• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.1
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• pp.33-41
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• 2011

This study presents modeling technologies applicable to an unbonded post-tension system using a finite element software package. In this study, both direct modeling method and multiple spring method were used. The direct modeling method adopts tube-to-tube contact elements to represent the physical feature of a post-tension system. The multiple spring method uses virtual tendons attached to the real tendons using a number of rigid axial springs that freely rotate at the ends. Both modeling technologies provide accurate predictions. However, only the multiple spring method provides numerically stable and reliable responses with a consideration of concrete tension stiffening effects. Therefore, the multiple spring method turned out to be a generally applicable modeling technology for the unbonded post-tension system. Comparisons were made for the analytical and experimental results for the verification of the selected method, and parameter studies were carried out to confirm the appropriateness of the modeling assumptions and parameters adopted in the analysis.

• Transactions of Materials Processing
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• v.11 no.1
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• pp.75-83
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• 2002

Recently, the hydroforming process is widely applied to the automotive industry and rapidly spreaded to other industries. In this paper, An implicit finite element formulation for simulating axisymmetric tube hydroforming processes is performed. In order to describe normal anisotropy of the tube, Hill's non-quadratic yield function is employed. The frictional contact between die and tube and the frictionless contact between tube and fluid are considered using the mesh-normal vectors computed from the finite element mesh of the tube. The complete set of the governing relations comprising equilibrium and interfacial equations is linearized for Newton-Raphson procedure. In order to verify the validity of the developed finite element formulation, the axisymmetric tube bulge test is simulated and the simulation results are compared with experimental measurements. In a simulation of stepped circular tube hydroforming processes, an optimal hydraulic pressure curve is pursued by considering simultaneously internal pressures and axial forces.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.58-61
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• 2001

An implicit finite element formulation for axisymmetric tube hydroforming is investigated. In order to describe normal anisotropy of the tube, Hill's non-quadratic yield function is employed. The frictional contact between die and tube and frictionless contact between tube and fluid are considered using the mesh-normal vector computed from finite element mesh of the tube. In order to verify the validity of the developed finite element formulation, the axisymmetric tube bulge test is simulated and simulation results are compared with experimental measurements. In the axisymmetric tube hydroforming process, an optimal hydraulic curve is pursued by performing the simulation with various internal pressures and axial forces.

• Transactions of Materials Processing
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• v.10 no.6
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• pp.478-484
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• 2001

Tube Process (TP) is a process to produce permanent magnets using a deformable tube for densification of magnet powder. This process claims that it can accomplish both densification and anisotropication in one step forming. This process is distinguished from other processes since it uses a deformable copper tube for densification of magnet powder. In this paper, simulation has been carried out for tile Tube Process in a closed die considering the compressibility of powdered material, arbitrary curved shape and deformable body contact between Nd-Fe-B magnet powder and a copper tube. Results show that the finite element analysis of the Tube Process plays an important role in the stage of preform design.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.82-85
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• 1999

Permanent magnets of Nd-Fe-B group have kept a key post in the permanent magnet market and used in various parts. Tube Process is a process to produce permanent magnets using a deformable tube for denslfication of powder magnets. Advantage claimed for this process is that it can accomplish both densification and anisotropication in one step forming. In this paper. the simulation has been carried out for a full Tube Process in a closed Qe considering the compressibility of material, arbitrary curved shape and deformable body contact between Nd-Fe-B powder magnet and copper tube. The results show that the analysis of Tube Process is applicable with great help in the stage of preform design.

• Transactions of Materials Processing
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• v.23 no.7
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• pp.419-424
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• 2014

In order to improve efficiency, an outdoor unit using a refrigerant cooling method is designed into many air conditioner systems. The heat exchanger is composed of a Cu tube and an plate. The optimal design for the cold plate is very important because the efficiency of the heat transfer depends on the contact area between the Cu tube and the cold plate. The current study focused on the design of the cold plate to obtain a uniform contact between the Cu tube and the cold plate. Both FE(finite element) analysis and optimization were used in the design. The contact area between the tube and plate was predicted and improved by 16% through the press forming simulations. The springback after press forming was also reduced when the optimized design parameters were used. To verify the validity of the optimal cold plate design, a verification test was conducted. As a result, the performance of the heat exchanger improved by 34% when compared to benchmarked products.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.7 no.4
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• pp.51-56
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• 2011

Steam generator is one of the main equipments that affect safety and long term operation in nuclear power plants. Fluid flows inside and outside of the steam generator tubes and induces vibration. To prevent the vibration the tubes are supported by AVB (anti vibration bar). When the steam generator tube contact to AVB, it is damaged by the accumulation of wear and corrosion. Therefore studies are required to determine the effects of the gap between the steam generator tube and AVB. In order to obtain the stress and the displacement distributions of the steam generator tube, three dimensional finite element analyses were performed by using the commercial program ANSYS. Using the calculated the stress and the displacement distributions, the static residual strength of the steam generator tube can be evaluated. The results show that the stress and displacement of the steam generator tube increase significantly compared with the results from a zero-gap model.

• Transactions of Materials Processing
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• v.7 no.1
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• pp.72-80
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• 1998

This study is concerned with the thermo-biscoplastic finite element analysis of hot tube extrusion through square dies with a mandrel. The problem is treated as a non-steady state and the ALE description is used due to abruptly turning flow at the die aperture. Since the contact heat transfer coefficient and the friction factor are required in the analysis experiments are also carried out to determine the values, In order to apply ceramics to an extrusion die the study is focussed on under-standing the characteristics of the process. The simulated results provide the useful informations such as metal flow temperature distribution stress state etc. The elastic analysis of the dies is carried out to obtain the stress state of the ceramic dies.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.5
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• pp.653-660
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• 2010

The stern tube bearing is installed to the stern tube and stern boss casting by using the method of the force pressured fitting. The adequate value of the interference between the stern tube bearing and casting should be considered owing to the slip. In this study, to review and compare the fitting force and the contact pressure, the theory of thick walled cylinder is considered to clarify the formula which received from the maker. Also the fitting force and contact pressure are calculated by using the standard value of interference, Young's modulus, Poisson's ratio and friction coefficient.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.133-140
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• 2018

A nonlinear finite element analysis was conducted in order to examine the moment capacity and flexural behaviour of hollow prestressed concrete filled steel tube(HCFT) piles which compose hollow PHC piles inside thin wall steel tubes. The parameters investigated in this study were various contact conditions between concrete and steel tube, thickness of concrete tube and various PC strands. A simple method is proposed to determine the ultimate flexural strength based on plastic stress distribution method. In order to verify the proposed method, calculated moment capacity of various HCFT piles are compared with the experiment and numerical analysis results.