• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
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• pp.81-88
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• 2000

The elastic wave equation is solved using the finite-difference method in 3D space to simulate the seismic wave propagation. It is based on the velocity-stress formulation of the equation of motion on a staggered grid. The nonreflecting boundary conditions are used to attenuate the wave field close to the numerical boundary. To satisfy the stress-free conditions at the free-surface boundary, a new formulation combining the zero-stress formalism with the vacuum one is applied. The effective media parameters are employed to satisfy the traction continuity condition across the media interface. With use of the moment-tensor components, the wide range of source mechanism parameters can be specified. The numerical experiments are carried out in order to test the applicability and accuracy of this scheme and to understand the fundamental features of the wave propagation under the generalized elastic media structure. Computational results show that the scheme is sufficiently accurate for modeling wave propagation in 3D elastic media and generates all the possible phases appropriately in under the given heterogeneous velocity structure. Also the characteristics of the ground motion in an sedimentary basin such as the amplification, trapping, and focusing of the elastic wave energy are well represented. These results demonstrate the use of this simulation method will be helpful for modeling the ground motion of seismological and engineering purpose like earthquake hazard assessment, seismic design, city planning, and etc..

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2006년도 학술발표회 논문집
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• pp.1925-1930
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• 2006

흐름의 연직분포를 가정하여 수면에서 바닥까지 적분하여 평균화한 방정식에 기초한 준2차원 흐름모형을 연안해역에서의 취송류해석을 위해 적용되었다. 바람장의 변동에 따른 취송류장의 변동이 크게 나타나므로 본 연구에서는 육상지형의 영향을 고려할 수 있는 3차원 중규모 지역기상장 모형을 통해 연안해역에서의 시간에 따른 바람장변동을 수치해석 하였다. 육상에서의 지표면 열수지 변화를 위해 식생모델을 적용하였다. 기상장과 취송류 해석을 위한 수치모형실험결과 바람장의 변동에 따른 연안역에서의 흐름특성을 효과적으로 예측하고 있음을 확인하였다.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2003년도 추계학술대회 논문집
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• pp.39-42
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• 2003

Leading edge extension(LEX) in a highly swept shape applied to a delta wing features the modern air-fighters. The LEX vortices generated upon the upper surface of the wing at high angle of attack enhance the lift force of the delta wing by way of increased negative suction pressure over the surfaces. The present 3-D stereo PIV includes the Identification of 2-D cross-correlation equation, stereo matching of 2-D velocity vectors of two cameras, accurate calculation of 3-D velocity vectors by homogeneous coordinate system, removal of error vectors by a statistical method followed by a continuity equation criterion and so on. A delta wing model with or without LEX was immersed in a circulating water channel. Two high-resolution, high-speed digital cameras$(1280pixel\times1024pixel)$ were used to allow the time-resolved animation work. The present dynamic stereo PIV represents the complicated vortex behavior, especially, in terms of time-dependent characteristics of the vortices at given measuring sections. Quantities such as three velocity vector components, vorticity and other flow information can be easily visualized via the 3D time-resolved post-processing to make the easy understanding of the LEX effect or vortex emerging and collapse which are important phenomena occurring in the field of delta wing aerodynamics.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.173-176
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• 2007

The characteristics of the tool system give many effects into the costs and qualities for the finished components. This study proposes a new method for manufacturing of high manufacturing productivity, production process reduction and low cost through back pressure forming. The Lock-up hub is manufactured through many processes, such as upsetting($1^{st}$ Forming), piercing, direct extrusion($2^{nd}$ Forming), final sizing process($3^{rd}$ Forming). In this study, process design for closed-die forging of a Lock-up hub used for a component of automobile transmission was made using three-dimensional finite element simulations, and the strain distributions and velocity distributions are investigated through the post processor. The rigid-plastic finite-element method for back pressure forging has been used in order to reduce development time and die cost. Using the FEM simulation, we found the optimum value of back pressure. The prototypes of Lock-up hub parts were forged into the net-shape. In the experiment, lead precision of tooth are measured by the CCMM(Contact Coordinate Measuring Machine). The dimensional accuracy of forged part was improved up to the 40% when back press was applied.

• 대한기계학회논문집
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• 제15권1호
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• pp.262-273
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• 1991

본 연구에서는 벽면에서의 압력은 압력측정 정치를 제작하여 측정하였으며 평 균유동 및 난류량들은 열선 유속계(hot wire system)을 사용하여 측정하였다.

