• Journal of the korean Society of Automotive Engineers
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• v.6 no.1
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• pp.36-45
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• 1984

The conventional heat transfer analysis methods based on the one-dimensional theory are not adequate to be applied for the purpose of finned surface design because the two-dimensional effects in fact are induced within the supporting wall by the presence of the finnes. In this study, the two-dimensional heat transfer of a straight fin assembly is analyzed by using the integral method. It is shown that all the effects of the system parameters i.e., the heat transfer parameters and geometrical parameters, on both the total heat transfer rate and the surface temperature effectiveness can be seen from the present analysis. The optimum combinations of these parameters for the design of finned surfaces may be estimated.

• Journal of the Korean Society of Safety
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• v.21 no.1 s.73
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• pp.15-20
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• 2006

The finite element alternating method is a convenient and efficient method to analyze three-dimensional cracks embedded in an infinite or a finite body because the method has the property that the uncracked body and cracks can be modeled independently. In this paper the method was applied for fatigue crack growth simulation. A surface crack in a cylinder was considered as an initial crack and the crack configurations and stress intensity factors during the crack growth were obtained. In this paper the finite element alternating method proposed by Nikishkov, Park and Atluri was used after modification. In the method, as the required solution for a crack in an infinite body, the symmetric Galerkin boundary element method formulated by Li and Mear was used. And a crack was modeled as distribution of displacement discontinuities, and the governing equation was formulated as singularity-reduced integral equations.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.335-338
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• 1988

A numerical method is presented for the scattering by the perfectly conducting cylinder with arbitrary cross sections. The relevant integral equation considered by the E-field formulation is solved by method of moments, and thereby the surface current induced as well as the radar cross section of the scatterer are numerically computed to specify the scattering nature of the scatterer. Two separate methods, one with point matching and the other Galerkin's method, are considered to make cross checks to the results obtained. Taking two half pulses suggested to expand the surface current shows savings in computation time and accurate solutions for the corners on the scatterer.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.10a
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• pp.45-51
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• 2002

An acoustic finite element model of a bridge is developed to evaluate the noise generated by the traffic-induced vibration of the bridge. The dynamic response of a multi-girder bridge, modeled by a 3-dimensional frame element model, is analyzed with a 3-axle 8 DOFs truck model and a 5-axle 13 DOFs semi-trailer. The flat plate element is used to analyze the acoustic pressure due to the fluid-structure interactions between the vibrating surface and contiguous acoustic fluid medium. The radiation fields of noise with a specified distribution of vibrating velocity and pressure on the structural surface are also computed using the Kirchhoff-Helmholtz integral. Although the noise produced by the bridge vibration is not serious in itself, which is below the audible frequency range, it should be considered as an interaction problem between vehicle noise and bridge vibration noise in order to evaluate the traffic noise around the bridge.

• Journal of Mechanical Science and Technology
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• v.19 no.8
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• pp.1611-1620
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• 2005

This paper shows the use of wavelet transformation combined with inverse acoustics to reconstruct the surface velocity of a noise source. This approach uses the boundary element analysis based on the measured sound pressure at a set of field points, the Helmholtz integral equations and wavelet transformation for reconstructing the normal surface velocity field. The reconstructed field can be diverged due to the small measurement errors in the case of nearfield acoustic holography (NAH) using an inverse boundary element method. In order to avoid this instability in the inverse problem, the reconstruction process should include some form of regularization for enhancing the resolution of source images. The usual method of regularization has been the truncation of wave vectors associated with small singular values, although the order of an optimal truncation is difficult to determine. In this paper, a wavelet transformation is applied to reduce the computation time for inverse acoustics and to enhance the reconstructed vibration field. The computational speed-up is achieved, with solution time being reduced to $14.5\%$.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.7
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• pp.1033-1041
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• 1990

In this paper, under pinch-off conditions, the gate-drain breakdown voltage characteristics of GaAs Power MESFET's as a function of device parameters such as channel thickness, doping concentration, gate length etc. are analyzed. Using the Green's function, the gate ionic charge induced by the depleted channel ionic charge is calculated. The impact ionization integral by avalanche multiplication between gate and drain is used to investigate breakdown phenomena. Especially, the localized excess surface charge effect as well as the uniform surface charge effect on breakdown voltage is considered.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.3
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• pp.916-923
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• 1991

본 연구에서는 표면 균열이 있는 평판의 탄소성 피로하중 상태에서 성장하는 균열 형태의 변화와, 작용하는 응력의 크기에 따른 균열 개페구 특성의 변화를 연구하 였다.또, 유효 응력 확대계수 범위, .DELTA.K$_{eff}$와 J적분범위, .DELTA.J가 탄소성 응력 상태에서의 표면 피로균열 진전속도를 나타내는 역학양으로 사용되는데 따른 적합성등 을 검토하였다.

• Proceedings of the ESK Conference
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• 1993.04a
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• pp.145-145
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• 1993

In bicycle design, saddle is the major part which effects the subjective comfort of rider. This study examines the correlation between the subjective comfort and elastic body pressure. The elastic body pressure measuring instrument for free-form surface such as saddle is developed by force sensor register, A/D converter and computer. The subjective comfort is measured quantit- atively by 11-point scale method and the elastic body pressure distribution is obtained through 3 different saddles at 4 postures. The pressure distribution is presented by computerized equi- pressure contour. While mean pressure, standard deviation of pressure, maximum pressure are inversely proportional to subjective comfort, the modified saddle-bearing weight which is the surface integral of pressure is directly proportional. Consequently, standard deviation of pressure is most important characteristic which affects variation of subjective comfort.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.8
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• pp.834-842
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• 2002

The method of moment is applied to the analysis of electromagnetic scattering from an arbitrarily-shaped conductor. The conducting surface is discretized into triangular patches using a GID tool. Surface currents on a conductor are expanded with a vector triangle basis function. By using the Duffy's method, the singular integration appeared in a triangle patch can be transformed into the non-singular integral form suitable for one dimensional Gaussian quadrature integration method. Mutual and self integration extracted singular terms are evaluated by two dimensional Gaussian quadrature techniques.

• Journal of electromagnetic engineering and science
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• v.18 no.2
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• pp.136-140
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• 2018

We propose an improved semi-empirical scattering model for X-band radar backscattering from rough sea surfaces. This new model has a wider validity range of wind speeds than does the existing semi-empirical sea spectrum (SESS) model. First, we retrieved the small-roughness parameters from the sea surfaces, which were numerically generated using the Pierson-Moskowitz spectrum and measurement datasets for various wind speeds. Then, we computed the backscattering coefficients of the small-roughness surfaces for various wind speeds using the integral equation method model. Finally, the large-roughness characteristics were taken into account by integrating the small-roughness backscattering coefficients multiplying them with the surface slope probability density function for all possible surface slopes. The new model includes a wind speed range below 3.46 m/s, which was not covered by the existing SESS model. The accuracy of the new model was verified with two measurement datasets for various wind speeds from 0.5 m/s to 14 m/s.