• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.531-537
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• 2016

The damage and fracture of machine or structure are caused by the crack happened from the defect existed at the inside of material. The properties of crack propagation and growth characteristic must be considered because there are many cases at which these cracks are densely existed. Therefore, this study investigates the fracture property due to the position of crack and hole inside the standard compact tension (C. T.) specimen. When the concentrated load is applied eccentrically at the standard C. T. specimen, the fracture mechanical behavior due to the existence or non-existence and the position of hole near crack is investigated. As the result of analysis study, model 3 (in case of the distance of 2mm on the horizontal direction between the end part and hole as the specimen model existed with one hole near the crack) has the maximum deformation, stress and deformation energy of the most values among three models. As the distance between the crack and hole inside the specimen becomes nearer, the maximum stress becomes higher in cases of three models. Apart from the number of holes, it is seen that the maximum stress becomes higher near the crack when the hole exists near the crack inside the specimen. If the hole inside the machine or the mechanical structure is punctured by using the result of this study, it is thought that the occurred breakage or breakdown can be prevented by reducing the fracture stress happened at the specimen.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.237-240
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• 2003

Deformation surrounding the hole in the tube during the hydro-piercing process has been investigated in this study. The tube is expanded and internally pressurized between upper and lower dies, and a piercing punch is driven forcefully through a cross passage in the die and through the wall of the tube. The pressurized fluid within the tube provides support to the wall of the tube during a piercing step to form a hole in the tube having less deformation surrounding the hole in the tube. The deformation area may be fully retracted to a substantially flat form or partially retracted to a countersunk form. In this study, a mathematical model that can predict deformation surrounding the hole has been proposed and experimentally verified by actual hydro-piercing test.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.435-441
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• 2010

In this study, numerical simulations were carried out to investigate the effect of verification core hole on the shaft tip capacity. The verification core extreted at shaft tip may deteriorate the shaft tip capacity when the clay shales (Taylor Marl) surrounding the shaft degrades and the empty core hole remains unfilled. Series of finite element analyses were conducted using Mohr-Coulomb model with total stress material parameters that were obtained from laboratory testing. The numerical analyses indicate that the shaft tip capacity does not decrease for most cases, and the maximum reduction does not exceed 5%.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.671-674
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• 2002

Pressure compensating temperature control valve(TCV) is one of the important control devices, which is used to maintain the constant temperature of working fluid in power and chemical plants. The ratio of cylinder hole diameters of inlet and outlet is the main design parameters of TCV. So this needs to be investigated to improve the function of control of temperature and void fraction. In this study, numerical analysis is carried out with various ratios of cylinder hole diameters of the inlet and outlet in the TCV. Especial1y, the distribution of the static pressure Is investigated to calculate the new coefficient($C_{\upsilon}$) and resistance coefficient(K). The governing equations are derived from making using of three-dimensional Naver-Stokes equations with standard $k-{\varepsilon}$ turbulence model and SIMPLE algorithm. Using a commercial code, PHOENICS, pressure and flow fields in TCV are calculated with different inlet and outlet diameters of the cylinder hole for cold and hot water passages.

• The KSFM Journal of Fluid Machinery
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• v.17 no.2
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• pp.12-23
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• 2014

A parametric study on anti-vortex holes for turbine blade cooling was investigated numerically. Three-dimensional Reynolds-averaged Navier-Stokes equations and shear stress transport turbulence model were used for analysis of anti-vortex film cooling. Validation of numerical results was carried out comparing with experimental data. The cooling performance of anti-vortex holes was assessed by two geometric variables, the ratio of diameters of holes and the lateral distances between the primary hole and anti-vortex hole at blowing ratios of 0.5 and 1.0. The results showed that the spatially-averaged film-cooling effectiveness increases as the ratio of the diameters increases and the distance between the primary hole and anti-vortex hole decreases.

