• Journal of the Korean Society for Precision Engineering
• /
• v.21 no.11
• /
• pp.155-162
• /
• 2004

The volume of the metal is not changed for the plastic deformation. For metal forming simulation, rigid-plastic FEM codes are widely used. Updating geometry using Euler method in the simulation, the volume loss is occurred. In this paper, hybrid method is introduced to perform a more accurate simulation reducing computation time. In the proposed hybrid method, RK2 method is used for geometry updating at first time step and after the boundary condition of the node is changed. At the others, Adams-Bashforth or theta method is applied to update geometry. The results show that the simulations of upsetting and side-pressing can be performed within 0.02％.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.5
• /
• pp.1601-1610
• /
• 1991

본 연구에서는 3차원 스트레칭 문제의 2차원화가 가능한 주요 단면에 대해서 박막요소와 적층 셸(degenerated shell) 요소를 혼합하여 사용하는 선택적 M/S 방법을 이용하여 2차원 문제로 해석하였다. M/S변환 조건으로는 변형형상의 기하학적 조건 을 고려하였다.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.17 no.1
• /
• pp.1-10
• /
• 2004

Adaptive finite element analysis, in which its solution error meets with the user defined allowable error, is recently used to improve the reliability of finite element analysis results. This adaptive analysis is composed of two procedures; one is the error estimation of an analysis result and the other is the reconstruction of finite elements. In the (p-method, an element size is controlled by relocating of nodal positions (r-method) and the order of an element shape function is determined by the hierarchical polynomial (p-method) corresponding to the clement solution error by the enhanced SPR. In order to show the effectiveness and the accuracy of the suggested rp-method, various numerical examples were analyzed and these analysis results were examined by comparing with those obtained by the existed methods.

• Computational Structural Engineering
• /
• v.4 no.2
• /
• pp.77-85
• /
• 1991

A new finite element technology based on the p-version of E.F.M. is discussed with reference to its potential for application to stress intensity factor computations in linear elastic fracture mechanics, especially cracked cylindrical shells. It is shown that the p-version model is far better suited for computing the stress intensity factors than the conventional h-version models with the help of three test problems. The main advantage of this technology is that the accuracy of approximation can be established without mesh refinement or the use of special procedures such as crack-tip element and mixed variational approach.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.6
• /
• pp.1592-1602
• /
• 1990

Mixed mode surface crack in finite-width plate subjected to uniform tension and bending has been analyzed in 3-D problem by using boundary element method. The calculations were carried out for the surface crack angles(.a/pha.) of 0.deg., 15.deg., 30.deg., 45.deg., 60.deg., and 75.deg., and for the aspect ratio(a/c) of 0.2, 0.4, 0.6 and 1.0 to get stress intensity factors at the boundary points of the surface crack. For the aspect ratio of 1.0 and the surface crack angles, finite element method was used to check the results in this study. Comparison of the results from both methods showed good agreement.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.3A
• /
• pp.439-445
• /
• 2006

Analysis problems of tunnels whose geometrical dimensions are very small compared with surrounding media can be treated as infinite region problems. In such cases, even if finite element models can be applied, excessive number of elements is required to obtain satisfactory accuracy. However, inaccurate results may be produced due to assumed artificial boundary conditions. To solve these problems, a hybrid model, which models the region of interest with finite elements and the surrounding infinite media with infinite elements, is introduced for the analysis of infinite region. Three-dimensional isoparametric infinite elements with various decay characteristics are formulated in this paper and the corresponding parameters are presented by means of parametric studies. Three-dimensional tunnel analysis performed on a representative example verifies the applicability of hybrid model using infinite elements.

• Journal of ILASS-Korea
• /
• v.23 no.1
• /
• pp.16-21
• /
• 2018

The current study has developed an in-house 3D FEM code in order to model thermoacoustic problems in a gas turbine combustion system and compared calculation results of main instability characteristics with measured ones from a lab-scale partially-premixed combustor. From the comparison of calculation results with the measured data, the current model could successfully capture the harmonic longitudinal instability frequencies and their spatial distributions of the acoustic field as well as the growth rate of self-excited modes.

• Computational Structural Engineering
• /
• v.18 no.3 s.69
• /
• pp.7-14
• /
• 2005

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.15 no.4
• /
• pp.224-231
• /
• 2003

In this study, the hybrid breakwater system - a breakwater system combining the floating breakwater with the submerged breakwater - is used to improve the wave screening performance that may not be achieved by using the floating breakwater or the submerged breakwater, separately. Two-dimensional finite element method is used for numerical analysis and the wave reflection ratio and the wave transmission ratio are analyzed for the proposed case. In case of using the hybrid breakwater system, wave screening performance is more effective than in case of using the floating breakwater or the submerged breakwater, separately. It also shows an effective wave screening on the long wave period and an advanced wave screening performance with low height of the submerged breakwater.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
• /
• v.4 no.1
• /
• pp.38-43
• /
• 1993

A Hybrid Finite Element Method(HFEM) is applied to solve the electrormagnetic scattering from multi-layered dielectric cylinders. An unbounde region is divided into local boundary regions where a practical differential equation solution is obtained, with the remaining unbounded region represented by a boundary integral equation. If sources, media inhomogeneities, and anisotropies are local, a surgace may be defined to enclose them. Therefore the integral region so defined is bounded, and differential techniques may be used there. Also, in the re- maining unbounded region a boundary integral equation may be formulated using only a simple free - space green's function. Therefore, The local boundary is represented by a boundary - value problem with boundary conditions and solved by the finite element method. The advantage of the proposed method is simple and efficient in the work of electromagnetic scattering. The validity of the results have been verified by comparing results of other method(boundary element method). Examples has been presented to calculate the scattered fields of lossy dielectric cylinders of arbitray cross section.