• Journal of the Korea Society of Computer and Information
• /
• v.22 no.12
• /
• pp.109-116
• /
• 2017

Short-lived pseudonym certificates as vehicle identities could satisfy both security and privacy requirements. However, to remove revoked certificates especially in vehicle communications, pseudonym certificate revocation list (CRL) should be distributed resource-efficiently from a practical deployment point of view and in a timely manner. In this paper, we propose a novel CRL distribution scheme capable of CRL multicast to only activated vehicles registered to the CRL multicast group using the group communication system enabler, namely, the GCSE which is being standardized. The scheme is resource efficient by using CRL distribution paths instead of paging processes to find out multicast vehicle(s) within a certain region. The analyzed results show that the proposed scheme outperforms in terms of paging cost, packets transmission cost, and the processing cost at the respective entities compared to the existing four schemes in the literature.

• Journal of Korea Multimedia Society
• /
• v.16 no.7
• /
• pp.862-869
• /
• 2013

In order to support a cell-independent traffic asymmetry, the conventional TDD system cannot avoid crossed time slot (CTS) interference. Moreover, the TDD/FDD hierarchical overlay cellular systems is taken into account as a generally accepted cell model in a heterogeneous radio environment. In this paper, we propose an interference resolving radio resource allocation technique in a TDD-OFDMA cellular system that overlays a FDD-CDMA cell. In our proposed scheme, we exploit under-used FDD-CDMA uplink resource by TDD mobile abiding by a region based time slot(TS) allocation which in turn mitigates CTS interference considerably. It is demonstrated that combined with under-used resource utilization scheme based on mobile's location, the proposed technique can reduce CTS interference considerably and support the asymmetric traffic in TDD system.

• Proceedings of the KIPE Conference
• /
• 2010.07a
• /
• pp.9-10
• /
• 2010

The lighting control power circuits should be designed in stable region according to the environment. A stable circuit is analyzed using ac equivalent circuits. The flyback converter with wide input voltage ranges is suitable for lighting control system. It is designed optimally for stability. The specifications are that the input voltage is 90V-230V, the output power is 12V/2.5A. The stability analysis is established using PSM(Phase Sensitive Multimeter) in experiment. As a result, it is confirmed that the gain margin and the phase margin are in stable area. The validity of the experimental measurement is verified.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2011.04a
• /
• pp.463-468
• /
• 2011

The prospect of Arctic trade transportation opening on a year-round basis creates a vast opportunity of exploring untapped resources and shortened navigational routes. However, the environment's remoteness and lack of technical experiences remains a big challenge for the maritime industry. With this, engine designers and makers are continually investigating, specifically optimizing propulsion shafting system design, to meet the environmental and technical challenges of the region. Further, classification societies recognize the need to upgrade the Unified Rules concerning elements to meet current Polar requirements. Hence in this paper, excitation torque calculation on Polar class vessels propulsion shafting system will be reviewed. The propeller - ice interaction load effect, which is a main consideration of excitation source of Polar Class propulsion shafting system, on shaft design calculation will be analyzed.

• Korean Journal of Metals and Materials
• /
• v.46 no.6
• /
• pp.345-350
• /
• 2008

The magnitude of constraint effect $A_2$ value was experimentally estimated by using crack tip opening displacement(CTOD) between elastic and plastic regions near crack tip front for CT specimen with $25.4t{\ss}{\AE}$ SS400 steel. The constraint effect, $A_2$ was dependent on specimen configuration and on the measured positions of CTOD near crack front. $A_2$ should be estimated using the opening displacement calculated within crack front plastic region. If not, it's not reliable to evaluate of constraint effect at crack growth initiation in this paper.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.9 no.4
• /
• pp.37-44
• /
• 2009

The characteristics of strong wind occurring over the southwestern part of the Korean peninsula are analyzed by using hourly mean wind data observed in Gusan, Mokpo, Yeosu and Wando from 1970 to 2008. The strong wind here is defined as wind speed of more than 13.9 m/s according to Korea Meteorological Administration (KMA)'s strong wind advisory. The causes of strong wind are classified into typhoon, monsoonal (wintertime continent polar air mass) and frontal (cyclone) winds. Typhoon wind is characterized by abrupt change of its speed and direction after and before landfall of typhoon and monsoonal wind by periodicity of wind speed. And frontal wind tend to be changed from southwesterly to northwesterly at observation site with location of frontal surface. Strong winds are mainly occurred in Yeosu by typhoon, Gusan and Mokpo by monsoonal wind, and Mokpo and Yeosu by frontal wind. In particular, in case of frontal wind, the frequency of strong wind in Mokpo decreases while in Yeosu it increases. Monthly frequency of strong wind is high in August in Mokpo and September in Yeosu by typhoon, January in Gusan and December in Mokpo by monsoonal wind, and in April in Mokpo and Yeosu by frontal wind. The duration less than 1 hour of strong wind is prominent in all stations.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2010.04a
• /
• pp.383-384
• /
• 2010

