• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.843-845
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• 2003

Shortest Path Problems are among the most studied network flow optimization problems, with interesting applications in various fields. One such field is the route determination service, where various kinds of shortest path problems need to be solved in location-based service. Our research aim is to propose a route technique in real-time locationbased service (LBS) environments according to user’s route preferences such as shortest, fastest, easiest and so on. Turn costs modeling and computation are important procedures in route planning. There are major two kinds of cost parameters in route planning. One is static cost parameter which can be pre-computed such as distance and number of traffic-lane. The other is dynamic cost parameter which can be computed in run-time such as number of turns and risk of congestion. In this paper, we propose a new cost modeling method for turn costs which are traditionally attached to edges in a graph. Our proposed route determination technique also has an advantage that can provide service interoperability by implementing XML web service for the OpenLS route determination service specification. In addition to, describing the details of our shortest path algorithms, we present a location-based service system by using proposed routing algorithms.

• KIEAE Journal
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• v.17 no.5
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• pp.69-76
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• 2017

Purpose: This study aimed at developing an Artificial Neural Network (ANN) model for predicting the amount of cooling energy consumption of the variable refrigerant flow (VRF) cooling system by the different set-points of the control variables, such as supply air temperature of air handling unit (AHU), condenser fluid temperature, condenser fluid pressure, and refrigerant evaporation temperature. Applying the predicted results for the different set-points, the control algorithm, which embedded the ANN model, will determine the most energy efficient control strategy. Method: The ANN model was developed and tested its prediction accuracy by using matrix laboratory (MATLAB) and its neural network toolbox. The field data sets were collected for the model training and performance evaluation. For completing the prediction model, three major steps were conducted - i) initial model development including input variable selection, ii) model optimization, and iii) performance evaluation. Result: Eight meaningful input variables were selected in the initial model development such as outdoor temperature, outdoor humidity, indoor temperature, cooling load of the previous cycle, supply air temperature of AHU, condenser fluid temperature, condenser fluid pressure, and refrigerant evaporation temperature. The initial model was optimized to have 2 hidden layers with 15 hidden neurons each, 0.3 learning rate, and 0.3 momentum. The optimized model proved its prediction accuracy with stable prediction results.

• Journal of the Korea Institute of Building Construction
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• v.9 no.3
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• pp.95-101
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• 2009

Constructing large-scale mat foundation mass concrete is increasing for the stability of building structure, because a lot of high rise building are being built in order to make full use of limited space. However, It is of increasing concerns that because limited placing equipments, available job-site and systems for mass concete placement in construction field do not allow to place great quantity of concrete at the same time in large scale mat foundation, consistency between placement lift can not be secured. And also, it is likely to crack due to stress caused by the difference of hydration heat generation time. To find out the solution against above problems, this study is to reconfirm the performance of normal concrete designed by mix proportion and super retarding concrete. The Fundamental test shows what happens if low heat proportioning and control method of setting time are applied at the job-site of newly constructed high rise building. The test result show that slump flow of concrete has been somewhat increased as the target retarding time gets longer, while the air content has been slightly decreased but this is no great difference from normal concrete. The setting time shows to be retarded as target retarding time gets longer, the range of retarding time increases. It is necessary to increase the amount of mix of super retarding agent in the proportion ration by setting curing temperature high since outdoor curing is about 6 hours faster than standard curing, which means the temperature of the concrete will be higher than the temperature of the surrounding environment, due to its high hydration heat when applying in a construction site. The compressive strength of super retarding concrete appears to be lower than normal concrete due to the retarding action in the early stage. However, as the time goes by, the compressive strength gets higher, and by the 28th day the strength becomes the same or higher than normal concrete.

• Journal of Korean Society of Transportation
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• v.19 no.6
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• pp.219-227
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• 2001

In this study, the simulation was constructed using CA(Cellular Automata) rule to analyze the effect of incidents, which was verified using real-time VDS data and data collected on the field. The study analyzed the effect of incidents on highways by the simulation. The result appears to be statistically available with 5% of significance level. In order to analyze the effect of incident, the study classified time period of incidents and types of incidents in relation with traffic volume. Also, the effect of each type of incidents was analyzed in terms of time difference in sectional travel and delay time. In conclusion, little effect of incidents on traffic flow is noticed with light traffic volume but it becomes serious as the traffic volume increases. In addition, the delay happens to appear without incidents as the traffic volume increases over 2000 veh/hour. Also, when incidents happened during 45 minutes, the delay was about 425-722 veh·hour.

• Journal of Korean Society of Transportation
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• v.27 no.5
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• pp.125-134
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• 2009

Recently, as IT technology and the ubiquitous environment have diffused, the application of these techniques are being attempted in the field of traffic operations and management. Therefore, it is necessary to develop data collection systems and signal control strategies that are suitable in the ubiquitous environment and that will improve efficiency and safety of signalized intersections. The authors conducted a study on the Wireless Sensor Network (WSN) signal control strategy using a wireless communication network between individual vehicles and a signal-control system and full actuated signal control technique to propose a new signal control strategy in the ubiquitous environment. The WSN was defined to evaluate the algorithm used with PARAMICS API simulation. The simulation produced results that the WSN signal control is more effective than other signal control methods. The WSN signal control could reduce vehicle delay time to a maximum of 64% in comparison with other signal control methods in low and near saturation flow conditions.