• 대한기계학회논문집
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• 제16권4호
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• pp.684-695
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• 1992

본 연구에서는 3차원 형상의 금형에 의한 박판금속 성형 공정을 에너지법으로 해석함에 있어 스윕곡면(SWeep surface)을 통해 기하학적 형상을 효과적으로 표현하는 방법을 제안하고, 이를 직사각형 격막의 정수압벌징의 해석에 으용하여 이에 의한 결 과를 이미 보고된 자료와 비교함으로써 일반적인 박판 성형공정을 해석하는데 본 이론 의 적용 가능성에 대하여 논의하고자 한다.

• 한국재료학회지
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• 제28권3호
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• pp.148-158
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• 2018

This study investigated the effect of the grinding media of a ball mill under various conditions on the raw material of copper powder during the milling process with a simulation of the discrete element method. Using the simulation of the three-dimensional motion of the grinding media in the stirred ball mill, we researched the grinding mechanism to calculate the force, kinetic energy, and medium velocity of the grinding media. The grinding behavior of the copper powder was investigated by scanning electron microscopy. We found that the particle size increased with an increasing rotation speed and milling time, and the particle morphology of the copper powder became more of a plate type. Nevertheless, the particle morphology slightly depended on the different grinding media of the ball mill. Moreover, the simulation results showed that rotation speed and ball size increased with the force and energy.

• Korean Chemical Engineering Research
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• 제55권4호
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• pp.456-466
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• 2017

이 연구는 교반볼밀을 이용한 금속기반 복합재 제조공정에 있어서 분쇄매체의 차이에 의한 입자형상의 변화를 관찰하고, 볼 거동의 DEM시뮬레이션을 행하였다. 교반볼밀에서 볼 거동의 3차원 시뮬레이션을 통해 분쇄메커니즘을 규명하기 위하여 분쇄매체의 힘, 운동에너지, 매체 운동속도 등을 계산하였다. 또한 복합재 제조를 위한 실험조건을 이전의 다른 볼밀에서에 같이 교반볼밀 회전속도를 변화시켰고, 볼 재질, 운동속도, 마찰계수 등도 동일한 조건으로 변화시키면서 투입되는 에너지의 변화량도 계산하였다. 교반볼밀의 회전속도가 증가함에 따라, 분쇄매체와 매체, 매체와 벽면, 그리고 매체와 교반기 사이의 충격에너지가 증가하는 것을 정량적으로 계산 할 수 있었다. 또한 같은 실험 조건에서 입자형상 변화를 명확하게 분석 할 수 있었으며, 볼 거동이 입자형상 변화에 매우 큰 영향을 미치는 것을 알 수 있었다.

• 한국전산유체공학회지
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• 제21권2호
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• pp.47-53
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• 2016

This study investigated natural convection flow behavior in airflow path designed in concrete dry storage cask to remove the decay heat from spent nuclear fuels. Using FLUENT 16.1 code, thermal analysis for natural convection was carried out for three dimensional, 1/4 symmetry model under the normal condition that inlet ducts are 100% open. The maximum temperatures on other components except the fuel regions were satisfied with allowable values suggested in nuclear regulation-1536. From velocity and temperature distributions along the flow direction, the flow behavior in horizontal duct of air inlet and outlet duct, annular flow-path and bent pipe was delineated in detail. Theses results will be used as the theoretical background for the composing of airflow path for the designing of passive heat removal system by understanding the flow phenomena in airflow path.

• 동력기계공학회지
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• 제21권6호
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• pp.5-12
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• 2017

The steady-state, incompressible and three-dimensional numerical analysis was carried out to investigate the internal flow fields characteristics according to wind tunnel contraction type. The turbulence model used in this study is a realizable $k-{\varepsilon}$ modified from the standard $k-{\varepsilon}$ model. As a results, the distribution of the axial mean velocity components along the central axis of the flow model is very similar to the ASME and BE types, and the cubic and cosine types. When the flow passes through the interior space of the analytical models, the flow resistance at the inlet of the plenum chamber is the largest at BS type contraction, but the smallest at cubic type contraction. The boundary layer thickness is the smallest in the cosine type contraction as the axial distance increases. The maximum turbulent kinetic energy in the test section is the smallest in the order of the contraction of cubic type and cosine type. Comprehensively, cubic type contraction is the best choice for wind tunnel performance, and cosine type contraction can be the next best solution.