• Journal of KSNVE
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• v.6 no.6
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• pp.827-834
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• 1996

The effect of pipe breaks in the secondary side is investigated as a part of the fuel assembly qualification program. Using the detailed dynamic analysis of a reactor core, peak responses for the motions induced from pipe breaks are obtained for a detailed core model. The secondary side pipe breaks such as main steam line and economizer feedwater line braksare considered because leak-before-break methodology has provided a technical basis for the elimination of double ended guillotine breaks of all high energy piping systems with a diameter of 10 inches or over in the primary side from the design basis. The dynamic responses such as fuel assembly shear force, bending moment, axial force and displacement, and spacer grid impact loads are carefully investigated. Also, the stress analysis is performed and the effect of the secondary side pipe breaks on the fuel assembly structural integrity under the faulted condition is addressed.

• Solar Energy
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• v.17 no.3
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• pp.59-66
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• 1997

The present study adopted the PTV method for the velocity acquisition. The system consists of an image grabber built-in a personal computer and a laser-based sheet light projector and particle identification softwares. Velocity vectors are obtained, by PTV and they are used as velocity components for Poisson equation for pressure. Related boundary conditions and no-slip condition at solid wall and the linear velocity extrapolation on the upper side of cavity are well examined for the present study. For calculation of pressure, resolution of grid is basically $40{\times}40$ and 2-dimensional uniform mesh using MAC staggered grid is adopted. The result of experiment reveal that, newly suggested measuring method is capable of estimating pressure and velocity distribution of flow field reasonably.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.311-317
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• 2011

The present paper deals with the continuous works of extending the multi-dimensional limiting process (MLP) for compressible flows, which has been quite successful in finite volume methods, into discontinuous Galerkin (DG) methods. From the series of the previous, it was observed that the MLP shows several superior characteristics, such as an efficient controlling of multi-dimensional oscillations and accurate capturing of both discontinuous and continuous flow features. Mathematically, fundamental mechanism of oscillation-control in multiple dimensions has been established by satisfaction of the maximum principle. The MLP limiting strategy is extended into DG framework, which takes advantage of higher-order reconstruction within compact stencil, to capture detailed flow structures very accurately. At the present, it is observed that the proposed approach yields outstanding performances in resolving non-compressive as well as compressive flaw features. In the presentation, further numerical analyses and results are going to be presented to validate that the newly developed DG-MLP methods provide quite desirable performances in controlling numerical oscillations as well as capturing key flow features.

• Journal of computational fluids engineering
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• v.19 no.2
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• pp.49-57
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• 2014

In the present study, 2-D gas-kinetic flow solver on unstructured meshes was developed for flows from continuum to transitional regimes. The gas-kinetic BGK scheme is based on numerical solutions of the BGK simplification of the Boltzmann transport equation. In the initial reconstruction, the unstructured version of the linear interpolation is applied to compute left and right states along a cell interface. In the gas evolution step, the numerical fluxes are computed from the evaluation of the time-dependent gas distribution function around a cell interface. Two-dimensional compressible flow calculations were performed to verify the accuracy and robustness of the current gas-kinetic approach. Gas-kinetic BGK scheme was successfully applied to two-dimensional steady and unsteady flow simulations with strong contact discontinuities. Exemplary hypersonic viscous simulations have been conducted to analyze the performances of the gas-kinetic scheme. The computed results show fair agreement with other standard particle-based approaches for both continuum part and transitional part.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.75-78
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• 2004

A mesh generation algorithm adapted to the mesh density map using the Delaunay mesh generation technique is developed. In the finite element analyses of the forging processes, the numerical error increases as the process goes on because of discrete property of the finite elements or severe distortion of elements. Especially, in the region where stresses and strains are concentrated, the numerical discretization error will be highly increased. However, it is too time consuming to use a uniformly fine mesh in the whole domain to reduce the expected numerical error. Therefore, it is necessary to construct locally refined mesh at the region where the error is concentrated such as at the die corner. In this study, the point insertion algorithm is used and the mesh size is controlled by moving nodes to optimized positions according to a mesh density map constructed with a posteriori error estimation. An optimization technique is adopted to obtain a good position of nodes. And optimized smoothing techniques are also adopted to have smooth distribution of the mesh and improve the mesh element quality.

