• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.344-347
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• 2000

We analyze the variation of coupling length as a function of the waveguide width for a directional coupler. It is interesting that the coupling length is not monotonic function of waveguide width for a given distance between the centers. The waveguide width for a maximum coupling length can be utilized for the optimum design of a directional coupler.

• Bulletin of the Korean Mathematical Society
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• v.58 no.2
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• pp.433-444
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• 2021

In this paper a new generating procedure of a random chord is presented. This problem has its roots in the Bertrand's paradox. A study of the limit behaviour of its maximum length and the rate of convergence is conducted. In addition, moments of record values of random chord length are obtained for this case, as well as other cases of solutions of Bertrand's paradox.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.121-127
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• 2003

Wave overtopping is one of the most important hydraulic responses of breakwater because it significantly affects its functional efficiency, the safety of transit and mooring on the rear side, wave transmission in the sheltered area, rear side armor stones and to some extent, the structural safety itself. In this study, hydraulic model tests has been carried out to investigate the influence of berm's size on overtopping rate by maximum overtopping rate and mean overtopping rate. The hydrodynamic characteristics of berm breakwater by the overtopping rate can be summarized as follows: 1. It is better to use maximum overtopping rate than to use mean overtopping rate for design of coastal structures in the point of view of stability. 2. When construct berm to decrease energy of waves that it was needed to make breaking conditions of wave on the berm. 3. Under the relative length of berm was over 0.13 overtopping rate was significantly decreased. 4. Overtopping rate affected significantly by the relative length of yhe berm than height of the berm.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1253-1261
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• 1993

Numerical analysis and measurements of the velocity and temperature distributions in buoyancy assisting laminar mixed convection flow over a vertically located, two-dimensional backward-facing step are reported. Laser-Doppler Velocimeter and Constant Temperature Anemometer operated in constant current were used to measure simultaneously the velocity and temperature distributions in the recirculation region downstream of the step. The reattachment length was measured by using flow visualization technique for different inlet velocities, wall temperatures and step heights. While the reattachment length $X_r$ increases as the inlet velocity or step height increase, it decreases as the buoyancy force increases, causing the size of the recirculation region to decrease. For the experimental range of $Gr_s$/$Re_{s}^{2}$$\times$$10^3$<17, a correlation equation for the reattachment length can be given by $X_{r}=1.05(2.13+0.021 Re_{s})exp$ $(-33.7_s^{-0.186}/Gr_{s}/Re_{s}^2).$ The Nusselt number is found to increase and the location of its maximum value moves closer to the step as the buoyancy force increases. The location of the maximum Nusselt number occurs downstream of the reattachment point, and distance between the reattachment point and the location of the maximum Nusselt mumber increases as the buoyancy force increases. Computational prediction agrees favorably well with measured results.

• Journal of the Korea Society of Computer and Information
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• v.17 no.9
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• pp.9-16
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• 2012

In this paper, we propose the two dimensional variable-length vector storage format which can be used for efficient storage of sparse matrix in the FEM (finite element method). The proposed storage format is the method storing only actual needed non-zero values of each row on upper triangular matrix with the total rows N, by using two dimensional variable-length vector instead of $N{\times}N$ large sparse matrix of entire equation of finite elements. This method only needs storage spaces of the number of minimum 1 to maximum 5 in 2D grid structure and the number of minimum 1 to maximum 14 in 3D grid structure of analysis target. The number doesn't excess two times although involving index number. From the experimental result, we can find out that the proposed storage format can reduce the memory space more effectively, as the total number of nodes increases, than the existing skyline storage format storing maximum column height.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.3
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• pp.236-247
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• 2015

In this paper, the experimental equipments for ventilated supercavitation in cavitation tunnel is constructed and the basic data of ventilated supercavitation regard to the entrainment coefficient and Froude number is fulfilled. The experiments are conducted for the disk cavitator with injecting air and the pressure inside cavity and the shape of cavity are measured. As the entrainment coefficient increases while the Froude number is kept constant, the ventilated cavitation number decreases to a minimum value which decreases no more even with increasing the air entrainment. The minimum value of ventilated cavitation number, caused by the blockage effect, decreases according to increasing the diameter ratio of test section to cavitator. The cavity length is rapidly enlarged near the minimum cavitation number. In low Froude numbers, the cavity tail is floating up due to buoyancy and the air inside the cavity is evacuated from its rear end with twin-vortex hollow tubes. However, in high Froude numbers, the buoyancy effect is almost negligible and there is no more twin-vortex tubes so that the cavity shape becomes close to axisymmetric. In order to measure the cavity length and width, the two methods, which are to be based on the cavity shapes and the maximum width of cavity, are applied. As the entrainment coefficient increases after the ventilated cavitation number gets down to the minimum cavitation number, the cavity length still increases gradually. These phenomenon can be confirmed by the measurement using the method based on the cavity shapes. On the other hand, when the method based on the maximum width of cavity is used, the length and width of the cavity agree well with a semi-empirical formular of natural cavity. So the method based on the maximum width of cavity can be a valid method for cavitator design.

