• Steel and Composite Structures
• /
• 제37권6호
• /
• pp.695-709
• /
• 2020

The buckling properties of a single-layered graphene sheet (SLGS) are examined using nonlocal integral first shear deformation theory (FSDT) by incorporating the influence of visco-Pasternak's medium. This model contains only four variables, which is even less than the conventional FSDT. The visco-Pasternak's medium is introduced by considering the damping influence to the conventional foundation model which modeled by the linear Winkler's coefficient and Pasternak's (shear) foundation coefficient. The nanoplate under consideration is subjected to compressive in- plane edge loads per unit length. The impacts of many parameters such as scale parameter, aspect ratio, the visco-Pasternak's coefficients, damping parameter, and mode numbers on the stability investigation of the SLGSs are examined in detail. The obtained results are compared with the corresponding available in the literature.

• Steel and Composite Structures
• /
• 제43권5호
• /
• pp.533-552
• /
• 2022

The current article deals with the dynamic stability, and structural improvement of vibrating electrically curved screen on the viscoelastic substrate. By considering optimum value for radius curvature of the electrically curved screen, the structure improvement of the system occurs. For modeling the electrically system, the Maxwell's' equation is developed. Hertz contact model in employed to obtain contact forces between impactor and structure. Moreover, variational methods and nonlinear von Kármán model are used to derive boundary conditions (BCs) and nonlinear governing equations of the vibrating electrically curved screen. Galerkin and Multiple scales solution approach are coupled to solve the nonlinear set of governing equations of the vibrating electrically curved screen. Along with the analytical solution, 3D finite element simulation via ABAQUS package is provided with the aid of a FE package for simulating the current system's response. The results are categorized in 3 different sections. First, effects of geometrical and material parameters on the vibrational performance and stability of the curves panel. Second, physical properties of the impactor are taken in to account and their effect on the absorbed energy and velocity profile of the impactor are presented. Finally, effect of the radius and initial velocity on the mode shapes of the current structure is demonstrated.

• Structural Engineering and Mechanics
• /
• 제86권2호
• /
• pp.249-260
• /
• 2023

The uncertainties involved in structural performances are of importance when the optimum number and property of seismic retrofit devices are determined. This paper proposes a seismic retrofit design framework for asymmetric soft-first-story buildings, considering uncertainties in the soil condition and seismic retrofit device. The effect of the uncertain parameters on the structural performance is used to find a robust and optimal seismic retrofit solution. The framework finds a robust and optimal seismic retrofit solution by finding the optimal locations and mechanical properties of the seismic retrofit device for different realizations of the uncertain parameters. The structural performance for each realization is computed to evaluate the effect of the uncertainty parameters on the seismic performance. The framework utilizes parallel processing to decrease the computationally intensive nonlinear dynamic analysis time. The framework returns a robust design solution that satisfies the given limit state for every realization of the uncertain parameters. The proposed framework is applied to the seismic retrofit design of a five-story asymmetric soft-first-story case study structure retrofitted with a viscoelastic damper. Robust optimal parameters for retrofitting a structure to satisfy the limit state for the different realizations of the uncertain parameter are found using the proposed framework. According to the performance evaluation results of the retrofitted structure, the developed framework is proved effective in the seismic retrofit of the asymmetric structure with inherent uncertainties.

• Earthquakes and Structures
• /
• 제24권2호
• /
• pp.127-140
• /
• 2023

The vibration of microtubule in human cells is the source of electrical field around it and inside cell structure. The induction of electrical field is a direct result of the existence of dipoles on the surface of the microtubules. Measuring the electrical fields could be performed using nano-scale sensors and the data could be transformed to other computers using internet of things (IoT) technology. Processing these data is feasible by artificial intelligence-based methods. However, the first step in analyzing the vibrational behavior is to study the mechanics of microtubules. In this regard, the vibrational behavior of the microtubules is investigated in the present study. A shell model is utilized to represent the microtubules' structure. The displacement field is assumed to obey first order shear deformation theory and classical theory of elasticity for anisotropic homogenous materials is utilized. The governing equations obtained by Hamilton's principle are further solved using analytical method engaging Navier's solution procedure. The results of the analytical solution are used to train, validate and test of the deep neural network. The results of the present study are validated by comparing to other results in the literature. The results indicate that several geometrical and material factors affect the vibrational behavior of microtubules.

• Journal of Electrochemical Science and Technology
• /
• 제14권4호
• /
• pp.369-376
• /
• 2023

The quick-charging performance of SiO electrodes is evaluated with a focus on solid electrolyte interphase (SEI)-reinforcing effects. The study reveals that the incorporation of fluoroethylene carbonate (FEC) into the SiO electrode significantly reduced the electrode fatigue, which is from the the viscoelastic properties of the FEC-derived SEI film. The impact of FEC is attributed to its ability to minimize the mechanical failure of the electrode caused by additional electrolyte decomposition. This beneficial outcome arises from volumetric stain-tolerant characteristics of the FEC-derived SEI film, which limited exposure of the bare SiO surface during 0.5 C-rate cycling. Notably, FEC greatly improves Li deposition during quick-charge cycles following aging at 0.5 C-rate cycling due to its ability to maintain a strong electrical connection between active materials and the current collector, even after extended cycling. Given these findings, we assert that mitigating SEI layer deterioration, which compromises the electrode structure, is vital. Hence, enhancing the interfacial attributes of the SiO electrode becomes crucial for maintaining kinetic efficiency of battery system.

