• 대한기계학회논문집
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• 제18권11호
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• pp.3039-3045
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• 1994

The k-$\varepsilon$ turbulence models by Launder et al.(1977, LPS) and Leschziner and Rodi(1981, LR) are modified to account for the secondary straining effect with having a generality in the present paper. The modified models are obtained by replacing the gradient Richardson number used to account for the secondary straining effect in the original models by a new parameter with a tensor-invariant correction form. These two modified models are used to predict the turbulent flow over a backward-facing step. In contrast to both standard and modified LR models, the modified LPS model is found to predict the reattachment point fairy well, as well as mean velocity, wall static pressure, turbulent kinetic energy and Reynolds shear stress in the recirculating region.

• 한국항공운항학회지
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• 제17권1호
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• pp.17-23
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• 2009

The purpose of this study is possibility of the heavy rainfall prediction using instability index. The convective instability index using this study is Convective Available Potential Energy(CAPE) concerned the growth energy of the storm, Bulk Richardson Number(BRN) concerned the type and strength of the storm, and Sotrm Relative Helicity(SRH) concerned maintenance of the storm. To verify the instability index, the simulation of heavy rainfall case experiment by Numerical Weather Prediction(NWP) model(MM5) are designed. The results of this study summarized that the heavy rainfall related to the high instability index and the proper combination of one more instability index made the higher heavy rainfall prediction.

• 설비공학논문집
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• 제19권12호
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• pp.831-841
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• 2007

This work is to extend the elliptic operator, which has been already adopted in turbulent stress model, to fully developed turbulent buoyant channel flows with changing the orientation of the buoyancy vector to be perpendicular to the channel walls. The turbulent heat flux models based on the elliptic concept are employed and closely linked to the elliptic blending second moment closure which is used for the prediction of Reynolds stresses. In order to reflect the stable or unstable stratification conditions, the present model introduces the gradient Richardson number into the thermal to mechanical time scale ratio and model coefficients. The present model has been applied for the computation of stably and unstably stratified turbulent channel flows and the prediction results are directly compared to the DNS data.

• 대한조선학회지
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• 제23권1호
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• pp.13-22
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• 1986

Axisymmetric turbulent thick boundary layers on a rotating body of revolution are calculated numerically in the paper. Richardson number is introduced to the mixing length to take account of swirl effects on Reynolds stresses. Interactions of the boundary layer and the external potential flow are included by adding the displacement thickness of boundary layers on the original body. Pressure distributions on the body surface are estimated by integrating normal momentum equation across the boundary layer. A model is designed and tested in the wind tunnel. Mean velocities are measured. Through the present study, swirl effects on the thick axisymmetric boundary layer development are considerable in comparison with those of non-totating cases. Rotational motion generally increase boundary layer thickness, axial skin friction coefficients, and form drags. Circumferential flow can be reversed to induce negative skin friction when the section area is reduced.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.879-882
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• 2004

Two-phase flow exists in many industrial components. Characteristics of two-phase flow have been studied by many researchers; however, a further study of the two-phase is required for flow-induced vibration. Characteristics of two-phase flow were measured by force sensor at the end of a vertical pipe. The predominant frequency of fluctuation was obtained for various speeds of flow pattern. A correlation to slug frequency for horizontal flow was obtained by Heywood & Richardson (1979), while Legius et al (1997) for vertical flow. A coefficient based on the correlation is estimated and then compared to the existing ones. The existing empirical formulations for average void fraction were proposed by Wallis (1969), Zuber et al (1967) and Ishii (1970). In the present result, flow parameters, such as flow quality and real velocity, are evaluated with void fraction.

• 한국어류학회지
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• 제11권1호
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• pp.23-28
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• 1999

1995년 남해 거제도 부근에서 채집된 어류를 동정한 결과 지금까지 우리나라에서는 서식이 알려지지 않은 Chaunax abei와 Bembrops curvatura로 확인되어 이 2종을 한국산 미기록종으로 보고한다. C. abei는 외부형태적으로 C. fimbriatus와 유사하나 체표의 녹색 무늬 형태가 원형이고 등지느러미의 앞쪽에는 노란 반점과 그 뒤에 약간 패인 곳이 없으며, 유인돌기와의 주변에는 돌기가 없다는 점이, 그리고 B. curvatura는 B. caudimacula와 유사하나 뒷지느러미 연조수 및 측선린 수와, 측선이 깊게 내려간 점 그리고 제 1 등지느러미의 첫 번째 막이 검다는 점 등이 이들 유사종들과 잘 구별되었다. 이들의 한국명으로는 Chaunacidae "점씬벵이과", Chaunax "점씬벵이속", C. abei를 "점씬벵이"로, 그리고 B. curvatura는 "줄굽은눈퉁이"라고 명명하였다.

