• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.10
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• pp.783-788
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• 2009

In this paper, we have performed a parametric study on the characteristics of multiphase laminar flow with density difference in various microchannels. The interface between multiphase fluids is rotated by the gravitational forces induced by density difference. The numerical simulations were carried out via commercial CFD package to study the characteristics of multiphase laminar flow. The results of the numerical simulations in this study were verified by comparing with the previously reported experimental results in the literature. We have also proposed a new dimensionless relationship between dimensionless rotation angle of interface and dimensionless parameters are proposed for square microchannels with various aspect ratios. The dimensionless relationship could be widely applied to the reliable design of various microfluidic devices dealing with multiphase laminar flow.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.53 no.4
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• pp.286-292
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• 2004

This paper presents a polyphase filtered orthogonal frequency division multiplexing (PF-OFDM) technique. The proposed structure uses a modified discrete Fourier transform (MDFT) transmultiplexer to achieve greater spectral efficiency than an OFDM system, while preserving backward compatibility with it. The prototype PF-OFDM filter has excellent time and frequency localization properties, which matte it possible to eliminate a guard interval (or cyclic prefix) and easily suppress interchannel interference (ICI). This modulation technique uses a single DFT structure, in contrast to a MDFT transmultiplexer, which requires two DFT polyphase filter banks. The PF-OFDM modulation is .justified over multipath Rayleigh fading channels.

• 전기의세계
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• v.13 no.1
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• pp.20-23
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• 1964

본 변환기는 교번자계의 원리에 의한 보통 변환기가 아니고 회전자계의 원리를 이용한 변환기로서 상변환, 주파수변화, A.C.에서 D.C. 전원변환, D.C.에서 A.C. 전원변환, 속도제어, 진상기 등을 얻을 수 있는 경제적이고 능률적인 변환기를 얻을 수 있다. 임의의 다상을 얻을 수 있는 이 변환기는 다상 전원을 필요로 하는 수은정류기 등에 응용할 수 있고 A.C.전원에서 D.C.전원의 대용량전원을 얻어 D.C.전원이 필요로 하는 직류전철의 전원, 직류송전의 전원등에 이용할 수 있고, D.C.전원에서 A.C.전원을 얻어 교류전력기를 운전할 수 있으며 D.C.송전선에서 A.C.로 변환하여 종전의 A.C.배전선에 공급하면 D.C.송전을 이용한 송전손실을 경감시킬수 있고 주파수를 변환하여 속도제어를 하는 등 광범위하게 그 응용이 가능한 것이다.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.214-219
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• 2007

Both the bubble rising in a fully filled container and the droplet splash are simulated by a solution code(PowerCFD). This code employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method (CICSAM) in a volume of fluid(VOF) scheme for phase interface capturing. The present results are compared with other numerical solutions found in the literature. It is found that the present code simulate complex free surface flows such as multi phase flows due to large density difference efficiently and accurately.

• Journal of computational fluids engineering
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• v.15 no.4
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• pp.99-108
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• 2010

Fractional Step Methods(FSM) are popular in simulation of unsteady incompressible flow. In this study, we demonstrate that FSM, combined with a Volume-Of-Fluid method, can be further applied to simulation of multiphase flow. The interface between the fluids is constructed by the effective least squares volume-of-fluid interface reconstruction algorithm and advected by the velocity using the operator split advection algorithm. To verify our numerical methodology, our results are compared with other authors' numerical and experimental results for the benchmark problems, revealing excellent agreement. The present FSM sheds light on accurate simulation of turbulent multiphase flow which is found in many engineering applications.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.269-270
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• 2006

A finite difference lattice Boltzmann model which allows us to simulate gas-liquid two-phase flows with large density difference, for instance, 800 times for air and water is considered. Two-particle model is used and the density difference is introduced by changing the acceleration according to the fluid density. Numerical measurement of surface tension agrees well with theoretical predictions. Simulations of two-phase phenomenon for phase-transition is carried out, showing applicability of the model for two-phase flows. The two-dimensional cavitating flow around a board set up in the fluid way is also simulated. As a result, it was confirmed that the FDLB method with two-particle model was effective in numerical simulation of cavitating flow and the bubble periodically grew up at the low pressure area behind the board, in which the fluid condition was influenced by the cavitation number.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.252-255
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• 2011

Supercavitating torpedo uses the supercavitation technology that can reduce dramatically the skin friction drag. The present work focuses on the numerical analysis of the non-condensable cavitating flow around the supercavitating torpedo. The governing equations are the Navier-Stokes equations based on the homogeneous mixture model. The cavitation model uses a new cavitation model which was developed by Merkle(2006). The multiphase flow solver uses an implicit preconditioning scheme in curvilinear coordinates. The ventilated cavitation is implemented by non-condensable gas injection on backward of cavitator cone and the base of the torpedo. The comparison between the without and with ventilated cavitation numerical results, with ventilated cavitation using non-condensable gas injection is more efficient method.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.259-260
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• 2011

Using modern techniques from scientific computing and numerical analysis, natural phenomena or scientific experiment can be simulated effectively with a computer and used for computer graphics, for example as special effects for the film industry, manufacturing the thin film, multi-phase simulation and image processing. The Level Set method can make those things happen without a lot of difficulties. This method was devised by Osher and Sethian(1988) to represent dynamically moving interfaces as the zero level set of a scalar function that evolves in time. Since then, many researchers have worked on many applications using a Level Set Method. I will give a talk about the applications of the Level Set Method.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.572-575
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• 2008

Two-dimensional multiphase flows due to density difference such as the Rayleigh-Taylor instability problem and the droplet splash are simulated by an in-house solution code(PowerCFD). This code employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method in a volume of fluid(VOF) scheme for phase interface capturing. The present results are compared with other numerical solutions found in the literature. It is found that the present code simulates complex free surface flows such as multiphase flows due to density difference efficiently and accurately.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.576-579
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• 2008

Electrical impedance(EIT) for the multi-phase flow visualization is an imaging modality in which the resistivity distribution of the unknown object is estimated based on the known sets of injected currents and measured voltages on the surface of the object. In this paper, an EIT reconstruction algorithm based on the extended Kalman filter(EKF) is proposed. The EIT reconstruction problem is formulated as a dynamic model which is composed of the state equation and the observation equation, and the unknown resistivity distribution is estimated recursively with the aid of the EKF. To verify the reconstruction performance of the proposed algorithm, experiments with simulated multi-phase flow are performed.