• 한국강구조학회 논문집
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• 제13권5호
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• pp.587-597
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• 2001

연속체 쉘을 이산화한 구조시스템은 돔형 구조물을 만들기 위해 많이 이용되고 있으며, 이러한 구조물은 하중레벨이 어느 임계값에 도달하면 구조물의 형상에 따라 뜀좌굴(snap-through) 또는 분기좌굴(bifurcation)에 의한 불안정 현상이 일어난다. 케이블 돔의 구조거동 특성은 초기장력 및 외력에 다라 비선형성이 강하게 나타나며 또한 초기조건에 매우 민감하게 반응한다. 본 연구에서는 케이블 돔의 불안정 문제를 파악하기 위해 Geiger 모델을 대상으로 하여 초기 장력도입에 의한 형상결정 문제를 다루고 이를 이용하여 완전형상 및 초기형상 불완전을 도입하여 외력에 의한 불안전성현상을 규명한다.

• 지구물리와물리탐사
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• 제9권1호
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• pp.10-18
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• 2006

물로 포화된 이방성 사암에 기체상, 액체상, 그리고 초임계상의 $CO_2$를 주입하면서 P 파의 속도 변화를 측정하였다. 층리면에 수직한 방향과 수평 방향을 따라 시추한 2 개의 원통 모양의 Tako 사암들에 압전 송수신 배열 시스템을 이용하여 P 파 속도를 측정하였다. $CO_2$ 주입으로 인한 속도 변화는 일반적으로 -6%의 평균값을 보였으며 초임계상의 $CO_2$를 주입하는 경우에 약 -16%의 최대값을 나타냈다. 차분도착주시법(differential arrival-time)으로부터 얻은 P 파 속도 토모그램은 $CO_2$의 유동이 층리면에 평행할 때보다 수직한 경우 $CO_2$의 이동 양상이 더 복잡하다는 것을 명백히 보여주고 있다. 또한 P 파 속도 영상의 차이가 $CO_2$의 상과 암석내 공극분포의 불균질성과 관련되었음을 발견하였다. 초임계상의 $CO_2$를 주입한 경우, 탄성파 영상은 기체상과 액체상의 $CO_2$를 주입한 경우에 비해 가장 큰 속도 감소를 보였다 이 결과는 지중 격리시 $CO_2$ 모니터링에 대한 탄성파 방법의 효용을 확신시켜 줄 것이다.

• Tribology and Lubricants
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• 제35권4호
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• pp.229-236
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• 2019

This study investigates the stress singularity that occurs at the contact edge of three bodies in a frictional complete contact. We use the asymptotic analysis method, wherein we constitute an eigenvalue problem and observe the eigenvalue behavior, which we use to obtain the order of the stress singularity. For the present geometry of three bodies in contact, a contact between a cracked indenter and half plane is considered. This is a typical geometry of the PCMI problem of a nuclear fuel rod. Thus, this paper, specifically presents the characteristics of the PCMI problem from the perspective of stress singularity. Consequently, it is noted that the behavior of the stress singularity varies with the difference in the crack angle, coefficient of friction, and material dissimilarity, as is observed in a frictional complete contact of two bodies. In addition, we find that the stress singularity changes essentially linearly with respect to the coefficient of friction, regardless of the variation in the crack angle and material dissimilarity. Concurrently, we find the order of singularity to be 0.5 at a certain coefficient of friction, irrespective of the crack angle, which we also observe in the crack problem of a homogeneous and isotropic body. The order of singularity can also exceed 0.5 in the frictional complete contact problem of three bodies. This implies that the propensity for failure when three bodies are in frictional complete contact can be even worse than that in case of a failure induced by a crack.

• 한국농공학회지
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• 제39권3호
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• pp.72-82
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• 1997

In all inelastic deformations time rate effects are always present to some degree. Whether or not their exclusion has a significant influence on the prediction of the material behaviour depends upon several factors. In the study of structural components under static loading conditions at normal temperature it is accepted that time rate effects are generally not important. However metals, especially under high temperatures, exhibit simultaneously the phenomena of creep and viscoplasticity. In this study, elastoplastic and elasto-viscoplastic models include nonlinear geometrical effects were developed and several numerical examples are also included to verify the computer programming work developed here in this work. Comparisons of the calculated results, for the elasto-viscoplastic analysis of an internally pressurised thick cylinder under plane strain condition, have shown that the model yields excellent results. The results obtained from the numerical examples for an elasto-viscoplastic analysis of the Nuclear Reinforced Concrete Containment Structure(NRCCS) subjected to an incrementally applied internal pressure were summarized as follows : 1. The steady state hoop stress distribution along the shell layer of dome and dome wall junction part of NRCCS were linearly behave and the stress in interior surfaces was larger than that in exterior. 2.However in the upper part of the wall of NRCCS the steady state hoop stress in creased linearly from its inner to outer surfaces, being the exact reverse to the previous case of dome/dome-wall junction part. 3.At the lower part of wall of NRCCS, the linear change of steady state hoop stress along its wall layer began to disturb above a certain level of load increase.

