• Journal of Advanced Marine Engineering and Technology
• /
• v.18 no.1
• /
• pp.41-50
• /
• 1994

동심 이중관내에서 외관내벽의 사각돌출형 조도요소에 의한 비대칭 난류유동과 열전달 특성을, 열전달과 마찰계수에 미치는 조도의 합성효과를 조사하기 위해, 연구하였다. 이론해석에서는 수정 플란틀 혼합길이(mixing length)이론의 난류모델을 속도분포와 마찰계수를 구하는데 사용하였다. 최대 속도지점에서 안쪽과 바깥쪽의 두 속도 형상들은 힘의 평형에 의해 일치시켰다. 그리고나서, 온도분포와 열전달 계수를 계산하였다. 속도형상과 마찰계수들의 해석결과는 반경비 (${\alpha}$)= 0.13, 0.26, 0.4, 그리고 0.56 경우의 실험과 매우 잘 일치하였다. 마찰계수와 Nusselt number에 미치는 반경비, 조도비, 그리고 조도에 대한 피치비 등과 같은 여러 변수들의 효과들을 조사하였다. 본 연구는 일정 조도 요소들이 전체적 효율 측면에서 볼 때 열전달을 우리하게 향상시킨다는 것을 증명하였다.

• 한국전산유체공학회:학술대회논문집
• /
• 2011.05a
• /
• pp.10-13
• /
• 2011

A level set method is proposed to simulate the incompressible two-phase flow considering the effect of surface tension. For reinitialization of level set junction, a direct approach method is employed, instead of solving hyperbolic type equation. A mixed element is adopted, so that the continuity mid Navier-Stokes equations are solved by using the quadratic elements (six-node triangular element mid nine-node quadrilateral element), mid the level set function is solved by using the linear elements (three-node triangular element mid four-node quadrilateral element). In order to verify the accuracy mid robustness of the codes, the present methods are applied to a few benchmark problems. It is confirmed that the present results are in good qualitative mid quantitative agreements with the existing studies.

• Transactions of Materials Processing
• /
• v.5 no.1
• /
• pp.55-60
• /
• 1996

In the finite element analysis of metal forming processes the updated Lagrangian approach has been widely and effectively used to simulate the non-steady state problems. however some difficulties have arisen from abrupt flow change as in extrusion through square dies. In the present work an ALE(arbitrary Lagrangian-Euleria) finite element formulation for deforma-tion analysis are presented fro rigid-viscoplastic materials. The developed finite element program is applied to the isothermal analysis of square die extrusion of a square section. The computational results are compared with those by the updated Lagrangian finite element analysis.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.14 no.4
• /
• pp.847-857
• /
• 1994

FESWMS-2DH developed by the U.S. Department of Transportation based on two-dimensional shallow water wave equation is used in this study to simulate the flow characteristecs of the river reach between Chamsil and Shingok submerged weirs, which acts as a tidal river under low flow conditions. The model uses Galerkin F.E.M and meshes are composed of triangular or quadrangular elements. The model shows accurate and stable results concerning mass conservation as well as velocity distribution and water surface elevation. The results obtained in the present study may provide useful informations on the planning of river pollution abatement measures and artificial structures.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.20 no.3
• /
• pp.265-272
• /
• 2007

The finite element linear buckling analysis of folded plate structures using adaptive h-refinement methods is presented in this paper. The variable-node flat shell element used in this study possesses the drilling D.O.F. which, in addition to improvement of the element behavior, permits an easy connection to other elements with six degrees of freedom per node. The Box-typed structures can be analyzed using these developed flat shell elements. By introducing the variable-node elements some difficulties associated with connecting the different layer patterns, which are common in the adaptive h-refinement on quadrilateral mesh, can be overcome. To obtain better stress field for the error estimation, the super-convergent patch recovery is used. The convergent buckling modes and the critical loads associated with these modes can be obtained.

