• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.4
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• pp.1-11
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• 1984

Developed is a nonlinear fracture theory which can model the complex fracture behavior of concrete. This theory is based on the nonlinear behavior due to progressive microcracking and strain-softening in the fracture process zone of concrete cracks. The simplified realistic fracture model which preserves the same fracture energy for the different fracture process zone widths is also derived. By modeling fracture through stress-strain behavior, the effect of compressive stresses parallel to the crack plane can be easily taken into account. The comparisons of the present theory with valuable fracture test data available in the literature show good agreements, and the existing linear theory exhibits in many cases large deviations from the actual test results. A simple approximate formula for the fracture energy of concrete which should, be necessary for the fracture analysis of concrete structures is derived. Finally, the application of fracture theory to reinforced concrete and the necessity of further research are discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.4
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• pp.381-387
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• 2016

In this paper, the methodology applied to the improvement of stress analyses is extended to free vibration and buckling analyses. The essence of the methodology is the Saint-Venant's principle that is applicable to beam and plate models. The principle allows one to dimensionally reduce three-dimensional elasticity problems. Thus the methodology can be employed to vibration and buckling as well as stress analysis. First, the principle is briefly revisited, and then the formations of classical beam theories are presented. To improve the predictions, the perturbed terms (unknowns) are introduced together with the warping functions that are calculated by stress equilibrium equations. The unknowns are then calculated by applying the equivalence of stress resultants (i.e., Saint-Venant's principle). As numerical examples, cantilever and simply supported beams are analytically solved. The results obtained are compared with those of the classical beam theories. It is shown that the methodology can be used to improve the predictions without introducing shear correction factors.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.3
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• pp.273-279
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• 2011

The yield strength of particle-reinforced composites increases as the size of the particle decreases. This kind of length scale has been mainly attributed to the geometrically necessary dislocation punched around the particle as a result of the mismatch of the thermal expansion coefficients of the particle and the matrix when the composites are cooled down after consolidation. In this study, two dislocation-punching theories that can be used in continuum structural modeling are assessed numerically. The two theories, presented by Shibata et al. and Dunand and Mortensen, calculate the size of the dislocationpunched zone. The composite yield strengths predicted by finite element analysis were qualitatively compared with experimental results. When the size of the particle is less than $2{\mu}m$, the patterns of the composite strength are quite different. The results obtained by Shibata et al. are in qualitatively better agreement with the experimental results.

• Nuclear Engineering and Technology
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• v.26 no.2
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• pp.212-224
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• 1994

A numerical method has been developed for studying the dynamics of a flexible cylinder in a coaxial cylindrical duct, immersed in inviscid flow. The unsteady inviscid fluid-dynamic force acting on the oscillating cylinder has been estimated more rigorously by means of a spectral collocation method without simplification of governing equations. This numerical approach is applicable to the system haying wider annular gap and/or shorter length of cylinder as compared to existing potential theory. The governing equation of the unsteady flow was obtained from Laplace equation. The equation of cylinder motion coupled with the fluid motion was discretized by Galerkin's method, from which the dynamic behaviour of the system has been evaluated. The effect of the length of the cylinder and the annular gap on the critical flour velocity, where the system loses stability by buckling, was investigated. To validate the numerical method, the potential flow theory developed by Hobson based on thin film approximation has been improved. Typical results of the present numerical theory on the dynamics and stability of the system are compared with those of available existing theory and the present approximate results. Good agreement was found between the results. It was also found that a nondimensional critical flow velocity becomes larger as increasing the annular gap and decreasing the length of cylinder.

• ICROS
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• v.17 no.3
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• pp.12-17
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• 2011

목표로 하는 성능 지수 함수를 여러 가지 제약 조건 하에서 최소 또는 최대 값을 찾는 문제에 관한 최적화 이론 (Optimization Theory)은 수확 및 공학 분야에서 가장 오래된 학문 영역 중 하나이다. 문제를 이루는 함수와 변수의 수학적 특성에 따라 그 문제를 푸는 많은 해석적 또는 수치적 해법에 관한 세부 이론들이 제시되어 왔다. 근래에는 빠른 계산 속도로 인해 과거에는 생각지 못했던 문제까지도 수치적인 접근을 통하여 그 해를 구할 수 있게 되었다. 본 기고에서는 몇몇 시스템 이론 분야에서 최적화 이론이 사용된 사례를 간략히 소개한다.

