• Proceedings of the Computational Structural Engineering Institute Conference
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• 1995.04a
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• pp.28-34
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• 1995

Behavior of underground structural systems is usually complicated because of various unknown parameters. In order to construct those structural systems safely and economically, exact identification of the system parameters and accurate analysis of the system behaviors are essentially required. In this study, a forward analysis program, which is able to eliminate numerical errors due to far field boundary effect, is developed by coupling finite and boundary elements. In this coupled analysis, boundary elements are used in the semi-infinite domain where stress variation is small, and finite elements in the stress concentration region where material nonlinearity should be considered. Then, a back analysis program which can identify the system parameters is developed using the direct method to be combined with the forward analysis program. The elastic modulus and initial stress, which are most important in the description of the behavior of underground structures, are taken as the system parameters. A simple example is examined 0 show that the method can be used effectively.

• Computational Structural Engineering
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• v.8 no.3
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• pp.91-102
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• 1995

For the wave propagation problems, the influence of time-dependent dynamic behavior must be accounted in the analysis. In this study, the dynamic analysis method which combines finite elements and boundary elements is developed for the wave propagation problem modelling the infinity of medium through 3-D boundary elements and underground structure through degenerated finite shell elements. Performing dynamic analysis of underground tunnels by the proposed coupling method of boundary and finite elements, it is found that the change of the stiffness of structures has a good effect on the response. It is also found that the consideration of the repeating effect due to moving traffic loads which is difficult with existing 2-D dynamic analysis can be possible with the 3-D analysis in time domain.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.439-442
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• 2003

This study presents a new computational model to analyze the grain deformation in a polycrystalline aggregate in a discrete manner and based directly in the underlying physical micro-mechanisms. As a result, specific characteristics have to be considered for the numerical analysis. The grains and grain boundary elements are introduced to model individual grains and grain boundary facets, respectively, to consider the size effects in the micro forming. The constitutive description of the grain elements accounts for the rigid-plastic and the grain boundary elements for elastic relationships. The capability of the proposed approach is demonstrated through application of grain element and grain boundary element in the micro forming.

• Structural Engineering and Mechanics
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• v.34 no.6
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• pp.703-718
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• 2010

In classical higher-order discontinuous boundary element formulation for two-dimensional elastostatics, interpolation functions for different boundary variables (i.e., boundary displacements and tractions) are assumed to be the same. However, there is a derivational relationship between these variables. This paper presents a boundary element formulation, called Mixed Boundary Element Formulation, for two dimensional elastostatic problems in which above mentioned relationship is taking into account. The formulations are performed by using discontinuous first and second-order mixed boundary elements. Based on the formulations presented in this study, two computer softwares are developed and verified through some example problems. The results show that the present formulation is credible.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.125-132
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• 2002

In this study, a numerical method is developed for nonlinear analysis for soil-pile-structure interaction system in time domain. Finite elements considering material nonlinearity are used for the near field and boundary elements for the far field. In the near field, frame elements are used for modeling a pile and plane-strain elements for surrounding soil and superstructure. In. the far field, boundary element formulation using the dynamic fundamental solution is adopted and coupled with the near field. Transformation of stiffness matrices of boundary elements into time domain is performed by inverse FFT. Stiffness matrices in the near field and far field are coupled. Newmark direct time integration method is applied. Developed soil-pile-structure interaction analysis method is verified with available literature and commercial code. Also, parametric studies by developed numerical method are performed. And seismic response analysis is performed using actual earthquake records.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1991.04a
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• pp.8-14
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• 1991

The finite element technique incorporating infinite elements is applied to analyzing the general three dimensional wave-structure interaction problems within the limits of linear wave theory. The hydrodynamic farces are assumed to be inertially dominated, and viscous effects are neglected. In order to analyze the corresponding boundary value problems efficiently, two types of elements are developed. One is the infinite element for modeling the radiation condition at infinity, and the other is the fictitious bottom boundary element for the case of deep water. To validate those elements, numerical analyses are performed for several floating structures. Comparisons with the results from culler available solution methods show that the present method incorporating tile infinite and the fictitious bottom boundary elements gives good results.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.275-283
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• 1999

To predict the dynamic behavior of the cylindrical liquid storage tank subjected to seismic ground motion three dimesional analysis with liquid-structure interaction must be performed, In this study a three dimensional dynamic analysis method over the frequency domain using FE-BE coupling technique which combines the efficiency of the boundary elements for liquid with the versatility of the finite shell elements for tank. The liquid region is modeled using boundary elements which can counter the sloshing effect at free surface and the structure region the tank itself is modeled using the degenerated finite shell elements. At the beginning of the procedure the equivalent mass matrix of the liquid is generated by boundary elements procedure. Then this equivalent mass matrix is combined with the mass matrix of the structure to produce the global mass matrix in the equation of the motion of fluid-structure interaction problem In order to demonstrate the accuracy and validity of the developed method the numerical results re compared with the previous studies. Finally the effects of the fluid-structure interaction on the natural frequency and dynamic response of the system are analyzed.

• Journal of the Optical Society of Korea
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• v.9 no.2
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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.

• Journal of the Korean Society for Precision Engineering
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• v.9 no.2
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• pp.44-51
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• 1992

This paper is concerned with the propram of the automatic mesh generation for 2-dimensional domain which contains the curved boundaries and holes. This program treats a new vertical-line drawing method. This method starts with 4-subdivisions of problem domain and the classification of the cross points of grid lines and boundaries. The new node is generated by the vertical line to the line connecting the two intersections of a boundary and two grid lines in gereral. And the node very close to the boundary is moved to the boundary. The automatic mesh generation composed of only rectangular elements is achieved by this procedure. The boundaries are piecewise-curves composed of lines, circles, arcs, and free curves. The free curves are generated by B-Spline form. Although there were some bad elements for the complex boundary, it was possible to obtain the acceptible rectangular elements for the given boundaries.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.3
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• pp.647-660
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• 1995

Given the tetrahedron-based octree approximation of a solid as described in part(I) of this thesis, in this part(II) a systematic procedure of 'boundary moving' is developed for the fully automatic generation of 3D finite element meshes. The algorithm moves some vertices of the octants near the boundary onto the exact surface of a solid without transforming the topology of octree leaf elements. As a result, the inner octree leaf elements can be used as exact tetrahedral finite element meshes. In addition, as a quality measure of a tetrahedral element, 'shape value' is propopsed and used for the generation of better finite elements during the boundary moving process.