• Journal of Internet Computing and Services
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• v.13 no.4
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• pp.95-102
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• 2012

The development of applications for vehicular ad hoc networks (VANETs) has very specific and clear goals such as providing intellectual safe transport systems. An emergency warning technic for public safety is one of the applications which requires an intelligent broadcast mechanism to transmit warning messages quickly and efficiently against the time restriction. The broadcast storm problem causing several packet collisions and extra delay has to be considered to design a broadcast protocol for VANETs, when multiple nodes attempt transmission simultaneously at the access control layer. In this paper, we propose an early intelligent alert broadcasting (EI-CAST) algorithm to resolve effectively the broadcast storm problem and meet time-critical requirement. The proposed algorithm uses not only the early alert technic on the basis of time to collision (TTC) but also the intelligent broadcasting technic on the basis of fuzzy logic, and the performance of the proposed algorithm was compared and evaluated through simulation with the existing broadcasting algorithms. It was demonstrated that the proposed algorithm shows a vehicle can receive the alert message before a collision and have no packet collision when the distance of alert region is less than 4 km.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.167-168
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• 2012

Films of CrN, $Cr_{40}Zr_9N$, and $Cr_{31}Zr_{16}N$ were deposited on a steel substrate by closed field unbalanced magnetron sputtering, and their oxidation behaviors at $700^{\circ}C$ and $800^{\circ}C$ for up to 60h in air were investigated. All the deposited films were composed of the CrN phase. Zirconium atoms in $Cr_{40}Zr_9N$ and $Cr_{31}Zr_{16}N$ films partially dissolved in the CrN phase. They advantageously refined the columnar structure, reduced the surface roughness, and increased the microhardness. The CrN film displayed relatively good oxidation resistance, owing to the formation of the highly protective $Cr_2O_3$ on its surface. The $Cr_{40}Zr_9N$ and $Cr_{31}Zr_{16}N$ films oxidized to $Cr_2O_3$ as the major phase and ${\alpha}-ZrO_2$ as the minor one. They oxidized primarily by the inward transport of oxygen. The addition of Zr could not increase the oxidation resistance of the CrN film, because the formed $ZrO_2$ that was intermixed in the $Cr_2O_3$-rich oxide layer was oxygen permeable, and developed the compressive stress in the oxide scale owing to the volume expansion during its formation.

• Journal of Navigation and Port Research
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• v.32 no.10
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• pp.771-776
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• 2008

The main purpose in having a control surface on a ship is to control the motion of it. It is the important element to determine the maneuvering characteristics of the ship. In this paper, the measured results has been compared with each other to predict the performance characteristics of flapped rudder's 2-dimensional section at $Re=3.0{\times}10^4$ using 2-frame grey level cross correlation PIV method. The side force of the rudder could be mainly improved by the lift force at 10 degrees angle of attack and the drag force at 20 degrees angle of attack. The separation point and boundary layer could be controlled by the change of the only flap's angle at 10 degrees angle of attack.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.210-210
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• 2010