• Advances in nano research
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• 제12권5호
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• pp.529-547
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• 2022

Graphene is one of the strongest, stiffest, and lightest nanoscale materials known to date, making it a potentially viable and attractive candidate for developing lightweight structural composites to prevent high-velocity ballistic impact, as commonly encountered in defense and space sectors. In-plane twist in bilayer graphene has recently revealed unprecedented electronic properties like superconductivity, which has now started attracting the attention for other multi-physical properties of such twisted structures. For example, the latest studies show that twisting can enhance the strength and stiffness of graphene by many folds, which in turn creates a strong rationale for their prospective exploitation in high-velocity impact. The present article investigates the ballistic performance of twisted bilayer graphene (tBLG) nanostructures. We have employed molecular dynamics (MD) simulations, augmented further by coupling gaussian process-based machine learning, for the nanoscale characterization of various tBLG structures with varying relative rotation angle (RRA). Spherical diamond impactors (with a diameter of 25Å) are enforced with high initial velocity (V_i) in the range of 1 km/s to 6.5 km/s to observe the ballistic performance of tBLG nanostructures. The specific penetration energy (E_p^*) of the impacted nanostructures and residual velocity (V_r) of the impactor are considered as the quantities of interest, wherein the effect of stochastic system parameters is computationally captured based on an efficient Gaussian process regression (GPR) based Monte Carlo simulation approach. A data-driven sensitivity analysis is carried out to quantify the relative importance of different critical system parameters. As an integral part of this study, we have deterministically investigated the resonant behaviour of graphene nanostructures, wherein the high-velocity impact is used as the initial actuation mechanism. The comprehensive dynamic investigation of bilayer graphene under the ballistic impact, as presented in this paper including the effect of twisting and random disorder for their prospective exploitation, would lead to the development of improved impact-resistant lightweight materials.

• Steel and Composite Structures
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• 제35권1호
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• pp.61-76
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• 2020

In this paper, the dynamic behaviour of an inclined functionally graded material (FGM) beam with different boundary conditions under a moving mass is investigated based on the first-order shear deformation theory (FSDT). The material properties vary continuously along the beam thickness based on the power-law distribution. The system of motion equations is derived by using Hamilton's principle. The finite element method (FEM) is adopted to develop a general solution procedure. The moving mass is considered on the top surface of the beam instead of supposing it on the mid-plane. In order to consider the Coriolis, centrifugal accelerations and the friction force, the contact force method is used. Moreover, the effects of boundary conditions, the moving mass velocity and various material distributions are studied. For verification of the present results, a comparative fundamental frequency analysis of an FGM beam is conducted and the dynamic transverse displacements of the homogeneous and FGM beams traversed by a moving mass are compared with those in the existing literature. There is a good accord in all compared cases. In this study for the first time in dynamic analysis of the inclined FGM beams, the Coriolis and centrifugal accelerations of the moving mass are taken into account, and it is observed that these accelerations can be ignored for the low-speeds of the moving mass. The new provided results for dynamics of the inclined FGM beams traversed by a moving mass can be significant for the scientific and engineering community in the area of FGM structures.

• 한국지반환경공학회 논문집
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• 제10권2호
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• pp.29-36
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• 2009

본 연구에서는 2차원 유한요소해석을 통하여 부마찰(negative skin friction) 이 작용하는 단독말뚝의 거동을 분석하였다. 압밀의 진행에 따른 부마찰의 변화를 검토하기 위하여 압밀해석을 실시하였으며, 말뚝과 주변지반 사이에서의 항복(yielding, slip)을 고려하였다. 일반적으로 널리 사용되는 -방법에 의해 부마찰력을 산정하는 경우 중립면 부근에서의 전단강도의 부분발현 및 지중응력의 감소를 반영할 수 없기 때문에 정밀유한요소 해석에 비하여 부마찰력이 25% 정도 과하게 평가된다. 압밀이 진행 중일 때 말뚝과 지반사이 대부분의 구간에서 항복이 발생하는 경우 더 이상의 부마찰력의 증가는 그리 크지 않은 것으로 나타났다. 부마찰이 발생하는 말뚝에 코팅을 실시하는 경우 부마찰력의 크기 및 말뚝의 침하를 효과적으로 감소시킬 수 있으나, 말뚝두부에 상재하중이 작용할 때 말뚝의 선단이 충분히 견고한 지지층에 설치되어 있지 않은 경우 말뚝의 마찰저항력이 매우 작아서 말뚝에 큰 침하가 발생할 우려가 있는 것으로 나타났다.

