• Journal of KIISE:Information Networking
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• v.32 no.2
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• pp.215-219
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• 2005

Generally, the mobile nodes in MANET have the limited power capacity available for actual communications. Thus, the power management is very important for packet routing or forwarding. Although MTPR, MBCR and MMBCR are proposed to treat the problem of power consumption, there have been few researches resolving the link breakdown that is occurred by the power exhaustion during transmission. In this sense, the reliable scheme should be required to ensure the routing connectivity. In this paper, we propose three schemes to enforce the routing connectivity. If the signal strength is dropped below a signal threshold, the candidate route is previously selected to prepare the link breakdown. Also, on multi-channel, we propose the lifetime increment scheme of a node that it manage its available power to the needed power of a new link. The simulation results show the enforcement of the link connectivity and the performance improvements of the delay time through the effective connection management.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.4
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• pp.298-304
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• 2014

The lifting-line method based on Weissinger's method is extended to be able to analyze the ground effect. The method is applied to predict the variation of aerodynamic performance due to ground effect for the elliptic wing with aspect ratio of 10 and the wing of human powered aircraft. While the vortex strength of the wing increases slightly, the downwash decreases significantly as the wing approaches to the ground. For the wing of human powered aircraft, the increment of lift at the height of 2m is 5% than the lift outside the influence of ground effect. The decrease of induced drag at the height of wing span is 10% and at the height of 2m is 55% than that out of ground effect.

• Elastomers and Composites
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• v.51 no.2
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• pp.113-121
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• 2016

Magneto-rheological elastomer (MRE) is a material which shows reversible and various modulus under magnetic field. Comparing to conventional rubber vibration isolator, MREs are able to absorb broader frequency range of vibration. These characteristic phenomena result from the orientation of magnetic particle (i.e., chain-like formation) in rubber matrix. In this study, silicone rubber was used as a matrix of MREs. Carbonyl iron particle (CIP) was used to give magnetic field reactive modulus of MRE. The surface of the CIP was modified with chemical reactants such as silane coupling agent and poly(glycidyl methacrylate), to improve interfacial adhesion between matrix and CIP. The mechanical properties of MREs were measured without the application of magnetic field. The results showed that the tensile strength was decreased while the hardness was increased with the addition of CIP. Also, surface modification of CIP resulted in the improvement of physical properties of MRE, but the degree of orientation of CIP became decreased. The analysis of MR effect was carried out using electromagnetic equipment with various magnetic flux. As the addition of CIP and magnetic flux increased, increment of MR effect was observed. Even though the surface modification of CIP gave positive effect on the mechanical properties of MRE, MR effect was decreased with the surface modification of CIP due to decrease of CIP orientation. Throughout this study, it was found that the loading amounts of CIP affected the mechanical properties of MRE, and surface property of CIP was an important factor on MR effect of MRE.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.2
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• pp.83-93
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• 2013

Generally the capacities of electric power transmission tower's members are improved by increasing their stiffness nature through injection of grout or attachment of other structural stiffeners. Those are for upgrading their axial strength by fulfillment of proper materials into pipe members, increment of member dimension by addition of section, or a combination of the two. However the use of innovative and unusual procedures would be positively recommended for getting more stable state. It is that buckled members are replaced with lengthened and strengthened members. In providing the structural restoration procedures for the existing electric power transform tower whose main members have been damaged due to unequal foundation settlement, structural damage inspection works and numerical analyses for the damaged one and the restored one were done in detail at first. secondarily member-exchanging works using a newly-generated jacking system and strengthened members were achieved. This figures are to point clearly to inherent advantages attending the management of the towers.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.17-20
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• 2008

As a part of a research program to study the shear reinforcement of flat plate system, this investigation aimed to determine the effect of shear reinforcement type on punching shear strength of monolithic slab-column connection. A total of 5 specimens were fabrication and tested. The dimension of the slab were $2.63{\ast}2.725{\ast}0.18m$, with a centrally located column $0.6{\ast}0.8m$ in cross section. Experimental results showed that the CFS shear reinforcement was not effective because of lack of proper bond with concrete. 3 shear reinforcement except of CFS showed high effectiveness, which resulted in a considerable increment of the punching shear resistance of the connection.

• Journal of the Korean GEO-environmental Society
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• v.2 no.1
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• pp.91-101
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• 2001

This paper investigates the effectiveness of quick lime piles for soft ground improvement. The field tests based on the results of the laboratory test were performed, and the results of field tests were compared with those of numerical analyses(FEM). The results of the field test showed that the domestic quick lime was very effective in reducing the water contents of the surrounding ground quickly due to its characteristics such as digestion, absorption, and exothermic reactions. Accordingly, consolidation occurred without any additional load increment and the shear strength of surrounding ground was increased more than twice. Therefore the quick lime pile method could be considered as an excellent improvement technique reducing the improvement period for soft ground. For the practical applications of the quick lime pile method, issues such as hydration heat, particulation and equipment enhancement should be solved through continuous research and development.

