• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.10a
• /
• pp.709-712
• /
• 2002

For the electro-discharge machining of an electro-conductive anisotropic composite, an unsteady state formulation was established and solved by Galerkin's finite element method. The distribution of temperature on work piece, the shape of the crater and the material removal rate were obtained in terms of the process parameters. As the spark was initiated the workpiece immediately started to melt and the heat affected zone was formed. The moving boundary of the crater was also identified with time. When the radial and axial conductivities were increased separately the temperature distribution and the shape of the crater were shifted in the same direction respectively and the material removal rate was found to be higher in the case of increasing radial conductivity rather than the axial conductivity.

• Communications for Statistical Applications and Methods
• /
• v.14 no.3
• /
• pp.507-516
• /
• 2007

Multinomial logistic regression is probably the most popular representative of probabilistic discriminative classifiers for multiclass classification problems. In this paper, a kernel variant of multinomial logistic regression is proposed by combining a Newton's method with a bound optimization approach. This formulation allows us to apply highly efficient approximation methods that effectively overcomes conceptual and numerical problems of standard multiclass kernel classifiers. We also provide the approximate cross validation (ACV) method for choosing the hyperparameters which affect the performance of the proposed approach. Experimental results are then presented to indicate the performance of the proposed procedure.

• Transactions of Materials Processing
• /
• v.16 no.4 s.94
• /
• pp.276-281
• /
• 2007

The hardening and the constitutive equation based on the crystal plasticity are introduced for the numerical simulation of hemispherical sheet metal forming. For calculating the deformation and the stress of the crystal, Taylor's model of the crystalline aggregate is employed. The hardening is evaluated by using the Taylor factor, the critical resolved shear stress of the slip system, and the sum of the crystallographic shears. During the hemispherical forming process, the texture of the sheet metal is evolved by the plastic deformation of the crystal. By calculating the Euler angles of the BCC sheet, the texture evolution of the sheet is traced during the forming process. Deformation texture of the BCC sheet is represented by using the pole figure. The comparison of the strain distribution and punch force in the hemispherical forming process between the prediction using crystal plasticity and experiment shows the verification of the crystal plasticity-based formulation and the accuracy of the hardening and constitutive equation obtained from the crystal plasticity.

• Journal of KSNVE
• /
• v.7 no.2
• /
• pp.331-345
• /
• 1997

A theoretical formulation for the analysis of free vibration of clamped-free cylindrical shells with plates attached at arbitrary axial position(s) was completed and it was programed to get the numerical results which yield natural frequencies and mode shape of the combined system of the plate and the shells. The frequencies and mode shapes from theoretical calculation were compared with those of commercial finite element code, ANSYS. In order to validate the theory, modal test was also performed by impact test and FFT analysis. The results shows good agreement with those of ANSYS and test results in frequencies and mode shapes. The method developed herein is likely to be used for the analysis of the free vibration of the clamped-free circular cylindrical shells with any kinds of lids such as hollow circular plates, conical shells, spherical shells, or semi-spherical shells.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.05a
• /
• pp.344-347
• /
• 2006

Noise reduction and control is an important problem in the performance of underwater acoustic system and on the habitability of the passenger ship for crew and passenger. Furthermore, sound generated by a propeller is critical in underwater detection and is often related to the survivability of the vessel especially for military purpose. Generally propeller noise is often the dominant noise source of marine vehicle. The flow field is analyzed with potential-based panel method, and then the time dependent pressure and sheet cavity volume data are used as the input for Ffowcs Williams-Hawkings formulation to predict the far-field acoustics. Through this study, the dominant noise source of underwater propeller is analyzed, which will provide a basis for proper noise control strategies.

• Steel and Composite Structures
• /
• v.34 no.4
• /
• pp.615-623
• /
• 2020

In this paper, free vibration analysis of a functionally graded cylindrical nanoshell resting on Pasternak foundation is presented based on the nonlocal elasticity theory. A two-dimensional formulation along the axial and radial directions is presented based on the first-order shear deformation shell theory. Hamilton's principle is employed for derivation of the governing equations of motion. The solution to formulated boundary value problem is obtained based on a harmonic solution and trigonometric functions for various boundary conditions. The numerical results show influence of significant parameters such as small scale parameter, stiffness of Pasternak foundation, mode number, various boundary conditions, and selected dimensionless geometric parameters on natural frequencies of nanoshell.

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

• Journal of Communications and Networks
• /
• v.17 no.3
• /
• pp.221-230
• /
• 2015

Rateless codes have been shown to be able to provide greater flexibility and efficiency than fixed-rate codes for multicast applications. In the following, we optimize rateless codes for unequal error protection (UEP) for multimedia multicasting to a set of heterogeneous users. The proposed designs have the objectives of providing either guaranteed or best-effort quality of service (QoS). A randomly interleaved rateless encoder is proposed whereby users only need to decode symbols up to their own QoS level. The proposed coder is optimized based on measured transmission properties of standardized raptor codes over wireless channels. It is shown that a guaranteed QoS problem formulation can be transformed into a convex optimization problem, yielding a globally optimal solution. Numerical results demonstrate that the proposed optimized random interleaved UEP rateless coder's performance compares favorably with that of other recently proposed UEP rateless codes.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.53 no.1
• /
• pp.41-46
• /
• 2004

In this paper, we present a new combined field integral equation (CFIE) formulation for the analysis of electromagnetic scattering from arbitrarily shaped three-dimensional perfectly conducting and piecewise homogeneous dielectric composite body. The conducting/dielectric structures are approximated by planar triangular patches, which have the ability to conform to any geometrical surface. The surface covering the conducting body is replaced by an equivalent surface electric current and the surface of the dielectric by equivalent electric and magnetic currents. The all equivalent currents are approximated in terms of RWG (Rao, Wilton, Glisson) functions. The objective of this paper is to illustrate that the CFIE is a valid methodology in removing defects, which occur at a frequency corresponding to an internal resonance of the structure. Numerical results are presented and compared with solutions obtained using other formulations.

• Steel and Composite Structures
• /
• v.35 no.4
• /
• pp.545-554
• /
• 2020

The present paper explores nonlinear dynamical properties of piezo-magnetic beams based on a nonlocal refined higher-order beam formulation and piezoelectric phase effect. The piezoelectric phase increment may lead to improved vibrational behaviors for the smart beams subjected to magnetic fields and external harmonic excitation. Nonlinear governing equations of a nonlocal intelligent beam have been achieved based upon the refined beam model and a numerical provided has been introduced to calculate nonlinear vibrational curves. The present study indicates that variation in the volume fraction of piezoelectric ingredient has a substantial impact on vibrational behaviors of intelligent nanobeam under electrical and magnetic fields. Also, it can be seen that nonlinear free/forced vibrational behaviors of intelligent nanobeam have dependency on the magnitudes of induced electrical voltages, magnetic potential, stiffening elastic substrate and shear deformation.