• 소음진동
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• 제2권2호
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• pp.99-106
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• 1992

The complex Young's modulus of a viscoelastic material can be obtained as a function of frequency from the measurements of relative motion between the two ends of a bar-type specimen. Non-resonance method is usually used to obtain the complex Young's modulus over wide range of frequency including resonance points, while in resonance method information at resonance frequencies only is used. However, the complex Young's modulus obtained by the non-resonance method is often unreliable in the anti-resonance frequency regions because of the measurement noise problems. In this study, the effects of the random measurement errors on estimating the complex Young's modulus are studied in the aspect of sensitivity, and how to obtain the reliable frequency region for a given measurement error level is shown. The usable frequency regions in determining the complex Young's modulus are represented by a non-dimensional parameter formed with the wave length and specimen length.

• 한국세라믹학회지
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• 제36권2호
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• pp.122-129
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• 1999

알루미나 분말/(알루미나+결합체+가소제)의 비(X)와 결합체/(결합체+가소제)의 비(Y)를 각각 변화시켜 제조한 알루미나 그린 테이프의 complex modulus를 Micro Fourier Rheometer를 이용하여 측정하였다. X와 Y의 증가에 따라 Transfer function(TF) magnitude는 증가하고 Transfer function(TF) phase는 감소하는 경향을 보였으며 이로부터 X비와 Y비의 증가가 테이프의 탄성을 증가시켜는 요인임을 알 수 있었다. 온도가 증가함에 따라 알루미나 테이프의 TF magnitude는 작아지고 TF phase는 커지는 것으로부터 테이프의 점성이 증가함을 알 수 있었다. 특히 Y비에 따른 complex modulus의 변화는 유리전이온도와 관련이 있으며 변화값은 측정 조성 범위 내에서 X비에 의한 변화값보다 큼을 볼 수 있었다. complex modulus 측정을 통하여 알루미나 테이프의 성형이 가능하기 위해서는 TF phase 값이 17$^{\circ}$이상이어야 함을 유추할 수 있었다.

• Journal of Biosystems Engineering
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• 제16권3호
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• pp.263-271
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• 1991

When grains is subjected to oscillating load, the dynamic viscoelastic behavior of the material will be describe the complex modulus of the material. The complex modulus and therefore the storage modulus, the loss modulus, and the phase angle for the sample should be obtainable with a given static viscoelastic property of the material under static load. The complex relaxation moduli of the rough rice kernel were computed from the Burger's model describing creep behavior of the material which were obtained in the previous study. Also, the effects of cyclic load and moisture content of grain on the dynamic viscoelastic behavior of the samples were analized. The storage modulus of the rough rice kernel slightly increased with the frequency applied but at above the frequency of 0.1 Hz it was nearly constant with the frequency, and the loss modulus of the sample very rapidly decreased with increase in the frequency on those frequency ranges. It was shown that the storage modulus and the loss modulus of the sample increased with decrease in grain moisture content. Effect of grain moisture content on the storage modulus of the sample was highly significant than effect of the frequency applied, but effect of the frequency on the loss modulus of the sample was more significant than effect of grain moisture content.

• 한국통신학회논문지
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• 제35권8A호
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• pp.760-767
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• 2010

For complex channel blind equalization, this study presents the performance and characteristics of two complex blind information theoretic learning algorithms (ITL) which are based on minimization of Euclidian distance (ED) between probability density functions compared to constant modulus algorithm which is based on mean squared error (MSE) criterion. The complex-valued ED algorithm employing constant modulus error and the complex-valued ED algorithm using a self-generated symbol set are analyzed to have the fact that the cost function of the latter forces the output signal to have correct symbol values and compensate amplitude and phase distortion simultaneously without any phase compensation process. Simulation results through MSE convergence and constellation comparison for severely distorted complex channels show significantly enhanced performance of symbol-point concentration with no phase rotation.

• 소음진동
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• 제1권2호
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• pp.121-128
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• 1991

In order to use viscoelastic materials efficiently for noise and vibration control, or th qualify newly developed materials, knowledge of the Young' s modulus and loss factor is essemtial. These material properties, the so-called complex Young' s modulus, are frequently treated as dynamic charicteristics because of their dependence upon the frequency. Many techniques have been developed and verified for measuring complex Young' s modulus of viscoelastic materials. Among them, the impedance method is preferable in order to obtain the frequency information in detail. In this method, a cylindrical or prismatic specimen is excited into longitudinal harmonic vibration at one end, the other being fixed, and the resulting force is measured at the driving or fixed end. The amplitude ratio of the two signals and phase angle between them are then used to compute the material properties using various mathematical models. In this paper, the impedance method is investigated theoretically and experimentally. A way to determine the specimen geometry which is most appropriate for the identification of complex Young' s modulus using the lumped mass model is presented and discussed. Then experimental results supporting the theoretical predictions are presented.

