• The KSFM Journal of Fluid Machinery
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• v.15 no.2
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• pp.45-50
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• 2012

The flow characteristics in a vaneless diffuser with a backswept radial impeller have been experimentally investigated according to the variation of discharge flow rate. Particle image velocimetry(PIV) system was applied to measure velocity fields with several operating conditions and on some diffuser horizontal planes. Pressure transducers were installed on hub wall of the diffuser in order to analyze the pressure fluctuations and their corresponding velocity fields. The results show that the location of the main flow center moves from the hub to the shroud side as the flow rate decreases, and the reverse flow is locally generated on the hub side.

• Proceedings of the Korea Port Economic Association Conference
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• 2007.07a
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• pp.37-50
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• 2007

Taking advantage of geographical position of Korea located on the main route of world-wide service, Port Logistics Industry can be strategic industry which secures international competitiveness necessary for Korea to be hub of Northeast Asian's logistics. Along with the advent of super large container vessel, world ports environment changed from "milkway" type, which means vessel calls every port for service to "Hub & Spoke" type, which means vessel calls regional central port and feeder service for the rest ports. As environment changes, regional ports in Northeast Asia are competing each other tougher and tougher and introducing or developing port logistics information system based on state-of-the-art technology in order to adapt themselves to new environment, thus to be Hub port. Taking this situation into consideration, we want to define clearly the meaning and scope of port logistics IT and review the global trend of port logistics IT. Finally we want to find future development of port logistics IT which we have to achieve.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1136-1141
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• 2008

The helicopter rotor system generates lift, thrust, maneuvering force and moment to the helicopter with the torque and pitch control force transferred from the main rotor hub/control. And the tail rotor system generates the thrust for yaw axis control of the helicopter with the torque and pitch control force transferred from the tail rotor hub/control. Ground whirl test shall be performed to verify the compliance of requirement performance test and dynamic test of rotor blade and hub/control. This paper describes a design of whirl tower test facility for helicopter rotor system test and evaluation. Design results are summarized and compared with design requirements.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.42 no.4
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• pp.16-22
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• 2019

After Dantzig and Rasmer introduced Vehicle Routing Problem in 1959, this field has been studied with numerous approaches so far. Classical Vehicle Routing Problem can be described as a problem of multiple number of homogeneous vehicles sharing a same starting node and having their own routes to meet the needs of demand nodes. After satisfying all the needs, they go back to the starting node. In order to apply the real world problem, this problem had been developed with additional constraints and pick up & delivery model is one of them. To enhance the effectiveness of pick up & delivery, hub became a popular concept, which often helps reducing the overall cost and improving the quality of service. Lots of studies have suggested heuristic methods to realize this problem because it often becomes a NP-hard problem. However, because of this characteristic, there are not many studies solving this problem optimally. If the problem can be solved in polynomial time, optimal solution is the best option. Therefore, this study proposes a new mathematical model to solve this problem optimally, verified by a real world problem. The main improvements of this study compared to real world case are firstly, make drivers visit every nodes once except hub, secondly, make drivers visit every nodes at the right time, and thirdly, make drivers start and end their journey at their own homes.

• Transactions of Materials Processing
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• v.14 no.7 s.79
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• pp.601-606
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• 2005

A hole expansion process is an important process in producing a hub-hole in a wheel disc of a vehicle. In this process, the main parameter is the formability of a material that is expressed as the hole expansion ratio. In the process, a crack is occurred in the upper edge of a hole as the hole is expanded. Since prediction of the forming limit by hole expansion experiment needs tremendous time and effort, an appropriate fracture criterion has to be developed for finite element analysis to define forming limit of the material. In this paper, the hole expansion process of a hub-hole is studied by finite element analysis with ABAQUS/standard considering several ductile fracture criteria. The fracture mode and hole expansion ratio are compared with respect to the various fracture criteria. These criteria do not predict its fracture mode or hole expansion ratio adequately and show deviation from experimental results of hole expansion. A modified ductile fracture criterion is newly proposed to consider the deformation characteristics of a material accurately in a hole expansion process. A fracture propagation analysis at the hub-hole edge is also performed for high accuracy of prediction using the new fracture criterion proposed.

• Journal of Korea Port Economic Association
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• v.22 no.4
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• pp.59-79
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• 2006

In this paper, we analyse the comparative competitiveness of the 10 major logistic hub cities in China. First, using the input distance function, we calculated the technical efficiencies and the opportunity costs of the transport infra structure investments. Then, based on not only these supply side factors but also demand side, the overall comparative competitiveness by cities are analyzed. Our main findings are as follows: early developed, larger cities such as Shanghai, Guangzhou, Shenzhen are technically efficient but their opportunity costs of the additional transport investments are higher than the other cities. We also found that overall competitiveness of these larger and leading logistic hub cities are dominant over the small and newly developed logistic cities.

