• 대한기계학회논문집
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• 제14권3호
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• pp.685-693
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• 1990

본 연구에서는 복사열전달 효과를 알아보기 위해 에너지 방정식을 수치적으로 풀었으며, 그 결과를 열전달계수 및 온도의 항으로 나타내었다. 수치 해석적 모델의 검증을 위해 여러사람들이 물질전달과정 해석을 위해 사용한 나프타린 승화법(naphth- alene sublimation technique)을 이용하여 실험을 수행하였다. 또한 실험에 사용된 다공질체(ceramic blocks)의 침투율도 측정하였다.

• 한국정보전자통신기술학회논문지
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• 제13권5호
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• pp.432-435
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• 2020

The elasticity tensor for water may be employed to model the fully saturated porous material. Mostly water is assumed to be incompressible with a bulk modulus, however, the upper and lower bounds of off-diagonal components of the elasticity tensor of porous materials filled with water are violated when the bulk modulus is relatively high. In many cases, the generalized Hill inequality describes the general bounds of Voigt and Reuss for eigenvalues, but the bounds for the component of elasticity tensor are more realistic because the principal axis of eigenvalues of two phases, matrix and water, are not coincident. Thus in this paper, for anisotropic material containing pores filled with water, the bounds for the component of elasticity tensor are expressed by the rule of mixture and the upper and lower bounds of fully saturated porous materials are violated for low porosity and high bulk modulus of water.

• 대한기계학회논문집B
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• 제20권1호
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• pp.336-345
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• 1996

A theoretical and experimental study was conducted in order to design highly efficient solar air heaters using porous material. Radiative characteristics of glass windows and porous absorbing media were correlated through spectral transmittances measured by the UV-Visible and the FT-IR spectrometers. Using those characteristics the efficiencies of collectors were numerically calculated with the use of the two-flux radiation model. Based on the theoretical results, an experimental solar collector was designed and constructed. Experimental results under various conditions show that the daily efficiencies are over 60% in general and agree well with the theoretically calculated ones.

• Steel and Composite Structures
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• 제38권5호
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• pp.523-531
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• 2021

The generalized thermoelastic analysis problem of a two-dimension porous medium with and without energy dissipation are obtained in the context of Green-Naghdi's (GNIII) model. The exact solutions are presented to obtain the studying fields due to the pulse heat flux that decay exponentially in the surface of porous media. By using Laplace and Fourier transform with the eigenvalues scheme, the physical quantities are analytically presented. The surface is shocked by thermal (pulse heat flux problems) and applying the traction free on its outer surfaces (mechanical boundary) through transport (diffusion) process of temperature to observe the analytical complete expression of the main physical fields. The change in volume fraction field, the variations of the displacement components, temperature and the components of stress are graphically presented. Suitable discussion and conclusions are presented.

• Computers and Concrete
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• 제27권3호
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• pp.269-282
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• 2021

A dynamic analytical solution for a simply supported, rectangular functionally graded plate with a porous middle layer under time-dependent load based on a refined third-order shear deformation theory with a cubic variation of in-plane displacements according to the thickness and linear/quadratic transverse displacement is presented. The solution achieved in the trigonometric series form and rests on the Green's function method. Two porosity types and their influence on material properties, and mechanical behavior are considered. The network of pores is assumed to be empty or filled with low-pressure air, and the material properties are calculated using the power-law distribution idealization. Numerical calculations have been carried out to demonstrate the accuracy of the kinematic model for the dynamic problem, the effect of porosity, thickness of porous layers, power-law index, and type of loading on the dynamic response of an imperfect functionally graded material plate.

