• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.644-655
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• 2008

Conventional hyperbolic model does not satisfactorily predict the overall stress-strain behaviors of various geomaterials. Tatsuoka and Shibuya(1992) suggest the generalized hyperbolic equation(GHE) considering strain dependency and calculated performance is in good agreement with precise triaxial compression test results of stress-strain relations over wide range of strains before peak stress condition in some cases, but GHE model also does not satisfactorily predict stress-strain relations as strain goes on state of peak stress in most cases. For improve a weak point of the GHE, in this study, modified form of generalized hyperbolic equation (MGHE model) is proposed which can predict highly nonlinear stress-strain behavior for various geomaterials from small strain to peak stress condition.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 춘계학술대회 논문집
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• pp.509-510
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• 2009

• 보건의료산업학회지
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• 제11권2호
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• pp.117-127
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• 2017

Objectives : This study aimed to identify factors of adolescents' cell-phone dependency using Agnew's General Strain Theory (GST) and the perspective of adolescents' micro-systems. A second aim was to verify the moderating effect of self-esteem. Methods : In total, 2,046 students who participated in a study on KCTPS mid. 1 panel 3 Wave by the National Youth Policy Institute were examined in this research. Data were analyzed through descriptive statistics, factor analysis, reliability tests, and hierarchical linear regression using SPSS Ver. 22.0. Results : The strain factors had a positive effect on adolescents' depression, and depression had a positive effect on cell-phone dependency. In addition, self-esteem had a negative moderating effect between depression and cell-phone dependency. Conclusions : Factors of cell-phone dependency were identified. The findings of the study indicate that an intervention is required to lower strain and depression and to enhance self-esteem among adolescents.

• Coupled systems mechanics
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• 제11권2호
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• pp.93-106
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• 2022

The total embankment settlement consists of three stages: the initial settlement, the primary consolidation settlement, and the secondary consolidation settlement. The total embankment settlement is largely controlled by the primary consolidation settlement, which is usually computed with numerical models that implement Biot's theory of consolidation. The key parameter that affects the primary consolidation time is the coefficient of permeability. Due to the complex stress and strain states in the foundation soil under the embankment, to be able to predict the consolidation time more precisely, aside from porosity-dependency, the strain-dependency of the coefficient of permeability should be also taken into account in numerical analyses. In this paper, we propose a two-dimensional plane strain numerical model of embankment primary consolidation, which implements Biot's theory of consolidation with both porosity-dependent and strain-dependent coefficient of permeability. We perform several numerical simulations. First, we demonstrate the influence of the strain-dependent coefficient of permeability on the computed results. Next, we validate our numerical model by comparing computed results against in-situ measurements for two road embankments: one near the city of Saga, and the other near the city of Boston. Finally, we give our concluding remarks.

• 디지털융복합연구
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• 제14권12호
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• pp.293-302
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• 2016

본 연구는 시간이 경과함에 따라 청소년의 학업긴장과 불행감, 휴대전화 의존이 어떠한 변화 추이를 가지고, 학업긴장의 변화가 불행감과 휴대전화 의존의 변화에 어떠한 종단적 복합적 영향을 파악하여 이들 간의 악순환을 방지하는 방안 모색을 목적으로 한다. 이를 위하여 일반긴장이론을 개념적 연구틀로 설정하고, 한국청소년정책연구원의 제 2~4차 한국아동 청소년패널 1,589명의 청소년 응답치를 사용하여 잠재성장모형 분석을 수행하였다. 분석결과, 청소년의 학업긴장과 불행감, 휴대전화 의존은 모두 시간의 경과에 따라 지속적으로 증가하였다. 학업긴장의 초기값은 불행감의 초기값 및 휴대전화 의존의 초기값과 변화율에는 정적 영향을 미쳤고, 학업긴장의 변화율은 불행감의 변화율에 정적 영향을 미쳤다. 불행감의 변화율은 휴대전화 의존 변화율에 정적 영향을 미쳤다. 또한, 학업긴장의 변화율이 불행감의 변화율을 매개로 하여 휴대전화 의존의 변화율에 정적 영향을 미치는 것으로 나타났다. 이상의 연구결과를 바탕으로 본 연구는 청소년의 학습과 부정적 정서, 휴대전화 의존에 대한 유용한 시사점을 제공하였고, 상기 변수들의 변화의 근거에 대한 후속 연구를 제안하였다.

