• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.76-80
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• 2001

Unsteady compressible Euler equation is solved and the high-order, high-resolution numerical solver, physical boundary condition, adaptive nonlinear artificial dissipation model and conformal mapping are applied to computation of steady transonic flow and unsteady acoustics. The acoustic characteristics of axi-symmetric duct and two dimensional straight/S channel are studied and the computation results shows good agreements with linear analysis. In transonic case, local time stepping and canceling-the-residual techniques are used for convergence acceleration. The aspect of flow and acoustics in S-channel and the Pattern of noise radiation is changed by inflow Mach no. and static pressure at fan-face.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.139-144
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• 1999

There have been many studies for heat transfer enhancement. Particularly, the study of flow in heat exchangers which have fin device has been main theme in heat transfer area. Practically, the circular tube which has internal fins is widely used for developing heat transfer rate. In this study, flow and heat transfer analysis of the circular tube with fins are investigated. The height and the number of fins are arbitrary. The flow field is assumed to be laminar. The conformal mapping is used for analytic solution of the laminar flow field. Discretization of governing equation, namely, FDM was used for numerical analysis. The velocity field, flow rate and shear stress are calculated for some numbers of fins in circular tube and for some heights of fin. Temperature fields are plotted along the tube length. It can be shown that the numerical solution agrees with the analytical solution.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.9
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• pp.1287-1292
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• 2010

In this paper, a hybrid technique is presented. First, the isochromatic fringe data of a given set of points are calculated by the finite element method and are used as input data in complex variable formulations. Then the numerical model of the specimen with a central inclined crack is transformed from the physical plane to the complex plane by conformal mapping. The stress field is analyzed and the mixed-mode stress intensity factors are calculated for this complex plane. The stress intensity factors are calculated by the finite element method as well as by a theoretical method and compared with each other. In order to conveniently compare these values with each other, both actual and regenerated photoelastic fringe patterns are multiplied by a factor of two and sharpened by digital image processing.

• The KIPS Transactions:PartA
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• v.11A no.2
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• pp.203-206
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• 2004

Wegmann's method has been known as the most efficient one for the Theodorsen equation that is needed to solve conformal mapping. It was researched in the earlier studies (1). However divergence was revealed in some difficult problems by numerical experiment using Wegmann's method. We analyzed the cause of divergence and proposed an improved method by applying a low frequency pass filter to Wegmann's method. Numerical experiments using the improved method showed convergence for all divergent problems using the Wegmann's method. In this paper, we prove theroretically the cause of convergence in the Numerical experiment using the improved method by applying a low frequency pass filter to Wegmann's method. We make use of Fourier transforms in this theoretical proof of convergence.

• Geomechanics and Engineering
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• v.3 no.1
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• pp.17-28
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• 2011

This paper presents an analytical solution for steady state flow into a close-ended cylindrical permeameter. The soil medium is considered to be uniform, isotropic, and of infinite thickness. Laplace equation is solved by considering rotational symmetry and by using curvilinear coordinates obtained from conformal mapping. The deduced shape factors, which are compared to approximate relationships obtained from both numerical and physical modelling, and idealizations involving ellipsoidal cavities, are proposed for use in field measurements. It is shown that some of the shape factors obtained are significantly different from published values and show a much higher dependence of the rate of flow on the aspect ratio, than deduced from approximate solutions.

• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.473-478
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• 2002

Circular slab waveguides are conformally mapped into straight waveguides. In the outer cladding region with monotonically increasing index profile, modified Airy functions (MAF) of traveling-wave form are introduced to express the leaky mode. Field distributions and losses calculated by the proposed method are compared with those obtained by the WKB (Wentzel-Kramers-Brillouin) method. Detailed numerical examples are presented and compared with the conventional WKB methods, demonstrating our method not only allows a converging field at turning points but also guarantees fine accuracy.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.1
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• pp.25-40
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• 2015

Understanding the effects of the parameters affecting the interaction of tandem hydrofoil system is a crucial subject in order to fully comprehend the aero/hydrodynamics of any vehicle moving inside a fluid. This study covers a parametric study on tandem hydrofoil interaction in both potential and viscous fluids using iterative Boundary Element Method (BEM) and RANSE. BEM allows a quick estimation of the flow around bodies and may be used for practical purposes to assess the interaction inside the fluid. The produced results are verified by conformal mapping and Finite Volume Method (FVM). RANSE is used for viscous flow conditions to assess the effects of viscosity compared to the inviscid solutions proposed by BEM. Six different parameters are investigated and they are the effects of distance, thickness, angle of attack, chord length, aspect ratio and tapered wings. A generalized 2-D code is developed implementing the iterative procedure and is adapted to generate results. Effects of free surface and cavitation are ignored. It is believed that the present work will provide insight into the parametric interference between hydrofoils inside the fluid.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.7 no.3
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• pp.160-166
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• 1978

Heat loss to the ground in ondol heating system is analyzed mathematically using conformal mapping and variable transformations, Both two-and three-dimensional systems are analyzed. Heated house is assumed to be rectangular shape. Mean value of heat loss to the ground can be obtained using Figure 2. Effects of thermal parameters to heat loss are discussed. Numerical examples are also given.

• Proceedings of the Korea Information Processing Society Conference
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• 2010.11a
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• pp.1839-1842
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• 2010

등각사상은 함수론의 기본적인 문제로 2차원 Laplace방정식이 나타나는 열전도, 정전(靜電) potential, 유체의 문제에 이용되는 등 공학이나 물리학에서 그 응용분야가 넓다. 수치등각사상의 목적은 보다 빠르고, 보다 정확하며, 보다 적용범위가 넓은 계산법을 연구하는데 있다. 단위원 내부로부터 Jordan 영역 내부로의 등각사상을 구하는 문제는 비선형 방정식인 Theodorsen 방정식을 푸는 것으로 귀결된다. Theodorsen 방정식에 관해서는 여러 가지 수치해법이 제안되어 있는데 본 논문에서는 그 중 SOR 법인 Niethammer와 Newton법인 Vertgeim의 방법을 다루어 비교, 분석하였다. 이 2가지 방법을 실제 계산기상에 실현시켜 수치실험을 하여 그 유효성을 비교, 분석한 결과 난이도가 낮은 문제에서는 Niethammer의 방법이 난이도가 높은 문제에서는 Vertgeim이 제안한 방법이 유효함을 알게 되었다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.1
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• pp.239-244
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• 2016

The polarization characteristics of polarization-insensitive directional coupler based on double sandwiched rib-type and curved waveguides are explored in detail by using conformal transformation method (CTM) and longitudinal modal transmission-line theory(L-MTLT). To obtain the polarization-insensitive condition of polarization-insensitive curved directional coupler(PI-CDC), the coupling length and coupling efficiency according to the inner radius of PI-CDC are analyzed for quasi-TE and quasi-TM modes. The numerical results show that the PI-CDC with a few micrometer scales can be realized by properly choosing the curvature and structural and material parameters of double sandwiched layers. Furthermore, the mode profiles propagating through PI-CDC are evaluated, and the influence on coupler performance has been investigated.