• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.71-80
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• 2005

More than 100 bridges have been annually collapsed or seriously damaged by scouring in Korea. It is extremely hard to understand the complicated scour mechanism and estimate the scour depth with accuracy in fields, however since scouring is a very complex manifestation of sediment transport unable to describe with a simple mathematical tool. In order to obtain the reasonable solution to bridge scouring, therefore, the interdisciplinary co-operation is strongly recommended. In this study the special task force team for the scour problems around Incheon 2nd bridge piers is made, in which all kinds of scour oriented researches such as oceangraphic survey, hydraulic model test, numerical simulation, scour rate test, real-time scour monitoring, etc will be carried out. This paper provides this interdisciplinary procedure in details.

• Journal of Communications and Networks
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• v.11 no.6
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• pp.626-633
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• 2009

Lawful interception (LI) involves legally accessing private communication such as telephone calls or email messages. Numerous countries have been drafting and enacting laws concerning the LI procedures. With the proliferation of portable Internet services such as the IEEE 802.16e wireless mobile networks, surveillance over illegal users is an emerging technical issue in LI. The evermigrating users and their changing IP's make it harder to provide support for seamless LI procedures on 802.16e networks. Few studies, however, on seamless LI support have been conducted on the 802.16e mobile networks environments. Proposed in this paper are a seamless LI architecture and algorithms for the 802.16e networks. The simulation results demonstrate that the proposed architecture improves recall rates in intercepting mobile user, when compared to the existing LI architectures.

• Journal of Electrical Engineering and Technology
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• v.1 no.1
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• pp.106-109
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• 2006

In this paper, the design and characteristics of a novel ultrasonic motor are investigated. Such a motor is appropriate far use in the optical zoom or auto focusing functions of the lens system in mobile phones. Its design and simulation of performances are carried out by FEM commercial software (ATILA). The shape of the motor is similar to a square without one side, on which an optical lens can be mounted. Two sheets of piezoelectric ceramics are adhered to both sides of two legs of the elastic body, respectively To drive the ultrasonic motor, the voltage is applied to two sheets of piezoelectric ceramics bonded to one leg. The rotation direction can be easily changed by switching the piezoelectric sheets bonded to the other leg, to which voltage is applied. A proto type of the motor is fabricated and its outer size is $10^*10^*2[mm3]$ including the camera lens of which the diameter is 7.5(mm). Its power consumption is about 0.3[W] and the speed of rotation is adjustable from 10 to 200[rpm] according to the applied voltage

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.5
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• pp.482-489
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• 2015

CSTR (Continuous Stirred Tank Reactor) which plays a key role in the chemical plants exhibits highly nonlinear behavior as well as time-varying behavior during operation. The control of CSTRs in the whole operating range has been a challenging problem to control engineers. So, a variety of feedback control forms and their tuning methods have been implemented to guarantee the satisfactory performance. This paper presents a scheme of designing a nonlinear PID controller incorporating with a GA (Genetic Algorithm) for the temperature control of a CSTR. The gains of the NPID controller are composed of easily implementable nonlinear functions based on the error and/or the error rate and its parameters are tuned using a GA by minimizing the ITAE (Integral of Absolute Error). Simulation works for reference tracking and disturbance rejecting performances and robustness to parameter changes show the feasibility of the proposed method.

• Journal of the Korean Solar Energy Society
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• v.29 no.5
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• pp.28-34
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• 2009

The atrium in the building has many advantages including its aesthetic and functional effect. But the upper part of the atrium has the thermal problem of overheating due to insolation through the window. But natural ventilation aided buoyancy effect can be a solution to make comfortable indoor environment. Proper design of openings is very important to improve thermal environment in the atrium. In this study, thermal evaluations were performed to improve thermal environment in the atrium. Indoor thermal environment of an atrium at Seoul was measured in the field and simulated with Computational Fluid Dynamics( CFD) code. The turbulent flow model adopted is $K-{\varepsilon}$ model. The results of computer simulations are compared with the measurements at the point in the atrium. In order to improve the indoor ventilation environment of the atrium, thermal environment evaluations of six alternatives were conducted. After evaluations of the results, the design guidelines of an atrium are suggested.

