• Ecology and Resilient Infrastructure
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• 제5권4호
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• pp.276-284
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• 2018

In order to analyze sediment transport characteristics of knickpoint migration, sediment transport length, and sediment transport weight through the under-flow type vertical lift gate, the hydraulic model experiment and dimensional analysis were performed. The correlations between Froude number and sediment transport characteristics were schematized. The multiple regression formulae for sediment transport characteristics with non-dimensional parameters were suggested. The determination coefficients of multiple regression equations appeared high as 0.618 for knickpoint migration, 0.632 for sediment transport length, and 0.866 for sediment transport weight. In order to evaluate the applicability of the developed hydraulic characteristic equations, 95% prediction interval analysis was conducted on the measured and the calculated by multiple regression equations, and it was determined that NSE (Nash-Sutcliffe Efficiency), RMSE (root mean square), and MAPE (mean absolute percentage error) are appropriate, for the accuracy analysis related to the prediction on sediment transport characteristics of kickpoint migration, sediment transport length and weight.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• 제47권1호
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• pp.17-25
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• 2019

An intake of Aircraft becomes S-shaped geometry due to spatial limitation or procuring survivability. But curvature of the S-shaped geometry makes secondary flow or flow separation which is the cause of non-uniform pressure distribution. In this study, boundary layer suction is applied to RAE M 2129 S-Duct by attaching sub duct. Design variable is suction location and angle. A mass flow rate drawn out by suction at the sub duct outlet is constant over every model. A grid dependency test was conducted to verify validity of computation. The comparison among the CFD (Computation Fluid Dynamics), ARA experimental result, and ARA computation result of non-dimensional pressure distribution on the Port side and Starboard Side confirmed the validity of CFD. In this study, Distortion Coefficient was used for evaluating aerodynamic performance of S-Duct. The analysis, which was about flow separation, vortex, mass flow rate distribution, and pressure distribution were also investigated. Maximum 26.14% reduction in Distortion Coefficient was verified.

• Journal of Korea Water Resources Association
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• 제56권2호
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• pp.125-137
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• 2023

In marine environments, plastics have become more abundant due to increasing plastic use. Especially, in coastal regions, particles may remain for a long time, and they interact with flows, wind, sand and human activities. This study aimed thus to observe how plastic debris interacts with and escape from sediments. A series of experiments were conducted in order to gain a better understanding of particle release from coastal sediments into water body. An oscillating water tunnel was built for the experiments, and used to generate oscillatory flows of relatively high Reynolds number and induce sediment transport. Spherical plastic particles of three different sizes was used in lieu of plastic debris in environments. It was observed that release of the particles was directly related to change of bedform, which is in turn determined by the flow condition. Also smaller particles tend to escape the sediment more readily. Critical values for dimensionless parameters are proposed.

• Korean Journal of Food Science and Technology
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• 제28권1호
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• pp.169-178
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• 1996

Target parameters such as water solubility index (WSI), intrinsic viscosity (IV), water holding capacity (WHC), oil holding capacity (OHC), soluble dietary fiber (SDF) and microstructure were investigated on three different screw configurations during twin-screw extrusion of wheat bran. WSI of raw wheat bran (RWB) was 13.7%, while that of extrudates ranged $16.3{\sim}23.2%$ when extruded using screw configurations with 5 reverse screw elements (RSE). It was found that the moisture content of RWB greatly affected WSI of extrudates. IV of wheat bran extrudates increased from 10.6 ml/g of RWB to $37.86{\sim}44.37\;ml/g$ of extrudates extruded using 3, 4 and 5 RSE, whose trend was highly related to the moisture content of RWB and the extrusion pressure. Multiplication of IV and soluble solid (SS) content exhibited good correlation $(R^2=0.85)$ with specific mechanical energy (SME). The results suggested that SS and molecular size are an important factor governed by the SME in solubilization of wheat bran. WHC increased with increasing feed rate and moisture content, while OHC decreased. SDF increased from 2.68% of RWB to $4.32{\sim}6.48%$ of extruded wheat bran, indicating the significant breakdown of cell wall components. Microstructure of the extrudates showed the distinct patterns of degradation and solubilization of cell wall structure, depending on the moisture content of RWB.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제7권1호
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• pp.11-22
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• 1987

A plane buoyant jet discharged vertically upward into a crossflow is analyzed by numerical solution of the governing equations of continuity, momentum and constituent transport. The turbulent transport is modelled by the Prandtl's mixing length theory. In the numerical solution procedure, the governing equations are transformed by stream function and vorticity transport, non-dimensionalyzed by discharge velocity, slot width, and parameters representing flow characteristics, and solved by Gauss-Seidel iteration method with successive underrelaxation. The numerical experiments were performed for the region of established flow of buoyant jet in the range of discharge densimetric Froude number of 4 to 32 and in the range of velocity ratio of 8 to 15, which is the ratio of discharge velocity to crossflow velocity. Variations of velocities and temperatures, flow patterns and vorticity patterns of receiving water due to buoyant jet were investigated. Also investigated are the effects of velocity ratio and discharge densimetric Froude number on the trajectories of buoyant jet. Computed are velocities, temperatures and local densimetric Froude numbers along the trajectory of the buoyant jet. Spreading rate and dispersion ratio were analyzed in terms of discharge densimetric Froude number, local densimetric Froude number and distance from the source along the jet trajectory. It was noted that the similarity law holds in both the profiles of velocity and temperatures across the jet trajectory and the integral type analysis of Gaussian distribution is applicable.

