• Journal of the Society of Naval Architects of Korea
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• v.36 no.1
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• pp.61-69
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• 1999

To promote the usability of CFD techniques for the basic hull form design, a hull surface mesh generating program, based on given station offsets and centerline profile, is developed. The new method employs non-uniform parametric splines with predetermined waterline end-shapes of natural spline, normal spline, ellipse, parabola hyperbola, and their combinations. Generated hull surface meshes can be utilized for potential panel method immediately and can be also used as a boundary grid surface for 3-D field grid system. Mesh topology chosen to represent hull surface can be transformed into a rectangle, which he1ps the flow solvers to transform surface meshes for the nonlinear free surface condition or to define the turbulence quantities. To prove the applicability, a container ship with bow and stem bulb is chosen, and the procedures generating hull surface meshes are described.

• Tunnel and Underground Space
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• v.14 no.3
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• pp.229-240
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• 2004

Coastal aquifers may serve as major sources fur freshwater. In many coastal aquifers, intrusion of seawater has become one of the major constraints imposed on groundwater utilization. The management of groundwater in coastal acquifers means making decision as to the pumping rate and the spatial distribution of wells. Several numerical techniques for flow and solute transport simulation can provide the means to achieve this goal. As a basic study to predict the intrusion of seawater in coastal phreatic aquifers, the coupled flow and solute transport analysis was conducted by use of the 3-D finite element code, SWICHA. In order to understand how the location and the shape of freshwater-seawater transition zone were affected by the boundary conditions and hydrogeologic variables, parametric study was carried out.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.18-24
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• 2003

A three node triangular element with drilling rotations incorporating improved higher-order zig-zag theory(HZZT) is developed to analyze the vibration of pretwisted composite plates with embedded damping layer. Shear force matching conditions are enforced along the interfaces between the embedded damping patch and the border patch by matching the shear forces of the embedded damping patch to the shear forces of the adjacent border patch. The natural frequencies and modal loss factors are calculated for cantilevered pretwisted composite blade with damping core with the present triangular element, and compared to experiments and MSC/NASTRAN using a layered combination of plate and solid elements.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.244-244
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• 2021

난류흐름 거동은 지형이나 수공구조물과 같은 고체 경계면의 변화에 민감하게 반응하며 특징 또한 다양하다. 보나 여수로 등과 같은 단차 구조물을 통과하는 흐름은 구조물의 모서리 같은 흐름 경계면이 급변하는 지점에서는 흐름분리(flow separation)가 발생하는 것이 특징이다. 이러한 흐름분리로 인해 전단층이 발생하며 흐름 재순환(recirculation)이 구조물 하류부에 형성된다. 이 연구에서는 낙차공 형식의 단차 구조물 하류부에서의 흐름 거동을 이해하기 위해 CFD모델링을 통하여 계산된 3차원 유동장을 분석한다. 난류 모의는 하이브리드 LES(large-eddy simulation)/RANS 계산 기법인 IDDES(improved delayed detached-eddy simulation)기법을 적용한다. IDDES의 기본 모형으로는 k-ω SST모형과 Spalart-Allmaras모형을 이용하여 두 모형의 성능을 평가한다. 자유수면의 변동은 VoF(volume of fluid)기법을 이용하여 계산하며, 각 지배방정식은 최소의 수치분산을 유지하면서 수치해의 안정성을 확보할 수 있는 2차 정확도의 유한체적법을 이용하여 이산화하였다. 수치해석 결과는 레이놀즈수 23,400과 후르드수 0.22의 조건에서 기존에 계측된 자료와 비교하여 수치모형의 정확도를 평가하고 하상 단차 하류부에서의 흐름 거동 특성을 분석한다. 계산 결과는 공학적으로 널리 사용되는 RANS 수치모의에서 볼 수 없는 전단층과 난류구조의 동적 거동 특성과 이에 따른 레이놀즈 응력분포의 특성을 설명해준다.

