• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2002.05a
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• pp.289-292
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• 2002

2계 선형 상미분방정식의 경계치 문제는 보통 해를 구하고자 하는 구간의 양 끝점에서 도함수의 값을 임의로 선정한 후 각 점에서 초기치 문제의 해를 구한 다음 적절한 1차 결합을 이용하여 구하게 된다. 이 경우 초기값과 도함수 값을 사용한 반복연산이 수반되며 따라서 오차의 누적이 불가피 하게 된다. 이 논문에서는 이같은 오차의 누적을 피할 뿐 아니라 3차 Spline 함수를 사용함으로써 오차가 O( $h^2$)인 해를 구하는 방법에 대하여 기술한다 두 개의 경계조건과 근사값을 구하고자 하는 점에서의 함수 값을 "If x is $B_{i}$, then f is $C_{i}$"와 같은 Fuzzy Rule들로 변형하고 주어진 미분방정식을 상수 $C_{i}$들의 관계식으로 변형하여 해를 구하였다. 산출된 결과로부터의 보간 연산은 Fuzzy System사용에 의하여 대체되었다. 이상의 방법으로 산출한 해의 근사오차가 O( $h^2$).임을 증명하였으며 3개의 예제에 대한 계산결과를 4계 Runge-Kutta 방법에 의한 해와 비교하여 기술하였다였다였다였다

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2009.04a
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• pp.147-154
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• 2009

화재와 같은 고온의 환경에서 콘크리트의 고강도화는 폭렬(Explosive Spalling)이라는 큰 위험성을 가지고 있으며, 이러한 폭렬의 원인으로는 콘크리트 내부의 수증기압이 가장 큰 원인으로 제기되고 있다. 본 논문은 콘크리트의 폭렬발생 있어서 압축강도 및 함수율이 초기 폭렬특성에 미치는 영향을 실험적으로 검토하기위하여 건축구조물의 화재 온도조건인 ISO834 화재온도이력곡선을 15분, 30분 적용하여 콘크리트의 초기 폭렬특성을 검토하였다. 그 결과 압축강도 가열시간 함수율이 증가할수록 폭렬발생 및 폭렬현상이 증대되는 경향이 나타났으며, 15분, 30분 가열시간에 따른 잔존강도율을 나타내었다. 또한, 압축강도 및 함수율에 따른 폭렬발생영역을 분석하였으며, 압축강도 50${\sim}$100 MPa의 경우 함수율 3%이하, 100 MPa이상의 경우는 1%이하로 제어할 경우 폭렬현상이 발생하지 않을 것으로 판단되었다.

• Journal of the Korea Society of Computer and Information
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• v.18 no.6
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• pp.9-19
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• 2013

This paper deals with fuzzy $H_{\infty}$ filtering problem of discrete-time nonlinear Markovian jump systems with state and output time delays. The purpose is to design fuzzy $H_{\infty}$ filter such that the corresponding estimation error system with time delays and initial state uncertainties is stochastically stable and satisfies an $H_{\infty}$ performance level. A sufficient condition for the existence of fuzzy $H_{\infty}$ filter is given in terms of matrix inequalities. In order to relax conservatism, a stochastic mode dependent fuzzy Lyapunov function is employed. The Lyapunov function not only is dependent on the operation modes of system, but also includes the fuzzy membership functions. An illustrative example is finally given to show the applicability and effectiveness of the proposed method.

• Journal of the Korean Wood Science and Technology
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• v.24 no.3
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• pp.37-44
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• 1996

포수상태(包水狀態)의 루부라참나무(Quercus rubra) 시험편을 3가지 등온조건(等溫條件)에서 건조한 결과를 비정상상태(非正常狀態)의 확산(擴散)모델로 추정한 결과와 비교하였다. 표면이 충분히 젖은 상태인 건조초기에는 불안정(不安定)한 확산현상(擴散現象)이 관찰되었으나, 함수율(含水率)별 건조속도의 변이를 Fick's의 확산법칙과 비교할 때 유사한 형태를 보였다. 실험에서 얻은 건조조건별 건조곡선은 확산모델의 수치해석(數値解析) 결과와 거의 일치하였으며, 같은 평위함수율(平衛含水率) 조건에서 건조온도의 증가는 목재표면 보다 내부의 함수율 변화에 더 크게 영향하여 결과적으로 낮은 온도에서의 건조조건이 목재 내의 수분경사(水分傾斜)를 급하게 하는 것으로 밝혀졌다. 본 연구를 통해 목재 건조 중의 내부에 발생하는 수분경사를 추정하는데 비정상상태의 확산모델이 모든 함수율 범위에 걸쳐 유용하게 사용될 수 있음이 밝혀졌다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.6
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• pp.2369-2379
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• 2013

The Soil-Water Characteristics Curve (SWCC) is affected by the initial density of soil under unsaturated condition. Also, the characteristic of hydraulic conductivity is changed by the initial density of soil. To study the effect of initial density of unsaturated soil, SWCC and the Hydraulic Conductivity Function (HCF) of Jumoonjin sand with various relative densities, 40%, 60% and 75% were measured in both drying and wetting processes. As the results of SWCC estimated by van Genuchten (1980) model, the parameter related to Air Entry Value(AEV), ${\alpha}$ in the wetting process is larger than that in drying process, but the parameters related to the SWCC slope, n and the residual water content, m are larger than those in wetting process. The AEV is increased or Water Entry Value (WEV) is decreased with increasing the relative density of sand. The AEV is larger than the WEV at the same relative density of sand. As the results of HCF estimated by van Genuchten (1980) model which is one of the parameter estimation methods, the unsaturated hydraulic conductivity maintained at a saturated one in the low level of matric suctions and then suddenly decreased just before the AEV or the WEV. The saturated hydraulic conductivity in drying process is larger than that in wetting process. The saturated hydraulic conductivity is decreased with increasing the relative density of sand in both drying and wetting processes. Also, the hysteresis in unsaturated HCFs between drying and wetting process was occurred like the hysteresis in SWCCs. According to the test results, the AEV on SWCC is decreased and the saturated hydraulic conductivity is increased with increasing the initial density. It means that SWCC and HCF are affected by the initial density in the unsaturated soil.

