• 한국지반공학회논문집
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• 제29권9호
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• pp.5-15
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• 2013

본 연구에서는 흡입응력을 고려한 불포화 사면의 안정해석기법(Lu and Godt, 2008)을 제시하고, 모래로 구성된 특정사면에 대하여 적용한 결과를 분석하였다. 흡입응력을 고려한 불포화 사면의 안정해석기법은 강우의 침투 및 비침투에 따른 해석이 가능하고, 토층내 깊이에 따른 사면안전율을 산정할 수 있다. 또한 지표면으로부터 일정깊이까지의 풍화작용에 의한 영향을 고려할 수 있다. 이를 위하여 상대밀도 60%의 주문진 표준사로 구성된 불포화 무한사면에 대하여 흡입응력을 고려한 안정해석기법을 적용하였다. 강우의 비침투 조건에서 흡입응력은 지하수위로부터 상부의 일정깊이까지만 영향을 미치는 것으로 나타났으나, 강우의 정상침투 조건에서 흡입응력은 토층내 전체적으로 영향을 미치며, 지표면 부근에서 흡입응력이 가장 크게 발현됨을 알 수 있다. 강우의 비침투 조건에서 무한사면의 안전율은 지하수위에 의한 흡입응력의 영향범위 내에서 급격하게 증가 및 감소하였다. 사면안정해석결과 지표면으로부터 2.4m사이에서 사면안전율이 1이하 이므로 해당깊이에서 사면파괴가 발생될 가능성이 높은 것으로 나타났다. 강우의 정상침투가 발생되는 조건에서 무한사면의 안전율은 침투로 인한 토층내 흡입응력의 영향으로 비침투 조건에 비해 증가함을 알 수 있다. 그러나 강우의 정상침투율이 포화투수계수에 가까워짐에 따라 사면안전율은 감소하는 경향이 나타났다. 강우의 정상침투율이 $-1.8{\times}10^{-3}cm/s$인 경우 무한사면의 안정해석결과 지표면으로부터 0.2m에서 3m 사이에서 사면안전율이 1 이하이므로 해당깊이에서 사면파괴가 발생될 가능성이 높으며, 이는 얕은 산사태의 발생형태임을 알 수 있다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.1901-1904
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• 2003

MPC or model predictive control is representative of control methods which are able to handle physical constraints. Closed-loop stability can therefore be ensured only locally in the presence of constraints of this type. However, if the system is neutrally stable, and if the constraints are imposed only on the input, global aymptotic stability can be obtained; until recently, use of infinite horizons was thought to be inevitable in this case. A globally stabilizing finite-horizon MPC has lately been suggested for neutrally stable continuous-time systems using a non-quadratic terminal cost which consists of cubic as well as quadratic functions of the state. The idea originates from the so-called small gain control, where the global stability is proven using a non-quadratic Lyapunov function. The newly developed finite-horizon MPC employs the same form of Lyapunov function as the terminal cost, thereby leading to global asymptotic stability. A discrete-time version of this finite-horizon MPC is presented here. The proposed MPC algorithm is also coded using an SQP (Sequential Quadratic Programming) algorithm, and simulation results are given to show the effectiveness of the method.

• Structural Engineering and Mechanics
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• 제63권3호
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• pp.269-280
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• 2017

One major concern that has occupied the mind of the designers is a structural failure as result of stress concentration in the geometrical discontinuities. Understanding the effective parameters contribute to stress concentration and proper selection of these parameters enables the designer get to a reliable design. In the analysis of perforated isotropic and orthotropic plates, the effective parameters on stress distribution around holes include load angle, curvature radius of the corner of the hole, hole orientation and fiber angle for orthotropic materials. This present paper tries to examine the possible effects of these parameters on stress analysis of infinite perforated plates with central quasi-square hole applying grey wolf optimizer (GWO) inspired by the particular leadership hierarchy and hunting behavior of grey wolves in nature, and also the present study tries to introduce general optimum parameters in order to achieve the minimum amount of stress concentration around this type of hole on isotropic and orthotropic plates. The advantages of grey wolf optimizer are stout, flexible, simple, and easy to be enforced. The used analytical solution is the expansion of Lekhnitskii's solution method. Lekhnitskii applied this method for the stress analysis of anisotropic plates containing circular and elliptical holes. Finite element numerical solution is employed to examine the results of present analytical solution. Results represent that by selecting the aforementioned parameters properly, fewer amounts of stress could be achieved around the hole leading to an increase in load-bearing capacity of the structure.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.281.2-281.2
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• 2016

