• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.10
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• pp.954-961
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• 2008

An experimental study has been conducted to investigate the flow field around the wing having a circular damage hole. The damage was represented by a circular hole passing through the model with 10% airfoil chord diameter and normal to the chord. The hole was centered at quarter or half chord. The PIV flow fields and static pressure measurements on the wing upper and lower surface were carried out at Rec=2.85×105 based on the chord length. The PIV results showed the two types of flow structures around a damage hole were formed. The first one was a weak jet that formed an attached wake behind the damage hole. The second one resulted from increased incidence; this was a strong jet where the flow through the hole penetrates into the free-stream resulting in extensive separation of oncoming boundary layer flow and development of a separated wake with reverse flow. The surface pressure data showed a big pressure alteration near the circular damage hole. The severity of pressure alteration was increased as a damage hole located nearer to the leading edge.

• Structural Engineering and Mechanics
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• v.81 no.1
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• pp.39-50
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• 2022

Layer separation (delamination) is an essential threat to fiber-reinforced polymer (FRP) plates under dynamic, static, and fatigue loads. Under compressive load, the growth of delamination will lead to structural instability. The aim of this paper is to present a method using shape memory alloy (SMA) stitches to suppress the delamination growth in a FRP plate and to improve the buckling behavior of the plate with a rectangular hole. The present paper is divided into two parts. Firstly, a closed-form (CF) formulation for evaluating the buckling load of the FRP plate is presented. Secondly, the finite element method (FEM) will be employed to calculate the buckling loads of the plates which serves to validate the results obtained from the closed-form method. The novelty of this work is the development of the closed-form solution using the p-Ritz energy approach regarding the stress-dependent phase transformation of SMA to trace the equilibrium path. For the FEM, the Lagoudas constitutive model of the SMA material is implemented in FORTRAN programming language using a user material subroutines (VUMAT). The model is simulated in ABAQUS/Explicit solver due to the nature of the loading type. The cohesive zone model (CZM) is applied to simulate the delamination growth.

• Tribology and Lubricants
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• v.18 no.6
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• pp.384-388
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• 2002

The adequate design of a passenger car braking system, which is directly related to the safety of a car, is very important since the safety is an essential design parameter of a car to keep men and car from the damage. The thermal behaviors of the ventilated disk has been investigated based on the air cooling effects during repeat braking operations. In this study, the thermal behavior of ventilated disk brake system was investigated by numerical method. The 3-Dimensional unsteady model was simulated by using a general purpose software package “FLUENT” to obtain the temperature distributions of disk and pad. The model includes the more realistic braking method, which repeats braking and release. The effects of aspect ratio of ventilated hole on the heat dissipation was investigated.

• Journal of The Korean Astronomical Society
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• v.23 no.1
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• pp.63-70
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• 1990

The original axisymmetric, stationary electrodynamic model of the central engine in an active galactic nucleus proposed by Macdonald and Thorne consists of a supermassive black hole with magnetic field lines that pass through the region just outside the event horizon of the black hole. Each magnetic field line rotates with a constant angular velocity which will exceed the speed of light at large radii. Even though the field lines are purely mathematical entities this condition sets a stringent physical constraint on the motion of the magnetic field lines and the particles on them. In this paper we will show that we can remove this auxiliary constraint in our model by allowing nonstationary processes. As a result the magnetic field lines can be twisted and wound up in a region lying outside of the quasi-stationary magnetosphere of the black hole. We conclude that astrophysical jets are formed in that region due to the twisted and wound magnetic field lines powered by the Blandford-Znajek process and the other driving forces.

• Water Engineering Research
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• v.3 no.3
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• pp.155-162
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• 2002

This study presents the theoretical approach for volume concentration, velocity profile, and granular discharge on the fluid-granule mixed flow downstream of the scour hole at the outlet of the hydraulic structure. Concept of dilatant model was applied for the stress-strain relationships of fluid-granule mixed flow since the flow downstream of the scour hole corresponds to debris flow, where momentum transfers through particle collisions. Mathematical formulations were derived using momentum equation and stress-strain relation of the fluid-granule mixture. Velocity profile under the assumption of uniform concentration over flowing layer showed the downward convex type. Deposition angle of downstream hump was found to be a function of an upstream slope angle, a dynamic friction angle and a volume concentration irrespective of flow itself, Granular discharge and the overflow depth were obtained with given values of inflow rates. Experimental results showed relatively good agreements with theoretical ones.

