• Structural Engineering and Mechanics
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• v.6 no.6
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• pp.693-710
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• 1998

This paper concerns studies on the shape formation of post-tensioned and shaped steel domes. The post-tensioned and shaped steel domes, assembled initially at ground level in an essentially flat condition, are shaped to a curved space form and erected into the final position by means of a post-tensioning technique. Based on previous studies on this shape formation principle, three post-tensioned and shaped steel domes have been constructed. The results of the shape formation tests and finite element analyses are reported in this paper. It is found that the first two test domes did not furnish a part-spherical shape as predicted by finite element analyses, because the movements of some mechanisms were not controlled sufficiently. With a revised post-tensioning method, the third dome obtained the theoretical prediction. The test results of the three post-tensioned and shaped domes have shown that a necessary condition to form a desired space shape from a planar layout with low joint stiffnesses is that the movements of all the existing mechanisms must be effectively controlled as indicated by the finite element analysis. The extent of the maximum elastic deformation of a post-tensioned and shaped steel structure is determined by the strength of the top chords and their joints. However, due to the semi-rigid characteristic of the top chord joints, the finite element analyses cannot give a close prediction for the maximum elastic deformations of the post-tensioned and shaped steel domes. The results of the current studies can be helpful for the design and construction of this type of structure.

• Advances in aircraft and spacecraft science
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• v.2 no.3
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• pp.275-302
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• 2015

Theoretical and numerical assessments of approximate evaluations and simplified analyses of piezoelectric structures transverse shear modal effective electromechanical coupling coefficient (EMCC) are presented. Therefore, the latter is first introduced theoretically and its approximate evaluations are reviewed; then, three-dimensional (3D) and simplified two-dimensional (2D) plane-strain (PStrain) and plane-stress (PStress) piezoelectric constitutive behaviors of electroded shear piezoceramic patches are derived and corresponding expected short-circuit (SC) and open-circuit (OC) frequencies and resulting EMCC are discussed; next, using a piezoceramic shear sandwich beam cantilever typical benchmark, a 3D finite element (FE) assessment of different evaluation techniques of the shear modal effective EMCC is conducted, including the equipotential (EP) constraints effect; finally, 2D PStrain and PStress FE modal analyses under SC and OC electric conditions, are conducted and corresponding results (SC/OC frequencies and resulting effective EMCC) are compared to 3D ones. It is found that: (i) physical EP constraints reduce drastically the shear modal effective EMCC; (ii) PStress and PStrain results depend strongly on the filling foam stiffness, rendering inadequate the use of popular equivalent single layer models for the transverse shear-mode sandwich configuration; (iii) in contrary to results of piezoelectric shunted damping and energy harvesting popular single-degree-of-freedom-based models, transverse shear modal effective EMCC values are very small in particular for the first mode which is the common target of these applications.

• Journal of Power Electronics
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• v.14 no.3
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• pp.413-420
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• 2014

The conventional Phase-Shift Full-Bridge (PSFB) converter has a serious voltage spike because of the ringing between the leakage inductance of the transformer and the parasitic output capacitance of the secondary side rectifier switches. To overcome this problem, an asynchronous active clamp technique employing an auxiliary DC/DC converter has been proposed. However, an exact analyses for designing the auxiliary DC/DC converter has not been presented. Therefore, the amount of power that is supposed to be handled in the auxiliary DC/DC converter is calculated through a precise mode analyses in this paper. In addition, this paper proposes a lossy snubber circuit with hysteresis characteristics to reduce the burden that the auxiliary DC/DC converter should take during the starting interval. This technique results in optimizing the size of the magnetic component of the auxiliary DC/DC converter. The operational principles and the theoretical analyses are validated through experiments with a 48V-to-30V/15A prototype.

• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.195-202
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• 2001

In this paper, the convergence characteristics of preconditioned multigrid methods are investigated. The preconditioning method is introduced to reduce the condition number of discrete governing equations. 6 preconditioners including a point, line and diagonalized line solvers are implemented and applied to 2-dimensional inviscid flow problems. Theoretical fourier analyses and numerical results are presented for the preconditioners.

• Journal of the Korean Chemical Society
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• v.15 no.6
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• pp.359-366
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• 1971

The extended Huckel calculations on five organic accelerators of vulcanization have been carried out. Various MO quantities e.g., electron populations and AO coefficients, are used to explain accelerator reactivity of the compounds. Results of these analyses lead us to support free radical mechanism of acceleration in vulcanization.

• Transactions of Materials Processing
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• v.6 no.3
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• pp.221-226
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• 1997

Chevron crack in cold extrusion has been studied in view of deformation conditions and material characteristics. There is V formed chevron crack is occasionally occurred in core part of shaft by multistage free extrusion. Although many research results were reported and theoretical analyses were accompanied, in this study we discussed practical method to prevent chevron crack in the field of working conditions and material characteristics. We have found that chevron crack is eliminated under condition of high hydrostatic state in deformation and decreased segregation, refinement of micro structure of materials.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2000.04a
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• pp.245-246
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• 2000

공기중의 오염 입자가 인체에 얼마나 많은 영향을 미치는가는 흡입된 입자 (inhaled particles) 중에서 얼마나 많은 양이 폐 (lung)에 침전되는가와 밀접한 관계가 있다. 또한 정상 및 비정상 (diseased) 폐에서, 흡입된 입자의 침전 위치와 침전양 (deposition site and dose)은 입자의 크기와 호흡 양식(breathing pattern)에 따라 큰 차이를 보이며, 이런 차이는 흡입오염입자 (inhaled pollutant particles)에 의한 건강 위험도 평가 (health risk assessment) 및 흡입용 약물 (inhaled drug aerosols)의 치료효과(therapeutic effects) 평가 등에 큰 영향을 미친다. (중략)

• Journal of the korean Society of Automotive Engineers
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• v.9 no.4
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• pp.61-68
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• 1987

The Bellows Joint which was used as a absorber or safety equipment to prevent the deformation or fracture of a structure, have been analyzed by the F.E.M using axi-symmetric conical frustum element. Using the F.E.M the general behavior of Bellows Joint corrugation can be investigated easily, and the stability of the analysis be guaranteed. In annular type corrugation, the F.E.M results were agreed with those of other theoretical analyses, but in the U type corrugation, the F.E.M results were more acceptable than those of others.

• Progress in Superconductivity and Cryogenics
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• v.4 no.2
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• pp.42-46
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• 2002

This research is conducted with the object of Piling up the foundation of design technologies for high temperature superconducting (HTS) power transformer which is thought to be as a powerful power transformer of next generation. In this study, not only the theoretical design of high temperature superconducting (HTS) transformer but also the arrangements of superconducting tape and the cooling method have been conducted. Moreover, electromagnetic analyses using finite element method (FEM) were conducted to confirm the efficiency of the designed transformer.

• Proceedings of the KSR Conference
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• 1998.05a
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• pp.474-481
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• 1998

Metal bonded rubber spring is used in primary suspension component of the high speed train. The aim of this study is to establish a finite element analysis technique for the metal bonded rubber spring. Some theoretical analyses were performed on the hyperelastic behavior in rubber material and test are carried out to acquire the constants in strain energy function for it. Also, finite element analysis were executed to evaluate the design parameter and behavior of deformation and stress distribution using by the commercial finite element code.