• 한국가시화정보학회지
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• 제8권3호
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• pp.35-40
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• 2010

We have investigated different radial temperature gradient effect on the stability of Taylor-Couette flow. The radius ratio and aspect ratio of the model was 0.825 and 48, respectively. Two heating exchangers were used for generating different temperature gradient along the radial direction. The change of flow regime in the Taylor-Couette flow was studied by increasing the Reynolds number. The results showed that: as Gr is increased in helical vortex flow regime, the vortices with the same direction of convection flow increased in size, and the vortex moving velocity also increased. It is also shown that the presence of temperature gradient obviously increased the flow instability when the Richardson number is larger than 0.0045.

• Journal of Information Science Theory and Practice
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• 제4권1호
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• pp.6-20
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• 2016

Scholarly communication plays a significant role in the development and dissemination of research outputs in library and information science (LIS). This study presents findings from a survey which examines the key attributes that characterize the publishing by Pakistani LIS scholars, i.e. academics and professionals, in national journals. A pilot-tested, electronic questionnaire was used to collect the data from the target population. 104 respondents (or 69.3% of target) provided feedback on areas such as number of articles published, number of citations, and the nature of any collaboration with other authors. The findings of this survey revealed that, among the various designated regions of Pakistan, the Punjab region was the most highly represented. In articles published in national journals, there was a clear preference among all respondents to collaborate with at least one other author. The citation metrics for LIS articles in national journals were relatively low (30.22%), which aligns with Scimago’s Journal and Country Rankings. The uptake of social scholarly networks mirrors international trends. Respondents were asked to score factors which could impact negatively on their ability to undertake research and/or publish the results. The study recommends that concerned stakeholders work together, as appropriate, to address concerns. In addition, it recommends that further research be undertaken to define patterns of Pakistani co-authorship in the social sciences.

• 태양에너지
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• 제10권3호
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• pp.3-12
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• 1990

본 실험연구에서는 탱크의 직경에 대한 높이의 비(H/D)가 3이고 유입 유량이 8LPM, 유입수의 온도와 기존 저장수와의 온도차, ${\Delta}T=30^{\circ}C$일때, 운동량교환을 최소화하여 가장 좋은 성층을 얻었고 또한 실험에서 사용한 유입구(Inlet Port)의 경우 수정 Richardson수(Modified Richardson Number), Ri가 0.004(Q=10LPM, ${\Delta}T=30^{\circ}C$) 이하의 값에서는 완전 혼합(Fully Mixing)이 발생하고 H/D가 작아질수록 혼합층의 두께($H^*/H$)가 증가하여 성층 축열에는 바람직하지 못하였다. 그리고 성층은 성층을 촉진시키기 위하여 Distributor를 사용했을 때가, Distributor를 사용하지 않은 유입구(Inlet Port)의 경우 보다 잘 형성되어 저장효율이 Distributor를 사용한 경우(Q=8LPM, ${\Delta}T=30^{\circ}C$, H/D=3)에 Distributor를 사용하지 않은 유입구(Inlet Port)의 최저효율 63%(Q=12LPM, ${\Delta}T=30^{\circ}C$, H/D=3인 경우)보다는 31% 정도, 최대효율 84%(Q=8LPM, ${\Delta}T=30^{\circ}C$, H/D=3인 경우)보다는 11% 정도 높은 95%까지 저장 효율을 증가시킬 수 있었다. 더 나아가서 단면이 균일한 원형 Distributor(A=D=Constant)의 경우에, 유량이 8LPM인 경우에 관내의 압력차가 작아 부분혼합(Partial Mixing)이 감소하여 안정된 성층을 얻을 수 있었다. 그리고, Distributor의 직경을 다음식과 같이 $$\frac{D}{D_L}=(\frac{x}{L})^{1/2}(1+\frac{fL}{2D})-\frac{fx}{2D_L}$$ 길이에 대하여 변화시켜 Distributor를 제작함으로써, 보다 안정된 열성층과 높은 열저장 효율을 얻을 수 있을 것으로 예상한다.

• 한국환경과학회지
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• 제10권5호
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• pp.329-336
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• 2001

Characgcteristics of nocturnal boundary layer(NBL) were analyzed by the upper-air observations data using with the airsonde and pilot balloons from 1994 to 1999 in Kyungpook province. The automate weather boundary layer can become stably stratified when the surface is cooler than the air. Stable nocturnal boundary layer height were estimated from the top of surface stable layer where the vertical gradient of temperature and mixing ratio tend to zero or negative. The depth of the stable nocturnal boundary layer depended largely on the thermal effect rather than the wind effect at nighttime. The NBL was more developed on the land than on the coastal region. The stability index (bulk Richardson number) showed that the NBL was stable when the wind was weak and the vertical gradient of the temperature was strong. The heat budget in the NBL was studied by considering the effect of the radiative and the cooled by both the longwave radiative flux and the divergence of the heat flux, while NBL under the cloudy sky the longwave radiative flux played a role of the warming. It was noted that the heat was not conserved in both cases. To complete the heat budget in the NBL the warming/cooling by advection and subsidence must be considered.