• Water Engineering Research
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• 제6권3호
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• pp.123-130
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• 2005

A good understanding of the interaction between flow, vegetation, and sediment is required for successful river restoration and sustainable flood management. The purpose of this paper is to provide a summary of available methods to determine flow resistance of natural rivers with vegetation, and discuss the influence of vegetation on erosion and sedimentation processes. Recently, significant advances have been made, but the effects of vegetation on flow and sediment dynamics are still not fully understood. Possible solutions to close the gaps in the current knowledge are suggested, with special focus directed to the determination of the interactive width between main channel and vegetated floodplains, the flow resistance of flexible vegetation with and without leaves, and the flow over submerged vegetation with low water depth.

• 한국기계기술학회지
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• 제13권1호
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• pp.41-47
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• 2011

In this study, the structural analysis of cooling fan is combined with 3-D flow analysis by using CFD on fluid domain. The smoothly cooling flow with optimum design of cooling parts is essential at automotive combustion engine. The fan shape is modeled with three kinds of shape by varying the radius of the fan blade. By the results of analysis, the flow at Model I is more uniform than Model II or III. And the displacement at Model I is less than Model II or III. As the flow resistance of cooling fan at Model I decreases more than Model II or III, the efficiency becomes better.

• 유변학
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• 제11권2호
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• pp.153-158
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• 1999

가스사출시 두개이상의 가스흐름가능방향이 존재 할 때 가스는 선택적인 방향으로 흐르게는데 여기에서는 이 가스흐름 방향을 예측하는 방법을 제시하였다. 지금까지는 가스흐름방향은 가스의 하류에 있는 수지의 저항값, 즉 압력손실필요량을 비교하여 예측되어 왔는데 이방법은 대부분의 경우에 정확한 예측력을 가지고 있었다. 그러나 수지의 저항값 또는 압력손실필요량을 비교하는 방법이 실제에는 경우에따라 맞지 아니하였다. 이 연구에서는 수지속도비교가 압력손실필요량비교 보다 한단계위의 판단기준(criterion)이 되는 것을 설명하고 그예를 들어 증명 하고 있다. 압력손실필요량비교 대신 수지속도비교방법을 쓰면 예외없이 모든 경우 정확하게 가스흐름방향을 예측을 할수 있다.

• Geomechanics and Engineering
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• 제8권6호
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• pp.811-828
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• 2015

Proper modelling of the basal resistance terms is key in simulating the motion of fluidized granular flow. In this paper, standard depth-averaged governing equations of granular flow are used together with the classical Coulomb, Voellmy, and velocity dependent friction models (VDFM). A high-resolution modified TVDLF method is implemented to solve the partial differential equations without numerical oscillations. The effects of basal resistance terms on the motion of granular flows such as geometric shape evolution, travel times and final deposits are analyzed. Based on the numerical results, the predictions of the front and rear end positions and developing length of granular flow with Coulomb friction model show excellent agreements with experiment results reported by Hutter et al. (1995), and illustrate the validity of the numerical approach. For the Voellmy model, the higher value of turbulent coefficient than reality may obtain more reasonable predicted runout for the small-scale avalanche or granular flow. The energy exchange laws indicate that VDFM is different from the Coulomb and Voellmy models, although the flow characteristics of both three models fit the measurements and observations very well.

• Journal of Biosystems Engineering
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• 제20권4호
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• pp.333-342
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• 1995

The resistance to air flow through fruits and vegetables in bulk was an important consideration in the design of the pressure cooling system. The amount of resistance to air flow through produce in bulk normally depended upon air flow rate, stacking depth, porosity, stacking patterns and shape and site of product. But, there was not enough information relating the effects of those factors on air flow resistance. The objectives of this study were to investigate the effect of stacking depth, stacking patterns, porosity and airflow rate on airflow resistance and to develop a statistical model to predict static pressure drop across the produce bed as a function of air flow rate, stacking depth, bed porosity, and product size. Mandarins and tomatoes were used in the experiment. The airflow rate were in the range of 0.1~1.0 ㎥/s.$m^2$, the porosity were in the range of 0.25~0.45, the depth were in the range of 0.3~0.9m and the equivalent diameters were 5.3cm and 6.3cm for mandarins, and 6.5cm and 8.5cm for tomatoes. Three methods of stacking arrangement were used i.e. cubic, square staggered, and staggered stacking arrangement. The results were summarized as follows. 1. The pressure drops across produce bed increased in proportion to stacking depth and superficial air velocity and decreased in proportion to porosity. 2. The increasing rates of pressure drop according to stacking patterns with the increase of superficial air velocity were different one another. The staggered stacking arrangement produced the highest increasing rate and the cubic stacking arrangement produced the lowest increasing rate. But it could be assumed that the stacking patterns had not influenced greatly on pressure drops if it was of equal porosity. 3. The statistical models to predict the pressure drop across produce bed as a function of superficial air velocity, stacking depth, porosity, and product diameter were developed from these experiments.

