• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2000년도 추계학술대회
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• pp.81-84
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• 2000

Two-layer aquifer system with fractional flow dimension is composed of contiguous two layers: Layer 1 (lower layer) and Layer 2 (upper layer) with different permeability and specific storage each other. For this aquifer system, we assume that groundwater flow originates only from Layer 1 on the pumping well. The aquifer system considers wellbore storage and skin effects on the pumping well. Dimensionless drawdown curves for different flow dimensions are analyzed for different lambda (λ, crossflow coefficient) values, kappa ($textsc{k}$, permeability ratio between Layer 1 and Layer 2) values and omega ($\omega$, storativity ratio between Layer 1 and Layer 2) values. The curves for Layer 1 and Layer 2 show characteristic trend each other.

• 한국수자원학회논문집
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• 제43권9호
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• pp.823-833
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• 2010

침수식생 개수로 흐름은 식생영역과 상부영역에 서로 다른 흐름구조를 보인다. 즉, 식생영역에서 전단으로 인해 생성되는 난류는 억제되며 비교적 균일한 유속 분포를 보이며 상부영역에서는 일반 개수로 흐름과 유사한 흐름구조를 보인다. 이와 같이 두 상이한흐름구조가 결합된 복잡한 흐름특성으로 인해 침수식생 개수로흐름은 공학적인 관심의 대상이 되어왔다. 본 연구에서는 침수식생 개수로 흐름의 층적분 모형의 비교 분석을 수행하였다. 일반적으로 식생흐름의 층적분 모형은 층의 수에 따라 2층 및 3층모형으로 구분한다. 즉, 전체 수심을 식생영역과 상부영역으로 구분하는 2층모형과 식생영역을 바닥 조도의 영향 유무에 따라 내부 및 외부 식생영역으로 구분하는 3층모형으로 분류된다. 본 연구에서는 2층모형과 3층모형을 비교하였다. 다양한 실험조건에 적용한 결과, 3층모형이 식생영역에서 유속의 변화를 고려할 수 있으나 결과는 레이놀즈응력 분포에 민감하며, 적분된 유속은 2층모형에 의한 예측 결과가 더욱 정확한 것으로 나타났다. 3층모형에서 내부 식생영역의 결과가 전체 흐름구조에 미치는 영향이 무시할 수 있으므로 이 점을 착안하여 식생영역에서 유속 변화가 고려되는 수정 2층모형을 제시하였다. 수정 2층모형에서 가정하는 레이놀즈응력 분포는 상부영역에서는 선형, 식생영역에서는 멱함수 형으로 변화한다. 다양한 조건에 적용한 결과, 수정 2층모형이 대체로 기존의 모형과 비슷한 정도의 예측을 수행하나 식생밀도가 매우 작은 흐름의 경우 예측 결과가 불량한 것으로 나타났다.

• Journal of Mechanical Science and Technology
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• 제16권12호
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• pp.1561-1575
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• 2002

A reduced-order linear feedback controller, which is used to control the linear disturbance in two-dimensional plane Poiseuille flow, is applied to a boundary layer flow for stability control. Using model reduction and linear-quadratic-Gaussian/loop-transfer-recovery control synthesis, a distributed controller is designed from the linearized two-dimensional Navier-Stokes equations. This reduced-order controller, requiring only the wall-shear information, is shown to effectively suppress the linear disturbance in boundary layer flow under the uncertainty of Reynolds number. The controller also suppresses the nonlinear disturbance in the boundary layer flow, which would lead to unstable flow regime without control. The flow is relaminarized in the long run. Other effects of the controller on the flow are also discussed.

• 기계저널
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• 제16권1호
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• pp.49-53
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• 1976

Groundwater flow in a two-layer aquifer is studied theoretically and experimentally. Nonlinear differential equations are independently linearized for the upper and the lower layer, and approximate solutions are obtained. Fine sands and coarse sands are used in experiments. For steady flow, theoretical solutions agrees excellently with experimental results For unsteady flow, however, agreement is not so good, because the experimental conditions do not match with theoretical assumptions.

• 대한수학회논문집
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• 제12권2호
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• pp.479-490
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• 1997

We consider long nonlinear waves in the two-layer flow of an inviscid and incompressible fluid bounded above by a free surface and below by a rigid boundary. The flow is forced by a bump on the bottom. The derivation of the forced KdV equation fails when the density ratio h and the depth ratio $\rho$ yields a condition $1 + h\rho = (2-h)((1-h)^2 + 4\rho h)^{1/2}$. To overcome this difficulty we derive a forced modified KdV equation by a refined asymptotic method. Numerical solutions are given and hydraulic fall solution of a two layer fluid is expressed analytically in the case that derivation of the forced KdV (FKdV) equation fails.

