• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.5
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• pp.368-376
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• 2001

Performance of heat exchanger was evaluated to heat exchanger using oscillating heat pipe for waste heat recovery of low temperature. Oscillating heat pipe used in this study was formed to the closed loop of serpentine shapes using copper tubes. Heat exchanger was formed to shell and tube type and composed of low finned tube. R-22 and R-141b were used to the working fluids of tube side and their charging ratio was 40%. And, water was used to the working fluid of shell side. As the experimental parameters, the inlet temperature difference of heating and cooling part of secondary fluid and the mass velocity of secondary fluid were used. The mass velocity of secondary fluid was changed from 90 kg/$m^2s\; to\;190 kg/m^2$s from the experimental results, heat recovery rate was linearly increased to the increment of the mass velocity of secondary fluid and the inlet temperature difference of secondary fluid. Finally, the performance of heat exchanger was evaluated by using $\varepsilon$-NTU method. It was found that NTU was about 1.5 when effectiveness was decided to 80%.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.3
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• pp.232-248
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• 2009

Numerical methodology to solve ship springing problem, which is basically fluid-structure interaction problem, was explored in this study. Solution of this hydroelasticity problem was sought by coupling higher order B-spline Rankine panel method and finite element method in time domain, each of which is introduced for fluid and structure domain respectively. Even though varieties of different combinations in terms of numerical scheme are possible and have been tried by many researchers to solve the problem, no systematic study regarding the characteristics of each scheme has been done so far. Here, extensive case studies have been done on the numerical schemes especially focusing on the iteration method, FE analysis of beam-like structure, handling of forward speed problem and so on. Two different iteration scheme, Newton style one and fixed point iteration, were tried in this study and results were compared between the two. For the solution of the FE-based equation of motion, direct integration and modal superposition method were compared with each other from the viewpoint of its efficiency and accuracy. Finally, calculation of second derivative of basis potential, which is difficult to obtain with accuracy within grid-based method like BEM was discussed.

• Transactions of The Korea Fluid Power Systems Society
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• v.2 no.2
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• pp.1-7
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• 2005

For the reliability evaluation of the track drive unit(TDU), firstly, we analyzed the major failure modes through FMEA(failure mode & effects analysis), FTA(failure tree analysis), and 2-stage QFD(quality function deployment), and then quantitatively determined the priority order of test items. The Minitab analysis was also performed for prediction of life distribution and parameters of TDU by use of field failure data collected from 430 excavators for two years. In addition, we converted the fluctuation load in field conditions into the equivalent load, and for evaluation of the accelerated lift by the cumulative fatigues, the equivalent load is again divided into the fluctuation load by reference of test time. And then, by use of the test method in this paper, the acceleration factor(AF) of needle bearing inside planetary gear which is the most weakly designed part of TDU is achieved as 5.3. This paper presents the quantitative selection method of test items for reliability evaluation, the determination method of the accelerated life test time, and the method of non-failure test time based on a few of samples. And, we proved the propriety of the proposed methods by experiments using a TDU for a 30 ton excavator.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.3
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• pp.329-338
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• 2001

In this paper, we designed microstrip patch antenna to enhance the weak point of general microstrip patch antenna that has narrow bandwidth and analyzed that. To reduce reactance in probe feed antenna, capacitive gap added to the patch. Using single patch and auxiliary wire, makes dual frequency resonant. So bandwidth is improved and gain also becomes higher. To verify with experiment, PCS band antenna is designed, fabricated. For PCS band antenna, bandwidth is 180 MHz in VSWR<1.5 and gain is 8.6 dBi.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.12B
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• pp.1063-1069
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• 2004

There are some problems with the methods of paging and routing cache(PRC) and quasi soft handoff that are proposed to improve the performance for the transmission of real time data. This paper proposed a reasonable solution of these problems by proposing a new method using a combined cache(CC) and applying a different handoff procedure according to each type of data. The combined cache dose not maintain the handoff state but the idlle/active state. The simulation results in a better performance than the above methods in terms of the control packet traffic load, initial recevied data packet traffic load and arrival tune of real time packet at the epoch of handoff.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.1B
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• pp.18-26
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• 2003

Earlier efforts on optical access concentrated on the design of PONs for the collection and distribution portion of the access network PON architecture is very simple but it requires MAC protocol for control of upstream traffic This paper proposes a Request-Counter MAC protocol for a broadband access network using an ATM Passive Optical Network supporting CBR/rtVBR, nrtVBR, UBR and ABR traffic For the proposed MAC scheme, we present Grant Field format, Minislot format, and bandwidth allocation algorithm From the simulation result, we have confirmed that our proposed scheme can reduce the average cell delay in comparison to that of conventional MAC schemes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.9B
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• pp.1342-1349
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• 2010

Full-mesh IPSec tunnels, which constitute a black network, are required so that the dynamically changing PT (Plain Text) networks can be reachable across the black network in military environments. In the secure and mobile black networks, dynamically re-configuring IPSec tunnels and security policy database (SPD) is very difficult to manage. In this paper, for the purpose of solving mobility and security issues in military networks, we suggest the relating main technologies in association with DMIDP (Dynamic Multicast-based IPSec Discovery Protocol) based on existing IPSec ESP (Encapsulating Security Payload) tunnels and IPSec key managements. We investigate the main parameters of the proposed DMIDP techniques and their operational schemes which have effects on mobility and analyze operational effectivemess of the DMIDP with proposed parameters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.8B
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• pp.1122-1128
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• 2010

In this paper, we proposed and designed a novel SNA protocol which operates in the way of a server and a client in the power control system. The proposed SNA protocol includes the information about the mode switching, the saving position of context information, the user trigger, and so forth, which are needed in the power management devices. We consider the application of the SNA protocol to the home network, where message flows between the SNA server and the SNA client. To verify the operation of the SNA protocol, the state transition diagrams of the server in the home gateway and the client in the network device are shown. Hence, we can conclude the SNA can operate without malfuction.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.5
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• pp.238-242
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• 2001

In this paper, we extracted design parameters for re-entrant mode microstrip directional coupler using FE(finite element) calculations. The microstrip directional coupler suffers from a poor directivity due to effect of the inhomogeneous dielectric including both dielectric substrate and air in microstrip transmission lines. Thus, the phase velocity of even mode is not equal to that of odd mode. In order to improve the directivity of microstrip directional coupler, a novel re-entrant mode microstrip directional coupler was employed. In microstrip configuration, the high directivity can be reached by matching the even- and odd-mode effective phase velocities. Through the values of capacitance obtained from 2-dimensional FE calculations, the phase velocities for each mode and the design parameter were extracted for the proposed parallel coupled-line configuration. Based on the extracted design parameter with phase matching condition, we designed and fabricated a 30dB directional coupler at 0.85GHz. Experimental results show good performance with excellent, isolation and directivity.

• The KIPS Transactions:PartC
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• v.13C no.4 s.107
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• pp.455-460
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• 2006

Currently, the IETF group is working on service differentiation in the Internet. However, in wireless environments such as Ad-hoc networks, where channel conditions are variable and bandwidth is scarce, the Internet differentiated services are suboptimal without lower layers' support. The IEEE 802.11 standard for Wireless LANs is the most widely used WLAN standard today. 1t has a mode of operation that can be used to provide service differentiation, but it has been shown to perform badly. In this paper, we present a new service differentiation scheme for support QoS in the wireless IEEE 802.11, which is based on a multiple queuing system to provide priority of user's flow. We simulate and analyze the performance of our algorithm and compare its performance with the original IEEE 802.11b protocol. Simulation results show that our approach increases overall throughput in the MAC layer.