The control surface on a ship is to control the motion of it in forward and backward states. In this paper, the measured results has been compared with each other to predict the backward flow characteristics of the single rudder's 2-dimensional section at $Re=2.0\times10^4$ using 2-frame grey level cross correlation PIV method especially, The separation region appears at 10 to 20 degrees angle of attack in a forward state. The separation point and boundary layer demonstrate in the same angle of attack compared it with the forward states.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.23 no.1
• /
• pp.104-111
• /
• 2017

This research focuses on simulation and visualization of flow field characteristics inside a centrifugal pump. The 3D numerical analysis was carried out by using a numerical CFD tool, addressing a Reynolds Average Navier-Stock code with a standard k-${\varepsilon}$ two-equation turbulence model. The simulation accounts for friction head loss due to rough walls at suction, impeller, discharge areas and volumetric head loss at impeller wear ring. A comparison of performance curves between simulation and experimentation is included, and it reveals a same trend of those results with a small difference of maximum 5 %. At best efficiency point, velocity vectors are smooth but it changes significantly under off-design point, a strong recirculation appears at the outlet of impeller passages near tongue area. A relatively uniform preassure distribution was observed around the impeller in despite of the tongue. Within the volute, because of its geometry, spiral vortexes formed, proving that the flow field in this region was relatively turbulent and unsteady.

• Corrosion Science and Technology
• /
• v.9 no.6
• /
• pp.331-337
• /
• 2010

This study compared the macro and micro electrochemical characteristics at the local area of welding metal on dissimilar welding parts for type 304 stainless steel (SS) and type 316L SS. The materials are used for double wall gas pipe of duel fuel engine for a ship. The various potentiodynamic experiments were performed several times in 10% ${H_2C_2O_2}{\cdot}{H_2O}$ solution using macro and micro methods, respectively. The micro electrochemical experiments conducted to resolve at local area on cross-section of dissimilar welding materials by micro-droplet cell device. The micro-droplet cell techniques can be used almost electrochemical experiments to resolve corrosion characteristics of the limited electrode area of the metallic surface between wetted spot of working electrode and tip of sharpened capillary tube. The results of macro electrochemical experiments show that resistance of active dissolution reaction at welding zone was high due to low current density by formation of passivation protection film at passive region. According to the micro electrochemical experiment, the corrosion current density of welding zone and bond zone were relatively high.

• Korean Journal of Environment and Ecology
• /
• v.30 no.4
• /
• pp.783-792
• /
• 2016

The purpose of this study is to investigate the characteristics of the vegetation structure and the location environment of Albizzia kalkora (AK) growing in Mt. Yudal located in Mokpo city and in the nearby islands. The AK community in Mt. Yudal in Mokpo city (Community I) is located in a region which is relatively high above the sea level. The average age of the major kinds of trees found in the region is about 30 years. The vegetation structure in the community shows an early stage of vegetation development due to continued disturbance. In Community IV, on the sandy soil in the flatland near the seashores, the average age of the major kinds of trees is about 9 years. In this community, a pure forest is presumed to have been formed in a poor environment which is artificially disturbed in relatively recent times even as AK with its strong adoptability was introduced into the region. In other communities (II, III), the vegetation state shows a competition between AK and deciduous oak trees, and the average age of the major kinds of trees is about 13 to 30 years. AK communities with a better developed vegetation structure are located on the higher steep slopes near the seashore. In the early stage of vegetation development, the forest floor received more effective light for photosynthesis, and thus more seedlings of AK emerged and grew. The probability of AK appearing in the damaged or sterile soil near the seashore was high because of its strong adaptability. However, as the vegetation structure developed further and the soil fertility increased, the domination of AK in the vegetation structure decreased as deciduous oak trees won the competition with AK.