• Bulletin of the Korean Mathematical Society
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• v.35 no.2
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• pp.345-362
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• 1998

We introduce and anlyze a naturally parallelizable frequency-domain method for parabolic problems with a Neumann boundary condition. After taking the Fourier transformation of given equations in the space-time domain into the space-frequency domain, we solve an indefinite, complex elliptic problem for each frequency. Fourier inversion will then recover the solution of the original problem in the space-time domain. Existence and uniqueness of a solution of the transformed problem corresponding to each frequency is established. Fourier invertibility of the solution in the frequency-domain is also examined. Error estimates for a finite element approximation to solutions fo transformed problems and full error estimates for solving the given problem using a discrete Fourier inverse transform are given.

• The Korean Journal of Applied Statistics
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• v.31 no.2
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• pp.189-204
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• 2018

This study is on forecasting the electricity consumption of an industrial manufacturing building called GGM from January 2014 to April 2017. We fitted models using SARIMA, SARIMA + GARCH, Holt-Winters method and ARIMA with Fourier transformation. We also forecasted electricity consumption for one month ahead and compared the predicted root mean square error as well as the predicted error rate of each model. The electricity consumption of GGM fluctuates weekly and annually; therefore, SARIMA + GARCH model considering both volatility and seasonality, shows the best fit and prediction.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.396-403
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• 1991

A solution is presented for the computation of the elastic-creep stresses in a hollow cylinder subjected to nonaxisymmetric temperature distribution. The creep problem is treated by the Maxwell creep model. Laplace transformation is used for reformation of the governing equation of elastic problem and Hooke's law in a function of .gamma. , .theta. , and creep constant. The governing equation is set up using the Airy stress function which leads to the biharmonic equation. The solution is obtained by using Fourer series method and Laplace inverse method used to obtain the stress components which include the variation of time. This solution shows excellent agreement with Lamkin's and Boley & Weiner's solution. The viscoelastic stresses are also obtained for the fuel rob tube subjecting nonaxisymmetric thermal load.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 2000.04a
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• pp.144-148
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• 2000

A new paradigm is urgently needed to create the textile product that appeal to human Kansei or Gosei. A future of textiles depends heavily on this new paradigm. In order to create new paradigm Kansei color designs by pleasant sound are tried. These computing color designs are treated by the method of Fast fourier Transformation. As several result good color designs are given in forms of ring color patterns and band. But these judgments depend finally on human kansei. These new technology give us good hints in order to create new paradigm that appeal to Kansei goods. This new concept should be developed to higher level by additional improvements.

• Journal of ILASS-Korea
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• v.7 no.4
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• pp.9-15
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• 2002

Convolution Fourier transformation tomographically reconstructs the spatially resolved spray injection rate from direct measuring cells. Asymmetric sprays generated from a twin-hole air shroud injector are tested with 12 equiangular projections of measurements. For each projection angle, line of sight integrated injection rate was measured at 35 positions with equal spacing measuring cells of 3 mm in width, 100 mm in length, 55 mm in depth and 0.5 mm thickness of separating wall. Interpolated data between the projection angles effectively increase the number of projections, which significantly enhances the signal-to-noise level in the reconstructed data. This modified convolution Fourier transformation scheme predicts well the structure of asymmetric sprays. Comparative study has been made between sprays with and without air shrouding. Tomograhpic reconstruction of injection rate from direct measuring cells obtained can be used to estimate the accuracy of volume fraction of spray from the LDPA tomographic reconstruction.

• Journal of Korean Association for Spatial Structures
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• v.5 no.1 s.15
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• pp.81-89
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• 2005

Walking loads are influenced by various parameters so that they need to be measured considering such parameters. Walking frequency(rate) is experimentally investigated as the most important parameter in determining the walking load expressed with dynamic load factor. This study focuses on the derivation of continuous walking load-time functions at any walking frequency ranging from 1.30Hz to 2.70Hz. Experiments were conducted to obtain time-histories of walking loads at the increment of 0.1Hz, which are decomposed into harmonic loads by the Fourier transformation. The polynomial load-time functions are proposed representing the relationship between harmonic coefficients and walking frequencies, thereby easily formulating walking load-time histories for dynamic load factor with various walking frequencies.

• Journal of Power System Engineering
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• v.9 no.4
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• pp.58-64
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• 2005

주파수 영역 민감도 해석법은 동적 시스템의 전달함수에 대한 설계 파라미터의 변화에 의한 효과를 파악하기 위해 사용되어 왔으며, 이때의 민감도 함수는 시스템 설계 파라미터에 대한 시스템 전달 함수의 편미분 값이다. 일반적으로 종래의 주파수 영역 민감도 해석은 직접 미분법이나 라플라스 변환이 사용되어 왔다. 라플라스 변환을 사용하는 경우에 시스템의 차수가 증가할수록 역행렬 조작은 매우 많은 시간을 필요로 하며 또한 어려운 작업이다. 본논문에서는 이러한 다점을 보완하기 위하여 푸리에변환을 이용한 민감도 기법을 제시하였다. 파라미터의 변화에 대한 진폭-주파수 특성의 민감도 해석을 간단한 2자유도 모델과 로터 다이나믹 시스템에 적용하였다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.12 no.1
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• pp.41-53
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• 2008

Polynomials are one of most important and widely used numerical tools in dealing with a smooth function on a bounded domain and trigonometric functions work for smooth periodic functions. However, they are not the best choice if a function has a bounded support in space and in frequency domain. The Prolate Spheroidal wave function (PSWF) of order zero has been known as a best candidate as a basis for band-limited functions. In this paper, we review some basic properties of PSWFs defined as eigenfunctions of bounded Fourier transformation. We also propose numerical inversion schemes based on PSWF and present some numerical examples to show their feasibilities as signal processing tools.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.2
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• pp.150-160
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• 2002

The free vibration characteristics of the triple cylindrical shells filled with fluid are investigated. The triple cylindrical shells are filled with compressible fluid. The boundary condition is clamped at both ends. Analytical method is developed to evaluate natural frequencies of triple cylindrical shells using Sanders' shell theory and courier series expansion by Stokes' transformation. Their results are compared with those of finite element method to verify the validation of the method developed. The modal characteristics of shells filled with fluid at region 1, 2 and 3 are evaluated.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.4 no.1
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• pp.17-21
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• 2003

It has been difficult to characterize the value of treated sapphires for gem stones with bare eyes. Color enhancing treatments by diffusion and annealing became sophisticated and customers and gemologists had asked a non-destructive and fast characterization method. We suggest that Fourier transformation infra-red (FTIR) offers to characterize the cobalt-doped synthetic sapphires successfully in 3 minutes. Our results imply that FTIR may be employed in jewelry business to identify the treated sapphires in quantitative way.