ABO2 형태를 가진 delafossite 구조 산화물은 p-type 투명전도체 소재로 유명하다. Delafossite 구조가 p-type 투명전도체에 적합한 결정적인 이유는 밴드갭이 넓고 공유결합에 유리하기 때문이다. 투명전도체는 가시광선의 흡수가 없도록 band gap을 넓히는 것이 우선인데 이러한 band gap이 넓은 구조가 delafossite이다. 또한 delafossite 구조는 구조적으로 각각의 산화물 이온들이 유사 사면체 배위(pseudo-tetrahedral coordination)을 갖는다. 이러한 사면체 배위결합구조에서 산소이온은 비결합면이 없기 때문에 더욱더 공유결합성을 향상시킬 것으로 생각된다. 여기서 A는 +1가 cation, B은 +3가 cation으로 구성되어 있다. A자리에는 1가 원소인 팔라듐, 플래티늄, 은, 구리 등을 가질 수 있고. B자리에 3가 원소이면서도 크기가 알루미늄보다는 크고 란타늄보다는 작은 금속이 들어갈 수 있다. Delafossite 구조는 상온에서 2종류의 polytype (상온에서 Rhombohedaral 구조와 hexagonal 구조)이 존재하며 이들은 각각 3R(Rm) 및2H (P63/mmc)의 결정 구조를 가지고 있다. CuCrO2는 일반적으로 3R결정구조를 가지는 것으로 알려져 있다. delafossite 구조는 전기적 이방성을 띄고 있는데 c-축 방향으로의 전기적 특성이 a-축 방향으로의 전기적 특성보다 약 1000배 높은 물성을 띈다고 한다. 이는 c-축 방향의 원자 위치 때문인데 CuCrO2의 경우 Cu-O-Cr-O-Cu로서 3d-2p-3d-2p-3d 궤도를 가지기 때문인 것으로 알려져 있다.[ref] 반면 c-축으로 에피성장된 박막의 경우 +3가 이온이 위치한 layer에서 hole hopping에 의해 캐리어가 전도된다고 알려져 있기도 하다. 본 연구에서는 PLD를 이용하여 c-plane 사파이어 기판위에 성장된 delafossite구조인 CuCrO2박막의 특성을 알아보았다. p-type 특성을 위하여 CuCrO2에 Ni를 첨가하였으며 그에 따른 구조적 전기적 특성을 조사하였다. 성장온도와 도핑농도를 변화시켜 특성을 연구하였다. 결정구조적 특성과 전기적 특성을 분석하려 한다.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.105-105
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• 2019

보나 여수로와 같은 수공구조물의 주변에서 발생하는 흐름 거동은 구조물 모서리에서 발생하는 흐름분리(flow separation)와 이에 따른 전단층(shear layer)과 재순환(recirculation) 흐름 영역의 발달 그리고 분리된 흐름의 재부착(reattachment)이 특징이다. 공학적으로 난류의 해석에 있어서 이러한 흐름 거동들을 정확하게 예측하는 것은 수공구조물 설계에 있어서 중요하다. 이 연구에서는 흐름 분리와 재순환 영역의 발달 그리고 흐름 재부착을 포함하는 후방계단(backward-facing step) 흐름을 155,000의 레이놀즈수 조건에서 하이브리드 RANS/LES 모델을 적용하여 해석결과를 평가한다. 하이브리드 모델로는 벽에 인접한 격자의 해상도에 상대적으로 민감하지 않은 SST(shear-stress transport) 난류 모델을 이용하는 DES(detached-eddy simulation) 기법을 적용하였다. 계단 높이가 h인 계산영역은 흐름방향 길이가 34h, 높이는 계단 상류와 하류에서 각각 1h와 2h 그리고 폭은 $2{\pi}$이다. 계단은 상류단으로부터 10h 하류부 지점에 위치한다. 경계조건으로 상부와 하부 벽면에 대해서는 비활조건을 적용한다. 상류부 수로에서 완전 발달한 흐름을 재현하기 위해서 유입경계조건은 유입부 하류 $2{\pi}h$ 지점에서 계산된 유속과 난류량을 매핑(mapping)기법을 이용하여 반복적으로 적용한다. 총 3.1백만개와 7.3백만개의 셀로 계산영역을 구현한 두 개의 계산격자 그리고 약 3.1백만개의 셀을 이용했지만 벽면 근처에서의 격자 구성을 다른 방식으로 설정한 두 가지 격자를 이용하여 격자 해상도가 DES 수치해석 결과에 미치는 영향을 분석하였다. 수치해석결과는 본 연구에서 상류단 조건으로 적용한 매핑기법이 대상 수로에서 완전 발달한 흐름을 잘 재현함을 보여주며, 합리적인 DES 해석 결과를 얻기 위해서는 벽에 수직한 방향으로 적절한 격자의 해상도와 분포가 필요함을 보여준다.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.1
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• pp.1-12
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• 1998

Industrial ejector system is a facility to transport, to compress or to pump out a low pressure secondary flow by using a high pressure primary flow. An advantage of the ejector system is in its geometrical simplicity, not having any moving part, compared with other fluid machinery. Most of the previous works have been performed experimentally and analytically. The obtained data. are too insufficient to improve our current understanding on the detailed flow field inside the ejector. In order to provide more comprehensive data on this ejector flow field, two-dimensional computations using Reynolds-averaged Navier-Stokes equations were performed for a very wide range of operating pressure ratio of the supersonic ejector with a secondary throat. The current results showed that the supersonic ejector system has an optimum pressure ratio for the secondary flow total pressure to be minimized. The numerical results clearly revealed the shock system, shock/boundary layer interaction, and secondary flow entrainment inside the supersonic ejector.

