• Computers and Concrete
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• 제7권4호
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• pp.365-386
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• 2010

This paper presents the physical formulation of a 1D material model suitable for seismic applications. It is written within the framework of thermodynamics with internal variables that is, especially, very efficient for the phenomenological representation of material behaviors at macroscale: those of the representative elementary volume. The model can reproduce the main characteristics observed for concrete, that is nonsymetric loading rate-dependent (viscoelasticity) behavior with appearance of permanent deformations and local hysteresis (continuum plasticity), stiffness degradation (continuum damage), cracking due to displacement localization (discrete plasticity or damage). The parameters have a clear physical meaning and can thus be easily identified. Although this point is not detailed in the paper, this material model is developed to be implemented in a finite element computer program. Therefore, for the benefit of the robustness of the numerical implementation, (i) linear state equations (no local iteration required) are defined whenever possible and (ii) the conditions in which the presented model can enter the generalized standard materials class - whose elements benefit from good global and local stability properties - are clearly established. To illustrate the capabilities of this model - among them for Earthquake Engineering applications - results of some numerical applications are presented.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.70-73
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• 2009

The aim of this research is to obtain a numerical material model for an amorphous glassy polymer, polycarbonate (PC), which can be used in finite element analysis (FEA) of the micro thermal imprint process near the glass transition temperature. An understanding of the deformation behavior of the PC specimens was acquired by performing tensile stress relaxation tests. The viscoelastic material model based on generalized Maxwell model was introduced for the material near Tg to establish the FE model based on the commercial FEA code ABAQUS/Standard with a suitable set of parameters obtained for this material model from the test data. Further validation of the model and parameters was performed by comparing the analysis of FE model results to the experimental data.

• Coupled systems mechanics
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• 제7권2호
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• pp.211-232
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• 2018

In this work we present an upscaling technique for multi-scale computations based on a stochastic model calibration technique. We consider a coarse-scale continuum material model described in the framework of generalized standard materials. The model parameters are considered uncertain, and are determined in a Bayesian framework for the given fine scale data in a form of stored energy and dissipation potential. The proposed stochastic upscaling approach is independent w.r.t. the choice of models on coarse and fine scales. Simple numerical examples are shown to demonstrate the ability of the proposed approach to calibrate coarse scale elastic and inelastic material parameters.

• 한국군사과학기술학회지
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• 제11권6호
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• pp.164-171
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• 2008

A modified generalized particle algorithm, MGPA, was suggested to improve the computational efficiency of standard SPH method in numerical analysis of high speed impact behavior. This method uses a numerical failure mechanism than material failure models to describe the target penetration. MGPA algorithm was more effective to describe the impact phenomena and new boundaries produced during the calculation process were well recognized and treated in the target penetration problem of a bullet. When bullet perforation problems were analyzed by this method, MGPA algorithm calculation gives the stable numerical solution and stress oscillation or particle penetration phenomena were not shown. The error range in ballistic velocity limit is less than $2{\sim}13%$ for various target thickness.

• Structural Engineering and Mechanics
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• 제70권2호
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• pp.179-197
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• 2019

In this article, the effect of different geometrical, materials and load parameters on the transient response of axisymmetric viscoelastic functionally graded annular plates with different boundary conditions are studied. The behavior of the plate is assumed the elastic in bulk and viscoelastic in shear with the standard linear solid model. Also, the graded properties vary through the thickness according to a power law function. Three types of mostly applied transient loading, i.e., step, impulse, and harmonic with different load distribution respect to radius coordinate are examined. The motion equations and the corresponding boundary conditions are extracted by applying the first order shear deformation theory which are three coupled partial differential equations with variable coefficients. The resulting motion equations are solved analytically using the perturbation technique and the generalized Fourier series. The sensitivity of the response to the graded indexes, different transverse loads, aspect ratios, boundary conditions and the material properties are investigated too. The results are compared with the finite element analysis.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.45-52
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• 2009

The research on miniature devices based on non-silicon materials, in particular polymeric materials has been attracting more and more attention in the research field of the micro/nano fabrication in recent years. Lost of applications and many literatures have been reported. However, the study on the micro thermal imprint process of glassy polymer is still not systematic and inadequate. The aim of this research I to obtain a numerical material model for an amorphous glassy polymer, polycarbonate (PC), which can be used in finite element analysis (FEA) of the micro thermal imprint process near the glass transition temperature (Tg). An understanding of the deformation behavior of the PC specimens was acquired by performing tensile stress relaxation tests. The viscoelastic material model based on generalized Maxwell model was introduced for the material near Tg to establish the FE model based on the commercial FEA code ABAQUS/Standard with a suitable set of parameters obtained for this material model form the test data. As a result, the feasibility of the established viscoelastic model for PC near Tg was confirmed and this material model can be used in FE analysis for the prediction and improvement of the micro thermal imprint process for pattern replication.

