• 대한기계학회논문집B
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• 제20권1호
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• pp.244-254
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• 1996

Flow velocity was measured by, use of hot wire anemometer. Turbulence intensity was in proportion to mean flow velocity regardless of swirl velocity. And integral length scale has proportional relation with swirl velocity regardless of measurement position. Turbulent burning speed during flame propagation which was determined by flame photograph and gas pressure of combustion chamber was increased with the lapse of time from spark and was decreased a little at later combustion period. Because of combustion promotion effect, turbulent burning speed was increased according to increase of turbulence intensity. Burning speed ratio i.e. ratio of turbulent burning speed ($S_BT$) to laminar burning speed ($S_BL$) was found out by use of turbulence intensity u' and integral length scale $l_x$ , $\delta_L$ is width of preheat zone in laminar flame.

• 한국통신학회논문지
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• 제34권5B호
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• pp.443-448
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• 2009

본 논문에서는 에너지가 제한적인 무선 센서네트워크에서 MIMO 기반 협력통신을 가능하게 하는 훈련심볼의 오버헤드와 데이터 수집노드(DGN)의 속도의 임계값을 제안한다. 두개의 송수신 안테나가 있는 경우에 대하여 에너지 효율과 지연값에 대한 성능을 분석하였다. 센서로부터 데이터 수집노드까지 장거리 통신을 할 경우에 대하여 기존의 SISO 보다 에너지를 적게 소모하는 MIMO 기반 협력통신 무선 센서 네트워크의 속도와 훈련심볼의 오버헤드 임계값들을 구하였으며 이들의 상관관계도 분석하였다.

• 한국화재소방학회논문지
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• 제20권4호
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• pp.91-97
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• 2006

본 연구는 도로터널 화재 시 최적의 방재시스템을 구축하기 위하여 실제터널의 축소모형을 대상으로 임계풍속 산정에 대한 적절성 검토를 위해 수행되었다. Froude scaling에 의해 실제터널의 약 1/29 축소모형에서 연기의 유동가시화 및 온도와의 상관관계 분석에 의해 임계풍속을 산정하였다. 실험결과 연기의 역류길이가 0이 되는 값으로 임계풍속을 산정한 결과 Kennedy 식에 의해 계산된 결과와 약 5% 이내의 차이로 근사함을 나타내었으며 연기 유동 및 온도분포의 관계는 화재강도의 변화에 큰 영향을 받지 않고 유사하게 나타났다.

• Nuclear Engineering and Technology
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• 제53권7호
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• pp.2221-2228
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• 2021

One-dimensional oxygen transport relation is indispensable to study the oxygen distribution in the LBE-cooled system with an oxygen control device. In this paper, a numerical research is carried out to study the oxygen transport characteristics in a gas-phase oxygen control device, including the static case and dynamic case. The model of static oxygen control is based on the two-phase VOF model and the results agree well with the theoretical expectation. The model of dynamic oxygen control is simplified and the gas-liquid interface is treated as a free surface boundary with a constant oxygen concentration. The influences of the inlet and interface oxygen concentration, mass flow rate, temperature, and the inlet pipe location on the mass transfer characteristics are discussed. Based on the results, an oxygen mass transport relation considering the temperature dependence and velocity dependence separately is obtained. The relation can be used in a one-dimensional system analysis code to predict the oxygen provided by the oxygen control device, which is an important part of the integral oxygen mass transfer models.

• 천문학회보
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• 제46권2호
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• pp.37.2-37.2
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• 2021