• Corrosion Science and Technology
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• v.20 no.5
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• pp.308-314
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• 2021

Neutron dose level at bottom head of a reactor pressure vessel (RPV) was calculated using reactor vessel neutron transport for a Korean nuclear power plant A. At 34 EFPY with a 40-year (2042) design life after plating repair, irradiation fast neutron effect was 6.6x10¹⁵ n/cm². As helium(He) gas can be generated by Ni only at 1/10⁶ level of 5 × 10²¹ n/cm², He generation possibility in the Ni plating layer is very little during 40 years of operation (2042, 34 EFPY). Thermal neutrons can significantly affect the generation of He from Ni metal. At 10 years after a repair, He can be generated at a level of about 0.06 appm, a level that can add general welding repair without any consideration. After 40 years of repair, 9.8 appm of He may be generated. Although this is a rather high value, it is within the range of 0.1 to 10 appm when welding repair can be applied. Clad repair by Ni electroplating technology is expected to greatly improve the operation efficiency by improving the safety and shortening the maintenance period of the nuclear power plant.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.7
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• pp.845-851
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• 2019

We design, implement, and evaluate a user-level ad hoc network routing protocol on the COTS (commercial off-the-shelf) mobile devices. In situations such as disaster recovery, emergency communication between mobile devices is necessary. For wide deployability and usability of such a system, we design and implement the networking protocols on the user level instead of modifying the kernel of mobile devices. In order to support reliable data transfer in high mobility scenarios, we selected to implement AODV (Ad Hoc On-Demand Distance Vector) as the routing protocol and TCP as the transport layer protocol. With our implementation of ad hoc networking stack on COTS smartphones, we conducted experiments in various networking environments. Our experimental results show that ad hoc networking is possible in up to 12 hops in a line topology and 5 concurrent devices in a star topology.

• Applied Chemistry for Engineering
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• v.22 no.6
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• pp.711-717
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• 2011

Two dimensional simulation results of a capacitively coupled oxygen plasma in a cylindrical reactor geometry are presented. Detailed electron impact reaction rates, which strongly depend on electron energy, are computed from collision cross sections of electrons with $O_2$ and O. Through the coupling of a three moment plasma model with a neutral chemistry/transport model are predicted spatiotemporal distributions of both charged species (electron, $O_2{^+}$, $O^+$, $O_2{^-}$, and $O^-$) and neutral species including ground states ($O_2$ and O) and metastables, known to play important roles in oxygen plasma, such as $O_2(a^1{\Delta}_g)$, $O_2(b^1{{\Sigma}_g}^+)$, $O(^1D)$, and $O(^1S)$. The simulation results clearly verify the existence of a double layer near sheath boundaries in the electronegative plasma.

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1676-1685
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• 2021

We develop a new high-fidelity multiphysics model to simulate boron chemistry in the porous Chalk River Unidentified Deposit (CRUD) deposits. Heat transfer, capillary flow, solute transport, and chemical reactions are fully coupled. The evaporation of coolant in the deposits is included in governing equations modified by the volume-averaged assumption of wick boiling. The axial offset anomaly (AOA) of the Seabrook nuclear power plant is simulated. The new model reasonably predicts the distributions of temperature, pressure, velocity, volumetric boiling heat density, and chemical concentrations. In the thicker CRUD regions, 60% of the total heat is removed by evaporative heat transfer, causing boron species accumulation. The new model successfully shows the quantitative effect of coolant evaporation on the local distributions of boron. The total amount of boron in the CRUD layer increases by a factor of 1.21 when an evaporation-driven increase of soluble and precipitated boron concentrations is reflected. In addition, the concentrations of B(OH)₃ and LiBO₂ are estimated according to various conditions such as different CRUD thickness and porosity. At the end of the cycle in the AOA case, the total mass of boron incorporated in CRUD deposits of a reference single fuel rod is estimated to be about 0.5 mg.