• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.04a
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• pp.366-369
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• 2004

조석의 효과가 대수층에 미치는 해안대수층에서 지하수-기표수 상호작용에 관한 모사를 위해 수치모델링을 이용하였다 모사에 사용한 모델은 하천경계와 해안경계가 서로 직교하며 하천은 대수층을 부분 관통하고 있다. 해안경계와 하천경계에 의한 동시영향을 함께 모사한 결과, 해안경계에 의한 효과는 일정한 범위까지만 나타났으나, 하천경계에 의한 영향은 시간의 증가에 따라 영향범위가 넓어졌다. 하천경계와 해안경계조건이 만나는 부근에서는 해안경계에 의한 지하수위의 반복적인 상승과 하강으로 인해 두 경계조건에 의한 지하수위가 상호 상승작용을 일으키기도 하고 상호 상쇄되어 지하수위의 변화가 없는 엉역이 나타나기도 한다. 따라서 이러한 하천과 해안경계조건이 상호 교차하는 주변 대수층에서의 수위를 측정하여 해안대수층에서의 수리상수를 추정하면 수리확산계수를 과대 혹은 과소평가하는 오류를 범할 수 있으므로 주의를 요한다.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1960-1963
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• 2009

본 연구에서는 부산시 용호만 해안대수층에서 전기전도도와 지하수위의 수직적인 관측을 통해, 조석에 의한 해수/담수 경계면의 변동을 산정하였다. 연구지역은 부경대학교 대연캠퍼스 기숙사 신축부지 주변 해안대수층이며, 응회질퇴적암과 안산암 및 안산암질 화산각력암 등으로 구성되어 있다. 관측공의 개발심도는 120 m, 케이싱심도는 19 m, 내경은 0.2 m, 관측공과 해안선의 이격거리는 180 m 정도이다. 전기전도도에 의해 산정된 밀도는 담수에서 997.58 $kg/m^3$, 해수에서 1020.36 $kg/m^3$ 이었다. 관측기간(2008년 8월 21일${\sim}$10월 18일) 동안 해수/담수 경계면의 변동 범위는 해수면 기준 -21.69${\sim}$-21.53 m 이었으며, 경계면의 평균 위치는 해수면 기준 -21.62 m 정도이었다. 해수/담수 경계면과 지하수위의 상관성은 매우 높게 나타났으며, 해안대수층 내 해수/담수 경계면의 변동은 조석의 일(고조, 저조) 및 보름(대조, 소조) 단위의 변동에 영향을 받고 있음이 확인되었다. 관측기간 동안 지하수위는 전반적으로 하강하는 경향을 나타내었으며, 이는 관측기간이 풍수기에서 갈수기로 전환되고 있었기 때문이다. 향후에는 지속적인 관측을 통해, 용호만 해안의 해수면 상승에 의한 내륙으로의 해수침투를 연구하고자 한다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.1
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• pp.41-47
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• 2024

This paper utilizes computational asymptotic analysis to compute the boundary layer solution for composite beams and validates the findings through a comparison with ANSYS results. The boundary layer solution, presented as a sum of the interior solution and pure boundary layer effects, necessitates a mathematically rigorous formalization for both interior and boundary layer aspects. Computational asymptotic analysis emerges as a robust technique for addressing such problems. However, the challenge lies in connecting the boundary layer and interior solutions. In this study, we systematically separate the principles of virtual work and the principles of Saint-Venant to tackle internal and boundary layer issues. The boundary layer solution is articulated by calculating the Papkovich-Fadle eigenfunctions, representing them as linear combinations of real and imaginary vectors. To address warping functions in the interior solutions, we employed a least squares method. The computed solutions exhibit excellent agreement with 2D finite element analysis results, both quantitatively and qualitatively. This validates the effectiveness and accuracy of the proposed approach in capturing the behavior of composite beams.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.285-288
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• 2007

Numerical study of the influence of the boundary layer of micro-supersonic jet impinging on a flat plate with a hole was performed, to investigate the role of gas jet to eject melted materials from the cut zone in the laser machining. The detailed shock structures and the information of the mass flow rate through the hole were compared to the results of the previous study, in which the effects of boundary layer inside nozzle was not accounted. It was found that the boundary layer inside the micro- nozzle introduced stronger Mach disc over the machining zone, and thus that the mass flow rate through the hole decreased.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.1
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• pp.47-53
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• 2017

