• Korean Chemical Engineering Research
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• v.48 no.3
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• pp.332-336
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• 2010

Ionic liquid immobilized on mesoporous amorphous silica was prepared from the coupling of 1-(triethoxysilylpropyl)-3-n-alkyl-imidzolium halides with tetraethyl orthosilicate(TEOS) through template-free condensation under strong acidic conditions. The immobilized 1-n-butyl-3-methyl imidazolium bromide ionic liquid on amorphous silica(BMImBr-AS) was proved to be an effective heterogeneous catalyst for the synthesis of dimethyl carbonate(DMC) from transesterification of ethylene carbonate(EC) with methanol. High temperature, high carbon dioxide pressure and long reaction time were favorable for the reactivity of BMImBr-AS. Kinetic studies based on two step reactions revealed that the proposed reaction model fitted well the experimental data. The apparent activation energy was estimated to be 67.4 kJ/mol.

• The KIPS Transactions:PartC
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• v.16C no.5
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• pp.653-660
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• 2009

A research for middleware of WSN can provide sensor applications with avoiding tight coupling of hardware, ease of development, and abstract data access. However, previous works have some limitations which should install their own middleware onto the all sensor nodes resulting in computational and communication overhead. In order to address it, we proposed a virtual sensor overlay network, called TinyONet-Lite which introduced virtual sensors to model a virtual counterpart of physical sensors. These virtual sensors dynamically grouped into an overlay network, Slice, which provides middleware services. We implemented TinyONet-Lite on mote class hardware with TinyOS. In accordance with experiments and comparison with existing researches, TinyONet-Lite was proved to show advantages of extensibility, dynamic service composition and reducing overhead.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1378-1383
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• 2008

댐 저수지에서 지속적인 탁도를 유발하는 물질은 쉽게 침강되지 않는 $20{\mu}m$이하의 작은 부유물질(SS)이며, 가을 수직혼합 시기까지 침강되지 않은 부유물질은 다시 재부상하는 경우도 발생한다. 저수지내 탁수의 장기 체류는 수자원 이용과 하류하천의 수생태계에 다양한 문제를 야기하고 있어 일부 댐에서는 실시간 탁도 감시 장치를 설치하고 취수설비를 개선하는 등의 탁수저감 대책의 노력을 기울이고 있으나, 시설의 최적 운영을 지원할 수 있는 탁수 거동 및 탁도 예측에 관한 연구는 아직 부족한 실정이다. 특히, 탁도는 물 속에 존재하는 부유물질의 광학적 특성(light attenuation)을 나타내는 지표로써 SS와는 물리적인 물성이 달라 실시간 계측자료(탁도)와 모델의 모의 변수(SS)가 다른 문제점 때문에 모델링에 어려움이 있었다. 지금까지 탁도 모델링은 대부분 탁도와 SS의 상관관계를 이용하는 방법을 사용하였다. 그러나 이 방법은 탁도-SS 관계가 실측지점과 입자크기분포에 따라 달라지는 특성 때문에 변환과정에 예측결과의 불확실성이 내재한다는 지적을 받아왔다. 본 연구의 목적은 저수지로 유입한 탁수의 보다 과학적이고 정확한 탁도 예측을 위해 탁도를 유발하는 부유물질의 입자크기 분포와 공간적으로 변하는 탁도-SS의 상관관계를 고려할 수 있는 표준화된 탁도 모델링 방법을 개발하고, 실측자료를 사용하여 제시된 탁도 모델링 방법의 예측 성능을 평가하는데 있다. 부유물질의 이송-확산-침강 모델은 2차원 횡방향 평균 수리 모델과 연결(coupling)되어 수행되며, 저수지 수면을 통한 열 교환, 바람과 바닥 조도에 의한 난류혼합과 성층해석, 하천 유입수의 저수지내 밀도류 유동, 그리고 입자 크기별 부유물질의 독립침강을 해석한다. 부유입자의 크기분포와 공간적으로 서로 다른 탁도-SS 관계를 고려한 탁도 예측모델은 기존의 탁도를 종속변수로 사용한 예측 방법 또는 단일 입자크기를 사용한 모델보다 개선된 모의결과를 보여주었다. 본 연구에서 제시된 탁도 예측 알고리즘은 실시간 탁수감시와 예측 모델링, 그리고 댐 방류수 탁도 관리를 위한 선택취수 설비의 운영을 위한 의사결정지원시스템에 적용 가능할 것으로 사료된다.

• Journal of the Korean Geotechnical Society
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• v.31 no.5
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• pp.67-74
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• 2015

Unlike the primary consolidation settlement, the settlement of ground water lowering is not considered separately because of relatively small residual settlement. But the allowed residual settlement (30 mm) of the concrete track in the high-speed railway may be exceeded due to unexpected excessive ground water lowering. This study analyzed the effect of the settlement according to the ground water level change using finite element analysis of stress-pore pressure coupling model, and compared the analysis results with the measured data. As a result, the range of elasticity modulus satisfying the allowable settlement was proposed, and it is suggested that settlement due to ground water level changes should be reflected in the design.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.2
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• pp.236-247
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• 2002

