• Journal of the Korea Society of Computer and Information
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• v.16 no.2
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• pp.131-140
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• 2011

Smart packet agent is an application that is proposed to provide routing protocol and service module in ubiquitous network environment. However, it uses multi-hop broadcast, thus it causes increasing network traffic, low-speed data transmission, and the unnecessary joining nodes. In this paper, a transmit technique that uses unicast-based multi-hop to have lower network traffic and faster transmission time than the multi-hop broadcast technique. In our scheme, u-Zone Master establishes temporary routing paths by calculating moving nodes' hop-counter. Therefore, it reduces smart packet agent's network traffic and retransmission rate. Besides, this paper proposed an UDP transmission that bases on sliding window. Hence, the Stop & Wait transmission speed is improved. The results, which are taken by analyzing performance prove that the proposed scheme has better performance.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.149-153
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• 2000

Substituting composite structures for conventional metallic structures has many advantages because of higher specific stiffness and specific strength of composite materials. In this work, one-piece propeller shafts composed of carbonfepoxy and glass/epoxy composites were designed and manufactured for a rear wheel drive automobile satisfying three design specifications, such as static torque transmission capability, torsional buckling and the fundamental natural bending frequency. Single lap adhesively bonded joint was employed to join the composite shaft and the aluminum yoke. For the optimal adhesive joining of the composite propeller shaft to the aluminum yoke, the torque transmission capability of the adhesively bonded composite shaft was calculated with respect to bonding length and yoke thickness by finite element method and compared with the experimental result. Then an optimal design method was proposed based on the failure model which incorporated the nonlinear mechanical behavior of aluminum yoke and epoxy adhesive. From the experiments and FEM analyses, it was found that the static torque transmission capability of composite propeller shaft was maximum at the critical yoke thickness, and it saturated beyond the critical length. Also, it was found that the one-piece composite propeller shaft had 40% weight saving effect compared with a two-piece steel propeller shaft.

• Journal of Communications and Networks
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• v.17 no.2
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• pp.172-183
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• 2015

To provide an efficient link maintenance approach, we propose a cross layer medium access control (LM-MAC) protocol for multichannel cognitive radio ad hoc networks. Link establishment and reliable transmission are two key problems for a perfect link maintenance mechanism. Since the cognitive user (CU) pairs have to reestablish their links each frame, in the proposed MAC protocol, three different access modes are designed to guarantee transmission efficiency in continuous frames. To enhance the transmission reliability, each CU will create a father spectrum list (FSL) after joining in the network. FSL is divided into three groups of sub-channels with different functions to compensate the packet loss caused by the primary users' appearance and the deep fading. Meanwhile, since the transmitter and the receiver will share the same FSL, periodical cooperative sensing is adopted to further optimize the former problem. Finally, compared with the existing opportunistic multichannel (OMC)-MAC protocol, the proposed LM-MAC protocol achieves better system performance in terms of saturation throughput, continuity and access delay.

• Journal of KIISE
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• v.44 no.8
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• pp.749-759
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• 2017

The weapon system based on voice call can cause delay, error or damage to the message during the exchange of information. Furthermore, since the weapon system has a unique message format, it has limited data distribution. Therefore, a Korea Variable Message Format(KVMF) has been developed in this study to utilize a standard sized data format to guarantee the transmission quality and minimize the transmission amount. The ground tactical data link system quickly and accurately shares tactical information by incorporating a field management system that utilizes the KVMF standard message in the mobile weapon system. In this study, we examine the possibility of performing the mission immediately by recovering the state of network joining when a normal/abnormal termination situation of the battlefield management system occurs.

• Journal of Welding and Joining
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• v.30 no.4
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• pp.31-37
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• 2012

In recent years, a demand for precision-welding is increasing in wide industrial fields for getting a high quality welded structures. Although laser welding is commonly used for precision-welding, gas tungsten arc (GTA) welding is also attempted as a precision-welding due to the cost benefit. However, welding heat causes an uneven temperature distribution leading to welding deformation. Since it causes geometric errors and degrades product quality, welding distortion recently rises as an important issue in the field of automobile parts. To control welding deformation, it is needed to design in shapes that can maximize stiffness against deformation during welding; control the welding sequence; minimize heat input; and weld allowing reverse deformation; etc. Thus it is necessary to find the one, among such approaches, that can minimize the deformation range by mathematical analysis and understand how effective it would be when it is actually used in industrial fields. This study performs analyses by numerical calculations and experiments for the De-Tent Lever, one of transmission part that requires precision the most among automobile parts, as the subject of experiment. Decrease in welding deformation is required for this part, since there is currently a trouble in guaranteeing precision due to angular deformation by welding between boss and plate. Finally the ways to minimize welding deformation has been suggested in this study through analyses on it.