A boundary layer integral combined with a 1-D isentropic core flow model has been successfully used to determine heat transfer rate on the surface of a supersonic nozzle. However its accuracy is affected by the core flow condition which is used as a boundary condition for the integral calculation. Because flow behavior near a nozzle throat deviates from 1-D isentropic condition due to 2-D flow turning and interaction between core flow and boundary layer, accuracy of heat transfer calculation decreases at a nozzle throat. Therefore, CFD is adopted to deduce improved core flow condition and increase accuracy of boundary layer integral at nozzle throat in this research. Euler model and SST $k-{\omega}$ model is solved by CFD code and used as a boundary condition for boundary layer integral. Developed code is tested in the supersonic nozzle from the previous research and improvement in accuracy is observed, especially at nozzle throat and diverging section of the nozzle. Error between experimental result and calculation result reduced by 16% when a calculation is made based on the SST $k-{\omega}$ model. Method developed in this research is expected to be used in thermal design of the rocket nozzle.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.262-270
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• 1987

A numerical method is presented which can solve the unsteady momentum and thermal boundary layers, coupled through the agency of buoyancy force, over a heated circular cylinder impulsively started from rest. By linearizing the nonlinear finite difference equations without sacrificing accuracy, numerical solutions are obtained at each time step without iteration. To get rid of the requirement of excessive number of grid points in the region of reversed flow, special form of transformed variables are used, by which the computational boundary layer thickness is maintained almost constant. These numerical properties enable the method to easily handle the region of reversed flow and how the singularity develops in the interior of the boundary layer. In order to investigated the thermal effects on the skin friction, heat flux, displacement thickness and on the separation, we have successfully solved three different cases of the buoyancy parameter .alpha.(Gr/Re$^{2}$).

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.4
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• pp.518-527
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• 1985

대류-대류의 복합 열전달 문제를 유한차분법을 사용하여 수치적으로 연구하였다. 아래로부터 가열되는 직사각형 공동 내에서의 자연 대류와 공동 위쪽의 외부 난류 경계층 유동이 복합된 경우의 열전당 현상을 고려하였다. 두개의 서로 다른 모우드의 대류가 온도 분포가 미리 알려져 있지 않은 얇은 수평평판에 의해 분리되어져 있다는 점이 본 논문의 특이점이다. 수치적 해석은 Reynolds 수와 Grashof 수 및 공동의 기하학적 종횡비의 매개 변수적 효과가 발견되도록 행하여 졌다. 외부 난류 경계층 유동의 강도에 따라 공동 내에서의 유동 형태가 변할 수 있음을 알았다. 즉 내부 부력 세포의 회전 방향은 외부 유동의 존재에 의해 특성적으로 정해지며 공동 내의 유동 세포의 수는 Grashof 수가 증가 할수록 많아진다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.5
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• pp.429-435
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• 2007

The present study proposed a method fer simulating reflective boundary conditions in Boussinesq wave propagation model by lining lateral boundaries like breakwaters and seawalls with artificial sponge layers. In order to find out the reflective characteristics of sponge layers, 1D numerical experiments were performed varying the relative sponge width (sponge width/wave length). The results showed that the reflection coefficient can be effectively realized from no reflection to full reflection simply by adjusting the relative sponge width. Based on the results, a multiple regression formula was proposed to delineate the relationship among the reflection coefficient and other dimensionless variables. Finally, the reflective sponge layer was applied to a semi-infinite breakwater, demonstrating that it can also be successfully employed in 2D applications.

• Journal of Soil and Groundwater Environment
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• v.9 no.4
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• pp.32-41
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• 2004

Analysis of water-level fluctuation due to goundwater-surface water interaction in coastal aquifers is carried out by numerical modeling. The conceptual model used in this study has a stream boundary and a tidal boundary that forms a right angle and the stream partially penetrates the aquifer. We analyzed the effect of each boundary and the simultaneous effect of the two boundary conditions. The area of influence caused by the stream boundary increased during the simulation, while the influence zone of the coastal boundary was relatively constant. The groundwater level near the zone where two boundaries meet may rise by the action of combined effect of the two boundaries or may not change by cancelling the effect of each boundary. Thereafter, care must be taken when hydraulic parameters are estimated using sinusoidal oscillations of hydraulic head in coastal aquifers. Sensitivity analysis is employed to develop insight into the controls on groundwater level fluctuations. In this study our analyses focused on the effect of conductance and the stream width to the aquifer nearby.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.6
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• pp.477-483
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• 2016

Velocity profiles of laminar, transition and turbulent boundary layers were investigated by using Particle Image Velocimetry(PIV) measurements on the flat plate at Mach 2.96. The Schlieren visualization and PIV measurements are also used to confirm whether the oblique shock wave generated from the leading edge affects the flow field over the flat plate. The laminar velocity profile measured from the experiment was well matched with the compressible Blasius solution. The velocity profile of the transition boundary layer was well correlated with the theoretical turbulent velocity profile from near the wall and the transition began from Re = $1.41{\times}106$. For the turbulent boundary layer, considering compressibility effects, the Van Driest-transformed velocity satisfies the incompressible log-law. It is found that the log region is extended farther in the wall-normal direction compared to the log region in incompressible boundary layer.