• Journal of the Korean GEO-environmental Society
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• v.11 no.12
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• pp.5-11
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• 2010

If the groundwater in rock joint is changed into ice, it induces the stress increment by volume increase. Also, if the ice is changed into groundwater again, the stress in joint decreases by volume decrease. The accumulated displacement and fatigues of joints are increased by the stress-hysterisis, induced from the continuous frost-thawing. Also the shear strength is decreased by them continuously. The stress-hysterisis is affected by the atmospheric temperature changes, whose behavior is visco-elasticity, usually. Therefore, Kelvin model could be used to analyze the frost-thawing behavior in winter. The measured data of total 5 points are examined, which are composed of 3 points of shallow joints and 2 points of deep joints. Because shallow weathered rocks have many joints, a lot of Kelvin model are connected and the behaviors are complicated. In case of deep joints, simple Kelvin model is applied and the behaviors are also simple.

• International Journal of Highway Engineering
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• v.9 no.3
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• pp.123-134
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• 2007

This study was carried out for evaluating correlation of aging level and deformation resistance of asphalt mixtures conditioned by artificial aging treatment. The specimens were made of the short-term aged loose asphalt mixture which was kept in a convection oven at $154^{\circ}C$ for 2 hours, and then were artificially aged at $110^{\circ}C$ for 24, 48, 72 and 96 hours for long-term aging. Deformation strength ($S_D$) and large molecular size ratio (LMS(%)) were measured after short-term and each long-term aging treatment to evaluate aging extents of each mixture with aging time using GPC(Gel-permeation chromatograph) test. It is shown that the $S_D$ and LMS(%) were increased with aging time increment, and that LMS(%) quantity and $S_D$ have relatively good correlation each other. This study found that the aged asphalt mixture had better resistance against rutting and it was possible to estimate rutting characteristics of asphalt mixtures by using LMS(%) without a binder recovery.

• Journal of Korean Society of Steel Construction
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• v.20 no.1
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• pp.67-79
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• 2008

In this study, a bending test with three encased composite beams were carried out and analyzed using FEM in order to find how chemical adhesion, interface interlock, friction and composite action by shear studs contribute to stiffness, strength and composite action in the interface of encased compo site beams. The test and results of the FEM analysis showed that the difference in the ultimate moment capacity of the composite beams with and without studs is under 10%. The reason is that the effect of chemical adhesion, interface interlock, and friction in the interface on the composite action is so high that the encased beams have a moment capacity above some defined magnitude. Also, the increment of moment capacity up to plastic moment is not large and the increase of linearly proportioned.

• Journal of Welding and Joining
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• v.31 no.6
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• pp.112-118
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• 2013

In this study, constant loading test (CLT) was performed to evaluate the hydrogen embrittlement resistance for multipass FCA weld metals of 600MPa tensile strength grade. The microstructures of weld metal-2 having the smallest carbon equivalent (Ceq=0.37) consisted of grain boundary ferrite and widmanstatten ferrite in the acicular ferrite matrix. The weld metal-1 having the largest Ceq=0.47, showed the microstructures of grain boundary ferrite, widmanstatten ferrite and the large amount of bainite (vol.%=19%) in the acicular ferrite matrix. The weld metal-3 having the Ceq=0.41, which was composed of grain boundary ferrite, widmanstatten ferrite, and the small amount of bainite (vol.%=9%) in the acicular ferrite matrix. Hydrogen desorption spectrometry (TDS) used to analyze the amount of diffusible hydrogen and trapping site for the hydrogen pre-charged specimens electrochemically for 24 hours. With increasing the current density of hydrogen pre-charging, the released amount of diffusible hydrogen was increased. Furthermore, as increasing carbon equivalent of weld metals, the released diffusible hydrogen was increased. The main trapping sites of diffusible hydrogen for the weld metal having a low carbon equivalent (Ceq=0.37) were grain boundaries and those of weld metals having a relatively high carbon equivalent (Ceq: 0.41~0.47) were grain boundaries and dislocation. The fracture time for the hydrogen pre-charged specimens in the constant loading test was decreased as the carbon equivalent increased from 0.37 to 0.47. This result is mainly due to the increment of bainite that is vulnerable to hydrogen embrittlement.