• Preventive Nutrition and Food Science
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• 제22권1호
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• pp.56-61
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• 2017

Rheological properties of waxy barley flour (WBF) dispersions mixed with various gums (carboxyl methyl celluleose, guar gum, gum arabic, konjac gum, locust bean gum, tara gum, and xanthan gum) at different gum concentrations were examined in steady and dynamic shear. WBF-gum mixture samples showed a clear trend of shear-thinning behavior and had a non-Newtonian nature with yield stress. Rheological tests indicated that the flow and dynamic rheological parameter (apparent viscosity, consistency index, yield stress, storage modulus, and loss modulus) values of WBF dispersions mixed with gums, except for gum arabic, were significantly higher than those of WBF with no gum, and also increased with an increase in gum concentration. In particular, konjac gum at 0.6% among other gums showed the highest rheological parameter values. Tan ${\delta}$ values of WBF-xanthan gum mixtures were lower than those of other gums, showing that there is a more pronounced synergistic effect on the elastic properties of WBF in the presence of xanthan gum. Such synergistic effect was hypothesized by considering thermodynamic compatibility between xanthan gum and WBF. These rheological results suggest that in the WBF-gum mixture systems, the addition of gums modified the flow and viscoelastic properties of WBF, and that these modifications were dependent on the type of gum and gum concentration.

• 한국소음진동공학회논문집
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• 제14권7호
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• pp.639-647
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• 2004

This paper concerns the analytical modeling and dynamic analysis of advanced rotating blade structure implemented by a dual approach based on structural tailoring and viscoelastic material technology. Whereas structural tailoring uses the directionality properties of advanced composite materials, the passive material technology exploits the damping capabilities of viscoelastic material (VEM) embedded into the host structure. The main structure is modeled as a composite thin-walled beam Incorporating a number of nonclassical features such as transverse shear. anisotropy of constituent materials, and rotary inertia etc. The VEM layer damping treatment is modeled by using the Golla-Hughes-McTavish (GHM) method, which is employed to account for the frequency-dependent characteristics of the VEM. The displayed numerical results provide a comprehensive picture of the synergistic implications of both techniques, namely, the tailoring and damping technology on dynamic response of a thin-walled beam structure exposed to external time-dependent excitation.

• Structural Engineering and Mechanics
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• 제11권3호
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• pp.273-286
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• 2001

Viscoelastic (VE) dampers have shown to be capable of providing structures with considerable additional damping to reduce the dynamic response of structures. However, the VE material appears to be sensitive to the variations in ambient temperature and vibration frequency. To minimize these effects, a new VE material has been developed. This new material shows less sensitivity to variations in vibration frequency and temperature. However, it is highly dependent on the shear strain. Experimental studies on the seismic behavior of a 2/5 scale five-story steel frame with these new VE dampers have been carried out. Test results show that the structural response can be effectively reduced due to the added stiffness and damping provided by the new type of VE dampers under both mild and strong earthquake ground motions. In addition, analytical studies have been carried out to describe the strain-dependent behavior of the VE damper. The dynamic properties and hysteresis behavior of the dampers can be simulated by a simple bilinear model based on the equivalent dissipated energy principle proposed in this study.

• 한국음향학회지
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• 제8권1호
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• pp.31-37
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• 1989

구속 점탄성 층을 갖는 복합보를 동흡진기로 이용하는 문제를 다루었다. 이 동흡진기의 효과를 조사하기 위해 양단고정 주진동 보에 설치했을 때의 변위전달율을 구하여 기존 균일 재질보 동흡진기 효과와 비교했다. 해석결과 최적 동흡진기를 구성하는 패러매터 값이 현재 활용되는 재질 측면에서 의미있는 범위내에 존재하고 있고 둘이상의 공진 진동수에서 전달율을 동시에 줄일 수 있었다. 이점으로 기존 제시된 비해 점탄성을 복합보가 유리하게 이용될 수 있음을 확인했다.