• Computational Structural Engineering
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• v.7 no.1
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• pp.117-124
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• 1994

Multi-level Multi-objective optimization(MLMO) for reinforced concrete framed structure is performed, and compared with the results of single-level single-objective optimization. MLMO method allows flexibility to meet the design needs such as deflection and cost of structures using weighting factors. Using Multi-level formulation, the numbers of constraints and variables are reduced at each levels, and the optimization formulation becomes simplified. The force approximation method is used to reflect the variation in design variables between the substructures, and thus coupling is maintained. And the linear approximated constraints and objective function are used to reduce the number of structural analysis in optimization process. It is shown that the developed algorithm with move limit can converge effectively to optimal solution.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.309-317
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• 2002

The mechanical characteristics of Light-Weighted Foam Soil(LWFS) are investigated in this research. LWFS is composed of the dredged soil from offshore, cement and foam to reduce the unit-weight and increase compressive strength. For this purpose, the unconfined compression tests and triaxial compression tests are carried out on the prepared specimens of LWFS with various conditions such as initial water contents, cement contents, curing conditions and confining stresses. The test results of LWFS indicated that the stress-strain relationship and the compressive strength are strongly influenced by the cement contents rather than the intial water contents of the dredged soils. On the other hand, the stress-strain relationship from triaxial compression test has shown strain-softening behavior regardless of curing conditions. The stress-strain behavior for the various confining stress exhibited remarkable change at the boundary where the confining stress approached to the unconfined compression strength of LWFS. In order to obtain the ground improvement of the compressive strength above 200kPa, the required LWFS mixing ratio is found to be 100%~160% of the initial water contents of dredged soil and 6.6% of cement contents.

• Journal of Ocean Engineering and Technology
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• v.12 no.1
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• pp.85-98
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• 1998

본 논문의 수치해법은 경계치문제를 풀기 위하여 코시이론(Cauchy's theorem)을 사용하였다. 경계치문제는 완전한 물체표면조건과 자유표면조건을 만족시키는 초기치문제로 귀결된다. 현 수치해법에서 무한영역은 수치계산 영역인 비선형 영역과 선형 자유표면조건을 만족하는 선형영역으로 나누어진다. 선형영역의 해는 과도 그린(Green)함수를 사용하여 정합조건을 부과함으로써, 수치계산은 비선형 영역에서만 수행된다. 본 논문에서 저자는 수치계산 영역에서 코시이론을 사용하여 적분방정식을 도출하였고, 무한영역의 해는 정합면에서 과도 그린함수를 사용하여 표현하였다. 본 수치계산에서 자유표면에 요소 재분배법을 적용함으로써 쇄파현상에 대해서도 안정적인 수치해석을 할 수 있었다. 본 논문에서 개발된 수치방법을 적용한 문제는 다음과 같다. 첫째는 자유표면에서 실린더가 강제동요하는 경우에 자유표면형상과 힘을 계산하여 이전의 실험치 및 계산치와 비교하였다. 두번째로는 실린더가 자유수면하에서 일정한 속도로 항주하는 경우에는 조파저항과 양력을 계산하여 고차 스펙트럴법과 비교하였다.

• Journal of Forest and Environmental Science
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• v.12 no.1
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• pp.1-12
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• 1996

This study was carried out to estimate drying schedule of Fagaceae four species grown in Kangwon-Do by oven-drying at $100^{\circ}C$ which aimed to elucidate the characteristics such as current moisture content, drying process, initial check, collapse and internal check during drying following each board thickness (1.5cm, 2.5cm, 3.5cm, 4.5cm). The results were as follows; Current moisture content of each board showed a rapid drying curve with the high initial moisture content of board. With the high initial moisture content, the incease of board thickness and the slowness of changing rate of moisture content, species took long to do drying. Also, the initial conditions of drying had to be mild condition with the increase of board thickness.

• Magazine of the Korea Concrete Institute
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• v.8 no.3
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• pp.197-207
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• 1996

Maturity is expressed as the integral of time and temperature of concrete above a datum temperature. The maturity concept proposes that concrete of the same mix at the same maturity has the same strength, whatever combination of temperature and time makes up that maturity. In this study, the Nurse-Saul function which was proposed to account for the effects of temperature and time on strength developrnent is used in computing maturity. After existing various functions are considered to relate concrete strength to the maturity value, new strength-maturity function is proposed. Tests ;ire conducted in order to determine d datum temperature and compare prechction value with measured concrete strength. The constants in proposed prediction equation are determined from test results, and the equation is adopted to predict the strength of slab. The slab was cast in the laboratory from the same batch of mold, and cores are cut from slab in order to estimate the actual strength. These values are used to compare with predicted value. The present study allows more realistic determination of early-age strength of concrete and can be efficiently used to control the quality in actual construction.