• Title, Summary, Keyword: Transfer function

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Time Lag Analysis Using Phase of Flame Transfer Function (화염전달함수의 위상차를 이용한 시간지연 분석)

  • Pyo, Yeongmin;Kim, Jihwan;Kim, Daesik
    • Journal of ILASS-Korea
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    • v.21 no.2
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    • pp.104-110
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    • 2016
  • Main purpose of the current paper is to show results of time lag analysis using phase information of flame transfer function in order to predict combustion instabilities in a gas turbine combustor. The flame transfer function (FTF) is modeled using a commercial Computational Fluid Dynamics (CFD) code (Fluent). Comparisons of the modeled flame shapes with the measured ones were made using the optimized heat transfer conditions and combustion models. The FTF modeling results show a quite good agreement with the measurement data in predicting the phase delay (i.e. time lag). Time lag analysis results using the phase of FTF shows better combustion instability prediction accuracy than using time lag calculated from the steady state flame length.

A Frequency Transfer Function Synthesis of QFT Using Total Least Squares Method (완전최소자승법을 이용한 QFT의 주파수 전달함수 합성법)

  • Kim, Ju-Sik;Lee, Sang-Hyuk
    • Journal of Institute of Control, Robotics and Systems
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    • v.8 no.8
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    • pp.649-654
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    • 2002
  • The essential philosophy of the QFT(Quantitative Feedback Theory) is that a suitable controller can be found by loop shaping a nominal loop transfer function such that the frequency response of this function does not violate the QFT bounds. The loop shaping synthesis involves the identification of a structure and its specialization by means of the parameter optimization. This paper presents an optimization algorithm to estimate the controller parameters from the frequency transfer function synthesis using the TLS(Total Least Squares) in the QFT loop shaping procedure. The proposed method identifies the parameter vector of the robust controller from an overdetermined linear system developed from rearranging the two dimensional system matrices and output vectors obtained from the QFT bounds. The feasibility of the suggested algorithm is illustrated with an example.

Optimization for Arrayed Waveguide Grating having MMI Coupler for Flattened Transfer Function

  • Jung, Jae-Hoon
    • Journal of the Optical Society of Korea
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    • v.10 no.4
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    • pp.169-173
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    • 2006
  • This paper describes an efficient optimal design method for an arrayed waveguide grating (AWG) having MMI coupler with flattened transfer function. The objective function is the norm of the difference between calculated and target spectra. To analyze the AWG transfer function, the Fresnel-Kirchhof diffraction formula was employed and the design variable was optical path difference of each array waveguide. The (1+1) Evolution Strategy was applied to an eight-channel coarse wavelength division multiplexing (CWDM) AWG as the optimization tool. For obtaining a broadened spectrum, we use a MMI coupler and the variation in optical path difference at each array waveguide changes the shape of the transfer function to obtain the optimal spectrum shape.

Deflection Limit on Vibration Serviceability of High-speed Railway Bridges Considering the Exposed Time Duration (진동지속시간을 고려한 고속철도교량의 진동 사용성 처짐 한계)

  • Jeon, Bub-Gyu;Kim, Nam-Sik;Kim, Sung-Il
    • Proceedings of the KSR Conference
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    • pp.1444-1451
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    • 2010
  • This paper aims for proposed the deflection limit on vibration serviceability of high-speed railway bridges considering the exposed time duration when a train passes a railway bridge. For this purpose, bridge-train transfer function was derived and bridge-train interaction analysis was performed by using the derived function. The vertical acceleration signals of passenger cars obtained from bridge-train interaction analysis were compared with them from the bridge-train transfer function by moving constant force analysis. Therefore it was estimated possible to induce the comfort deflection limit of railway bridge by using bridge-train transfer function. The deflections by moving force of single span bridge and continuous bridge were assumed as sine and haversine wave. The deflection limit on vibration serviceability of high-speed railway bridges considering the exposed time duration can be expanded using bridge-train transfer function and bridge comfort limit considering serviceability due to bridge vibration. And it was compared to other allowable deflection limits of railway bridge design specifications.

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A Simplification of Linear System via Frequency Transfer Function Synthesis (주파수 전달함수 합성법에 의한 선형시스템의 간소화)

  • 김주식;김종근;유정웅
    • The Transactions of the Korean Institute of Electrical Engineers D
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    • v.53 no.1
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    • pp.16-21
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    • 2004
  • This paper presents an approximation method for simplifying a high-order transfer function to a low-order transfer function. A model reduction is based on minimizing the error function weighted by the numerator polynomial of reduced systems. The proposed methods provide better low frequency fit and a computer aided algorithm that estimates the coefficients vector for the numerator and denominator polynomial on the simplified systems from an overdetermined linear system constructed by frequency responses of the original systems. Two examples are given to illustrate the feasibilities of the suggested schemes.