• Korea-Australia Rheology Journal
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• 제16권1호
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• pp.17-26
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• 2004

We examine rigorous computations on microstructural as well as rheological properties of concentrated dispersions of bidisperse colloids. The NVT Monte Carlo simulation is applied to obtain the radial distribution function for the concentrated system. The long-range electrostatic interactions between dissimilar spherical colloids are determined using the singularity method, which provides explicit solutions to the linearized electrostatic field. The increasing trend of osmotic pressure with increasing total particle concentration is reduced as the concentration ratio between large and small particles is increased. From the estimation of total structure factor, we observe the strong correlations developed between dissimilar spheres. As the particle concentration increases at a given ionic strength, the magnitude of the first peak in structure factors increases and also moves to higher wave number values. The increase of electrostatic interaction between same charged particles caused by the Debye screening effect provides an increase in both the osmotic pressure and the shear modulus. The higher volume fraction ratio providing larger interparticle spacing yields decreasing high frequency limit of the shear modulus, due to decreasing the particle interaction energy.

• 한국소음진동공학회논문집
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• 제16권4호
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• pp.372-379
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• 2006

Little attention has been paid to static-strain-dependence of dynamic complex modulus of viscolelastic materials in computational analysisso far. Current commercial Finite Element Method (FEM) codes do not take such characteristics into consideration in constitutive equations of viscoelastic materials. Recent experimental observations that static-strain-dependence of dynamic complex modulus of viscolelastic materials, especially filled rubbers, are significant, however, require that solutions somehow are necessary. In this study, a simple technique of using a commercial FEM code, ABAQUS, is introduced, which seems to be far more cost/time saving than development of a new software with such capabilities. A static-strain-dependent correction factor is used to reflect the influence of static-strains in Merman model, which is currently the base of the ABAQUS. The proposed technique is applied to viscoelastic components of rather complicated shape to predict the dynamic stiffness under static-strain and the predictions are compared with experimental results.

• 대한화장품학회지
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• 제24권3호
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• pp.129-133
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• 1998

We have studied a relationship between the pattern of complex modulus change versus internal phase volume ratio and the rheological consistency of concentrated W/O emulsions with Magnesium Sulfate in the range 0.0 to 0.5 wt% and with different oil polarities, respectively. The rheological consistency with time of concentrated W/O emulsion was checked using Fudoh Rheometer and the coalescence of deformed water droplets was examined using polarized light microscope(LEICA DMRP). To find the pattern of complex modulus change of the concentrated emulsions versus internal phase volume ratio, the effect of varying water phase volume fraction from 0.78 up to 0.85 on viscoelastic measurements was investigated using rotational rheometer (HAAKE Rheostress RS 50). The rheological consistency was mainly destroyed by the coalescence of the deformed water droplets. The greater the increase of complex modulus was, the less coalescence occurred and the more consistent the concentrated emulsions were. And the pattern of complex modulus increase versus volume ratio has been explained with the resistance to coalescence of the deformed interfacial film of water droplets in concentrated W/O emulsion.

• 한국정보전자통신기술학회논문지
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• 제3권3호
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• pp.73-80
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• 2010

상수 모듈러스 오차와 두확률 밀도 함수의 유클리드 거리에 기본을 둔 블라인드 알고리듬은 정보 이론적 학습 방법의 장점에도 불구하고 복소 채널의 위상 회전을 극복하지 못해 열악한 성능을 보인다. 이 논문에서는, 출력 전력이 다중 모듈러스 값의 근방에 있을 때 decision-directed 모드로 동작하는 기법을 정보 이론적 학습에 추가하므로서 복소 채널의 위상 회전 문제를 해결할 수 있음를 보였다. 복소 채널 모델과 16 QAM 방식에 대한 시뮬레이션 결과에서 복소 채널의 위상 회전 문제가 해결되어 현격한 성능 향상을 보였다.

• 한국소음진동공학회논문집
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• 제21권1호
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• pp.9-17
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• 2011

In this paper, the general equation of motion of damped sandwich beam with multi-viscoelastic material layer was derived based on the equation presented by Mead and Markus. The viscoelastic layer, which has characteristics of complex shear modulus, was assumed to be dominantly under shear deformation. The equation of motion of n-layered damped sandwich beam in bending could be represented by (n+3)th order ordinary differential equation. Finite element model for the n-layered damped sandwich beam was formulated and programmed using higher order shape functions. Several numerical examples were implemented to show the effects of damped material.