• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.385-392
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• 2001

Time-dependent frequency and energy of free vibration of the Spagetti problem, that is the axially moving continuum with time-varying length, are investigated. Exact expressions for the natural frequency and time-varying vibration energy are derived by dealing with traveling waves. When the string length is increased, the vibration period increases, but the free vibration energy varies as a function of both translating velocity and boundary velocity of the continuum. However, when the string undergoes retraction, the vibration energy increases with time, String tension together with non-zero instantaneous velocity at the moving boundary results in energy variation.

• Computational Structural Engineering : An International Journal
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• 제1권1호
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• pp.21-29
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• 2001

The general topology optimization can be considered as optimal material distribution. Such an approach can be unstable, unless composite materials are introduced. In this research, a nodal volume fraction method is used to obtain the optimum topology of continuum structures. This method is conducted from a composite material model composed of isotropic matter and spherical void. Because the appearance of the chessboard patterns makes the interpretation of the optimal material layout very difficult, this method contains a chessboard prevention strategy. In this research, several topology optimization problems are presented to demonstrate the validity of the present method and the recursive quadratic programming algorithm is used to solve the topology optimization problems.

• Structural Engineering and Mechanics
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• 제67권1호
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• pp.79-85
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• 2018

Topology optimization of steel and concrete composite based on truss-like material model is studied in this paper. First, the initial design domain is filled with concrete, and the steel is distributed in it. The problem of topology optimization is to minimize the volume of steel material and solved by full stress method. Then the optimized steel and concrete composite truss-like continuum is obtained. Finally, the distribution of steel material is determined based on the optimized truss-like continuum. Several numerical results indicate the numerical instability and rough boundary are settled. And more details of manufacture and construction can be presented based on the truss-like material model. Hence, the truss-like material model of steel and concrete is efficient to establish the distribution of steel material in concrete.

• Structural Engineering and Mechanics
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• 제75권1호
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• pp.101-108
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• 2020

The present study intends to analyze damage in thin-walled steel cylinders undergoing constant internal pressure and thermal cycles through use of anisotropic continuum damage mechanics (CDM) model coupled with nonlinear kinematic hardening rule of Chaboche. Materials damage in each direction was defined based on plastic strain and its direction. Stress and strain distribution over wall-thickness was described based on the CDM model and the return mapping algorithm was employed based on the consistency condition. Plastic zone expansion across the wall thickness of cylinders was noticeably affected with change in internal pressure and temperature gradients. Expansion of plastic zone over wall-thickness at inner and outer surfaces and their boundaries demarking elastic and plastic regions was attributed to the magnitude of damage induced over thermomechanical cycles on the thin-walled samples tested at various pressure stresses.

• Korean Journal of Mathematics
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• 제5권1호
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• pp.55-60
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• 1997

A continuum structure function(CSF) is a non-decreasing mapping from the unit hypercube to the unit interval. The reliability importance of component $i$ in a CSF at system level ${\alpha}$, $R_i({\alpha})$) say, is zero if and only if component $i$ is almost irrelevant to the system at level ${\alpha}$. A condition to check whether a component is almost irrelevant to the system is presented. It is shown that $R^{(m)}_i({\alpha}){\rightarrow}R_i({\alpha})$ uniformly as $m{\rightarrow}{\infty}$ where each $R^{(m)}_i({\alpha})$ is readily calculated.

• 소음진동
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• 제6권1호
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• pp.27-34
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• 1996

In this paper, design sensitivity of vibration displacement and acceleration is computed and design sensitivity, the derivative information of responses with respect to design perameters, is used as a design guidance tool to reduce the vibration. First, the harmonic vibration analysis of deck and simplified ship structures is performed by finite element method and secondly continuum disign sensityivity for excessive dynamic response is computed by continuum method. Both the direct and modal frequency response methods for the finite element analysis are adopted. Sensitivities of structural components such as upper plate, side wall, bilge, bottom plate are compared and the reductionof vibration is obtained by the proper increase of thickness of each component.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 추계학술대회논문집
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• pp.24-27
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• 1997

In the present work, rigid-plastic continuum elements employing the shape change and anisotropic effects are derived for the purpose of applying more realistic blankholding force condition in three-dimensional finite element analysis of sheet metal forming process. In order to incorporate the effect of shape change effectively in the derivation of finite element equation using continuum element for sheet metal forming, the convected coordinate system is introduced, rendering the analysis more rigorous and accurate. The formulation is extended to cover the orthotropic material using Hill's quadratic yield function. For the purpose of applying more realistic blankholding force condition, distributed normal and associated frictional tangent forces are employed in the blankholder, which is pressed normal and associated frictional tangent forces are employed in the blankholder, which is pressed against the flange until the resultant contact force with the blank reaches the prescribed value. As an example of sheet metal forming process coupling the effect of planar anisotropy and that of blankholding boundary condition, circular cup deep drawing has been analyzed considering both effects together.

• 한국농공학회논문집
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• 제51권3호
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• pp.45-52
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• 2009

Generally, structures are analyzed as continuum. However, sometimes it is more efficient to analyze structure as a discrete model rather than as a continuum model in case of the structure has complex shape or loading condition. This study, therefore, suggests an improved analysis discrete model, named Equivalent Truss Model (further as "ETM"), which can obtain similar results with analyzing continuums analysis. ETM adopts a lattice truss to compose the members of the model, and analyses the structures. As a consequence, the ETM produced the identical outcome with the continuums analysis in section force of different structures and loading conditions. Similar results have been shown in internal stress analysis as well. Make use of that ETM is discrete, fractural path of beam was analyzed by ETM and the result was reasonable.

• 천문학회보
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• 제36권2호
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• pp.102.2-102.2
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• 2011

Sunspots usually appear in a group which can be classified by certain morphological criteria. In this study we examine the moments which are statistical parameters computed by summing over every pixels of contours, in order to quantify the morphological characteristics of a sunspot group. The moments can be additional characteristics to the sunspot group classification such as McIntosh classification. We are developing a program for image processing, detection of contours and computation of the moments using continuum images from SOHO/MDI. We apply the program to count the sunspot numbers from 303 continuum images in 2003. The sunspot numbers obtained by the program are compared with those by SIDC. The comparison shows that they have a good correlation (r=89%). We are extending this application to automatic sunspot classification (e.g., McIntosh classification) and flare forecasting.

• Journal of the Optical Society of Korea
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• 제9권2호
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• pp.39-44
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• 2005

Unlike for the bound states, several different boundary conditions are used for the continuum states above the barrier in semiconductor quantum wells. We employed three boundary conditions, infinite potential barrier boundary condition, periodic boundary condition and scattering boundary condition, and calculated the local number of states, wavefunctions and optical matrix elements for the symmetric and asymmetric quantum wells. We discussed how these quantities are related in the three boundary conditions. We argue that the scattering boundary condition has several advantages over the other two cases. These results would be useful in understanding quantum well lasers and detectors involving continuum states.