• Composites Research
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• v.16 no.4
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• pp.1-9
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• 2003

2 ply laminated composite is regarded to simulate the interply behavior of the belt layer of the tire. It was cone with 3 dimensional FE(Finite Element) analysis to determine interply shear stress and strain. Widthwise, the shear strain was measured by the pin method. These results are compared with those of CLT(classical lamination theory) in center region and those of Kassapoglou's and Kelsey's theory in edge region. In the FE analysis. rubber is assumed as linear elastic material. and rubber/cord laminate as the orthotropic material composed of cord and rubber In the FE result, interlaminar shear stress causing the interlaminar delamination has the largest value in the edge region of the inner rubber layer. Numerical results obtained coincides with CLT well in the center region, and agrees with other theoretical result little in the edge region.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.2
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• pp.51-58
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• 1988

When a R.C. slab is designed by the yield line theory, there is a possibility of local failure caused by an extreme moment distribution on the yield lines. To reduce the local failures the use of the formula in which the plastic resistence moment in the middle strips is different from that in the column strips was suggested. The formula also has a few other parameters for which the values have to be determined to design the R.C. slab. An attempt was made to determine the ideal values of all these parameters. This will make it easy and realistic to design the R.C. slab by the yield line method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.1
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• pp.129-138
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• 2000

Composites are finding increasing use in a wide variety of engineering applications due to their outstanding mechanical properties. A number of studies have focused on the development of new materials as well as the response of composite structures to static and dynamic loads by assuming the external driving forces to be deterministic. However, there ate many situations in practice where the exciting forces vary randomly. In this work, the nonlinear response of laminated composite plates excited by stochastic loading is studied by the finite element method. Classical, first-order and third-order shear theories for plates are used in the finite element formulation. Since most composites exhibit significant nonlinearity in the shear stress-strain law, this is included in the present analysis.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.323-329
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• 1989

In the stress analysis of plate, Classical plate theories are generally used. But, in applying these theories the stresses underneath the concentrated load point cannot be analyzed because the solution of stress fails to converge. In this paper, therefore, an attempt is made to analyze the stresses directly underneath the concentrated load point for a supported square plate by using the three dimensional theory of elasticity and the potential theory of displacement on the supposition that uniformly distributed load acts on the central part of it. In order to clarify the validity of the theoretical analysis, experiments for strain are carride out with a square plate. It is shown that these theoretical results are in close agreement with experimental results. Specially, this analysis is in a good agreement with actual phenomenon in case of the thick plate.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.380-380
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• 2019

본 연구에서는 일반 상호보완이론(Generalized Complementary Relationship, GCR)을 활용하여 실제증발산량을 추정하고, 추정한 실제증발산량기반 가뭄지수로부터 미국 전역에 대한 가뭄을 해석하는 것이다. 월강수량, 최고 최저기온, 이슬점온도 등의 필요한 기상자료는 Parameter-elevation Relationships on Independent Slopes Model(PRISM)으로부터 수집하였으며, 1981년부터 2015년까지 총 35년의 미국 전역에 대한 실제증발산량을 추정하였다. 대상지역의 유역평균 강수량과 유출량의 차(P-Q)와 North American Land Data Assimilation System(NLDAS-2) Noah 지표모형(Land surface models)으로 산정한 실제증발산량과 비교 검증하였다. GCR로부터 증발산 부족량(ET Deficit, ETD)을 산정하고 이를 표준정규화하여 미국 전역에 대해 Standardized Evapotranspiration Deficit Index(SEDI)를 산정하였다. 본 연구로부터 GCR 기반 실제증발산량은 P-Q의 값과 상관계수가 0.94로 매우 높은 상관성을 보였으며, NLDAS-2 Noah모형의 실제증발산량보다 다소 크게 추정하는 경향을 보였다. SEDI와 Standard Precipitation Index(SPI)의 상관성은 지속시간이 클수록 더 크게 나타났다. 증발산 상호보완이론활용 실제증발산기반 SEDI이 강수자료를 사용하지 않고서도 적절한 가뭄해석에 이용될 수 있을 것으로 판단된다.