• Structural Engineering and Mechanics
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• 제64권6권
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• pp.683-693
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• 2017

According to a generalized nonlocal strain gradient theory (NSGT), dynamic modeling and free vibrational analysis of nanoporous inhomogeneous nanoplates is presented. The present model incorporates two scale coefficients to examine vibration behavior of nanoplates much accurately. Porosity-dependent material properties of the nanoplate are defined via a modified power-law function. The nanoplate is resting on a viscoelastic substrate and is subjected to hygro-thermal environment and in-plane linearly varying mechanical loads. The governing equations and related classical and non-classical boundary conditions are derived based on Hamilton's principle. These equations are solved for hinged nanoplates via Galerkin's method. Obtained results show the importance of hygro-thermal loading, viscoelastic medium, in-plane bending load, gradient index, nonlocal parameter, strain gradient parameter and porosities on vibrational characteristics of size-dependent FG nanoplates.

• 한국항공운항학회지
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• 제15권3호
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• pp.6-14
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• 2007

In this research, vibration reduction and aeroelastic stability of a composite hingeless rotor hub flexure with viscoelastic constrained layer damping treatment(CLDT) were investigated. The composite flexures with viscoelastic CLDT were applied to hingeless rotor system to improve the in-plane stability of the lead-lag motion causing resonance. The modal test was performed and dynamic properties(natural frequency and loss factor) were acquired. Also, complex eigenvalue analysis(SOLlO7) in the NASTRAN structural analysis module was performed and compared with results of the modal test. To insure aeroelastic stability, damping ratio analyses of the hingeless rotor system with CLDT were accomplished at hovering condition due to collective pitch angle changes. Satisfactory results of increasing structural damping and stability were obtained.

• Korean Chemical Engineering Research
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• 제43권3호
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• pp.401-406
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• 2005

본 연구에서는 다중벽 탄소나노튜브의 화학적 표면처리가 에폭시 매트릭스 복합재료의 유리전이온도, 열안정성 그리고 동적 점탄성거동에 미치는 영향을 고찰하기 위하여 시차주사열량계(DSC), 열중량분석기(TGA) 그리고 동적 기계적 분석기(DMA)를 통하여 각각 측정하였다. 탄소나노튜브의 표면처리는 35 wt％의 $H_3PO_4$(A-MWNTs) 혹은 35 wt％ KOH(B-MWNTs) 용액으로 화학적 표면처리를 하였으며, 표면처리 후 표면특성 변화는 pH, 표면 산 및 염기도, 적외선 분광법(FT-IR)과 자외선 광전자 스펙트럼(XPS) 분석을 통하여 알아보았다. 그 결과로서, 산-염기 상호반응에 의한 각각의 표면처리는 탄소나노튜브의 표면특성 및 화학적 조성 변화를 가져오며, 산처리한 MWNTs/에폭시 복합재료의 경우가 염기처리 및 미처리 시편과 비교하여 열안정성 및 동적 점탄성 특성에 있어서 탄소나노튜브 표면에 도입된 산성 관능기 그룹의 영향으로 큰 값을 나타내었다. 이는 염기성을 가지는 에폭시 수지와 산성을 가지는 탄소나노튜브와의 산-염기 및 수소결합에 의한 계면결합력의 향상 때문이라 생각된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 춘계학술대회 논문집
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• pp.281-282
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• 2014

• 한국응용과학기술학회지
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• 제18권4호
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• pp.261-272
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• 2001

An ACR/HMMM film was prepared by blending high-solid ACR with curing agent, hexamethoxymethyl melamine (HMMM). An active curing reaction was observed at $170^{\circ}C$. The dynamic viscoelastic $T_{g}$ of the final film increased with the static viscoelastic $T_{g}$ of the film. The log damp value, which means a viscoelastic ratio, decreased with the increase in the curing temperature of the film. Physical properties of the films were within a suitable range for films, and by an accelerated weathering resistance test the films were proved weather resistible ones.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.189-195
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• 2008

The vibration isolator system(VIS) which has very low natural frequency could be designed by applying an axial compressive force to the beam-column flexure(BCF). In this paper a new shape of the BCF is suggested. It has stepwise axially varying properties by viscoelastic damping layer. So it has internal structural damping by damping layer during deformation. First the analytic solution is obtained for the BCF. And its critical load, buckling mode, stiffness and stress distributions are investigated. Also the dynamic properties of the VIS consist of the damping layered BCF are studied. Finally the optimal design procedure of damping layered BCF for the VIS is suggested. The improved performance of suggested VIS is verified by some experiments.