• Journal of the Korean Society for Aviation and Aeronautics
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• v.14 no.4
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• pp.38-47
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• 2006

This study analyzes the expense structure of the air transport industry, based on the cost and income data of 18 major airlines, estimates the economic effectiveness of scale and conducts comparative analysis. As for the method of analysis, Translog cost function and the Fourier flexible function were used. The result showed that big companies had the economy of scale based on the Translog cost function, while the Fourier flexible function led to a estimation that expanding the input is not recommended, for the expansion of scale entails the poor economy of scale. It can be presumed that the economy of scale was estimated according to the U shape of the Translog cost function in the given data. On the other hand, the Fourier flexible cost function approaches the unknown function, as it is a Fourier series, and correctly infers the economy of scale based on the analyzed data. As for the flag carrier's economy of scale, it was inferred that the economy of scale existed by any of two functions. Therefore, the conclusion was that further expanding the scale will not cause any problem.

• Proceedings of the KIEE Conference
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• 1987.11a
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• pp.457-462
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• 1987

This paper deals with the PWM controlled active AC power filter. A new PWM control method from the viewpoint of speed and simplicity is proposed. And a microprocessor-based controller is used to realize the active AC power filter. The existing PWM control methods are primarily based on Fourier series expansion and these methods need FFT calculation and solving nonlinear harmonic equations, which are heavy burden to real-time control. The proposed method is based upon generalized pulse series expansion and needs only definite integrals of harmonic signal. So, computational effort can be reduced by a large margin. The digital circuit using 16-bit microprocessor is designed to implement the actual active power filler.

• Computational Structural Engineering
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• v.10 no.4
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• pp.291-302
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• 1997

This paper presents an analytical method for evaluating the free vibration of a circular cylindrical tank filled with bounded compressible fluid. The analytical method was developed by means of the finite Fourier series expansion method. The compressible fluid motion was determined by means of the linear velocity potential theory. To clarify the validity of the analytical method, the natural frequencies of a circular cylindrical tank with the clamped-clamped boundary condition, and filled with water, were obtained by the analytical method and the finite element method using a comercial ANSYS 5.2 software. Excellent agreement on the natural frequencies of the liquid-filled tank structure was found. The compressiblity and the fluid density effects on the normalized coupled natural frequencies were investigated. The density of fluid affects on all coupled natural frequencies of the tank, whereas the compressibility of fluid affects mainly on the natural frequencies of lower circumferential modes.

• Communications of the Korean Mathematical Society
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• v.20 no.4
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• pp.657-669
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• 2005

Calculations of some integrals on the n-dimensional vector space over $\mathbb{Q}_p$ are useful in getting some other formulations of quantum mechanics and the field theory of p-adic mathematical physics. For reasons of these, we estimate several integrals. As an application, we derive some properties for the p-adic Green functions.

• Journal of the Korean Statistical Society
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• v.25 no.2
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• pp.161-173
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• 1996

When we deal with a Hilbert space-valued Stochastic Differential Equation (SDE) (or Stochastic Partial Differential Equation (SPDE)), depending on some unknown parameters, the solution usually has a Fourier series expansion. In this situation we consider the maximum likelihood method for the statistical estimation problem and derive the asymptotic properties (consistency and normality) of the Maximum Likelihood Estimator (MLE).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.1
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• pp.214-223
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• 1996

Noise effects on image profiles reconstructed by the spectral inverse scattering technique is studied based on moment method with series-expanded basis function. It is found that the Fourier series expansion to the field distribution and the averaging of the reconstructed profile in each enlarged cell provides an effective tool for the reduction of noise effects.

• Wind and Structures
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• v.30 no.5
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• pp.485-497
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• 2020

A study, using potential water wave theory, is conducted on the oblique water wave motion over two fixed submerged rectangular blocks (breakwaters) placed over a finite step bottom. We have considered infinite and semi-infinite fluid domains. In both domains, the Fourier expansion method is employed to obtain the velocity potentials explicitly in terms of the infinite Fourier series. The unknown coefficients appearing in the velocity potentials are determined by the eigenfunction expansion matching method at the interfaces. The derived velocity potentials are used to compute the hydrodynamic horizontal and vertical forces acting on the submerged blocks for different values of block thickness, gap spacing between the two blocks, and submergence depth of the upper block from the mean free surface. In addition, the wave load on the vertical wall is computed in the case of the semi-infinite fluid domain for different values of blocks width and the incident wave angle. It is observed that the amplitudes of hydrodynamic forces are negligible for larger values of the wavenumber. Furthermore, the upper block experiences a higher hydrodynamic force than the lower block, regardless of the gap spacing, submergence depth, and block thickness.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.55 no.3
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• pp.141-145
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• 2006

The line current problem(2-dimensional space : point source) is not easy to analyze the magnetic field using the standard finite element method(FEM), such as overhead trolley line or transmission line. To supplement such a defect this paper is proposed the coupling scheme of analytical solution and FEM. In analysis of the magnetic field using the standard FEM. If the current region is a relatively small compared to the whole region. Therefore the current region must be finely divided using a large number of elements. And the large number of elements increase the number of unknown variables and the use of computer memories. In this paper, an analytical solution is suggested to supplement this weak points. When source is line current and the part of interest is far from line current, the analytical solution can be coupling with FEM at the boundary. Analytical solution can be described by the multiplication of two functions. One is power function of radius, the other is a trigonometric function of angle in the cylindrical coordinate system. There are integral constants of two types which can be established by fourier series expansion. Also fourier series is represented as the factor to apply the continuity of the magnetic vector potential and magnetic field intensity with tangential component at the boundary. To verify the proposed algorithm, we chose simplified model existing magnetic material in FE region. The results are compared with standard FE solution. And it is good agreed by increasing harmonic order.

• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.343-346
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• 2005

In this study, a basic concept of wavelet encoding and its advantages over Fourier based phase encoding application. Wavelet encoding has been proposed as an alternative way to Fourier based phase encoding in magnetic resonance imaging. In wavelet encoding, the RF pulse is designed to generate wavelet-shaped excitation profile of spins. From the resulting echo signals, the wavelet transform coefficients of spin distribution are acquired and an original spin density is reconstructed from wavelet expansion. Wavelet encoding has several advantages over phase encoding. By minimizing redundancy of the data acquisition in a dynamic series of images, we can avoid some encoding steps without serious loss of quality in reconstructed image. This strategy may be regarded as data compression during imaging. Although there are some limitations in wavelet encoding, it is a promising scheme in a dynamic imaging.

• Computational Structural Engineering
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• v.8 no.1
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• pp.147-160
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• 1995

Based on the weighted residual concept[4], a three-dimensional plate theory is derived using a Fourier series expansion of a dependent variable and a weighted residual approximation of the basic elasticity equations. The weighted residual equilibrium equations of the plate are expressed in terms of weighted displaced quantities, and the results are then interpreted by means of a potential energy functional. The potential energy expression is used to develop a finite element implementation. For illustrative purposes, the application of the theory to a strip plate is considered and two numerical examples of a cantilever and a simply-supported strip plate are studied.