• 제목/요약/키워드: Far wake

검색결과 54건 처리시간 0.027초

PIV를 이용한 직렬배열에서 2원주 주위의 유동장 특성 연구 (The Characteristic Investigation of the Flowfield around Two Circular Cylinders in the Tandem Arrangement Using the PIV)

  • 노기덕;김광석;박지태;오세경
    • Journal of Advanced Marine Engineering and Technology
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    • 제31권2호
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    • pp.159-165
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    • 2007
  • The Characteristics of the flowfield around two circular cylinders in tandem arrangement was investigated by PIV. Strouhal numbers. velocity vectors and velocity profiles were observed at centre-to-centre space ratios of P/D= 1.5. 2.0 and 2.5, and Reynolds number of $Re=3.0{\times}10^3{\sim}5.0{\times}10^3$. As the results the Strouhal numbers measured in the rear region of the cylinder of wake side were decreased with the space ratios. The flow between two cylinders was almost stagnated and the size of the stagnated region was larger in the close side than in the far side of the front cylinder. The direction of vortex between two cylinders was opposed each other with the small difference(${\alpha}\;{\pm}1.0^{\circ}$) of the attack angle ${\alpha}$.

틸트로터에서 발생하는 공력소음의 측정에 관한 연구 (Measurements on the Aerodynamic Noise Generated from a Tiltrotor)

  • 홍석호;박성;최종수;김규영;이덕주
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2005년도 춘계학술대회논문집
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    • pp.158-163
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    • 2005
  • In this paper the aeroacoustic characteristics of a tilt-rotor system is measured by using a sealed model tilt-rotor. With a microphone array system and the do-dopplerization algorithm, the location and the characteristics of rotor noise are successfully measured. The most of high frequency noise (4kHz) is found to be located at rotor blade tips, but the low frequency tonal noise is dominant on the middle of the rotor blades. The measured tonal noise characteristics are compared to the results of theoretical calculation. At 0.5m distance from the rotor plane, measured and calculated data are relatively well matched regardless of rotating speed and collective pitch angie for the azimuthal angles between $0^{\circ}\;and\;60^{\circ}$. However, the data on the azimuthal angles between $70^{\circ}\;and\;90^{\circ}$ are not quite comparable. In addition, the compared data for far-field case (1.5m) are quite different. This is probably due to the unsteady effect which if not included in the theoretical calculation.

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전산해석을 활용한 두께비 18%익형(Case1)의 공력특성 분석 (Aerodynamic Analysis of 18% Thick Airfoil(Case 1) with Computational Fluid Dynamics)

  • 김철완;이융교
    • 한국항공우주학회지
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    • 제45권3호
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    • pp.212-216
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    • 2017
  • 두께비 18% 익형(KARI-11-180)에 대한 공력특성 분석이 전산해석기법을 활용해 수행되었다. 익형주위의 격자는 벽면에서 수직으로 투영하여 경계층 격자를 형성하였고 익형 후방에는 정밀한 후류 예측을 위해 조밀한 격자를 위치하였다. 원방경계까지의 거리는 익형 코드의 100배로 정하였고 익형시험결과와의 비교를 위해 자유류 속도, 익형 코드 및 Reynolds수를 풍동시험과 동일하게 정하였다. 또한 난류 모델은 천이지점 예측이 우수한 transition SST 및 DES 모델을 사용하였다. 3차원 전산해석은 세장비가 2와 5인 익형모델에 대해 수행되었는데 양력은 풍동시험결과보다 높은 값을 항력은 낮은 값을 예측하였다.

열성층유동장에 놓인 원주후류의 특성에 대한 연구 (3) -선형열원으로부터의 난류확산- (Study on the Characteristics of Cylinder Wake Placed in Thermally Stratified Flow(III) - Turbulent Dispersion from a Line Heat Source-)

  • 김경천;정양범
    • 대한기계학회논문집
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    • 제19권5호
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    • pp.1300-1307
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    • 1995
  • The effect of thermal stratification on the turbulent dispersion from a fine cylindrical heat source was experimentally examined in a wind tunnel with and without a strong temperature gradient. A 0.5 mm dia. nichrome wire was used as a line heat source. Turbulent intensities, r.m.s. value of temperature and convective heat fluxes were measured by using a hot-wire and cold-wire combination probe. The results show that the peack value and the spread of the vertical turbulent intensity for the stratified case are far lower than those in the neutral case, which indicates that the stable temperature gradient suppresses the vertical velocity component. All of the third order moments including heat fluxes measured in the stable condition have very small values than those of the neutral case. This nature suggests that the decrease of scalar fluctuations in the stably stratified flow is mainly due to the suppression ofthe turbulent diffusion processes by the stable stratification. A simple gradient model with a composite timescale which has a simple weighted algebraic mean between dynamic and thermal time scale yields reasonably good numerical values in comparison with the experimental data.