• 한국지반공학회지:지반
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• 제4권2호
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• pp.33-44
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• 1988

1980년에 완공된 대청댐은 콘크리트댐과 석괴댐으로 혼합된 복슴댐으로서 결합부에는 제체에서 가장 취약한 곳인 원합면이 존재하므로 댐 건설시 계측기를 매설하여 토려 및 간극수려을 계속 측 정하고 있다. 본연구에서는 해석적 방법으로 평면변형하에서 건설단계를 하중증분형태로 보는 비선형증가 유한 요소해석방법을 적용하였으며, 이에 대한 심벽재료의 파라미터들은 토취장에서 채취한 점토를 현장 밀도 및 함수비로 다진후 삼축압축시험을 실시하여 추정하였고 휠터 및 제각부의 파라미터들은 관계 문헌을 이용하여 추정하였다. 비교분석결과 심벽부의 토압은 대체적으로 예측치와 실측치가 일치하는 경향을 보였으나 제설부에서는 다소의 차이가 있었다. 또한 간선수압 모델은 심압부의 간선수압예측에 좋은 결과를 보여 주었다.

• 한국농공학회논문집
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• 제50권4호
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• pp.67-75
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• 2008

In construction facilities such as bridges, the fluid boundary layer(or water film) is formed at the structure-soil interface by the inflow into the system due to rainfall or/and rising ground-water. As a result, the structure-soil interaction(SSI) state changes into the structure-fluid-soil interaction(SFSI) state. In general, construction facilities may be endangered by the inflow of water into the soil foundation. Thus, it is important to predict the dynamic SFSI responses accurately so that the facilities may be properly designed against such dangers. It is desired to have the robust tools of attaining such a purpose. However, there has not been any report of a method for the SFSI analyses. The objective of this study is to propose an efficient method of finite element modelling using the new interface element named hybrid interface element capable of giving reasonable predictions of the dynamic SFSI response. This element enables the simulation of the limited normal tensile resistance and the tangential hydro-plane behaviour, which has not been preceded in the previous studies. The hybrid interface element was tested numerically for its validity and employed in the analysis of SFSI responses of the continuous bridge subjected to seismic load under rainfall or/and rising ground-water condition. It showed that dynamic responses of the continuous bridge resting on direct foundation may be amplified under rainfall condition and consequently lead to significant variation of stresses.

• 한국전기전자재료학회논문지
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• 제15권1호
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• pp.67-74
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• 2002

A phosphor for Plasma Display Panel, BaMgAl$_{10}$ O$_{17}$ :Eu$^{2+}$, showing a blue emission band at about 450nm was prepared by a solid-state reaction using BaCO$_3$, $Al_2$O$_3$, MgO, Eu$_2$O$_3$ as starting materials wish flux AlF$_3$. The study of the behaviour of Eu in BAM phosphor was carried out by the photoluminescence spectra and the Rietveld method with X-ray and neutron powder diffraction data to refine the structural parameters such as lattice constants, the valence state of Eu, the preferential site of Mg atom and the site fraction of each atom. The phenomenon of the concentration quenching was abound 2.25~2.3wt% of Eu due to a decrease in the critical distance for energy transfer of inter-atomic Eu. Through the combined Rietveld refinement, R-factor, R$_{wp}$, was 8.11%, and the occupancy of Eu and Mg was 0.0882 and 0.526 at critical concentration. The critical distance of Eu$^{2+}$ in BAM was 18.8$\AA$ at 2.25% Eu of the concentration quenching. Furthermore, c/a ratio was decreased to 3.0wt% and no more change was observed over that concentration. The maximum entropy electron density was found that the modeling of $\beta$-alumina structure in BaMgAl$_{10}$ O$_{17}$ :Eu$^{2+}$correct coincided showing Ba, Eu, O atoms of z= 1/4 mirror plane.e.ane.e.