• Journal of Biomedical Engineering Research
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• v.18 no.3
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• pp.253-259
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• 1997

Von Mises stress and compliance distribution was evaluated using a finite element analysis on the anastomosis of an artery with length of 20mm(z direction, along the horizental artery), inner diameter of 4mm, thickness fo 0.5mm and a PTFE graft with length of 5.7mm, inner diameter of 2mm, thickness of 0.2mm when anastomotic angle was $45^{\circ}$ and inner pressure of 1330 dyne/mm2 was applied inside the 2 conduits. From the analysis results were obtained as follows. (1) Artery diameter increased in both horizontal x(along the length of artery) and vertical y(perpendicular to the length of artery)directions and the magnitude of that in x direction was bigger than that in y direction. (2) The compliance was maximum on the anastomosis, especially on that with acute angle. The reduction of compliance was observed from the anastomosis area to the either right or left end. (3) The equivalent stress was maximum on top in the y direction and minimum on the nodes apart $110^{\circ}$ in circumferential direction from the top. (4) The equivalent stress was maximum in t도 vicinity of anastomosis with acute angle along the longitudinal direction of the artery. This trend was also observed along the PTFE graft.

• Restorative Dentistry and Endodontics
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• v.21 no.1
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• pp.70-86
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• 1996

The purpose of this study was to analyze the stress distribution in mandibular second premolars restored with different post and core techniques. Sixteen two-dimensional finite element model of mandibular second premolars restored with post and core and complete crown were developed according to the diameter, length, and material of post and core. Vertical force, 10N in magnitude, was applied first to the central fossa and then $45^{\circ}$ oblique force of same magnitude was applied to the buccal contact surface of buccal cusp. The obtained results were as follows : 1. Stress distribution within the dentin 1) Regardless of the material of the post and core and the diameter and length of the post, the pattern of stress distribution within the dentin was similar. 2) Maximum dentinal stress was observed on the lingual root surface of alveolar crest level with oblique loading and on lingual side of root dentin at the crown margin on vertical loading. 3) Cast post and cores produced the lowest dentinal stress concentrations and the highest stress concentration was observed in composite resin post and cores. 2. Stress distribution within the post and core 1) Within the amalgam and composite resin post and core, the patterns and maximum values of stress were similar. Maximum stress located at the central fossa of core portion on vertical loading and at the lingual junction of post and core with oblique loading. 2) Among the all post and cores, the cast post and core registered the highest stress concentration and maximum stress value within the post. Maximum stress located at the post apex on vertical loading and at lingual half of the post surface with oblique loading. 3) In case of Para-post and amalgam core, maximum stress located at the central fossa of core portion and lingual tip of the post head on vertical loading. With oblique loading, maximum stress located at the lingual half of the post surface.

• The Korean Journal of Cytopathology
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• v.17 no.2
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• pp.116-119
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• 2006

The diagnosis of papillary thyroid cancer is generally based on the findings of intranuclear cytoplasmic inclusions and nuclear grooves. Although anisokaryosis and poikilokaryosis, in papillary thyroid cancer, are not distinct when compared to other cancers, cytological examination can provide useful preoperative information. Our study evaluated the diagnostic role of computer-assisted image analysis for the pre-surgical assessment of papillary thyroid carcinoma. Thyroid aspirates from twenty female patients who were histologically confirmed to have both papillary carcinoma and benign nodules were studied. Different populations of 50 benign cells and 50 malignant cells were analyzed. Five morphometric parameters were selected for analysis: nuclear area, perimeter, maximum length, maximum width and intensity standard variation. The values obtained for papillary carcinomas were higher than the surrounding benign nodules as follows: nuclear area 63.5 vs. 36.1 (p=0.000), nuclear perimeter were 29.4 vs. 22.0 (p=0.000), maximum length 9.6 vs. 7.1 (p=0.000), maximum width 8.2 vs. 6.3 (p=0.000), the ratio between maximal length and maximal width 1.16 vs. 1.13 (p=0.000), the standard variation of intensity 14.9 vs. 15.9 (p=0.101) respectively. Therefore, morphometric information can be helpful for the differential cytological diagnosis of papillary thyroid carcinoma.

• Journal of Korean Society of Disaster and Security
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• v.10 no.1
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• pp.75-84
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• 2017

This study is concerned with the estimation of daily instantaneous maximum wind velocity in the meteorological major cities (selected each 17 points) during the yearly 1973-2016. The purpose of this paper is to present the turbulence statistic characteristics (probability distribution, correlation coefficient, turbulency intensity, shear velocity, roughness length, turbulence integral length, skewness, and kurtosis) of the daily instantaneous maximum wind velocity. In the processes of analysis, used observations data obtained at Korea Meteorological Adminstration (KMA). The estimation of non-Gaussian load effects for design applications has often been treated tacitly by invoking a conventional wind design load on the basis of Gaussian processes. This assumption breaks down when the instantaneous wind velocity processes exhibits non-Gaussianity. From the analysis results, the probability distribution of the daily instantaneous maximum wind velocity shows a very closed with non-Gaussian in the ensemble population 748, the correlation coefficient shows larger at inland area more than coastal area.