구 주위의 유동으로 인해 발생하는 유동 소음의 특성 (Characteristics of Flow-Induced Noise around a Sphere)

  • 윤기웅;최해천
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2003년도 추계학술대회
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    • pp.810-815
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    • 2003
  • Flow-induced noise propagated from flow over a sphere is numerically investigated for laminar flow at Re = 300 and 425, and for turbulent flow at Re = 3700 and $10^4$, where the Reynolds number is based on the freestream velocity and the sphere diameter. The numerical method used for obtaining the flow over a sphere is based on an immersed boundary method in a cylindrical coordinate system. The Curle’s solutions of the Lighthill’s acoustic analogy with and without the far-field and compact-source approximation are used in order to investigate the noise field from flow over a sphere. Since the drag and lift forces change irregularly in time at Re = 425, 3700 and $10^{4}$, the noise propagates in a complicated manner. At Re = 300, 425 and $10^{4}$, the noise from dipole sources is much larger than that from quadrupole sources. On the other hand, at Re = 3700, the quadrupole source becomes dominant. The temporal variation of the flow-induced noise around a sphere is obtained at some observation points, which shows that the peak frequency corresponds to the Strouhal number associated with the wake instability.

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자유수면과 움직이는 벽면 사이에 놓인 원형 실린더 주위의 층류 유동구조 (Laminar Flow Structures Near a Circular Cylinder in between a Free-Surface and a Moving Wall)

  • 서장훈;정재환;윤현식;박동우;전호환
    • 대한조선학회논문집
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    • 제49권3호
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    • pp.213-221
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    • 2012
  • The present study numerically investigates the interaction between a free-surface and flow around a circular cylinder over a moving wall. In order to simulate the flow past the circular cylinder over a moving wall near a free-surface, this study has adopted the direct-forcing/fictitious domain (DF/FD) method with the level set method in the Cartesian coordinates. Numerical simulation is performed for a Reynolds numbers of 100 in the range of $0.25{\leq}g/D{\leq}2.00$ and $0.5{\leq}h/D{\leq}2.00$, where g/D and h/D are the gaps between the cylinder and a moving wall and the cylinder and a free-surface normalized by cylinder diameter D, respectively. According to g/D and h/D, the vortex structures have been classified into three patterns of the two-row, one-row, steady elongation. In general, both of g/D and h/D have the large values which mean the cylinder is far away from the wall and the free-surface, two-row vortex structure forms in the wake. When g/D decreases, the two-row vortex structure gradually transfers into the one-row vortex structure. When the g/D reveals the critical value below which the flow becomes steady state, resulting in the steady elongation vortex.

마을건강원 역할 및 업무내용에 관한 고찰 (A Review on the Role and Functions of the Village Health Worker)

  • 이명숙;한명화;이금련
    • 한국보건간호학회지
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    • 제7권1호
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    • pp.1-16
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    • 1993
  • The objective of this study is to review the role and function of the village health worker in the wake of the recent social changes in Korea. The stud}' also aimed at' elucidating' the characteristics of the village health worker organizations developed through community participation in this country. The study methods employed were: a review of literature and other existing information related to VHW's activities ; the use of Questionnaire and interview with VHW's on their activities in one selected county in 1992. The major findings obtained are as follows: 1. So far the community health care activities have been carried out by medical colleges, foreign aid agencies and religious organizations with a view to improving health care for the population in rural area. 2. The VHWs employed by the local community health services received remuneratiorin cash or in kind. However, presently no remuneration is paid to VHWs employed by the government village health projects. The training for VHWs is organized by County Health Center once a year for 1-2days regardless of pre-employment or refresher. 3. The needs of care for maternal and child health and family planning has been decline due to the decrease of the target population, but on the other hand, the needs of care by VHW for prevention of infectious diseases, health of the aging, management of geriatric diseases, prevention of poisoning of pesticides and environmental sanitation has beer increased. 4. It was felt strongly that the training for VHWs should be strengthened by means of developing a problem-solving oriented educational program in order to improve practical skills of VHWs.

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비선형 와류격자법을 이용한 낮은 종횡비 날개의 공력특성 계산 (Calculation of Low Aspect Ratio Wing Aerodynamics by Using Nonlinear Vortex Lattice Method)

  • 이태승;박승오
    • 한국항공우주학회지
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    • 제36권11호
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    • pp.1039-1048
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    • 2008
  • 본 논문에서는 새로운 비선형 와류격자법 계산 과정이 제안된다. 기존의 계산 과정은 자유와의 형태 계산을 위해 내부 반복계산 및 하향이완법을 포함한다. 하지만 본 논문에서는 유사 정상 개념에 기초한 새로운 수식을 제안하여 자유와의 형태를 계산함으로써, 계산 과정에서 내부 반복계산 및 하향이완법을 생략한다. 또한 반복계산이 진행됨에 따라 각 분절에 유도되는 유속도를 적절히 평균해 줌으로써 알고리듬의 수치적 안정성을 향상시킨다. 그리고 낮은 종횡비 날개에 대한 수치실험을 수행하여 분절의 길이, 와류중심반경, 후류영역 계산범위 등과 같은 중요 인자들의 적절한 기준을 경험적으로 결정한다.

