• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.904-913
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• 2002

In this paper, the dynamic stress intensity factors of fracture mechanics are numerically computed in time domain using the FEM. For which the finite element formulations are derived applying the Galerkin method to the equations of motion in convolution integral as has been presented in the previous paper. To assure the strain fields of r$^{-1}$ 2/ singularity near the crack tip, the triangular quarter-point singular elements are imbedded in the finite element mesh discretized by the isoparametric quadratic quadrilateral elements. Two-dimensional problems of the elastodynamic fracture mechanics under the impact load are solved and compared with the existing numerical and analytical solutions, being shown that numerical results of good accuracy are obtained by the presented method.

• Journal of the Optical Society of Korea
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• v.15 no.3
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• pp.283-288
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• 2011

In this study, a wide-band photonic crystal Y-splitter for TE modes is proposed. A triangular lattice of air holes etched in a GaAs slab is used as the platform. In order to numerically analyze the structures, plane wave expansion (PWE) and finite difference time domain (FDTD) methods are used. In comparison with the structures reported in the literature, the proposed topology has a less complexity while it provides more than 100nm bandwidth. The simplicity of the design, its high transmission ratio and its wide bandwidth makes it a suitable choice for the implementation of photonic crystal integrated circuits.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.36-41
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• 1998

The cross-flow fan performance and its sound noise characteristics are predicted by computational methods. The unsteady incompressible Navier-Stokes equations in moving coordinates are solved by a SMAC method on unstructured triangular meshes, using a sliding mesh technique at the interface between the domain rotating with blades and the rest stationary part. The computationally predicted fan performance was favorably compared with experiment, and some numerical aspects of simulating the cross-flow fan are discussed. With the computed unsteady flow field, aeroacoustic sound noise of the fan is predicted by the Lighthill-Curie equation. The unsteady surface pressure fluctuations on stabilizer enables a prediction of BPF noise of the uniform pitch blade fan quite accurately. The aeroacoustic sound noise characteristics of both uniform and random pitch blade fans are also examined by SPL spectrum analysis.

• Journal of Mechanical Science and Technology
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• v.17 no.1
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• pp.64-76
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• 2003

In this work, a new penalty formulation is proposed for the analysis of Mindlin-Reissner plates by using the element-free Galerkin method. A penalized weak form for the Mindlin-Reissner Plates is constructed through the exterior penalty method to enforce the essential boundary conditions of rotations as well as transverse displacements. In the numerical examples, some typical problems of Mindlin-Reissner plates are analyzed, and parametric studies on the order of integration and the size of influence domain are also carried out. The effect of the types of background cells on the accuracy of numerical solutions is observed and a proper type of background cell for obtaining optimal accuracy is suggested. Further, optimal order of integration and basis order of Moving Least Squares approximation are suggested to efficiently handle the irregularly distributed nodes through the triangular type of background cells. From the numerical tests, it is identified that unlike the finite element method, the proposed element-free Galerkin method with penalty technique gives highly accurate solution without shear locking in dealing with Mindlin-Reissner plates.

• Ocean Systems Engineering
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• v.3 no.2
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• pp.149-165
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• 2013

Tension leg platforms (TLP's) are highly nonlinear due to large structural displacements and fluid motion-structure interaction. Therefore, the nonlinear dynamic response of TLP's under hydrodynamic wave loading is necessary to determine their deformations and dynamic characteristics. In this paper, a numerical study using modified Morison Equation was carried out in the time domain to investigate the influence of nonlinearities due to hydrodynamic forces and the coupling effect between all degrees of freedom on the dynamic behavior of a TLP. The stiffness of the TLP was derived from a combination of hydrostatic restoring forces and restoring forces due to cables and the nonlinear equations of motion were solved utilizing Newmark's beta integration scheme. The effect of wave characteristics was considered.

• Korean Journal of Computational Design and Engineering
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• v.8 no.4
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• pp.270-277
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• 2003

In two dimensional mechanical design analysis, quadrilateral element mesh is preferred because it provides more accurate result than triangular element mesh. However, automation of quadrilateral element mesh generation is much more complex because of its geometrical complexities. In this study, an automatic quadrilateral element mesh generation algorithm based on the boundary normal offsetting method and the boundary decomposition method is developed. In so doing, nodes are automatically placed using the boundary normal offsetting method and the decomposition method is applied to decompose the designed domain into a set of convex subdomains. The generated elements are improved by relocation of the existing nodes based on the four criteria - uniformity, aspect ratio, skewness and taper degree. The developed algorithm requires minimal user inputs such as boundary data and the distance between nodes.

• 한국전산유체공학회:학술대회논문집
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• 1996.05a
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• pp.111-117
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• 1996

The Delaunay triangulation technique was tested for complicated shapes of computational domain. While a simple geometry, both in topology and in geometry, was discretized well into triangular elements. a complex geometry often failed in triangularization. A complex geometry should be devided into smaller sub-domains whose shape is simple both topologically and geometrically. The present study developed the data structures not only for relationships among neibering elements but also for shape information, and coupled these into the Delaunay triangulation technique. This approach was able to enhance greatly the reliability of triangularization specially in complicated shapes of computational domains. The GUI (Graphic User Interface) and OOP (Object-Oriented Programming) were used in order to develop the user-friendly and efficient computer code.

• Proceedings of the KIEE Conference
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• 1987.11a
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• pp.33-36
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• 1987

Is this study it is proposed a method which is able to compute preciously using time-difference method to the air-gap magnetic field in electric machines take into account of eddy current induced. The air-gap magnetic field has slot harmonics which are due to the structure of machines and the shape of slot harmonics varies with the related positions of slots when the rotor moves. Accordingly, considering the influence of slot-harmonics, we coupled macro-air-gap element with first-order triangular elements in domain and used direct-convergence method for magnetic saturation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.8
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• pp.45-51
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• 2000

The distortion of an electrical pulse, which has a rise/fall time due to the dispersion and the reflection, on tapered microstrip lines has investigated In time domain. The voltage and current transfer functions are shown for the tapered line. The dispersion distortion obtained by using these trans(or functions are represented for the nonideal square pulse along the triangular, Tchebycheff and exponential tapered lines, and analyzed the influence of the reflection and the frequency dispersion on the distorted voltage wave in the tapered lines. The observed overshoot in front of the distorted wane is caused due to the frequency dispersion and the sustained tail of that comes from the reflection in the tapered line.

• Korean Journal of Computational Design and Engineering
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• v.14 no.3
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• pp.197-206
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• 2009

In a finite element analysis of the metal forming processes having large plastic deformation, largely distorted elements are unstable and hence they influence upon the result toward negative way so that adaptive remeshing is required to avoid a failure in the numerical computation. Therefore automatic mesh generation and regeneration is very important to avoid a numerical failure in a finite element analysis. In case of generating quadrilateral mesh, the automation is more difficult than that of triangular mesh because of its geometric complexity. However its demand is very high due to the precision of analysis. Thus, in this study, an automatic quadrilateral mesh generation and regeneration method using grid-based approach is developed. The developed method contains decision of grid size to generate initial mesh inside a two dimensional domain, classification of boundary angles and inner boundary nodes to improve element qualities in case of concave domains, and boundary projection to construct the final mesh.