• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.313-316
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• 2007

Ground-penetrating radar (GPR) is an effectiveness tool for imaging spatial distribution of hydrogeologic parameters. An artificial groundwater recharge test has been conducted in Nagaoka City in Japan, and time-lapse crosshole GPR data were collected to monitor infiltration processes in a vadose zone. Since radiowave velocities in a vadose zone are largely controlled by variations in water content, the increase in traveltimes is interpreted as an increase in saturation in the test zone. We use a finite-difference time-domain method in two-dimensional cylindrical coordinates to simulate field results. Numerical modeling successfully reproduces the major feature of velocity changes in the filtration process.

• 한국전산유체공학회:학술대회논문집
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• 1999.05a
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• pp.11-22
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• 1999

A numerical prediction method has been proposed to predict non-linear free surface oscillation in a three-dimensional container. The fluid motions are numerically predicted with Navier-Stokes equations discretized in a Lagrangian scheme with sufficient numerical accuracy. The profile of a free surface is precisely represented with three-dimensional body-fitted coordinates (BFC), which are regenerated in each computational step on the basis of the arbitrary Lagrangian-Eulerian (ALE) formulation. In order to confirm the reliability of the computational method, it was firstly applied to three-dimensional flows within complicated-shaped rigid boundaries, such as curved pipes and ducts. Than it was applied to benchmark computations related to free surface oscillations. Following these basic verifications, non-linear sloshings in a cylindrical tank and transitions from sloshing to swirling motions were numerically predicted. Throughout these computations, the applicability of the present computational method has been confirmed and some of the predicted free surface motions were visualized as sequential images and animations to understand their dynamic futures.

• Structural Engineering and Mechanics
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• v.35 no.4
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• pp.409-430
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• 2010

The present paper will be concerned to the investigation of the stress-strain field around the cavity that is loaded or partially loaded at the inner surface by the rotationally symmetric loading. The cavity of the spherical, cylindrical or elliptical shape is situated in a stressed elastic continuum, subjected to the gravitation field. As the contribution to the similar investigations, the paper introduces the new function of loading in the form of the infinite sine series. Besides, in this paper the solution of stresses around an oblong ellipsoid cavity, has been obtained using appropriate curvilinear elliptical coordinates. This analytical approach avoids the solutions of the same problem that lead to expressions that contain rather complex integrations. Thus the presented solutions provide the applicable and explicit expressions for stresses and strains developed in infinite series with easily determinable coefficients by the use of contemporary mathematical packages. The numerical examples are also included to confirm the convergence of the obtained solutions.

• Steel and Composite Structures
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• v.51 no.4
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• pp.377-389
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• 2024

In the present study, thermoelsatoplastic stresses and displacement for rotating hollow disks made of functionally graded materials (FGMs) has been investigated. The linear elastic-fully plastic condition is considered. The material properties except Poisson's ratio are assumed to vary in the radial direction as a power-law function. The heat conduction equation for the one-dimensional problem in cylindrical coordinates is used to obtain temperature distribution in the disk. The plastic model is based on the Tresca yield criterion and its associated flow rules under the assumption of perfectly plastic material behavior. Exact solutions of field equations for elastic and plastic deformations are obtained. It is shown that the elastoplastic response of the functionally graded (FG) disk is affected notably by the radial variation of material properties. It is also shown that, depending on material properties and disk dimensions, different modes of plastic deformation may occur.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.45-53
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• 1991

The underground structure, which has infinite or semi-infinite boundary conditions, is subjected by body forces and in-situ stresses. It also has stress concentration, which causes material nonlinear behavior, in the vicinity of the excavated surface. In this paper, some methods which can be used to transform domain integrals into boundary integrals are reviewed in order to analyze the effect of the body forces and the in-situ stresses. First, the domain integral of the body force is transformed into boundary integral by using the Galerkin tensor and divergence theorem. Second, it is transformed by writing the domain integral in cylindrical coordinates and using direct integration. The domain integral of the in-situ stress is transformed into boundary integral applying the direct integral method in cylindrical coordinates. The methodology is verified by comparing the results from the boundary element analysis with those of the finite element analysis. Coupling the above boundary elements with finite elements, the nonlinear behavior that occurs locally in the vicinity of the excavation is analyzed and the results are verified. Thus, it is concluded that the domain integrals of body forces and in-situ stresses could be performed effectively by transforming them into the boundary integrals, and the nonlinear behavior can be reasonably analyzed by coupled nonlinear finite element and boundary element method. The result of this research is expected to he used for the analysis of the underground structures in the effective manner.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.14 no.2
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• pp.121-136
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• 1989