Two-dimensional van der Waals (2D vdWs) materials have been extensively studied for future electronics and materials sciences due to their unique properties. Among them, black phosphorous (BP) has shown infinite potential for various device applications because of its high mobility and direct narrow band gap (~0.3 eV). In this work, we demonstrate a few-nm thick BP-based nonvolatile memory devices with an well-known poly(vinylidenefluoride-trifluoroethylene) [P(VDF-TrFE)] ferroelectric polymer gate insulator. Our BP ferroelectric memory devices show the highest linear mobility value of $1159cm^2/Vs$ with a $10^3$ on/off current ratio in our knowledge. Moreover, we successfully fabricate the ferroelectric complementary metal-oxide-semiconductor (CMOS) memory inverter circuits, combined with an n-type $MoS_2$ nanosheet transistor. Our memory CMOS inverter circuits show clear memory properties with a high output voltage memory efficiency of 95%. We thus conclude that the results of our ferroelectric memory devices exhibit promising perspectives for the future of 2D nanoelectronics and material science. More and advanced details will be discussed in the meeting.

• 한국해양공학회지
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• 제22권5호
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• pp.25-30
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• 2008

A B-spline based high order panel method was developed for the motion of bodies in an ideal fluid, either of infinite extent or with a free boundarysurface. In this method, both the geometry and the potential are represented by the B-spline, which guarantees more accurate results than most potential based low order methods. In the present work, we applied this B-spline based high order method to the radiation problem of floating bodies. The boundary condition on the free surface was satisfied by adopting a Kelvin-type Green function and irregular frequencies were removed by placing additional control points on the free surface surrounding the body. The numerical results were validated by comparison with existing numerical and experimental results.

• 한국전자파학회논문지
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• 제14권2호
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• pp.111-118
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• 2003

넛치 안테나는 진행파형 안테나로서 공진형 안테나에 비해 광대역 특성과 넓은 빔 폭을 가지므로 광대역 위상 배열 안테나의 복사 소자로 사용되어진다. 본 논문에서는 단일 복사 소자의 해석으로 무한 배열 안테나를 모의할 수 있는 도파관 시뮬레이터를 이용하여 3 : 1 이상의 주파수 대역과 $\pm$45$^{\circ}$의 빔 조향 범위를 만족하는 광대역 E-평면 넛치 위상 배열 안테나를 설계하였다. 설계된 단일 소자의 등가회로 모델링을 통해 단일 소자와 무한 배열소자에서의 임피던스 특성을 비교하였으며, 설계된 결과를 이용하여 1$\times$9배열 E-평면 넛치 위상 배열 안테나 전체를 해석하였다. 이때 구해진 안테나간 상호 결합 계수를 이용하여 각 소자의 빔 조향 각도에 따른 능동 반사 계수를 구하였으며, 능동 소자 패턴을 통해 빔 조향에 따른 이득의 변화를 살펴보았다.

• 대한기계학회논문집A
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• 제33권2호
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• pp.99-107
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• 2009

This study produced a design curve and fatigue limit for a variation in volume ratio and reduction ratio of TiNi/Al composites. In many cases, stress-life curve does not indicate fatigue limit, so it was presented by probabilistic-stress-life curve. Goodman diagram was used to analyze the fatigue strength of materials with a finite life determined by repeated load and the fatigue strength of endurance limit with an infinite life. The fatigue experiment was conducted using the scenk-type plane bending specimen in same shape. The result of the fatigue test, which had been conducted under consistent stress amplitude, was examined. (i) The optimal condition for TiNi/Al in accordance with hot pressing (ii) Impacts of fatigue limit caused by a variation in reduction ratio and volume ratio of TiNi/Al composites (iii) Probability distribution for fatigue limit of TiNi/Al2024 and TiNi/Al6061.

