• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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• pp.217-224
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• 2005

A higher order zig-zag shell theory is developed to refine the predictions of the mechanical and thermal behaviors partially coupled. The in-plane displacement fields are constructed by superimposing linear zig-zag field to the smooth globally cubic varying field through the thickness. Smooth parabolic distribution through the thickness is assumed in the out-of-plane displacement in order to consider transverse normal deformation and stress. The layer-dependent degrees of freedom of displacement fields are expressed in terms of reference primary degrees of freedom by applying interface continuity conditions as well as bounding surface conditions of transverse shear stresses. Thus the proposed theory has only seven primary unknowns and they do not depend upon the number of layers. In the description of geometry and deformation of shell surface, all rigorous exact expressions are used. Through the numerical examples of partially coupled analysis, the accuracy and efficiency of the present theory are demonstrated. The present theory is suitable in the predictions of deformation and stresses of thick composite shell under mechanical and thermal loads combined.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.20-25
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• 2008

The finite element analysis for porous media is severe job because constituents have different physical peoperties, and element's continuity and stability should be considered. Thus, we propose the new mixed finite element method in order to overcome the problems. In this method, multi time step, remeshing step, and sub iteration step are introduced. The multi time step and remeshing step make it possible to satisfy a stability and an accuracy during sub iteration in which global time is determined. Finally, the proposed method is compared with the ABAQUS(2007) software and exact solution(Schiffman 1967) through two dimensional consolidation model.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권4호
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• pp.429-438
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• 2017

Cranke-Nicolson scheme in native OpenFOAM source libraries was not able to provide 2nd order temporal accuracy of velocity and pressure since the volume flux of convective nonlinear terms was 1st accurate in time. In the present study the simplest way of getting the volume flux with 2nd order accuracy was proposed by using old fluxes. A possible numerical instability originated from an explicit estimation of volume fluxes could be handled by introducing a weighting factor which was determined by observing the ratio of the finally corrected volume flux to the intermediate volume flux at the previous step. The new calculation of volume fluxes was able to provide temporally accurate velocity and pressure with 2nd order. The improvement of temporal accuracy was validated by performing numerical simulations of 2D Taylor-Green vortex of which an exact solution was known and 2D vortex shedding from a circular cylinder.

• 한국기계가공학회지
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• 제19권6호
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• pp.23-28
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• 2020

A non-linear vibration isolation system composed of a non-linear spring and a linear damper was presented in a previous study. The advantage of the proposed isolator is the simple structure of the system. When the base of the isolator is harmonically excited, the response component of the mass at the excitation frequency was approximated using three different methods: linear approximation, harmonic balance, and higher-order frequency response functions (FRFs). The method using higher-order FRFs produces significantly more accurate results compared with the other methods. The error between the exact and approximate responses does not increase monotonously with the excitation amplitude and is less than 2%.

• 에너지공학
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• 제11권1호
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• pp.47-58
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• 2002

본 논문은 민자발전소의 회피 발전비용을 계산하는 새로운 방법을 제안하였다. 제안된 방법은 기존의 부하감소법과 달리 민자발전소의 고장정지율과 경제적 투입순서를 정확히 고려할 수가 있다. 그러므로 더욱 정확한 회피 발전비용을 계산할 수가 있다. 또한 확률적 시뮬레이션을 수행하여 계산하므로 민자발전소의 비용에 대한 영향도 정확히 고려할 수가 있다. 부가적으로 한 개 이상의 민자발전소가 참여하였을 때에 회피 발전비용을 할당하는 방법도 제안하였다. 다양한 사례연구를 통해 제안한 방법의 결과를 분석하였다.

• International Journal of Aeronautical and Space Sciences
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• 제18권4호
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• pp.816-826
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• 2017

In this paper, a generalized discretization scheme is proposed that can derive general-order finite difference equations representing the joint probability density function of dynamic response of stochastic systems. The various order of finite difference equations are applied to solutions of the Fokker-Planck-Kolmogorov (FPK) equation. The finite difference equations derived by the proposed method can greatly increase accuracy even at the tail parts of the probability density function, giving accurate reliability estimations. Compared with exact solutions and finite element solutions, the generalized finite difference method showed increasing accuracy as the order increases. With the proposed method, it is allowed to use different orders and types (i.e. forward, central or backward) of discretization in the finite difference method to solve FPK and other partial differential equations in various engineering fields having requirements of accuracy or specific boundary conditions.

• Steel and Composite Structures
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• 제23권3호
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• pp.339-350
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• 2017

In this paper, various nonlocal higher-order shear deformation beam theories that consider the size dependent effects in Functionally Graded Material (FGM) beam are examined. The presented theories fulfill the zero traction boundary conditions on the top and bottom surface of the beam and a shear correction factor is not required. Hamilton's principle is used to derive equation of motion as well as related boundary condition. The Navier solution is applied to solve the simply supported boundary conditions and exact formulas are proposed for the bending and static buckling. A parametric study is also included to investigate the effect of gradient index, length scale parameter and length-to-thickness ratio (aspect ratio) on the bending and the static buckling characteristics of FG nanobeams.

• Smart Structures and Systems
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• 제21권1호
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• pp.113-122
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• 2018

In this article, an exact analytical solution for mechanical buckling analysis of magnetoelectroelastic plate resting on pasternak foundation is investigated based on the third-order shear deformation plate theory. The in-plane electric and magnetic fields can be ignored for plates. According to Maxwell equation and magnetoelectric boundary condition, the variation of electric and magnetic potentials along the thickness direction of the plate is determined. The von Karman model is exploited to capture the effect of nonlinearity. Navier's approach has been used to solve the governing equations for all edges simply supported boundary conditions. Numerical results reveal the effects of (i) lateral load, (ii) electric load, (iii) magnetic load and (iv) higher order shear deformation theory on the critical buckling load have been investigated. These results must be the analysis of intelligent structures constructed from magnetoelectroelastic materials.

• Journal of applied mathematics & informatics
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• 제36권3_4호
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• pp.181-203
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• 2018

In this paper, we have constructed an overlapping Schwarz method for singularly perturbed second order convection-diffusion equations. The method splits the original domain into two overlapping subdomains. A hybrid difference scheme is proposed in which on the boundary layer region we use the central finite difference scheme on a uniform mesh while on the non-layer region we use the mid-point difference scheme on a uniform mesh. It is shown that the numerical approximations which converge in the maximum norm to the exact solution. When appropriate subdomains are used, the numerical approximations generated from the method are shown to be first order convergent. Furthermore it is shown that, two iterations are sufficient to achieve the expected accuracy. Numerical examples are presented to support the theoretical results. The main advantages of this method used with the proposed scheme is it reduces iteration counts very much and easily identifies in which iteration the Schwarz iterate terminates.

• 대한임베디드공학회논문지
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• 제10권1호
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• pp.33-40
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• 2015

The number of people who are suffering from chronic sleep disorder has been growing dramatically in modern era. In order to diagonse the sleep disorder, sleep doctors perform polysomnography: Patients sleep with attaching several vital sign sensors on their body, and doctors monitor the patients in order to find the exact reason of the sleep disorder. Typical polysmonography makes patients sleep with several sensors on their bodies, which prevents the patients from making a comfortable sleep. Furthermore, it is impossible to have a long-term monitoring since the measurements should be done in sleep hosiptal within a few hours. In order to tackle these problems in the typical polysomnography, we envision the development of a non-contact long-term home polysomnography system using UWB radar and related technologies such as multi-modal signal processing.