• Journal of the Korean Society of Visualization
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• v.20 no.2
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• pp.28-37
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• 2022

Flow characteristics of jet impingement over concave hemispherical surface with effusion cooling holes is relatively more complex than that of a flat surface, so the experimental validation for computational fluid dynamics (CFD) results is important. In this study, experimental results were compared with simulation results obtained by assuming different turbulence models. The vortex was observed in the region between the central jets where the recirculation structure appeared. The different patterns of vorticity distributions were observed for each turbulence models due to different interaction of the injected jet flow. Among them, the transition k-kl-ω model predicted similarly not only the jet potential core region with higher velocity, but also the recirculation region between the central jets. From the validation, it may be helpful to accurately predict heat and mass transfer in jet impingement/effusion hole system.

• International conference on construction engineering and project management
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• 2009.05a
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• pp.1053-1059
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• 2009

Construction system modeling can enhance work performance by following the behaviors of a system. System behaviors may originate from physical aspects of a system, namely operation level variables, or from non-physical aspects of a system known as context level variables. However, construction system modelers usually focus on only one type of system variable (i.e., operation level or context level) which can lead to less accurate results. Hybrid modeling with System Dynamics (SD) and Discrete Event Simulation (DES) is one of the approaches that has been utilized to address this issue. In this research, an SD-DES hybrid model of a steel fabrication shop is developed, and the benefits of capturing context level variables together with operation level variables in the model are discussed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.2
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• pp.163-173
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• 2012

This study covers the nonlinear analysis of anchor head for high strength prestressing strand and presents necessary process in improving the performance of anchor head. The surface of wedge for strand is contacted to the surface of the wedge hole on anchor head when it is fitted into the wedge hole, and the contact condition changes according to the level of load applied through the wedge. In order to analyze detailed behavior, nonlinear material model and contact element were used in analysis. It was found from the analysis that the behavior of anchor head is affected by the interaction with the wedge contacted so that the wedge in FE model should have the same figure as the actual object. Circular array of wedge hole presents better stress distribution than layer array even though the small difference in maximum deformation. Increment of thickness of anchor head and distance of wedge hole also improve the performance of anchor head.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.4
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• pp.67-80
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• 1989

This Paper is concerned with the fracture behavoir of Unidirectional Laminate(UD) and the characteristic length of Multidirectional Laminate(MD) around hole under the Uniform Tensial Strain. Two fracture mechanical concepts of the Waddoups-Eisenman-Kaminski(WEK) model based on the Linear Elastic Fracture Mechanics(LEFM) and the Whitney-Nuismer Model based on Point and Average Stress Criteria were applied. The characteristic length of a laminate with a hole is then obtained using the coefficient of stress reduction and the experimental results, and it can be utilized in predicting the stress level at which the specimen will fracture. The results of the fracture characteristics and the strength of the specimens having a hole in the center can be used as the important experimental data in the research branch of the mechanical fastening of laminated structures. The Ultrasonic scanning and the Acoustic Emission(AE) method were utilized in order to find out the initial defects and the fracture behavior, respectively.

• Publications of The Korean Astronomical Society
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• v.10 no.1
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• pp.79-90
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• 1995

The unique compact radio source, Sgr $A^*$, at the Galactic center show many observational signs that it is powered by supermassive black hole. Recent observations also imply that it is surrounded by winds from nearby IR sources. So we explore the model in which multiwavelength spectrum from Sgr $A^*$ is due to the spherical accretion of these winds onto the central supermassive black hole. Improving upon the previous work, we allowed the possibility that ions and electrons have different temperatures, included the Compton effects and pair processes. Electrons radiate via cyclosynchrotron and bresstrahlung with comptoniztion. We find that ion approaches the virial temperature ${\sim}10^{13}K$ while electron temperature saturates at ${\sim}10^{10}K$. However, decoupling between ion and electron does not greatly affect the shape of the emission spectrum. When the mass of the black hole is ${\sim}10^6M_{\odot}$, radio, IR, X-ray, $\gamma$-ray band spectrum is reasonably explained by the model. Yet Compton effect which is neglected in previous works produces significant emission in IR band, which is marginally compatible with observations. Pair production is negligible and annihilation lines cannot be observed.