We propose a cell－multiplexing scheme for the real－time communication service in ATM network and a new service discipline guarantee end-to-end delay based on pseudo-isochronous cell switching. The proposed scheme consists of two level frame hierarchy, upper and lower frame, which is used to assign the bandwidth and to guarantee the requested delay bound, respectively. Since the Proposed algorithm employs two level frame hierarchy, it can overcome the coupling problem which is inherent to the framing strategy It can be comparatively reduce the complexity, and still guarantee the diverse delay bounds of end-to-end. Besides, it consists of two components, traffic controller and scheduller, as the imput traffic description model and regulates the input traffic specification. The function of the traffic controller is to shape real -time traffic to have the same input pattern at every switch along the path. The end-to-end delay is bounded by the scheduller which can limit the delay variation without using per-session jitter controllers, and therefore it can decrease the required buffer size. The proposed algorithm can support the QoS's of non-real time traffic as well as those of real time traffic.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.5C
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• pp.445-453
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• 2002

We propose a cell-multiplexing scheme for the real-time communication service in ATM network and a new service discipline guarantee end-to-end delay based on pseudo-isochronous cell switching. The proposed scheme consists of two level frame hierarchy, upper and lower frame, which is used to assign the bandwidth and to guarantee the requested delay bound, respectively. Since the proposed algorithm employs two level frame hierarchy, it can overcome the coupling problem which is inherent to the framing strategy. The proposed scheme consists of two components, traffic controller and scheduller, as the imput traffic description model and regulates the input traffic specification. The function of the traffic controller is to shape real-time traffic to have the same input pattern at every switch along the path. The end-to-end delay is bounded by the scheduller which can limit the delay variation without using per-session jitter controllers, and therefore it can decrease the required buffer size. The proposed algorithm can support the QoS's of non-real time traffic as well as those of real time traffic

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.125-129
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• 2000

In this paper, We designed and fabricated C-band bandpass filter using dielectric resonators. From waveguide cutoff frequency which applied the region between adjacent dielectric resonators, the height of cavity is determined. The cavity's diameter is determined to the twice of dielectric resonator's diameter considering the conductor loss. The resonant frequency of the DR-cavity is calculated with travelling wave mode analysis. Conventionally, circular cylindrical dielectric resonator is analysed by Cohn's model which use the evanescent mode in the region between dielectric resonator wall and circular cavity wall, which is an approximated method. The external quality factor, Q$_{ex}$ has found with simulation result using Ansoft's Maxwell simulation tool. The designed filter using dielectric resonators with dielectric constant of 45 has the passband center at 5.065GHz. The bandpass filter using dielectric resonators have about 1dB insertion loss. 20MHz bandwidth and more than 30dB attenuation at f$_{0}$$\pm$15MHz.z.z.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.8
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• pp.1129-1136
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• 2010

Damper springs in a drive-line absorb the impulsive torque generated when a lock-up clutch is connected directly, instead of via a fluid coupling. Design optimization and finite element analysis were performed to improve the shock- and vibration-absorption capacity of the lock-up clutch. For this purpose, a multi-body dynamics model was developed by including the main parts of a vehicle, such as an engine with a clutch, a transmission, drive shafts and wheels, and a whole mass of a vehicle. The spring constants were selected so that resonance of a system could be avoided. Damper springs were optimized on the basis of the spring constants, impulsive torques, compressed angles, spring counts, fatigue constraints, etc. Topology optimization was performed for three plates with the damper springs. The compliance was set up as an objective function, and volume fraction was fixed below 0.3. A new shape for the plates was proposed on the basis of the topology result.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.2
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• pp.69-78
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• 2013

This study is constructed to investigate the sloshing effect on the motions of a two-dimensional rectangular cylinder experimentally and numerically. The modes of motion under consideration are sway and roll, and also experimental cases are divided by two categories; 1-DoF roll motion and 2-DoF motion (Coupling sway and roll). It is found that the sway response is considerably affected by the motion of the fluid, particularly near the sloshing natural frequency, while the roll response changes comparatively small. The dominant mode of motion is analyzed for 2-DoF experiments as well. The measured data for 1-DoF motions is compared with numerical results obtained by the Multi-modal approach. The numerical schemes vary in detail with the number of dominant sloshing modes; i.e. there is a single dominant mode for the Single-dominant method, while the Model 2 method assumes that the first two modes are superior. For the roll motion, numerical results obtained by the two different methods are relatively in good agreement with the experiments, and these two results are similar in most wave frequency range. However, the discrepancies are apparent where the fluid motion is not governed by a single mode. But both of numerical methods over-predict the motion at the vicinity of the sloshing natural frequency. In order to correct the discrepancy, the modal damping needs to be investigated more precisely. Furthermore, another multi-modal approach, such as the Boussinesq-type method, seems to be required in the region of the intermediate liquid.

• Journal of Energy Engineering
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• v.5 no.1
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• pp.50-55
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• 1996

A numerical simulation on a primary calcinator of porcelain was performed with using Fluent to calculate the heat efficiency by studying velocity vector and temperature profile according to variables such as the location of outlet and porcelain. Control-Volume based Finite Difference Method and Up-wind scheme are used for discretization of differential equation. SIMPLEC Algorithm and standard k-$\varepsilon$ turbulent model are selected to resolve the pressure-velocity coupling and the turbulent. The result of simulation showed that the whole velocity vector field in a calcinator was varied greatly according to the location of outlet. But the whole temperature profile at each zone was still high regardless of the location of outlet because of the radiation. But the temperature of a case with a outlet at sidepart of preheating or cooling zone was little high compared to the case with a outlet on the top of preheating zone. The velocity vector field and temperature profile in a calcinator were almost not affected by the location of porcelain, but the temperature inside a porcelain was much affected according to the place where it was located. The heat efficiency in a calcinator was 44.6% and the gas temperature in the outlet was about 1000 K.