Turbulence produces the density and velocity fluctuations in molecular clouds, and dense regions within the density fluctuation are the birthplace of stars. Also, turbulence can produce non-thermal pressure against gravity. Thus, turbulence plays a crucial roles in controlling star formation. However, despite many years of study, the detailed relation between turbulence and star formation remain poorly understood. As part of the Taeduk Radio Astronomy Observatory (TRAO) Key Science Program (KSP), "mapping Turbulent properties In star-forming MolEcular clouds down to the Sonic scale (TIMES; PI: Jeong-Eun Lee)", we mapped two star-forming molecular clouds, the Orion A and the ρ Ophiuchus molecular clouds, in six molecular lines (¹³CO 1-0/C¹⁸O 1-0, HCN 1-0/HCO⁺ 1-0, and CS 2-1/N₂H⁺ 1-0) using the TRAO 14-m telescope. We applied the Principal Component Analysis (PCA) to the observed data in two different ways. The first method is analyzing the variation of line intensities in velocity space to evaluate the velocity power spectrum of underlying turbulence. We investigated the relation between the star formation activities and properties of turbulence. The other method is analyzing the variation of the integrated intensities between the molecular lines to find the characteristic correlation between them. We found that the HCN, HCO⁺, and CS lines well correlate with each other in the integral shaped filament in the Orion A cloud, while the HCO⁺ line is anti-correlate with the HCN and CS lines in L1688 of the Ophiuchus cloud.

• Journal of applied mathematics & informatics
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• 제41권1호
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• pp.51-70
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• 2023

The flow of an incompressible Ellis fluid in an inclined asymmetric channel, driven by peristaltic waves was studied under low Reynolds number and long wavelength assumptions. The wave on each side of the channel are assumed to be an infinite train of sinusoidal waves, both having the same constant wave speed and wavelength however, they vary in wave amplitude, channel half width and phase angle. We derived expressions for the axial and transverse velocities, volume flow rate, pressure rise per unit wavelength and streamlines. The effects of varying the wave amplitudes, the phase angle, the channel width, the angle of inclination of the channel as well as the fluid parameters on the flow were analyzed. Trapping conditions were determined and the presence of reflux highlighted using the streamlines for the necessary channel and fluid conditions. By varying the fluid parameters, changes in the fluid that deviated from the Newtonian case resulted in a reduction in the axial velocity in the neighborhood of the center of the channel and a simultaneous increase in the velocity at the periphery of the channel. A nonlinear relation was observed with the pressure rise and the volume flow rate. This nonlinear relation is more pronounced with an increase in the absolute value of the volume flow rate. For Newtonian fluids a linear relation exists between these two variables. The fluid parameters had little effects on the streamlines. However, variations of the wave amplitudes, volume flow, channel width and phase angle had greater effects on the streamlines and hence the trapped region.

• International Journal of Fluid Machinery and Systems
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• 제8권4호
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• pp.283-293
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• 2015

The effect of the inlet swirling flow in a hydraulic turbine draft tube is a very complex phenomenon, which has been extensively investigated both theoretically and experimentally. In fact, the finding of the optimal flow distribution at the draft tube inlet in order to get the best performance has remained a challenge. Thus, attempting to answer this question, it was assumed that through an automatic optimization process a Genetic Algorithm would be able to manage a parameterized inlet velocity profile in order to achieve the best flow field for a particular draft tube. As a result of the optimization process, it was possible to obtain different draft-tube flow structures generated by the automatic manipulation of parameterized inlet velocity profiles. Thus, this work develops a qualitative and quantitative analysis of these new draft tube flow field structures provoked by the redesigned inlet velocity profiles. The comparisons among the different flow fields obtained clearly illustrate the importance of the flow uniformity at the end of the conduit. Another important aspect has been the elimination of the re-circulating flow area which used to promote an adverse pressure gradient in the cone, deteriorating the pressure recovery effect. Thanks to the evolutionary optimization strategy, it has been possible to demonstrate that the optimized inlet velocity profile can suppress or mitigate, at least numerically, the undesirable draft tube flow characteristics. Finally, since there is only a single swirl number for which the objective function has been minimized, the energy loss factor might be slightly affected by the flow rate if the same relation of the axial-tangential velocity components is maintained, which makes it possible to scale the inlet velocity field to different operating points.

