• Wind and Structures
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• 제28권2호
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• pp.71-87
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• 2019

The yaw and interference effects of blades affect aerodynamic performance of large wind turbine system significantly, thus influencing wind-induced response and stability performance of the tower-blade system. In this study, the 5MW wind turbine which was developed by Nanjing University of Aeronautics and Astronautics (NUAA) was chosen as the research object. Large eddy simulation on flow field and aerodynamics of its wind turbine system with different yaw angles($0^{\circ}$, $5^{\circ}$, $10^{\circ}$, $20^{\circ}$, $30^{\circ}$ and $45^{\circ}$) under the most unfavorable blade position was carried out. Results were compared with codes and measurement results at home and abroad, which verified validity of large eddy simulation. On this basis, effects of yaw angle on average wind pressure, fluctuating wind pressure, lift coefficient, resistance coefficient,streaming and wake characteristics on different interference zone of tower of wind turbine were analyzed. Next, the blade-cabin-tower-foundation integrated coupling model of the large wind turbine was constructed based on finite element method. Dynamic characteristics, wind-induced response and stability performance of the wind turbine structural system under different yaw angle were analyzed systematically. Research results demonstrate that with the increase of yaw angle, the maximum negative pressure and extreme negative pressure of the significant interference zone of the tower present a V-shaped variation trend, whereas the layer resistance coefficient increases gradually. By contrast, the maximum negative pressure, extreme negative pressure and layer resistance coefficient of the non-interference zone remain basically same. Effects of streaming and wake weaken gradually. When the yaw angle increases to $45^{\circ}$, aerodynamic force of the tower is close with that when there's no blade yaw and interference. As the height of significant interference zone increases, layer resistance coefficient decreases firstly and then increases under different yaw angles. Maximum means and mean square error (MSE) of radial displacement under different yaw angles all occur at circumferential $0^{\circ}$ and $180^{\circ}$ of the tower. The maximum bending moment at tower bottom is at circumferential $20^{\circ}$. When the yaw angle is $0^{\circ}$, the maximum downwind displacement responses of different blades are higher than 2.7 m. With the increase of yaw angle, MSEs of radial displacement at tower top, downwind displacement of blades, internal force at blade roots all decrease gradually, while the critical wind speed decreases firstly and then increases and finally decreases. The comprehensive analysis shows that the worst aerodynamic performance and wind-induced response of the wind turbine system are achieved when the yaw angle is $0^{\circ}$, whereas the worst stability performance and ultimate bearing capacity are achieved when the yaw angle is $45^{\circ}$.

• 한국통신학회논문지
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• 제37권6B호
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• pp.443-452
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• 2012

Mobile Ad-hoc Networks 환경에서 노드의 이동성을 고려하기 위한 라우팅 알고리즘은 그 특성에 따라 Proactive와 Reactive 방식으로 구분되며, 두 가지 라우팅의 장점을 조합하는 많은 Hybrid 라우팅이 ZRP (Zone Routing Protocol) 알고리즘을 기반으로 설계되어왔다. ZRP는 특정 지역의 Zone을 생성한 후, Zone 내부에는 Proactive, 외부에는 Reactive 방식을 운영하여 근거리 노드들을 향하는 데이터의 경로 탐색 패킷 발생의 비용을 최소화 하였다. 하지만 실제 네트워크에서의 데이터 전송은 짧은 시간 영역에서 특정 노드에게만 요구되는 경향이 있으며, 이에 대한 고려가 없는 ZRP는 이러한 요구를 만족시키기에는 제한적이다. 본 연구는 실시간 데이터 전송량과 전송 경로의 홉 수를 고려하여, 소스 노드와 목적지 노드를 근간으로 하는 Zone을 on-demand로 형성하는 효율적인 Hybrid 라우팅을 제안하고, 이를 위하여 Zone의 생성 및 소멸을 결정하는 DZD (Dynamic Zone Decision) 알고리즘을 고안한다. 또한, 본 연구의 성능을 검증하기 위하여 기존의 Proactive, Reactive, Hybrid 라우팅 알고리즘과의 비교결과를 분석하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제28회 춘계학술대회논문집
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• pp.71-74
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• 2007

희박 예혼합 스월 연소기의 난류 연소와 화학반응간의 간섭 메커니즘을 파악하기 위하여 Large Eddy Simulation(LES)을 수행하였다. 난류 화염의 유동 특성을 자세히 살펴보기 위하여 비정상 난류 연소 수치해석 기법을 적용하여, 약간의 연료 덩어리가 일차연소영역(Primary combustion zone)에서 빠져나와 선회 방향으로 흘러 국부적 핫스팟(hot spot)을 발생시키며, 이는 large vortical structure를 만들어 내는 것을 관찰 할 수 있었다. 압력변동과 비정상 열 방출 사이의 관계는 공간 및 시간적 Rayleigh parameter에 의해 고찰되었다.

