• Proceedings of the KSME Conference
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• 2005.11a
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• pp.57.2-57.2
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• 2005

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.12
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• pp.1153-1161
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• 2010

An efficient solution method for harmonic balance techniques with Fourier transform is presented for periodic unsteady flow problems. The present partially-implicit harmonic balance treats the flux terms implicitly and the harmonic source term is solved explicitly. The convergence of the partially Implicit method is much faster than the explicit Runge-Kutta harmonic balance method. The method does not need to compute the additional flux Jacobian matrix from the implicit harmonic source term. Compared with fully implicit harmonic balance method, this partial approach turns out to have good convergence property. Oscillating flows over NACA0012 airfoil are considered to verify the method and to compare with results of explicit R-K(Runge-Kutta) and dual time stepping methods.

• Proceedings of the KAIS Fall Conference
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• 2010.05b
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• pp.1245-1248
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• 2010

플라스틱은 가공이 용이하기 때문에 우리 생활에 널리 이용되고 있다. 과거에는 단순히 제품의 외장제로 이용되었지만 산업이 발달함에 따라 금속을 대체 할 정도로 사용 범위가 증가하고 있다. 또한 사용량이 증가함에 따라 제품의 생산량을 증가시키기 위해선 다수 캐비티의 금형 사용이 필수적으로 되었다. 다수 캐비티 사출성형에서 각 캐비티 간 제품의 품질 및 물성을 향상시키기 위해선 각 캐비티로 충전되는 수지가 균형을 이루어야 한다. 하지만 기하학적으로 균형을 갖추고 있는 러너를 설계하여도 실제 사출성형에서는 불균형 충전이 일어나게 된다. 이러한 불균형 충전은 미국의 Beaumont에 의해서 처음 규명된 뒤 충전불균형 현상을 해결하기 위해 많은 연구가 진행되었다. 본 논문에서는 다수 캐비티 사출성형에서 균형충전을 위한 러너시스템을 제안하였다. 이 러너시스템은 온도가 불균일한 수지의 흐름을 혼합함으로써 수지의 흐름을 균일하게 하여 균형충전을 이루도록 하였다. 또한 사출성형해석프로그램인 Moldflow를 이용한 유동해석을 통해 그 효과를 나타내 보았다.

• Proceedings of the KAIS Fall Conference
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• 2010.11a
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• pp.301-304
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• 2010

본 논문에서는 다수 캐비티 금형의 러너 내 불균일한 전단분포로 인해 발생되는 충전불균형에 따른 치수정밀도, 기계적 강도 등 물성의 차이가 발생되는 문제점을 해소하기 위해서 수지가 처음 분기되는 2차 러너의 구조에 변화를 주어 다수 캐비티 사출성형에서 충전균형을 위한 러너시스템을 제시하였다. 이 러너시스템은 전단률차이에 의한 즉, 온도가 불균일한 수지의 흐름을 혼합함으로써 수지의 흐름을 균일하게 하여 충전균형을 이루도록 하였다. PP수지를 대상으로 각 캐비티 간 균형충전에 대해 이 러너시스템이 효과가 있는지 검증하기 위해 CAE프로그램(Moldflow)을 이용한 유동해석을 통해 그 효과를 나타내 보았다.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2001.05a
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• pp.63-70
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• 2001

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.10
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• pp.5968-5973
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• 2014

The gate location in injection molding has a significant influence on the quality and productivity. Therefore, injection molding CAE is used to determine the gate location. With increasing injection molding CAE and the adoption of a 3D mesh, which takes more computation time for analysis, gate location optimization in the shortest time and least resources is the most challenging issue. In this paper, we propose a methodology for optimization based on the flow length to consider the flow balance and weld line. In addition, the flow balance is obtained in the disc-type plate while the weld lines exit the slit-holes to avoid a stress concentration.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.999-1011
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• 1989

A consideration on the trubulence models for describing the redeveloping turbulent boundary layer beyond separation-reattachment in the flow over a backward-facing step is given through experimental and numerical studies. By considering the blance among the measured values of respective terms in the transport equations for the turbulent kinetic energy and the turbulent shear stress, the recovering process of the redeveloping boundary layer from non-equilibrium to equilibrium has been investigated, which takes place slowly over a substantial distance in the downstream direction. In the numerical study, the standard K-.epsilon. model and the Reynolds stress model have been applied to two kinds of flow regions, one for the entire downstream region after the backward-facing step and another for the downstream region after reattachment. Then the results are compared to a meaningful extent, with the experimental values of the turbulent kinetic energy k, the turbulent energy production term P, the dissipation term K-.epsilon. model, a necessity for a new modelling has been brought forward, which can be also applied to the case of the nonequlibrium turbulent flow.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.4
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• pp.114-122
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• 2013

This study introduces an optimization methodology for the determination of gate location that ensures the melt flow balance within a part cavity of injection mold. A new sequential direct-search scheme based on the recursive reduction of the designer-specified gate design area is developed, and it is integrated with a commercial flow simulation tool for optimization. To quantify the level of melt flow balance, we employ the maximum difference among the fill times for the melt fronts to reach the boundary elements of part cavity as objective function. The proposed methodology is successfully applied in the case study of melt flow balancing in molding of a bar code scanner model. The result shows that the melt flow balance at the optimized gate positions is significantly improved from that for the initial gate position.

• Journal of computational fluids engineering
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• v.16 no.4
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• pp.21-27
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• 2011

In this paper, the diagonal implicit harmonic balance method is applied to analyze helicopter rotor blade flow. The periodic boundary condition for Fourier coefficients is also applied in hover and forward flight conditions. It is available enough to simulate the forward flight problem with only one rotor blade using the periodic boundary condition in the frequency domain. In order to demonstrate the present method, Caradonna & Tung's rotor blades were used and the results were compared to the time-accurate method and experimental data.

• Journal of computational fluids engineering
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• v.17 no.1
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• pp.70-77
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• 2012

In this paper, diagonal implicit harmonic balance method with overset grid technique is applied to analyze helicopter rotor blade flow in hover and forward flight condition. The chimera grid need interpolation time with sub-grid and background grid in moving problem such as forward flight on every time step. Present method is available enough to reduce the grid module interpolation time. In order to demonstrate present method, Caradonna & Tung's and AH-1G rotor blades are used and the results are compared to other researchers' result and experimental data.