• Ecology and Resilient Infrastructure
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• 제5권4호
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• pp.246-256
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• 2018

In order to analyze hydraulic characteristics of discharge coefficient, hydraulic jump height, and hydraulic jump length, accompanied sediment transport, in the under-flow type vertical lift gate, the hydraulic model experiment and dimensional analysis were performed. The correlations between Froude number and hydraulic characteristics were schematized according to the presence and absence of sediment transport; the correlation of hydraulic characteristics and non-dimensional parameters was analyzed and multiple regression formulae were developed. In the hydraulic characteristics accompanied the sediment transport, by identifying the aspect different from the case that the sediment transport is absent, we verified that it is necessary to introduce variables that can express the characteristics of sediment transport. The multiple regression equations were suggested and each determination coefficient appeared high as 0.749 for discharge coefficient, 0.896 for hydraulic jump height, and 0.955 for hydraulic jump length. In order to evaluate the applicability of the developed hydraulic characteristic equations, 95% prediction interval analysis was conducted on the measured and the calculated by regression equations, and it was determined that NSE (Nash-Sutcliffe Efficiency), RMSE (root mean square), and MAPE (mean absolute percentage error) are appropriate, for the accuracy analysis related to the prediction on hydraulic characteristics of discharge coefficient, hydraulic jump height and length.

• Clean Technology
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• 제25권3호
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• pp.198-205
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• 2019

The adsorption equilibrium, kinetic, and thermodynamic parameters of brilliant green adsorbed by coconut based granular activated carbon were determined from various initial concentrations ($300{\sim}500mg\;L^{-1}$), contact time (1 ~ 12 h), and adsorption temperature (303 ~ 323 K) through batch experiments. The equilibrium adsorption data were analyzed by Langmuir, Freundlich, Temkin, Harkins-Jura, and Elovich isotherm models. The estimated Langmuir dimensionless separation factor ($R_L=0.018{\sim}0.040$) and Freundlich constant ($n^{-1}=0.176{\sim}0.206$) show that adsorption of brilliant green by activated carbon is an effective treatment process. Adsorption heat constants ($B=12.43{\sim}17.15J\;mol^{-1}$) estimated by the Temkin equation corresponded to physical adsorption. The isothermal parameter ($A_{HJ}$) by the Harkins-Jura equation showed that the heterogeneous pore distribution increased with increasing temperature. The maximum adsorption capacity by the Elovich equation was found to be much smaller than the experimental value. The adsorption process was best described by the pseudo second order model, and intraparticle diffusion was a rate limiting step in the adsorption process. The intraparticle diffusion rate constant increased because the dye activity increased with increases in the initial concentration. Also, as the initial concentration increased, the influence of the boundary layer also increased. Negative Gibbs free energy ($-10.3{\sim}-11.4kJ\;mol^{-1}$), positive enthalpy change ($18.63kJ\;mol^{-1}$), and activation energy ($26.28kJ\;mol^{-1}$) indicate respectively that the adsorption process is spontaneous, endothermic, and physical adsorption.

• Journal of Korean Society of Disaster and Security
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• 제12권1호
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• pp.57-66
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• 2019

One of the most serious problems with concrete small dams or barriers installed in small/median rivers is the deposit of sediments, especially, in Korea. An effective way to discharge such sediments to downstream is to construct a bypass pipe under the river bed. However, efficiency may become lowered if ripraps are entered into the bypass pipe. Therefore, in this study, we derived the threshold condition for the exclusion of ripraps from the bypass pipe using 3D numerical analysis. Upstream flow of the small dam was assumed to be stationary, and the energy concept was applied to the control volume containing the bypass pipe and its periphery. As a result, when the ratio of the water level difference between upstream and downstream to the diameter of the riprap was approximately equal to 1.2, the threshold condition for exclusion of the stones or riprap from the bypass pipe was affirmatively determined. If the characteristics of the adsorptive sediment adversely affecting the river environment in the future would be taken into account, results from this study are expected to put to practical use in the management of concrete small dam with bypass pipe system.

• Transactions of the Korean Society of Mechanical Engineers
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• 제15권6호
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• pp.1975-1981
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• 1991

A new numerical solution of the elastohydrodynamic lubrication(EHL) problem of an axially profiled cylindrical roller is presented. A finite difference method and the Newton-Raphson method are used to solve the nonlinear system equations. A non-uniform grid system is adopted to reduce the number of grid points and to obtain accurate solution. For two different types of profiles which have similar elastostatic pressure distribution, the EHL results show large differences. Especially the difference in film shape is larger than in pressure distribution. Therefore, the magnitude of the minimum film thickness should be a major criteria to design the axial profile of the roller. Variations of the minimum film thickness with dimensionless parameters show considerably different behavior from those of infinite solution and show a good agreement with the experimental data in literatures. Present numerical scheme can be used generally in the analysis of three-dimensional EHL problem.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• 제21권4호
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• pp.601-607
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• 2012

The magnetic abrasive polishing (MAP), for online monitoring with AE sensor attachment, was performed in this study. To predict the surface roughness after the magnetic abrasive polishing of NAK80, the signal data acquired from the AE sensor were analyzed. A dimensionless coefficient, which consisted of average of AErms and standard deviation of AE signal, was defined as a characteristic of the MAP and a prediction model was obtained using least square method. A neural network, which had multiple input parameters from AE signals and polishing conditions, was applied for predicting the surface roughness. As a result of this study, it was seen that there was very close correlation between the AE signal and the surface roughness in the MAP. And then on-line prediction of the surface roughness after the MAP of the NAK80 was possible by the developed prediction model.