• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.748-751
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• 2011

일반적으로 물체의 거동을 해석하기 위해 고체영역에서는 Lagrangian 기법이 유체영역에서는 Eulerian 기법이 수치해석에 적용된다. Lagranian 기법은 서로 다른 물질의 경계와 자유표면에 대한 거동을 쉽게 추적할 수 있는 반면 물체의 대변형시 해석의 정확성이 떨어지는 단점이 있다. 또한 Eulerian 기법은 물질이동만을 고려하여 변형의 제한이 없는 장점을 가지고 있지만 이동하는 경계에 대해서 조건을 변화 시켜야하는 어려움이 있다. 따라서 이 두기법의 장단점을 서로 보안하기 위해 ALE(Arbitrary Lagrangian Eulerian)기법이 제안되었으며 이를 적용한 유체-구조물의 상호작용 해석에 대하여 많은 연구가 진행되고 있다. 본 논문에서는 이러한 ALE기법을 이용한 자유경계면에 대한 새로운 알고리즘이 제안된다.

• Journal of Ocean Engineering and Technology
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• v.4 no.1
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• pp.62-70
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• 1990

Cauchy의 적분공식을 복소속도(complex velocity)에 적용하여 포텐시얼 유동을 해석하는 복소경계요소법이 개발되었다. 이 결과로 얻어지는 적분방정식은 경계면에서의 접선속도(tangential velocity)와 법선속도(normal velocity)의 함수로 주어진다. 자유수면에서의 접선속도의 시간변화(evolution of tangential velocity)를 수식화하기 위하여 새로운 비선형 동역학적 자유수면경계조건(nonlinear dynamic free surface boundary condition)을 유도하였다. 복소포텐시얼 대신 복소속도를 이용하는 이 방법은 유장내의 특이점(field singularity)을 용이하게 고려할 수 있으며, 수치미분없이 직접 경계면에서의 유속을 해로서 구하게 된다. 그러나 자유수면이 존재하는 문제의 경우에는, 자유수면에서의 동역학적 경계조건을 만족 시키기 위한 계산과정에 접선 벡타의 변화량을 추정하는 것이 포함되게 되어, 계산과정이 다소 복잡하게 된다.

• The Journal of Engineering Geology
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• v.13 no.1
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• pp.17-27
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• 2003

In this study, a phenomenon of saltwater intrusion was monitored under various conditions regarding recharge and pumping rate using time domain reflectometry for a laboratory scale unconfined aquifer to verify the basic theory behind seawater intrusion and to investigate movement of salt-freshwater interface in accordance with the ratio of pumping and recharge rate. Results showed that a thick mixing zone was formed at the boundary instead of a sharp salt-freshwater interface that was assumed by Ghyben and Herzberg who derived an equation relating the water table depth $(H_f)$ to the depth to the interface $(H_s)$. Therefore our experimental results did not agree with the calculated values obtained from the Ghyben and Herzberg equation. Position of interface which was adopted as 0.5 g/L isochlor moved rapidly as the Pumping rate $(Q_p)$ increased for a given recharge rate $(Q_r)$. In addition, interface movement was found to be about 7 times the ratio of $Q_p/Q_r$ in our experimental condition. This indicates that Pumping rate becomes an important factor controlling the seawater intrusion in coastal aquifer.

• Computational Structural Engineering
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• v.8 no.3
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• pp.75-78
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• 1995

The boundary element analysis has been attempted for investigating the singular stress at the interface edge of infinitely layered structure. The subdomain technique has been employed and the analysis model has been divided into two subdomains, which are respectively homogeneous elastic zones. The boundary element equation has been formulated using the equilibrium and continuity conditions at the common interface. The numerical results of example problem has been presented.