• Journal of Magnetics
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• v.20 no.3
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• pp.284-289
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• 2015

This paper discusses general methods of modelling magnetic saturation in steady-state, two-axis (d & q) frame models of dual stator induction generators (DSIG). In particular, the important role of the magnetic coupling between the d-q axes (cross-magnetizing phenomenon) is demonstrated, with and without cross-saturation. For that purpose, two distinct models of DSIGs, with and without cross-saturation, are specified. These two models are verified by an application that is sensitive to the presence of cross-saturation, to prove the validity of these final methods and the equivalence between all developed models. Advantages of some of the models over the existing ones and their applicability are discussed. In addition, an alternative is given to evaluate all saturation factors (static and dynamic) by just calculating the static magnetizing inductance which is simply the magnitude of the ratio of the magnetizing flux to the current. The comparison between the simulation results of the proposed model with experimental results gives a good correspondence, especially at startup.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.12
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• pp.1093-1100
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• 2014

The goal of this paper is to investigate preliminary the applicability of 3D printing technologies for the development of the hot bulk forming process and die. 3D printing technology based on the plastic material was applied to the preform design of the hot forging process. Plastic hot forging dies were fabricated by Polyjet process for the physical simulation of the workpiece deformation. The feasibility of application of Laser-aided Direct Metal Rapid Tooling (DMT) process to the fabrication of the hot bulk metal forming die was investigated. The SKD61 hot-working tool steel was deposited on the heat treated SKD61 using the DMT process. Fundamental characteristics of SKD 61 hot-working tool steel deposited specimen were examined via hardness and wear experiments as well as the observation of the morphology. Using the results of the examination of fundamental characteristics, the applicability of the DMT process to manufacture hot bulk forming die was discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.197-203
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• 2004

A full finite element (FE)-based approach is presented for the precision analysis of the strip profile in flat rolling. Basic FE models for the analysis of the mechanical behavior of the strip and of the rolls are described in detail. Also described is an iterative strategy for a rigorous treatment of the mechanical contact occurring at the roll-strip interface and at the roll-roll interface. Then, presented is an integrated FE process model for the coupled analysis of the mechanical behavior of the strip, work roll, and backup roll in four-high mill. A series of process simulation are conducted and the results are compared with the measurements made in hot and cold rolling experiments.

• International journal of advanced smart convergence
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• v.2 no.1
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• pp.6-11
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• 2013

Network Coding (NC) is a new paradigm for network communication. In network coding, intermediate nodes create new packets by algebraically combining ingress packets and send it to its neighbor node by broadcast manner. NC has rapidly emerged as a major research area in information theory due to its wide applicability to communication through real networks. Network coding is expected to improve throughput and channel efficiency in the wireless multi-hop network. Many researches have been carried out to employ network coding to wireless ad-hoc network. In this paper, we proposed a dynamic queue management to improve coding opportunistic to enhance efficiency of NC. In our design, intermediate nodes are buffering incoming packets to encode queue. We expect that the proposed algorithm shall improve encoding rate of network coded packet and also reduce end to end latency. From the simulation, the proposed algorithm achieved better performance in terms of coding gain and packet delivery rate than static queue management scheme.

• Journal of Ocean Engineering and Technology
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• v.22 no.6
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• pp.20-26
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• 2008

In this paper, in order to set up the management system of water quality environment in Gwangyang Bay, the cluster analysis of water quality environment, the estimation of inflowing pollutant loads and residence time of pollutants in this bay was carried out. The Gwangyang Bay was divided into eight sea areas by cluster analysis and spatio-temporal change of water quality. The river discharges in the Bay were calculated about $11,681{\times}103m^3/day$ from the numerical simulation by Tank model. In addition, inflowing pollutant loads of COD, SS, TN, TP, DIN and DIP in Gwangyang Bay were estimated at 398 ton-COD/day, 2,846 ton-SS/day, 195 ton-TN/day, 5 ton-TP/day, 126 ton-DIN/day and 3 ton-DIP/day, respectively. Moreover, residence times of COD, TN and TP in the Bay was estimated at 6 days-COD, 20 days-TN and 195 days-TP, respectively in the dry season, and 3 days-COD, 6 days-TN and 21 days- TP, respectively, in the flood season. The central part of Gwangyang Bay (Region IV) has the longest residence time of overall pollutants.