• Journal of the Korean Society for Marine Environment & Energy
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• v.10 no.2
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• pp.107-111
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• 2007

A two-dimensional numerical method for inviscid two-fluid flows with evolution of density interface is developed, and an initially stationary two-dimensional fluid sheet surrounded by another fluid is studied. The interface between two fluids is modeled as a vortex sheet, and the flow field with the evolution of interface is solved by using vortex-in-cell/front-tracking method. The edge of the sheet is pulled back into the sheet due to surface tension and a blob is formed at the edge. This blob and fluid sheet are connected by a thin neck. In the inviscid limit, such process of the blob and neck formation is examined in detail and their kinematic characteristics are summarized with dimensionless parameters. The edge recedes at and the capillary wave propagating into the fluid sheet must be considered for better understanding of the edge receding.

• Journal of the Korean Society for Railway
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• v.18 no.4
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• pp.289-300
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• 2015

An important source of noise from railways is rolling noise caused by wheel and rail vibrations induced by acoustic roughness at the wheel-rail contact. In conventional approaches to predicting rail noise, the rail is regarded as placed in a free space so that the reflection from the ground is not included. However, in order to predict rail noise close to the rail, the effect of the ground should be contained in the analysis. In this study the rail noise reflected from the ground is investigated using the wavenumber domain finite element and boundary element methods. First, two rail models, one using rail attached to the rigid ground and one using rail located above rigid ground, are considered and examined to determine the rigid ground effect in terms of the radiation efficiency. From this analysis, it was found that the two models give considerably different results, so that the distance between the rail and the ground is an important factor. Second, an impedance condition was set for the ground and the effect of the ground impedance on the rail noise was evaluated for the two rail models.

• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.687-694
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• 2014

This study established a displacement ductility ratio model for ductile design for the boundary element of shear walls. To determine the curvature distribution along the member length and displacement at the free end of the member, the distributions of strains and internal forces along the shear wall section depth were idealized based on the Bernoulli's principle, strain compatibility condition, and equilibrium condition of forces. The confinement effect at the boundary element, provided by transverse reinforcement, was calculated using the stress-strain relationship of confined concrete proposed by Razvi and Saatcioglu. The curvatures corresponding to the initial yielding moment and 80% of the ultimate state after the peak strength were then conversed into displacement values based on the concept of equivalent hinge length. The derived displacement ductility ratio model was simplified by the regression approach using the comprehensive analytical data obtained from the parametric study. The proposed model is in good agreement with test results, indicating that the mean and standard deviation of the ratios between predictions and experiments are 1.05 and 0.19, respectively. Overall, the proposed model is expected to be available for determining the transverse reinforcement ratio at the boundary element for a targeted displacement ductility ratio.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.177-184
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• 2002

Large amplitude sloshing can occur in contained fluid region due to the seismic ground motion. Also, The pressure by large amplitude sloshing damages the connections between the wall and roof of a fluid container and causes outflow of contained fluid. Therefore, to predict the dynamic behavior accurately, three dimensional analysis with the nonlinear boundary condition must be performed. In this study, the numerical solution procedure is developed using the boundary element method with the Lagrangian particle approach. In order to demonstrate the accuracy and validity of the developed method, the fluid motion for a free oscillation with small amplitude and a forced vibration are analyzed. And the numerical results are compared with the linear theory results and the previous studies with the nonlinear boundary condition.

• Transactions of Materials Processing
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• v.4 no.1
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• pp.48-58
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• 1995

In this study, a contact algorithm for the finite element analysis of free surface contact problem in materials forming is presented. The proposed contact algorithm consists of two parts. The first is the contact searching part, and the second, the constraint part. The contact searching algorithm does not require any a priori knowledge of the pairs of contact nodes or segments and the impenetrability constraint is satisfied using the penalty function scheme. void colsure in open-die forging was simulated to verify the accuracy and capability of the currently developed contact algorithm. The simulation results, obtained from ABAQUS simulation, were compared well to the experimental data available in the literature.

• Journal of Korean Society of Steel Construction
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• v.10 no.4 s.37
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• pp.601-613
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• 1998

This paper reports the first-of-its-kind free vibration solutions for sectorial plates having re-entrant corners causing stress singularities when the circular edge is either clamped or simply supported. The Ritz method is employed with two sets of admissible functions assumed for the transverse vibratory displacements. Accurate frequencies and normalized contours of the transverse vibratory displacement are presented for the spectra of sector angles.