• Title, Summary, Keyword: frequency-space domain

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A FREQUENCY-DOMAIN METE10D FOR FINITE ELEMENT SOLUTIONS OF PARABOLIC PROBLEMS

  • Lee, Chang-Ock;Lee, Jongwoo;Sheen, Dongwoo
    • Bulletin of the Korean Mathematical Society
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    • v.39 no.4
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    • pp.589-606
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    • 2002
  • We introduce and analyze a frequency-domain method for parabolic partial differential equations. The method is naturally parallelizable. After taking the Fourier transformation of given equations in the space-time domain into the space-frequency domain, we propose to solve an indefinite, complex elliptic problem for each frequency. Fourier inversion will then recover the solution in the space-time domain. Existence and uniqueness as well as error estimates are given. Fourier invertibility is also examined. Numerical experiments are presented.

ERROR ESTIMATIES FOR A FREQUENCY-DOMAIN FINITE ELEMENT METHOD FOR PARABOLIC PROBLEMS WITH A NEUMANN BOUNDARY CONDITION

  • Lee, Jong-Woo
    • 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.

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Seismic waveform tomography in the frequency-space domain: selection of the optimal temporal frequency for inversion

  • Yokota Toshiyuki;Matsushima Jun
    • Geophysics and Geophysical Exploration
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    • v.7 no.1
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    • pp.19-24
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    • 2004
  • Frequency-space domain full-wave tomography is a promising technique for delineating detailed subsurface structure with high resolution. However, this method requires criteria for the selection of a set of optimal temporal frequency components, to achieve stability in the sequence of inversion processes together with computational efficiency. We propose a method of selecting optimal temporal frequencies, based on wavenumber continuity. The proposed method is tested numerically and is shown to be able to select an optimal set of frequency components that are sufficient to image the anomalies.

Frequency Domain Analysis of Lifting Problems with Explicit Kutta Condition

  • Kim, Jong-Un;Kim, Gun-Do;Lee, Chang-Sup
    • Journal of Ship and Ocean Technology
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    • v.7 no.3
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    • pp.34-55
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    • 2003
  • Explicit Kutta condition approximation, proved useful in existing time-domain solver of the unsteady propeller problem, requires a specified functional behavior of the vorticity in space near the trailing edge. In this paper, the strength of the discrete vortices is controlled to have a specified behavior in space in the frequency domain approach. A new formulation is introduced and is implemented for analysis of a lifting surface of a rectangular planform. Sample computations carried out according to the new formulation compares well with that of existing unsteady lifting problem in the time domain.

Multiplexed Space-Frequency Block Coding technique for Single-Carrier Modulation with Frequency Domain Equalization (주파수 영역 등화기를 사용하는 단일 반송파 전송 시스템을 위한 다중 공간 주파수 블록 코딩 기법)

  • Jung, Hyeok Koo
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.61 no.4
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    • pp.234-238
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    • 2012
  • This paper proposes a multiplexed space-frequency block coding (SFBC) technique for single-carrier modulation with frequency domain equalization. Multiplexed space-frequency block coding technique for single-carrier modulation uses multiple groups of two transmitters and suppresses the interference signals of other SFBC groups at the receiver. In this paper, we reconfigure transmit signals to adapt them for multiplexed SFBC for single-carrier modulation with frequency domain equalization and receiver structures and propose a structure for transmitter and receiver, show its performance is better than the traditional algorithm by simulations.

Time domain earthquake response analysis method for 2-D soil-structure interaction systems

  • Kim, Doo-Kie;Yun, Chung-Bang
    • Structural Engineering and Mechanics
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    • v.15 no.6
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    • pp.717-733
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    • 2003
  • A time domain method is presented for soil-structure interaction analysis under seismic excitations. It is based on the finite element formulation incorporating infinite elements for the far field soil region. Equivalent earthquake input forces are calculated based on the free field responses along the interface between the near and far field soil regions utilizing the fixed exterior boundary method in the frequency domain. Then, the input forces are transformed into the time domain by using inverse Fourier transform. The dynamic stiffness matrices of the far field soil region formulated using the analytical frequency-dependent infinite elements in the frequency domain can be easily transformed into the corresponding matrices in the time domain. Hence, the response can be analytically computed in the time domain. A recursive procedure is proposed to compute the interaction forces along the interface and the responses of the soil-structure system in the time domain. Earthquake response analyses have been carried out on a multi-layered half-space and a tunnel embedded in a layered half-space with the assumption of the linearity of the near and far field soil region, and results are compared with those obtained by the conventional method in the frequency domain.