• Tribology and Lubricants
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• v.32 no.3
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• pp.101-105
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• 2016

Trap effect of groove is evaluated in a lubricating system using computational fluid dynamics (CFD) analysis. The simulation is based on the standard k-ε turbulence model and the discrete phase model (DPM) using a commercial CFD code FLUENT. The simulation results are also capable of showing the particle trajectories in flow field. Computational domain is meshed using the GAMBIT pre-processor. The various grooves are applied in order to improve lubrication characteristics such as reduction of friction loss, increase in load carrying capacity, and trapping of the wear particles. Trap effect of groove is investigated with variations in cross-sectional shape and Reynolds number in this research. Various cross-sectional shapes of groove (rectangular, triangle, U shaped, trapezoid, elliptical shapes) are considered to evaluate the trap effect in simplified two-dimensional sliding bearing. The particles are assumed to steel, and defined a single particle injection condition in various positions. The “reflect” boundary condition for discrete phase is applied to the wall boundary, and the “escape” boundary condition to “pressure inlet” and “pressure outlet” conditions. The streamlines are compared with particles trajectories in the groove. From the results of numerical analysis in the study, it is found that the cross-sectional shapes favorable to the creation of vortex and small eddy current are effective in terms of particle trapping effect. Moreover, it is found that the Reynolds number has a strong influence on the pattern of vortex or small eddy current in the groove, and that the pattern of the vortex or small eddy current affects the trap effect of the groove.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1150-1157
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• 1988

Two-dimensional turbulent plane jet which is under the pressure gradient in the transverse direction is studied numerically. Full Navier-Stokes equations are used to correctly account for the pressure variation in the transverse direction. Using the standard k-.epsilon. turbulence model as a closure relationship, a time marching procedure gives the velocity field. The temperature fields are obtained for two different cases : (1) Hot jet is issued into the cold still air, and (2) Hot jet is issued into the surrounding across which exists a temperature difference. The velocity and temperature fields along with other flow and heat-transfer characteristics for two different pressure gradients are presented. A simple formula that relates the jet trajectory to the pressure gradient is also proposed. The mass flux in the longitudinal direction and the jet halfwidth seem insensitive to the pressure gradient. However, the pressure gradient increases the heat flux in the longitudinal direction as well as in the transverse direction.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.5
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• pp.545-550
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• 2012

Steam generator is one of the major components of nuclear power plant and steam generator tubes are the pressure boundary between primary and secondary side, which makes them critical for nuclear safety. As the operating time of nuclear power plant increases, not only damage mechanisms but also scaled deposits on steam generator tubes are known to be problematic causing tube support flow hole blockage and heat fouling. The ability to assess the extent and location of scaled deposits on tubes became essential for management and maintenance of steam generator and eddy current bobbin data can be utilized to measure thickness of scale on tubes. In this paper, tube reference standards with various thickness of scaled deposit has been set up to provide information about the overall deposit condition of steam generator tubes, providing essential tool for steam generator management and maintenance to predict and prevent future damages. Also, methodology to automatically measure scale thickness on tubes has been developed and applied to field data to estimate overall scale amount.

• Journal of the korean society of oceanography
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• v.31 no.2
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• pp.75-88
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• 1996

The analytic and numerical solution of the 1$\frac{1}{2}$-layer and 2$\frac{1}{2}$-layer models are derived. The large coastal-sea level drop and the fast westward speed of the anticyclonic gyre due to strong offshore winds using two ocean models are investigated. The models are forced by wind stress fields similar in structure to the intense mountain-pass jets(${\sim}$20 dyne/$cm^{2}$) that appear in the Gulfs of Tehuantepec and Papagayo in the Central America for periods of 3${\sim}$7 days. Analytic and numerical solutions compare favorably with observations, the large sea-level drop (${\sim}$30 cm) at the coast and the fast westward propagation speeds (${\sim}$13 km/day) of the gyres. The coastal sea-level drop is enhanced by several factors: horizontal mixing, enhanced forcing, coastal geometry, and the existence of a second active layer in the 2$\frac{1}{2}$-layer model. Horizontal mixing enhances the sea-level drop because the coastal boundary layer is actually narrower with mixing. The forcing ${\tau}$/h is enhanced near the coast where h is thin. Especially, in analytic solutions to the 2$\frac{1}{2}$-layer model the presence of two baroclinic modes increases the sea-level drop to some degree. Of theses factors the strengthened forcing ${\tau}$/h has the largest effect on the magnitude of the drop, and when all of them are included the resulting maximum drop is -30.0 cm, close to observed values. To investigate the processes that influence the propagation speeds of anticyclonic gyre, several test wind-forced calculations were carried out. Solutions to dynamically simpler versions of the 1$\frac{1}{2}$-layer model show that the speed is increased both by ${\beta}$-induced self-advection and by larger h at the center ofthe gyres. Solutions to the 2$\frac{1}{2}$-layer model indicate that the lower-layer flow field advects the gyre westward and southward, significantly increasing their propagation speed. The Papagayo gyre propagates westward at a speed of 12.8 km/day, close to observed speeds.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.5
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• pp.2044-2062
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• 2018

Information theory progression along with the advancements being made in the field of Vehicular Ad hoc NETworks (VANETs) supports the use of coding-aware opportunistic routing for efficient data forwarding. In this work, we propose and investigate an adaptive coding-aware routing scheme in a specific VANET scenario known as a vehicular platoon. Availability of coding opportunities may vary with time and therefore, the accurate identification of available coding opportunities at a specific time is a quite challenging task in the highly dynamic scenario of VANETs. In the proposed approach, while estimating the topology of the network at any time instance, a forwarding vehicle contemplates the composition of multiple unicast data flows to encode the correct data packets that can be decoded successfully at destinations. The results obtained by using OMNeT++ simulator reveal that higher throughput can be achieved with minimum possible packet transmissions through the proposed adaptive coding-aware routing approach. In addition, the proposed adaptive scheme outperforms static transmissions of the encoded packets in terms of coding gain, transmission percentage, and encoded packet transmission. To the best of our knowledge, the use of coding-aware opportunistic routing has not been exploited extensively in available literature with reference to its implications in VANETs.