings of the ESK Conference
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• 1994.04a
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• pp.158-170
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• 1994

인간-기계 시스템이 점차적으로 복잡하고 거대해짐에 따라 인간-기계 계면(man-machine interface)에서의 인간은 근운동을 요하는 육체적 작업에서 경계(vigilance), 제어(control), 감시 (monitoring), 추적(tracking) 등 정신적 업무로그 역할이 전이되는 등 시스템내에서의 인적요소의 중요성이 더욱 증가되고 있다. 이러한 시스템내에서의 주된 계면은 표시장치(display)와 제어장치 (control)들이며, 이들에 대한 인간공학적 설계와 배치가 효율적인 인간-기계 계면의 중요한 설계 요인이 된다. 본 연구에서는 동일한 작업에 대해 서로다른 배치를 가진 4개의 컴퓨터 시뮬레이션 표시장치 panel 실험을 통하여 panel 제어 작업에서의 표시장치와 제어장치의 설계형태나 배치에 따라 발생하는 인적오류를 정량적으로 예측, 검출하는 것을 그 목적으로 한다. 그리고 각 panel에 따른 수행도 척도로서 작업수행시간(operation time)과 오류율(error rate)을 검출하고, 그 결과에 의한 인적 오류 예측모형을 제시하여 인적오류를 감소시키는 보다 나은 panel을 설계하는데 활용가능 하게 하고, 더 나아가서는 인간신뢰성 기법에 적용시킬 수 있도록 기초자료를 분석하고 제시하고자 한다.

• Composites Research
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• v.16 no.1
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• pp.42-49
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• 2003

Brittle matrix composites often have interfacial debonding between the fiber and matrix which may lead to strength and stiffness degradation. The effect of interfacial debonding and fiber volume fraction on the mechanical properties of composite material were studied by using finite element method. Firstly, the modelling of fiber and matrix constituting the composite material was simplified under some assumptions. Traction and displacement continuity conditions were imposed along the boundary of adjacent representative volume elements. In order to obtain the effective material properties of composite material, stiffness constants were inverted. Numerical values of longitudinal moduli in case of perfect bonding were compared with theoretical values obtained by rule of mixtures and yielded consistency. Material properties of composite with large debonding an81e were found to decrease even though the fiber volume fraction increased.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.359-370
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• 1993

Up to now, most studies are on interface crack problems in isotropic-isotropic dissimilar materials, but it seems to be not so much on anisotropic dissimlar materials. In this study, the stress intensity factors for an interface crack in anisotropic dissimilar materials are analysed using author's proposed extrapolation method by BEM and we have done a parametric study about material properties or shapes of crack affecting to the stress intensity factors. However, as there are not other's comparable numerical results on these anisotropic dissimilar materials to the best of author's knowledge, the reliability of the present results was proved by following two methods. The first is considering the asymptotic characteristic about stress intensity factors for an interface crack in anisotropic materials when the ansiotropic material approachs to the isotropic material. The second is considering the discontinuity of stress intensity factors between of a crack in an identical homogeneous anisotropic material and an interface crack in anisotropic dissimilar materials.

• Computational Structural Engineering
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• v.10 no.3
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• pp.185-193
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• 1997

The order of the stress singularity that occurs at the termination of an interface between materials exhibiting bilinear stress-strain response under plane strain conditions has been calculated, The governing equation of elasticity together with traction-free boundary condition and interface continuity condition defines a two-point boundary value problem. The stress components near the free edge are assumed to be proportional to r/sup s-1/, with solutions existing only for certain values of s. Finding these values entails the solution of an eigenvalue problem. Because it has been impossible to integrate the differential equations analytically, the integration has been performed numerically with a shooting method coupled with a Newton improvement scheme.