• Journal of Astronomy and Space Sciences
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• v.38 no.1
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• pp.39-44
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• 2021

In the general accretion disk model theory, the accretion disk surrounding an astronomical object comprises fluid rings obeying Keplerian motion. However, we should consider relativistic and rotational effects as we close in toward the center of accretion disk surrounding spinning compact massive objects such as a black hole or a neutron star. In this study, we explore the geometry of the inner portion of the accretion disk in the context of Mukhopadhyay's pseudo-Newtonian potential approximation for the full general relativity theory. We found that the shape of the accretion disk "puffs up" or becomes thicker and the luminosity of the disk could exceed the Eddington luminosity near the surface of the compact spinning black hole.

• Explosives and Blasting
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• v.36 no.2
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• pp.1-9
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• 2018

In this paper, AUTODYN blasting simulation of single blast hole were conducted to evaluate the blasting effects of Polymer Gel. The coupling mediums used as the filling material around an explosive charge were air and gelatin. each simulation case was D I(decoupling index) 1.0, 1.25, 1.56 with air or polymer gel coupling materials. In order to evaluate blast effects full charge model was used as a reference for evaluation of blasting effects. The results of numerical analysis showed that fragmentation of a limestone model of were much more fractured by polymer gel medium than by air medium. As expected, the transmitted peak pressure was higher polymer gel coupled model than in air medium.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.2
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• pp.413-421
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• 1990

Acoustic emission signals due to leak from circular holes of 0.4, 1, 2 and 4mm diameter and rectangular slits of different geometry having the same cross section as 4mm diameter hole was studied both analytically and experimentally. Acoustic emission signals from a wide-band type transducer were transformed to digital signals through a digital oscilloscope, and $V_{rms}$ and frequency spectrum were obtained by processing digital signals. Relationships between acoustic parameters and fluid mechanical parameters were derived analytically. A quadrapole aerodynamic model was applied in the analysis of leak from the circular holes and $V_{rms}$ was found to be proportional to the root square of leak rate through the circular hole. A modified model based on dipole source mechanism and laminar equivalent diameter was applied in the analysis of leak signals from the rectangular slits. In the case of constant pressure, $V_{rms}$ increased as the laminar equivalent diameter of slit decreased. In the case of constant laminar equivalent diameter, however the result was similar to that for leak from the circular hole. The frequency spectra of leak signals shows the same frequency characteristics irrespective of the pressure difference.rence.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.2053-2061
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• 1994

The static and fatigue tensile tests have been conduted to predict the fatigue life of 8-harness satin woven and plain woven carbon/epoxy composite plates containing a circular hole. A fatigue residual strength degradation model, based on the assumption that the residual strength for unnotched specimen decreases monotonically, has been applied to predict statistically the fatigue life of materials used in this study. To determine the parameters(c, b and K) of the residual strength degradation model, the minimization technique and the maximum likelihood method are used. Agreement of the converted ultimate strength by using the minimization technique with the static ultimate strength is reasonably good. Therefore, the minimization technique is more adjustable in the determination of the parameter and the prediction of the fatigue life than the maximum likelihood method.

• Electrical & Electronic Materials
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• v.8 no.1
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• pp.64-70
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• 1995

We discussed the thermal analysis for a recording media with the variation of the laser pulse duration, the laser power and the temperature distribution in order to optimize the Te-based antireflection structure from the computer calculations. In the case that the radial heat diffusion is negligible, we can calculate the maximum temperature of the recording layer at the center of the spot by the Simple Model. The temperature profile of the recording layer is obtained from the Numerical Model by considering the total specific heat and the latent heat. As a result, the effect of the heat sinking acting as a thermal loss for the hole formation could be minimized by introducing the pulse with the hole formation duration(.tau.) below the thermal time constant(.tau.$_{D}$) of a dielectric layer. These requirments can be satisfied by using the dielectric thickness of the 2nd ART(Anti-Reflection Trilayer) condition or the dielectric materials with a low thermal diffusivity.y.