• 수산해양기술연구
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• 제20권1호
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• pp.30-36
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• 1984

대규모의 소성역을 동반하면서 파괴하는 고인성 재료의 탄소성 파괴 반가를 위하여 제안된 바 있는 CPE 모형의 유효성을 입증하고자 소성역의 영향을 보정한 선형 파괴역학과의 이론적 검토와 오오스테나이트계 스테인레스강에 대한 실험적 비교검토를 통하여 얻은 결론은 다음과 같다. 예측한 바와 같이 선형 파괴역학의 적용은 소규모 항복조건이 성립하는 경우에만 가능하며 CPE 모형은 대변형을 형성하면서 파괴하는 경우의 파괴모형으로서 유효하다. 더욱 엄밀한 유효성을 입증하기 위하여 다음의 사항이 필요하다고 본다. 1. 크랙의 길이가 짧은 시험편에 대한 실험이 필요하다. 2. 크랙성장 개시점을 정확하게 찾을 수 있는 방법이 필요하다. 3. 파괴 진행영역에 대한 두께의 영향을 고려해 보아야 할 필요성이 있다.

• 한국환경과학회지
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• 제7권6호
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• pp.745-751
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• 1998

The well-mixed room model has been traditionally used to predict the concentrations of contaminants in indoor environments. However, this is inappropriate because the flow fields in many indoor environments distribute contaminants non-uniformly, due to imperfect air mixing. Thus, some means used to describe an imperfectly mixed room are needed. The simplest model that accounts for imperfect air mixing is a two-zone model. Therefore, this study on development of computer program far the two-zone model is carried out to propose techniques of estimating the concentration of contaminants in the room. To do this, an important consideration is to divide a room into two-zone, i.e. the lower and upper zone assuming that the air and contaminants are well mixed within each zone. And between the zones the air recirculation is characterized through the air exchange parameter. By this basic assumption, the equations for the conservation of mass are derived for each zone. These equations are solved by using the computational technique. The language used to develope the program is a VISUAL BASIC. The value of air exchange coefficient($f_12$) is the most difficult to forecast when the concentrations of contaminants in an imperfectly mixed room are estimated by the two-zone model. But, as the value of $f_12$ increases, the air exchange between each zone increases. When the value of $f_12$ is approximately 15, the concentrations in both zone approach each other, and the entire room may be approximately treated as a single well-mixed room. Therefore, this study is available for designing of the ventilation to improve the air quality of indoor environments. Also, the two-zone model produces the theoretical base which may be extended to the theory for the multi-zone model, that will be contributed to estimate the air pollution in large enclosures, such as shopping malls, atria buildings, atria terminals, and covered sports stadia.

• 농촌계획
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• 제22권1호
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• pp.25-35
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• 2016

This study targets Korean culture theme park in Yeongju-Zone and World confucian scholar culture park in Bonghwa-Zone among the Three Major Cultural Areas Projects supervised by Ministry of Culture, Sports and Tourism. The study analyzes the Historical and Cultural Authenticity of each project on the basis of the reports and the report materials for meeting with related organizations. The results of the study are drawn as follows. First, through the theoretical consideration, this study drew the types of authenticity: originality, identity, specificity and visibility, which are evaluation items on the Historical and Cultural Authenticity. Second, Bonghwa-Zone succeeded in acquiring originality with tangible cultural properties but Yeongju-Zone chose a project site without it. Third, with originality, Bonghwa-zone was evaluated as having resources and concept with high traditional culture connectivity and fulfilled identity. It led the feature showing the high affinity between originality and identity. Fourth, compared to the projects of Andong-Zone in the Three Major Cultural Areas Projects, these two projects failed to acquire the distinctions since the primary and the secondary influence area and major facilities & programs coincided with those of the projects of Andong-Zone. Fifth, compared to Bonghwa-Zone, Yeongju-Zone realized visibility faithfully by the conceptual flexibility of "Korean Culture" and a large-scale development. Sixth, in terms of the Historical and Cultural Authenticity of project plan, it is evaluated that Yeongju-Zone and Bonghwa-Zone only fulfilled visibility and specificity respectively.

