• Proceedings of the Korea Society for Simulation Conference
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• 2000.11a
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• pp.165-173
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• 2000

Analytic models have been developed to solve integrated production-distribution problems in supply chain management (SCM). As one of major constraints in analytic models, capacity, which is the total operation time in this paper has mostly been known or disregarded assuming infinite capacity. Also, as major factors, machine processing time to fabricate or assemble a part or product at a certain machine center in production system and vehicle processing time to deliver a product to a customer by a certain vehicle in distribution system have been fixed and regarded as a static factor, But in the real systems significant differences exit between capacity and the required time to achieve the production-distribution plan and between processing time and consumed time to process a part or product. In this paper, capacity and processing times in the analytic model are considered as dynamic factors and adjusted by the results from independently developed simulation model, which includes general production-distribution characteristics. Through experiments, we obtain the more realistic solutions reflecting stochastic natures by performing the iterative analytic-simulation procedure.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.2
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• pp.397-407
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• 2017

This study investigated current status of rest area for drowsy drivers on the highways and drew the related issues to define specifications and design criteria regarding expressway rest area for drowsy drivers on the highways. Based on the investigation result, geometric structure specifications and improvement plans are suggested. The entry part of a rest area for drowsy drivers on the highways was divided into deceleration transition section, deceleration lane and entry connection road while the exit part was divided into exit connection road, acceleration lane and acceleration transition section. The optimum length was estimated by considering the main lane vehicle traveling speed, traveling speed at the beginning/end point of entry/exit connection roads, deceleration and acceleration. In addition, reasonable design criteria were suggested by dividing the parking section of rest area for drowsy drivers according to parking style and cross-section composition, and length of parking space and then considering the ratio of vehicles using rest area for drowsy drivers, the ratio of heavy vehicles, and the design speed within a rest area for drowsy drivers. It is believed that the suggested design criteria on rest area for drowsy drivers on the highways can be utilized in the future planning and maintenance of rest area for drowsy drivers. Additionally, the defined criteria on installing rest area for drowsy drivers on the highways will prevent traffic accidents in resting facilities and highways as well as improve usage and safety of them.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.52 no.3
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• pp.263-270
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• 2016

This study is aimed to design the mechanical gascyclone precipitator with an outstanding collection efficiency as one of ways to reduce exhaust gas of small-scale vessels. It estimated fine particles generated from diesel engines which has become one of the biggest environmental issues currently. Specifically, it quantitatively analyzed the flowing process from the cyclone gas exit; a duct via part to the collecting part of Cylindrical lower using DPIV (Digital Particle Image Velocimetry). Since the gas inlet height part became wider the previous theoretical dimensions, internal fluid characteristics of cyclone where the speed of internal swirl had been slow were investigated by temporary streamline of fine particles at $14-20{\mu}m$. The results showed that collecting efficiency was three times higher than the conical type utilized previously. In addition, this study supplemented imprecision problems from the previous theoretical equation and CFD interpretation with an experimental method. It also provided a basic data to design the cyclone precipitator by size of diesel engines for vessels.

• Journal of the Korean Institute of Gas
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• v.22 no.3
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• pp.7-12
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• 2018

Thermal NOx is generated in a high temperature environment in a combustion facilities. Exhaust gas recirculation method is widely used among various methods for reducing nitrogen oxides in combustion devices. In the present study, the computational fluid dynamic analysis was accomplished to elucidate the cold flow characteristics in the flue gas recirculation burner with both outlets opening. Because the reciculation pipes is installed toward the tangential direction, the swirling flow is formulated in the burner and the phenomenon of the reverse flow creation is detected at the center area of circular burner. We are confirmed that this is the similar trend with the burner with one side outlet closed. From the present study, it was seen that the recirculated inflow from both recirculated burner outlets increased by about 5% compared to the burner with one side outlet opening. At the outlet located at the exhaust gas recirculation pipe inlet(gas exit 1), the inlet flow was formed in the entire region. At the opposite outlet(gas exit 2), the total flow was discharged, but the center part of the burner was observed to have a reverse flow. The flow rate at the gas exit 2 was 3 ~ 5 times larger than the flow rate at the gas exit 1.