• Journal of Welding and Joining
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• v.26 no.3
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• pp.45-50
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• 2008

SM45C steel rods being used generally for power transmission shafts and machine components was selected and welded by Butt-GMAW(Gas Metal Arc Welding) method. An estimation of fatigue life was studied by constructing S-N curve. Fatigue strength of base metal zone showed higher values than one of weld zone in low cycles between $10^4$ and $10^6$cycles. However, significant decrease in fatigue strength of base metal was found around $10^6$cycles, which were almost same as one of heat affected zone. This decrease was attributed that initial residual stress of the steel rods distributed by drawing process was diminished by continually applied load, and resulted in softening of base metal. The fatigue limit of the weld zone was highest in the boundary between deposited metal zone and heat affected zone, and followed by in the order of deposited metal zone, base metal zone, and heat affected zone. Based on these results, it is revealed that the stress for safety design of machine components using SM45C butt-welded steel rods must be selected within the region of the lowest fatigue limit of heat affected zone.

• Journal of Welding and Joining
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• v.14 no.5
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• pp.95-105
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• 1996

Korea Gas Corporation has operated high pressure gas transmission line of about 600 kilometers and, therefore, a series of repair welding processes are required in order to cope with external defects such as dent, gouge, cracking usually due to mechanical attacks. Most of gas pipelines repair processes are performed after completely venting remaining gas. However, in some case, though it is very unusual, repairs require without venting gas. For instance, this case is that damaged pipeline is remedied with split sleeve by welding. In this paper, in an effort to confirm a safe application of the split sleeve welding, residual stress, strain and temperature distributions are evaluated by computer simulation and experiments. The results obtained are as follows : 1) Computer modelling is supposed to be reasonable because microstructure changes due to welding is simulated coincidently as compare to that of real condition. 2) The maximal temperature on inside surface of pipeline is 50$0^{\circ}C$ for the repair welding process. 3) The amount of residual stress is estimated as the stress corresponding to 0.8% strain. 4) The repair process employed is determined to be technically preferable because of its avoiding cracks and fractures in the course of welding.

• Journal of Welding and Joining
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• v.13 no.2
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• pp.122-131
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• 1995

The effects of cooling rate on the microstructures, precipitation of Cu-cluster, .epsilon.-Cu and impact toughness of high strength low alloy(HSLA) steel were studied using hardness tester, impact tester, DSC(differential scanning calorimetry), AES(auger electron spectroscopy) and TEM(transmission electron microscopy). Not only the Cu-precipitates but also the segregation of Cu, As, Sb, P, S, N, Sn along grain boundary were not observed at the specimens heat treated from 800.deg. C to 300.deg. C with the cooling time of 12-125 sec. The Cu-cluster, .epsilon.-Cu are formed by introducing ageing after cooling and the effect of precipitates on hardening increase after cooling was the same in all cooling rate. The peak hardness was obtained at an ageing of 500.deg. C in all cooling conditions. The impact energy become higher as the cooling time increases. This fact can be explained to be due to the tempering effect applied on the cooling stage since the present alloy has a relatively high Ms temperature and the local high concentration of the retained austenite.

• Journal of Welding and Joining
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• v.21 no.2
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• pp.97-101
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• 2003

The change of microstructures in the base metal during transient liquid phase bonding process of directionally Ni base superalloy, GID-111 was investigated. Bonds were fabricated using a series of holding times(0~7.2ks) at three different temperatures. The flip chip bonding utilizing self-aligning characteristic of solder becomes mandatory to meet tolerances for the optical device. In this paper, a parametric study of aging condition and pad size of samples was evaluated. A TiW/Cu/electroplated Cu UBM structure was selected and the samples were aging treated to analyze the effect of intermetallic compounds with the time variations. An FIB technique was applied to the preparation of samples for TEM observations. An FIB technique is very useful to prepare TEM thin foil specimens from the solder joint interface. After aging treatment, the tendency to decrease in shear strength was measured and the structure of the solder and the UBM was observed by using SEM, TEM and EDS. As a result, the shear strength was decreased of about 21% in the 100${\mu}{\textrm}{m}$ sample at 17$0^{\circ}C$ aging compared with the maximum shear strength of the sample with the same pad size. In the case of the 12$0^{\circ}C$ aging treatment, 18% of decrease in shear strength was measured at the 100${\mu}{\textrm}{m}$ pad size sample. An intermetallic compound of Cu6Sn5 and Cu3Sn were also observed through the TEM measurement by using.

• Journal of Welding and Joining
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• v.27 no.2
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• pp.51-56
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• 2009

Film based radiography imaging technique has been applied to the non-destructive test in medical, aircraft, and power industries contributing to the development of the industries. However, the complex process for imaging and analysis has increasingly demanded the reformation of the radiography test. A digital radiography imaging technologies has been com out from the demand. This study was mainly focused on the assessment on the accuracy for the each image from digital radiography test and film radiography test was proven to crate a better image in sensitivity than film radiography test. In the IQI(Image quality indicator) transmission test, one or two more line can be seen in digital image than in film image. When applying to the boiler tube weld, film image is detectable to the 1.0mm depth flaw; and digital image to the 0.5mm depth flaw. As a result of this study, digital radiography technology is determined to enhance the image quality, compared to film radiography technologies