• Korean Journal of Cognitive Science
• /
• v.2 no.2
• /
• pp.261-278
• /
• 1990

Two experiments were performed to test whether the perception of subjective contours occurs not only through bottom-up processes but also throught top-down processes by manipilating such cognitive factors as superimposition cues and selective attention.In the first experiment,the phenomenon of neon color spreading effect was used to investigate the effect of superimpoed Kanizsa triangles.To identify the effect of superimposition, two different colors were used,one for each overlapped Kanizsa triangle,and the subjects were asked which neon-like color they saw for the overlapped portion.Result indicates that the only neon-like color of the superimposing triangle can be perceived,which implies that super impostition cues may act upon the formation process of subjective contour as a a sort of top-down information.In the second experiment,two partially ovwelapped Kanizsa squares of which direction of superimposition were ambiguous and thus reversable depending on the observer's mental set were used to inverstigate the effect of selective attention.Subjects were instructed to pay attention only to one of the squares and report the neon- like color of the overlapped portion of them.Result shows that the subjects perceive only the neon-like color of superimposing square,which implies that such cognitive factors as selective attention may strongly influence the formation of subjective contours. In conclusion,the results of this study show that the subective contour does not depend only on bottom-up processes but also on such cognitive factors as super-imposition cues and selective attention.

• Composites Research
• /
• v.36 no.6
• /
• pp.454-460
• /
• 2023

Recently, regulations on greenhouse gas emissions have been strengthened, and the International Maritime Organization (IMO) has been strengthening greenhouse gas regulations with a goal of net 'zero' emissions by 2050. In addition, in the shipbuilding/offshore sector, it is important to reduce operating costs, such as improving propulsion efficiency and lightening structures. In this regard, research is currently being conducted on topology optimization using 3D printed composite materials to satisfy structural lightness and high rigidity. In this study, three topology shapes (hexagonal, square, and triangular) were applied to the interior of a rudder, a ship structure, using 3D printed composite materials. Structural analysis was performed to determine the appropriate shape for the rudder. CFD analysis was performed at 10° intervals from 0° to 30° for each rudder angle under the condition of 8 knots, and the load conditions were set based on the CFD analysis results. As a result of the structural analysis considering the internal topology shape of the rudder, it was confirmed that the triangular, square, and hexagonal topology shapes have excellent performance. The rudder with a square topology shape weighs 78.5% of the rudder with a triangular shape, and the square topology shape is considered to superior in terms of weight reduction.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.23 no.7 s.166
• /
• pp.1205-1214
• /
• 1999

A new quadrilateral plane stress element is developed for efficient and accurate analysis of thermal stress problems. It is convenient to use the same mesh and the same shape functions for thermal analysis and stress analysis. But, because of the inconsistency between deformation related strain field and thermal strain field, oscillatory responses and considerable errors in stresses are resulted in. To avoid undesired oscillations, strain approximation is enhanced by supplementing several assumed strain terms based on the variational principle. Thermal deformation is incorporated into the generalized mixed variational principle for displacement, strain and stress fields, and basic equations for the modified enhanced assumed strain method are derived. For the stress approximation of bilinear elements, the $5{\beta}$ version of Pian and Sumihara is adopted. The numerical results for several problems show that the present element behaves well and reduces oscillatory responses. it also results in almost the same magnitude of error as compared with the quadratic element.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.20 no.2
• /
• pp.91-101
• /
• 2000

Modeling of radiation beam from ultrasonic transducers has been investigated extensively, since it is one of the most important, fundamental issues that have great influence on the accuracy of an ultrasonic measurement model. Here, three popular radiation models, namely the Rayleigh-Sommerfeld integral model, the boundary diffraction wave model and the edge element model, are discussed briefly, and the radiation beam fields from ultrasonic transducers with planar, circular and rectangular cross-sections are calculated using these three models. Then, the accuracy and the time-efficiency of these methods are compared based on the calculation results.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.5
• /
• pp.1129-1137
• /
• 1990

Based on the formulation which incorporates large deformation and anisotropy, an elastic-plastic finite element code is developed with membrane element to include the contact treatment. For the analysis of the general sheet metal forming process with contact condition, the treatment of contact is considered by employing the successive skew coordinate system. Three kinds of sheet metal forming processes with contact conditions are analyzed; stretching of a square diaphragm with a hemispherical punch, deep drawing of a circular cup and deep drawing of a square cup. Then the computational results are compared with the experiment. The computed loads and the distribution of the thickness strain are in good agreement with the experiment for all cases. However, the computational results of the thickness strain show the effect of bending can not be ignored in the deep drawing process whereas the effect of bending is negligible in stretching.