• 한국방재학회 논문집
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• 제8권2호
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• pp.129-138
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• 2008

차수성이 요구되는 제체나 댐체에 대하여 안정성을 판단하고자 할 경우 파이핑 현상발생 여부를 검토한다. 제체나 댐체는 층 다짐을 수행하면서 축조되므로 투수성은 수평방향 투수계수($k_x$)와 연직방향 투수계수($k_y$)가 서로 다른 이방성이 될 수 있다. 본 연구에서는 여러 가지 투수계수 비(k-ratio=$k_y/k_x$k)에 따른 침투해석을 수행하여 유출동수경사와 침투유속을 파악하고, 이론식에 의한 한계동수경사와 경험식에 의한 한계유속과 각각 비교.검토하여 파이핑에 미치는 영향을 검토하였다. 연구결과 투수계수 비는 한계동수경사 개념으로 파이핑 현상발생에 대한 안정성을 검토할 경우 매우 중요한 요소로 작용하나, 한계유속 개념에 대해서는 상대적으로 중요도가 매우 낮은 것으로 확인되었다.

• 대한토목학회논문집
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• 제29권4B호
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• pp.357-363
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• 2009

일반적으로 사용되는 관수로의 평균유속을 구하려면 Darcy-Weisbach의 마찰손실수두공식을 사용하면 되나, 그러나 이 식의 마찰손실계수 f는 Reynolds수와 상대조도(${\varepsilon}$/d)의 함수이므로 사용하기에 매우 불편하며 따라서 보다 편리한 식이 요구된다. 이에 본 연구에서 Chiu 유속공식의 신뢰성과 정확성을 증명하기 위하여 관수로에서 비삽입식 유속측정 장치인 레이저 유속계(Laser Doppler Velocimeter: LDV) 및 초음파 유량계(Ultrasonic Flowmeter: U/F), 삽입식 유속측정장치인 피토관 (Pitot Tube)을 이용하여 실측한 유속측정 자료와 Chiu의 공식을 이용한 유속분포가 매우 잘 일치함을 증명하였다. 유량의 증감에 관계없이 실험실 수로에서의 최대유속과 평균유속간의 이론적인 선형관계를 증명함으로써 관수로내 유속의 평형상태, 즉 엔트로피 파라미터 M값에 대응하는 평형상태에 도달하려 하고 이 평형상태를 지속적으로 유지하려고 하는 경향이 있음을 증명하였다. 또한, 한 단면을 대표하는 엔트로피 파라미터 M값이 결정되면 최대유속이 발생하는 지점에서의 유속 측정만으로 단면 전체의 평균유속을 쉽게 구할 수 있고 이로부터 간단히 유량을 산정할 수 있음을 증명하였으며, 이는 추후 관수로 설계 및 운영관리 시 가장 중요한 평균유량을 측정할 수 있는 이론적인 도구로 사용될 수 있음을 의미하는 것이다.

• 대한물리의학회지
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• 제6권1호
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• pp.59-69
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• 2011

Purpose : The purposes of this study were to find correlations among Fugl-Meyer Assessment Scale, walking velocity, walking asymmetry and balance ability. Methods : The study sample consisted of 50 stroke patients referred to the Department of Rehabilitation Medicine in the Sanggye Paik, Ilsan Paik, Seoul Paik, and Dobong Hospital. All subjects were ambulatory with or without an assistive device. All participants were assessed on Fugl-Meyer Assessment scale and walking velocity, walking asymmetry. The data were analyzed using independent t-test, ANOVA, and multiple regression. Results : The results revealed that upper extremity coordination, balance and pain items of Fugl-Meyer Assessment scale were significantly correlated with walking velocity and upper extremity and upper extremity motor and balance items of Fugl-Meyer Assessment scale were significantly correlated with walking asymmetry. Fugl-Meyer Assessment scale was not significantly correlated with Static Balance Index, Dynamic Balance Index and Weight Distribution Asymmetry Index. Their power of explanation regarding comfortable walking velocity and comfortable walking asymmetry were 60.3%, 42.5% respectively. Conclusion : These results showed that Fugl-Meyer Assessment scale is significantly correlated with walking velocity, asymmetry and not significantly correlated with balance ability. Therefore Fugl-Meyer Assessment scale is an appropriate assessment tool to predict walking ability of patients with stroke. Futher study about walking velocity and asymmetry by change of Fugl-Meyer Assessment scale is needed using a longitudinal study design.