• 한국정보과학회논문지:정보통신
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• 제33권4호
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• pp.299-309
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• 2006

Ad hoc 환경에서 사용되는 On-demand 방식인 AODV 라우팅 프로토콜은 경로를 찾기 위하여 노드들이 가지고 있는 라우팅 테이블을 우선 검사하고, 만약 적합한 경로가 존재하지 않거나 유효하지 않은 경로, 또는 중간노드에서 경로손실이 발생하였을 경우 Route Discovery Process(RDP)를 수행하여 새로운 경로를 찾게 된다. 하지만 중 / 대형 Ad hoc 환경에서 이러한 RDP의 증가는 네트워크 성능의 저하를 초래한다. 본 논문에서는 경로설정을 위해 사용되는 AODV 라우팅 프로토콜에 Zone 개념을 도입한 AOZDV(Ad hoc On-demand Zone and Distance-Vector Routing Protocol)를 제안한다. AOZDV는 노드의 트래픽과 전력정보를 활용하여 소스 / 목적지 노드에 Zone을 형성하고, Zone 내부에서의 라우팅은 Destination-Vector Table을 활용하는 기법으로서, 시뮬레이션을 통해 AOZDV 가 기존의 라우팅 프로토콜들에 비해 노드들의 이동성으로 인해 발생하는 경로손실 및 RDP 가 감소함을 확인할 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.365-371
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• 2004

Generally, fracture of a material is influenced by plastic zone size developed near the crack tip. Hence, according to the relative size of plastic zone in the material, the mechanics as a tool for analyzing the fracture process are classified into three kinds, that is, Linear Elastic Fracture Mechanics, Elastic Plastic Fracture Mechanics, Large Deformation Fracture Mechanics. Even though the plastic zone size is such an important parameter, the practical measurement techniques are very limited and the one for in-situ measurement is not virtually available. Therefore, elastic-plastic FEA has been performed to estimate the plastic zone size. In this study, it is noticed that side necking at the surface is a consequence of plastic deformation and lateral contraction and the relation between the plastic zone and side necking is investigated. FEA for modified boundary layer models with finite thickness, various mode mixities $0^{\circ}$, $30^{\circ}$, $60^{\circ}$, $90^{\circ}$ and strain hardening exponent n=3, 10 are performed. The results are presented and the implication regarding to application to experiment is discussed.

• 한국레이저가공학회지
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• 제7권3호
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• pp.25-36
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• 2004

This study was performed to clarification of the formation of weld discontinuities in the dissimilar laser fusion zone. Welding parameters were beam power of 1300, 1430, 1560, and 1700 W and travel speed of 1, 1.3, and 1.7 m/min. Most cavities in the fusion zone were observed near the tip. Cavities in the fusion zone observed to be formed and grown from pores in the tip. More cavities were formed as the beam position moves to the tip side. Small cavities were decreased but large cavities were increased when the energy input increased. W content in the fusion zone was increased with heat input and as the beam position close to the tip. In the fusion zone, W content in the dendrite boundary was increased with heat input. Considering the propagation path and fracture morphology, cracks were solidification cracking, and were initiated and propagated along the dendrite boundaries. The formation of cracks might be related with the W rich ${\mu}$ phase which was formed in the grain boundaries and dendrite boundaries.

• Archives of Reconstructive Microsurgery
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• 제8권1호
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• pp.44-49
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• 1999

From January 1990 to December 1998, 449 consecutive single-digital replantations were reviewed retrospectively in order to determine the essential number of vascular anastomoses for successful finger replantation. The correlations between the number of anastomosed vessels and survival rate were examined according to the amputated digital levels and all of the correlated results were compared with each other statistically. In zone I, The survival rate of the digits with a repaired vein was higher than that of digits treated with external bleeding method. In zone II, the equal number(s) between the arterial and venous repair was an important factor in successful replantation. And the repaired arteries more than repaired veins in number led to venous congestion and resulted in a failure of replantation, which was maybe due to the large amount of arterial input relative to small volume of amputated stump with small sized vein. In zone III, the equal number(s) between the arterial and venous repair was also an important factor in successful replantation. But unlike in zone II, venous congestion was scarcely happened if the venous drainage was sufficient with a repaired large vein alone. In zone IV, two or more arteries and veins were required for successful replantation. In conclusion, it is desirable that the repair of vessels as many as possible to increase the possibility of a good result. But digital amputations and their condition for replantation were variable, therefore, the numbers in vascular repair should to be modified and straightforward as the case may be.