• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.10a
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• pp.444-451
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• 2003

In this study, a new three-dimensional finite element analysis model of high-speed railway bridges considering train-bridge interaction, in which various improved finite elements are used for modeling structural members, is proposed. The box-type bridge deck of a railway bridge is modeled by the NFS(Nonconforming Flat Shell) elements with 6 degrees of freedom. Track structures are idealized using the beam finite elements with the offset of beam nodes and those on Winkler foundation with two parameters. And, the vehicle model devised for a high-speed train is employed, which has an articulated bogie system. By Lagrange's equations of motion, the equations of motion of a bridge-train system can be formulated. Finally, by deriving the equations of the forces acting on a bridge considering bridge-train interaction the complete system matrices of total bridge-train system can be constructed. As numerical examples of this study, 2-span PC box-girder bridge is analyzed and results are compared with experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.7
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• pp.745-751
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• 2011

This study proposes finite element modeling of dislocation punching at cooling after consolidation in order to calculate the strength of particle-reinforced aluminum composites. The Taylor dislocation model combined with strain gradient plasticity around the reinforced particle is adopted to take into account the size-dependency of different volume fractions of the particle. The strain gradients were obtained from the equivalent plastic strain calculated during the cooling of the spherical unit cell, when the dislocation punching due to CTE (Coefficient of Thermal Expansion) mismatch is activated. The enhanced yield stress was observed by including the strain gradients, in an average sense, over the punched zone. The tensile strength of the SiCp/Al 356-T6 composite was predicted through the finite element analysis of an axisymmetric unit cell for various sizes and volume fractions of the particle. The predicted strengths were found to be in good agreement with the experimental data. Further, the particle-size dependency was clearly established.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.17 no.1
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• pp.36-48
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• 2021

As the material aging of nuclear power plants has been progressing in domestic and overseas, crack growth becomes one of the most important issues. In this respect, the crack growth assessment has been considered an essential part of structural integrity. The crack growth assessment for nuclear power plants has been generally performed based on ASME B&PV Code, Sec. XI but the idealization of crack shape and the conservative solutions of stress intensity factor (SIF) are used. Although finite element analysis (FEA) based on iterative crack growth analysis is considered as an alternative method to simulate crack growth, there are yet no guidelines to model the crack-tip spider-web mesh for such analysis. In this study, effects of various meshing factors on FE SIF calculation are systematically examined. Based on FEA results, proper criteria for spider-web mesh in crack-tip are suggested. The validation of SIF calculation method through mapping initial stress field is investigated to consider initial residual stress on crack growth. The iterative crack-tip modeling program to simulate crack growth is developed using the proposed criteria for spider-web mesh design. The SIF results from the developed program are validated by comparing with those from technical reports of other institutes.

• Journal of Aerospace System Engineering
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• v.18 no.3
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• pp.17-26
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• 2024

Aircraft engines are exposed to high temperatures, high pressures, and stress caused by the rotation of the turbine shaft during flight. These loads can result in microcracks both on the inside and outside surfaces of the structure. Consequently, this can lead to structural defects and negatively impact the lifespan of the parts. To proactively prevent these defects, a finite element analysis is carried out to identify cracks. However, this process is time-consuming and requires significant effort due to the repetitive nature of crack modeling. This study aims to develop a crack modeling method based on the finite element model. To achieve this, the Constrained Delaunay Triangulation (CDT) technique is employed to triangulate the space while considering limitations on point connections. The effectiveness of this method is validated by comparing stress intensity factors for semi-elliptical cracks in plates and cylindrical vessels. This approach proves to be a valuable tool for crack analysis studies.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.6
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• pp.528-537
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• 2002

In this paper, the extended FDTD is used for the analysis of microwave circuits including active elements. Lumped elements such as R, L, C which are inserted into a microstrip line are analyzed with the FDTD lumped element modeling. Parasitic capacitance and inductance could be obtained using network modeling and so it is sure that FDTD lumped element modeling makes it possible to get more accurate data which include parasite components. Moreover, a balanced mixer using two diodes that are modeled by an extended FDTD is designed and the more exact characteristic of the mixer is acquired than in current circuit simulator.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.128-133
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• 2003

In this paper, we have proposed a method by using virtual simulation to calculate the behaviors of spacers to avoid conductor galloping with the hanging composite polymer spacer between conductors on different phases. We have considered with three types of modeling considerations for the analysis of galloping in power transmission lines, such as iced-single conductors without spacer, iced-single conductors with spacers, and iced-two bundle conductors with spacers. In simulation, the finite element method is used to calculate the structural response with geometric nonlinear behavior. The iced conductor is modeled by two beam-element faces with which it is connected. The ANSYS program is applied too. First, the calculation results show that the two beam-element model is very suitable to make a virtual simulation. Second, the amplitude of conductor galloping is reduced after hanged spacers. Third, when number of spacer is increased, the maximum magnitude of natural frequency of iced conductor will reduce. Final, the behaviors of spacers are verified in viewpoint of standard cases.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1411-1421
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• 1995

A rigid visco-plastic finite element method has been developed for modeling superplastic forming processes. The optimum pressure-time relationship for a target strain rate and thickness distributions was predicted using two-node line element based on membrane approximation for plane strain and axisymmetric condition. Analysis of superplastic forming was carried out using the developed program and the numerical results were compared to the values available in the literature for plane strain problems. For description of the contact between the dies and sheet, the direct projection method was applied to the complicated problem and the validity of the scheme was tested. Experiments for the various geometries such as hemisphere and cone were performed with the developed forming machine using the calculated optimum pressure-time curves. Comparison between analysis and experiments showed good agreement.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.2
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• pp.153-168
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• 2016

Sloshing phenomenon is a complicated free surface flow problem that increases the dynamic pressure on the sidewalls and the bottom of the storage tanks. When the storage tanks are partially filled, it is essential to be able to evaluate the fluid dynamic loads on the tank's perimeter. In this paper, a numerical code was developed to determine the pressure distribution on the rectangular and trapezoidal storage tanks' perimeters due to liquid sloshing phenomenon. Assuming the fluid to be inviscid, the Laplace equation and the nonlinear free surface boundary conditions were solved using coupled boundary element - finite element method. The code performance for sloshing modeling was validated using Nakayama and Washizu's results. Finally, this code was used for partially filled rectangular and trapezoidal storage tanks and free surface displacement, pressure distribution and horizontal and vertical forces exerted on the tanks' perimeters due to liquid sloshing phenomenon were estimated and discussed.

• Journal of the Korean Society of Safety
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• v.12 no.4
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• pp.169-179
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• 1997

The dynamic response of the human brain to direct impact was studied by three-dimensional finite element modeling. The model includes a layered shell closely representing the cranial bones with the interior contents occupied by an incompressible continuum to simulate the brain. Falx and tentorium modeled with 4 node membrane element were also incorporated. The computed pressure-time histories at 4 locations within the brain element compared quite favorably with previously published experimental data from cadaver experiments. Therefore, the purpose of this study was to determine the effects of the impact direction on the dynamic response of the brain in children. A parametric study was subsequently conducted to identify the model response when the age and impact site were varied.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.4
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• pp.97-106
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• 1996

The impact response of the human brain has been determined by three-dimensional finite element modeling. The model includes a layered shell closely representing the cranial bones with the interior contents occupied by an incompressible contimuum to simulate the brain. Flax and tentorium modeled with 4 node membrane element were also incorporated. The computed pressure-time histories at 4 locations within the brain element compared quite favorably with previously published experimental data from cadaver experiments. A parametric study was subsequently conducted to identify the model response when the impact were varied.