• Journal of KSNVE
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• v.2 no.4
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• pp.265-272
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• 1992

The simplest method which has been used extensively for vibration analysis is the transfer matrix method introduced by Myklestad and was later extended by many researchers. The crude approximation results in considerable error on the predicted natural frequencies and to increase the accuracy the number of elements used in the analysis must be increased. In addition, numerical instability can occur as a result of matrix multiplication. Also the main disadvantage of the finite element method is the large computer memory requirements for complex systems. The new method proposed in this paper combines the transfer matrix and finite dynamic element techniques to form a powerful algorithm for vibration analysis of rotor system. It is shown that the accuracy improves significantly when the transfer matrix for each segment is obtained from finite dynamic element techniques.

• Earthquakes and Structures
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• v.22 no.6
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• pp.549-559
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• 2022

The quasi-static finite element (FE) approaches are widely used for the seismic analysis of tunnels. However, the conventional quasi-static approaches may cause significant deviations when the tunnel excavation process is simulated prior to the quasi-static analysis. In addition, they cannot account for vertical excitations. Therefore, this paper first highlights the limitations of conventional approaches. A hybrid quasi-static FE approach is subsequently proposed and extensively validated for various conditions. The hybrid approach is simple and not time consuming, and it can be used for the preliminary seismic design of tunnels, especially when the tunnel excavation and vertically propagating P-waves are considered.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.12
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• pp.1200-1207
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• 2007

An experimental test is presented for photoelastic stress analysis around a crack tip in tensile loaded plate. The hybrid method coupling photoelastsic fringe inputs calculated by finite element method and complex variable formulations involving conformal mappings and analytical continuity is used to calculate full-field stress around the crack tip in uniaxially loaded, finite width tensile plate. In order to accurately compare calculated fringes with experimental ones, both actual and regenerated photoelastic fringe patterns are two times multiplied and sharpened by digital image processing. Regenerated fringes by hybrid method are quite comparable to actual fringes. The experimental results indicate that Mode I stress intensity factor analyzed by the hybrid method are accurate within three percent compared with ones obtained by empirical equation and finite element analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.1
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• pp.163-171
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• 1996

For the effective analysis of two dimensional plane problems, Treffiz finite elements and cavity elements have been proposed. These element matrix equaitons were formulated on the basis of hybrid variational principle and Treffiz function sets derived consitstently from the complex theoy of plane elasticity. In order to suggest the accuracy chatacteristics of the proposed Treffiz elements typical plane problems were analyzed and these results were compared with ones obtained by using the conveintional displacement type elements. The accuracy of the proposed elements is less sensitive to the element size and shape than the conventional displacement type elements. These elements, being able to be formed with multi-nodes, give the convenient modeling of an analytic domain. The cavity elements give the comparatively exact values of stress concentration factors of stress intensity factors and can be effectively used for the analysis of mechanical stuctures containing various cavities.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.193-196
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• 2006

Recently many research are going on in the field of application of Laser and Laser-Arc hybrid welding for superstructures such as ship-structures, transport vehicles etc. Therefore in this study an optimized welding condition and numerical simulation for hybrid welding by using previous numerical analysis which is used to calculate the heat source for Laser and Laser-Arc hybrid welding has been analyzed. For this purpose, fundamental welding phenomena of hybrid process(Laser+MIG) are determined based on the experiments. In order to calculate temperature and residual stress distribution in Laser and Laser-Arc hybrid welds, finite element heat source model is developed on the basis of experiment results and characteristics of temperature and residual stress distribution in Laser and Laser-Arc hybrid welds are understood from the result of simulation and found comparable to the experimental values.

• Ocean Systems Engineering
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• v.1 no.4
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• pp.317-336
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• 2011

A time domain finite element based method is employed to analyze wave radiation by multiple cylinders. The nonlinear free surface and body surface boundary conditions are satisfied based on the perturbation method up to the second order. The first- and second-order velocity potential problems at each time step are solved through a finite element method (FEM). The matrix equation of the FEM is solved through an iteration and the initial solution is obtained from the result at the previous time step. The three-dimensional (3D) mesh required is generated based on a two-dimensional (2D) hybrid mesh on a horizontal plane and its extension in the vertical direction. The hybrid mesh is generated by combining an unstructured grid away from cylinders and two structured grids near the cylinder and the artificial boundary, respectively. The fluid velocity on the free surface and the cylinder surface are calculated by using a differential method. Results for various configurations including two-cylinder and four-cylinder cases are provided to show the mutual influence due to cylinders on the first and second waves and forces.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.12
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• pp.2468-2478
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• 1994

A hybrid finite element method is presented for a characterization of scattering an radiation properties of microstrip patch and arrays residing in a cavity recessed in a ground plane. The technique combines the finite element and boundary integral methods to formulate a system for the solution of fields at the aperture and the scattering field and radar cross sections at free space. By virture of the finite element method, the proposed technique is applicable to patch antennas and arrays residing on or embeded in a layered dielectric loss/lossless substrate and is also capable of treating various feed configuration. Several numerical results are presented demonstrating the validity, efficiency and capability of the technique.

• The Journal of the Acoustical Society of Korea
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• v.18 no.1E
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• pp.37-43
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• 1999

This paper deals with a hybrid finite element method for wave scattering problems in infinite domains. Scattering of waves involving complex geometries, in conjunction with infinite domains is modeled by introducing a mathematical boundary within which a finite element representation is employed. On the mathematical boundary, the finite element representation is matched with a known analytical solution in the infinite domain in terms of fields and their derivatives. The derivative continuity is implemented by using a slope constraint. Drilling degrees of freedom at each node of the finite element model are introduced to make the numerical model more sensitive to the transverse component of the elastodynamic field. To verify the effects of drilling degrees freedom and slope constraints individually, reflection of normally incident P and SV waves on a traction free half spaces is considered. For the P-wave incidence, the results indicate that the use of slope constraint is more effective because it suppresses artificial reflection at the mathematical boundary. For the SV-wave case, the use of drilling degrees freedom is more effective by reducing numerical error at irregular frequencies.

• Journal of the Korean Mathematical Society
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• v.52 no.2
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• pp.373-388
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• 2015

In this paper, a novel parallel hybrid iterative method is proposed for finding a common element of the set of solutions of a system of equilibrium problems, the set of solutions of variational inequalities for inverse strongly monotone mappings and the set of fixed points of a finite family of nonexpansive mappings in Hilbert space. Strong convergence theorem is proved for the sequence generated by the scheme. Finally, a parallel iterative algorithm for two finite families of variational inequalities and nonexpansive mappings is established.

• Structural Engineering and Mechanics
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• v.19 no.2
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• pp.199-215
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• 2005

An assumed stress quadrilateral thin/moderately thick plate element HQP4 based on the Mindlin/Reissner plate theory is proposed. The formulation is based on Hellinger-Reissner variational principle. Static and free vibration analyses of plates are carried out. Numerical examples are presented to show that the validity and efficiency of the present element for static and free vibration analysis of plates. Satisfactory accuracy for thin and moderately thick plates is obtained and it is free from shear locking for thin plate analysis.