• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.242-245
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• 1999

In aerospace industry improvement of structural performance of flight structure without increasing weight has great advantage. In this study, an innovative design method to increase the buckling load and tension failure load at the same time without increasing the weight was investigated by using the curvilinear fiber format in composite plates with central hole. It was investigated how much gain can be obtained with curvilinear fiber format for the plates with different hole size and different stacking sequence.

• Journal of The Korean Astronomical Society
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• v.28 no.2
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• pp.147-152
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• 1995

An axisymmetric, stationary electrodynamic model of the central engine of an active galactic nucleus has been well formulated by Macdonald and Thorne. In this model the relativistic region around the central black hole must be filled by highly conducting plasma. We analyze plasma wave propagation in this region and discuss the results. We find that the ionosphere cannot exist right outside of the event horizon of the black hole. Another interesting aspect is that certain resonance phenomena can occur in this case.

• Journal of Mechanical Science and Technology
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• v.16 no.12
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• pp.1693-1701
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• 2002

The intermittent spray characteristics of a multi-hole and a single-hole diesel nozzle were experimentally investigated. The hole number of the multi-hole nozzle was 5, and the hole diameter of the 5-hole and the single-hole nozzle was the same as d$\_$n/=0.32 ㎜ with the constant hole length to diameter ratio(l$\_$n//d$\_$n/=2.81). The droplet diameters of the spray, including the time-resolved droplet diameter, SMD (Sauter mean diameter) and AMD (arithmetic mean diameter) , injected intermittently from the two nozzles into the still ambient were measured by using a 2-D PDPA (phase Doppler particle analyzer). Through the time-resolved evolutions of the droplet diameter, it was found that the structure of the multi-hole and the single-hole nozzle spray consisted of the three main parts : (a) the leading edge affected by surrounding air. and composed of small droplets; (b) the central part surrounded by the leading edge and mixing flow region and scarcely affected by the resistance of air, (c) the trailing edge formed by the passage of the central part. The SMD decreases gradually with the increase in the radial distance, and the constant value is obtained at the outer region of the radial distance (normalized by hole diameter) of 7-8 and 6 for the 5-hole and single-hole nozzle, respectively. The SMD along the centerline of the spray decrease shapely with the increase in the axial distance after showing the maximum value near the nozzle tip. The SMD remains the constant value near the axial distance(normalized by hole diameter) of 150 and 180 for the 5-hole and the single-hole nozzle, respectively.

• Publications of The Korean Astronomical Society
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• v.7 no.1
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• pp.71-77
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• 1992

An axisymmetric, stationary electrodynamic model of the central engine of an active galactic nucleus has been well formulated by Macdonald and Thorne. In this model the relativistic region around the central black hole must be filled by highly conducting plasma and the equations of magnetohydrodynamics are then satisfied. In this paper we analyze magnetohydrodynamic wave propagation in this region. We find that there are three distinct types of waves - the Alfven wave and two magnetosonic waves. The wave equations turn out to be not very different from those in nonrelativistic case except they are redshifted.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.212-216
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• 2007

Predicting microcracking properties of the composite laminates in nonuniform stress conditions was the subject in this paper. The uniform stress field meant the stresses were independent of the width direction. The material was the 954-2A/IM7 laminates containing a central hole. Microcracks initiated at the edge of the hole and propagated into the laminate. Because the tensile stress concentration decreased with distance, the microcracks were arrested before the edge of the laminate. Because carbon fiber composites were opaque, a x-ray method was used to detect the length of the propagating microcracks. The microcracking at the near edge of the hole could be reasonably predicted by considering the local laminate stresses and the microcracking toughness measured in unnotched laminates. However, the date away from the hole did not agree with the predictions. The local microcrack density was always much higher than that predicted by the local laminate stress.

• Structural Engineering and Mechanics
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• v.58 no.5
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• pp.783-797
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• 2016

Exact solutions for stresses, strains, and displacements of a perforated rectangular plate by an arbitrarily located circular hole subjected to both linearly varying in-plane normal stresses on the two opposite edges and in-plane shear stresses are investigated using the Airy stress function. The hoop stress occurring at the edge of the non-central circular hole are computed and plotted. Stress concentration factors (the maximum non-dimensional hoop stresses) depending on the location and size of the non-central circular hole and the loading condition are tabularized.

• Journal of The Korean Astronomical Society
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• v.28 no.1
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• pp.71-75
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• 1995

In the previous work we made a long term evolution code for the central black hole in an active galactic nucleus under the assumption that the Blandford-Znajek process is the source of the emission. Using our code we get the evolution of the angular velocity of the precession for a supermassive black hole. We consider a hole at the center of an axisymmetric, ellipsoidal galactic nucleus. Our numerical results show that, only for the cases such that the stellar density or the mass of the black hole is large enough, the precession of the black hole - presumably the precession of the galactic jet - is interestingly large.

• Publications of The Korean Astronomical Society
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• v.18 no.1
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• pp.11-14
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• 2003

In the earlier papers we analyzed the axisymmetric, nonstationary electrodynamics of the central black hole and a surrounding thin accretion disk in an active galactic nucleus. Based on those papers we analyze the axisymmetric, nonstationary force-free black hole magnetosphere and the motion of the plasma. We concentrate on deriving the totally new equations for the entropy incrrease and the angular momentum, energy extraction of the black hole.

• Journal of KSNVE
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• v.4 no.3
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• pp.283-295
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• 1994

This work presents the experimental and finite element analysis results for the free vibration of 4 edges clamped, isotropic square plates with 2 collinear circular holes. Natural frequencies of finite element analysis are obtained for the complete square plate, the square plates with a central circular hole and the square plates with 2 collinear circulare holes. And natural frequencies are experimentally measured for the complete square plate, the square plate with a central circular hole(d = 150 mm) and the square plates with 2 collinear circular holes. Agreement between experimental and FEM results is excellent. Mode shapes in special case are presented. The conclusions of the study are as follows. There is little variation of nondimensional frequency parameters for the first six mode when the aspect ratio of circular hole is less than 1/6 in the isotropic square plates with 2 collinear circular holes. And the first nondimensional frequency parameter doesn't vary as the aspect ratio of circular hole increase.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.345-347
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• 2015

We present evolutionary models of rotating self-gravitating systems (e.g. globular clusters, galaxy cores). These models are characterized by the presence of an initial axi-symmetry due to rotation. Central black hole seeds are included in our models, and black hole growth due to the consumption of stellar matter is simulated until the central potential dominates the kinematics of the core. Our goal is to study the long-term evolution (Gyr) of relaxed dense stellar systems which deviate from spherical symmetry, and their morphology and final kinematics. With this purpose in mind, we developed a 2D Fokker-Planck analytical code, and confirmed its results using detailed N-Body simulations, applying a high performance code developed for GPU machines. We conclude that the initial rotation significantly modifies the shape and lifetime of these systems, and cannot be neglected in the study of the evolution of globular clusters, and the galaxy itself. Our models give a constraint for the final intermediate black hole masses expected to be present in globular clusters.