• Tribology and Lubricants
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• v.32 no.2
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• pp.61-66
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• 2016

Total thickness variation (TTV), BOW, and surface roughness are essential characteristics for high quality sapphire substrates. Many researchers have attempted to increase removal rate by controlling the key process parameters like pressure and velocity owing to the high cost of consumables in sapphire chemical mechanical polishing (CMP). In case of the pressure approach, increased pressure owing to higher deviation of pressure over the wafer leads to significant degradation of the TTV. In this study, the authors focused on reducing TTV under the high-pressure conditions. When the production equipment polishes multiple wafers attached on a carrier, higher loads seem to be concentrated around the leading edge of the head; this occurs because of frictional force generated by the combination of table rotation and the height of the gimbal of the polishing head. We believe the skewed pressure distribution during polishing to be the main reason of within-wafer non-uniformity (WIWNU). The insertion of a hub ring between the polishing head and substrate carrier helped reduce the pressure deviation. Adjusting the location of the hub ring enables tuning of the pressure distribution. The results indicated that the position of the hub ring strongly affected the removal profile, which confirmed that the position of the hub ring changes the pressure distribution. Furthermore, we analyzed the deformation of the head via finite element method (FEM) to verify the pressure non-uniformity over the contact area Based on experiment and FEM results, we determined the optimal position of hub ring for achieving uniform polishing of the substrate.

• Journal of IKEEE
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• v.21 no.2
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• pp.158-161
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• 2017

In this paper, we propose Total RMS(Radiation Monitoring System) for nuclear and nuclear medicine. The proposed system can expand and control Stack Monitor, Area Monitor, and Water(Liquid) Monitor into one system, and can monitor the signals measured by each radiation detector in an integrated manner. The proposed system consists of a sensor module that detects the radiation, a display unit that displays the radiation dose near the radiation detection location, an alarm unit that reports the alarm when the detected radiation dose reaches the danger level, A Main Hub for collecting and storing the contents to the remote monitoring system, and an RMS Monitoring Unit for clearly displaying the measured radiation dose at the remote site. In order to evaluate the performance of Total RMS for the proposed nuclear and nuclear medicine field, it is confirmed that the measurement uncertainty is less than 8.5% and it operates normally within ${\pm}15%$ of the international standard.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2006.10a
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• pp.203-212
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• 2006

The purpose of this research is to suggest the activation plan of Busan port. In the past years, Busan port enjoyed the golden days because of the China's rapid economic growth. But China's continuous development of ports, the trend of increasing container ship size and increasing direct call to China are coming threats to Busan port. So Korea needs to revise the 'Northeast Logistics Hub' strategy because it is considered that Korea ports continuously will handle China's transshipment cargoes. But now China's transshipment cargo share has decreased by direct call to China ports. It means that China has a lot of its local cargoes, so many ship companies change liner service route to handle China cargoes except Bussan ports although Busan port is included in the main trunk route. In the future, Bussan port will not be able to compete again about throughput with China ports if Busan port's transshipment cargo share decreases. So we must find out and develop Busan port's strength which is the competitive edge. By good luck, Busan port has a few opportunities such as the developed feeder network service and geographical advantages. Busan port has many feeder network service like spider's web in any northeast countries so we can suggest that if Japanese shippers use Busan port to distribute their cargoes to Japanese local areas, its transport costs are cheaper than when they use Japan's main ports. In this paper analyzed side of cost when they use Bussan port like hub to distribute their cargo to their local areas. Because most companies tried to reduce the total cost about logistics. Finally, this paper suggests when northeast shippers(China, Japan) use Bussan port which is more economical than their local main ports.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.4
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• pp.352-357
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• 2012

The ground resonance instability of a helicopter with bearingless main rotor hub were investigated. The ground resonance instability is caused by an interaction between the blade lag motion and hub inplane motion. This instability occurs when the helicopter is on the ground and is important for soft-inplane rotors where the rotating lag mode frequency is less than the rotor rotational speed. For the analysis, the bearingless rotor was composed of blades, flexbeam, torque tube, damper, shear restrainer, and pitch links. The fuselage was modeled as a mass-damper-spring system having natural frequencies in roll and pitch motions. The rotor-fuselage coupling equations are derived in non-rotating frame to consider the rotor and fuselage equations in the same frame. The ground resonance instabilities for three cases where are without lead-lag damper and fuselage damping, with lead-lag damper and without fuselage damping, and finally with lead-lag damper and fuselage damping. There is no ground resonance instability in the only rotor-fuselage configuration with lead-lag damper and fuselage damping.