• 한국정보통신학회논문지
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• 제12권10호
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• pp.1875-1882
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• 2008

최근 IEEE 802.16 WiMAX에서는 인터넷 기반의 다양한 서비스와 애플리케이션의 빈번한 사용으로 인하여 저비용, 고효율의 특성을 가지는 이동 단말기의 사용이 일반화되고 있다. 이동 단말기의 사용이 일반화되면서 고속 인터넷 서비스의 보안 문제를 해결하기 위한 연구가 IEEE 802.16e 표준을 중심으로 연구되고 있다. 이 논문에서는 IEEE 802.16 WiMAX의 보안 요구사항을 충족하기 위해 IEEE 802.16e 표준에서 제공하는 기본 기능이외에 SS의 인증부하 및 보안공격(reply 공격과 man-in-the-middle 공격)에 안전한 보안 메커니즘을 제안한다. 제안된 메커니즘은 SS와 BS가 생성한 난수와 비밀값을 이용하여 TEK과 데이터 암호에 필요한 키 정보를 교환한다. 또한 SS의 초기 인증정보와 인증서를 이용하여 BS의 추가 인증 과정을 수행하지 않도록 하여 BS의 성능 부하를 줄인다.

• 가정과삶의질연구
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• 제29권2호
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• pp.13-22
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• 2011

Since environmental problems were globalized, discussions on 'Sustainable Development' started from Rio Declaration on Environment and Development(Rio Agenda 21). In Korea, the idea of 'Green Growth' was introduced and generalized since the celebration speech made on 8.15(Independence Day of South Korea) on 2008. And Low Carbon- Green Growth Basic Law was established on 2010. There are 3 strategies and 10 sub-tasks to achieve green country-traffic and green revolution of life. Family resource management is capable of changing life style from energy wasty to ecologically green. The value of family resource management plays a critical role in changing the lifestyle through influencing the goal and standard setting. So, this study is aimed to suggest the green value and green way of life from the perspective of family resource management. Results are as follow. First, the green value is to change from 'material-oriented' to 'people-oriented'. The 'material-oriented value pursues pleasure from possessing, but the 'people-oriented' value pursues pleasure from being itself. Second, the change from the value of 'human-mastery of the nature' to the value of 'mother -nature' is necessary. The value of 'human-mastery of the nature' seeks pleasure from the velocity and tangible outcome. But the value of 'mother- nature' seeks pleasure from the time to relax and slow way of life. 'Third, the change from the value of 'individualism' to the value of 'community sprit' is necessary. Individualism focuses on man's achievement, which may fall into family egoism. And the green way of life suggests the change from 'results-oriented' to 'enjoy the process itself", from 'consumption' to 'ecological restoration' and from 'work to home and then home to community'.

• 대한기계학회논문집
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• 제17권1호
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• pp.141-152
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• 1993

본 연구에서는 축대칭 열전도 고체의 형상설계민감도 해석을 위하여 2차원 문 제를 다룬 Lee, Choi와 Kwak의 방법을 축대칭 문제로 확장하였다.축대칭 형태로 표 시된 직접 및 간접 경계적분방정식의 정식화에 기초하여 전미분방접과 보조변수방법으 로 형상최적화 문제에서 발생하는 일반적인 성능 범함수의 형상설계민감도 공식을 유 도하고, 온도 및 열속의 제한조건에 이를 응용하였다. 제시된 민감도해석방법의 정 확성을 검증하기 위하여 해석적인 해를 갖는 원통문제와 구문제를 다루었는데, 두 문 제에 대하여 민감도 공식을 이용하여 수치계산된 결과를 해석적인 민감도와 비교하였 다. 또한 복잡한 수치해로서 냉각핀(cooling fin)문제를 다루었으며, 민감도 공식에 의한 계산 결과를 유한차분(finite difference)으로 수치미분한 결과와 비교하였다.

• 한국전산구조공학회논문집
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• 제28권3호
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• pp.301-307
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• 2015

결합 기반 페리다이나믹 모델을 통해 다양한 동적취성파괴 현상을 해석할 수 있었지만, 결합 기반 모델은 다양한 재료 구성 모델을 표현하는데 여러 한계를 보여왔다. 특히 결합 기반 모델은 각 결합들이 서로 독립적으로 작용하도록 가정하였기 때문에 3차원 모델에서 포아송비가 1/4로 고정되며 전단 변형이 표현되지 못하고 체적 변형만이 모사되는 문제점이 있다. 본 연구에서는 상태 기반 페리다이나믹 모델을 통한 동적취성파괴 해석을 제시한다. 상태 기반 모델은 일종의 일반화된 페리다이나믹 모델로서 일반적인 재료 구성모델로부터 직접 페리다이나믹 재료 모델을 구성한다. 또한 연결된 모든 결합의 변형을 통해 각 절점의 재료 응답이 결정되기 때문에 체적 및 전단 변형이 모두 표현된다. 본 논문에서는 선형 탄성체에 대해서 상태 기반 평면 응력 페리다이나믹 모델을 소개하고 상태 기반 모델에 적합한 손상 모델에 대해 논의한다. 페리다이나믹 비국부 영역을 축소시키는 $\delta$-수렴성 연구를 통해 동적파괴 모델을 검증하고 상태 기반 모델이 동적 균열 전파를 모델링하는데 적합함을 확인하였다.