• The Journal of the Acoustical Society of Korea
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• v.18 no.5
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• pp.28-34
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• 1999

The effects of the viscosity of an adjacent viscous fluid on the characteristics of the elastic waves have been studied theoretically and experimentally. Expressions for the wave speed and attenuation of the elastic waves of transverse motion, such as the torsional wave propagating in a circular cylinder and the Love wave in a layered half-space solid, have been obtained as functions of the viscosity and mass density of the fluid by exact and asymptotic analyses. The theoretical results have been compared with experimental observations, and it has been demonstrated that a device described herein can be used as a sensor for measuring the viscosity of a fluid with a known mass density.

• Bulletin of the Korean Mathematical Society
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• v.50 no.5
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• pp.1737-1751
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• 2013

An efficient and stable point collocation scheme based on a meshfree method is studied for the stationary incompressible Navier-Stokes equations. We describe the diffuse derivatives associated with the moving least square method. Using these diffuse derivatives, we propose a point collocation method to fit in solving the Navier-Stokes equations which improves the stability of the direct point collocation scheme. The convergence of the numerical solution is investigated from numerical examples. The driven cavity ow and the backward facing step ow are implemented for the reliability of the scheme. Also, the viscous ow on complicated geometry is successfully calculated such as the ow past a circular cylinder in duct.

• The Journal of the Acoustical Society of Korea
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• v.20 no.4E
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• pp.17-23
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• 2001

To develop the code of predicting flow-field and aeroacoustic noise by an electrical cable, a combined CFD-Acoustic analogy approach is selected. The two dimensional, unsteady and incompressible Reynolds-averaged Navier-Stokes solver with κ-ω and κ-ω SST turbulence modeling is used to calculate the near flow-field around an electric cable. Near-field results are then coupled with two-dimensional Curle's integral formulation based upon Lighthill's acoustic analogy with the assumption of acoustic compactness. To validate this code, numerical results are compared with experimental data for a circular cylinder. The simulation shows an overprediction on acoustic amplitudes, but overally speaking, the spectrum pattern of sound pressure agrees well with experiment within an acceptable amount of error. In addition, a few cross-sections of the cable were selected and tested with each other in terms of drag and radiated noise

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.87-88
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• 2010

The strength and ductile capacity of reinforced concrete column can be improved by confinement using transverse reinforcement. Variety stress-strain models about the reinforced concrete confined by transverse reinforcement has been proposed. In this paper, parameters which effect to the ultimate confinement stress of circular cylinder confined by high strength transverse steel is examined. And the possion's ratio equation is proposed by analysis of strain between concrete and transverse reinforcement.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.134.1-134
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• 2001

The paper presents a sonar based map building method. The environment is a room or area inside a building, which is composed of four types of geometric primitives(corners, edges, cylinders, and walls). We also assume the environment can be modeled into two dimensional map in terms of planes(walls), points(corner and edge), and circle(cylinder). In a real world where most of the object surfaces are specular ones, a sonar sensor suffers from a multipath effect which results in a wrong interpretation of the location of an object. To reduce the effect and uncertainty, the method employs a simple thresholding technique for extracting circular arc features called regions of constant depth(RCD) from scanning sonar data. The usefulness of the approach is illustrated with the results produced by sets of experiments.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.97.3-97
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• 2002

This paper presents the vibration characteristics of an intelligent cantilever beam in contact with a fluid using a PZT actuator and PVDF film. The dynamic behaviors of a flexible beam-water interaction system are examined. The effect of the liquid level on free vibration of the composite beam in a partially liquid-filled circular cylinder is investigated. The coupled system is subject to an undisturbed boundary condition in the fluid domain. It was found that the coupled natural frequencies decreased with the fluid level for the identical composite beam due to added mass effect. In case of the free-free boundary condition, the natural frequency gently decreased at fluid water level betw...

• Journal of electromagnetic engineering and science
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• v.13 no.3
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• pp.158-164
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• 2013

This paper expands a previously proposed optimized higher order (2, 4) finite-difference time-domain scheme (H(2, 4) scheme) for use with lossy material. A low dispersion error is obtained by introducing a weighting factor and two scaling factors. The weighting factor creates isotropic dispersion, and the two scaling factors dramatically reduce the numerical dispersion error at an operating frequency. In addition, the results confirm that the proposed scheme performs better than the H(2, 4) scheme for wideband analysis. Lastly, the validity of the proposed scheme is verified by calculating a scattering problem of a lossy circular dielectric cylinder.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.397-403
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• 2010

The Immersed boundary method(IBM) is one of CFD techniques which can simulate flow field around complex objectives using simple Cartesian grid system. In the previous studies the IBM has mostly been implemented to fractional step method based Navier-Stokes solvers. In these cases, pressure buildup near IB was found to occur when linear interpolation and stadard mass conservation is used and the interpolation scheme became complicated when higher order of interpolation is adopted. In this study, we implement the IBM to an incompressible Navier-Stokes solver which uses SIMPLE algorithm. Bi-linear and quadratic interpolation equations were formulated by using only geometric information of boundary to reconstruct velocities near IB. Flow around 2D circular cylinder at Re=40 and 100 was solved by using these formulations. It was found that the pressure buildup was not observed even when the bi-linear interpolation was adopted. The use of quadratic interpolation made the predicted aerodynamic forces in good agreement with those of previous studies.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.289-294
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• 2010

Numerical stud of an oscillating body in incompressible fluid is performed. Stabilized finite element method comprising of Streamline-Upwind/Petrov-Galerkin (SUPG) and Pressure-Stabilizing/Petrov-Galerkin (PSPG) formulations of linear triangular elements was employed to solve 2D incompressible Navier-Stokes equations whereas the motion of the body was considered by incorporating the arbitrary Langrangian-Eulerian(ALE) formulation. An algebraic moving mesh strategy is utilized for obtaining body conforming mesh deformation at each time step. Two tests cases, namely motion of a circular cylinder and of an airfoil in incompressible flow were analyzed. The model is first validated against the stationary cases and then the capability to handle moving boundaries is demonstrated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.416-425
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• 1993

To investigate the characteristics of the merged jet arising from the interaction of two opposing curved wall jets over a circular cylinder in still air, mean velocity, Reynolds stresses, triple moments and integral length scale were measured using hot-wire anenometry. The turbulent kinetic energy and shear stress budget were evaluated using the measured data. The variations of the Reynolds stresses, the triple moment and integral length scale are severe in the interaction region. The pressure diffusion terms are found to be very large when compared the other terms in the interaction region. The distributions of the Reynolds stress and the triple moment in the similar region are found to be similar to those of conventional plane jets.