• Geophysics and Geophysical Exploration
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• v.6 no.2
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• pp.77-86
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• 2003

We designed a new time-domain, finite-difference, elastic wave modeling technique, based on a displacement formulation. which yields nearly correct solutions to Lamb's problem. Unlike the conventional, displacement-based, finite-difference method using a node-based grid set (where both displacements and material properties such as density and Lame constants are assigned to nodal points), in our new finite-difference method, we use a cell-based grid set (where displacements are still defined at nodal points but material properties within cells). In the case of using the cell-based grid set, stress-free conditions at the free surface are naturally described by the changes in the material properties without any additional free-surface boundary condition. Through numerical tests, we confirmed that the new second-order finite differences formulated in the cell-based grid let generate numerical solutions compatible with analytic solutions unlike the old second-order finite-differences formulated in the node-based grid set.

• Journal of the Korean Society for Marine Environment & Energy
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• v.3 no.1
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• pp.25-34
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• 2000

A panoramic-PIV technique is employed to characterize the travelling tip vortices and the profile of oil-water Interface in the tandem fence arrangement. Instantaneous as well as time-averaged velocity profiles of the water layer close to the interface were obtained to evaluate the possibility of measuring the shear stress distribution on oil-water interface. It was proven that the present technique could provide some qualify data precise enough to resolve detailed flow structures inside a shear layer formed on oil-water interface provided it is nearly stationary.

• Computational Structural Engineering
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• v.10 no.3
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• pp.185-193
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• 1997

The order of the stress singularity that occurs at the termination of an interface between materials exhibiting bilinear stress-strain response under plane strain conditions has been calculated, The governing equation of elasticity together with traction-free boundary condition and interface continuity condition defines a two-point boundary value problem. The stress components near the free edge are assumed to be proportional to r/sup s-1/, with solutions existing only for certain values of s. Finding these values entails the solution of an eigenvalue problem. Because it has been impossible to integrate the differential equations analytically, the integration has been performed numerically with a shooting method coupled with a Newton improvement scheme.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2015.10a
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• pp.100-103
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• 2015

본 연구에서는 선박의 내항 및 조종성능평가를 위해 사용되는 2차원부가질량계수와 파랑감쇠계쉬를 desingularized indirect boundary integral method를 이용하여 주파수영역에서 계산하였다. 본 방법을 Rankine source를 유체경계면 전체에 분포하는 방법으로 수학적으로 간단하고 경계조건의 변경 및 적용이 용이하다는 장점이 있다. 하지만 물체표면, 자유수면 그리고 방사경계면의 계산영역 및 요소의 배치에 따라 계산정확도에 차이가 발생한다. 따라서 본 연구에서는 수치시험을 통해, 자유수면과 방사계면의 적절한 계산영역과 요소의 개수를 결정하였다. 계산의 정도와 효율성을 확보하기 위하여, 자유수면과 방사경계면의 계산영역과 요소의 분포를 파의주파수에 따라 달리 적용하였다. 본 연구에서 제안된 수치방법을 활용하여 계산된 동유체력과 실험에서 계측된 동유체력을 비교하여 본 방법의 정도를 확인하였다.

• Computational Structural Engineering
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• v.9 no.4
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• pp.181-187
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• 1996

This paper concerns the singular thermal stresses at the interface corner between the elastic fiber and the viscoelastic matrix of a two-dimensional unidirectional laminate model induced during cooling from cure temperature down to room temperature. Time-domain boundary element method is employed to investigate the nature of residual thermal stresses at the interface. Numerical results show that very large stress gradients are present at the interface corner and such stress singularity might lead to local yielding or fiber-matrix debonding.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1991.07a
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• pp.93-97
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• 1991

수표면에 방류되는 온배수등의 흐름과 같은 표층방류밀도분류는 자유난류의 전단류 효과와, 방류수와 주위수의 밀도차에 기인하는 부력효과를 동시에 받는 흐름장을 형성한다. 또한, 이 흐름은 수표면 및 밀도계면에 의해 2 개의 자유경계에 둘러싸인 특이한 경계조건때문에 개수로 흐름으로 대표되는 자유전단류와 구별된다.(중략)