• 한국광물학회지
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• 제10권2호
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• pp.97-104
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• 1997

Based on the method of determination for relative stability of each phase from the difference among the interaction parameters of the phases consisting the mixed layer, the types of interactions between layers were specified and interaction parameter between layers in ordered domain was analytically derived as a function parameter between layers in ordered domain was analytically derived as a function of not only temperature and mole fraction of layers but also ordering parameter. Interaction parameter between the different layers in ordered phase, L is as follows:{{{{ {L }_{1 } (X,Q,T)= { C} over { Q} -4(1-2Q) { L}^{2 } - { RT} over {2} ln { 1} over {2 } - { 2RT} over { { X}_{ s} } ln { { 4QX}`_{s } ^{2 } } over {(1- { X}_{s }- { QX}_{s })( { X}_{s }- {QX }_{s } ) } }}}}L2 is the interaction parameter between ordered and disordered phase in domain and is the mole fraction of the domain which represent the infinite length of mixed layer mineral and Q and C are the reaction progress parameter and arbitrary constant, respectively. This equation was used for the I/S mixed layer clay minerals to infer the relative stability of R1 type I/S mixed layer in the temperature range from 373K to 450K. The result of calculation suggest that, owing to the decrease in interaction parameter with increasing temperature. The interaction parameter decreases more rapidly with decreasing mole fraction of smectite in domain, which is consistent with the fact that the probability of finding the series smectite layer is lo in the domain with small mole fraction of smectite layers in natural system.

• 한국해안해양공학회지
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• 제18권1호
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• pp.1-14
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• 2006

본 논문에서 직사각형 격자 체계에서 원호형 내부조파에 의한 선 조파기법을 개발하였다. 총 다섯 가지 조파형식의 수치실험이 다음의 조건에 수행되었다. 즉, 일정수심에서의 파랑의 전파, 일정경사를 가지는 평면에서의 굴절과 천수, 반무한 방파제에서 회절 실험을 수행하였다. 수치실험 수행 시 기본방정식으로 Suh et al. (1997)이 제안한 확장형 완경사방정식을 이용하였다. 두 개의 평행한 직선이 반원으로 연결된 제5형식 조파기법을 사용하면 가장 우수한 결과를 얻을 수 있었다. 특히, 격자간격이 작은 경우에 그 우수성이 확연히 드러났다.

• Structural Engineering and Mechanics
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• 제49권1호
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• pp.1-22
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• 2014

A seismic evaluation is made of the response to horizontal ground shaking of cantilever retaining walls using the finite element model in three dimensional space whose verification is provided analytically through the modal analysis technique in case of the assumptions of fixed base, complete bonding behavior at the wall-soil interface, and elastic behavior of soil. Thanks to the versatility of the finite element model, the retained medium is then idealized as a uniform, elastoplastic stratum of constant thickness and semi-infinite extent in the horizontal direction considering debonding behavior at the interface in order to perform comprehensive soil-structure interaction (SSI) analyses. The parameters varied include the flexibility of the wall, the properties of the soil medium, and the characteristics of the ground motion. Two different finite element models corresponding with flexible and rigid wall configurations are studied for six different soil types under the effects of two different ground motions. The response quantities examined incorporate the lateral displacements of the wall relative to the moving base and the stresses in the wall in all directions. The results show that the wall flexibility and soil properties have a major effect on seismic behavior of cantilever retaining walls and should be considered in design criteria of cantilever walls. Furthermore, the results of the numerical investigations are expected to be useful for the better understanding and the optimization of seismic design of this particular type of retaining structure.