Vibration Serviceability Evaluation of Railway Bridges Considering Bridge-train Transfer function (열차-교량 진동전달특성을 이용한 철도교량의 진동사용성 평가기법)

  • Jeon, Bub-Gyu;Kim, Nam Sik;Kim, Sung-Il
    • Proceedings of the KSR Conference
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    • pp.359-366
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    • 2009
  • This paper aims for analyzing the vibration serviceability of train by simply expressing its vertical vibration when it passes a railway bridge. For this purpose, bridge-train transfer function was derived and bridge-train interaction analysis was performed by using the derived function. The bridge-train transfer function was developed with the assumption that train is a single mass-spring system, and bridge-train interaction analysis was performed on simple beams of KTX passenger car. The vertical acceleration signals of passenger cars obtained from bridge-train interaction analysis were compared with them of cars obtained from the bridge-train transfer function. As a result, it could be estimated to express the vertical vibration inside the passenger car required for vibration serviceability evaluation by using the vertical vibration of bridges obtained from moving load analysis. Therefore, it may be possible to evaluate the vibration serviceability of railway bridges considering bridge-train interaction effect.

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EXPERIMENTAL INVESTIGATION OF CONVECTIVE HEAT TRANSFER IN A NARROW RECTANGULAR CHANNEL FOR UPWARD AND DOWNWARD FLOWS

  • Jo, Daeseong;Al-Yahia, Omar S.;Altamimi, Raga'i M.;Park, Jonghark;Chae, Heetaek
    • Nuclear Engineering and Technology
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    • v.46 no.2
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    • pp.195-206
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    • 2014
  • Heat transfer characteristics in a narrow rectangular channel are experimentally investigated for upward and downward flows. The experimental data obtained are compared with existing data and predictions by many correlations. Based on the observations, there are differences from others: (1) there are no different heat transfer characteristics between upward and downward flows, (2) most of the existing correlations under-estimate heat transfer characteristics, and (3) existing correlations do not predict the high heat transfer in the entrance region for a wide range of Re. In addition, there are a few heat transfer correlations applicable to narrow rectangular channels. Therefore, a new set of correlations is proposed with and without consideration of the entrance region. Without consideration of the entrance region, heat transfer characteristics are expressed as a function of Re and Pr for turbulent flows, and as a function of Gz for laminar flows. The correlation proposed for turbulent and laminar flows has errors of ${\pm}18.25$ and ${\pm}13.62%$, respectively. With consideration of the entrance region, the heat transfer characteristics are expressed as a function of Re, Pr, and $z^*$ for both laminar and turbulent flows. The correlation for turbulent and laminar flows has errors of ${\pm}19.5$ and ${\pm}22.0%$, respectively.

Prediction of visual performance using contrast sensitivity function and modulation transfer function (대비감도함수와 변조전달함수를 이용한 시기능 예측)

  • Kim Sang Gee;Park Sung Chan
    • Korean Journal of Optics and Photonics
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    • v.15 no.5
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    • pp.461-468
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    • 2004
  • A finite model eye of visual acuity 24/20 in emmertropia was presented. We determined the image intensity profile on retina using optical transfer function of model eye, and compared with clinical data. The retinal contrast sensitivity function based on the Stiles-Crawford effect, photopic response, diffraction, aberration, retinal contrast sensitivity, and pupil size is calculated. Visual acuity for human eye could be predicted by examining the modulation transfer function of a bar target and retinal contrast sensitivity function. This visual acuity was evaluated for pupil diameters ranging from 1 to 8 mm.

Measurement of the Modulation Transfer Function of Infrared Imaging System by Modified Slant Edge Method

  • Li, Hang;Yan, Changxiang;Shao, Jianbing
    • Journal of the Optical Society of Korea
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    • v.20 no.3
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    • pp.381-388
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    • 2016
  • The performance of a staring infrared imaging system can be characterized based on estimating the modulation transfer function (MTF). The slant edge method is a widely used MTF estimation method, which can effectively solve the aliasing problem caused by the discrete undersampling of the infrared focal plane array. However, the traditional slant edge method has some limitations such as the low precision of the edge angle extraction and using the approximate function to fit the edge spread function (ESF), which affects the accuracy of the MTF estimation. In this paper, we propose a modified slant edge method, including an edge angle extraction method that can improve the precision of the edge angle extraction and an ESF fitting algorithm which is based on the transfer function model of the imaging system, to enhance the accuracy of the MTF estimation. This modified slant edge method presents higher estimation accuracy and better immunity to noise and edge angle than other traditional methods, which is demonstrated by the simulation and application experiments operated in our study.

Graphic Hardware Based Visualization of Three Dimensional Object Boundaries in Volume Data Set Using Three Dimensional Textures (그래픽 하드웨어기반의 3차원 질감을 사용한 볼륨 데이터의 3차원 객체 경계 가시화)

  • Kim, Hong-Jae;Choi, Heung-Kook
    • Journal of Korea Multimedia Society
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    • v.11 no.5
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    • pp.623-632
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    • 2008
  • In this paper, we used the color transfer function and the opacity transfer function for the internal 3D object visualization of an image volume data. In transfer function, creating values of between boundaries generally is ambiguous. We concentrated to extract boundary features for segmenting the visual volume rendering objects. Consequently we extracted an image gradient feature in spatial domain and created a multi-dimensional transfer function according to the GPU efficient improvement. Finally using these functions we obtained a good research result as an implementing object boundary visualization of the graphic hardware based 3D texture mapping.

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