• Architectural research
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• 제14권4호
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• pp.153-161
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• 2012

This paper presents an integrated procedure to predict the temperature and moisture distributions in hardening concrete considering the effects of temperature and aging. The degree of hydration is employed as a fundamental parameter to evaluate hydro-thermal-mechanical properties of hardening concrete. The temperature history and temperature distribution in hardening concrete is evaluated by combining cement hydration model with three-dimensional finite element thermal analysis. On the other hand, the influences of both self-desiccation and moisture diffusion on variation of relative humidity are considered. The self-desiccation is evaluated by using a semi-empirical expression with desorption isotherm and degree of hydration. The moisture diffusivity is expressed as a function of degree of hydration and current relative humidity. The proposed procedure is verified with experimental results and can be used to evaluate the early-age crack of hardening concrete.

• Journal of the Korean Wood Science and Technology
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• 제24권2호
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• pp.36-41
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• 1996

목재(木材)의 건조과정(乾燥過程) 중에 발생하는 목재 내부의 수분경사(水分傾斜)를 예측하기 위해 비정상상태(非定常狀態)의 확산(擴散)모델을 지배방정식(支配方程式)으로 적용하였으며, 목재 표면에서의 증발저항(蒸發抵抗)과 내부의 대칭적 수분분포를 경계조건(境界條件)으로 채택하였다. 주어진 경계조건에서의 지배방정식에 대한 일반해(一般解)가 무한수열 형태로 이루어지기 때문에, 유한차분법(有限差分法)을 이용하여 수치해석(數値解析)하였으며, 유한차분법(有限差分法) 중 오차범위(誤差範圍)가 안정한 상태인 Crank-Nicolson Scheme 알고리즘을 채택하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.1096-1101
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• 2008

Concrete is shown the time dependent behavior after placing. The time dependent behavior of normal strength concrete that is used usually in present, were already examined closely lots of parameters by several investigators. however, high strength concrete is that the material characteristics are not definite and the experimental data are lacking. So, The goal of this study is to propose the material characteristics models, and to develop the routine of the time dependent behavior above 60 MPa. The thermal conductivity, the specific heat, the moisture diffusion coefficient, and the surface coefficient are proposed the suitable models through the parametric study. The structural element is used the 8-node solid element. The matrix equation is developed considering the transient heat transfer and moisture diffusion theory. The application of the time dependent behavior is used the finite differential method.

• 콘크리트학회지
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• 제6권4호
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• pp.102-112
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• 1994

콘크리트의 건조수축은 수분확산과 밀접한 관계가 있으며, 수분확산과정은 온도와 습도에 의해 많은 영향을 받는다. 또한 물-시멘트비나 골재의 품질등에 의해서도 영향을 받기 때문에 고차의 비선형성을 보인다. 이 연구에서는 먼저 시간에 따른 콘크리트내의 수분분포를 해석하는 프로그램을 개발하고, 그리고 크리이프 및 온도와 숙성도에 따른 탄성계수의 변화를 고려하여 부등건조수축 및 부등응력을 계산하는 프로그램을 개발하였다. 이 프로그램에 의한 해석값들을 BP-KX 모델에 의해 계산된 건조수축값 및 실험값과 비교하여 좋은 결과를 보여 주었으며, 콘크리트내의 응력은 시간과 위치에 따라 정량적으로 계산되었다.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 1998년도 동계 학술대회 논문집
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• pp.297-301
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• 1998

• 한국작물학회:학술대회논문집
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• 한국작물학회 2004년도 춘계 학술대회지
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• pp.276-277
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• 2004

• 농업과학연구
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• 제47권3호
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• pp.519-532
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• 2020

Because lotus root has a short shelf life, the quality easily deteriorates. Thus, the harvested lotus roots are processed into a variety of products. Drying is one of the simplest food preservation methods, which can increase food stability. However, the convective drying method takes a long time and requires high energy consumption. Combination drying methods have emerged to overcome the limitations of the convective drying method. This study investigated the drying characteristics of lotus root and determined the optimal drying model of lotus root depending on the microwave and hot-air combination drying conditions. The lotus root slices (5 mm in thickness and 40 mm in diameter) were dried by different drying conditions that were combined with three microwave power levels (50, 100, and 150 W) and two hot air temperatures (50 and 60℃) at a velocity of 5 m·s^-1. Eight drying models were tested to evaluate the fit to the experimental drying data, and the effective moisture diffusion (D_eff) values of the lotus root slices dried by combination drying were estimated. The combination drying time of the lotus root was significantly reduced with the high air temperature and microwave power. The effective moisture diffusion (D_eff) of lotus root was more affected by the air temperature than microwave power intensity. Logarithmic model was most suitable to describe the drying curve of lotus root in the microwave-hot air combination drying method.

• Journal of the Korean Wood Science and Technology
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• 제24권1호
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• pp.75-80
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• 1996

The purpose of this study is to clarify the mechanism of moisture transfer depend on the thickness of the spruce(Picea sitchensis Carr.). Therefore, as the basic research of moisture transmission, the amount of moisture transmission and the moisture distribution in specimens and temperature of it's surfaces in vapor transmission process were investigated. The experiment was conducted in a steady state. and the moisture distribution was measured by knife cutting and weighing the specimens. The following conclusions were obtained ; 1. It can be found that distribution of moisture in the specimen can be approximated by two different straight lines intersecting at nine or ten percent moisture content. The amount of moisture movement defends on the gradient of moisture in the wood. 2. It is investigated that the wood surface moisture contents(MCs) are less for thinner specimens than for thick ones on the absorption side. On the other hand, the wood surface MCs are greater for thinner specimens than for thick ones on the desorption side. The main factor that affects the EMC of wood would be temperature when the relative humidity of atmosphere is constant. The specimen generate heat with the absorption and desorption process. In addition, the velocities of moisture transmission varied with the thicknesses of specimens. If the temperature of wood becomes greater, its MC decreases. Then the difference between surface MC and EMC of adsorption and desorption side becomes greater for thinner specimens. Therefore it is considered that the coefficients of moisture transfer decreases with the increases of the specimens' thicknesses.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1994년도 봄 학술발표회 논문집
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• pp.155-162
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• 1994

The drying shrinkage of concrete has a close relation to the water movement, Since the diffusion process of water in concrete is strongly dependent on the temperature and pore humidity, the process is highly nonlinear phenomena. It is shown that the analytical results of this study are in good agreement with experimental data in the literatures, and results calculated by BP-KX model. The internal stress caused by moisture distribution which was resulted from the diffusion process, was calculated quantitatively. The tensile stress which occurred in the drying outer zone mostly exceeded the tensile strength of concrete, and necessarily would result in crack formation.

• 한국해양공학회지
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• 제9권2호
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• pp.133-140
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• 1995

This paper deals with the residual strength characteristics of composite materials under the environment of high temperature and humidity. Two types of GFRP, one with unidirection and randomly oriented, are used to investigate the features of moisture absorption and the residual strength. The results show that, when exposed longterms in high temperature and humidity, the randomly oriented composites is more stable than the unidirection one.