• 한국가시화정보학회지
• /
• 제22권2호
• /
• pp.63-73
• /
• 2024

The injection of polymer can significantly reduce drag, particularly in the turbulent flow region where the mutual interaction between the polymer and turbulent vortices occurs. In this study, Taylor-Couette flow of PEO-in-water solutions with a rotating inner cylinder was analyzed. Despite the shear-thinning behaviour of PEO-in-water solutions being well-documented, for a given range of shear rates their viscosity remains nearly constant. By varying the polymer concentration, we analyzed the torque evolution of different solutions followed by the viscoelasticity effects of the polymer on the interphase transition points. The torque was analyzed using a dimensionless torque scaling method, which allows for the assessment of the fluid's momentum transport capabilities. It was observed that for low concentrations of PEO, the flow behaviour exhibited only minor differences in comparison to that of water, the Newtonian fluid. However, once the PEO concentration exceeded the polymer overlap concentration, the flow behaviour was significantly altered.

• Macromolecular Research
• /
• 제17권5호
• /
• pp.332-338
• /
• 2009

Rheological behavior of natural hydrogel produced from seeds of three Salvia spp. (S. miltiorrhiza (SM), S. sclarea (SS), S. viridis (SV)) was investigated by using a Rheometer equipped with a cone and plate geometry measuring system under never-dried condition. Different chemical contents of such hydrogels give significant effects on their rheological properties. Because of incomplete penetration of water inside the hydrogels after drying before-dried hydrogels were used for rheological analysis. To know molecular interactions which predominated in the gel formation, some constituents were externally added to the 1.0% (w/w) hydrogel. Addition of urea to disrupt hydrogen bonds reduced 3.4-67% viscosity of the untreated hydrogels and changed viscoelastic properties from gel to liquid-like behavior. Neutral salts added to the hydrogel solution at 0.1 M also lowered the viscosity in a manner related with increase in size of cations and temperature. Changing from gel state to liquid-like state was also easily confirmed by oscillation measurement (storage, G', and loss, G", modulii) typically observed in the cases of potassium sulfate and potassium thiocyanate. Influence of pH variation on the viscosity explained that weak alkaline condition (pH 8-9) creates a higher resistance to flow due to increasingly electrostatic repulsions between negative charges ($COO^-$) Importance of calcium bridges was also demonstrated by recovery of viscosity of the hydrogels by addition of calcium after acidification. The summarized results indicate that electrostatic repulsion is a major contributor for production of hydrogel structure.

• 한국도로학회논문집
• /
• 제7권4호
• /
• pp.203-210
• /
• 2005

바인더의 노화로 인한 성능변화는 침입도 또는 점도시험을 실시하여 판정하여왔다. 기존의 시험방법으로 아스팔트 바인더의 점탄성 특성과 실제거동을 평가할 수 없기 때문에 새로운 분석방법이 요구되어 왔다. 본 연구에서는 기존시험 방법을 사용하여 침입도지수와 잔류침입도를 판정하였고, 양방향 반복회전 모드와 일방향 반복회전 모드 시험을 실시하여 단기 노화된 아스팔트 바인더의 유변학적 특성을 분석하였다. 시험결과 단기 노화된 아스팔트 바인더는 시험주기(frequency) 즉, 차량속도의 변화에 따라 서로 다른 복합계수와 위상각을 나타냈으며 단기 노화 전후의 크리프 컴플라이언스 및 전단점도 시험결과에도 영향을 미치는 것으로 나타나서 포장 설계시 이러한 특성이 고려되어야 한다.

• 대한기계학회논문집A
• /
• 제36권12호
• /
• pp.1585-1590
• /
• 2012

플라스틱 소재는 온도, 습도 및 자외선 등 다양한 환경의 영향으로 인해 기계적 물성변화가 심하기 때문에 체결부의 견고함이 느슨해지고 형태의 변형에 의해 부품간의 마찰 등을 유발하여 잡음이 발생하게 된다. 따라서, 본 논문에서는 자동차 칵핏 모듈에 사용되는 다양한 플라스틱 소재에 대해 온도변화에 따른 동 특성시험을 통해 유리전이온도, 저장탄성계수, 손실계수 등을 측정하여 상온 및 열화조건에 따른 물성변화를 파악하였다. 시험결과, 온도가 높을수록 저장탄성계수는 감소하고 손실계수는 증가하는 경향을 나타내었다.

• Journal of the Korean Wood Science and Technology
• /
• 제34권1호
• /
• pp.32-39
• /
• 2006

본 연구는 현악기에 사용되는 현악기용 도료가 현악기의 음향성능에 미치는 영향을 조사하였다. 음향분석장치(FFT)를 이용하여 목재악기용 도료의 도막두께에 따른 음향적 성능을 평가하였다. 목재악기용으로 사용된 도료는 악기용 우레탄계 상도도료, 오일 스테인계 도료, 자외선 경화형 에폭시 도료이다. 형성된 도막의 음향적인 특성은 FFT 분석기에서 측정된 공명주파수와 댐핑값(damping factor)으로부터 동적탄성계수와 전단탄성계수를 계산하여 얻고, 밀도와의 관계와 탄성계수간의 관계를 통하여 도막의 두께에 따른 음향적인 특성을 측정하고 비교분석하여 상관관계를 조사하였다.