A Consensus Plan for Action to Improve Access to Cancer Care in the Association of Southeast Asian Nations (ASEAN) Region

  • Woodward, Mark
    • Asian Pacific Journal of Cancer Prevention
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    • 제15권19호
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    • pp.8521-8526
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    • 2014
  • In many countries of the Association of Southeast Asian Nations (ASEAN), cancer is an increasing problem due to ageing and a transition to Western lifestyles. Governments have been slow to react to the health consequences of these socioeconomic changes, leading to the risk of a cancer epidemic overwhelming the region. A major limitation to motivating change is the paucity of high-quality data on cancer, and its socioeconomic repercussions, in ASEAN. Two initiatives have been launched to address these issues. First, a study of over 9000 new cancer patients in ASEAN - the ACTION study - which records information on financial difficulties, as well as clinical outcomes, subsequent to the diagnosis. Second, a series of roundtable meetings of key stakeholders and experts, with the broad aim of producing advice for governments in ASEAN to take appropriate account of issues relating to cancer, as well as to generate knowledge and interest through engagement with the media. An important product of these roundtables has been the Jakarta Call to Action on Cancer Control. The growth and ageing of populations is a global challenge for cancer services. In the less developed parts of Asia, and elsewhere, these problems are compounded by the epidemiological transition to Western lifestyles and lack of awareness of cancer at the government level. For many years, health services in less developed countries have concentrated on infectious diseases and mother-and-child health; despite a recent wake-up call (United Nations, 2010), these health services have so far failed to allow for the huge increase in cancer cases to come. It has been estimated that, in Asia, the number of new cancer cases per year will grow from 6.1 million in 2008 to 10.6 million in 2030 (Sankaranarayanan et al., 2014). In the countries of the Association of Southeast Asian Nations (ASEAN), corresponding figures are 770 thousand in 2012 (Figure 1), rising to 1.3 million in 2030 (Ferlay et al., 2012). ASEAN consists of Brunei Darussalam, Cambodia, Indonesia, Lao, Malaysia, Myanmar, the Philippines, Singapore, Thailand and Viet Nam. It, thus, includes low- and middle-income countries where the double whammy of infectious and chronic diseases will pose an enormous challenge in allocating limited resources to competing health issues. Cancer statistics, even at the sub-national level, only tell part of the story. Many individuals who contract cancer in poor countries have no medical insurance and no, or limited, expectation of public assistance. Whilst any person who has a family member with cancer can expect to bear some consequential burden of care or expense, in a poor family in a poor environment the burden will surely be greater. This additional burden from cancer is rarely considered, and even more rarely quantified, even in developed nations.

새로운 방송 서비스로의 이전 : 이주 이론을 통한 MCN으로 전환의도 연구 (A Study on Switching Intention of Broadcasting Service to MCN Service by Migration Theory)

  • 김용희
    • 산경연구논집
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    • 제10권1호
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    • pp.59-67
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    • 2019
  • Purpose - The Millennial Generation, which grew in the wake of the spread of the Internet and rapid changes in the media environment, is rapidly moving from the traditional broadcasting environment to the Internet-broadcasting environment in terms of content acceptance. With the emergence of UGC (User-generated content), the change in the status of single-person content creators enables the growth of multi-channel networks (MCN), a new content-distribution platform and an agency concept for single creators. Youtube-based MCN produces multiple single star producers and casts and provides its own video series through Youtube. It is also emerging as a major M&A target for global media providers in terms of providing content to a wide range of consumers with the same interests and consumption characteristics. In addition, for the Millennials generation, which are part of their lives, MCN is becoming the most suitable media for TGIF (Twitter, Google, i-phone, Facebook). Accordingly, this study defines newly emerging MCNs and analyzes the factors for accepting MCN-produced content based on the push-pull-mooring (PPM) model. Research design, data, and methodology - An empirical analysis is performed through a questionnaire survey. For this purpose, 204 people who have experience of watching MCN were studied. Collected data is processed through analysis of a structural equation model using R to test the hypothesis. Results - For the MCN service to become an alternative to existing media, it is necessary to continuously promote cultural diversity and diversity of attempts that conventional media cannot provide. It is the attractiveness of the alternative that has the greatest influence on the intention to switch to a MCN service. When we look at MCN content so far, certain patterns such as game progress, introduction, food, and chat rooms have already appeared. We need to overcome this and develop a completely new conceptual content that we have never seen before. This requires a more generous viewer perception of the topics covered. For diversity, linguistic and verbal violence should be tolerant in common sense to provide a foundation for securing cultural diversity. Conclusions - In this study, we tried to develop a comprehensive approach to the substitution effect of MCN. In terms of academic achievement, the PPM model is used to enhance the utilization of media and broadcasting. Practical implications are to provide an analytical framework for verifying alternative or complementary effects when viewers switch to MCN.