Defect evaluations of weld zone in rails considering phase space-frequency demain (위상공간-주파수 영역을 고려한 레일 용접부의 결함 평가)

  • 윤인식;권성태;장영권;정우현;이찬석
    • Journal of the Korean Society for Railway
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    • v.2 no.2
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    • pp.21-30
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    • 1999
  • This study proposes the analysis and evaluation method of time series ultrasonic signal using the phase space-frequency domain. Features extracted from time series signal analyze quantitatively characteristics of weld defects. For this purpose, analysis objectives in this study are features of time domain and frequency domain. Trajectory changes in the attractor indicated a substantial difference in fractal characteristics resulting from distance shifts such as parts of head and flange even though the types of defects are identified. These differences in characteristics of weld defects enables the evaluation of unique characteristics of defects in the weld zone. In quantitative fractal feature extraction, feature values of 3.848 in the case of part of head(crack) and 4.102 in the case of part of web(side hole) and 3.711 in the case of part of flange(crack) were proposed on the basis of fractal dimension. Proposed phase space-frequency domain method in this study can integrity evaluation for defect signals of rail weld zone such as side hole and crack.

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A Study on Frequency and Time Domain Interpretation for Safety Evaluation of old Concrete Structure (노후된 콘크리트 구조물의 안전도 평가를 위한 초음파기법의 주파수 및 시간영역 해석에 관한 연구)

  • Suh Backsoo;Sohn Kwon-Ik
    • Tunnel and Underground Space
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    • v.15 no.5
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    • pp.352-358
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    • 2005
  • For non-destructive testing of concrete structures, time and frequency domain method were applied to detect cavity in underground model and pier model. To interpret the measured data, time domain method made use of tomography which was completed with first arrivaltime and inversion method. In this steady, frequency domain method using Fourier transform was tried. Maximum frequency in the frequency domain was analyzed to calculate location of cavity.

Reduced Complexity Signal Detection for OFDM Systems with Transmit Diversity

  • Kim, Jae-Kwon;Heath Jr. Robert W.;Powers Edward J.
    • Journal of Communications and Networks
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    • v.9 no.1
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    • pp.75-83
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    • 2007
  • Orthogonal frequency division multiplexing (OFDM) systems with multiple transmit antennas can exploit space-time block coding on each subchannel for reliable data transmission. Spacetime coded OFDM systems, however, are very sensitive to time variant channels because the channels need to be static over multiple OFDM symbol periods. In this paper, we propose to mitigate the channel variations in the frequency domain using a linear filter in the frequency domain that exploits the sparse structure of the system matrix in the frequency domain. Our approach has reduced complexity compared with alternative approaches based on time domain block-linear filters. Simulation results demonstrate that our proposed frequency domain block-linear filter reduces computational complexity by more than a factor of ten at the cost of small performance degradation, compared with a time domain block-linear filter.

LEAST-SQUARES SPECTRAL COLLOCATION PARALLEL METHODS FOR PARABOLIC PROBLEMS

  • SEO, JEONG-KWEON;SHIN, BYEONG-CHUN
    • Honam Mathematical Journal
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    • v.37 no.3
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    • pp.299-315
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    • 2015
  • In this paper, we study the first-order system least-squares (FOSLS) spectral method for parabolic partial differential equations. There were lots of least-squares approaches to solve elliptic partial differential equations using finite element approximation. Also, some approaches using spectral methods have been studied in recent. In order to solve the parabolic partial differential equations in parallel, we consider a parallel numerical method based on a hybrid method of the frequency-domain method and first-order system least-squares method. First, we transform the parabolic problem in the space-time domain to the elliptic problems in the space-frequency domain. Second, we solve each elliptic problem in parallel for some frequencies using the first-order system least-squares method. And then we take the discrete inverse Fourier transforms in order to obtain the approximate solution in the space-time domain. We will introduce such a hybrid method and then present a numerical experiment.