• Composites Research
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• 제17권6호
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• pp.8-13
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• 2004

Eshelby의 등가개재물범과 Mori-Tanaka의 평균장 이론을 이용하여 다공성 형상기억합금에 대한 새로운 3차원 응력-변형률 모델을 제안하였다. 12%의 기공도를 갖는 Ni-Ti 형상기억합금에 대한 압축실험으로부터 구한 응력-변형률 선도와 본 연구에서 제안한 모델링에 의한 응력-변형률 관계를 비교한 결과 잘 일치함을 알 수 있었다. 기존의 다른 연구에서는 대부분 상변태 구간이 선형적으로 예측되었지만 본 연구에서는 비선형으로 예측되어 실험결과를 보다 잘 모사할 수 있었다.

• Structural Engineering and Mechanics
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• 제64권5호
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• pp.527-541
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• 2017

In this work, a new hyperbolic shear deformation beam theory is proposed based on a modified couple stress theory (MCST) to investigate the bending and free vibration responses of functionally graded (FG) micro beam made of porous material. This non-classical micro-beam model introduces the material length scale coefficient which can capture the size influence. The non-classical beam model reduces to the classical beam model when the material length scale coefficient is set to zero. The mechanical material properties of the FG micro-beam are assumed to vary in the thickness direction and are estimated through the classical rule of mixture which is modified to approximate the porous material properties with even and uneven distributions of porosities phases. Effects of several important parameters such as power-law exponents, porosity distributions, porosity volume fractions, the material length scale parameter and slenderness ratios on bending and dynamic responses of FG micro-beams are investigated and discussed in detail. It is concluded that these effects play significant role in the mechanical behavior of porous FG micro-beams.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 고액공존금속의 성형기술 심포지엄
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• pp.5-15
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• 1997

It is the objective of this study that by conducting the serni-solid extrusion using A12024, the effect of various process variables on the quality of extruded product and extrusion force is understood. The results of experiment are compared with those of finite element simulation in order to verify the effectiveness of the developed FE-simulation code. In order to simulate densification in the deformation of serni-solid material, the semi-solid material is assumed to be composed of solid region as porous skeleton following compressible visco-plastic model and liquid region following Darcy's equation for the liquid flow saturated in the interstitial space. Then the flow and deformation of the semi-solid alloy are analyzed by coupling the deformation of the porous skeleton and the flow of the eutectic liquid. It is assumed that initial solid fraction is homogeneous. Yield and plastic potential function presented by Kuhn and constitutive model developed by Gunasekera are used for solid skeleton.

• 한국항공우주학회지
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• 제39권8호
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• pp.711-718
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• 2011

본 논문에서는 열화학적 분해 및 열기계학적 변형이 고려된 구성 방정식을 사용하여 다공성 탄소/페놀릭 복합재료의 열탄성 거동을 예측하였다. 다공성 복합재료의 온도 의존성 및 열화학적 분해 과정에서의 기공도, 분해 가스에 의한 기공 압력, 재료의 수축을 고려하였다. 기공도와 기공 압력이 고려된 대표 체적 요소 모델의 유한요소 해석을 통해 산출된 거시적 기공 탄성 계수를 구성 방정식에 적용하였다. 간단한 수치 실험을 통해 기공탄성 계수가 다공성 재료의 열탄성 거동에 미치는 영향을 분석하였으며, 재료 내부에 형성된 기공과 기공 압력에 의한 응력 구배 및 변형을 확인하였다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2017년도 학술발표회
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• pp.384-384
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• 2017

본 연구에서는 다공성 매질에서의 비선형 흐름에 대한 수치적 분석을 수행하였다. 적용된 수치모형은 ANSYS CFX 3차원 유동해석 모형이며, 모형의 검증은 Mayer et al. (2011)에 의해 수행된 실험결과의 적용을 통해 수행되었다. 유속과 레이놀즈수-마찰계수 관계에 대한 실험결과와 수치결과를 비교한 결과 비교적 잘 일치하였다. 검증에서 적용된 실험결과를 바탕으로 투수성 계수, 점성계수 그리고 공극율의 변화에 따른 유속과 레이놀즈수-마찰계수 관계를 분석하였으며, 각각의 경우에 대해 best curve-fitting을 통해 변화 경향을 정량적으로 분석하였다.