• Earthquakes and Structures
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• 제4권2호
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• pp.181-202
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• 2013

It is well known that the properties of the soil deposits, especially the damping, depend on both frequency and strain amplitude. Therefore it is important to consider both dependencies to calculate the soil response against earthquakes in order to estimate input motions to buildings. However, it has been difficult to calculate the seismic response of the soil considering both dependencies directly. The author has studied the time domain evaluation of the frequency dependent dynamic stiffness, and proposed a simple hysteretic damping model that satisfies the causality condition. In this paper, this model was applied to nonlinear analyses considering the effects of the strain amplitude dependency of the soil. The basic characteristics of the proposed method were studied using a two layered soil model. The response behavior was compared with the conventional model e.g. the Ramberg-Osgood model and the SHAKE model. The characteristics of the proposed model were studied with regard to the effects of element divisions and the frequency dependency that is a key feature of the model. The efficiency of the model was confirmed by these studies.

• Coupled systems mechanics
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• 제11권1호
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• pp.1-14
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• 2022

The key parameter that affects the consolidation process of soil is the coefficient of permeability. The common assumption in the consolidation analysis is that the coefficient of permeability is porosity-dependent. However, various authors suggest that the strain-dependency of the coefficient of permeability should also be taken into account. In this paper, we present results of experimental and numerical analyses, with an aim to determine the strain-dependency of the coefficient of permeability. We present in detail both the experimental procedure and the finite element formulation of the two-dimensional axisymmetric numerical model of the oedometer test (standard and modified). We perform a set of experimental standard and modified oedometer tests. We use these experimental results to validate our numerical model and to define the model input parameter. Finally, by combining the experimental and numerical results, we propose the expression for the strain-dependent coefficient of permeability.

• 소성∙가공
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• 제13권5호
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• pp.409-414
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• 2004

TRIP steel has got attention in automobile industry because of its high strength and high formability. However, the information on deformation behavior of TRIP steel, including bending and springback, is not enough until now. In this research, the V-die bending experiment and analysis have been done to obtain the information of springback of TRIP steel. And a new numerical method, where elastic modulus is varied with the change of the strain, was suggested. Tensile test for TRIP steel was done to get tensile properties as well as strain dependency of elastic modulus of the material. Strain-dependency of elastic modulus was used the numerical analysis of V-die bending and unbending process to predict springback amount. The results were compared with experiment, showing reasonable agreement. Through the analysis of V-die bending as well as draw bending of TRIP steel, the proposed scheme with variable elastic modulus was proven to well predict the deformation behavior of TRIP steel during bending and springback.

• Computers and Concrete
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• 제20권1호
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• pp.1-10
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• 2017

This paper focuses on the mesh-size dependency in numerical simulations of reinforced concrete (RC) structures subjected to blast loading. A tensile failure criterion that can minimize the mesh-dependency of simulation results is introduced based on the fracture energy theory. In addition, conventional plasticity based damage models for concrete such as the CSC model and the HJC model, which are widely used for blast analyses of concrete structures, are compared with the orthotropic model that adopts the introduced tensile failure criterion in blast tests to verify the proposed criterion. The numerical predictions of the time-displacement relations at the mid-span of RC beams subjected to blast loading are compared with experimental results. The analytical results show that the numerical error according to the change in the finite element mesh size is substantially reduced and the accuracy of the numerical results is improved by applying a unique failure strain value determined by the proposed criterion.

• Structural Engineering and Mechanics
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• 제80권5호
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• pp.539-551
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• 2021

With the continuous increase of computational capacity, more and more complex nonlinear elastoplastic constitutive models were developed to study the mechanical behavior of elastoplastic materials. These constitutive models generally contain a large amount of physical and phenomenological parameters, which often require a large amount of computational costs to determine. In this paper, an inverse parameter determination method is proposed to identify the constitutive parameters of elastoplastic materials, with the consideration of both strain rate effect and temperature effect. To carry out an efficient design, a hybrid optimization algorithm that combines the genetic algorithm and the Nelder-Mead simplex algorithm is proposed and developed. The proposed inverse method was employed to determine the parameters for an elasto-viscoplastic constitutive model and Johnson-cook model, which demonstrates the capability of this method in considering strain rate and temperature effect, simultaneously. This hybrid optimization algorithm shows a better accuracy and efficiency than using a single algorithm. Finally, the predictability analysis using partial experimental data is completed to further demonstrate the feasibility of the proposed method.