• Journal of Labour Economics
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• v.24 no.2
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• pp.1-34
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• 2001

This study analyzes the male-female difference in self-employment rates in Korea using panel data constructed from the Economically Active Population Survey in 1999. Given that most studies on self-employment have focused on male self-employment and have not examined why self-employment rate is usually higher among males than females, this study certainly extends the existing literature on this subject This study consists of two parts. The first part deals with estimating self-employment rates for males and female within a Markov framework. The second part presents decomposition results of the male-female differential in self-employment rates. Major findings of the study are (1) self-employment rate is higher for males than females because entry into self-employment is larger but exit from self-employment is smaller for males than female, (2) higher entry probability for males is due to differences in coefficients of transition probability functions while lower exit probability for males is due to differences in characteristics, (3) a large part of male-female gap in self-employment rates results from differences in being a head of family, marital status and age between males and females.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.16 no.6
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• pp.79-89
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• 2017

Current intersection with collectors allow entry and exit in the relevant sections just as defined by the pertinent design criteria without considering driving behavior of the vehicles coming in and out of the intersection. This study analyzed the roads in the weaving sections to review driving behavior. As a result, vehicles entering a main line are found to try to change a driving lane at a section 50~55m away from a nose part, while those entering a ramp from a main line try to change it at 35~40m from a nose part. Accordingly vehicles exiting to a connecting road from a main line were found to take prior action to change a lane earlier than those entering a main line. Conflict took place intensively at 35~40m section from the nose part entering a main line. Consequently, such conflict at an weaving section may be controlled by adjusting the length of driving lane making use of a double line (solid and dotted line) that can control changing a lane. Outcome of this study may be used as a basic data for operating and maintaining an weaving section of a intersection of a road and improving traffic safety.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.2160-2170
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• 1991

Three-dimensional turbulent structures in the near field of elliptic jet were experimentally investigated by using a three-color, three-component Laser Doppler Velocimeter. The Reynolds number based on the nozzle exit velocity and nozzle equivalent diameter(De) was about 4*10$^{4}$. The turbulent characteristics of a sharp-edged elliptic nozzle with aspect ratio of 2 were analyzed along major and minor axis at X/De=2,3,5,7 and along the centerline up to X/De=14. Quantities measured at each point with the 3-D LDV system were three orthogonal velocity components, turbulent intensity, skewness, flatness, and Reynolds shear stress. The nondimensional mean velocities coincided well with the Schlichting's empirical curve with going downstream. Elliptic jet of AR=2 had two switching points at about X/De=2 and 16. The turbulent intensity along the minor axis was distributed widely than that along the major axis. In the near field, X/De<5, the Reynolds shear stresses of the inner part of the elliptic jet had negative value, which indicated the enhancement of entrainment toward the inner part.

• Journal of the Korean Society of Safety
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• v.14 no.4
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• pp.158-167
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• 1999

In parallel flow condition, to estimate the stability of the extended embankment constructed on a permeable foundation ground, a laboratory model test was performed due to extended materials and water level increasing velocity of a flood period. A laboratory model test was peformed for different permeability coefficients ($K_1=2.0{\times}10^{-5}cm/sec,\;K_2=1.5{\times}10^{-4}cm/sec,\;K_3=2.3{\times}10^{-3}cm/sec$) using seepage. The fluctuation of water level occurring to an extended embankment was analyzed by laboratory model tests as vary the increasing velocity of water level with 0.6cm/min, 1.2cm/min, 2.4cm/min respectively. In analysis results, the increase of water level into embankment occurs rapidly because seepage water moving along with a permeable soil flow into embankment. The larger the permeability coefficient of an extended part is the longer initial seepage distance, and the exit point of downstream slope is gradually increased and then shows unstable seepage behavior as occurring partial collapse. As the increasing velocity of water level increase, the initial seepage line is formed low, and the discharge increases. Therefore, the embankment extended by a lower permeable soil than existing embankment shows stable seepage behavior because an existing embankment plays a role as filter for an extended part.

• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.98-107
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• 2009

Vibration analysis of a turbo compressor test rig was carried out in order to investigate the vibrational characteristics of the compressor facility in KARI before conducting the compressor performance test of 5MW-class gas turbine engine for generation. The overall compressor test facility consists largely of inlet and exit ducts, a test section and a driving part. Vibration was measured with accelerometers at the test section and the driving part, especially at a main housing, a collector, a bearing carrier, a torquemeter, a gearbox, and an electric motor. Gap sensors are also installed to measure the rotordynamic characteristics of compressor shaft.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.863-878
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• 2009

Unsteady three-dimensional flowfield generated by transverse fuel injection into a supersonic mainstream is simulated with a DES turbulence model. Comparisons are made with experimental results in terms of the temporal eddy position and eddy formation frequency. The vorticity field around the jet exit is also analyzed to understand the formation mechanism of the large eddy structures. Results indicate that the DES model correctly predicts the convection characteristics of the large scale eddies. However, it is also observed that the numerical results slightly over-predict the eddy formation frequency. The large eddy structures are generated as the counter-rotating vortices are detached alternately in the upstream recirculation region.