• Journal of Advanced Marine Engineering and Technology
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• 제24권6호
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• pp.120-127
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• 2000

This study is concerned with evaluating the effects of acoustic excitation on the development of two stream mixing layer generated by split plate. The ratios of two velocities U1 and U2 either side of the splitter plate were such that $U_1/U_2$=1.0 (uniform flow) or $U_1/U_2$<1.0(shear flow). The mixing layers were disturbed acoustically through the edge of split plate. Quantitative data were obtained with hot-wire anemometry. Flow visualization with smoke-wire was also employed for qualitative study. the results show that the large scale structures of mixing layers are strongly affected by excitation frequency and amplitude in both uniform and shear flows. The maximum streamwise and vertical turbulent intensities of the excited flow fields are apt to be decreased as compared with those of without excitation. The flow characteristics of uniform flow are more influenced by acoustic excitation than those of shear flow.

• Membrane and Water Treatment
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• 제15권1호
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• pp.31-39
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• 2024

The flow in a nanopore of filtration membrane is often multiscale and consists of both the adsorbed layer flow and the intermediate continuum fluid flow. There is a controversy on which interface the slippage should occur in the nanopore filtration: On the adsorbed layer-pore wall interface or on the adsorbed layer-continuum fluid interface? What is the difference between these two slippage effects? We address these subjects in the present study by using the multiscale flow equations incorporating the slippage on different interfaces. Based on the limiting shear strength model for the slippage, it was found from the calculation results that for the hydrophobic pore wall the slippage surely occurs on the adsorbed layer-pore wall interface, however for the hydrophilic pore wall, the slippage can occur on either of the two interfaces, dependent on the competition between the interfacial shear strength on the adsorbed layer-pore wall interface and that on the adsorbed layer-continuum fluid interface. Since the slippage on the adsorbed layer-pore wall interface can be designed while that on the adsorbed layer-continuum fluid interface can not, the former slippage can result in the flux through the nanopore much higher than the latter slippage by designing a highly hydrophobic pore wall surface. The obtained results are of significant interest to the design and application of the interfacial slippage in nanoporous filtration membranes for both improving the flux and conserving the energy cost.

• Coupled systems mechanics
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• 제7권1호
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• pp.95-109
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• 2018

The relevance of turbulent mixing in estuarine numerical models for stratified two-layer shallow water flows is analysed in this paper. A one-dimensional numerical model was developed for this purpose by extending an immiscible two-layer model with an additional source term, which accounts for turbulent mixing effects, namely the entrainment of fluid from the lower to the upper layer. The entrainment rate is quantified by an empirical equation as a function of the bulk Richardson number. A finite volume method based on an approximated Roe solver was used to solve the governing coupled system of partial differential equations. A comparison of numerical results with and without entrainment is presented to illustrate the influence of entrainment on both the salt-water intrusion length and lower layer dynamics. Furthermore, one example is given to demonstrate how entrainment terms may help to stabilize the numerical scheme and prevent a possible loss of hyperbolicity. Finally, the model with entrainment is validated by comparing the numerical results to field measurements.

• 대한기계학회논문집
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• 제19권9호
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• pp.2283-2296
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• 1995

Experiments of normal shock wave/turbulent boundary layer interaction were conducted in a supersonic diffuser. The flow Mach number just upstream of the normal shock wave was in the range of 1.10 to 1.70 and Reynolds number based upon the turbulent boundary layer thickness was varied in the range of 2.2*10$^{[-994]}$ -4.4*10$^{[-994]}$ . The wall pressures in streamwise and spanwise directions were measured for two test cases, in which the turbulent boundary layer thickness incoming into the supersonic diffuser was changed. The results show that the interactions of normal shock wave with turbulent boundary layer in the supersonic diffuser can be divided into three patterns, i.e., transonic interaction, weak interaction and strong interaction, depending on Mach number. The weak interactions generate the post-shock expansion which its strength is strong as the Mach number increases and the strong interactions form the pseudo-shock waves. From the spanwise measurements of wall pressure, it is known that if the flow Mach number is low, the interacting flow fields essentially appear two-dimensional, but they have an apparent 3-dimensionality for the higher Mach numbers.

• 한국환경과학회지
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• 제5권6호
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• pp.713-718
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• 1996

We identified two characteristic turbulent flow cases, weakening and strengthening, which appear at the downwind side. Observations were made two times, Dec. 2-3. 1995 and Feb. 13-14. 1996 at Pusan National University site located downwind side of Kumjeong mountain. Meteorological observation system, tethersonde, was adopted to present observation. In the case of the west wind which blows perpendicular to Sanghak mountain located westward from the site, the wind speed highly increased in exponential with height. Therefore, the low level wind speed was so weak just like Taylor(1988)'s review. While the wind speed was intensified at 200-400m layer when the northwest wind blows from the continental Siberian high. We suppose 기 is because of the strong vertical convergence of flow between the surface inversion layer and the upper one, and also the horizontal convergence along the saddle and valley between the two mountains, Kumjeong and Sanghak-because of Bernoulli's effect. The inversion layer existed at surface-l00m and 500-600m level and the strong wind existed at about 200-400m layer.