• 한국융합학회논문지
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• 제5권2호
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• pp.19-23
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• 2014

본 연구에서는 자동차 차체의 형상에 따른 차체 주위의 유동해석을 이용하여 공기 저항을 연구하였다. 입구평면에서 들어가는 공기 유동 속도가 70km/h과 100km/h인 2가지 경우이다. 승용차의 고속 주행 시(100km/h) 정속 주행(70km/h)보다 큰 항력이 나타나는 것을 알 수 있고 차체의 전방 단면적이 넓은 차가 단면적이 좁은 차보다 항력이 더 크게 나타나는 것을 알 수 있다. 본 해석 결과를 이용하여 공기 저항을 줄일 수 있는 자동차 차체의 형상 설계를 효율적으로 할 수 있다고 사료된다.

• 수산해양기술연구
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• 제51권2호
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• pp.203-211
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• 2015

The purpose of this study is to identify the flow resistance of the bottom pair trawl nets. The bottom pair trawl nets being used in fishing vessel (100G/T, 550ps) was selected as a full-scale net, and 1/10, 1/25 and 1/50 of the model nets were made. Converted into the full-scale net by Tauti's modeling rule and Kim's modeling rule, when resistance coefficient k of each net was calculated by substituting into above equation for flow resistance R and wall area of nets S values of each net ${\upsilon}$. Because resistant coefficient k decreases exponentially according as flow velocity ${\upsilon}$ increases to make $k=c{\upsilon}^{-m}$, c and m values of each net were compared. As a result, as the model was smaller, c and m values was smaller in the two rule into standard of 1/10 model value, decrease degree of 1/25 model was almost same in the two rule, decrease degree of 1/50 model was very big in Tauti's modeling rule. Therefore, in the result of experiment, because average of c and m values for similarly 1/10 and 1/25 model were given $c=4.9(kgf{\cdot}s^2/m^4)$ and m=0.45, R (kgf) of bottom pair trawl net could show $R=4.9S{\upsilon}^{1.55}$ using these values. As in the order of cod-end, wing and bag part for 1/25 and 1/50 model net were removed in turn, measured flow resistance of each, converted into the full-scale, total resistance of the net and the resistance of each part net were calculated. The resistance ratio of each part for total net was not same in 1/25 and 1/50 model each other, but average of two nets was perfectly same area ratio of each part as the wing, bag and cod-end part was 43%, 45% and 12%. However, the resistance of each part divided area of the part, calculated the resistance of per unit area, wing and bag part were not big difference each other, while the resistance of cod-end part was very large.

• Journal of Advanced Marine Engineering and Technology
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• 제19권2호
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• pp.1-9
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• 1995

The processing paper has devoted to the theory of the flow equations, the basic derivative procedure, the meaning of a valve flow coefficient $C_v$, the valve Reynolds R$R_{ev}$ and its application for liquid control valves, which applicable under the condition of a non-critical flow and the case of piping geometry factor $F_p$=1.0. However there is no information on the effects of fittings, a critical flow and the flow resistance coefficient of a valve equivalent to that of pipe which is conveniently used in the piping design. Since the piping systems of plants or ships generally contain various fittings such as expanders and reducers due to different size between pipes and valves and there may occur a critical flow, that a mass flowrate is maintained to be constant, due to the pressure drop in a piping when a liquid is initially maintainder ar a saturated temperature or at nearby corresponding to upstream pressure, system designer should have a knowledge of the effect to flow due to fittings and the critical flow phenomenon of a liquid. This study is performed to inform system designers with the critical flow phenomenon of a liquid, a valve resistance coefficient, a valve geometry factor and their applications.

• Corrosion Science and Technology
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• 제12권5호
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• pp.220-226
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• 2013

The uncertainty in statistical noise resistance measurement was evaluated for a type 316 stainless steel in NaCl solutions at room temperature. Sensitivity coefficients were determined for measurands or variables such as NaCl concentration, pH, solution temperature, surface roughness, inert gas flow rate and bias potential amplitude. The coefficients were larger for the variables such as NaCl concentration, pH, inert gas flow rate and solution temperature, and they were the major factors increasing the combined standard uncertainty of noise resistance. However, the contribution to the uncertainty in noise resistance measurement from the above variables was remarkably low compared to that from repeated measurements of noise resistance, and thus, it is difficult to lower the uncertainty in noise resistance measurement significantly by lowering the uncertainties related with NaCl concentration, pH, inert gas flow rate and solution temperature. In addition, the uncertainty in noise resistance measurement was high amounting to 17.3 % of the mean, indicating that the reliability in measurement of noise resistance is low.

• 한국정밀공학회지
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• 제30권9호
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• pp.943-950
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• 2013

This paper describes the thermal contact resistance and its effect on the performance of thermal interface material. An ASTM D 5470 based apparatus is used to measure the thermal interface resistance. Bulk thermal conductivity of different interface material is measured and compared with manufacturers' data. Also, the effect of grease void in the contact surface is investigated using the same apparatus. The flat type thermal interface tester is proposed and compared with conventional one to consider the effect of lateral heat flow. The results show that bulk thermal conductivity alone is not the basis to select the interface material because high bulk thermal conductivity interface material can have high thermal contact resistance, and that the center voiding affects the thermal interface resistance seriously. On the aspect of heat flow direction, thermal impedance of the lateral heat flow shows higher than that of the longitudinal heat flow by sixteen percent.