• Journal of radiological science and technology
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• v.37 no.2
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• pp.93-100
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• 2014

Recently the development of portable digital wireless imaging system, which acquires digital radiation images by using wireless LAN telecommunications function in an easy and fast way, provides lots of convenience for people. Considering the characteristics of portable imaging tests on emergency and critical patients, this study aims to suggest guidelines for Digital wireless detector by evaluating the effect of de-centering of focus-grid and displacement of subject in detector on the quality of image. The equipments used for this study were Elmo-T6 Digital Mobile X-ray system (SIMAZU Corp.), el' Tor ($14{\times}17$ "Wireless detector), Grid (10:1) and Chest & head phantom. After acquiring post-processing image according to dose increase and de-centering image of grid-focus and head phantom displacement image, this study compared, analyzed and evaluated these images by using a digital image analysis program by Image J. In the change of images based on dose increase, images were rough in the dose of 0.5 mAs, while there was no difference among images in the proper dose of 1~2 mAs and, especially from 2.5 mAs, average value of pixels radically decreased, affecting contrast. Over 3 mAs, contrast dropped due to saturation phenomenon of lungs. As the result of analysis using Image J program, with the increase of displacement between focus-grid and head phantom, the frequency of low pixel value also increase, causing the outline of surface image to disappear, which in turn affects contrast. For better quality imaging, a radiographer must be aware before the time of test that the image quality can be changed based on the critical patient's posture, movement, respiration, displacement of X-ray tube and distance of imaging.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.10
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• pp.90-97
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• 1996

A numerical method for scattering of electromagnetic waves from a periodic strip grating over a grounded dielectric slab is considered for TE and TM polarization cases from the viewpoints of both reflection grating problem and leaky wave antenna problem. The analysis is based on a mode expansion method, floquet's theorem, and the method of moments. Numerical results involving some combinations of geometric parameters are presented in terms of complex propagation constant (kd-$\beta$d diagram), radiation pattern, and relative scattered powers of spectral modes. In particular, the relationship between complex propagatio constnat form the viewpoint of leaky wqve antenna problem and Off-bragg and bragg blazing phenomena from the viewpoint of reflecton graing problem is investigated.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.665-668
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• 1997

We fabricated a number of optical fiber Bragg gratings by varying the UV beam parameters such as the laser energy density, pulse repetition rate and exposing time. The reflectance and the Bragg wavelength shift of the fiber Bragg gratings formed with a KrF excimer laser in real time depend strongly on the UV beam parameters. The index changes in the gratings during the exposing time are well fitted to the well known equations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.10
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• pp.2710-2723
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• 1996

2-dimensional scattering problem of electromagnetic waves by a periodic strip grating on a grounded dielectric slab in case of oblique incidence and arbitrary polarization is analyed by the vector Floquet modal expansion method. Solution convergence versus number of Chebyshev polynomial terms representing the unknown strip current density and number of space harmonics is examined, and some numerical results such as variation of power of significant space harmonics(scattered mode) are compared with those obtained by previous method. In particaluar, the relationship between Bragg blazing phonmena and characteristics mode(current) on the srip is discussed in detail.

• Korean Journal of Optics and Photonics
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• v.10 no.5
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• pp.424-429
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• 1999

The amplifier properties of single distributed feedback dye laser with 106 ps pulse width and 616 nm wavelength were invested using only one XeCl-excimer laser as pump source. For optimized amplification of DFDL, the three-stage amplifiers were arranged with increasing cross-section and accordingly increasing pump energies. The first AmpI, II stages were dye cell of 5 mm, 10 mm and contained a $6{\times}10^{-4}$ [mol/l](solvent : Methanol) of Rhodamine 610. Double-pass amplification in the AmPII was measured to suppress the ASE by using a diffraction grating. The beam intensity of AmpI, II was saturated with a gain of respectively 10 and 48. The last AmpIII was Bethune cell of 30 mm and contained a $3{\times}10^ {-4}$ [mol/l] (solvent : Ethanol) of Rhodamine 610. In the single-pass and double-pass amplification, the output energy was obtained 168.2 $\mu$J and 471$\mu$J respectively.