In this paper, an attempt has been made to analyze the theoretically and verify experimentally the effect of curvature on the radiation characteristics of microstrip array antennas mounted conformally on the concave surface and the convex surface of the cylindrical body. The analysis of single element microstrip antenna is made by using the analysis method of Transmission Line Model. The theory of array antennas is established by application of the method of transformed coordinates, in which the translation and the ratation about each single element arrayed two-demensionally on the nonplanar surface are under consideration, and it is investigated by computation of the synthetic electric field strength in the far zone. In addition, various radiation characteristics, such as return loss, resonant frequency, radiation pattern, half-power, beamwidth, gain, are measrued and compared with the theroetical values according to the variation of curvature, by designing and building 4-element array microstrip antenna operating at 10 GHz, and microstrip feed lines. As predicted in theroy, it is verified that radiation pattern of antennas mounted on the concave and the convex surfaces alike broadens as the radius of curvature decreases. And for the curved surfaces, aggrement between computed values of the total synthetic radiation power pattern by the method of transformed coordinates and measured valuse is good. Besides, it is found that resonant frequency, input impedance and gain are hardly affected by the radius of curvature.

• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.1026-1035
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• 2004

An immersed boundary method for solving the Navier-Stokes and thermal energy equations is developed to compute the heat transfer over or inside the complex geometries in the Cartesian or cylindrical coordinates by introducing the momentum forcing, mass source/sink, and heat source/sink. The present method is based on the finite volume approach on a staggered mesh together with a fractional step method. The method of applying the momentum forcing and mass source/sink to satisfy the no-slip condition on the body surface is explained in detail in Kim, Kim and Choi (2001, Journal of Computational Physics). In this paper, the heat source/sink is introduced on the body surface or inside the body to satisfy the iso-thermal or iso-heat-flux condition on the immersed boundary. The present method is applied to three different problems : forced convection around a circular cylinder, mixed convection around a pair of circular cylinders, and forced convection around a main cylinder with a secondary small cylinder. The results show good agreements with those obtained by previous experiments and numerical simulations, verifying the accuracy of the present method.

• The Journal of the Acoustical Society of Korea
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• v.14 no.1
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• pp.108-114
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• 1995

Cylindrical chamber mufflers with an extended inlet or outlet are extensively used in many application fields to reduce the propagated noise in ducts. The basic attenuation effectivencess in the low frequency region can be explained by the reactive wave action inside the expansion chamber associated with the geometric configurations of the inlet and outlet locations, and the area expansion of the jacket. In this study, an acoustic analysis is carried out for a concentric extended pipe inserted into a simple expansion chamber. An algebraic equation is derived by using the eigenfuction expansion and orthogonality principle in which the acoustic pressures and particle velocities defined on each subdivided surface are expressed by the separable coordinates. By using the proposed analytical method, transmission losses are predicted for several configurations of the concentric extended systems and they agree very well with experimental results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.273-278
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• 2013

This paper presents optimal design procedures of mount based on a magnetorheological (MR) fluid to isolate the vibration in heavy diesel engine system. At first, frequency response and force-displacement transmissibility methods are used to get required damping force that is necessary for effective vibration isolation. From this result, a new type of high damping force engine mount is proposed and the governing equation of Bingham plastic behavior of MR fluid in flow path is mathematically derived under cylindrical coordinates. Finally, parametric design optimization featuring finite element is performed using ANSYS software to get the required damping force in MR mount system which can be used to reduce engine vibration. Damping force of the MR mount is then determined as an objective function in this analysis based on ANSYS. Furthermore, Magnetic analysis is then applied in this process.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.5
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• pp.472-478
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• 2013

This paper presents optimal design procedures of mount based on a magnetorheological(MR) fluid to isolate the vibration in heavy diesel engine system. At first, frequency response and force-displacement transmissibility methods are used to get required damping force that is necessary for effective vibration isolation. From this result, a new type of high damping force engine mount is proposed and the governing equation of Bingham plastic behavior of MR fluid in flow path is mathematically derived under cylindrical coordinates. Finally, parametric design optimization featuring finite element is performed using ANSYS software to get the required damping force in MR mount system which can be used to reduce engine vibration. Damping force of the MR mount is then determined as an objective function in this analysis based on ANSYS. Furthermore, Magnetic analysis is then applied in this process.